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CHESTERTOWN WASTEWATER TREATMENT PLANT
The Chestertown treatment plant is a two stage aerated lagoon system that serves
Chestertown and surrounding communities in Kent County, on the Eastern Shore of MD,
and discharges to the tidal Chester River. The plant is designed to treat a flow of 0.9
MOD, and currently receives an average flow of 0.60 MOD. The plant consists of two
very large lagoons aerated through plastic tubing. The last section of the second lagoon is
relatively quiescent to encourage settling of suspended biomass solids. Data for the
period from Jan 97 - May 98 was obtained for evaluation.
During the evaluation period, effluent BODs and TSS values averaged 16.1 and 37.3
mg/L, respectively. Very good DO concentrations were maintained in the aerated lagoons,
and the effluent NUt and TP concentrations were within the discharge limits. Complete
nitrification was obtained during warm weather but not throughout the winters. However,
while the ammonia levels sometimes exceeded 7 mg/L during the winter, the plant
discharged a year round average NHj-N value of only 3.0 mg/L. Effluent NOX
concentrations also were low indicating substantial denitrification of the formed nitrates
within the aerated lagoons. However, effluent organic nitrogen concentrations frequently
reached significant values, such as 19 mg/L in April 98. It appears that substantial algae
growth occurs in the lagoons, and are discharged in the effluent rather than settling.
Because of the high organic nitrogen content, the average TN concentration in the final
effluent was 10.7 mg/L. Effluent TP averaged 2.9 mg/L.
The main units of the plant are two aerated lagoons, an anaerobic digester and a chlorine
contact tank. The surface areas of the lagoons are 23 and 32 acres, and each lagoon has a
side water depth (SWD) of 6 feet. The liquid depth can vary by as much as two inches.
Each lagoon is equipped with two 100 HP blower. An anaerobic digester with a volume
of 280,000 gallons was designed to digest the sludges produced in the aerobic lagoons.
The final treatment unit is a five-pass chlorine contact tank designed for disinfection of
the effluent before discharge.
The plant is already accomplishing nitrification and denitrification to an extent sufficient
to comply with the Chesapeake Bay goal of 8 mg/L on an annual average. However, the
effluent contains excessive amounts of total nitrogen because of the biomass suspended
solids being discharged in the effluent. Thus, it is recommended that a deep bed sand
filter be added to the treatment system between the second aerated lagoon and the
chlorine contact basin to remove the suspended solids and thereby reduce the effluent
organic nitrogen concentration. In addition to reducing the organic nitrogen in the
effluent, some removal of organic phosphorus is expected, even though the soluble
phosphorus PC>4 and the TP values in the effluent usually were approximately the same
except during April and May 98. Nonetheless, an average TP value of 2.9 mg/L suggests
that the plant does not need any modification to reduce to remove phosphorus.
Analysis of the data indicates that installation and operation of deep bed sand filters will
reduce the effluent TN to an average of 5.5 mg/L at both current and design flow rates. It
Appendix II
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backh n ' M °f ^ d£eP bed fllter5' indudinS filter in^t P^ps
backwash pumps, air scour blowers and control units, plus site work yard pipiLTd
electrical upgrade, will be $ 1,350,000. Estimated changes in annual M&O cosUotaTs
4 500 Estimated additional TN removals following the upgrade are 9 500 a^d 4 250
bs/yr for current and design flowrate conditions, respectively. The esi rr/ateTcost'per
additional pound nitrogen removed is $5.92/lb. »"«wica cost per
Appendix II
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CITY OF CRISFIELD WWTP
The Crisfield WWTP is a contact stabilization design activated sludge plant located on
the southern end of the Eastern Shore of Maryland. It discharges into the Chesapeake
Bay. Because the plant is located at or just above sea level, it suffers from infiltration-
inflow of seawater during high tides in addition to normal infiltration-inflow. The plant
is permitted for a flow of 1.0 MOD, and effluent concentrations of 30 mg/L BODs, 30
mg/L TSS and 2.0 mg/L TP. There are no effluent ammonia or nitrogen requirements in
the current permit.
According to 1995 data, the loading and flow decrease substantially in winter, to almost
75% of summer flows and loads. Raw influent BODS and TSS samples are collected
twice a week, whereas only one or two sets of samples are analyzed each month for TKN
and TP tests. The average BOD5/TKN and BOD5/TP ratios were 5.93 and 42.4,
respectively. The average BODS value for the year 1995 was 125 mg/L at an average raw
influent flow of 0.6 MOD.
The raw influent is screened through a 1 inch mechanical bar screen and flows from there
to a rectangular grit chamber, or to an influent surge tank that is used during high flows.
The grit chamber does not perform adequately and during high flows some of the grit
enters the AS tanks and accumulates at the bottom. The AS basins are contact
stabilization units designed in a donut shape with clarifiers in the middle. The outer ring
has three chambers: reaeration, contact and aerobic digester zones. The basins are aerated
with coarse bubble diffusers installed on swing-arms. The nominal HRT is 7.8 hours at
1.2 MOD and 9.4 hours at 1.0 MOD. Without any primary clarifiers, the AS basins have
to treat a higher load for the same flow as compared to facilities with primary clarifiers.
In 1995, the plant maintained complete nitrification all year round at flows of 0.5 MOD in
winter and 0.65 MOD in summer. The effluent NOx averaged 13.6 mg/L with an average
TN of 15.6 mg/L.
The plant has two secondary clarifiers with SORs of 622 gpd/ft2 at 1 MOD and 750
gpd/ft2 at 1.2 MOD wastewater flow. These rates exceed the MDE guidelines for a
conventional WWTP, which are 600 gpd/ft2, and would correspond to a flow of 0.9
MOD. The solids loading rate exceeds 20 Ib/d/ft2 at MLSS of 2600 mg/L with an
influent flow rate of 1.0 MOD and a RAS flow rate of 50% of influent. The plant does
not have the flexibility to take a clarifier out for maintenance. Additional secondary
clarifier capacity is necessary to operate with nitrification at design flows of 1.0 or 1.2
MOD. The secondary effluent is chlorinated in two parallel contact tanks with an HRT of
65 minutes. It is dechlorinated and reaerated before discharge. Two aerated holding
tanks are used for sludge digestion. Typically a MLSS below 10,000 mg/L is maintained.
Besides the suggested modifications for operational improvement to the headworks and
grit chambers, three options were considered for AS basin modifications for BNR:
1. Operation of the AS basin volume of 0.2 MG in each tank (current configuration),
Appendix II
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2. Conversion of the two AS basins to a volume of 0.305 MG each by incorporating the
aerobic digestion section into the activated sludge basin. The digestion section would
be moved into the existing clarifiers, with new units constructed to replace the
existing units; F e
3. Conversion of only a part of each aerobic digester into an AS basin to provide a total
volume^of 0.235 MG for aerobic digestion. Each AS basin would have a volume of
It is recommended that the AS basins be reconfigured into anaerobic(15%)-anoxic(25%)
aerobic order with step feed capabilities for handling high flows. The RAS would be sent
to the head of the anaerobic zone. The nitrate recycle could be fed to the head of the
anoxic cell for BPR in addition to nitrogen removal, or to the first anaerobic cell for
nitrogen removal with chemical P removal. Based on the analyses performed it is
recommended that one AS basin be taken out of service in winter while operating with
both clanfiers when the flows decrease to 75 % of summer flow. The coarse bubble
diiiusers should be replaced with membrane or ceramic fine bubble diffusers With the
addition of two new clarifiers, the system should be able to operate satisfactorily for one
month with one clarifier out of service in winter when both AS basins are in operation A
RAS pump station that can independently control flows from individual clarifiers would
have to be designed to operate with the new clarifiers. The station should have WAS
pumps, also. Existing secondary clarifiers shall be converted to aerated sludge holding
tanks that can be used as aerobic digesters. It is proposed that a ferric chloride or alum
teed system be available as a backup for BPR.
Cost estimates were made without including the grit removal system modifications They
include construction of RAS and WAS pump stations. Total capital cost was estimated to
^ ™1 MGD' ^ $2'° M at L0 MGD- Total chanSe in Bating costs at 0 7
MGD is $9,894. The total cost per adc tional Ib of N removed is $7.40 at 1 2 MGD and
$4.95 at 1.0 MGD with one secondary clarifier.
Appendix II
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TOWN OF ELKTON WWTP
The Town of Elkton WWTP is a rotating biological contactor (RBC) plant located in
Cecil County. The current permit is based on a maximum monthly average wastewater
flow of 1.6 MOD, and limits the BOD5 to 30mg/L, TKN to 20 mg/L, and TP to 2.0 mg/L
on a monthly average. Furthermore, the permit specifies an effluent TN level of 8 mg/L
which should be achievable through installation of biological nutrient removal (BNR)
facilities designed to meet a seasonal (May through October) average of 8 mg/L. Actual
dry weather and wet weather flows are 1.4 MOD and 2.5 to 3.0 MOD, respectively.
The WWTP is rated for an average flow rate of 2.7 MOD, whereas the monthly average
and maximum flow rates to the plant during the period of July 1997 through June 1998
were 1.37 MOD and 1.70 MOD, respectively. The monthly average of raw influent
BODS was 172 mg/L for this period, and TKN averaged 28 mg/L. The primary effluent
has not been monitored at the Elkton WWTP. For this reason, primary effluent
characteristics were calculated using typical removal efficiencies of primary clarifiers
(BODS: 35%; TKN: 20%; TP: 15%). The data show that the plant is not able to achieve
good nitrification, as both the annual average and the monthly average values of ammonia
concentration in the final effluent are all 9.0 mg/L or greater. The DO levels in the RBC
troughs seemed to be sufficient for nitrification; hence, other approaches should be
considered to improve nitrogen removal. NOx, on the other hand averaged 4.1 mg/L
monthly.
Preliminary treatment consists of an Aqua Guard screen with O.Sinch openings, a
comminutor, a grit collector, and two primary clarifiers. The grit chambers were not
operating at the time of the visit, but the flow passes through them. The SOR and HRT at
the average flow of 1.37 MOD with both units operating are 242 gpd/ft2 and 2 hours,
respectively. The clarifiers are operated with an 8 inch sludge blanket, and the sludge is
pumped directly to the belt filter press at a rate of 6 hours per day and 3 days per week.
Polymer is added for sludge conditioning, and eventually the sludge is composted.
Clarifier effluent is by-passed to an aerated surge tank during high flow times, whereas
the regular flow goes to the RBCs after alum addition. The overflow is then diverted
from the surge tank to the pump station and then recycled back to the headworks. There
are two banks of "BioSpiral" RBCs and two banks of two rectangular secondary
clarifiers. Each bank of RBCs is made up of four trains of three RBCs. Eight of the
twelve RBCs have standard media shafts at 100,000 ft2 and four have high density shafts
at 150,000 ft2. The RBC troughs are aerated in order to increase sloughing. C116
Polytreat polymer is added to the effluent of the contactors to improve settling properties.
Mixed liquor from the RBCs flows into two banks of two secondary clarifiers each, one
of which is in operation in each bank. Each clarifier has an SOR of 360 gpd/ft2 and an
HRT of 1.26 hours at 1.37 MOD, with two of the clarifiers operating. Link belt sludge
and scum collection is employed. The sludge is returned back to the primary clarifiers for
settling. There is also a sludge recycle line from each clarifier to the flow control
chamber immediately upstream of the RBCs. Two chlorine contact tanks are used for
disinfection purposes, and the center channel between them is used for dechlorination.
Appendix II
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The tanks have a contact time of 35 min. at peak flow. Caustic is also fed to the
secondary effluent with chlorine. Cascade aeration of the effluent is used to maintain a
final effluent minimum DO concentration of 5 mg/L. Final effluent is then discharged to
Big Elk Creek.
The following two process alternatives were considered for implementing BNR:
1. Construct a nitrification-denitrification filter downstream of the existing secondary
clarifiers: BOD removal would occur in the RBCs and both nitrification and
denitrification would occur within the attached growth of the biological filters.
Examples of nitrification-denitrification filters are Biofor® Filters, which use
expanded shale as the filter media; BiostyrRFilters, which use lighter than water
plastic media; and the Kaldnes Process, which uses polyethylene media with a
density slightly less than that of water. Because the BOD present in the influent is
removed in the RBCs, a methanol feed system would be constructed to provide an
organic carbon source for denitrification in the tertiary filters.
2. Decommission the existing RBC units and Construct an Oxidation Ditch Activated
Sludge System: It is recommended that an oxidation ditch system with two parallel
ditches be constructed to replace the existing RBC units in the treatment train.
Oxidation ditches are high internal recycle systems that can be operated for excellent
nitrogen removal by optimizing the oxygen inputs. Typically, effluent TN
concentrations of less than 5 mg/L are easily achievable. If it is desired to implement
biological phosphorus removal as well, an anaerobic reactor could be constructed
upstream of the ditches. This configuration at Bowie, Maryland typically averages
<0.3 mg/L TP and <4 mg/L TN. Other types of BNR activated sludge processes such
as A2/O, VIP, modified UCT or sequencing batch reactors also would perform
satisfactorily and could be used instead of the oxidation ditch configuration if desired.
If the oxidation ditch system is constructed, the primary cl . ifiers become e: -,mdable
and could be modified into anaerobic reactors for biolo^cal phosphorus :moval.
The existing secondary clarifiers probably could be used for activated sludge
operation, but should be examined and evaluated for this purpose because they have
shallow side water depths (10 ft.). They are likely to be usable for current flows, but
may become limiting as the influent flow approaches the design flow of 2.7 MOD.
The estimated capital costs for the two- alternatives are $3,019,030 and $3,674,720,
respectively. The cost of Alternative 2 would increase to $4,271,720 if the anaerobic
reactor is included. Alternative 1 would have very high energy costs because it would not
be possible to reduce aeration costs in the RBCs, and additional organics would have to
be purchased for denitrification. Additionally, there would be the cost of aerating the
nitrifying filters, the costs of backwashing the filters, air sour blowers, and the cost of
purchasing an organic carbon source such as methanol for denitrification. Consequently,
the O&M costs for Alternative 1 are projected as $80,500 per year. The O&M costs for
Alternative 1 >re projected to be only $10,700, for the maintenance of the aeration
brushes and RAS pumps. The estimated total costs for implementing nitrogen removal is
$2.72 for Alternative 1 and $2.62 for Alternative 2, per Ib additional N removal.
Appendix II
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FEDERALSBURG WWTP
The Federalsburg WWTP is a trickling filter plant located in Caroline County on the
Eastern Shore of Maryland. It discharges into Marshyhope Creek, which eventually flows
into the Nanticoke River, a tributary of the Chesapeake Bay. The current permit is valid
until August 1999, and it limits the WWTP discharge to average TKN and TP
concentrations of 10 mg/L and 2 mg/L, respectively. The average effluent BOD limit is
30 mg/L for the period from October 1st through April 30th, and is 20 mg/L for May 1st
through September 30th. The current average wastewater flow to the plant is 0.36 MOD,
and the design flow is 0.75 MOD.
The effluent characteristics were summarized from operating data for the period from
November 1996 through April 1998. The average effluent concentrations for BOD, TSS,
TKN and NOx-N were 6.6, 12.1, 2.4, and 15.5 mg/L," respectively. The plant achieved
complete nitrification throughout the period with effluent ammonia values well below 1.0
mg/L most of the time. The total nitrogen discharged from the plant, mostly in the form
of oxidized nitrogen, was 53 Ibs/day in an average flow rate of 0.355 MOD. The average
effluent TP concentration of 1.9 mg/L was slightly less than the permit limit.
Preliminary treatment processes at the Federalsburg WWTP include 3 Celco type static
screens and 2 Evtec Teacup grit removal units. The screens have a mesh size of 0.10
inches, and their flow capacities are 750 gpm each for a total of 2250 gpm. The
centrifugal grit removal units have a flow capacity of 900 gpm each. The design of the
grit removal system was based on the removal of 95% of particles 1 OOum and larger.
Flow from the grit removal units is combined with secondary sludge flow and diverted to
the primary clarifiers through 3 flow distribution pits, only one of which was in operation
at the time of this evaluation. There are 2 primary clarifiers with sufficient space for one
more unit. However, currently only one clarifier is in use. The design sludge production
rate was 2708 gpd at 3% solids concentration. The clarifiers have diameters of 50 ft with
surface areas of 1963 ft2 and surface overflow rates of 275 gal/day/ft2 at the design flow
of 750 gpm.
Following .an equalization step, biological treatment at the Federalsburg WWTP is
achieved with 2 parallel trickling filters filled with synthetic high cone media. The media
depth and surface area are 13.5 ft and 30 ft2/ft3. The current total recycle rate around the
filters is 1200 gpm, and the full recycle capacity is 1200 gpm per filter. The design total
and soluble BOD loadings to the trickling filters are 1038 and 769 Ibs/day. The design
ammonia loading, on the other hand is 125 Ibs/day. Two secondary clarifiers with
diameters of 50 ft and minimum side water depths of 12 ft are operated for solids
separation. The surface overflow rate at a design flow rate of 375 gpm per unit is 275
gpd/ft2. The secondary sludge concentrated to 0.5%, and is pumped to the primary
clarifiers at a design rate of 16,306 gpd by pumps that operate for 10 min. every hour.
Secondary effluent is disinfected by chlorination in a contact tank with a hydraulic
retention time of 60 minutes. Following dechlorination, treated water passes through a 6-
Appendix II
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step cascade aerator prior to discharge. Combined primary and secondary sludge is
further treated anaerobic digestion. The digester volume 249,000 gallons and the waste
sludge production rate at 3% solids concentration is 5,017 gal/day. The digester contents
are mixed with 2 mixers. The digested sludge goes to two sand drying beds of 9,220 ft2
surface area for dewatering.
Because complete nitrification was successfully achieved throughout the period of
evaluation, the installation of a tertiary denitrification filter built downstream of the
secondary clarifier is recommended for enhanced nitrogen removal. In this alternative
BOD removal and nitrification will take place in the existing trickling filters and
denitrification will be accomplished in the tertiary bio-filters. Operation of the
denitrification filters will require the addition of an external carbon source. Methanol is
the most widely used organic carbon in similar situations because it usually is the most
economical. Examples of denitrification filters are Terra® filters, which use sand as the
filter media, and Biofor® filters which use expanded shale as the filter media. A
pumping station would be needed to pump the clarifier effluent to the denitrification
filters. A methanol feed system is also needed.
The capital cost for implementing nitrogen removal at the Federalsburg WWTP was
estimated to be $1.5 M. This amount includes concrete structure and manufacturer's
equipment. The cost for the methanol feed system includes storage tank, chemical
metering pumps, containment area, fire suppression system, safety equipment, piping and
a prefabricated enclosure to house pumps. On the other hand, the estimated changes in
annual M&O costs were calculated to be S11.3K at current flow, and S18.8K for the
design flow. The overall cost for the removal of each additional pound of nitrogen is
$3.37.
Appendix II 10
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GEORGES CREEK WWTP, ALLEGANY COUNTY
The Georges Creek WWTP is an oxidation ditch activated sludge facility permitted to
treat a flow of 0.6 MOD, and the annual flows and loads are close to the design capacity.
Operating data for 1995 was analyzed for the purposes of this study. The plant received
an average flow of 0.626 MOD, and the average monthly BOD5 was 146 mg/L. In the
absence of data for TKN and TP, they were estimated to be 29.1 mg/L and 4.9 mg/L,
respectively, using the ratios for BOD5/TKN (5:1) and BOD5/TP (30:1) that are typical
for Maryland. The plant did not have any data on ammonium-N, NOx or TP in the final
effluent.
The influent enters the plant through a wet well and then it is pumped to the oxidation
ditch. As the plant does not have a grit removal unit, grit accumulates in the wet well and
in the ditch. The ditch is aerated and mixed with jet aerators. The velocity of the water in
the ditch is not enough to keep grit in suspension. Based on operating information, a
significant volume (10% or higher) of the ditch may now be filled with grit. Because
there is only one ditch, the plant cannot take it out of service for maintenance. Ditch
effluent is controlled manually with a valve. The pipe carrying the mixed liquor from the
ditch to the clarifier is smaller than the influent pipe, and this causes a hydraulic
bottleneck, which causes the ditch to overflow. The overflow should be corrected to
prevent nitrifier loss and discharge of mixed liquor to Georges Creek. Because only one
blower is used for aeration of the ditch, the DO concentrations are only 1 mg/L close to
the jets. It is even lower between the jets. The plant has two secondary clarifiers with
SORs of 565 gpd/ft2 at design flow with both units in operation. With a SWD of 8 ft, this
SOR is high for a nitrifying mixed liquor. The plant cannot operate with one clarifier,
and it has to bypass as much as half of the normal flow around the facility to prevent
solids washout. Sludge is wasted through a Wye connection on the RAS line. Secondary
effluent is disinfected using a UV system, which has to be replaced or upgraded to allow
the peak design flow of 2.1 MGD to pass through the plant.
Based on DO levels in the ditch and an evaluation of the existing aeration system, it
appears that nitrification would be limited by the capacity of the aeration system.
Because of anoxic conditions at the lower depths of the ditch, any generated NOx would
get denitrified.
The following modifications should be considered to implement BNR:
1. Improve the aeration system for nitrification: According to the calculations, the jet
aeration system already in use can provide 1440 Ib of oxygen per day. However, due
to clogging of the jet nozzles this capacity is probably only about 85% of design at
present. For an MLE configuration, the oxygen demand for BOD and nitrogen
removal will be 1440 Ibs per day at average load. For BOD removal alone, 1150 Ibs
of oxygen are needed daily. Therefore the current system needs to be upgraded for
nitrification. One alternative is the installation of two 25 HP brush aerators, with
timers or PLCs and DO probes. The brush aerators will also help increase the liquid
Appendix II
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velocities in the ditch, reducing the quantity of grit settling out. Another alternative is
the installation of a ceramic or membrane fine bubble diffuser system with new
piping. The peak demand could be met with two 30 to 35 HP blowers.
2. Correct the overflow of raw influent and mixed liquor to the Creek by providing the
plant with the capacity to treat the MDE recommended peaking factors for a facility
of this size: Construction of a new clarifier with its own RAS system must have the
highest priority. Flow distribution boxes and appropriate piping must also be
considered.
3. Provide redundancy to take part of the oxidation ditch out of service to remove grit:
This will prevent loss of nitrification capacity when the system needs to be taken out
of service. The ditch can be partitioned into two U-shaped AS basins, and 30% of
each basin should be anoxic according to the calculations. The nitrate recycle pump
should be able to operate in a range from 120 and 300 % of the influent flow.
4. Add a grit removal system to protect equipment such as diffusers and mixer blades:
T1 'O grit removal systems were found to be feasible: a Schreiber channel type grit
re -oval system and a Pfsta-grit system on the influent sewer line upstream of the
influent wet well.
5. Add a chemical P removal system: Predictable Biological P removal would require an
anaerobic reactor before the oxidation ditch. Chemical P removal would decrease the
capital costs.
The cost calculations were done for each item listed above. Implementation of N
removal, at a minimum, requires that the aeration system be improved as recommended
under Item 1, and sufficient redundancy be established to permit an activated sludge unit
to be taken offline, as recommended in Item 3. It is recommended that the approach of
Item 3 be considered instead of Item 1 to provide the plant with a desired level of
operability. Item 5 has to be implemented for P removal. The capital costs of the five
items are $456,000; $1,156,000; $1,663,000; to be estimated; and $1,920,000,
respectively, corresponding to the items listed in the above order. Additional Derating
costs with nitrification and denitrification sum to $1,748, and the projected tota. ..ost per
Ib of additional N removed excluding P removal is $3.55.
Appendix II 12
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INDIAN HEAD WWTP
The Indian Head WWTP is a small, activated sludge plant located in Charles County,
Maryland, and it services the Town of Indian Head. The plant is permitted for a flow of
0.49 MOD, and the current permit requires the plant to maintain seasonal nitrification.
The plant discharges to Ginny Creek, which is a tributary of the Mattawoman River and a
sub-tributary of the Potomac River. At present, the plant receives an annual average flow
that is 50 to 60 % of the design flow of 0.5 MOD.
In 1995, the raw influent BOD5 averaged 287 mg/L, which is a fairly high value for the
Mid-Atlantic region. For the purposes of this design, a COD/BOD ratio of 1.5 was
assumed; however, if in the future the COD/BOD ratio exceeds 2.0, the plant may have
difficulty nitrifying without addition of media in the existing tanks or adding additional
tanks. The raw influent BOD/TKN ratio averages 12.0.
