-------
                             Table 3
                 Unit Process and Equipment Data
     Equipment

Raw Sewage Pumps



Primary Clarifier
RBC Units
RBC Effluent Pumps

Secondary Clarifiers



Chlorine Contact


Primary Digester
Secondary Digester




Tank Truck


Drying Beds



Liquid Alum Storage
          Design Data

30 1,400  gpm (88.3 I/sec), 2
variable speed,  1 constant speed
lag pump

1 rectangular 70,000 gallon (265
cu m) capacity with 1.5 hr.
detention and 895 gpd/sq ft
(36.5 cu m/day/sq m) overflow
rate

Bio-Surf by Autotrol.  Two
parallel paths with three shafts
and six stages in each, 515,500
ft2 (47,890  sq m) of media,
90 minutes retention and 1.94
gpd/sq ft (0.097) cu m/day/sq m)
hydraulic loading rate

Same as raw sewage pumps

2 rectangular, 2.75 hr detention
and 620  gpd/sq ft (25.3 cu
m/day/m2) overflow rate

2 baffled tanks, 35 min reten-
tion

1 fixed cover, 100,000 gal
(378.5 cu m) capacity with 15.5
days detention at design
loading, heated, mixed by gas
recirculation

1 floating cover, 100,000 gallon
(378.5  cu m) capacity with
supernatant discharge to raw
wastewater wet well

1 2,500 gallon (9.4 m3)
capacity

Adjoining sanitary landfill
site, 600' x 200' (183 m x 61 m)
without underdrains

2 tanks, each 2,600 gallons (9.8
cu m) capacity
                                96

-------
clarifiers.  Secondary effluent is chlorinated prior to



discharge to Lake Michigan.






Grit is manually cleaned from the grit chambers and disposed of



at a sanitary landfill.  Settled primary and secondary sludges



are pumped to a primary anaerobic digester that is heated and



equipped with gas recirculation and mixing apparatus.  Settled,



digested sludge from the secondary digester is withdrawn by tank



truck to sludge drying beds off-site.  Dried sludge is disposed



of in a sanitary landfill.  Supernatant from the secondary



digester is drained by gravity to the raw wastewater wet well.





INITIAL OPERATING EXPERIENCE



The operation of the plant was begun on March 1, 1974.  At the



same time, an 18-month testing and shakedown program was begun



to monitor the performance of the plant and to make operational



improvements where necessary.  During this period, wastewater



flows averaged 0.755 mgd (2,875 cu m/day) and were influenced



occasionally by sewer infiltration and inflows.  At start-up,



wastewater temperatures averaged 45°F (7.2°C), then gradually



increased to the low 60's (°F) by mid-summer.






Influent BOD-5 concentrations ranged from 129 to 219 mg/1 and



influent total suspended solids concentrations ranged from 101



mg/1 to 168 mg/1.   The average influent BOD-5 and total



suspended solids concentrations for the test period were 164



mg/1 and 132 mg/1, respectively.
                               97

-------
The results of the initial 18-month test period are summarized

as follows:

     Because the influent wastewater temperatures were quite
     cold at start-up, it took 18 days before heavy sloughings
     of biomass were observed and several months to achieve a
     steady state operation.

     During the last 12 months of the testing period (September
     1974 through September 1975) with the addition of 70 mg/1
     of alum and 0.8 mg/1 of  polymer, effluent BOD-5's were
     generally less than 10 mg/1; effluent suspended solids
     averaged 15 mg/1; and effluent total phosphorus con-
     centrations were less than 1.6 mg/1.

     In January 1975, design  flow conditions were simulated for
     two weeks by shutting down one of the parallel RBC paths
     and one of the final clarifiers.  The effluent BOD-5 for
     this two-week test period averaged 19 mg/1, while the
     average wastewater temperature was 47°F (8.3°C).
     Because of low hydraulic loadings (1.0 to 2.1
     nitrification occurred; 50% to 60% reductions in ammonia
     nitrogen occurred during the winter months and 85% to 95%
     reductions occurred during summer months.

     After one of the RBC paths was restarted in February 1975,
     after being shut down for full scale tests, nitrifiers did
     not re-establish dominant cultures on latter stages until
     June, when wastewater temperatures approached 60 °F
     Excellent BOD-5, suspended solids and ammonia nitrogen
     removals permitted reductions in effluent chlorine doses,
     from 6-7 mg/1 to 2-3 mg/1.

     Recycling of secondary sludge through the primary clarifier
     was required to thicken the combined sludges from 2% - 3%
     solids to 4% - 5% solids content.

     Slug releases of digester supernatant to the head end of
     the plant were detrimental to overall nitrification
     results.  Controlled release of digester supernatant is
     considered essential to achieve consistent ammonia
     nitrogen reduction.

     No significant differences were noticed in the digesti-
     bility of sludges with or without alum addition.  Phos-
     phorus release, volatile solids reduction, or gas
     production were not significantly affected by alum
     addition.  The average total sludge production was 0.83 Ib
     of total solids per pound of BOD-5 removed.  This figure
     takes into account chemical sludge production.


                                98

-------
     The measured power usage by the rotating biological
     contactor shafts ranged from 5.6 hp to 3.5 hp.  The average
     running horsepower per shaft was 4.2 hp.


PLANT PERFORMANCE (1976-1979)

The overall performance of the plant, subsequent to the 18-month

test program, is summarized in Table 4.  The data covers the

period from January 1976 through December 1979.  Table 5 shows a

comparison of plant performance under summer and winter con-

ditions.  Data for these tables was obtained from the monthly

operating reports prepared by the plant operators.


This data shows that the plant is consistently removing over 90%

of influent BOD-5 even under winter conditions and at hydraulic

loading rates of between 1.0 and 1.4 gpd/ft2.  Wastewater

strength is affected by increased infiltration and inflow during

warm weather months.  During winter months, effluent BOD-5

concentrations increase as wastewater temperatures decrease to

lows of 45°F.  Effluent dissolved oxygen concentrations are

consistently above 7 mg/1.


Effluent total suspended solids concentrations remained fairly

consistent throughout the period at an average of about 16 mg/1.

The hydraulic profile of the plant is such that secondary solids

are pumped twice prior to removal with settled primary solids.

The addition of polymer assists secondary sedimentation, and

lower suspended solids concentrations could probably be obtained

in the final effluent if flocculants were not disturbed by the

centrifugal pumps.
                               99

-------
                                    Table 4
                              Performance Summary
     Parameter
 1976
- - Annual Averages •
    1977        1978
             1979
BOD-5 (mg/1)
  -Influent
  -Effluent
  -% Removed
TSS (mg/1)
  -Influent
  -Effluent
VSS (mg/1)
  -Influent
  -Effluent
Total Phosphorus (mg/1)
  -Influent
  -Effluent
  -% Removed
Ammonia-N (mg/1)
  -Influent
  -Effluent
  -% Removed
Eff. Dissolved Oxygen  (mg/1)
Raw Sludge Pumped (Ib VSS/day)
Digester Gas Prod, (cu.ft./day)
Chemicals Used  (Ib/day)
  -Chlorine
  -Alum
  -Polymer
   182
     6
    97%

   135
    15

   111
     8
7.8
1.4
    82%
7.3
   576
 4,307

    13
   435
1.5

1







6
1

15
3

7




.725
.41
143
7
95%
122
16
95
7
.3
.1
83%
.5
.5
77%
.6
544
3,981
19
485
.612
1.19
155
7
95%
139
17
112
8
4.7
0.9
81%
17.4
2.1
88%
7.6
512
3,954
12
365
.712
1.38
129
12
91%
118
16
92
9
3.5
0.9
74%
15.9
2.0
87%
8.2
544
3,718
12
262
    1.7
1.5
1.4
                                    100

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                               Table  5

                    Comparative Performance Summary

                      Winter vs Summer Operation
                                   Average Winter    Average Summer
                                     Values I/         Values 2/
Flow  (mgd)                          0.530             0.726
Hydraulic Loading (gpd/sq.ft.)       1.03              1.41
Waste Temperature (°F)              46                64
BOD-5  (mg/1)
  -Influent                        181               128
  -Effluent                         10                 9
  -% Removed                        94                93
TSS (mg/1)
  -Influent                        140               130
  -Effluent                         16                16
Total Phosphorus (mg/1)
  -Influent                          5.8               4.7
  -Effluent                          0.8               1.0
  -% Removed                        86                79
Ammonia-N (mg/1)
  -Influent                         20.0              15.1
  -Effluent                          4.9               1.0
  -% Removed                        76                93
Effluent Dissolved Oxygen (mg/1)     8.1               7.3
\J From January, February, March, 1977 through 1979 reported data.