The raw influent enters the facility through three separate sewer lines into a Parkson
Aquaguard screen. Following screening, the wastewater is degritted in a Pistagrit unit
and sent to the AS basins. The AS basins are an old package plant with a concentric
clarifier that has since been retrofitted to operate with external clarifiers. The outer ring
is partitioned to yield two semicircular basins, each of which can be step fed. The HRT
in the basins is 14.2 hours at the design flow of 0.5 MOD. Aeration is accomplished with
ceramic disc diffusers. The mixed liquor leaves the basins through a submerged port that
does not allow foam to pass through to the secondary clarifiers. The two clarifiers have
SORs of 354 gpd/ft2 at 0.5 MOD. A telescopic valve is used to control the RAS flow
rate from each clarifier, and RAS is then pumped to the AS basins. The flow rates for
RAS and WAS are controlled by a Programmable Logic Controller. Secondary effluent
is disinfected with chlorine gas and dechlorinated with sulfur dioxide prior to discharge to
Ginny Run.
The secondary clarifiers located in the midst of the AS basins were converted to primary
aerobic digesters, and aerated with coarse bubble diffusers. Thickened and digested
sludge is pumped into a secondary digester. Supernatant is returned to the AS basins.
Sludge is then trucked to Mattawoman WWTP at the rate of three truck-loads each day.
Two alternatives for BNR were evaluated. Both alternatives use the entire AS tank
volume; therefore, a separate surge tank or effluent pumping is required to overcome the
hydraulic limitations downstream of the secondary clarifiers, which causes the weirs to
become submerged and solids to overflow:
1. Conversion of existing AS basins to anoxic and aerobic zones: The design
calculations showed that the plant would have to operate at MLSS levels of 2800
mg/L during average month loads in winter and 3750 mg/L during a peak month.
Because of limited aeration volume, a dedicated anaerobic zone was not included for
biological P removal. P removal can be accomplished by chemical precipitation. It is
recommended that two anoxic cells, each with a volume of 12.5 % of the AS tank
Appendix II
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m^^
is recommended that a nitrate recycle ?60 to 150 % ofTnflt t. pr£Ven< Settlin§' «
control of RAS withdrawal from each
automated DO contro system should be installed, including DO probes a PLC
motor control on the blowers. A side mounted submersible mixer should be i
to prevent settling. It is recommended that a nitrate recycle (60 to 150
The first alternative can be implemented at a lower cost but it has a lower safety factor
The second alternative provides a higher safety factor when one tank is taken out of
Appendix II
14
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MATT A WOMAN WWTP
The Mattawoman WWTP is an activated sludge plant that services most of Charles
County. The plant is rated for a flow of 15 MOD. Currently the flow ranges from 7.5
MOD in dry months to 10 MOD in wet months, including the recycle flows from filter
backwash, belt filterate, and gravity thickener overflow, which adds up to an average of
1.28 MOD. Operational data for the year 1995 was analyzed for this study.
Raw influent BODS averaged 182 mg/L during 1995. The primary effluent
measurements for BOD5 and TKN were 104 and 28.1 mg/L, respectively. There was a
large increase in primary effluent TKN from June through October, possibly due to
increased trucking of sludge from other facilities and septage. Final effluent nitrogen
concentrations were determined by averaging the two consecutive samples analyzed each
month. Although ammonium-N concentrations averaged 3.46 mg/L, presence of a
substantial amount of nitrification between June and February is apparent from the other
nitrogen species. The average organic N concentration was 3.30 mg/L, which is higher
than the averages at other facilities in the region. The difference may be a result of low
MCRTs (3 to 4 days) causing incomplete hydrolysis of organic nitrogen to ammonium-N.
Effluent TN averaged 13.8 mg/L, which is much lower than primary effluent TKN,
indicating the presence of denitrification. The amount of denitrification taking place was
calculated from a nitrogen mass balance to be 7.28 mg/L. The reduction in primary
effluent BOD5/TKN ratio should be monitored as it can adversely affect denitrification
because of insufficient organic carbon levels.
The WWTP has screening and grit removal for preliminary treatment. The wastewater
leaving the grit chamber enters a wet well where it mixes with the recycle flows. Primary
clarification takes place in four old and one new clarifier. The new clarifier has an SOR
of 800 gpd/ft2. The old clarifiers do not perform as efficiently as the new one at 800
gpd/ft2 and a raw influent flow of 7.4 MGD. Without the large clarifier, the four small
units are operated .at 1800 gpd/ft2, necessitating the addition of coagulants for suitable
operation. There are six parallel rectangular AS basins with a nominal HRT of 6.0 hours
at the design flow rate of 15 MGD. Aeration is achieved by coarse bubble diffusers. The
basins have a submerged pipe outlet for the mixed liquor to pass to six clarifiers; four old
and two new. The SOR at the design flow of 15 MGD is 550 gpoVft2 and the solids flow
rate at 3000 mg/L MLSS and 50% RAS flow rate is 21 lb/d/ft2, both of which are higher
than normal design practice. Therefore, additional secondary clarification is
recommended. The plant uses a P removal tertiary system that includes four
clariflocculators followed by final effluent filters. Ferric chloride is used for
precipitation.
Primary and WAS are thickened in two open gravity thickeners. The thickened sludge is
held in aerated holding tanks prior to dewatering. Belt presses are used for solids
dewatering.
Appendix II 15
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A review of the plant operation data showed that the plant nitrified at low MCRTs, and
the kinetics of nitrification can be enhanced by the plug flow pattern of flow in the AS
basins by operating with the DO maintained between 4 mg/L (summer) and 8 mg/L
(winter). The observed denitrification may be a result of reduced aeration with high
temperature, low DO zones in the basin created by the plug flow pattern, and low
operating MCRTs, which cause a relatively high biodegradable SCOD in the first half of
the basin. Data from 1995 show a substantial increase in primary effluent TKN in
summer without a corresponding increase in BOD5, which indicates an inadequate
organic carbon source for denitrification. Besides, as the plant approaches design flow,
nitrification is expected to decrease. For this reason, septage receiving procedures must
be examined and COD/TKN ratios must be monitored.
In order to achieve a seasonal average goal of 8 mg/L effluent TN, two alternatives were
developed:
1. Modification of the AS system to six parallel basins with anoxic and aerobic zones
(MLE configuration); flexibility to take one AS basin out of service between June and
December; flexibility to take one clarifier out of service; step feed to handle high
flows above 25 MOD: Modifications are recommended to pump septage to either the
gravity thickeners or an aerobic digester when the raw influent flow exceeds 12.5
MOD. It is recommended that an additional primary clarifier of the same size as the
existing large clarifier be added for the design primary effluent rate of 17.5 MOD.
This will reduce the SOR to 650 gpd/ft2 at a primary effluent flow rate of 17.5 MOD
when two large units are in service. Without a new clarifier, Stamford baffles and
chemical coagulant addition can enhance primary settling when the large clarifier is
out of service. A minimum of two anoxic cells are recommended in the first 25 to 40
% of the AS basin. An anoxic volume of 45% is recommended to maintain
denitrification during periods of low COD/TKN ratio in the primary effluent. The
nitrate recycle pump should be capable of pumping a maximum of 250% of the raw
influent flow. Automated DO control is optional. The existing secondary clarifiers
are shallow for BNR (10 ft). It is recommended that an additional secondary clarifier
be constructed to upgrade the plant. The RAS from the new clarifier will be piped to
the secondary sludge pump station. The plant can use two point chemical addition for
P removal, using the final clarifiers as secondary clarifiers.
2. Modification of the AS system to three, two-pass step feed reactors with anoxic zones
at the head of each pass; addition of one secondary and one primary clarifier; the
flexibility to take one AS basin out of service at any time of the year; flexibility to take
one clarifier out of service at any time of the year: The influent to the two pass
system will be step fed to the beginning of the first pass and the beginning of the
second pass. An anoxic zone will be created at the beginning of each pass, followed
by a multi-cell aerobic zone. Effluent soluble organic N is expected to be 0.5 mg/L
higher then Alternative 1. Without a nitrate recycle the effluent TN may be higher
than 8 mg/L during the months with peak nitrogen loads.
Appendix II 16
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At the time the report was prepared, it was not clear whether the addition of wastewater
flow contributions from a power plant would be considered to be a part of the 15 MOD of
wastewater flow allocated for this facility. If it is not, the potential raw influent flow and
primary effluent flow will increase by an additional 1.5 to 2.5 MOD, and this will have an
impact on the primary and secondary clarifier requirements.
In the cost calculations for both alternatives, the modifications for septage handling and
for constructing a common effluent channel are not included. The County would realize
operational savings in excess of $ 114,400 per year at 15 MOD by the conversion from
coarse bubble to fine bubble aeration. Also, there would be additional savings of
$103,000 per year in sludge dewatering and hauling costs at 15 MOD because of an
increase in operating MCRT from 3 days to 8 days. With the addition of a primary
clarifier, the projected total capital costs for the project is $8.5 M. Without the addition,
the plant maintains its hydraulic capacity at 15 MOD and the capital costs of
modifications is $5.8 M. The cost per Ib of additional N removed with Alternative 1
implementation, and with Primary Clarifier addition, is $0.94 . Without the primary
clarifier the cost per pound of N removed would be $0.07.
Appendix II 17
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WASHINGTON COUNTY WINEBRENNER WWTP
The Winebrenner WWTP is a rotating biological contactor (RBC) plant located at Fort
Richie, Washington County, Maryland. Originally the plant was constructed to serve Fort
Richie Military Base and the civilian population. The Base has been scheduled for
closure and currently personnel are in the process of moving out of Fort Richie. The
current permit based on an average flow of 0.6 MOD does not limit the TKN or TN
discharge. The current average flow rate is approximately 0.3 MOD, and the plant
discharges to Falls Creek, which flows into the Potomac River.
Raw influent COD, TKN and TP levels are not measured at this facility, and they were
estimated based on typical ratios for municipal wastewater. The measured monthly
average values for raw influent BODs and NH3 are 125 and 12.2 mg/L, respectively.
Assuming a TKN to ammonia ratio of 2:1, the raw influent TKN concentration was
estimated a-. 25 mg/L. The facility is currently accomplishing complete nitrification
because the Affluent ammonia concentration is less than 1.0 mg/L year round. Final
effluent BOD5, TKN, NOx and NH3 are 3.6, 3.0, 14.5, and 0.6 mg/L, respectively.
Preliminary treatment processes consist of a manually cleaned coarse bar screen followed
by a communitor, aerated grit chamber, flow equalization tank and two primary clarifiers.
The flow metering system consists of a Parshall flume and an ultrasonic level sensor.
The SOR of the primary clarifiers is 611 gpd/ft2 at the permitted flow rate of 0.6 MOD,
which is an adequate value for the existing clarifier configuration. Secondary treatment
consists of six RBCs with multilayer stacked polyethylene discs, and three circular
secondary clarifiers. The RBCs can be operated as two parallel trains with three RBCs in
each train, or as one train with six units in series. Coarse bubble diffusers provide
supplemental aeration to the RBC units. The SOR of the secondary clarifiers is 283
gpd/ft2 at the permitted flow rate of 0.6 MOD, so the clarifiers have excellent capacity.
Overflow from the clarifiers flows into two chlorination tanks with an HRT of 55 minutes
at 0.6 MOD, and then to the dechlorination unit with an HRT of 16.6 minutes at 0.6
MOD.
Two alternatives are proposed for the implementation of BNR:
1. Construct an AS basin with anoxic zones upstream of the RBC units and integrate the
RBC system into the AS system: Because nitrification occurs in the RBC units, a
nitrate recycle system would be constructed to recycle nitrified RBC effluent to the
unaerated zones of the AS system. Submersible mixers will be needed in the anoxic
zones to prevent settling of mixed liquor suspended solids. The RAS line would
recycle solids from the final clarifier to the anoxic zones. The anticipated effluent TN
concentration would be 8 mg/L year round.
2. Construct a :; ;trification filter downstream of the existing secondary clarifiers: Both
BOD remova; and nitrification will take place in the RBCs, and denitrification will
take place in the tertiary filters (e.g.: Tetra or Biofor filters). A methanol feed system
Appendix II 18
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would be needed because the BOD would be consumed before the flow enters the
tertiary filters. The anticipated effluent TN concentration will be 3 mg/L year round.
Capital costs for the two alternatives are $1,320,000 and $1,480,000, respectively. The
capital cost for the denitrification filter includes concrete structure and manufacturers
equipment. The estimated change in O&M costs are $5,700 for the first alternative, and
$10,200 for the second for current flow conditions, with the difference attributable to the
methanol feed. All costs presented are for denitrification, as the plant is already
nitrifying. The cost per Ib of additional nitrogen removed for alternatives 1 and 2 are
$4.96 and $3.77, respectively. Thus, alternative 2 removes more nitrogen at a lower unit
cost.
Appendix II 19
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New York Reports
BINGHAMTON-JOHNSON CITY JOINT SEWAGE TREATMENT PLANT
The Binghamton-Johnson City Joint Sewage Treatment Plant (BJCJSTP) is an activated
sludge facility that receives wastewater from the City of Binghamton, Village of Johnson
City, Town of Vestal and a number of other smaller towns and villages along
Susquehanna River. The plant has an effluent permit for 20 MOD of flow. However, the
annual average flow has exceeded this level, and primary clarifier influent flow was
measured to be close to 25 MGD.
The plant has a new permit specifying the BOD and TSS discharge levels to be 30 mg/L
at 20 MGD. The permit also specifies a seasonal ammonia limit of 11 mg/L as a monthly
average, effective between June and October. As the plant influent TKN fluctuates
between 10 mg/L in wet weather and less than 20 mg/L in dry weather, the plant was able
to maintain the effluent ammonia below 11 mg/L during most months without
nitrification with a high rate AS process. However, the high rate process discharges a
significant amount of N as soluble organic N.
After screening through coarse bar screens, Binghamton wastewaters constituting 85 % of
the total flow mixes with Johnson City wastewaters in the grit chambers. The flow then
passes through communitors and the combined influent mixes with plant recycles, and
then fed to primary clarifiers. The performance of the clarifiers is not known. 24-hour
composite samples shall be used in determination of the clarifier effluent quality. The
plant has six rectangular primary clarifiers with an overflow rate of 1,365 gpm/ft2 at 25
MGD. Six parallel AS basins follow the clarifiers. The HRT is 2.5 hours at a combined
influent flow of 25 MGD. Such a r'- >rt retention time does nof allow the plant to
maintain sufficient biomass in the b: s. Aeration is achieved with coarse bubble
diffusers. As the plant operates one jwer at a time , the quantity of the oxygen
transferred with one blower may be <: .miting factor in treatment. There are seven
rectangular secondary clarifiers after the AS basins. At the design flow, the SOR of the
clarifiers is 820 gpm/ft2, which is substantially higher than what is acceptable for
nitrification systems operating without polymer addition. It is suggested that the covers
of the secondary clarifiers be removed for the operators to be able to visually monitor the
performance. Secondary effluent is chlorinated in a contact tank.
The combined sludge is thickened in a covered gravity thickener. Thickened sludge with
3.5 to 5 % total solids content is pumped to three anaerobic digesters. At an sludge flow
rate of 0.085 MGD, the HRT in the digesters is 15 days. Digested sludge is dewatered in
three belt filter presses, one or two of them operating at a time. Sludge is composted with
an in-vessel system. It is recommended that the capacity of the whole solids handling
system be evaluated, especially considerin-i the future changes in sludge volume.
Three alternatives were suggested for the implementation of BNR:
Appendix II 20
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1. Upgrade of existing AS system with moving bed of plastic media: Hollow plastic
cylinders with serrated surfaces have to be installed in the AS basin to support
additional biomass in biofilms. Sufficient media will be installed to support all the
nitrification in the biofilm. Each aeration tank will be modified to operate with 25%
anoxic volume and media will be installed in both anoxic and aerobic zones. The
system can be operated with or without RAS. Each aeration tank will be
compartmentalize into four cells with mixers. Nitrate recycle would be required to be
100% of influent flow.
2. Construction of a parallel biological filter system with 12.5 MOD treatment capacity
to operate in parallel with the existing AS system which would be modified for
nitrogen removal to treat 12.5 MGD of flow: Biofor system and Biostyr system can
be used for the filters. Biofor would be designed with anoxic filters upstream of
aerobic filters. Biostyr, on the other hand, incorporates the anoxic and aerobic media
in one filter. The filters will have a recycle from the aerobic zone to the anoxic zone.
Each aeration tank will also be modified to include 25 to 33 % anoxic volume. A
nitrate recycle system should be installed in each tank.
3. Replacement of entire AS system with a two stage biological filters/anoxic-aerobic
biological filters for BOD and N removal: Half of the secondary clarifiers can be
used as additional primary treatment units, while the other half is demolished with the
AS system.
The estimated capital costs of the three alternatives are $13,057,000; $17,541,000; and
$24,541,000, and the estimated annual change in the O&M costs are $266,875; $166,875;
and $226,046. The estimated costs of additional nitrogen removal are $2.24 and $2.62
per Ib N removed, for Alternatives 1 and 2, respectively. It is recommended that
Alternatives 1 and 2 be evaluated further. Alternative 2 may be the easiest to operate,
provided that qualified instrumentation staff is available at the plant.
Appendix II 21
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VILLAGE OF ENDICOTT WWTP
The Village of Endicott in Broome County, New York operates an 8 MOD trickling filter
wastewater treatment plant which has difficulty meeting the permit limit of 30 mg/L for
BOD and TSS in winter. A seasonal ammonia permit valid between June and October
limits the ammonia-N loads to 830 Ibs/day. The annual average daily flow was 7.39
MOD for the 1995-1996 period, and the average daily loads of influent BOD and
primary effluent TKN were 6585 Ibs/day and 1187 Ibs/day, corresponding to 107 mg/L
and 19 mg/L, respectively. Wastewater flows and loads are higher in winter, with peak
hourly flows exceeding 30 MOD.
The WWTP site is bordered by a landfill on two sides, and on the other two sides by
wetlands which restricts the any pi nt expansions to remain within the property limits.
The raw influent is treated throug: a barminuter, an aerated grit chamber, and two
primary clarifiers. The primary effluent is then fed to two 120 ft diameter rock media
trickling filters operated in parallel. The effluent from the filters is sent to a pump station
from where it is pumped to two secondary clarifiers. Secondary effluent flows to a
chlorine contact tank from where it is discharged to Susquehanna River. The primary and
secondary sludges are anaerobically digested and composted. At present, the trickling
filters do not nitrify.
Three options were recommended for the implementation of BNR:
1. Modify the existing trickling filters with plastic media to increase the height to 18 ft.
Then load the process with 50% of the primary effluent to allow year round
nitrification. Install an AS/solids contact basin with sufficient anoxic volume (40% of
the total volume) for denitrification, using the remaining 50% of the primary effluent
as the organic carbon source. The aerobic volume could be used for nitrification of
the ammonium-N present in the trickling filter effluent and in the primary effluent.
Upgrade the secondary clarifiers by the addition of three new clarifiers to
accommodate operation in this mode. A nitrate recycle is not required to maintain an
effluent NOx of 6 mg/L.
2. Retain the rock media and feed 50% of the primary effluent just for BOD removal.
Install an anoxic-aerobic AS basin to treat a mixture of primary effluent and trickling
filter effluent, and achieve nitrification and denitrification. Feed at least 50% of
primary effluent to the AS basins to supply the organic carbon required for
denitrification in the anoxic zone of the AS basin. Upgrade the secondary clarifier
capacity to accommodate this operation. A nitrate recycle with a maximum capacity
of 250% of the influent flow is necessary.
If the existing two shallow clarifiers are demolished, the space can be used for the new
AS basins and for four new secondary clarifiers for the Options 1 and 2.
Appendix II . 22
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3. Install an anoxic-aerobic biofilter system downstream of the trickling filters. Operate
the biofilters with 50 to 100% of the primary effluent, nitrify in the aerobic filter and
recycle the nitrates to the anoxic filter upstream for denitrification. The effluent from
the aerobic biofilter is to be discharged to the chlorine contact tank. An anoxic and
aerobic filter sequence can be designed with Biofor expanded shale media or Biostyr
polystyrene media. The maximum nitrate recycle rate required will be 2.2 Q. It is
recommended that four Biostyr filters be installed and operated in parallel. This
alternative does not use the trickling filter or the secondary clarifiers. However, it is
possible to benefit by reducing some of the primary effluent BOD with the trickling
filters.
Option 1 has the highest cost, $10,032,000; Option 2 has the lowest cost as it does not
include any modifications to the trickling filters, $6,656,000. If the demolition of the
existing clarifiers is to be included the additional cost will be $1,300,000. Option 3 will
cost $8,004,000. The estimated changes in the O&M costs are $168,381; $124,003; and
$115,863 for the Options 1, 2 and 3. The total cost of additional N removal is $3.35 per
Ib of N removed for Option 2. If Option 2 is implemented with new clarifiers, the cost
will increase to $3.86. The total cost of additional N removal is $3.83 per Ib of N
removed for Option 3.
Appendix II 23
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Pennsylvania Reports
ALTOONA CITY AUTHORITY EASTERLY PLANT
The Altoona Easterly WWTP is an activated sludge facility designed for an annual
average flow of 9 MOD. The plant services the eastern sections of the City of Altoona
and discharges to a tributary of the Susquehanna River.
The discharge permit sets the effluent NH4-N at 2.5 mg/L from May 1st to October 31st,
and at 4.0 mg/L for the rest of the year. The plant has to and does nitrify year round to
meet the monthly average limits for NHU-N. The layout of the facility is amenable for
implementation of nitrogen removal to achieve a TN value of 8 to 10 mg/L N.
The average flow for the July 1996 to June 1997 period was 6.7 MOD. Average raw
influent BOD5 was 77 mg/L, which is fairly dilute, indicating the presence of significant
infiltration/inflow effects. It was assumed that the raw influent TKN was 20% of the raw
influent BODs, as the plant does not have any data on influent TKN values. An increase
proportional to the increase in flow was assumed to take place for COD and TKN levels.
Preliminary treatment units consist of two mechanically cleaned screens, and two aerated
flow holding tanks. The activated sludge system, on the other hand, consists of two
separate trains of four basins each, which can be operated either in parallel or in series.
Each cell is aerated with Sanitaire ceramic plate diffusers. The first cell has the highest
density of diffusers. Foam entrapment occurs in the Easterly plant because of the
configuration of the basins. There is an imbalance in flow distribution from the center
channel to the aeration cells. Thus, it was recommended that one of the three influent
gates be closed or the two flow trains be operated in series.
Mixed liquor leaving the aeration tanks flows to secondary clarifiers, each with a SOR of
346 gpd/ft2 with all tr-?e units in service. The RAS drains into a common wet well and
the plant does not ha • j independent control of RAS withdrawal rate from each clarifier.
WAS also is pumped out of the RAS wet well. Disinfection of the treated water is
achieved by two Katadyn UV units. WAS is pumped to an Eimco gravity belt thickener,
from where the RAS is discharged at 3 to 4 % TSS to two aerobic digesters, which are
operated in series. Sludge from the digesters is dewatered using an Eimco belt filter
press.
For the BNR modification assessment, TKN was assumed to be 20 ± 2.5% of the influent
BOD5 concentration. According to the calculations, at a ten day MCRT with maximum
month COD loads in summer, the MLSS would be 2200 mg/L, and it would increase to
2500 mg/L if one of the eight activated sludge cells were taken out of service. The
former value would v 3000 mg/L for the corresponding COD loads in winter at 15 day
MCRT. For both . .ditions, 75 % of the activated sludge tank volume would be
operated under aerobr- conditions. The first cell of each train will be operated anoxically
with mixers installed to minimize settling. The density of the diffusers in the first aerobic
Appendix II ' 24
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cell should be increased to have 33% more aeration capacity. The automated DO control
system also would be upgraded and put in service.
Nitrate recycle pumps, designed for a maximum flow rate of 1.5 times the influent flow
of 9.0 MOD should be installed in the last aerobic cell of each train. It is recommended
that the plant be operated at a RAS flow rate of 75 to 100 % of the influent flow, and a
chlorination system be used to maintain SVIs below 175 mL/g. The modifications also
should consider the prevention of foam entrapment in the activated sludge basins.
The capital costs of the suggested modifications at an average daily flow of 9.0 MOD
total $1,230,452. The change in operating costs following conversion will be small at
$1,733 per year. Although there will be energy savings from a decrease in aeration
requirements, they will be offset by the energy cost of the mixers in the anoxic zones.
The estimated cost per pound of additional nitrogen removed over a 20 year period is
$0.51 per IbN.
Appendix II 25
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ALTOONA CITY AUTHORITY WESTERLY PLANT
The Altoona City Westerly WWTP is an activated sludge plant that went online in 1991
with a design flow of 9 MOD, and it services the western sections of the City of Altoona
and the Alleghany Township. It discharges to the Beaverdam Branch of Juniata River, a
tributary of the Susquehanna River. According to the discharge permit, the plant has to
nitrify on a year round basis to meet average limits for ammonium-N of 2.5 mg/L from
May 1st to October 31st, and 4.0 mg/L for the rest of the year. The plant has nitrified since
start-up, and the layout is amenable for nitrogen removal. Because of high
infiltration/inflow rates from combined sewers in old sections of Altoona, the target
average effluent TN will be 8 to 10 mg/L on an annual basis.
The average flow for the June 1996-June 1997 period was 9.1 MOD, which is almost the
design value set for the plant. The average raw influent BODs of 92mg/L is indicative of
a very dilute influent and also indicates the presence of excessive infiltration/inflow. The
plant does not have any data on raw influent TKN. For this reason, it was assumed that
the raw influent TKN was 20 % of the raw BOD5, yielding an average value of 18.3
mg/L. The final effluent data shows that the plant completely nitrifies as the average
NH4-N concentration was 0.24 mg/L. The average final effluent total nitrogen value was
13.8 mg/L for the 1996-1997 period.
The raw influent is first screened by two Envirex mechanically cleaned bar screens with 1
inch openings and then passes through three aerated grit chambers. The wastewater is
then sent to the activated sludge basin through an aerated channel. During high flow
conditions, 2.5 MG aerated holding tanks and the primary clarifiers and activated sludge
tanks of the old plant are used for holding, and the maximum instantaneous flow is
limited to 20 MOD (13.890 gpm). Secondary treatment has two trains of four cells each.
These cells with a. nominal HRT of 9 hours can be operated in parallel or in series. Each
cell is aerated with Sanitaire ceramic plate diffusers, and each cell has installed DO
probes. The configuration of the plant has caused Nocardia problems (foaming) from
time to time. There are three secondary clarifiers, with a combined SOR of 315 gpd/ft2 at
9 MOD. The plant does not have independent control of the RAS withdrawal rate from
each clarifier as the RAS drains into a common wet well. The RAS flow is typically set
at 100% of the influent flow. The WAS is removed from the RAS wet well by six
pumps. -The secondary effluent is disinfected by two Katadyn UV units, each unit rated at
10 MOD. Waste sludge is pumped to a Komline Sanderson gravity belt thickener that is
operated 24 hours per day. Thickened sludge is discharged at 3 to 4 % TSS to two
aerobic digesters. Sludge from the digester is sent to a Komline Sanderson press and the
dewatered sludge is stored in a covered area and land applied.
The desired effluent TN was set at 7 to 9 mg/L for the BNR implementation analysis and
the effluent NO vas set at 5 to 7 mg/L, on an annual basis. To achieve these values, an
anoxic zone wi; )e created in \ Irst cell of each flow train with mixers installed, and
75% of the acthaied sludge tanl- lume will be operated under aerobic conditions. The
ceramic diffuser caps should be replaced with membrane disks. One downcomer should
Appendix II 26
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be installed to feed the diffusers in each anoxic cell. The density of the diffusers in the
first aerobic cell should be increased to be 33% greater than the average density. The
automated DO control system should be put back into service.
Nitrate recycle pumps, designed for a maximum flow rate of 1.5 times the influent flow
of 13.5 MGD, should be installed in the last aerobic cell of each train. It is recommended
that the plant be operated at a RAS flow rate of 75 to 100 %, and a chlorination system be
used to maintain SVIs below 150 mL/g. The modifications also should consider the
prevention of foam entrapment in the activated sludge basins.
The capital costs of the suggested modifications for the flow of 13.5 MGD total
$1,232,956. The change in operating costs following conversion will be small; $1,733
per year. Although there will be energy savings in the aeration requirements, they will be
offset by the energy cost of the mixers in the anoxic zones. The estimated cost per pound
of additional nitrogen removed amortized over a 20 year period is $0.42 per Ib N.
Appendix II 27
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CHAMBERSBURG WWTP
The Chambersburg WWTP is a three stage trickling filter plant designed to treat an
average flow of 4.5 MOD with both BOD/COD removal and nitrification. The
wastewater is domestic sewage with a substantial amount of flow from food processing
industries.
The treatment train includes flow equalization, grit removal, primary clarifiers, two rock
media trickling filters in series, secondary clarifiers, nitrification filters with plastic
media, final clarifiers, tertiary filters, and chlorination.
The BNR evaluation considered two options:
1. Trickling filters for BOD removal and nitrification, followed by denitrification filters
using methanol: In order to increase the capacity from 4.5 to 6.8 MOD, it is
recommended that the rock media in the primary filters be replaced with plastic
media. Also, a forced draft aeration system should be constructed to improve DO
levels at the surface of the biofilm. The secondary filters used for nitrification should
have sufficient surface area for reliable performance. The ammonium-N concentration
average would vary between 1 and 5 mg/L in winter. A third and larger secondary
clarifier should be constructed. An additional effluent sand filter would be installed
in parallel to the first effluent filter. Methanol would be added to the influent to the
filters. This would help develop a biofilm for denitrification on the deep bed filters.
The effluent TN would be reduced from 15 mg/L to 4 mg/L. The nitrogen removal
for each year was calculated for denitrification of an additional 11 mg/L of nitrogen at
the flow projected for that year.
2. An AS system for BOD removal, nitrification and denitrification: The AS system
would replace the primary filters, secondary filters, final clarifiers, and tertiary filters.
Two examples of several possible AS configurations are MLE and oxidation ditch
systems. Based on site constraints, a MLE process with an HRT of 12 hours is
recommended. Use of membrane diffusers is recommended over surface aerators to
reduce the long term operating cost. One or two additional secondary clarifiers would
have to be constructed at a recommended SOR of 400 gpd/ft2 at average flow.
The capital costs of implementing Option 1 would be $6,347,250 in 1995 dollars, with an
increase in annual operating costs of $129,096. The cost per Ib of additional N removed
is estimated to be $2.69. For Option 2, the capital costs are estimated as $8,060,000 and
the total incremental annual operating costs as $137,660. For this option, the cost per Ib
of additional N removed would be $4.55.
Appendix II 28
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GREATER HAZLETON JOINT SEWER AUTHORITY WWTP
The Greater Hazleton WWTP is an activated sludge plant located in Luzerne County,
Pennsylvania. The plant is adjacent to an industrial park and receives a combination of
municipal and industrial wastes (18%). It is rated for an average flow of 8.9 MOD and a
maximum flow of 14.6 MOD. Flows above 14.6 MOD can be bypassed. Currently, the
flows vary from 5.0 MOD during a dry month to an excess of 9.0 MOD during a wet
month. The plant discharges to Black Creek, which is a tributary of the Susquehanna
River. Because of two textile plants that do not pre-treat their dye wastewaters, the
influent to the plant is colored, and it causes Black Creek to be colored and the aquatic
life to be in a sharp decline downstream of the discharge point. The facility has not
nitrified even though the MCRTs has been increased above 5 days during warm weather.
This may be because of a lack of adequate AS tank volume and/or some possible
inhibition from the industrial wastewaters. However, as of June 1996, most of the
industries had implemented pre-treatment systems. The only major dischargers yet to
implement pretreatment were the textile plants.
Ammonium-N or TKN are not among the routinely measured parameters like BODs and
TSS. The only final effluent nitrogen species concentrations available were from the
Chesapeake Bay Nutrient Sampling Program for the year 1994. Those data indicated that
the plant accomplished limited nitrification from July to October 1994, as the effluent
ammonium-N concentrations ranged between 9 and 10 mg/L for flows between 5 to 8
MOD. Maximum effluent NOx was 3.6 mg/L, with an average TN value of 16 mg/L at
an average flow of 6.2 MOD.
The raw municipal wastewater is pre-screened by a coarse manual bar screen, and sent to
a rectangular aerated grit chamber. Then the industrial wastewaters combine with the
pre-treated municipal wastewater, and pass through a second coarse screen before
entering a building where it is screened with two mechanically cleaned Dorr Oliver
screens. The flow passes through a Parshall flume and enters a chamber with three sluice
gates, two of which divert the flow to two primary clarifiers that have SORs of 1007
gpd/ft2 at 8.9 MOD. Primary effluent is then pumped to two trickling filters, which can
be bypassed if necessary. The effluent from the filters enters a distribution box with
automated valves that can bypass flows above 9.4 MOD. BODS removal in the trickling
filters reduces the primary effluent BODs to 90 mg/L from 110 mg/L. Two rectangular
AS basins, with nominal hydraulic retention times of 2 hours at 8.9 MOD follow the
filters. Each basin can be step fed through four gates spaced 30 ft apart. Basins are
aerated with ceramic fine bubble diffusers arranged such that there is a decrease in
density from the front end to the downstream end. The effluent from the two activated
sludge basins enters a box with four telescopic valves that distribute the flow to four
secondary clarifiers. The SOR is 550 gpd/ft2 at design flow. The plant does not have
separate piping from each clarifier to adequately control RAS flow rates. As a result, one
of the clarifiers has a tendency to accumulate sludge. Secondary effluent is then
chlorinated in two contact tanks with HRTs of 34 minutes at design flow.
Appendix II 29
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RAS pumps withdraw sludge from a central collection box. At an average flow rate of 5
MOD, RAS averages 35 %. It decreases to 25 % when flow increases to 8.9 MOD in a
wet month.
The WWTP does not have adequate AS tank volume and secondary clarifier capacity for
nitrification. Thus, any upgrade for BNR will have to provide the capacity for
nitrification and denitrification. A nitrification rate test should be conducted to see
whether one or more of the industrial wastes are inhibitory. Should the magnitude of
inhibition be such that it results in a substantial increase in volume requirements, the
compounds causing the inhibition will have to be removed by pre-treatment.
There are two options for enhancing the secondary treatment system:
1. -Addition of extra AS volume and clarifiers: It may be difficult to implement this
option because of space limitations. The existing basins would be modified to an
anoxic-aerobic configuration for denitrification, with nitrate recycle. The HRT of the
existing basins would be 5 hours. Two new AS tanks with a HRT of 6.5 hours would
have to be constructed, also in an anoxic-aerobic configuration. A circular clarifier
with a diameter of 75 ft or a rectangular clarifier with a surface area of 4500 ft2 would
be added. These additions would require construction of a flow distribution structure.
, A new RAS pump station is also proposed. The aeration system would have to be
upgraded to service the new basins.
2. Addition ofbiofilters:. A Biostyr aerated filter, or equivalent, arranged in an anoxic-
aerobic configuration could be added. Nitrification rate will determine the size of the
filter. With the small footprint of the filters, this option would not cause any space
problems. The effluent from the filter would have a TSS of 10 to 15 mg/L,
eliminating the need for new clarifiers. The existing RAS system would not be
modified. Existing secondary clarifiers would be treating only 3.4 MGD, which
would reduce the SOR below 200 gpd/ft2.
The -capital and annual O&M costs for modifying the existing AS basins and adding the
Biostyr system are $7.84 M and $130 K, respectively. The annual operating costs are for
8.9 MGD. The cost per Ib of N removed was calculated from the Net Present Value of
annual costs, and was found to be $3.24.
Appendix II 30
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HANOVER AREA REGIONAL WWTP
The Hanover Area Regional WWTP services Perm Township, most of the Borough of
Hanover, all of the Borough of McSherrystown and all of Conewago Township. The
facility is an oxidation ditch activated sludge plant that is permitted to treat a maximum
monthly average flow of 5.5 MOD, and discharge to the South Branch of Conewago
Creek. The permit limits are based on an average daily flow of 4.5 MOD. The plant has
a monthly average ammonium-N permit of 1.5 mg/L from May 1st to October 31st, and
4.5 mg/L for the rest of the year. Thus, the plant has to nitrify year round. The
corresponding CBOD permits are 15 and 25 mg/L, respectively.
The raw influent and primary effluent flows and loads were analyzed for the year 1995,
during which the average flow was 3.46 MOD and the average raw influent BOD5 was
201 mg/L. The estimated contribution of industries to the organic load was 40 %. The
ammonium-N levels in the primary clarifier effluent averaged 24 mg/L, 20 to 30 % of
which possibly was from the recycles (digester supernatant and belt filtrate). MCRTs
were manitained between 9 and 14 days. Effluent ammonium-N averaged less than 1
mg/L for 1995, and the effluent TN averaged 19.7 mg/L for the same period. Mass
balances were performed on the nitrogen species for different conditions in the oxidation
ditches. It was found that partial denitrification was taking place in the ditches.
Raw influent is screened by an automatic bar screen with 1 inch openings. Wastewater
then flows through a Parshall flume into a wet well. Recycles from solids dewatering and
falter backwash are also brought into the same well. Influent is then pumped into a grit
chamber. There are two primary clarifiers following grit removal, with SORs of 630
gpd/ft2 at a flow rate of 4.2 MOD. A flow distribution box is used to distribute the raw
influent between the two clarifiers. The plant has two oxidation ditches, each with two
passes. The average length of liquid flow path is 487 ft. Operating volume of each ditch
is 1.43 MG. Aeration is achieved by brush aerators with variable submergence. Two
secondary clarifiers with SORs of 475 gpd/ft2 at a flow rate of 4.2 MGD follow the
ditches. Secondary effluent is filtered, then chlorinated and aerated prior to discharge
into a 7000 ft long outfall pipe.
The primary sludge is pumped directly to the anaerobic digesters, and the WAS is
thickened in two DAF thickeners to 4 % solids and pumped into the digesters. The
primary digester has a fixed cover, and the secondary digester has a floating top.
Digested sludge is dewatered by two presses of different sizes.
The following options were considered for the implementation of BNR:
1. Continuous aeration with three or four brush aerators while adjusting the water level
in the oxidation ditches with a moveable effluent weir to create anoxic conditions
over a section of the ditch;
2. Cycling brush aerators on and off to create anoxic and aerobic conditions at different
times;
Appendix II 31
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3 with variabie D° ieveis
to allow an adequate DO drop. However, this alternative is not recommended
In cyclic mode of operation all four brush aerators can be cycled. During off-cycle DO is
allowed to drop throughout the ditch to create anoxic conditions for denitrificat on Off
cycles shall be short enough to prevent settling. During the on cycle all four brthes wi
be turned on at high speed to aerate the ditch. The durations of the on and off cycle Jan
be .adjusted based on effluent ammonium-N and NOx levels. According to S
calculations, the aerators can be turned off 30 to 50 % of the time, and stilf achieve
complete nitrification. owucve
The third option allows the operator to run one brush aerator continuously while others
are cycled off in a staggered pattern. The on and off times can be controlled by a
Programmable Logic Controller or individual electronic timers.
Both options 2 and 3 are viable if filamentous bacteria growth at low DO is inhibited by
high DO during aerobic periods. Automated DO control is not recommended in any
option unless DO levels are used to cycle the brush aerators on and off. A DO control
system can be used to control the levels of the weirs. The weir level would be adjusted
when the on times or off times exceed preset maximum values.
The capital cost for using a logic controller, installing DO probes and automated liquid
leve adjustment is estimated to be $250,000. The annual savings in the operation of the
plant would be $16,227 because of reduced aeration requirements. The plant has
sufficient alkalinity to nitrify without the aid of alkalinity recovery from denitrification.
The effluent TN would be reduced from 19.7 mg/L to 6 mg/L. The cost per pound of
additional N removed over a 20-year period is estimated to be $0.08 based on 1996
dollars.
Appendix II
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HARRISBURG WWTP
The Harrisburg WWTP is a pure oxygen activated sludge plant designed for a flow rate of
30 MOD, located on a compact site adjacent to the Susquehanna River. Nitrification is
not achieved any time of the year, with effluent unoxidized nitrogen levels averaging
between 17 and 22 mg/L during dry weather. P is removed chemically with ferric
chloride addition to the primary clarifier effluent to meet a permit limit of 2 mg/L for TP.
Raw wastewater enters the plant through grit chambers, then flows to four flocculation
chambers upstream of the rectangular primary clarifiers, which SORs of 975 gpd/ft2 at an
average daily flow rate of 30 MOD. Primary effluent is pumped to a distribution box
which feeds three parallel AS basins. At design flow, the nominal HRT is only 2.5 hours.
The mixed liquor from the AS basins flows through a second set of flocculating chambers
to secondary clarifiers with SORs of 610 gpd/ft2 at the design flow of 30 MOD. The
secondary effluent is disinfected in two chlorine contact tanks prior to discharge to the
Susquehanna River. The AS basins are aerated with pure oxygen, but the installed
automated DO control probes are not currently being used. Primary and secondary
sludges are thickened in gravity thickeners and sent to two heated primary anaerobic
digesters. The primary digesters are followed by two secondary digesters.
Considering the low MCRTs used at the plant (2 to 3 days), the mix of industrial and
municipal wastes received in the influent, and DO levels less than 2 mg/L in the first cell
of each AS basin, it is not surprising that the plant does not nitrify. The final effluent
TKN typically ranges between 18 and 21 mg/L during dry weather flow. The available
space limits the alternatives for the implementation of BNR to two:
1. The flow through the pure oxygen basins would have to be reduced to 12 MOD.
These trains would be operated in the MLE configuration for nitrogen removal at a
design HRT of 6.25 hours. A parallel 18MGD Biostyr train would be constructed for
nitrogen removal. Primary effluent organic carbon would be used for denitrification.
This alternative could produce a year round effluent quality of 8 to 10 mg/L TN.
2. The pure oxygen system would continue to be operated as a high rate system without
nitrification as designed at present. Aerated biological filters like Biostyr, Biofor, or
Safe would be added for nitrification. These would be followed by denitrification in
fluidized bed filters or additional Biostyr filters. The cost estimates are based on
using fluidized bed filters. This alternative uses methanol for denitrification and it
can meet an effluent TN of 3 to 5 mg/L on a year round basis.
The capital and operating costs for the two alternatives are similar. For Alternative 1,
these costs are $27,637,740 and $499,772, respectively, and the cost of additional N
removal is $2.19. For alternative 2, capital and operating costs are$25,447,500 and
$1,182,222, respectively, and the cost of additional N removal is $2.00 per Ib N removed.
Appendix II 33
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LANCASTER WWTP
The Lancaster WWTP is an activated sludge plant that is rated at a capacity of 29.7
MOD, and it is required to nitrify to satisfy an effluent permit of 2.5 mg/L ammonium-N
from May 1st to October 31st, and a winter permit of 7.5 mg/L. The newer section of the
plant treats a flow that averages 20.7 MOD. It has four anaerobic-oxic pure oxygen trains
followed by three circular clarifiers, each with a diameter of 150 ft, whereas the older
section treats 9 MOD and has three anaerobic-oxic pure oxygen trains followed by two
circular clarifiers each with a diameter of 100 ft. The secondary effluents from the two
systems combine immediately prior to the chlorine contact tanks.
In older trains, the ratio of the anaerobic volume to the total reactor volume is 14.5 %,
which is adequate for biological P removal. However, it is on the low side for conversion
to an anoxic zone for biological nitrogen removal except in instances where the primary
effluent has substantial concentrations of readily biodegradable organic carbon for rapid
denitrification. The average primary effluent TKN is possibly between 17 and 22 mg/L.
On dry days (20 to 23 MOD), effluent NOx has ranged between 7 and 10 mg/L. Thus, it
is possible that denitrification occurs in the anaerobic cells with nitrates recycled via
RAS, and in the third cell of the aerobic zone which has low DO levels. It should be
possible to achieve nitrification and denitrification with nitrate recycle. To overcome the
lack of sufficient organic carbon in the third aerobic cell, step feeding can be practiced.
The secondary clarifiers have an SOR of 575 gpd/ft2 at 9 MOD, which is somewhat high
for a BNR plant. Precautions shall be taken to maintain an SVI less than 85 mL/g.
There are four new trains that have anaerobic cells which occupy 16.5% of the total
volume of the AS basins. This percentage is also on the low side for operation as an
anoxic zone. Twenty (20) to 30 % of the dry weather primary effluent flow should
continue to be step fed to the third aerobic cell. The three secondan clarifiers have SORs
of 390 gpd/ft2 at 20.7 MOD, and they have adequate capacity at des.gn flow for SVIs up
to 150 mL/g.
Ferric chloride can be used for chemical P removal as it produces the least amount of
solids when compared with alum and lime. Experience with BNR facilities shows that
the dose of ferric chloride required for satisfying an effluent TP permit can be less than 20
gallons per MOD of waste water treated.
Three options for implementing BNR are proposed:
1. Fluidized bed or static bed upflow/downflow denitrification filters;
2. Conversion of anaerobic zones to anoxic zones with additional modifications in the
reactor and implementation of chemical P removal;
3. Conversion of reactors to incorporate anaerobic, anoxic and aerobic zones for
biological N and excess P removal.
Appendix II ' 34
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The cost of biological nitrogen removal with chemical P removal without step feed
(Option 2) is the lowest of the options evaluated. Without step feed, the capital costs
would be $1,077,180, and with step feed it will be $2,381,054. The predicted annual
change in operating costs is $20,944 for both feeding configurations. The cost per Ib of
additional N removed is estimated as $0.190 without step feed, and $0.373 with step feed.
Capital costs for implementing biological nitrogen removal with excess P removal within
the available reactor volume (Option 3) are $2,884,630 and $3,762,304 for without and
with step feed to the third aerobic cell. The annual change in operating costs is projected
to be $40,669 for both feeding configurations. The cost per Ib of additional N removed is
$0.331 without step feed, and $0.455 with step feed.
Appendix II 35
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CITY OF LEBANON WWTP
The City of Lebanon \VWTP is an activated sludge plant that serves seven municipalities
in the Lebanon area of central Pennsylvania. These include the City of Lebanon, Cleona
and Cornwall Buroughs, North Cornwall, North Lebanon, South Lebanon and West
Lebanon Townships. The plant is rated for a capacity of 8 MOD, and it has to nitrify all
year round because it discharges to Quittapahilla Creek, which is in the Susquehanna
River watershed. The permitted effluent ammonium-N is 2.5 mg/L for summer and 7.5
mg/L for winter. The TP limit is 2 mg/L. The uniqueness of the Lebanon WWTP comes
from its configuration: primary effluent is pretreated in 21.5 ft tall trickling filters with
vinyl core plastic media. Then the effluent is treated in four AS tanks for nitrification.
Phosphorus is removed chemically with waste pickle liquor.
The wastewater flows thr. "jgh an aerated grit chamber where lirre is added to supplement
alakalinity. It then flov,. .rough a coarse bar screen for rat .'emoval and through a
Parshall flume for the mea - rment of the flow rate. Following uiis, the flow is valved to
a rapid mix basin and flocculation tank. Waste pickle liquor is added to the rapid mix
basin for chemical P removal. Two primary clarifiers with an SOR of 800 gpd/ft2 follow
P removal. The clarifiers are shallower than depths used in current design practice.
Addition of lime, waste pickle liquor and a polymer enhances the BODs and solids
removal across the clarifiers. Primary sludge is withdrawn at an average solids content of
3% and it is fed to an anaerobic digester. Primary effluent is pumped up to two trickling
filters, each with a diameter of 39.5 ft and a media depth of 21.5 ft. A minimum flow rate
of 3000 gpm is maintained through the filters. Four rectangular AS basins follow the
trickling filters with a hydraulic retention time of 5.0 hours at 8 MOD. Each basin is
aerated with five 25 HP vertical turbine aerators, and the DO levels are maintained in a
range between 2 and 4 mg/T The plant has two old, shallower (8ft) clarifiers and two
new, deeper clarifiers (12f The plant has four effluent filters to which the secondary
effluent is pumped. Curre. •', the filters are operated as single media anthracite coal
filters. The filters are not kept in service during normal operation, and they are put into
service for only a few days each year to be tested.
All four clarfiers drain to a common return sludge well. The plant has difficulty
maintaining satisfactory control over RAS withdrawal rate from individual clarifiers
because- of the lack of independent sludge pumping from each clarifier. WASis
discharged to primary clarifiers where it is co-thickened. Primary sludge is then pumped
to a primary digester where the storage time is 30 to 60 days. The sludge is then
dewatered with an Envirodyne filter press and land applied. Digester supernatant and
filtrate from the belt filter press are recycled to headworks.