2/ From July, August, September, 1977 through 1979 reported data.
                                101

-------
More than 80% of influent total phosphorus concentrations are



removed by the addition of alum (hydrated aluminum sulfate).



Plant operators attempt to maintain a liquid alum dosage rate



sufficient to provide 1.5 moles of aluminum to 1.0 mole of



influent total phosphorus.






The plant was not designed to accomplish nitrification.



However, because it is currently operated at hydraulic loadings



of less than 2 gpd/ft^, nitrification does occur.  Ammonia



analyses show that average influent ammonia concentrations of 16



mg/1 to 18 mg/1 are reduced to 2 mg/1 to 4 mg/1 through the



plant.  As might be expected, less nitrification occurs during



winter months.






In 1979, an average of 710 pounds per day of sludge was pumped



to the primary digester with an average solids content of 3.7%




by weight.  The volatile content of the sludge averaged 74% by



weight.  Total sludge production, including chemical sludges,



averaged 1.14 pounds per pound of BOD-5 removed, or approxi-



mately 1,000 pounds per million gallons treated.  Approximately



262 pounds per day of alum was added to remove an average of 2.6



mg/1 of total phosphorus.





OVERALL OPERATIONS AND MAINTENANCE




The Gladstone plant is staffed by one superintendent and three



shift operators.  The plant is manned 16 hours per day, five



days a week; eight hours per day on week-ends and holidays.  The



superintendent also has the responsibility of the water



filtration plant, staffed by two operators.  Most of the





                               102

-------
operators are cross-trained to provide flexibility.  All opera-



tors are state certified and operate shifts on a rotational



basis.





All laboratory tests are conducted according to "Standard




Methods", 14th edition.






Flows are measured weekly at the Parshall flume to check the




flow meter.  The chlorinator, sampler, alum and polymer feeders




are regulated by the flow meter.






Secondary sludge is returned at least five times per day to the



primary clarifier to thicken the combined sludges from 2%-3% to



4%-5% solids content.  The combined sludge is then pumped to the



primary anaerobic digester.  Digesting sludges are monitored



weekly for volatile acid/alkalinity relationships and volatile



content.  When the volatile percentage is less than 50% and the



supernatant shows excessive solids, sludge is hauled by tanker




to the drying beds.  The digesters are cleaned and inspected at



three year intervals.






The RBC units are greased at the main bearings twice per week



with 5 to 6 shots of grease.  The oil in the chain casings and



speed reducers is changed yearly or more often if the oil should



become diluted with water.  The walkways and the area around the



disks are scrubbed weekly.  The tanks are drained and flushed



yearly for a general inspection.  Very little accumulation has



ever been found.  The three V-belts on the drive units are



replaced about yearly upon breakage.   One main shaft bearing



failed in the six years of operation.



                               103

-------
The plant staff also maintains the six lift stations throughout



the 22 miles (35.4 km) of the collection system, which ranges in



size from 4 inches (10.2 cm) to 3D inches (76.2 cm).  Most of



the collection system was installed during the 1920's  and



1930's, and was a combined system until new storm sewers were




installed in the late 1950's.  This contributes at  times, to



excessive infiltration and inflow during snow melts, severe



rains and high lake levels.  Step I studies are presently being




conducted to locate the problem areas of the system.



Maintenance of the collection system other than the lift



stations is performed by the Public Works Department.






PROBLEMS THAT DEVELOPED



During the first years of operation a few problems  developed and



were solved by the operators.  These included changes in alum



feed points, sampling equipment, digester piping, and sludge



handling.  The problems as well as the solutions we employed are



explained below.






ALUM APPLICATION POINTS



It was found that during low flows the alum dosages needed to be



increased considerably to remove the required amounts.  Also,



with low flows, concentrations of phosphorus increased, creating




the need for an increase in alum application.






Feed points at the secondary wet well did not provide enough



turbulance for proper mixing, so a temporary feed line was



installed to the sixth stage of each RBC path.  This provided



enough dispersion for coagulation and flocculation, but after






                                104

-------
passing over a weir, through the wet well, and being pumped  to



the secondary clarifier, the floe was broken up.  By adding  alum



to the primary wet well, dosages could be reduced at times,  but



results were not consistent.






Temporary lines were installed in 1979 to the discharge side of



the primary pumps.  A 30% reduction in the feed rate was found



to achieve the same results.  Permanent feed lines were then



installed to each of the primary pumps.  This has proven




effective during both low and high flows.






METHANE GAS UTILIZATION



The heating system of the building and the primary anaerobic



digester was designed to use both methane and natural gas.




Methane gas has a content of about 650 BTU per cubic foot, and



the boiler needed a rate of 5090 cubic feet per hour.  The gas



pressure in the digester would raise a column of water 10 inches



(25.4 cm).  A 2-inch (5.1 cm) gas pipe had been installed from




both digesters.  The floating cover of the secondary digester



can hold about 4,000 cubic feet of gas.  A sufficient gas rate



was not available to sustain the gas boiler, since the piping



extends some 70 feet (21.5 m),  plus the meter, check valve,



flame arrester, and etc.  By reducing the orifices of the



burner, some gas could be burned at times.






With the cleaning of the digesters in 1977, the portion of



2-inch (5.1 cm) pipe inside the secondary digester was changed



to 4-inch (10.2 cm) with the intent of changing all the piping



to this larger size.






                               105

-------
After temporarily connecting to clean the primary digester and
to burn off the gas, we found the boiler would operate at all
times.  The remainder of the pipe has never been changed.

SLUDGE ODORS
Sludge, especially when controlling ammonia, must be removed at
intervals of 2 to 3 hours to eliminate bulking and its odors.
Sludge remaining at the bottom of the clarifiers will soon
become anaerobic and de-nitrify.  Higher temperatures will also
accelerate bulking.

Secondary sludge must be removed manually.  When the plant is
not manned on week-ends and holidays, we occasionally experience
rising sludge.  An automatic sludge removal system would be
advantageous, as these clarifiers are uncovered and the odors
are readily noticed by our neighbors.

Combined sludges are pumped to the anaerobic digesters at two to
three hour intervals to assure proper utilization of digester
capacity and functions.

DIGESTER UPSET
In the six years of operations, only once were the digesters
upset.  This happened in 1976, when gas production ceased and
the digesters went  "sour".  The nitrifiers on the RBC units were
disrupted as well.

The supernatant from the primary digester contained small
cellophane-type pieces of irregular shapes, somewhat resembling
bleached potato peelings.  The volatile acid/alkalinity ratio
rose above 1.0 and  the pH was dropping below 6.4.
                                106

-------
To correct the problem, heat was maintained at 90°F in the



digester and continuous mixing was was employed.  About 300




pounds of soda ash were added over a 10-day period to hold the



pH near 7.0.  Within two weeks the digesters were back



functioning normally.