Data from 1995 were evaluated for this study. The plant operates the AS basins at
MCRTs of 6 days in summer and 15 days in winter. The operating MLSS increased from
2000 mg/! n su: ner with all basins in service to 4n :0 mg/L in winter. The monthly
average o: .aw iu. aent and primary effluent BOD5 weie 310 and 197 mg/L respectively.
These numbers are higher then typical values because the influent includes industrial
Appendix II 36
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wastewaters as well. The data shows that a substantial reduction in BOD and COD
loading to AS basins can be achieved if intermediate clarifiers are installed between the
trickling filter and the AS basins. Overall, the percent reduction in COD in the primary
clarifiers and trickling filters increases from 46 % to 71 %. The COD available in the
trickling filter effluent will limit the quantity of nitrates that can be denitrified in the
anoxic zones.
Final effluent ammonium-N concentrations show that the plant is capable of maintaining
complete nitrification all year round at the'present flows of 5.7 MOD. A mass balance
for nitrogen indicates that 20 to 25 % of the primary effluent TKN is removed in the
WAS and trickling filter waste solids. If there were no denitrification, complete
nitrification would result in an effluent NOx of 16.4 mg/L and TN of 18.3 mg/L. The
accuracy of the mass balance is confirmed by the TN concentration of 18.5 mg/L
calculated for 5.7 MOD of flow.
To improve denitrification it will be necessary to bypass a certain amount of primary
effluent feed directly to the AS basins. The organic load will increase the secondary
sludge and it will be limited by the AS tank volume. The mixture of 10% primary
effluent and 90% trickling filter effluent should contain at least 20 mg/L of additional
biodegradable COD for denitrification, which will help denitrify an additional 4 to 5
mg/L of NOx. Trickling filter effluent COD will increase from 129 mg/L to 175 mg/L as
a result of the bypass.
For BNR implementation three options were considered:
1. An anoxic-aerobic configuration within the existing AS basins with primary effluent
bypass around the trickling filters, to remove an additional 7 mg/L of nitrogen and to
achieve a TN level of 11 mg/L on an annual average. The dedicated aerobic zone will
occupy 60% of the tank volume, and nitrates will be recycled from the end of the
aerobic zone to the anoxic zone. Nitrate recycle could be eliminated by increasing the
RAS flow to 70% of the influent flow. The Recommended MCRT is 8 days in
summer and a maximum of 16 days in winter. The MLSS is expected to be 3800
mg/L at an MCRT of 16 days.
2. An anoxic-aerobic configuration with the addition of a fifth AS basin in parallel to
the existing four and with a 20 to 25 % bypass, to yield an effluent TN of 8.5 mg/L.
The configuration of the fifth basin will be similar to that of Option 1, but the
increased bypass will bring in additional organic carbon that would increase the
quantity of denitrification. The capacity of the nitrate recycle pumps will, therefore,
be increased from 40% to 200%.
3. Addition of a denitrification filter, preferrably in addition to the modifications of
Option 1, to denitrify 14 mg/L of nitrates: This option will allow denitrification to
yield an effluent NOx concentration of about 2 mg/L. Existing filters can be modified
with methanol addition, but it needs to be examined in a pilot study.
Appendix II 37
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™ J °f thC thiee °Pti°nS in the °rder of 1, 2 and 3 are as follows: $1 251 600-
,600; and $5 501,600. There is a wide gap between the changes in the annual'
operating costs with nitrification and denitrification of the three options: $153- $15 837-
f t%L°P*°n 2 ^ 3 haS the mixinS re^™*nt, which is estimateto coll
$4^0 F°0nand,0pti0n thfee ^ ^ C°St °f methan01 addition to the filters 5
S^i 10 H «? ?oC°St Per adftional nitr°gen rem°v^ for Options 1, 2 and 3 are
$0.61, $1.19, and $1.39, respectively. The costs and the amount of nitrogen removed are
m an increasing order, the lowest being Option 1.
Appendix II
38
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SCRANTON SEWER AUTHORITY WWTP
The Scranton Sewer Authority WWTP is an activated sludge facility that services the
population of both Scranton and Dunmore in North East Pennsylvania, and discharges to
the Lackawanna River, a tributary of the Susquehanna River. The plant was permitted to
treat a flow of 20 MGD. In 1995, the annual average primary effluent flow was 13.8
MOD, including 1 MGD of recycle flow. The average raw wastewater flow was 12.9
MGD. The BNR study was based on an annual average flow of 16 MGD, with a
maximum month flow of 20 MGD.
TKN has not been among the parameters measured at the plant, and therefore it was
assumed to be 1/5.5 of the BOD5 concentration (110 mg/L) in the primary effluent, for an
average TKN concentration of 20 mg/L. According to the effluent data, the plant nitrified
all year round. Effluent NOx concentrations were measured by Hach colorimetric method
and they averaged just below 7.0 mg/L in November and December of 1995. For
comparison, NOx measured at other plants by the Cadmium reduction column method
and Hach kit showed that the Hach kit yields 20 to 40 % lower results. Chesapeake Bay
Nutrient Sampling Data showed an effluent TN of 9.9 to 11.9 mg/L at 12.3 to 14 MGD.
The plant has two Parkson Aquaguard screens with 3/4 inch mesh, and two rectangular
non-aerated grit chambers. There are four rectangular primary clarifiers with SORs of
819 gpd/ft2 at 16 MGD. The primary effluent flow rate is monitored by a flow meter in
the channel connecting each clarifier to an activated sludge basin. Each AS basin is
divided into two separate passes operating in parallel, each with five downcomers from a
650 tubular membrane diffuser system. Based on a primary effluent flow rate of 16
MGD, the nominal HRT is 9.83 hours. Each basin has the flexibility to be step fed, with
primary effluent introduced at ten locations. The RAS is also fed to the front end of the
basin. Operation at a RAS flow of 8 MGD results in a substantial recycle of NOx to the
first third of the basin. The plug flow configuration encourages denitrification of some of
the recycled nitrates. Overall, the existing arrangement can denitrify 25 % of the nitrates
generated. The four rectangular secondary clarifiers that follow the four AS basins have
SORs of 490 gpd/ft2 at 16 MGD. The plant uses a Stranco ORP meter to control the
chlorine dose for disinfection. For sludge thickening, two DAF units are used, and filter
presses are used for further dewatering. Lime is added to dewatered sludge to stabilize it,
and the s-ludge is then landfilled.
Nitrogen mass balance evaluation based on a primary effluent TKN of 20 mg/L shows
that as much as 14 mg/L of NOx can be generated through nitrification. After
denitrification of 25 % of the generated NOx, the average effluent NOx concentration
will be 10.5 mg/L. To overcome possible Nocardia problems, the plant has installed an
RAS chlorination system that is used at high SVIs. Magnesium hydroxide slurry is used
to supplement alkalinity.
The Scranton WWTP is an excellent candidate for BNR, as the plug flow nature of the
AS basins allows nitrogen removal to be implemented using the MLE configuration.
Appendix II 39
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According to the plant data, effluent temperature averaged 8°C in January. Therefore
BNR evaluations were performed for an MLE configuration and water temperatures of 8
to 23°C. The operating MCRT required for nitrogen removal varied from 7 days in
summer to 12 days in winter. The maximum predicted MLSS was 2750 mg/L in winter.
An annual average effluent TN value of 6 mg/L can be maintained with MLE
configuration which represents a reduction of 5 mg/L in the TN from the present average
of 11 mg/L. TN levels of 7 mg/L and lower are expected at temperatures lower than
10°C. The anoxic volume used in the calculations was 30 % of the AS tank volume. A
nitrate recycle rate of 100 % was selected for design purposes. The nitrate recycle pumps
should be connected to variable frequency drives which can vary the flow rate from 40 to
100 % of the influent flow. Each anoxic section would be mixed with submerged mixers.
Nitrogen removal for flows up to the existing capacity of 20 MOD also is feasible with
the existing volume of the AS tanks and clarifiers with the use of Integrated Fixed Film
Activated Sludge (IFAS) process. The cost of implementing an IFAS process with
sponge media would be about $3.0 Million.
As a result of denitrification, the cost of aeration is expected to decrease by 15 to 20 %.
This will result in 100 HP less power draw by the blowers. However, the operation of 12
mixers and nitrate recycle pumps will result in an additional power requirement of 96 HP.
Therefore, the aeration savings will be almost negated by the increase in power
requirement for mixers and nitrate recycle pumps. The plant also will realize an
alkalinity recovery as a result of denitrification, which will reduce or eliminate the need
for magnesium hydroxide addition.
The capital costs for modification of eight passes in four tanks to the MLE configuration
is $2.816 M. The cost of maintenance on mixers and pumps is expected to average
$6,000 per year. The annual savings in magnesium hydroxide as a result of alkalinity
recovery from denitrification would increase from $18,000 in Year 1 to $34,700 in Year
20. The present worth of annual savings, discounted at 3 %, is $252,325. The total
present worth cost of the project over a 20 year period would be $3,283,076. Additional
nitrogen removed would be 4.463 M Ib over a 20 year period, yielding a cost of $0.76 per
Ib of additional N removed.
Appendix II 40
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STATE COLLEGE, UNIVERSITY AREA JOINT AUTHORITY
The University Area Joint Authority (UAJA) WWTP is an A/O process plant rated for a
flow of 6 MOD, and the existing permit requires nitrification and seasonal phosphorus
removal. The plant discharges to Spring Creek, which is a tributary of the Susquehanna
River.
Data collected from January 1996 to June 1997 were analyzed for the study. The plant
receives higher flows when the University is in session. The flows and loads decrease
20% during the period between May and August, the summer break for the school. Raw
influent BOD5 concentration averaged 257 mg/L for the year 1996 and 294 mg/L for the
January 1997 to June 1997 period, which was relatively dry. The NH4-N content was
approximately 10% of BOD5, and the TKN was estimated to be 1.5 times the NH4-N
concentrations. The average NFLrN concentration in the final effluent was 0.9mg/L,
showing that the plant achieves complete nitrification all year round. However, when the
infiltration from snowmelt runoff resulted in a sharp and sudden decrease in liquid
temperature, the effluent NH4-N concentration increased above 20 mg/L in April of 1996.
Average effluent TN for 1997 was 15.5 mg/L, and 13.0 mg/L of this was NOx remaining
after denitrification. According to the nitrogen mass balance, nitrification converted 75%
of the TKN present in the primary effluent to oxidized-N, and denitrification then reduced
the N concentration to 11.8 mg/L (57% of NOx formed). Phosphorus removal is
achieved via alum addition, and after filtration effluent P content is below the permit
requirement of 0.13 mg/L. However, during winter months when the permit is not in
effect, alum addition is ceased and the effluent rises above 3 mg/L, because the anaerobic
zones are kept anoxic instead of anaerobic with the introduction of NOx in the RAS.
Raw wastewater enters the plant through a Worthington comminutor and passes through
primary clarification. A flow distribution box is used to distribute the primary effluent
and RAS between the two circular and one rectangular activated sludge tanks, all with
A/O configuration. The anoxic cells are mixed to prevent settling, and aerobic cells are
aerated with membrane disc diffusers. Preceding the three secondary clarifiers is a flash
mix and flocculation tank for alum addition. The clarifiers have SORs of 400 gpd/ft2 at
the design flow. Secondary effluent is then filtered in dual media filters in eight filter
cells, which use anthracite as the top layer and sand as the lower layer. Disinfection
(chlorination) is the next and final step in the treatment train.
The upgrade will consist of conversion of the A/O tanks to the MLE configuration by
creating anoxic zones with inclusion of a nitrate recycle. According to the nitrogen
balance, the average concentration of NH4-N nitrified to NOx was 27 mg/L. For a TN
concentration of 8 mg/L, 6 mg/L of which is TKN, 21 mg/L of NOx will be denitrified
following modification. In order to prevent Nocardia foams, gates can be installed at the
surface of each baffle located within the aerobic zone. A chlorine spray system is also
suggested. Alum would continue to be used for P removal.
Appendix II 41
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The estimated total capital cost is $783,793, based on 1997 dollars O/M costs would
increase to $4,634, although there would be savings in aeration energy cos™ The oZal
removed * C°llege WWT? W°Uld be $OJ3 per Ib of additional N
Appendix II
42
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SUSQUEHANNA WATER POLLUTION CONTROL PLANT
LANCASTER AREA SEWER AUTHORITY
The service area of the Lancaster Area Sewer Authority is located south of Route 30 and
to the east of the Susquehanna River in Eastern Pennsylvania. The activated sludge plant
owned and operated by this authority is located near the Susquehanna River, but
discharges to Dry Run which is a very small tributary of the River. During dry weather,
the entire flow in Dry Run is made up of the plant effluent. The plant has an effluent total
P permit of 2 mg/L, and the ammonium-N permit is 12 mg/L from May 1st to October
31st. The ammonium-N permit is being changed to 5 mg/L as a monthly average
applicable over the same period.
The WPCP is rated at 12 MOD, and the average flow for the July 1995 - July 1996 period
was 9.45 MOD. The plant receives a mixture of municipal and industrial wastewaters,
with 10% of the flow and 30% of the BOD load originating from the industries. The
influent BODs averaged 169 mg/L, and the primary effluent BODs averaged 110 mg/L
during the period of evaluation. Raw influent TKN was 29 mg/L, and the primary
effluent TKN was assumed to be 80 % of the raw value. The average effluent TKN and
ammonium-N were 1.8 mg/L and 0.6 mg/L, respectively. The average effluent TN was
10.2 mg/L, which indicates that a substantial amount of denitrification is taking place in
the anaerobic zones as a result of NOx recycle with the RAS. A mass balance performed
on the nitrogen species showed that 50% of the NOx generated during nitrification was
denitrified in the system as operated.
The raw influent is screened through 3/4inch screens and degritted in aerated grit
chambers. Then, the wastewater passes through two Worthington comminutors. The
plant has two 90ft diameter primary clarifiers, and a third clarifier (30ft diameter) was
being added at the time the report was written. The plant then separates into two flow
trains, and each train has three anaerobic cells (17 % of total volume) and three aerobic
cells (83 % of total volume) connected in series. The nominal hydraulic retention time at
a design flow of 12 MOD is 5.68 hours. The air diffusers are arranged for tapered
aeration. The plant maintains an MCRT of 6 to 10 days. At these MCRTs, MLVSS is
only 65 to 70 % of MLSS, which implies the presence of a substantial amount of inert
material. There are two 100 ft diameter secondary clarifiers equipped with Rapid Sludge
Removal (RSR) systems. The third clarifier has a 140 ft diameter and the sludge is
removed via a Tow-bro unit. The SOR with all clarifiers in service is 385 gpd/ft2 at 12
MOD.
The RAS flow rate from each clarifier can be controlled by telescopic valves. The WAS
is collected in a wet well and from there it is pumped to the primary clarifiers where it is
co-thickened and sent to the gravity thickeners. The average TP increases from a range of
3 to 7 mg/L in the raw influent to concentrations greater than 10 mg/L in the primary
clarifier effluent because of release under anaerobic conditions. Thickened sludge is sent
to belt filters and lime is added after dewatering to stabilize the sludge.
Appendix II 43
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The proposed modifications are aimed at decreasing the average effluent NOx
concentrate from 8.3 to 5 mg/L, and thus reduce the TN concentration from 10 2 to 7
mg/L. The proposed configuration includes anoxic zones immediately after the anaerobic
zones and a nitrate recycle system for additional denitrification. The aerobic vo ume
would decrease, however, and the density of the diffusers would need to be increased™
maintain the current amount of oxygen transfer. The nitrate recycle system would be
installed in each tram to pump Nox from the end of the aerobic zone to L begging of
the anoxic zone It is recommended that the plant install a nitrate recycle system whha
Krn A ^ t0 handle,denitrification requirements at a peak month flow r'e of
15 MOD. A small increase in the ferrous sulfate dose to maintain 2 mg/L total P should
De adequate.
The primary effluent BOD levels are expected to decrease with the addition of a third
clarifier, and this reduction will provide adequate capacity to maintain performance as
flows increase from an annual average of 9.5 MOD to 12 MOD. To accomodate further
increases in flow, the anaerobic zone can be operated as an anoxic zone or a third AS
train can be added.
The costs/savings of the proposed modifications would arise from:
1. Electrical costs of operating nitrate recycle pumps and mixers;
2. Electrical savings in aeration costs from denitrification of'an additional 32 me/L
NOx ' &
3. Increase in chemical costs if the plant switches to chemical P removal-
4. Associated operator time for maintenance and the cost of repairs on new equipment.
The capital cost for N removal with biological excess P removal is $1,618 500 and the
operating costs are $23,258. The cost per pound of additional N removed over a 20-year
period is $1.12 based on 1996 dollars. The annual operating costs would increase in
proportion to the flow and at the rate of inflation. The capital and operating costs of N
removal with chemical P removal would be the same as bio-P removal. However an
additional $15,000 would be spent for the chemicals. Thus, the cost of an additional
pound of N removed would increase to $1.24.
Appendix II
44
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THROOP WWTP, LACKAWANNA RIVER BASIN SEWER AUTHORITY
The Throop regional WWTP is an activated sludge plant that services municipal and
industrial customers to the east and south of the City of Scranton. The plant is permitted
to treat a flow of 7 MOD, and the design peak wet weather flow is 14 MOD. Plant
operation during 1995 was examined, as the flow conditions were considered to be more
representative of current conditions than those in 1996. The average flow was 4.26 MOD
for 1995.
The raw influent BODs averaged 105 mg/L, which is approximately 50 % of average
levels observed at plants where the raw influent is transported through new sewers with
low levels of infiltration/inflow. NH4-N levels reaching the plant were 70 % of TKN,
with an average TKN value of 29 mg/L. The effluent ammonium-N levels were less than
1 mg/L in 1995. A nitrogen mass balance showed that of 20 mg/L of TKN in the primary
effluent, 4.5 mg/L was removed in the biomass, 1.5 mg/L was discharged as soluble
organic nitrogen in the plant effluent, and the remaining 14 mg/L of ammonium-N was
nitrified, resulting in a total of 11.1 mg/L of oxidized nitrogen. The resulting deficiency
in alkalinity was satisfied by adding hydrated lime. Denitrification of 6.5 mg/L of
oxidized-N will also recover 23 mg/L alkalinity as CaCOs, which is equivalent to the
alkalinity of 570 Ib/day of pure lime added to a flow of 4.5 MOD.
The plant's headworks consist of two grit chambers, a Parshall flume and Weisflo
mechanical bar screens. Primary clarification is achieved in four 93 ft by 33 ft tanks with
SWD depths of 10 ft, yielding an SOR of 570 gpd/ft2 at 7 MOD. The four activated
sludge basins of 169ft x 29ft x 15ft have an HRT of 11.7 at 4.5 MOD and they are
followed by four secondary clarifiers with 570 gpd/ft2 SORs at 7 MOD. Space is
available to the left of the existing units to add an additional secondary clarifier. The
secondary effluent is chlorinated and aerated prior to discharge. From analysis of DO
concentrations in the activated sludge tanks and the pattern of fluctuations observed in
chlorine demand, it was concluded that during times of low DO, incomplete oxidation of
NH4-N to NO3-N was occurring, resulting in NO2-N consumption of chlorine. Primary
and secondary waste sludges are processed in a DAF unit, a digester and a belt filter.
The evaluations showed that the activated sludge basin volume and secondary clarifier
capacity are limiting factors for implementation of further removal of nitrogen.
According to the calculations, an additional activated sludge basin and a clarifier are
required at the design flow. Besides, the existing tanks need to be retrofitted to include
anoxic and aerobic zones with nitrate recycle pumps. Therefore, it is recommended that
all the activated sludge basins be converted to a Modified Lutzack Ettinger (MLE)
configuration. The nitrate recycle pump should be sized to operate at flow rates of 50 to
200 percent of the influent flow to be able to supply sufficient oxidized-N to the anoxic
zones where the denitrification will take place.
Following items were considered to be essential for the BNR upgrade at the design flow
of 7.0 MOD:
Appendix II 45
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• Improvement of plant hydraulics and flow distribution structures;
• Addition of a new activated sludge basin-
• Modification of the existing basins to MLE configuration-
• Addition of a new secondary clarifier
. Upgrade of the RAS system to meet the needs of the new configuration-
• Upgrade of the aeration system
Appendix II
46
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WILLIAMSPORT SANITARY AUTHORITY CENTRAL PLANT
The Williamsport Central WWTP is an activated sludge facility located on a narrow tract
of land between 1-180 and a railroad track that runs parallel to the Susquehanna River.
The plant is rated for a flow of 7.2 MOD, with most of the flow being from domestic
sources. Currently, during wet weather periods, the flows can increase above 7.2 MOD
because of infiltration/inflow, part of which comes from combined sewers.
Operating data from 1996 showed that the average flow rate of raw influent was 8.98
MOD and the plant has limited capacity for seasonal nitrification. Because denitrification
causes problems with rising sludge in the secondary clarifiers, the plant operator prefers
not to nitrify. Average raw influent BODs was 102 mg/L, which represents a fairly dilute
wastewater. This value was 175 mg/L during dry weather (August) when the influent
flow averaged 6.50 MOD. Analysis of data showed that the maximum month to average
month COD ratio was 1.17. .Fluctuations in COD must be considered, as COD load
determines the MLSS levels at which the AS basins should be operated at the MCRTs
required for nitrogen removal. The plant was operated at the low MLSS value of 1318
mg/L during 1996, with a VSS percentage of 85.5%. Plant effluent data show partial
nitrification of NFLt-N at warmer temperatures. Increased nitrification caused a 90 to 100
mg/L drop in effluent alkalinity.
Pretreatment consists of 3/4 inch mechanically cleaned screens followed by grit removal
channels. The plant also has covered preaeration tanks that were built as part of the
original primary treatment facility, and they are used to strip odors from the sewage. The
three primary clarifiers following pretreatment are rectangular with SORs of 950 gpd/ft2.
The clarifiers accomplished 50% TSS and 25% BODs removal at an average flow of 9.0
MOD in 1996. The plant has eight AS tanks (HRT of 5.27 hours at 7.2 MOD), arranged
in two sets of four tanks on two sides of a feed channel, and under normal operation
conditions all eight tanks are operated in parallel. Aeration of the basins is accomplished
by two Sutorbilt positive displacement blowers. RAS can be fed either to the primary
effluent channel or directly to the AS tanks. Three rectangular secondary clarifiers have a
SOR of 667 gpd/ft2 at the design flow. Sludge wastage is from the RAS lines and the
WAS is sent to the gravity thickener. The Plant has two chlorine contact tanks located
adjacent to the secondary clarifiers. Two of three digesters are used as primary anaerobic
digesters, and the primary digested sludge is sent to the old elutriation tanks for further
thickening. Sludge from the secondary digester is passed through a belt filter press and is
landfilled.
Under these conditions, it was recommended that the AS system be designed with three
anoxic cells in each train, all of which can be operated aerobically. The first two anoxic
cells should be installed within the first aerobic tank. The third anoxic cell should be
constructed within the second AS tank and occupy 33%of its volume.
A nitrate recycle system should be constructed for each flow train and the capacity should
be 2.5 imes the influent flow of 7.2 MOD. Operation at 4000 mg/L MLSS in winter and
Appendix II 47
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at 2300 mg/L m summer necessitates two additional clarifiers. A flow distribution
structure shall also be constructed to distribute flow between the existing and new
clarifiers. Also a new RAS pumping station must be added. By increasing the
dimensions of the new secondary clarifiers, step feeding the primary effluent under high
flow conditions, and using fixed film media integrated into the activated sludge aerobic
zone, a nitrogen removal safety factor can be obtained.
The capital costs of the modifications recommended for nitrogen removal implementation
are estimated to be $6,339,416. The operating costs would increase by $36 675 per year
because of the energy costs of operating the blowers, etc., compared to the current cost of
operation. The cost of removing an additional pound of nitrogen would be $1 36 in 1997
dollars.
Appendix II
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WILLIAMSPORT SANITARY AUTHORITY WEST PLANT
The Williamsport West Plant is an activated sludge plant that receives wastewater from
Duboistown, Old Lycoming Township, Parts of Loyalstock Township, and Western
Williamsport on the westside of Lycomick Creek. The plant discharges to the
Susquehanna River. Sixty-five (65) to 70 % of the load treated at this plant is from an
industrial park. A significant portion of the fairly high COD load is not biodegraded
during activated sludge treatment because of a high non-biodegradable organic fraction.
It is not known if inhibitive compounds are present. The plant is permitted for a flow of
4.5 MOD, and for effluent concentrations of 2 mg/L TP, 2.5 mg/L ammonia-N, and 7.5
mg/L ammonia-N in winter.
The year 1996 was a fairly wet year with raw influent flows fluctuating between 2.2 and
4.6 MOD, with an average annual flow of 3.5 MOD. The primary effluent COD to BOD5
ratio averaged 3.4, which is substantially higher than the corresponding ratio for
municipal wastewater (1.5 - 2.5). This implies the presence of slowly biodegradable or
non-biodegradable COD. Also, the COD of the plant effluent averaged 138 mg/L, which
typically varies between 30 and 60 mg/L for municipal WWTP effluents. An analysis of
secondary effluent showed the absence of oxidized nitrogen forms and the presence of
high levels of NH4-N (21 mg/L). Plant effluent NKrN averaged 57% of the primary
effluent TKN, which further indicates the absence of nitrification.
Preliminary treatment consists of mechanical bar screens with linch openings and a
rectangular grit chamber. Raw influent is then pumped to a pre-aeration chamber used
for scrubbing odors, especially from May to October. Two primary clarifiers follow, with
SORs of 1500 gpm/ft2 at the peak month flow of 4.5 MOD. Primary sludge is sent to the
gravity thickener. Primary clarifier effluent is mixed with RAS before it is fed to the
activated sludge system that is comprised of six tanks (cells). Each cell has an HRT of
5.3 hours at the design flow of 4.5 MOD, and they are aerated with Lightnin' draft tube
aerators (DTAs). These aerators have a mixer with impellers located within an air sparge
ring. Air is injected through nozzles in the ring. Each day the DO drops below 0.5 mg/L
during peak load hours, which occur after 10 am when all of the industries have resumed
operation. The AS basins are operated at MLSS levels of 1000 to 1500 mg/L,
corresponding to an MCRT of 5 to 7 days, because the aeration system capacity is not
capable of supporting higher biomass concentrations. Also, the secondary clarifiers
cannont support higher SORs or SVIs between 200 and 400 mL/g. Flow from one half of
the plant goes to two square secondary clarifiers, each with an SOR of 700 gpd/ft2 at
maximum flow. The remaining flow enters a secondary clarifier with an SOR of 950
gpd/ft2, which is very high for an activated sludge system. WAS is pumped to the gravity
thickener. The plant has two chlorine contact tanks for disinfection. Final effluent is not
dechlorinated.
The Williamsport West Plant has the following limitations for the implementation of
nitrification: limited space for new construction, absence of nitrification / denitrification
under existing conditions, and possibly the presence of inhibitory compounds in the
Annenriix II 49
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influent. Two options are suggested for implementing nitrogen removal. The first option
is designed to treat 130 mg/L of primary effluent BODs, and remove 300 mg/L of primary
effluent COD. Effluent COD would average at 130 mg/L. The AS tank volume would
be expanded to include the volume of the two existing square clarifiers. The total basin
volume with eight cells would be 1.22 MG, and the nominal HRT at the flow of 3.5
MOD average daily flow would be 8.4 hours. The system would be designed in an
anoxic-aerobic sequence, with the anoxic zone occupying 27% of the total tank volume.
Nitrates would be recycled from the end of the last aerobic cell to the anoxic cell in each
pass. The existing aeration system would be modified with membrane or ceramic fine
bubble diffusers. Secondary clarifier capacity needs to be increased to be able to operate
with MLSS levels of 3000 mg/L in summer and 4000 mg/L in winter. Two new
rectangular clarifiers could be accomodated within the space available. The AS system
must have a new instrumentation system for DO control. During some months
supplemental alkalinity may have to be added to nitrify an average of 21 mg/L NHrN.
The second option is plant expansion to:
1. A Single Stage Activated Sludge System: Additional AS cells, possibly downstream
of the existing tanks would be constructed. A third train of four cells also should be
added in parallel to the existing ones. Three new clarifiers and a new RAS pump
station should be added, too. A new chlorine contact tank would be added to provide
adequate time for disinfection.
2. Separate Stage Fixed Film: Expansion will include two new clarifiers, and high rate
biofilters such as Biofor or Biostyr. The advantages of separate stage treatment are
the smaller footprint, and possibly removal/concentration reduction of inhibitory
chemicals. The disadvantages are additional aeration energy consumption, additional
alkalinity needs, and methanol addition for post-denitrification.
3. Integrated Fixed Film AS (IFAS) Process: This alternative would be insertion of
Fixed film media into the aerobic zone. Floating sponges such as Linpor media or
plastic Kaldnes media would be the most effective.
The cost of modifying the existing treatment system for Option 1 was estimated. The
construction cost estimate totals $5,245,557 based on 1997 dollars. Capital costs total
$6,800,000 based on a 20 year life. Annual operating costs would increase by an
estimated $72,675 per year. The present worth of the increased M&O would be
$1,500,000. Cost per pound of additional nitrogen removed would be $2.58 per Ib N
removed.
Appendix II 50
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WYOMING VALLEY SANITARY AUTHORITY WWTP
The plant services 35 municipalities in and around Luzerne County in Central
Pennsylvania. The plant is designed to treat a dry weather flow of 32 MOD and wet
weather flow of 50 MOD for conventional treatment, and it discharges to the
Susquehanna River. In 1995, the dry weather flow averaged 19 MOD, and the annual
average flow was 22 MOD. Evaluation of 1995 data showed that the plant maintained
good nitrogen removal by operating at high MCRTs (above 25 days), and by maintaining
MLSS concentrations of 5000 mg/L with AS basin DO concentrations of 0.5 to 1.5 mg/L.
However, effluent ammonium-N will increase unless the plant undertakes modifications
to maintain N removal at lower MCRTs.
In 1995, the raw influent BOD5 and TKN values averaged 200.7 mg/L and 26.6 mg/L,
respectively. Nitrification was limited by the capacity of the aeration system, as indicated
by effluent ammonium-N levels that varied between 3 and 6.5 mg/L for several months of
the year and averaged 2.21 mg/L. The effluent NOx was low with a 2.24 mg/L average,
indicating good denitrification in the reactors. Total N in the effluent was 6.52 mg/L.
During normal flows, the influent is screened through two Weismann Wiesflo fine screens
prior to being pumped by centrifugal pumps to the grit chambers. When the flow exceeds
the capacity of the centrifugal pumps or the Weisflo screens, the excess flow is diverted to a
set of Archimedes screw pumps. The plant has four Schreiber grit and scum removal units.
Following grit removal, the raw influent is distributed between four activated sludge flow
trains. Each train has two circular activated sludge tanks designated as the Schreiber GRD
(with central anoxic zone) and GRO basins (with intermittent aeration capacity) followed by
a circular secondary clarifier. The flow is aerated in the outer ring of the GRD basin and it
exits the GRD basin to enter the GRO basin. Each train has its own set of Aerzen positive
displacement blowers. Basins have O2 minimizers that control DO injection on the basis of
change in turbidity resulting from the presence of unstabilized colloidal organics in the
mixed liquor. It is used for cycling the aeration. However, due to poor mixing between the
sludges in the different rings of the basins, the minimizers can not be used effectively for
cyclic aeration purposes.
Analysis of the secondary clarifiers at the design flow rate of 8 MGD per train shows a
surface overflow rate of 315 gpd/ft2 which is lower than the typical design rate of 400
gpd/ft2 used for secondary clarifiers at facilities which incorporate nitrification. The layout
requires a clarifier to be taken out of service if a basin is taken out of service. Each train has
three RAS archimedes screw pumps (Schreiber tube pumps, Model 1400) installed in a
RAS well. Each pump can discharge at a maximum flow rate of 8 MGD. Therefore, in
theory, the RAS flow rate can be increased to 200 percent with all pumps in operation.
Optimum operation has been observed at RAS flow rates of 100 percent at the present
average flow of 24 MGD. Each GRO and GRD basin has a pipe which can be used in the
future as part of a nitrate recycle system. Because of extensive denitrification, the nitrate
recycle required to maintain an effluent total nitrogen less than 8 mg/L at design flow is
expected to be less than 100 percent of the influent wastewater flow.
Appendix II 51
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Sludge is wasted by a telescopic valve located in the discharge
box. Waste sludge enters a thickening pit located below th<
maintaining continuous WAS feed and clear liquid decanting,
above 2% solids in the pit. This sludge is then dewatere
centrifuges, with the final sludge having a 24 % solids content
dewatered sludge to raise the pH prior to incineration at temperati
BNR implementation will require operation at lower MCRTs and
maintain complete nitrification. DO set point is expected to 1
mg/L. This will decrease the denitrification in the aerobic zone i
NOx unless cyclic aeration or a nitrate recycle system is also ins
volume of the plant is only 20% of the total volume, but this is
adequate amounts of NOx. Thus, it was recommended that 50C
place in the aerobic zone via cyclic aeration. Cycle time can be
the monthly average effluent ammonium-N and NOx. Suggest
summer and 20 days in winter. Some structural modification will
studies show that cyclic aeration does not have sufficient capacity
nitrogen removal at dry weather flows above 24 MOD.
The installation of programmable timers is the only modificati*
removal. The cost will be $100,100 at 24 MOD, and the cost
projected as $0.023/lb. For a dry weather flow of 32 MOD, a ni
an aeration control system needs to be installed. The cost of th
$762,600, with the cost per Ib of additional N removed being $0.!
Appendix II
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YORK CITY SEWER AUTHORITY STP
The York City sewage treatment plant (STP) is a combination pure oxygen and A/O
activated sludge plant that discharges to Codorus Creek in Manchester Township, York
County, Pennsylvania. Codorus Creek is classified for warm water fish, recreation, water
supply and aquatic life. Hence, the discharge permit regulates nitrogen species as
follows: all year round nitrification is required with effluent ammonium-N values not to
exceed a monthly average of 1.7 mg/L from May 1st to October 31st, and a monthly
average of 2.1 mg/L for the rest of the year. Permitted weekly average and instantaneous
maximum levels are 1.5 and 2.0 times the monthly average values, respectively. The total
phosphorus permit of the plant is for 2 mg/L as a monthly average.
This plant was evaluated for the period from May 1995 through April 1996, during which
the plant achieved complete nitrification all year round. The effluent ammonium-N
averaged 0.1 mg/L, with a peak monthly concentration of 0.2 mg/L. A nitrogen balance
revealed that total nitrification averaged 12.9 mg/L, and 2.2 mg/L of nitrogen was being
denitrified. The phosphorus content of the WAS was 3.5 to 4.0 % on a VSS basis. The
average influent flow to the plant was 13 MOD.
The York City STP was designed to treat a flow of 26 MOD. The treatment train consists
of bar screens, grit removal, 8 primary clarifiers with a surface overflow rate of 960
gpd/ft2, activated sludge basins and secondary clarifiers in three independent trains,
secondary effluent filtration, and disinfection. The oldest section is an 8 MOD pure
oxygen train with two tanks and receives raw influent. This train is used when the raw
influent flow exceeds 18 MGD. The second train has a 7.5 MOD A/0™ process
configured as two parallel tanks, and primary effluent is fed into this train. Finally, the
third train also has an A/O™ configuration, but has three' parallel tanks receiving a
mixture of primary effluent and raw influent. The surface overflow rates of the secondary
clarifiers of the trains are 630 gpd/ft2, 318 gpd/ft2, and 242 gpd/ft2, respectively.
Phosphorus removal is biological in Trains 2 & 3, but in Train 1 it is achieved chemically
by the addition of ferrous sulfate.
With the existing flow arrangements, Train 1 cannot nitrify, and it would have to be down
rated to 1.5 MGD and operated with 3600 mg/L MLSS in a peak month in winter to
facilitate nitrification. Additionally, the hydraulic and load treatment capacity of the
other two trains should be increased to accomodate the flow not sent to Train 1 with
consideration given to the surface overflow rates of the secondary clarifiers. Besides the
above suggestions, the following modifications were also suggested for the activated
sludge basins for better nitrogen removal at York City STP:
/. Cyclic aeration of the first two aerobic cells with / without a nitrate recycle system:
With a cycle time of 30 min for the air on and off periods and without nitrate recycle
6 mg/L of N can be denitrified. With nitrate recycle, an additional 2 mg/L of N can
be removed.
Appendix II 53
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2. Conversion of the first aerobic cell in each activated sludge tank to an anoxic cell
with a nitrate recycle;
With a modification of the surface aerators in Trains 2 and 3 to obtain anoxic cells
that will be mixed a few minutes every 30 min to prevent settling. The pure oxygen
supply in the first aerobic tank of Train 1 should be shut off.
3. Conversion of the anaerobic cells to anoxic cells with the addition of nitrate recycle;
addition of ferrous sulfatefor chemical phosphorus removal.
The anaerobic zones of Trains 2 and 3 will be made anoxic, with nitrate recycle.
Phosphorus removal will be achieved chemically with ferrous sulfate addition to the
raw influent.
The cost calculations showed that all alternatives that include denitrification result in
savings because of reductions in aeration costs. The Capital cost of Alternative 1 without
a nitrate recycle system and for treatment of 18 MOD of raw influent flow is $30,000, and
there will be substantial savings in operating costs ($20,000 per year) because of
denitrification. Alternatives 2 'and 3 both include nitrate recycle systems, and their total
capital costs are similar. Alternative 3 includes chemical phosphorus removal with the
additional cost of ferrous sulfate addition. At the design flow of 26 MOD, the annual
operating cost is $30,000. The additional operating costs of nitrification and
denitrification are $25,993 to obtain an additional 5.5 mg/L of N removal, for a cost of
$0.42 per Ib of N removed.
Appendix [I • 54
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Virginia Files - Potomac River Discharges
ARLINGTON WWTP
The Arlington Wastewater Treatment Plant located in Northern Virginia is currently
being expanded and upgraded for BNR. However, construction of the BNR upgrade is
not expected to be completed by the year 2000, and thus, will not meet the goal of 40%
reduction of controllable nitrogen inputs to the Chesapeake Bay agreed upon by the
governors of the three states. Therefore, the USEPA and the Virginia Department of
Environmental Quality are considering the option of implementing temporary BNR
modifications at this facility in order to accomplish some degree of nutrient removal in
the interim period before the final upgrades, if the upgrades can be accomplished at a
reasonable cost.
The Arlington WWTP is rated for an average daily flow rate of 30 MOD. The facility is
currently operating at its design capacity. The current average daily flow rate is 32.4
MOD, which exceeds the permitted flow and illustrates the need for a capacity upgrade.
The facility has preliminary, primary, secondary, and tertiary treatment facilities. The
secondary treatment process consists of three activated sludge basins and each basin has
four passes. Coarse bubble diffusers are used in the activated sludge basins to aerate the
mixed liquor. The hydraulic retention time (HRT) of the activated sludge basins is
approximately six hours at the design average flow rate of 30 MOD. The activated sludge
basins are followed by six circular secondary clarifiers. The secondary clarifiers have a
diameter of 115 feet and a side water depth of 11 feet.
The facility is currently operated in the step feed configuration with four primary effluent
feed points in each activated sludge basin. Approximately 25% of the influent is fed at
each step feed point. The average effluent TN during the year of evaluation was 9.0
mg/L, which is only 1 mg/L higher than the Chesapeake Bay goal of 8.0 mg/L.
The current operation of the plant is optimized for nitrogen removal. However, the lack
of baffle walls between the anoxic and aerobic zones results in back-mixing between the
zones and promotes growth of low DO filamentous bacteria, causing poor activated
sludge settlability. Installation of baffle walls could provide sufficient control of the
filamentous bacteria and make improved nitrogen removal possible. This would reduce
the effluent total nitrogen to a maximum of approximately 8.0 mg/L, and would result in
a reduction of approximately 11% from the current average effluent TN level of 9.0
mg/L. It is likely that the annual average would be closer to 6 mg/L if the baffles and
mixers were installed. However the following economic analysis assume that the effluent
nitrogen would average 8 mg/L.
Capital cost for implementing interim nitrogen and phosphorus removal modifications is
$560,000, and it is planning level estimate with a 20% contingency. Since the plant is
Appendix II 55
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already optimized for nitrogen removal, additional aeration cost savings will be
6' ^ 6Stimated 2° year increase in maintenance and operation cost is
-, ~ - •>— —**•**«"" •" *"«"ncuiuii;c ouu operation cost is
$544,000 The overall cost for implementing nitrogen removal includes the cost of
achieving demtrification only, and it is $0.605 per pound of additional nitrogen removed
Appendix II
56
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COLONIAL BEACH WWTP
The Colonial Beach WWTP is an activated sludge facility that serves the town of
Colonial Beach, and is located in Westmoreland County, VA. It discharges to Monroe
Bay, an inlet of the tidal Potomac River. The current permit requires the plant to maintain
an average BODs and TSS of 21 mg/L and 28 mg/L, respectively, at all times. An effluent
ammonia concentration of 4.63 mg/L or less must be met April through September. The
DO concentration in the plant effluent must be no less than 6.5 mg/L and the permitted
effluent flow rate is 2 MGD. At present the plant receives an average flow of 0.64 MGD.
The flows, concentrations and loads to the plant over the twelve month period from
August 1996 through July 1997 were analyzed. The raw influent BOD5 averaged 89 mg/L
for that period. The influent TKN, NHs and TP values were usually measured once a
month, and no TKN or NHs measurements were recorded on the same day during the
period from March 1997 through July 1997. Therefore, in some months, the NHs values
seemed to be higher than the TKN values, and these values were not considered in the
analysis. The Influent TP values averaged 3.5 mg/L over an 8 month period. TP
measurements were not available for the remaining 4 months. Effluent TKN and NOx
concentrations averaged 0.44 and 13.1 mg/L, respectively.
A mechanical bar screen is installed in the influent channel. Following screening, grit is
removed from the wastewater via a stirred grit chamber. The plant has two grit chambers,
each of which is equipped with a 0.75 HP constant speed paddle mixer to control velocity
in the chamber. Flow, then, enters a wet well that distributes the flow to the equalization
tanks. The plant has two equalization tanks, but only one tank was in operation. These
basins are equipped with a coarse bubble air diffusion system. Flow fromthe EQ basin
enters activated sludge tanks. The facility has two completely mixed activated sludge
(CMAS) tanks, currently, only one is operated at a time. Lime is fed to the tanks to
control the pH. The flow passes to one of the two clarifiers in operation, and clarified
water then enters one of the two chlorine contact units. A post aeration chamber is
provided at the end of the chlorine contact unit to achieve dissolved oxygen concentration
of at least 6.5 mg/L in the final effluent.
The plant has two aerobic digesters for waste sludges, and flow from the digesters enters
the belt filter press. Dewatered sludge consisting of 17 % ODS (oven dried solids) is
applied to landfill. Filtrates generated during filtration and supernatant from the aerobic
digesters are returned to the equalization basin.
Considering the effluent values, complete nitrification of the ammonia formed from the
complete ammonification of all the sources of organic-N was assumed to be possible.
Because of the current low flows relative to design flow, it was concluded that successful
nitrogen removal could be accomplished by cycling the aerators on and off in the CMAS
tank. Thus, the capital costs will include a DO control system with a DO probe in each
AS tank, a PLC, and electrical work for the installation, for the estimated sum of $90,000.
The estimated annual change in O&M costs would be a total reduction of $7,100 at
57
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current flow and $15,500 at design flow. The estimated total cost for implementing BNR
I' *°n n*f n If ^ °nly'IafIthe fadlityis ca?able of nitrifying year round, and it sums up
to $0.065 per Ib additional N removed. H
Appendix II
58
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TOWN OF DAHLGREN WWTP
The Dahlgren Wastewater Treatment Plant (WWTP) is an Orbal configuration oxidation
ditch activated sludge plant owned and operated by the Utilities Division of King George
County, VA and it discharges to the Potomac River. The current permitted flow is 0.325
MOD, but an expansion scheduled for 1998 will increase the plant capacity up to 0.5
MOD. The plant received an average flow of 0.28 MOD from October, 1996 through
October, 1997, which is about 86 % of the design flow of 0.325 MOD. Discharge permit
limits effluent average ammonium-N concentrations to 1.35 mg/L, but the plant does not
have a discharge limit on TN.
The raw influent BODs averaged 251 mg/L over the thirteen month period, and during
periods of high infiltration, BOD concentrations decreased down to monthly averages as
low as 197 mg/L. The highest monthly average was 370 mg/L during August, 1997. The
raw influent TKN values were not routinely measured during plant operation. However,
influent ammonia concentrations were measured at least once a week. TKN values were
estimated based upon an ammonia-TKN ratio of 0.7 was assumed.
The average water quality values for each month were in compliance with the permit
requirements, except for May and June of 1997 when the effluent ammonia levels
exceeded the permit requirement of 1.35 mg/L by 70% because of low DO concentrations
in the mixed liquor. Effluent ammoniuni-N averaged 0.92 for the period of evaluation.
Overall, the data indicate that the Dahlgren Orbal-like oxidation ditch system is capable
of maintaining complete nitrification all year round for the current flows and loads.
The first unit of the WWTP is an equalization basin. From equalization, wastewater
flows directly to the oxidation ditch. The existing equalization volume is sufficient to
equalize the BOD and TSS of the influent wastewater, but it is operated as an overflow
basin, which means it does nothing to equalize the flow. The biological process of the
plant consists of a single Orbal-type oxidation ditch, with three concentric rings. Flow
enters the inner ring of the oxidation ditch, and then flows successively through the
middle and outer rings before exiting to the secondary clarifiers. The ditch has a
hydraulic detention time (HRT) of 1.25 days at the design flow of 325,000 gpd, and will
provide an HRT of 0.81 days for the planned flow of 0.5 MOD. Aeration is provided by
vertical discs mounted on horizontal shafts. The number of discs on each rotor in each
ring can be varied to control the amount of aeration within each ring. The facility has two
solids-contact type secondary clarifiers, designed for an average overflow rate of 350
gpd/ft2, and a weir loading rate of 2,500 gpm/ft. The overflow rate is very adequate for
the current design flow of 0.325 MOD. When the flow is increased to 0.5 MOD, the
overflow rate would be 536 gpd/ft2. The plant has two aerobic digesters. Secondary
effluent passes through a 3 pass chlorine contact tank. This provides an HRT of 50
minutes at design flow. Sludge dewatering is accomplished using a Model 3500 Envirex
type belt filter press. Polymer is added during dewatering. Dewatered sludge is
transported to a landfill 3 days a week.
Appendix II 59
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The Orbal-type oxidation ditch operated at this facility was designed to accomplish
substantial amounts of nitrogen removal if the oxygen inputs are carefully controlled.
This can be accomplished by placing the appropriate number of discs on the aerators in
the three ditches. If this proves to be too insensitive, further control can be accomplished
by cycling aerators on and off. Once the appropriate disc configuration and on-off
cycling periods are established, the cycling can be accomplished using timers to turn the
aerators on and off throughout the day. The objective is to supply enough oxygen to
remove much of the BOD and to completely nitrify all of the available ammonia, but
limit the oxygen inputs so that a substantial fraction of the influent BOD will be removed
by denitrification. It will be necessary for the operators to measure effluent ammonia and
NOx at least three times during the work day, and make appropriate adjustments to the
timers for the rest of the 24 hour period, to optimize N removal. Once the patterns are
determined, the adjustments will be simple to make. A Hach kit could be obtained and
used by the operators to determine the ammonia and NOX concentrations. The control of
oxygen transfer for optimum nitrogen removal can be accomplished by adjusting the
numbers of discs on the rotors so that the first ring acts as an anoxic zone with an internal
nitrate recycle from the second ring, which will continue to be used as an aerobic zone.
Effluent total phosphorus (TP) concentrations exceeded the permit limit of 2.0 mg/L only
one month during the thirteen-month evaluation period. Thus, no modifications are
needed to improve phosphorus removal unless the managers/operators are interested in
implementing biological phosphorus removal rather than chemical phosphorus removal.
Capital costs for implementing BNR are based on installing timers in the MCCs of the
aerators to operate the aerators in cyclical aeration mode if necessary, and two DO probes
for continuous DO monitoring in the ditch, yielding a total of $30,000. The projected net
decrease in O&M cost is $4,900 as a result of savings from energy consumption
reduction. The net additional cost/savings per Ib of N removed is estimated as $0.12.
Appendix II '60
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DALE SERVICES SECTION 1 AND SECTION 8 WWTPs
The Dale Services Corporation operates two WWTPs designated as Section 1 and Section
8, and both discharge into a tributary of the Potomac River Tidal Estuary. The plants are
contact stabilization activated sludge design facilities permitted for flows of 3 MOD each.
At present the plants meet the P, BOD and TSS permit limits of 0.1 mg/L P, 2 mg/L
BOD, and 3 mg/L SS. However, TKN concentrations in the effluent are 10 to 15 mg/L,
which exceeds the ammonia limit as well as the TN concentration goals for effluents
discharging into tributaries of the Chesapeake Bay.