The only explanation as to the cause of the upset was that the



city fire department floor had been stripped of several layers



of paint using paint remover which was flushed to the sanitary



sewers.






SAMPLING EQUIPMENT INADEQUACIES



The original sampling equipment supplied with the plant did not




provide representative samples.  The three samples required were



raw wastewater, primary effluent, and final effluent.  Only the



final effluent samples could be collected continuously.






The samplers had a small opening about the size of the lead in a



pencil, and the raw and primary effluent samples soon clogged



the orifice.  The pumps for raw and primary effluent had 1



1/2-inch (3.8 cm) suction piping but only 1-inch (2.54 cm)



discharges.  The primary effluent would pass easily enough,



however, the raw pump would plug at the 1-inch opening almost



immediately.






In 1975, a dipper type three-stage sampler with refrigeration



was purchased from "Sonford Products" of Minneapolis, Minnesota



and installed by the plant operators.  All piping to the sampler



was increased to 1 1/2-inch (3.8 cm) with provisions provided
                               107

-------
for backflushing with final effluent.  A submersible raw sample



pump was installed directly behind the bar screen.  The pump



delivers 15 gallons per minute to the sampler and seldom causes



any problems.  The new sampling system works well with very



little maintenance and we are assured of representative samples.





ENERGY AND CHEMICAL COSTS



The energy and chemical uses and costs associated with the plant



operation for 1978 are summarized in Table 6.  The costs shown



per million gallons reflect actual prices Gladstone paid for the



respective commodities in 1978.





Electricity consumption is of primary interest and the table



shows electrical power consumption in terms of raw sewage



pumping, secondary (RBC) treatment, and anaerobic digestion.



The power consumption for the RBC units actually includes power



consumption by clarifier drives, intermediate pumps, lights,



ventilating equipment, etc., and computes to an average of



approximately 38 running horsepower at any given time.  Of this,



approximately 80 percent (30 hp), including power draw by the



RBC units, could be considered independent of actual flows.



Based on measured power consumptions by the six RBC drive units



in 1975, the RBC system draws an average of 25-26 horsepower at



any given time.





TOTAL FACILITY BUDGET



Table 7 begins with the total facility budget and is followed by
                                                          f


some of the major operating expenses.  The remainder of the



budget  incorporates items such as the collection system, audit,



administration, engineering, insurances, and etc.

                               108

-------
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                                                       109

-------
                             Table 7

                     1979 Fiscal Year Budget



Total Facility Budget                               $178,000.00


Power
     Lift Stations     32,607 KWH
     Plant            313,627 KWH

     Total Power Costs                                14,781.97

Natural Gas         1,185,490 cu ft                    2,861,87

Chlorine                4,550 Ibs                        827.25

Aluminum Sulfate       95,648 Ibs                      4,497.96

Polymer                   501 Ibs                      1,005.52

Labor                   7,136 man-hours               57,088.00

Plant Maintenance                                      3,000.00

Parts, Supplies, Miscellaneous                         4,000.00

Equipment Rentals                                      3,000.00
                                110

-------
REVENUE TO OPERATE

In 1972, water meters were installed in every home.  The water

plant staff maintains these meters.  All meters larger than

1-inch are checked at three year intervals.  Small household

meters are checked to assure accuracy as needed.  Ten percent of

the meters have registered 1 million gallons since 1972 and a

routine maintenance program is being initiated.


The water distribution system originally began in 1889 and at

the present, approximately 72% of the water produced can be

accounted for..  63% of the water treated at the wastewater plant

comes from inflow and infiltration.


Prior to 1969, no wastewater charges were collected, with the

system operating solely on taxes.  Water charges prior to 1970

averaged $1.00 per month.  Today, with the new water filtration

plant and the upgraded wastewater facility, the average house-

hold using 5,000 gallons of water pays $11.65 for water and

$10.49 for wastewater per month.

                           i
SUMMARY

We believe the RBC treatment system is an ideal treatment

process for the city of Gladstone, Michigan.  Excellent

treatment results are being obtained and plant effluent quality

is well within design limits.   Consistent nitrification at

loading below 2 gpd/sq ft is being achieved as an added bonus

toward high quality treatment.
                              Ill

-------
The system has been very consistent in achieving wastewater



treatment and permitting stable solids handling procedures.  Few



problems have occurred with the day-to-day operation of our RBC



secondary treatment system.






ACKNOWLEDGEMENTS



The author wishes to thank Williams & Works of Grand Rapids,



Michigan for their cooperation in the preparation of this paper.
                               112

-------
              CONTROL TECHNOLOGY FOR NUTRIENTS IN
           MUNICIPAL WASTEWATER TREATMENT IN SWEDEN

                       Bengt G. Hultman
                       Research Engineer
        Swedish Water and Waste Water Works Association
                       Regeringsgatan 86
                      S-lll 39  STOCKHOLM
                             Sweden
NEED FOR NUTRIENTS CONTROL

Sweden is comparatively rich in lakes with more than 20,000 ex-

ceeding 0.1 sq. km in area. Most of them are fairly shallow. In

their natural states the lakes and coastal areas are deficient in

nutrients. This means that the lakes and coastal areas will react

to artificial supply of nutrients from for instance urban areas.


At the end of the 1950~s limnologists began to warn about the

deterioration of the water quality in lakes and coastal areas

due to the increased rate of the growth of algae and other vege-

tation. Rodhe  (1958) pointed out that the phosphorus in sewage

could increase the productivity in natural waters as much as com-

mersial fertilisers applied on land. Different investigations on

lakes indicated a significant rise in the water's content of

phosphorus and biomass.


During two weeks in August 19-72 an extensive lake survey was car-

ried out by the National Swedish Environment Protection Board and

the County Administrations (Johansson and Karlgren, 1974). A to-

tal of 1250 minor and medium-sized lakes were examined. Although

not being the primary aim of the study, an attempt was made to

estimate the degree of nutritional influence on the lakes resul-
                                 113

-------
ting from human activities.  It was found that the inorganic phos-

phate content in water showed similar regional variations as that

of total phosphorus and of total nitrogen with low concentrations

in the low-productive lakes in northern Sweden and parts of south-

ern Sweden and high concentrations in the high-productive lakes

of the plains.


Based on the lake survey and complementary studies Hannerz and

Forsberg (1975) estimated that less than 10 % of the Swedish la-

kes were eutrophic. In south Sweden about 10 to 20 % of the lakes

were eutrophic and the percentage of eutrophic lakes in the Stock-

holm county amounted to about 50 %.


Several substances such as phosphorus, nitrogen, carbon dioxide,

iron and vitamins can stimulate algal growth. Of these substances

only phosphorus and nitrogen have been considered as main factors

for stimulating eutrophication. A strong emphasis has been laid

on phosphorus removal as the method for control of eutrophication

especially from the National Swedish Environment Protection Board,

while nitrogen has been considered to be of minor importance. The

reasons for this view seem to be:

         Phosphorus seems to be rate limiting for algal growth
         in most Swedish lakes based on values of the weight pro-
         portion of nitrogen to phosphorus, which is about 25:1
         for natural or low polluted lakes. '

         A large fraction of phosphorus comes from point sources
         which may be more easily controlled than diffusive sour-
         ces.

      -  Algae have the possibility of taking up nitrogen from the
         atmosphere if nitrogen is a limiting growth factor.
                                 114

-------
       In the end of the 1960's phosphorus removal was a much
       more wellknown technique than nitrogen removal in Sweden.


For a total of about 900 samples from surface water from 20 waste

affected lakes in Sweden during August-October 1972 Forsberg et

al. (1975)  found phosphorus to be the growth limiting nutrient

in waters having total-P values less than 0.05 mg/1. Above 0.1

mg P/l nitrogen played the principal role. Between these values

the growth was primarily limited by phosphorus or nitrogen or

chelating agents.


Nitrogen seems to be the primarily rate limiting factor for algal

growth in case of eutrophic lakes (Forsberg, 1977) and in some

coastal waters as the Stockholm archipelago  (Lindahl and Melin,

1973). In this case the policy of the National Swedish Environ-

ment Protection Board has been to try to reduce the phosphorus

supply to the water body as much as possible in order to make

phosphorus the growth limiting substance  (Anonymous, 1971).


IMPLEMENTATION OF NUTRIENTS CONTROL


LEGISLATION AND ADMINISTRATION

Legislation concerning discharge of waste water into lakes and

rivers has been in existence in Sweden since the end of the

1930's. A new law, the Environment Protection Act, came into for-

ce in July 1969 and tightened up regulations considerably.


The Environment Protection Act applies to what are termed pollu-

ting activities, i.e. the discharge of effluent, solids or gas
                                 115

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from land, a building or an installation or the use of such pro-



perty in a manner liable to cause water pollution, atmospheric



pollution, noise, vibration, the emission of light etc., if the



nuisance thus caused is more than temporary (National Swedish



Environment Protection Board, 1979a).






The chief principle of the act is to prevent environmental dis-



turbances as far as possible. The precautionary measures, such



as effective methods of wastewater treatment,  shall be "economi-



cally feasible" and "technically practible".






Sewage from locations with more than 200 inhabitants must not be



emitted without a permit. A special board, the Franchise Board



for Protection of the Environment, holds the responsibility for



the granting of permits. The obligation to apply for a permit is



however not compulsory. The National Swedish Environment Protection



Board may after due examination exempt an applicant from the need



to apply to the Franchise Board for a permit.  In exemption cases,



the Board attempts through negotiations to come to an agreement



with the applicant as to the conditions to be applied to the ac-



tivity. An exemption granted lacks formal legal validity - as



opposed to a permit - and may be withdrawn  (National Swedish En-



vironment Protection Board, 1979a).






SOURCE CONTROL



The synthetic detergents which were introduced in Sweden during




the 1950"s have greatly improved laundry cleaning efficiency. Po-



lyphosphates were totally dominating as complexing agents in the
                                 116

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detergents. In the end of the 1960"s the average phosphate con-



centration was about 35 % in cleaning agents and in some special



products the phosphate concentration could amount to more than



60 % (Kjellman, 1975).





In the middle of the 1960"s municipal sewage from urban areas



contained phosphorus corresponding to about 4 g P per person and



day. Approximately half of this amount originated from detergents



(Ahl et al., 1967). The general opinion that phosphorus was the



main agent causing eutrophication lead to investigations of dif-



ferent methods to reduce the phosphate concentration in detergents.



In order to comply with authorities different manufacturers dimi-



nished the amount of phosphates in their detergents. As can be



seen from Table 1 the use of phosphate in detergents diminished



from about 3.9«106 kg in year 1968 to about 2.65»106 kg in 1972,



corresponding to a decrease of 32 %. Due to the decrease of phos-



phate in detergents the phosphorus content in sewage diminished



to about 3.3 g P per person and day of which about 30 % originated



from detergents (Kjellman, 1975). The use of phosphorus in deter-



gents has increased a little after 1972.





The trisodium salt of NTA may be used as a partial substitute for



or a complement to sodium tripolyphosphate as builder in house-



hold detergents. NTA was introduced on the market at the end of



the 1960"s (see Table 1). Several studies were performed in order



to evaluate the biodegradability of NTA (Forsberg and Lindquist,



1967, Bouveng et al., 1968 and 1970, and Bjorndal et al., 1972).
                                 117

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The results obtained showed that aerobic biological processes



are capable of degrading NTA fairly efficient under normal con-



ditions of operation.  However,  different foreign reports, for




instance the Epstein report, raised some doubts that NTA could



be safely used without negative consequences on the environment.



These doubts lead to a decreased interest in using NTA in deter-



gents (National Swedish Environment Protection Board, 1970)  and



the use of NTA in detergents has decreased during the 1970~s.






CHOICE OF PROCESS TECHNOLOGY FOR NUTRIENTS CONTROL



The first sewage works with chemical precipitation was built in




1961 in Aker, a small municipality with about 2,000 persons con-



nected to the sewage works. The treatment plant was equipped for



primary sedimentation with subsequent chemical precipitation whe-



re the floes were separated in a flotation unit. The chemical




precipitation agent was aluminium sulphate.






The sewage works in Aker was built before any significant research



had started in chemical precipitation. In the middle of the 1960"s



several research projects started on combined biological and che-



mical treatment of sewage. At that time the two processes which



were considered were simultaneous precipitation and post-precipi-



tation. Studies were performed in a laboratory scale, pilot plant



scale and as full scale experiments.






Early studies on the simultaneous precipitation process gave rat-



her high effluent values of total phosphorus. Pilot plant studies



with simultaneous precipitation with aluminium sulphate gave eff-
                                118

-------
luent values of total phosphorus of about 2 mg P/l (Balm§r et



al., 1968). Full scale tests at Eolshalls sewage works in Stock-



holm during a short test period showed effluent values of total



phosphorus of about 1-1.5 mg P/l. Addition of aluminium sulphate



caused a lower reduction of the BOD-values due to separation




problems in the final sedimentation basin (Cronholm,  1968). Ulm-



gren (1969) reports other full scale tests in which simultaneous



precipitation were studied giving high effluent values of total



phosphorus. Laboratory studies of the simultaneous precipitation



process, however, showed that it was possible to reach effluent




values of total phosphorus below 1 mg P/l (Ericsson,  1967).






Laboratory experiments with post-precipitation showed that an



effluent value could be reached of total phosphorus below 1 mg P/l



(Ericsson, 1967, and Weijman-Hane, 1968). Similar results were



obtained in evaluation of the first built sewage works with post-




precipitation (National Swedish Environment Protection Board,



1969) .






Based on the rather few experimental studies performed in Sweden



concerning chemical precipitation and foreign experiences for



instance in Switzerland the National Swedish Environment Protec-



tion Board strongly recommended post-precipitation instead of si-



multaneous precipitation as the removal method of phosphorus. In



1968 the expansion period began with chemical treatment plants



with the purpose of reducing as much as possible of the phospho-



rus content in wastewaters.
                                 119

-------
No significant interest was laid on nitrogen removal. However,



some research started in the middle of the 1960"s concerning



nitrogen removal, especially by use of biological methods




(Hultman, 1973, and Ericsson, 1975).






DESIGN GUIDELINES



To guide those who prepare or scrutinize proposals for treatment



plants the National Swedish Environment Protection Board  (1971)



prepared "Guidelines for design of sewage treatment plants". In




the guidelines the following are given: design values for sludge



loads on the activated sludge process, BOD loads on trickling



filters, detention time in flocculating units, surface loads in



sedimentation basins etc  (Ulmgren, 1975a).






EMISSION CONTROL




Instructions for emission control in Sweden have been issued by




the National Swedish Environment Protection Board  (1973). The



sampling frequency in relation to the required parameters total



BODj, total COD and total phosphorus is given in Table 2. In ad-



dition local authorities may demand more extensive emission cont-



rol and programs for recipient control.