Raw wastewater arrives at the treatment plants to pass through a coarse bar screen and a
Parshall flume. The flow proceeds to a splitter box where the flow is appropriately
divided among three contact stabilization AS units. The flow is introduced into a contact
(mixing) zone where the raw wastewater is mixed with AS using compressed air
generated by blowers. The bioreactors perhaps can be more accurately described as
"modified orbal systems". The flow then passes to the secondary clarifiers. The RAS is
pumped to the reaeration zone where the bacteria are given time to stabilize any stored or
trapped organics, and the flow is then re-introduced to the contact zone. The WAS is sent
to a primary and then to a secondary aerobic digester, from where it is sent a gravity
thickener for dewatering. Secondary effluent is pumped to chemical clarifiers for
precipitation of phosphorus and coagulation of suspended solids with aluminum chloride.
When necessary the pH of the clarified water can be adjusted with lime addition.
Effluent is then pumped to four multi-media pressure filters, and further to the UV
disinfection unit.
Although the wastewater quality was similar, the average flow to Section 8 was 2.12
MOD, whereas it was 3.0 MOD to Section 1 in 1996. The raw and final effluent TKN
concentrations were 40 and 12 mg/L, respectively. Phosphorus concentration in the raw
wastewater was 5.2 mg/L, and it was reduced to 0.08 mg/L after tertiary treatment. As
the NOx concentration in the effluent was below 1 mg/L, the TKN can be assumed to be
a measure of the ammonia concentration in the final effluent, which is relatively high.
Although the reactors were designed to operate as Contact Stabilization Process Units,
currently the contact and reaeration basins are operated at similar, but unusually high
MLSS concentrations: 4200 to 6400 mg/L, and MLVSS constitute 75 % of MLSS. This
is a result of strong backmixing and high RAS rates. The HRT of each one of the reactors
in Section 1 can be approximated as 0.4 days (9.6 hours) at an average flow rate of 3
MOD. The HRT of the reactors in Section 8 are 0.56 days (13.4 hours) at an average
flow of 2.15 MOD. As the flow will reach 3 MOD in 5 to 6 years, the calculations for
both plants were made using 3 MOD. The operating MCRT was calculated to be 15
days. The raw influent pH varied at a low range of 6.7 to 6.9. Raw wastewater and
bioreactor alkalinities were measured to be between 125 and 175 mg/L as CaCOs, and 65
to 125 mg/L as CaCO3. These numbers indicate either a high CO2 partial pressure or
alkalinity due to non-carbonate sources.
Appendix II 61
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Full nitrification at Dale City WWTPs can be achieved by addition of alkalinity,
maintaining the pH at 7.2 and the DO at 2.0 to 2.5 mg/L, without any changes in
configuration and operation. For denitrification to take place, an anoxic zone of at least 2
hours HRT is required. It is recommended that part of the volume of aerobic sludge
digesters be incorporated into the bioreactor zones, thereby increasing the total reactor
volumes to 12 hours HRT. The designed air supply facilities at the Dale City WWTPs
have a total capacity of 21,000 ft3/min. However, at present the real air supply capacity
of the blowers is not known. These should be determined by testing. If denitrification
can be achieved, the air requirements will be significantly lowered (approximately 20 %).
A separate sludge digester at each plant shall be designed and constructed for treatment of
WAS, as in the future the whole volume of the aerobic digesters will be. needed for
anoxic zone.
The capital costs for the three stages (adjustment of alkalinity and pH for implementation
of nitrification, separation of an anoxic zone in the aerobic digester, and use of the whole
volume of the digester for anoxic zone) of modifications are $330,000; $220,000; and
$1,080,000. Capital costs for second stage are based on an effluent TN concentration of
8.0 mg/L, and for third stage are based on an effluent TN of 4.0 mg/L. The estimated
annual change in the O&M costs are an increase of $430,000 for the first stage, and
reductions of $140,000 and $180,000 for the second and third stages. The estimated total
costs of additional N removal at the Dale City WWTPs are $0.68 and $0.29 per Ib of N
removed for the first and second stages. A cost calculation for the third stage is not
presented.
Appendix II 62
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H. L. MOONEY WWTP, PRINCE WILLIAM COUNTY AUTHORITY
The Mooney WWTP is rated for an average daily flow of 18 MOD. However, the
existing tertiary filters can only treat up to 12 MGD, which is sligntly less than the current
annual average flow rate of 12.8 MGD. After preliminary and primary treatment,
wastewater flows into four activated sludge basins, each with two passes and two baffle
walls at the upstream and downstream ends. The hydraulic retention time (HRT) of the
activated sludge basins is 6.3 hours at the design average flow rate of 18 MGD, and it is
9.4 hours at the current annual average flow rate of 12 MGD. Fine bubble membrane
diffusers are used in the activated sludge basins to aerate the mixed liquor. The activated
sludge basis are followed by four 95 foot diameter secondary clarifiers. Three of the
secondary clarifiers have a side water depth of 12 feet, and the fourth clarifier has a side
water depth of 16 feet.
In the current operating mode, both effluent from the primary clarifiers and the return
activated sludge are fed into the first pass of the activated sludge basins. High chemical
doses are used in the primary clarifiers to increase BOD and phosphorus removal. The
two passes of the activated sludge basins are operated under aerobic condition to
accomplish BOD removal and nitrification. However, nitrification has sometimes been
inconsistent in the past. The facility is currently conducting a study to determine the
cause for the occasional loss of nitrification. For the most part, the facility nitrifies year
round. Mathematical analysis of the process shows that the facility can nitrify year round,
unless nitrification is inhibited due to toxicity.
To accomplish denitrification it is recommended that the activated sludge basins be
operated in the modified Ludzack-Ettinger (MLE) mode. All of the primary effluent and
the RAS would be fed into the first zone of each basin, which would be an anoxic zone
occupying 15% of the total basin volume. It is predicted that this would result in an
effluent TN concentration of 14 mg/L or less. A second anoxic zone would decrease the
TN concentration down to less than 8 mg/L year round. At design flow, the nitrification
and denitrification capacity of the facility will be limited by the secondary clarifiers
because of the high surface overflow rates and high solids loading rates. Additional
secondary clarifiers will be required to maintain adequate treatment at design capacity.
However, additional secondary clarifiers are not required to accomplish an effluent total
nitrogen concentration of less than 8.0 mg/L at the current annual average flow rate. The
modifications recommended will result in reducing the effluent total nitrogen by
approximately 50% from the current level.
Capital cost for implementing interim nitrogen and phosphorus removal modifications is
$490,000, and it is a planning level estimate with a 20% contingency. The estimated 20
year decrease in maintenance and operation cost is $124,000. The overall cost for
implementing nitrogen removal includes the cost of achieving denitrification only, and it
is $0.063 -per pound of nitrogen removed.
Appendix II 63
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LEESBURG WATER POLLUTION CONTROL FACILITY
The WWTP of the Town of Leesburg is an in-series combination trickling filter-activated
sludge facility with intermediate clarifiers. It currently is rated for an average daily flow
of 4.85 MOD, and the facility discharges into the freshwater Potomac River. The plant
has a discharge permit that regulates the ammonium-N and TKN concentrations in the
final effluent. The monthly average ammonium-N concentration is required to be 3.0
mg/L or less between May and October, and the TKN concentration is required to be 6.0
mg/L or less for the same period. A review of the plant operating data from September
1995 to August 1996 showed that the facility received a current annual average flow of
2.86 MOD, and that the current monthly average BOD and TKN concentrations ranged
from 124 to 247 mg/L and 15.3 to 30.7 mg/L, respectively.
Preliminary treatment facilities at the Leesburg WWTP include mechanical screens, raw
sewage pumps and grit chambers. Flow then goes to three circular primary clarifiers with
SORs of 572 gpd/ft2 at the design average flow of 4.85 MOD. The secondary treatment
process consists of four trickling filters and three circular intermediate clarifiers, followed
by an AS system and two rectangular final clarifiers. The trickling filters are also known
as roughing filters, two of which have plastic media in their entire filter depth of 4.0 ft
whereas the other two filters have 1.0 ft of plastic media on top of 3.0 ft of rock media.
Currently, the filters are removing 70 to 85 % of the BOD present in the primary effluent,
and partially nitrifying at the current average flow. The intermediate clarifiers have SORs
of 572 gpd/ft2 at the design average flow. The clarifier effluent is pumped to two single
pass AS basins, with a HRTs of 4.7 hours at the design average flow. They have a
tapered aeration system with ceramic diffusers. The SORs of the final clarifiers are 379
gpd/ft2 at the design average flow. The RAS flow rate from clarifier underflow varies
between 60 and 150%. P removal is achieved by ferric chloride addition to the final
clarifier influent. Tertiary treatment consists of mainly two automatic backwashing
gravity sand filters. Filtered effluent is pumped to an outfall structure consisting of two
cascade aerators, and flows by gravity to the Potomac River. Disinfection is achieved by
chlorinating the final clarifier effluent. Sodium bisulfite is fed prior to discharge for
dechlorination.
The existing roughing filters remove most of the BOD and insufficient amounts of
organic carbon are left available for efficient denitrification. The Following
modifications are recommended for implementation of BNR at the Leesburg WPCF:
1. Level I - Effluent TN concentration of 9 to 12 mg/L in summer; 16 to 18 mg/L in
winter. No additional tanks will be constructed, and the modifications will be limited
to changes within the existing AS system, and roughing filters will be kept in service:
An anoxic zone shall be created at the influent end of each of the two AS basins and a
portion of the primary effluent shall be bypassed to the anoxic zones. Each anoxic
zone shall occupy approximately 30% of the AS volume, with a HRT of 1.86 hours.
The nitrate recycle pumping system shall be capable of pumping 50 to 150 % of the
Appendix II 64
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primary effluent. Bypassing 50% of the flow around the filters will decrease the
loading on the filters, which would enable them to partially or completely nitrify
during the wanner months. The anticipated range of effluent TN level is 9 12 mg/L,
May through October. During the colder months, TN may range as high as 16 to 18
mg/L.
2. a) Level 2 - Year round effluent TN concentrations of about 8 mg/L, and 6 to 8 mg/L
from April to October. Requires modifications of the existing AS system and
replacement of two of the roughing filters with new AS basins: The remaining two
filters would treat up to 1.0 MOD under average conditions, and would be able to
nitrify year round. The total HRT of the AS system would increase from 4.65 hours
to 9.3 hours. A MLSS concentration of 3000 to 3500 mg/L is anticipated in four
parallel operating AS basins. Each basin will have an anoxic zone (30%) at the
influent end. Submersible mixers are needed to keep mixed liquor in suspension. A
nitrate recycle pumping system capable of pumping 100 to 300 % of the flow is
required. P removal will be achieved with chemical addition.
3. b) Level 2 - Nitrogen removal with BPR: A2/O process is recommended. Two of the
existing filters will be demolished and two additional AS basins constructed. A total
HRT of the AS basins will be 9.3 hours. Anaerobic and anoxic zones would occupy
approximately 15% and 30% of the basin volume, respectively. All other
modifications and nitrogen removal capacity would be similar to Alternative 2. The
effluent P level would range from 1.0 to 2.0 mg/L on a monthly average basis.
Capital costs of the three alternatives can be listed as $290,000; $2,770,000; and
$2,980,000 in the order presented above. The calculations for the estimated changes in
the annual O&M costs showed that Alternative 1 results in an increase of $1,400;
whereas Alternatives 2 and 3 result in reductions of $1,000 and $38,900. The total cost
of additional N removal are $0.13; $0.73; and $0.68 per Ib of N removed for the three
alternatives.
Appendix II 65
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LOWER POTOMAC POLLUTION CONTROL PLANT, FAIRFAX COUNTY
The Lower Potomac Wastewater Treatment Plant, originally rated for an average daily
flow of 54 MOD, is currently being upgraded to a design flow rate of 67 MOD with
biological nitrogen removal. The current annual average flow rate is approximately 45
MOD. The average BOD, TSS, TN and TP concentrations reaching the plant are 250
mg/L, 200 mg/L, 33 mg/L and 6.5 mg/L, respectively. The corresponding current average
effluent concentrations are 4 mgBOD/L, 6 mgTSS/L, 12.5 mgNH3-N/L, 2.0 mgNO3-N/L,
15 mgTN/L, and 0.22 mgTP/L.
The original treatment system consists of preliminary, primary, secondary, and tertiary
treatment processes. The secondary treatment process consists of six parallel step-feed
design activated sludge basins, with three passes in each basin. The basins are equipped
with medium bubble diffusers (Pearlcomb®) manufactured by FMC Corporation to aerate
the mixed liquor. The hydraulic retention time of the activated sludge basins is
approximately five hours at the design average flow of 54 MOD. Four of the existing
eight clarifiers which were built as part of the most recent upgrade, have a diameter of
145 feet and side water depth of 16 feet. The four older clarifiers have a diameter of 120
feet and side water depth of 10.5 feet. The activated sludge basins were operated at the
time of the evaluation by feeding all of the primary effluent at the beginning of the third
pass, and by feeding the return activated sludge into the first pass. Therefore, the first
two passes in each basin were used to reaerate the return sludge and the third pass was
used as a contact stabilization basin for primary effluent. The purpose was to reduce the
suspended solids loading to the clarifiers, because they were considered to be the primary
treatment limitation. Because of the short hydraulic retention time and clarifier
limitations, the facility was unable to nitrify in the current mode of operation when the
mixed liquor temperature was slightly below 20 °C.
After dewatering, the sludge is incenerated onsite in a multiple hearth furnace. It is
known that the incinerator stack scrubber water contains cyanide, and is recycled back to
the headworks. It is possible this inhibits the nitrification rate.
The current upgrade is aimed primarily at increasing the plant capacity and resolving the
secondary clarifier problems, but will include provisions for biological nitrogen removal.
The plant capacity is being increased to 67 MOD, and six new rectangular clarifiers with
a SWD of 16 ft are being built to replace the four old shallow ones. The total aeration
basin volume is being expanded by 14.7 MG with a SWD of 22 ft. Three aeration basins
will be step-fed into six passes with alternating anoxic-aerobic zones. The anoxic
volume will be 5.1 to 7.3 MG total, i.e. 1.7 to 2.43 MG per basin. Four new blowers will
be installed for increasing the air capacity in deep aeration basins. After the upgrade is
completed, currently projected as January 10th, 2002, the plant is supposed to maintain an
effluent TN concentration of 8 mg/L and less year round. This would remove an
Appendix II 66
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additional 0.96 Mlbs of TN per year at the current average flow of 45 MOD, and an
additional 1.43 Mlbs of TN per year at the design flow of 67 MOD.
The construction cost of the expansion and BNR upgrade is currently budgeted at $20.8
M. Assuming the total costs are necessary for BNR implementation, the cost per pound
of additional nitrogen removal would be approximately $0.50/lb. In actuality, the flow
expansion costs should be deducted and the cost per pound should be further discounted
by the reductions in O&M costs that are likely to be realized by the implementation of
denitrification.
Appendix II 67
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PURCELLVILLE WWTP
The Purcellville Wastewater Treatment Plant is located in Loudoun County, Virginia, and
it discharges into a small unnamed tributary of the north fork of Goose Creek which
eventually flows into the Potomac River. The existing plant is going to be abandoned
when the new plant under construction is completed, presumably by the end of the year
2001. the main reason for the construction of the new plant at a different location was
that the existing plant is in the flood plain. Also, the new plant will double the capacity
from 0.5 MOD to 1.0 MOD. The current average flow rate reaching the plant is 0.31
MOD.
The existing plant is an -tpgrade of a trickling filter (TF) plant, and it operates an
activated sludge system a ^ a trickling filter process in series for secondary treatment,
with the TF serving as a polishing step. The new plant is going to be a step feed MLE
system with 3-pass aeration basins. The activated sludge process will consist of a three-
stage anoxic zone, and the last stage of it designed to be a swing zone which can be
operated as either an aerobic or an anoxic zone. The preliminary and primary treatment
units preceding the secondary treatment basins will consist of a mechanical bar screen,
grit and grease removal unit and primary clarifiers. Chemical phosphorus removal will be
achieved by addition of ferric chloride. Flow from the equalization basin downstream of
the primary clarifier will be distributed between the activated sludge basins. The center
feed secondary clarifiers have a side water depth of 14 ft, and are designed with large floe
zones for secondary phosphorus precipitation. Downstream of the secondary clarifiers,
will be AquaRobics disk filters, UV disinfection and cascade aeration prior to final
discharge. Sludge from the primary clarifier and the waste activated sludge from the
secondary clarifier will be sent to a gravity thickener, and then to two aerobic digesters
and a sludge holding tank prior to disposal.
The projected cost of the new plant is between $5.1 M and $5.4 M without BNR, and it is
between $6.4 M and $6.7 M with BNR. Thus, the cost of including BNR into the new
plant will be $1.3 M. The projected increase in nitrogen removal with the new plant is
17,000 Ibs for the first year, and 720,000 pounds over the 20 year design life. The
estimated cost per pound of additional nitrogen removed is $1.80/lb over the 20 year
period.
Appendix II 68
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Virginia Reports - Shenandoah Valley WWTPS
DUPONT WAYNESBORO WWTP
The Du Pont Waynesboro nylon manufacturing plant, located in Waynesboro, Virginia,
produces a variety of synthetic fibers, and the manufacturing processes generate a
wastewater that has a high nitrogen content. The wastewater originating from the
manufacturing processes had an average flow rate of 341 gpm from January-July, 1997,
and this flow is treated on site in an activated sludge facility. The domestic wastewater
generated within the facility is not mixed with the process wastes, and is directly
discharged to the sewerage system of the town. Treated effluent from the Du Pont
WWTP is discharged to the nearby South River, a tributary of the South Fork of the
Shenandoah River, and flows to the Potomac River. The existing discharge permit limits
ammonium-N to a maximum of 0.801 mg/L between January 1st and May 31st, and to a
maximum of 0.689 mg/L between June 1st and December 31st.
Wastewater from the Lycra, Permasep, Nylon and DI sumps of the manufacturing
processes has an average temperature of 31°C, and first flows into an equalization blend
tank. The nominal EQ hydraulic retention time (HRT) for an average flow of 253 gpm is
8.2 days at maximum water level. The effluent maintains a temperature of 20°C even in
cold month. Mixing is provided via the aeration system, which consists of blowers and
Kenix mixers. Here, backwash water from the anthracite coal filters which provide final
treatment of the effluent discharge, mixes with the process water. Flow from a
wastewater retention tank also occasionally discharges to the blend tank. The filter
backwash water provides a source of microbial seed for the aerated blend tank.
Consequently, bacteria convert the organic nitrogen, present primarily as dimethyl
acetamide (DMAc) and hexametylene diamine (HMD), to ammonia (ammonification).
Bacterial activity in the equalization tank also results in 30 % COD and 33 % TN
removals. The aeration feed tank is the next step before six 0.25 MG aeration tanks and
five clarifiers, i.e., the activated sludge process. Currently, only three aeration tanks and
two clarifiers are being used, and only one clarifier is used at a time. There are plans to
remove the two smaller of the remaining three clarifiers. Nominal volume of each
circular aeration tank is 0.25 MG, yielding an HRT of 1.55 days at an average flow of 341
gpm. Mixing is provided via 4 ft Kenix static aerators, and 15 ft3/min per 1000 ft3 tank
volume of air flow was used as mixing criteria. At average conditions, the F:M ratio was
0.052 for the first half of 1997. Alkalinity adjustments are accomplished by adding lime.
When only one clarifier is used at average flow conditions (341 gpm), the SOR is 148
gal/ft2/day.
Secondary effluent from the clarifiers is passed through a 10 MG polishing tank, also
aerated via Kenix mixers. Currently, Du Pont is planning to remove this tank as the
effluent from the clarifiers is well nitrified and the large tank is no longer needed. Two
parallel 2 ft deep anthracite coal filters follow the polishing tank before discharge. The
filters are backwashed once daily, and the backwash water is sent back to the blend tank.
Final effluent is combined with the effluent from the consolidated sump, which receives
Appendix II 69
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process waters from a chemical sump, acid recovery ditch, textile sewer and pumphouse
sewer. Storm water overflow is also combined at the final discharge point. Currently, the
centrifuges are not in operation, and the sludge is settled periodically and land applied via
spraying.
The average BOD5 was 431 mg/L for the influent and 233 mg/L for the aeration feed
effluent, indicating a 46 % reduction between the two points. TKN was not one of the
measured parameters. Total nitrogen measurements were performed using an ANTEK
7000V Nitrogen Analyzer, and ammonia and nitrate nitrogen were believed to be absent
in the blend tank influent, indicating that the nitrogen was almost entirely in the organic
nitrogen form. The average concentration of nitrogen entering the AS process is 63
mg/L, and the effluent data shows that excellent nitrification is accomplished, and the
effluent ammonia averaged only 0.09 mg/L during the period of evaluation. However,
high levels of TN (46 mg/L) are discharged, and almost 100% of it is in the form of
nitrates.
Two alternatives were considered for improved nitrogen removal:
1. Sequencing aerated/nonaerated periods in the existing aeration tanks, accomplished
by cycling the air on and off. The tanks would continue to be used in parallel, and no
structural modifications would be necessary.
2. Converting one of the aeration basins into an anoxic tank for denitrification, and
keeping two tanks aerated for nitrification (Bardenpho Process). This alternative will
require some piping work because the existing piping does not allow the operation of
the basins in series. Methanol addition in a post-anoxic tank would be required in all
cases to achieve an effluent nitrate nitrogen level of 5 mg/L. If desired, methanol can
be added at the coal filters, converting them to denitrification filters. They would
require methanol addition equal in amount to that of :e post-anoxic tank.. The
alternatives for the methanol application point should be iield tested to determine the
most suitable one.
The results of the cost calculations for each alternative are as follows:
1. If cyclic aeration is implemented manually by turning the aerators on and off, there
would be no capital costs and it could result in an estimated 48% reduction in the
amount of quicklime that has to be added for pH adjustment. The estimated benefit to
the company would be $0.11 per Ib additional N removed.
2. If automated cyclic aeration is desired, a DO control system and instrumentation can
be installed for approximately $290,000, and the cost per Ib of additional N removed
would be $0.17.
3. Capital c sts for installing mixers in the AS tanks for Alternative 1, in addition to
installatb- of an aeration control system and a PLC, would be $400,000, and the net
decrease ID O&M would be $4,300. The total cost per !b of additional N removed
would be $0.33.
4. Capital costs for Alternative 2 are for modifying the existing basins to operate as two
Appendix II 70
-------
parallel trains of two tanks in series operating in the MLE configuration. The sum is
$560,000. Mixers, DO control and monitoring system, and a nitrate recycle pumping
system are the items that need to be installed. The net decrease in O&M costs for this
alternative is 51,600, with a total cost per Ib of additional N removed of $0.51.
The existing basins would be modified to operate as two parallel trains, each basin
consisting of three tanks in series operating in the Bardenpho configuration. The
capital cost and the net increase in O&M costs would be $630,000 and $900,
respectively. The total project cost per Ib of additional N removed would be $0.54.
71
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FISHERSVILLE WWTP
The Fishersville WWTP is an activated sludge plant that is currently rated for an average
daily flow rate of 1.4 MOD. It discharges into Christian Creek, which flows into Middle
River, which is a tributary of the South Fork of the Shenandoah River. The discharge
permit limits ammonium-N concentrations to a monthly average of 8.14 mg/L between
June and December, and to 10.6 mg/L between January and May. The current annual
average flow rate is 1.30 MOD, and the current annual average BOD and TKN
concentrations in the plant influent are 135 mg/L and 17 mg/L, respectively.
After screening and grit removal, wastewater is pumped into a common channel that
distributes the flow between two AS basins. The HRT of the basins at the design average
flow of 2.0 MOD is 10.1 hours. The aeration system consists of medium bubble diffusers
and three positive displacement blowers. The AS basins are followed by four rectangular
secondary clarifers with SORs. of 550 gpd/ft2 each at design average flow. Secondary
effluent is chlorinated, dechlorinated and reaerated prior to discharge. The facility has
four aerobic digesters equipped with coarse bubble diffusers. The sludge is then
dewatered and land applied.
Flow distribution between the AS basins is accomplished in the influent channel. Rags
and debri accumulate around the stem of the weir gate and obstruct the influent flow and
affect the flow distribution between the basins. This unequal distribution causes
difficulty in optimizing the process for best results. The effluent of the Fishersville
WWTP has an average TN value of 11.2 mg/L and an average TP value of 2.5 mg/L. The
N and P removal can be enhanced by operating the AS system in the A2/0 configuration.
Flexibility should be provided to operate the AS system in the MLE configuration for
BNR and chemical P removal during the winter months. The following modifications are
recommended:
1. Replace the existing weir gates with slide gates;
2. Create an anaerobic/anoxic switch zone followed by an anoxic and an anoxic/aerobic
switch zone at the influent end by turning off the air;
3. Construct three baffle walls in each AS basin;
4. Install submersible mixers in the anaerobic and anoxic zones;
5. Install a DO control system;
6. Install a nitrate recycle system;
7. Install a chemical P removal system.
These modifications would enable the facility to meet a year round average of 8.0 mg/L
for TN with both reactors in service.
The total capital costs of implementing BNR is $980,000 with an estimated annual
reduction in O&M costs of $3,800 without chemical P removal, and an increase in O&M
costs of 52,600 with chemical P removal. The estimated total cost is $2.20 and $2.90 per
Ib of additional N removed annually, with and without chemical P removal, respectively.
Appendix II 72
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FRONT ROYAL WWTP
The Front Royal WWTP is an activated sludge facility located in Warren County, VA,
and it discharges to the Shenandoah River. The facility was upgraded to a 4.0 MOD
treatment facility in 1992, and designed to handle a peak flow of 12.0 MGD. Average
and maximum influent ammonia concentrations for the period from January to May
usuallly vary from 13.0 to 16.6, and from 7.0 to 13.9 mg/L for the period from June
through December, respectively. Nitrogen and phosphorus removals are not required
under the current permit. At present the plant receives an average flow of 2.4 MGD.
During the 14 month evaluation period (September 96 - October 96), the raw influent
BODs and TSS concentrations averaged 143 mg/L and 182 mg/L, respectively. The raw
influent TKN, NH4-N and TP analyses were not performed during the evaluation period,
so the BODs to TKN ratio was assumed to be 6.7:1.
The first stage of the plant consists of equalization basins. Following equalization, two
aerated grit chambers are provided, followed by primary clarification. Each grit chamber
is provided with diffused aeration. Following grit removal, the plant has two rectangular
primary clarifiers. The average detention time and the surface overflow rate at 2.04 MGD
are 1.3 hours and 1,370 gpd/ft2, respectively. There are four aeration basins, and the
average detention time is 6.9 hours at 1.02 MGD per basin. Aeration is provided by two
mechanical aerators in each basin. The plant has four final clarifiers. Two of the clarifiers
have a diameter of 52 ft and the remaining two clarifiers have a diameter of 63 ft. The
side water depth of all four final clarifers is 12.5 ft. At 4.07 MGD, the surface overflow
rate of all four final clarifiers is 503 gpd/ft2 each. The weir loading rate of the smaller
clarifiers are 4,260 gpd/ft2 at 4.07 MGD, while the larger clarifiers operate at a weir
loading rate of 6,770 gpd/ft2 at the same flow rate. Each clarifier includes a circular
sludge collector mechanism manufactured by Envirex. Aerobic digesters are used to
digest both primary and secondary sludges plus foam. Primary clarifier sludges directly
enter the digesters. However, the sludge from the secondary clarifiers first enter a gravity
thickener before being transferred to the digesters. "
The aeration basins have adequate capacity to accomplish both denitrification and
complete nitrification at the current flow rate of 2.4 MGD. However, at design flow (4.0
MGD), two additional aeration basins will be needed to accomplish an effluent TN level
of 8.0 mg/L year round. The minimum aeration basin HRT required at this facility is 9.0
hours to meet the TN goal of this project.
Calculations for the implementation of cyclic aeration to achieve nitrification and
denitrification indicated that total cycle periods of 3.64, 3.35 and 3.06 hours with
unaerated periods of approximately 46% would provide NOx concentrations of 5, 6 and 7
mg/L, respectively, in the final effluent without nitrate recycle. However, pilot studies
should be run to determine exact cycle durations for final design.
Appendix II 73
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The cap,tal cost for miplementing nitrogen removal at current flow is based on installing
a PLC for cychcal aerauon and DO control, and sums up to $50,000. The capUaHSf"8
,a*a.I,ng narogen removal at design flow is based'on constructing two 1°
aeration basms tdentical to the existing basins, a primary effluent flow dis
suture, and a secondary clarifler influent flow distribution^ sums up™ $7
2*5(5 T^^ ChangeS ? " & ° °OStS at C™' flow ^d « design flowe
$2,500 and $2,900, respect.vely. Cost savings due to alkalinity recoveredfr™
sUDmDu"Catt10" t °l b\'ealiZed 3t ^ fadHty *«»« » <"' ^ added ,"
supplement alkahmty m the wastewater. The estimated total costs for implementing
n^ogen removal are $0.02 and $1.16 per Ib of additional N removed, for cu^Tflow
and des,gn flow cond,,,ons. All costs presented are for implementing denitrifSZ oT
not for mmficauon, because the facility is already capable of year round nitrification
Appendix II
74
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HARRISONBURG WWTP
The Harrisonburg WWTP is an activated sludge plant designed for a flow rate of 16
MOD, and at present the plant receives flows of 7.5 to 8.0 MOD, with wet weather flows
of 24 to 25 MOD. The plant is located off 1-81, south of the City of Harrisonburg. At
present, the plant receives 40% of its total load from industrial sources, which includes
three large poultry processing facilities and one dairy. The Plant has a draft permit which
requires it to nitrify and meet effluent TKN concentrations of 9 mg/L (January to May)
and 4 mg/L (June to December).
The raw influent reaching the plant is screened through two mechanical bar screens,
degritted in two sets of grit chambers, and flows by gravity to four primary clarifiers, each
of which has an integrated DAF section. The clarifiers were designed with a SOR of 510
gpd/ft2 at the design average flow. In the recently completed upgrade, the old primary
clarifier flocculation basins were converted to anoxic/anaerobic selectors with a nominal
HRT of 11.3 min at average flow. The selector effluent is distributed between eight AS
basins, with a nominal HRT of 10 hours. Aeration is provided with ceramic fine bubble
diffusers. There are four secondary clarifiers, with SOR of 379 gpd/ft2 at average flow.
The secondary effluent is pumped to eight anthracite filters, each with a loading rate of
1.65 gpm/ft2 at 16 MOD. The effluent is chlorinated, dechlorinated and post aerated prior
to discharge.
The plant is operated at aerobic MCRTs of 5 to 12 days. Between June and December,
complete nitrification is achieved except a few instances where ammonium-N exceeded 4
mg/L between January and April. Effluent nitrate concentrations average at 16 mg/L.
In a pilot study being run for the evaluation of BNR, 25% of one of the AS basins has
been converted to an anoxic zone by turning the air off without mixers. The only nitrate
recycle was with the RAS operated at 75 %. The results showed that between November
and December, an average denitrification of 3 to 4 mg/L of NOx was achieved compared
to a control basin without an anoxic zone.
Analysis of the raw influent BOD shows an average of 200 mg/L with a peak month
value of 237 mg/L for the period between September 1994 and June 1995. Using a
computer model and assuming a 70% aerobic volume, an effluent TN of 8 mg/L between
May and November and 10 mg/L for the rest of the year, it was found that the average
month MLSS would be 2900 mg/L, and during summer months one of the AS basins
could be taken off service. Thus, the analysis shows that the plant can achieve nitrogen
removal without any additional basins or clarifiers. Some features such as step feed could
be added to handle high flows. RAS chlorination could be used to control SVIs when
they are out of the upper boundary of the range of 60 to 125 mL/g.
Essentially, most of the modifications for BNR are in-basin modifications with some
improvements for automated control. Two dedicated anoxic zones should be constructed
using baffles in the AS basins, with one switch cell. The nitrate recycle pump should be
Appendix II 75
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designed for a maximum recycle rate of 3 times the influx* n
may be included, with two DO probe T ft iS' Automated °O control
overaeratio, ThcptohMwfB<^3 -mgs by preventing
The capital costs of these modifications are calculi t« u *? ^ A ^
reduction of $570 in the O&M costs. £e ^Sj ^f Lv 'f Lr' 4?'
reduction of 1 1 mg/L in the effluent ^ "54^ Ib N
Appendix II
76
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LURAY WWTP
The WWTP for the Town of Luray is an oxidation ditch activated sludge system designed
to treat a combined municipal-industrial wastewater with an average flow of 1.6 MOD
and a peak flow of 2.2 MOD. Average dry weather flow during 1997 was about 1.2
MOD, while average flow during wet months was about 2.0 MOD. Of this flow, between
650,000 and 750,000 gpd is wastewater from the Wrangler textile plant located in Luray.
The typical Wrangler wastewater strength is BOD5 640 mg/L, COD 1280 mg/L, TSS 115
mg/L, NH3-N 0.6 mg/L, and pH 6.8. However, the Wrangler wastewater contains very
high non-biodegradable organic-N concentrations, i.e., 100 to 120 mg/L. Typical
combined wastewater strength is BOD5 220 mg/L, COD 495 mg/L, TSS 125 mg/L, TKN
50 mg/L, NHs-N 6.4, and pH 7.2. The combined wastewater is nitrogen deficient for
activated sludge metabolism, and an available source of nitrogen has to be added to
accomplish BOD removal.
The Luray plant is required to meet monthly average effluent concentrations of 30 mg/L
TSS and 30 mg/L BOD5, and weekly average effluent concentrations of 45 mg/L TSS and
45 mg/L BOD5. In addition the minimum acceptable pH is 6.5, and the fecal coliforms
should not exceed 200 per 100 mL. The facility had not effluent TN and TP requirements
when this evaluation was performed, but limitations of 8 mg/L TN year round, and 1.5
mg/L TP year round.
The treatment system consists of: dual 40 inch Rotamat Fine Screens and a bar screen
bypass in the head works, dual oxidation ditches with 8 20 HP, 16 ft Magna rotor brush
aerators per ditch, dual 50 ftdia. Spiraflo clarifiers with 8.5 ft. SWD and full surface
skimming, dual 28 ft. dia. Hydro-Flow clarifiers with 9.75 ft. SWD, disinfection by UV,
and cascade aeration. In addition, the plant has two stage dual thickeners for sludge
processing, followed by aerobic digestion and belt filter press dewatering. The plant also
is equipped with a septage pretreatment system, which consists of aeration. The
dewatered solids go to the Page County landfill for final disposal.
The plant effluent concentrations from June 3 - July 10, 1996 averaged 44 mg/L BOD5,
167 mg/L COD, 128 mg/L TSS, and 39 mg/L TKN, but only 0.29 mg/L NH3-N. By
contrast, effluent concentrations averaged 7.6 mg/L BOD5, 30 mg/L COD, 10.6 mg/L
TSS, and 0.25 mg/L NH3-N during September, 1996. February, 1997 averages were 10
mg/L BOD5,40 mg/L COD, 20 mg/L TSS, and 0.22 mg/L NH3-N. A review of the
operating data for 1996 and 1997 indicated that these values were fairly typical, although
during dry periods the plant performed much better. TKN data was not available for
September and February.
The data show that the treatment processes work very well except when rainfall events
occur. Then high infiltration and inflow results in very high flows through the treatment
plant, and the washout of activated sludge solids from the clarifiers. The impacts of the
TSS concentrations on the effluent concentrations of BOD and COD can be seen in the
data listed above. Both parameters vary directly with the magnitude of the TSS
Appendix II 77
-------
concentration. In contrast, the effluent ammonia concentration is not affected by the high
TSS concentrations because ammonia is soluble. The data clearly show that the
biological process is capable nf near complete nitrification under nearly all conditions,
including high flows. Howe .T, when the mixed liquor temperature dropped below 11° C
during December, 1996, the effluent ammonia concentration increased to as much as 7
mg/L, and averaged 5.8 mg/L over a seven day period. However, the average for the
month was only 1.95 mg/L. Apparently the operating SRT was not high enough to
prevent partial washout of the nitrifiers during the low temperature period.
A special investigation of the soluble effluent concentrations from the Luray WWTP was
performed from 6/3 - 7/9, 1996. During the period the activated sludge process nitrified
completely, to an average of 0.018 mg/L NHa-N, the effluent oxidized nitrogen
concentration was low (3.02 mg/L), and the soluble phosphorus concentration was
typically below 2.0 mg/L. However, the soluble organic nitrogen was very high and
averaged 42.2 mg/L. It was clear from the results that the biological process was
effectively nitrifying and denitrifying all of the biologically available nitrogen, but a large
quantity of non-biodegradable organic nitrogen was present in the waste water. The
effluent wastewater also has a dark blue color from the dyes used by Wrangler in the
production of stone washed jeans, and these dyes are the likely source of the non-
biodegradable organic nitrogen.
It was concluded from the investigation that the non-biodegradable organic nitrogen was
not having an effect on the eutrophication of the receiving waters, and that any efforts to
remove it would be very expensive. The most economical technically feasible treatment
would involve the addition of activated carbon. Considering the unlikely environmental
impact of the discharged nitrogen, it is recommended that no modifications be made to
the Luray WWTP for purposes of nitrogen removal. The operator could operate the
aerobic digesters cyclic aeration to reduce the electricity costs, and this would reduce the
nitrogen in the digesters, but the impact on the effluent nitrogen concentration would be
small. No other efforts to improve nitrogen removal are recommended. However, it is
recommended that efforts be made to reduce the amount of inflow and infiltration into the
town sewers, and it is noted that such a project is ongoing at the present time (1999).
Appendix II . 78
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THE MERCK AND CO., INC WWTP
The Merck WWTP is an activated sludge plant with a permitted flow of 1.2 MOD.
Merck & Co., Inc.'s facility in Elkton,VA is a pharmaceutical manufacturing plant, and it
historically has been producing Amprolium, resulting in a high COD and nitrogen
wastewater. Recently, however, the production line was switched to CRIXIVAN, and the
wastewater now has a higher COD strength, but is nitrogen deficient. Consequently the
activated sludge WWTP was upgraded to treat the high COD load with addition of
ammonia to satisfy the nitrogen requirements. Nitrogen remaining in the final effluent is
discharged to the receiving water. Currently, the average TN in the final effluent after
mixing with cooling water is approximately 3.5 mg/L. Therefore, the facility does not
have to implement any modifications to the existing treatment plant, as long as future
changes in the raw water quality do not result in higher final effluent nitrogen levels.
Hence, Merck should have a, contingency plan to modify the existing system, when
necessary.
Current operational data shows that the raw influent contains 98 mg/L of TKN and 45
mg/L of ammonium-N, after addition of ammonia. BOD and COD values are 2,402 and
5,077 mg/L, respectively, at an average flow of 0.906 MOD. Projected flows and loads
of raw influent for maximum CRDQVAN production indicate that influent concentrations
will remain the same, but the influent flow rate will increase to 1.20 MOD, increasing the
loads to the treatment plant. As the industry is unsure about the future nitrogen loads,
BNR evaluation was performed at three different levels of N loading:
1. Current maximum month N load for maximum production.
2. Future N load of 2,400 Ib/day which is approximately twice the current maximum
month load.
3. Future N loads of up to 3,500 Ib/day.
Current treatment processes start with equalization and neutralization (with phosphoric
acid or magnesium hydroxide), and follow with two AS treatment trains. Each train has a
maximum of three basins used in series for AS operation. The aeration system consists of
coarse bubble diffusers in the basins and four centrifugal blowers. The effluent from the
AS basins is'distributed between two clariflocculators, the overflow from which is sent to
two trickling filters as a polishing step. The underflow from the clariflocculators is
recycled to the first AS basin in each train. Treated effluent from the trickling filters is
distributed between two final clarifiers. The final effluent is then mixed with cooling
water and discharged into a receiving stream.
WAS is pumped to the waste sludge storage tank and dewatered using two belt filter
presses. The dewatered sludge can be dried, incinerated or both. Filtrate from the presses
is fed to the trickling filters.
At Level 1 N load, the plant does not require any modifications for nitrogen removal as
the water is nitrogen deficient and ammonia is externally added. Better monitoring of
ammonia and nitrate levels in the treated effluent prior to mixing with cooling water is
Appendix II
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recommended to minimize addition of excess nitrogen to the process. As the MCRT
increases, the nitrogen requirement decreases due to a decrease in generated biomass.
Therefore, Merck may choose to operate with three basins : each train and at high
MCRTs.
At Level 2 N loads, a Bardenpho system is recommended to produce a final effluent TN
concentration of 8 mg/L. The required modifications consist of creating an anoxic zone
at the influent and effluent ends of each AS basin train and recycling nitrified mixed
liquor from the aerobic zone effluent to the anoxic zone at the influent end. TN
concentrations lower than 8 mg/L could be achieved by endogenous denitrification in the
second anoxic zone. Furthermore, a 3 mg/L effluent TN level could be achieved by the
addition of biodegradable COD to the second anoxic zone. Each of the two anoxic zones
would occupy 16 % of the train volume. Submersible mixers would be installed in the
unaerated zones to prevent settling of mixed liquor. A reaeration zone following the
second anoxic zone would strip the nitrogen gas.
For Level 3 N loads, in addition to recommended modifications for Level 2 N loads, a
feed system for a supplemental carbon source such as methanol should be provided.
Implementation of denitrification at levels 2 and 3 would lower the aeration requirements
because the denitrification process consumes COD under anoxic conditions.
There is no capital cost for treating the Level 1 nitrogen load. Capital cost for the Level 2
nitrogen load is for converting the system to a Bardenpho process, and it sums up to
$840,000. For Level 3, the modifications include a methanol feed system and an
additional blower in addition to the requirements for Level 2 modifications. It sums up to
$1,440,000. The estimated changes in annual O&M costs for the Levels 1, 2, and 3 are
$0, $37,000 reduction and $113,000 increase, respectively. If the Bardenpho process is
implemented for Level 3 with larger anoxic zones, methanol feed could be avoided.
However, additional tank volume wiould be necessary. The total costs for additional
nitrogen removal for this plant is $0, as currently no modifications are required.
Appendix II 80
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MIDDLE RIVER/VERONA WWTPS
The Middle River WWTP is an oxidation ditch activated sludge facility currently rated
for an average daily flow rate of 4.5 MOD, and it discharges into the Middle River which
is a tributary of the South Fork of the Shenandoah River. The Augusta County Sanitary
Authority owns and operates the plant, and also owns and operates the much smaller
Verona RBC WWTP which is located adjacent to the Middle River WWTP, and their
final effluents are combined prior to discharge. The discharge permit limits ammonium-
N concentrations to a monthly average of 3.1 mg/L between June and October, and to 3.8
mg/L between November and May. The current annual average flow rate to the plant is
3.65 MOD. The annual average BOD and TKN concentrations in the plant influent are
130 mg/L and 22 mg/L, respectively.
After preliminary treatment, the wastewater is pumped into two oxidation ditches each of
which has an HRT of 1.2 days at the design average flow of 4.5 MOD. Two brush
aerators are used in each ditch. The brush aerators in each one of the inner, middle and
outer channel of the ditches are constructed with a common shaft. Thus, the operator
does not have the flexibility to control the DO level in the ditches to optimize nitrogen
removal. Mixed liquor than flows into two circular clarifiers with an overall SOR of 448
gpd/ft2 at design flow rate. The secondary effluent is disinfected using UV light and
reaerated using cascade aeration before discharge into Middle River. The WAS is
aerobically digested in the inside channel of the oxidation ditches, then dewatered and
land applied.
The effluent monitoring data from August 1996 to April 1997 showed that the facility
currently accomplishes nitrogen removal to levels below 8.0 mg/L even after combining
with the effluent from the Verona WWTP. The combined effluent of the Middle River
and Verona WWTPs had an average TN value of 5.9 mg/L and an average TP value of
1.3 mg/L. The performance of the plant for BNR can be further improved by installing a
DO control system consisting of a PLC and two DO probes in each ditch, to optimize the
DO levels in the ditches for cyclic aeration. It is also recommended that the nitrified
effluent from the Verona WWTP be combined with the raw influent to the Middle River
WWTP so that the nitrates it contains are denitrified in the Middle River WWTP. These
modifications would enable the plant to achieve an average effluent TN of 3.5 to 4.5
mg/L year round. A chemical P removal system is not necessary as the current effluent
level is less than 2.0 mg/L.
The total capital costs of implementing controlled BNR would be $150,000, with a
negligible estimated annual change in O&M costs. The estimated total cost of additional
N removed is $0.30 per Ib.
Appendix II
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OPEQUON WRF, CITY OF WINCHESTER
The Opequon WRP is an activated j ,
of 5 MOD, and the plant was rer '
MOD. The facility discharges into
and on to the Chesapeake Bay via
limits the effluent monthly ave^e
February 1st to April 30th, and to 044
average daily flow rate for 1995 was 5
10. 20 MOD. T, 1995 average daily Bc
p
^
*? " aVera8e flow
dfrcflow rate <*
° ^ Shenand^ River
diSCh^e P«nit
O °'9 mg/L fr°m
31sL ^ CUITen<
HRT of 10.9 hours at the design ave age flow
bubble diffusers. Mixed liquor flowTlntn'
with SOR, of 550 gpd/ft2 a;"igs °
discharge end of the RAS line to coc
flows into gravity filters for addition
using chlorine prior to discharge. SUSpended
SORS °f
™& ^ ^° AS basins
lapered aeration
r condary
VaJveS « "^ at
rfes' Secondary effluent
removal, and is then disinfected
» « -unts of RAS
feeding in the AS basins can be impTemented to H - JUSted manUaIly- SteP
The facility has m excessive ^^^^^^^^M^
denitrification, the air demand will decreased ' ?h ^^ ^ lmPlementation of
then disrupt the denitrification process "^ IeVek Ove^ration may
could be created at the
three anoxic zones RAS however^oulTh/f ^ ^^ W°Uld be fed to ^ of the
prevent dilution of RAS.' Cons^^ %£*£*! JtT8 ^ ^ ^ tO
intermediate in the second, and fully dilmed in ^,T, ^^ m ^ first P358'
permits a higher MCRT wimout o^oStafth? f % US' ^ ^ °peration
RAS and those produced fo °dJ ^c ^ "? f'5- Although *e nitrates in the
denitrified, most of the nitrates p^Sd LS^W ^l-"11 "^ ^^ ^ be
the effluent. P m the third aeroblc Pass will be discharged in
Four different levels of modifications are recommended for different BNR goals:
of 10 to 15
first 60 ft of eac.
DO levels m the aerobic zones
««
Appendix II
82
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2. Level 2 - Modifications that can achieve 8 to 10 mg/L TN without BPR: A dedicated
anox,c zone shall be created m the first 60 ft of each pass by installing baffle walls
miXerS' C°ncentrations in the aerobic zones should be Hmite?to
Level 3 -Modifications that can achieve effluent TN concentrations of less than 8
mg/L without BPR: In addition to the modifications of Level 2, a submersTbTe nlatf
recycle pump would be installed in the downstream end of the third pass aeroWc zone
£ol™ of denitrification could be achieved by installing baffles after 1 ^ee
4. Level 4 - Modifications that can achieve effluent TN concentrations of less than 8
mg/L with BPR to less than 1 mg/L: In addition to the modifications of Level 3, an
anaerobic zone with an HRT of 1.5 hours is recommended at the beginning of the first
pass for BPR. Greater control of denitrification could be achieved by installing
baffles after all three anoxic zones.
Costs for level 1 were not calculated as it only includes operational modifications and
diffuser relocations. The capital costs for the Levels 2, 3 and 4 are $370,000; $510,000;
and $570,000 respectively. The estimated annual increase are in O&M costs for the three
Levels are $6000; $7000; and $7000. The estimated total costs of additional N removal
for Levels 1, 2, 3, and 4 are then $0; $ 0.13; $0.17; and $0.16, respectively.
Appendix II
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PARKINS MILL WWTP
The Parkins Mill wastewater treatment plant is an oxidation ditch facility that consists of
four ditches, and is located in Frederick County, VA, where it discharges to Opequon
Creek. The design average flow rate is 2.0 MOD and peak flow (one d<:y instantaneous)
is 5.0 MOD. However, current average flow is approximately 1.09 MOD. The current
discharge permit requires that the average ammonium-N concentration be 1.7 mg/L
between December 1st and April 31st, and 1.5 mg/L from May 1st through November
31st. There are no limitations on TN levels.
Available plant operating data, influent wastewater characteristics, and performance data
for the 12-month period from November 1996 to October 1997 were examined.