STATE GRANTS



State grants are since 1st of July 1968 payable on certain con-




ditions for the construction, enlargement or alteration of sewage



purification plants, outfalls and, in some cases, intercepting



mains as well  (National Swedish Environment Protection Board,



1968) .
                                 120

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TABLE 1.  YEARLY CONSUMPTION OF RAW MATERIALS FOR WASHING,
          DISH-WASHING AND OTHER CLEANING MATERIALS USED  IN
          HOUSEHOLDS IN SWEDEN 1968-1972  (The consumption
          figures are given in thousand kilograms; 1 kg =
	2.205 Ib)  (Kjallman, 1965).	
Raw material
              Year

1968   1969   1970   1971   1972
Soap
Synthetic tensides
Phosphates
NTA
Other organic com-
plexing agents
1377
7500
3920
111
116
2037
7704
3644
1019
115
2624
7450
2855
1711
226
2597
7443
2797
1525
330
2766
8483
2650
1373
492
TABLE 2.  FREQUENCY OF SAMPLING IN EMISSION CONTROL
          (National Swedish Environment Protection Board/  1970)
Parameter
Person
equivalents (p.e.) connected to treatment plant
200-2000 2000-5000
COD(a)
BOD20000
4 /month
I/month
4 /month


                               121

-------
Grants are gauged according to degree of purification and are



payable at rates between 30 and 50 per cent of approved con-



struction costs (see Table 3). During the fiscal years 1971/72-



1973/74 grants were payable 25 per cent in excess of those rates



given in Table 3.  This formed a part of a programme to create



jobs (National Swedish Environment Protection Board, 1979a).



Grants given for different types of treatment are exemplified



in Table 4 based on rates in Table 3.





PRESENT SITUATION



The general policies for implementation of the Environment Pro-



tection Act on sewage treatment as developed in the end of the



1960*s has essentially been maintained. Thus, a combined biologi-



cal and chemical treatment of municipal wastewater is normally



prescribed. In certain relatively few cases, only biological or



only chemical treatment may be allowed. In localities with poor



recipient conditions in relation to the discharge complementary



treatment  (mainly post-filtration) is prescribed in addition to



biological and chemical treatment. Recently, requirements of nit-



rification has been prescribed for a sewage works in the Stock-



holm area. The main reason for this requirement is to diminish



the oxygen demand of the wastewater which may give rise to oxygen



deficit at the bottom of certain parts of the Stockholm archipe-



lago and thereby cause leakage of phosphorus from the bottom se-



diments. Thus, the requirement of nitrification is to prevent



phosphorus leakage and thereby according to the general view



decrease algal growth.
                                 122

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TABLE 3.  STATE GRANTS FOR MUNICIPAL WASTEWATER WORKS
	(National Swedish Environment Protection Board, 1968)

Percentage BOD-, pu-       Percentage phosphorus purifica-

rification effect         tion effect

                             <50       50-89      >90
                          Percentage grant:

      60-74                   30         35        40

      75-89                   30         35        45

        >90                   35         40        50
TABLE 4.  PERCENTAGE GRANTS FOR DIFFERENT PROCESS COMBINATIONS
	(National Swedish Environment Protection Board, 1969)


Process combination                  Percentage grant

Simultaneous precipitation                 35

Direct precipitation                       40

Post-precipitation                        45-50
                                 123

-------
Sewage purification facilities in Sweden have expanded very



quickly during the last decade (see Figure 1). In the beginning



of 1979 about 640 municipal wastewater treatment plants were ope-



rated with combined biological and chemical treatment correspon-




ding to about 72 % of the total amount of wastewater from urban



areas.






The dominating process combination is post-precipitation with a



share of more than 80 % calculated on the number of treatment




plants with chemical precipitation (see Table 5). However, some



of the largest sewage works, for instance in the Stockholm region,



use pre-precipitation or simultaneous precipitation.






Aluminium sulphate has been the dominating precipitation agent.



During the last years especially larger sewage works have changed




to iron salts (see Table 6). This depends on that the production




of ferric chloride from waste products has considerably lowered



the price of the chemical. Besides there are some benificial ef-



fects on the sludge properties in the use of iron salts compared



with aluminium sulphate.






EVALUATION OF NUTRIENTS CONTROL MEASURES






OPERATIONAL RESULTS



Several papers have been written on experiences of full scale



operations of chemical precipitation in Sweden  (Eklund, 1974,



Gronqvist et al., 1978, Hultman, 1978, Isgard and Ericsson, 1976,



and 1978, and Ulmgren, 1975a and 1975b). These papers discuss
                                 124

-------
    Percent of the population in urban areas(localities)
                               1979-01-01
100
                           1970
              1975
                                                                           Chemical
                                                                           treatment
                                                                      	Biological-
                                                                      71%| chemical
                                                                           treatment
                                                                           Complementary
                                                                     1,5%J treatment
                                                                           (filtration etc.)
            1980
   Type of sewage treatment
Number of
treatment plants
Number of persons
served
   No treatment
   Sedimentation
   Biological treatment
   Chemical treatment
   Bio. chemical treatment
   Complementary treatment
   156  (-34)
   380  (-37)
   141  (+  3)
   625  (+18)
    18  (+  2)
    7 000  (-   1 000)
  181 000  (-  21 000)
1 398000  (-110000)
  324000  (+  22000)
4833000  (+ 106000)
  107000  (+   7000)
                                        1 320 (-48)
  The figures in brackets refer to the change since January 1 st, 1978
                          6 850 000
            Figure 1.   Sewage Treatment  in  Sweden  1965-1979

                                        125

-------
TABLE 5.  DIFFERENT TYPES OF SEWAGE WORKS WITH CHEMICAL PRECIPI-
          TATION IN SWEDEN IN THE BEGINNING OF 1978
	(National Swedish Environment Protection Board, 1979b)
PROCESS COMBINATION:

Direct precipitation

Pre-precipitation

Simultaneous precipitation

Post-precipitation
NUMBER OF PLANTS

      138

       17

       35

      554
Post-precipitation systems;

     Trickling filters

     Activated sludge

     Separation of chemical floes
     by contact filtration

     Polishing by deep-bed filters
       49

      505


       11

       16
TABLE 6.  USE OF DIFFERENT PRECIPITATION AGENTS AT MUNICIPAL  SE-
          WAGE WORKS IN SWEDEN IN THE BEGINNING OF 1977 AND 1979
	(National Swedish Environment Protection Board,  1979b)

                    TYPE OF CHEMICAL PRECIPITATION AGENT:

Number of
plants
Aluminium
sulphate
600 (578)
Ferric & Lime
ferrous
iron
92 (60) 60 (48)
Iron
salts &
lime
26 (22)
Aluminium
sulphate &
iron salts
4 (3)
Percentage of
connected po-
pulation          49  (69)   42  (23)     5  (3)     2  (3)     2  (2)
Numbers from the beginning of 1977 are within brackets,
                                  126

-------
different process configurations, the influence of different ope-



rational parameters such as dosage, pH-value in the flocculation



step and type of chemical precipitation agent and the influence



of separation methods.





Data from the emission control at municipal sewage works shall be



sent to the National Swedish Environment Protection Board once a



year. Compilations of such data have been published by the Natio-



nal Swedish Environment Protection Board (1977 and 1979b). Obtai-



ned results for different treatment systems are shown in Table 7.



The results are compared in the table with expected results from



treatment plants with a good operation and no significant distur-



bances based on results reported by Gronqvist et al. (1978).





A large fraction of the Swedish municipal sewage works do not



operate reliably. Investigations of post-precipitation plants in-



dicate that effluent values of BOD- are not below 15 mg/1 (requi-



red limit)  for about 30 % of the plants and effluent values of



total phosphorus are not below 0.5 mg P/l (required limit) for



about 40 % of the plants (National Swedish Environment Protection



Board, 1977).





Full scale experiences of simultaneous precipitation plants in



the Nordic countries have been put together by Gronqvist and



Arvin (1979). It was shown that much better results could be ob-



tained for the treatment plants than results shown in Table 7.



The average concentration of total phosphorus from five simulta-



neous precipitation plants in the Stockholm area was 0.6 mg P/l.
                                 127

-------
TABLE 7.  OPERATIONAL RESULTS BY USE OF DIFFERENT CHEMICAL PRECI-
          PITATION METHODS
PROCESS COMBINATION





Direct precipitation
Pre-precipitation
Simultaneous preci-
pitation
Post-precipitation
OPERATIONAL RESULTS
IN 1977

ROD
±J\-/ LJ n
mg/1
39
35

28
10
(1)


tot
mg/1
0.70
0.98

1.48
0.53
EXPECTED RESULTS
FOR PLANTS WITH NO
SIGNIFICANT

BANCES (2)
Ptot' mg
-
0.5-0.

0.5-0.
0.5-1.
DISTUR-


/l

8

8
2 (3)
Post-precipitation
followed by deep-
bed filtration
0.22
                                                    0.2-0.4  (4)
0.15-0.3 (5)
Notes:   (1)  Average values from different plants. Data from
              National Swedish Environment Protection Board  (1979b)

         (2)  According to Gronquist et al.  (1978).

         (3)  Post-precipitation with aluminium sulphate at pH
              6.5-7.2 or lime in single stage at normal loaded
              plants.

         (4)  Post-precipitation with aluminium sulphate at pH
              5.5-6.4, with ferric chloride and recirculation of
              sludge to the aeration basin or with lime in single
              stage  at low loaded plants.

         (5)  Post-precipitation with aluminium sulphate at pH
              5.5-6.4.
                                128

-------
In order to elucidate the reasons of the unsatisfactory removal




efficiencies of certain sewage works an enquiry was sent in spring



1979 to the County Councils. These were requested to give their



opinion of the reasons for the unsatisfactory results of sewage



works with effluent values of BOD_ and total phosphorus above 15



mg/1 and 0.5 mg P/l, respectively. Several explanations were gi-



ven such as hydraulic problems, difficult industrial wastes and



unreliable machinery equipment. The percentage distribution of



reasons to unsatisfactory results is given in Table 8.






COSTS OF POST-PRECIPITATION PLANTS



The costs for post-precipitation plants based on average values



from different Swedish reports are put together in Table 9. The



capital costs are somewhat higher than the operating costs. Due



to increasing treatment costs for diminishing sizes of the sewage



works there is a tendency to centralize the wastewater treatment.



The grant system has promoted this development. The use of comple-



mentary treatment by deep-bed filtration will increase the total



costs for a post-precipitation plant 15-20 %.  Different cost



factors for the operating costs are shown in Table 10.






EFFECTS ON RECIPIENTS



In order to elucidate the effects of biological and chemical



treatment on the water quality in the recipient the National Swe-



dish Environment Protection Board started a program in 1972 for




analyzing the conditions in a number of different recipient lakes




(Forsberg et al., 1975).
                                 129

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TABLE 8.  CAUSES OF UNSATISFACTORY REMOVAL EFFICIENCIES OF POST-
	PRECIPITATION PLANTS (Carlsson and Nordstrom, 1979)
CAUSE

Hydraulic problems

Industrial wastes

Machinary equipment

Process technology

Maintenance

Repairs, reconstruction

Unreliable analysis  (1)

Unknown causes
PERCENTAGE DISTRIBUTION, %

             18

             12

             19

             17

              2

              4

             17

             12
Note:  (1)  Probably depending on significant nitrification  in
            BOD-bottles during the BOD7~measurement.
                                 130

-------
TABLE 9.  APPROXIMATE COSTS FOR SEWAGE TREATMENT (1978).
Number of per-
son equivalents
(p.e.)
Costs for post-preci-
pitation plants (inclu-
ding sludge treatment)
                    Capital
                    costs
                      Skr
                    p.e.-year
             Operating
             costs
               Skr
             p.e.-year
Additional costs
for deep-bed filt-
ration
Capital     Operating
costs       costs
  Skr         Skr
p.e.-year   p.e.«year
2,000
5,000
20,000
50,000
130
100
60
45
100
70
50
40
—
25
10
7
—
8
4
3
Notes:     1 Skr = 0.24 US dollars
           In calculation of capital costs the annuity used is 10 %
           and 13 % for post-precipitation plants and deep-bed fil-
           ters, respectively.
           Average municipal water consumption is about 400 1 per
           person and day in Sweden.
TABLE 10.  OPERATING COSTS FOR POST-PRECIPITATION PLANTS  (INCLU-
           DING SLUDGE TREATMENT)  (1978)
COST FACTOR
Labour and administration
Chemicals
     For chemical precipitation
     For sludge conditioning
Energy
Sludge transportation
Other costs factors
                 PERCENTAL COSTS, %
                        30
                        25
                        (15)
                        (10)
                        20
                        10
                        15
                       Too
                                 131

-------
From the experiences of phosphorus removal positive responses



have been reported from some water bodies. In other lakes delayed



recovery has been observed after nutrient reduction. In some la-



kes, where the phosphorus load was reduced by 30-40 %, no marked



improvements were noted. The results available indicate that a



comparatively great change in phosphorus load must occur in or-



der to get significant improvement in water clarity in the lakes.



As the phosphorus load from treatment plants is often the domi-



nant phosphorus source, reduction of phosphorus by advanced treat-



ment seems to be a good tool for controlling eutrophication in



many lakes (Ryding, 1978a and 1978b).






TRENDS IN IMPROVEMENT OF CONTROL OF NUTRIENTS



The operating costs have steadily increased at Swedish sewage



works. Therefore great interest has been directed towards biolo-



gical-chemical treatment methods which can reduce the operating




costs and which are more efficient. Such methods include the use



of counterflow of precipitated sludges, two-step precipitation,



regulation of the alkalinity and automatic control.






For a constant value of the suspended solids in the effluent it



is advantageous to have a low fraction of phosphorus in the sus-



pended solids in order to obtain low effluent values of phospho-



rus. If the effluent concentration of suspended solids is 10 mg/1



and the fraction of phosphorus in the suspended solids 6 % and 2




% the effluent concentration of suspended phosphorus will be 0.6




and 0.2 mg P/l, respectively.
                                 132

-------
A suitable way to diminish the fraction of phosphorus in the sus-

pended solids is to decrease the influent phosphorus concentration

before the precipitation step. This technique has been tried in

full scale at several sewage works in Sweden. Different examples

are:
          Two-step precipitation at Balinge sewage works (Holm-
          strom, 1977)  by use of the combination of simultaneous
          precipitation and contact filtration in which process
          combination the principal part of phosphorus removal
          occurs in the simultaneous precipitation step after
          which still more phosphorus is removed by the addition
          of low concentrations of ferric iron before a deep-bed
          filter.

          Two-step precipitation at Kappala (Isgard and Ericsson,
          1978) and Bankeryd sewage works in which simultaneous
          precipitation is followed by post-precipitation.

          Recirculation of post-precipitated sludge to the aera-
          tion basin of the activated sludge process (Gronqvist
          et al., 1978). The phosphorus reduction in the biologi-
          cal step is hereby improved and the phosphorus concent-
          ration before the post-precipitation step will be much
          lower than if no recirculation takes place. Some preli-
          minary results indicate, however, that nitrification
          may be inhibited by recirculation of aluminium contai-
          ning post-precipitated sludges.

          Use of biological phosphorus reduction at Kristianstad
          sewage works by use of an anaerobic zone in the first
          part of the aeration basin. In this way the phosphorus
          concentration is diminished before the post-precipita-
          tion step.