Measurement of effluent NC^-N was not among the routine daily analyses. For this
reason NOa-N was monitored between 12/29/97 and 1/9/98 at times corresponding to
three different operational changes. Average flow for the above mentioned 12-month
period was 0.98 MOD, with a minimum and a maximum monthly average of 0.82 and
1.60 MOD, respectively. The following ratios were assumed to be valid for the Parkins
Mill WWTP to enable nitrogen balance analysis: CBOD to TKN of 5.5, CBOD to TP of
30, and TKN to NH,-N of 1.5.
Preliminary treatment consists of mechanical screens and a vortex grit chamber. Flow
from the grit chamber is measured via a Parshall flume and sent to the wet well of the
influent pump station. The influent pump station (3 pumps) sends the wastewater to the
primary splitter from where it is distributed to four oxidation ditches. Flow is split
between the four oxidation ditches, with 12.5 % going to each of ditches 1 and 2, and
37.5 % to each of ditches 3 and 4. Oxidation ditches 1 and 2 are the original units at the
plant, and they are 56 % smaller than oxidation ditches 3 and 4. The hydraulic retention
time (HRT) for secondary treatment at average flow conditions is 26.2 hours at the design
average flow of 2.0 MOD. Return activated sludge (RAS) varies between 80 and 100 %
of the influent flow. Currently, the aerators in all ditches are turned off for a 2 to 3 hour
period every night. The plant has four clarifiers, two of which (Cl and C2) are used for
waste sludge thickening. The two larger and newer clarifiers (C3 and C4) are used for
secondary clarification. It is likely that additional clarification will be needed as flows
approach 4.0 MOD. An additional 70 ft. diameter clarifier would provide an overflow
rate of 346 gpd/ft2, and a solids loading rate of 17.4 Ibs/d/ft2. Because the site is area
limited, a better choice may be to use all four clarifiers for clarification and go to either a
centrifuge or a belt filter for initial sludge thickening. Clarifier effluent is filtered by two
sand filters that are operated continuously and backwashed one compartment at a time. A
chlorine residual of 0.3 ppm is maintained on the filters, and because this residual is not
sufficient for proper disinfection, the filtered water is passed through a UV disinfection
step. The final effluent is further oxygenated by cascade aeration before being discharged
to Opequon Creek.
Sludges wasted from clarifiers 3 and 4 and thickened in clarifiers 1 and 2 are pumped to
the two aerobic digesters. They are operated with downcomer headers and coarse bubble
Appendix II 84
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diffusers. A belt filter press follows the digesters for further thickening, and it dewaters
the waste sludge up to a dry solids content of approximately 12 %. A high molecular
weight cationic polymer is used as the flocculant aid. Thickened sludge is then
transferred to a landfill via trucks.
measurements on 24-hour composite samples of plant effluent taken between
12/29/97 and 1/9/98 showed NO3-N levels from 0.0 to 13.2 mg/L in the final effluent,
with an average of 6.6 mg/L for 1 0 samples. Effluent samples from ditch 1 taken on the
same days, but collected 1 5 minutes after the daily 2-hour shutdown, showed significant
denitrification, i.e., zero NOs-N values for 6 out of 10 days, with one high value of 17.6
mg/L, and an average value of 3.5 mg/L. However, denitrification was not occurring
steadily and in a predictable way. This was probably because of the varying location of
the aerobic and probable anoxic zones in the ditches, depending on the location of the
resting brush aerator. In other words, the anoxic and aerobic zones are not fixed and do
not ensure consistent nitrification and denitrification.
The first alternative recommended for BNR implementation is air-on/air-off cycling with
short air-off periods and one brush operating at a slow pace to maintain forward flow in
each ditch. The operators should determine the optimum air-on and air-off periods for
combined nitrification and denitrification by experimenting with the system while
monitoring the effluent nitrate and ammonia concentrations.
A second alternative for BNR implementation is to modify the ditches and operate them
in the Bio-Denitro configuration, a process described by Randall et al, (1992). Basically,
the sequence is to alternatively operate one of the paired ditches as an anoxic reactor and
the other as an aerobic reactor, with the influent being introduced into the anoxic ditch.
During the remaining cycle time, both ditches are operated as aerobic reactors. Effluent
should be discharged from the aerobic ditch at all times to obtain the best performance.
Because the ditches have a common wall, piping work for this modification should be
minor.
The capital costs for Alternative 1 include installation of an aeration control system with
PLC based instrumentation and DO probes for cycling aerators on and off, and they sum
up to $97,000. Alternative 2 requires the modifications to be able to feed one anoxic
ditch at a time, cycling of aerators in each ditch to provide completely anoxic or aerobic
conditions in each one, and variable effluent withdrawal always from the aerobic ditch.
Two submersible mixers are required in each ditch to provide mixing and water
movement during anoxic periods. The capital costs sum up to $680,000.
The estimated annual reductions in O&M costs for Alternatives 1 and 2 are $3 1 ,400 and
$25,800, respectively. The estimated total costs for implementing BNR with Alternative
1 shows savings of $0.79 per Ib additional N removed, whereas with Alternative 2 the
cost would be $0.96 per Ib additional N removed.
Appendix II 85
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ROCCO FARM FOODS WWTP
Rocco Farm Foods Inc. in Edinburg, VA is a poultry-processing industry, and the WWTP
is currently rated for an average flow rate of 1.2 MGD. The WWTP is a Schreiber
Process activated sludge plant that discharges to Stoney Creek, which is a tributary of the
North Fork of the Shenandoah River. The current discharge permit limits ammonium-N
concentrations in the final effluent to 6.84 mg/L January through May, and to 1.95 mg/L
June through December. The effluent TKN is limited to 50 mg/L and 4.15 mg/L for the
same periods of the year, respectively.
Currently, the wastewater contains 34.6 mg/L ammonia, 140 mg/L TKN and 140 mg/L
TN after preliminary treatment by dissolved air flotation (DAF), and the final effluent
concentrations are 0.3 mg/L ammonia, 2.2 mg/L TKN, 125.5 mg/L NOx and 128 mg/L
TN. Phosphate phosphorus is reduced from 35 mg/L to 15.7 mg/L, as P, without
chemical addition.
The pretreatment facilities at the Rocco WWTP include screening, flow equalization, and
grease removal using DAF. Process wastewater then flows into a pumping station to
combine with the plant storm water and domestic wastewater. Wastewater is pumped to
an anaerobic lagoon, and most of the lagoon effluent is sent to an aerobic "Schreiber
Process" AS basin. The remainder of the flow is sent to an equalization lagoon and then
sent to the AS basin. The Schreiber basin has an HRT of 24 hours at the design flow rate
of 1.2 MGD. The Schreiber basin is equipped with a DO probe to monitor DO levels
continuously. Aeration is accomplished by stationary fine bubble diffusers. The mixed
liquor flows into a circular secondary clarifier with an SOR of 211 gpd/ft2 at the design
flow. The underflow from the clarifiers goes to the RAS wet well, from where the WAS
flow is also withdrawn. Part of the WAS is sent back to the anaerobic lagoon, with the
rest sent to dewatering by filter press. The dewatered waste sludge is land applied. The
secondary effluent flows into a chlorine contact tank for disinfection and subsequent
dechlorination using sulfur dioxide.
The anaerobic lagoons remove 80 to 90 % of BOD present in the raw wastewater, but no
significant nitrogen removal occurs. The BOD to TKN ratio in the influent to the AS
basin is approximately 1.5, which is not adequate to accomplish denitrification to meet an
effluent limit of 8 mg/L. Five alternatives were considered for implementation of BNR:
1. Construct a dedicated anoxic zone outside the existing AS reactor and operate the
resulting total AS process in the MLE configuration: A new pumping station would
be required to recycle the nitrified effluent from the aerated AS basin to the unaerated,
anoxic basin. Submersible mixers would be installed in the anoxic tank to prevent
settling of the mixed liquor. Since the anaerobic lagoon effluent has limited BOD, the
amount of denitrification that can be achieved is also limited. The anticipated effluent
TN would be 20 mg/L at a nitrate recycle flow rate of 5.8 MGD (4.8 Q).
Appendix II 86
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2. Construct a dedicated anoxic zone inside the existing AS reactor and operate the
resulting AS process in the MLE configuration: A concentric anoxic zone could be
constructed inside the Schreiber reactor. Because most of the BOD is removed
upstream in the anaerobic lagoon, the existing Schreiber reactor should have
sufficient volume for the anoxic-aerobic configuration. The piping should be
modified to feed the reactor from the center (i.e. the anoxic zone). Submersible
mixers .would not be necessary in the anoxic zone as the traveling bridge can be
modified to have paddles for mixing. The anticipated effluent TN is 20 mg/L at a
nitrate recycle flow rate of 5.8 MOD because of the limited BOD available after the
anaerobic lagoon. One disadvantage of this alternative is that the Schreiber reactor
would have to be taken out of service for the construction of the anoxic zone.
Nitrification and denitrification can be accomplished in the existing reactor by some
operational changes. These changes in the aeration patterns can be accurately
determined only by experimenting with the Schreiber Process.
3. Construct a dedicated anoxic zone upstream of the existing AS reactor and construct
a pumping station to divert a portion of the anaerobic lagoon influent to the anoxic
zone to enhance denitrification: An in-line macerator would be installed on the
suction piping of the anaerobic lagoon influent pumps to prevent large objects from
being transferred to the anoxic tank. By bypassing approximately 0.05 MOD around
the lagoon, the denitrification in the anoxic zone would be benefited. This alternative
will require a nitrate recycle rate of 11.5 MOD to achieve an effluent TN
concentration of 12 mg/L. Such a high recycle would also recycle excessive amounts
of DO from the aerobic zone and would significantly reduce denitrification capacity.
4. Construct an anoxic tank upstream of the AS basin, a nitrate recycle pumping system,
and a denitrification filter downstream of the secondary clarifier for additional N
removal with methanol addition: In addition to the modifications presented in
Alternative 1, a denitrification filter and a new pumping station would be constructed.
Because the flow to the filter would be BOD deficient, a methanol feed system also
would be necessary. The anticipated effluent TN is 3.0 mg/L.
5. Construct an additional Schreiber reactor to operate the AS process with cyclic
aeration controlled by the DO probe system: The Schreiber Process is designed to
remove nitrogen by simultaneous nitrification and denitrification accomplished
through DO control. However, because the ammonia load is so high, the existing
reactor cannot optimally achieve nitrogen removal. Therefore, a second reactor is
needed. This alternative can produce an effluent with 12 mg/L of TN.
The capital costs of the alternatives are $2,020,000; $610,000; $2,200,000; $4,480,000;
and $1,740,000 for the Alternatives 1, 2, 3, 4, and 5, respectively. The calculations of the
estimated annual changes in the O&M costs showed that each one of the Alternatives 1
through 5 will bring a reduction in O&M costs: $148,200; $153,700; $162,200;
$106,800; and $168,100, respectively. The calculations of estimated total costs of
additional nitrogen removal indicated that Alternatives 1, 3, and 4 will bring an increase
Appendix II S7
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in the costs of $0.038; $0.038; and $0.338, respectively; whereas Alternatives 2 and 5
results in reductions of $0.137 and $0.021 per Ib of additional N removed, respectively.
Appendix II 88
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STRASBURG WWTP
The Strasburg WWTP is an oxidation ditch activated sludge facility currently rated for an
average flow of 0.975 MOD, and the facility discharges to the North Fork of the
Shenandoah River. The plant has a maximum ammonium-N permit limit of 10.4 mg/L
between January and May, and 4.9 mg/L between June and December. Current annual
average effluent flow from the facility is 0.6 MOD. The facility is currently
accomplishing complete nitrification as the effluent ammonia concentration is less than 1
mg/L year round.
Preliminary treatment facilities include a mechanical screen installed in an influent
channel in the headworks building. After screening, the wastewater flows into a manhole
from which the flow is diverted to two oxidation ditches, which are operated in parallel
with an HRT of 24.2 hours at the design average flow of 0.975 MOD. Aeration is
accomplished via brush aerators. Mixed liquor from the ditches is distributed between
two secondary clarifiers. The SOR of the clarifiers is 388 gpd/ft2 at the design flow. The
RAS and WAS flow rates are adjusted with a PLC, which is used to adjust the valves.
Secondary effluent flows into achlorine contact tank for disinfection, followed by
dechlorination with sulfur dioxide.
WAS is pumped into an aerobic digester for VSS reduction. The underflow from the
digester is pumped into a storage tank where sludge is mixed with polymer and then
transferred to a Plate & Frame press for dewatering to a concentration of 25 to 30 %
solids.
Because of the lack of a flow distribution structure, flow distribution between the ditches
is sometimes uneven causing one of the ditches to be either under or over loaded, which
also affects the BNR capacity.
BNR can be accomplished by operating the ditches with cyclic aeration, where two brush
aerators in each oxidation ditch will be turned off periodically to establish anoxic
conditions. The existing DO probes will be used to continuously monitor the DO levels.
With a PLC installed, automatic adjustment of the effluent weir elevation will provide
DO control at the set point. It is recommended that DO levels be maintained at 1 to 2
mg/L. The PLC will also control the timing sequence of the aerators to accomplish cyclic
aeration. The cycle durations should be determined by the operators through full-scale
pilot testing.
Capital costs are based on modifying the existing oxidation ditches to operate in a cyclic
aeration mode, and total $120,000. The estimated annual change in O&M costs would be
a reduction of $120,000. The estimated total costs for implementing BNR consist of
denitrification costs as the plant is currently nitrifying. The savings per Ib additional N
removed is estimated to be $0.14.
Appendix II
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STUARTS DRAFT WWTP
The Stuarts Draft WWTP is an oxidation ditch activated sludge plant that is currently
rated for an average daily flow rate of 1.4 MOD. It discharges into South River, which
flows into the South Fork of the Shenandoah River. The discharge permit limits TKN
concentrations to a monthly average of 4.0 mg/L between June and December, and to
12.6 mg/L between January and May. The required weekly averages are 6.0 mg/L and
18.9 mg/L for the same periods. The current annual average flow rate is 0.98 MOD, and
the current annual average BOD and TKN concentrations in the plant influent are 198
mg/L and 31 mg/L, respectively.
After preliminary treatment, wastewater is combined with RAS and distributed between
three oxidation ditches, of which two were part of the original design. The combined
HRT of the ditches is 19.7 hours at the design average flow of 1.4 MOD. Each ditch is
provided with brush aerators, and the mixed liquor flows into three circular secondary
clarifiers. The SORs of the clarifiers are 396 gpd/ft2 at design average flow. Following
clarification, the wastewater is chlorinated, dechlorinated and reaerated prior to discharge.
WAS is pumped into the aerobic digesters, dewatered using a mobile belt filter press, and
land applied.
The influent flow distribution between the ditches is not even because headless in the
pipes varies at different flows. As a result of unequal flow distribution, some basins are
over loaded. Improper loading also causes unequal loading to the secondary clarifiers,
and as a result, the facility experiences a significant amount of solids washout. Because
of these design limitations, the facility has not been able to accomplish consistent
nitrogen removal. The effluent of the Stuarts Draft WWTP has an average TN value of
10.4 mg/L and an average TP value of 1.8 mg/L. The data for the period August 1996
through April 1997 was used for the BNR evaluations. BNR can be improved by:
1. Constructing a new oxidation ditch flow distribution structure, ensuring that the
ditches are loaded in proportion to their volume.
2. Installing a DO control system for the oxidation ditches to operate them cyclically.
3. Constructing a new secondary clarifier influent flow distribution structure.
4. Constructing a 52 ft diameter secondary clarifier to ensure that excessive amounts of
biosolids are not washed away.
These modifications will enable the facility to meet an effluent TN limit of 4.0 to 5.0
mg/L. A chemical P removal system is not necessary as the current effluent level is 2.0
mg/L.
The total capital costs of implementing BNR is $ 1,240,000 with an estimated annual
reduction in O&M costs of $5,900. The estimated total cost is $2.36 per Ib of additional
N removed annually.
Appendix II • 90
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CITY OF WAYNESBORO WWTP
The Waynesboro WWTP is a combination trickling filter-RJBC that serves the City of
Waynesboro, Virginia. The plant discharges to the South Fork of the Shenandoah River,
which eventually flows into the Potomac River. The current permit requires the plant to
maintain average effluent ammonia and BODs concentrations of 2 mg/L and 7.5 mg/L,
respectively, June through October. The average BOD5 limit for November through May
is 15 mg/L and there is no limit for ammonia for that period. At present, the plant
receives an average flow of 3.63 MOD, which is more than 90 percent of the design flow
of 4 MOD. The plant also has a severe I&I problem which can result in flows exceeding 9
MOD, which is the maximum flow that can be pushed through the plant.
The flows and loads received at the facility over the twenty two month period from
January 95 through October 96 were analyzed for this evaluation. The raw influent BOD5
averaged 135 mg/L for that period. The raw influent BOD5 to TKN and BOD5 to TP
ratios were not determined during the period except for two TKN and TP measurements
performed on June 1, 19 96. Based upon these measurements, BODs to TKN and BOD5
to TP ratios were calculated to be 6.7 and 75, respectively.
A Parkson Aquaguard type automatic screen is installed in the influent channel. The
screen utilizes a continuous belt made up of filter elements that fit together providing
horizontal and vertical clear spacings of 6 mm and 25 mm, respectively. Following
screening, grit is removed from the wastewater via a Smith & Loveless Size 11 Pista Grit
System. All flows then enter a wet well that was designed to maintain flow to the
trickling filters. The plant has two primary clarifiers. Each clarifier has a diameter of 57
feet and a side water depth (SWD) of 10 ft. The design overflow rate is 790 gpd/ft2 and
the current overflow rate at average flow is 711 gpd/ft2. The clarified liquid flows over
the peripheral weir into a control well, from where it flows to the trickling filters. Sludge
is pumped from the bottom of the clarifiers to the anaerobic digester. The plant has two
high rate trickling filters that are 92 ft in diameter. Each filter contains 6 ft x 6 ft plastic
media blocks, which have a very high void fraction (0.95%). Effluent from both filters
returns to the control well where the flow is split and recirculated to the filters. The
secondary clarifiers are similar in design to the primary clarifiers but slightly larger
because trickling filter biomass solids do not settle and concentrate as readily as sewage
organic solids. The design overflow rate is 600 gpd/ft2 and the current overflow rate is
547 gpd/ft2. During normal operation, clarified water enters the wet well of the tertiary
pumping station. The tertiary pumps lift the flow to the inlet channels of the RBC's.
There are two RBC trains, each containing 7 rotating assemblies. Each rotating assembly
consists of a series of polyethylene disks (Walker Process Corporation, Model F-89 and
F- 89 N). Flow from the RBC's next flows to the tertiary filters where suspended
material is removed and returned to the treatment process. The plant utilizes 3 automatic
backwash filters manufactured by Infilco. Disinfection is currently accomplished by
chlorination, which is followed by dechlorination. Gas chlorination also is used when the
tertiary treatment process is bypassed. To remove excess chlorine in the effluent, the
Appendix II
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plant is equipped with a SO2 feed system. To achieve a minimum of 6 mg/L dissolved
oxygen (DO) in the effluent, flow passes over a 5 step cascade aerator. Aerated effluent
is finally discharged to the South River via a 24 inch pipe.
The facility has two anaerobic digesters that are normally operated in series. The sludge
is heated by means of an external heat exchanger. There is no mixing in the secondary
digester. The sludge is drawn off the bottom of the secondary digester and sent to
dewatering. Flow from the digester enters to the belt press, an Ashbrook-Simon-Hartley
Klampress size 3, Type 85. Dewatered sludge is transported for land application.
Effluent characteristics for the period from January, 1995 through October, 1996 show
that the WWTP successfully nitrifies all year round, and produces an average effluent
ammonium concentration of 1.21 mg/L, with a monthly average range of 0.46 to 3.61
mg/L. Therefore, the wastewater could be denitrified by the addition of tertiary
denitrifying filters, and the desired effluent nitrate concentration could be selected by
controlling the addition of an organic carbon source such as methanol to accomplish
denitrification. Thus, an effluent total nitrogen (TN) concentration of either 8 mg/L
(Alternative 1; 329,000 Ib methanol per year) or 4 mg/L (Alternative 2; 432,000 Ib
methanol per year) could be selected, as desired.
Capital costs include construction of the denitrification filters for both alternatives, and
thus the total is same for each: $3,500,000. The two alternatives vary in terms of O&M
costs, with increases of $69,400 and $89,500 for alternatives 1 and 2, respectively. The
estimated costs per Ib of additional N removed is $1.61 and $1.27 for the first and second
alternatives, respectively.
Appendix II ' 92
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TOWN OF WOODSTOCK WWTP
The Town of Woodstock WWTP is an oxidation ditch activated sludge plant located in
Shenandoah County, VA, and the treated wastewater is discharged to the North Fork of
the Shenandoah River. It is an oxidation ditch activated sludge plant with a design
capacity of 1.0 MOD, and the dry and wet weather flows received at the plant are
approximately 0.6 MOD and 1.0 MOD. Operators are on site 10 to 11 hours every day.
Current discharge permit does not put any limitations on effluent nitrogen species.
Data for the 12-month period from January 1997 to December 1997 were examined.
Historically, measurements of effluent NOs-N have not been performed. Influent TKN,
effluent ammonia-N and nitrate-N measurements typically are not performed at the plant,
either. Effluent ammonia-N values from April 1992 through February 1993 were
available, however, and these data were used for this evaluation. BOD5 values showed a
wide range of variance during the period under study; with the lowest and highest values
being 77.5 mg/L (March 1997) and 2.24.6 mg/L (December 1997), respectively. The
average raw influent TKN concentration, calculated from a for BODS to TKN ratio of 6,
was 20.4 mg/L. The effluent pH, BOD5 and TSS concentrations rountinely achieved by
the plant are in compliance with the permit requirements. The effluent ammonia values
varied between 0.02 mg/L and 0.43 mg/L, except for an average of 2.46 mg/L during
November. Apparently nitrification was mildly upset that month, because it is believed
that the Woodstock WWTP oxidation ditch AS system is capable of accomplishing year
round nitrification.
The influent flow enters the treatment plant through a gravity main and, after screening,
passes through a Rotating Hydro degritter unit. There is also a bypass line equipped with
a Rotosheer™ screen unit with bar screens in a 2 ft wide channel. After flow
measurement, flow is divided between the oxidation ditches via a splitter box. The
facility has two 650,000 gal oxidation ditches identical in size and operation, and each
ditch is equipped with two 30 HP brush aerators. Two identical rim-fed circular
secondary clarifiers follow the ditches. The nominal hydraulic retention time (HRT) is 4
hours, and the actual HRT is 2.54 hours at the average influent and return activated
sludge (RAS) flows of 0.77 and 0.45 MOD, respectively. At these average flow rates and
with a total surface area of 1,816 ft, the surface loading rate of the clarifiers is 672
gpd/ft2, which is high for BNR treatment with clarifiers of this design. A 27,000 gal
chlorination tank follows the clarifiers. Following disinfection, the effluent is
dechlorinated by the use of sulfur dioxide. The chlorinator and the sulfonator used are
both Advance type. Final effluent is discharged to the North Fork of the Shenandoah
River. Sludge is wasted to the two 20,000 gal capacity aerobic digesters three times a
week. Digested sludge is hauled by trucks once per week for land application.
Because they have a large internal recycle rate (usually 80 to 120 times the influent flow),
oxidation ditches can obtain near complete denitrification if anoxic zones can be
established within the ditches. It is recommended that this primarily operational
Appendix II 93
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modification be made at the Woodstock WWTP Th,,* •* •
aerator be operated continuously, while Ae^er iTcvH 7 nc°^°^ed ** ™ brush
the BOD loading. The operator^ nee ^ to dete^Tne Z °D °ff * aCCOrdanCe with
experimentation. TimJshould be fn Li dTthe SffTT f" "* ^ ^^ by
especially when the operators are not tfflM nTpm f , 6aSe of oPeration,
RAS flow should also'be constructed ^m^nBEPR^T ^ ** ^°^°n °f Ae
accomplished by building a small .-cSrS^S^?'*?!? '" ^ f^ Jt C3n be
HRT of 2 to 4 hours with 30 to 50 % of Te Luen L u °Xldatl°n ditch' An
be sufficient for efficient biological phosphont "mova? *"*** ^^ *** ™* Sh°uld
, DO in the
chlorination system to control growth of flll^ti!' mStaIling * new retum sl"dge
costs for thesemodification^ Twou^ota S^^T "^ ditCheS" ^ Ca^
costs are estimated to be $1 1,000 The cost of add^ ^ ^ Change in °&M
$0.22 per Ib. °St °f addltl°nal N removal is estimated to be
Appendix II
94
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