These operational modifications of an existing post-precipitation

plant have shown very promising results including better removal

efficiencies of total phosphorus, lower total amount of chemical

precipitation agents and better sludge properties. It therefore

seems probable that a large fraction of the Swedish post-precipi-

tation plants will change to a modified operating scheme.
                                 133

-------
The alkalinity of the effluent from a biological step is mainly



determined by the influent alkalinity and the degree of nitrifi-



cation and denitrification. In nitrification the produced amount



of hydrogen ions reduces the alkalinity of the wastewater. This



reduction often leads to reduced requirements of aluminium sulp-



hate or lime in post-precipitation and several treatment plants



are operated in this way in Sweden (Ericsson et al., 1976, and



Gronqvist et al., 1978). Promising results have been shown by



regulation of the alkalinity of the effluent from an activated



sludge process by regulation of the degree of nitrification and



denitrification by the supply of oxygen (Olsson, 1980) .






SUMMARY



During the 1950's observations were made and the conclusion drawn



that the water quality in some lakes and coastal waters had dete-



rioted. Different recipient studies indicated that phosphorus was




the main factor which caused this deterioration. Some efforts were



made to decrease the phosphate concentrations in the synthetic de-



tergents and approximately a 30 % reduction of the phosphate



amount in synthetic detergents was obtained between 1968 and 1972.




In 1968 the expansion period began with chemical treatment plants



and in the beginning of 1979 about 640 municipal wastewater treat-



ment plants were operated with combined biological and chemical



treatment corresponding to about 72 % of the total amount of



wastewater from urban areas. At present a large interest has been



directed towards modified operating schemes in order to get bet-



ter removal efficiencies and savings in operating costs.
                                 134

-------
REFERENCES

Ahl, T. ,  Karlgren, L., Olsson, E. and Tullander, V.  (1967): Hus-
          hallsavloppsvattnet. Vatten, 23, 3, pp 178-204  (in
          Swedish).

Anonymous (1971): Eutrofieringsproblemet. Vatten, 27, 4, pp 463-
          465 (in Swedish).

Balmer, P.,  Blomquist, M. and Lindholm, M. (1968): Simultanfall-
          ning i en hogbelastad aktivslamprocess. Vatten, 24, 2,
          pp 112-116 (in Swedish).

Bjorndal, H., Bouveng, H.O., Solyom, P. and Werner, J.  (1972):
          NTA in sewage treatment. Part 3. Biochemical stability
          of some metal chelates. Vatten, 28, 1, pp 5-16.

Bouveng,  H.O., Davidsson, G. and Steinberg, E.-M.  (1968): NTA in
          sewage treatment. Vatten, 24, 4, pp 348-359.

Bouveng,  H.O., Solyom, P. and Werner, J.  (1970): NTA in sewage
          treatment. Part 2. Degradation of NTA in a trickling
          filter and an oxidation pond. Vatten, 26, 4, pp 389-402.

Carlsson, A. and Nordstrom, B. (1979): Orsaker till otillfreds-
          stallande reningsresultat vid kommunala avloppsrenings-
          verk.  National Swedish Environment Protection Board,
          SNV PM 1248 (in Swedish).

Cronholm, M.  (1968): Fosforreduktion medelst aluminiumsulfat vid
          Eolshalls reningsverk,  Stockholm. Vatten, 24, 2, pp 117-
          124 (in Swedish).

Eklund, L.  (1974): Bearbetning av resultat fran driftundersoknin-
          gar vid kommunala reningsverk. National Swedish Environ-
          ment Protection Board,  SNV PM 556  (in Swedish).

Ericsson, B.  (1967): Narsaltreduktion vid avloppsverk. Vatten, 23,
          2, pp 92-102 (in Swedish).

Ericsson, B.  (1975): Nitrogen removal in a pilot plant. J. Water
          Pollution Control Federation, 47, 4, pp 727-740.

Ericsson, B., Mard, G. and Akesson, M.  (1976): Drifterfarenheter
          med biologisk nitrifikation vid Orebro reningsverk.
          Vatten, 32, 3, pp 301-310  (in Swedish with an English
          summary).

Forsberg, C.  (1977): Nitrogen as a growth factor in fresh water.
          Prog.  Wat. Tech., Vol 8, Nos 4/5, pp 275-290.
                                 135

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Forsberg, C. and Lindqvist, G. (1967):  Experimental studies on
          bacterial degradation of nitrilotriacetate,  NTA. Vatten,
          23, 4, pp 265-277.

Forsberg, C. , Ryding, S.-O. and Claesson, A. (1975): Recovery of
          polluted lakes. A Swedish research program on the effects
          of advanced waste water treatment and sewage diversion.
          Water Research, 9, 1, pp 51-59.

Gronqvist, S. and Arvin, E. (1979):  Simultanfalining - erfaren-
          heter och FoU-behov. Nordforsk-prosjektet: Drift av
          renseanlegg, rapport 5  (in Swedish).

Gronqvist, S., Holmstrom, H.,  Hultman,  B. and Reinius, L.-G.  (1978)
          Experiences and process development in biological-che-
          mical treatment of municipal wastewaters in Sweden.
          Prog. Wat. Tech., Vol 10,  Nos 5/6, pp 701-713.

Hannerz, L. and Forsberg, C.  (1975): Eutrofieringssituationen i
          Sverige. Tionde nordiska symposiet om vattenforskning.
          Nordforsk, Miljovardssekretariatet, Publ. 1975:1  (in
          Swedish).

Holmstrom, H.  (1977): Simultanfallning och kontaktfiltrering vid
          Balinge reningsverk. Swedish Water and Waste Water Works
          Association, Rapport 1/77 (in Swedish with an English
          summary).

Hultman, B.  (1973): Biological nitrogen reduction studied as a ge-
          neral microbiological engineering process. In "Environ-
          mental Engineering." G. Lindner and K. Nyberg (Eds.),
          D. Reidel Publ. Co., Dordrecht, Netherlands, pp 264-275.

Hultman, B.  (1978): Chemical precipitation in Sweden - Present
          situation and trends in process improvement and cost
          reduction. Paper presented at 2nd International Congress
          of the Environment 4-8 Dec.  1978, Palais de Congres,
          Paris, France.

Isgard, E. and Ericsson, B. (1976):  Chemical and biological sewage
          treatment in Sweden. Effluent and Water Treatment Con-
          vention, Manchester 1976.

Isgard, E. and Ericsson, B. (1978):  A review of the Swedish situa-
          tion in combined wastewater treatment. Paper presented
          at "Colloque International 16-19 mai 1978, Traitement
          combine1 des eaux usees domestiques et industrielles."
          Universitg de LiSge - Section d'Environnement.

Johansson, K. and Karlgren, L. (1974):  Tusen sjoar. Rapport fran
          en inventering. National Swedish Environment Protection
          Board, Publ. 1974:11 (in Swedish).
                                 136

-------
Kjallman, A.  (1975) : Tvatt- och diskmedel som narsaltkalla. Tion-
          de nordiska symposiet om vattenforskning. Nordforsk,
          Miljovardssekretariatet, Publ. 1975:1  (in Swedish).

Lindahl, P.E.B. and Melin, R.  (1973): Algal assays of archipelago
          waters. Quantitative aspects. OIKOS, 24, pp 171-178.

National Swedish Environment Protection Board (1968): Statsbidrag
          till avloppsreningsverk. Meddelande V  5  (in Swedish).

National Swedish Environment Protection Board (1969): Experience
          of chemical purification. Publ. 1969:10 E.

National Swedish Environment Protection Board (1970): Tvattmedel
          som miljoproblem. Publ. 1970:4 (in Swedish).

National Swedish Environment Protection Board (1971): Dimensione-
          ring av kommunala reningsverk (in Swedish).

National Swedish Environment Protection Board (1973): Utslapps-
          kontroll vid kommunala avloppsanlaggningar. Publ. 1973:
          16 (in Swedish).

National Swedish Environment Protection Board (1977): Sewage treat-
          ment in built up areas in Sweden as at 1st January 1977.
          SNV PM 911 E.

National Swedish Environment Protection Board (1979a): Water Pro-
          tection in Sweden. Bulletin, SNV PM 1153 E.

National Swedish Environment Protection Board (1979b): Avlopps-
          rening - tatorternas avloppsforhallande den 1 januari
          1979. Meddelande 4/1979 (in Swedish).

Olsson, G.  (1980): Automatic control in wastewater treatment
          plants. Trib. Cebedeau, Vol 33, N  436, pp 121-130.

Rodhe, W. (1978): Aktuella problem inom limnologin. Svensk Natur-
          vetenskap, pp 55-107 (in Swedish).

Ryding, S.-O.  (1978a): The significance of sewage effluent for the
          hydraulic and nutrient loads on lakes. Prog. Wat. Tech.,
          Vol 10, Nos 5/6, pp 907-916.

Ryding, S.-O.  (1978b): Research on recovery of polluted lakes.
          Loading, water quality and responses to nutrient reduc-
          tion. Acta Universitas Upsaliensis, Abstracts of Uppsala
          Dissertations from the Faculty of Science, 459.

Ulmgren, L.   (1969): Drifterfarenheter fran nagra reningsverk for
          narsaltreduktion. Vatten,  25, 2,  pp 140-145 (in Swedish).
                                 137

-------
Ulmgren, L. (1975a):  Experiences and results from chemical pre-
          cipitation of domestic waste water in full-scale
          plants. Prog. Wat. Tech., Vol 7, Nos 3/4, pp 409-416.

Ulmgren, L. (1975b):  Swedish experiences in chemical treatment
          of wastewater. J. Water Pollution Control Federation,
          47,  4, pp 696-703.

Weijman-Hane,  G. (1968): Narsaltreduktion. Vatten, 24, 2, pp 106-
          111 (in Swedish).
                                 138

-------
           ECONOMICAL AND EFFICIENT PHOSPHORUS CONTROL
            AT A DOMESTIC-INDUSTRIAL WASTEWATER PLANT

                          Doris Van Dam
            Wastewater Treatment Plant Superintendent
       Grand Haven - Spring Lake, Michigan Sewer Authority
INTRODUCTION

In 1968/  the Michigan Water Resources Commission (MWRC) issued

orders for phosphorus and other pollutant reductions to commun-

ities and industries whose wastes were being discharged to the

waters or tributaries of the Great Lakes by December 1972.  The

MWRC adopted its standard from the Federal State Conference on

the pollution of Lake Michigan and its tributary basin held in

Chicago,  Illinois in March 1968.


The response at Grand Haven and Spring Lake, Michigan, located

on the sandy coast where the Grand River enters Lake Michigan,

was to form a combined sewer authority and build a new central

treatment plant.  The plant was designed not only to process

domestic wastes, but also to receive a substantial contribution

from the Eagle Ottawa Leather Co., a chrome and vegetable tan-

ner of 12,000 hides per week and a principal employer in the

Grand Haven - Spring Lake area.   (Figure 1).


It is the purpose of this paper to discuss the special challen-

ges the merged waste flow posed to design and subsequent opera-

tion of the treatment plant.  How concentrated side streams,

such as heat treatment supernatants, must be considered in over-

all plant efficiency is discussed.  The techniques used to control
                                139

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phosphorus at a very low cost are presented.  A summary of sev-



eral years of plant efficiency and cost figures accompany the text.





BACKGROUND



The MWRC requirements called for an 80 percent removal of phos-



phorus for Grand Haven, Spring Lake, and the Eagle Ottawa Leather



Co., as well as combined maximums from all three sources of 1,126



pounds per day  (511.2 kg) of BOD, and 30 mg/1 of suspended solids.





At the time, Grand Haven, population 10,500, was served by an out-



dated primary treatment plant, Spring Lake, population 3,034, em-



ployed an overloaded Imhoff tank, and Eagle Ottawa Tannery efflu-



ent was simply screened before discharge to the Grand River.





To meet the requirements, the newly-formed joint district construct-



ed a single 5.0 mgd (18,925 cu m/day)  activated sludge plant.  The



plant went on line in November, 1973,  and 1978-1979 average con-



tributions from the three sources were 2.1 mgd (7,759 cu m/day)



from Grand Haven, 0.4 mgd (1,476 cu m/day) from Spring Lake, and



0.8 mgd (3,179 cu m/day) from Eagle Ottawa (Figure 2 ).





Although tannery wastes have amounted to just 26 percent of treat-



ment plant flow, they represent 81 percent of total influent BOD,



and 80 percent of influent suspended solids.  The tannery waste



contains in mg/1 60 sulfides, 34 chromium, 57 ammonia, 2911 CODf



and a total nitrogen as N of 106 (Figure 2 ).





The treatment plant employs grit removal, phosphorus removal, pri-



mary clarification, activated sludge and chlorine contact; solids




are conditioned thermally prior to vacuum filtration (Figures).
                                141

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                          143

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All domestic flow is comminuted prior to reaching the grit tank.



Eagle Ottawa wastes are screened at the tannery.  Grit collected



on the bottom of a square, aerated-type grit collector is removed



by means of an air lift pump from the hoppered end of the tank.



Grit is washed by means of a mechanical inclined screw mechanism.





Ferrous sulfate for phosphorus removal is added to the total flow



in the rapid mix tank located in the grit building.





Air flocculcation is provided in the primary clarifiers for poly-



mer flocculation.





The plant includes three 60-foot (18.29 m) diameter, primary clari-



fiers, 200,000 gallon (757 cu m) capacity each.  The three aeration



tanks have a total capacity of 1,700,000 gallons (6,434.5 cu m), and



and are equipped with duo-spargers and coarse bubble diffusion.



The aeration tanks are arranged so that the activated sludge pro-



cess can be operated in one of four modes:  conventional, complete



mix, step aeration, or contact stabilization.  Air is provided by



four centrifugal blowers, each having a capacity of 5,200 cubic



feet  (145.6 cu m) per minute.





The three final clarifiers are the same size as the primaries, and



are equipped with suction-type sludge removal mechanisms.  The chlo-



rine contact tank has been constructed to provide two separated tanks



with gates so that either tank may be isolated for cleaning.





Effluent water is used for lawn sprinkling, the incinerator scrubber,



filter belt wash, foam suppression, line flushing, thickener, and



chlorinators.
                                144

-------
Return sludge pumps are 20 hp  (14.914 kw) , and can provide 100



percent return sludge capacity.  Sludge from primary clarifiers



is drawn off from a sump at the center of the clarifier by means



of positive displacement pumps, and pumped directly to two 45-



foot (13.716 m) diameter, 20-foot  (6.096 m) deep covered thicken-



ing tanks, with total capacity of 1,000,000 gallons (3,785 cu m) ,



or 28,000 pounds (12,712 kg) per day of solids.





After thickening, sludge is processed through a wet oxidation unit



where it is thermally conditioned at a rate of 68 gallons (257.38



liters) per minute.  Sludge is first ground in one of two grinders



which are piped in parallel to insure operation if one is out of



service.





Air is supplied by a 50 hp  (37.29 kw), 134 scfm (3.75 cu m/min)



§ 500 spig  (35.15 kg/sq cm) compressor, and the sludge-air mix-



ture is pumped to reactor pressure of 306 psig (21.51 kg/sq cm) by



a high pressure positive displacement ram-type pump.  The material



is fed through stainless steel heat exchangers to a stainless steel-



clad reactor.  A steam boiler maintains reactor temperature at 385°F



(195.9°C).  A standby boiler, and a second high pressure pump, pro-



vide backup capability.





Oxidized sludge is decanted in a separate tank and dewatered on



one of two cloth-covered, 370 square foot  (34.37 sq m) vacuum fil-



ters.  When the incinerator is bypassed, sludge cake is hauled to



landfill or used on agricultural land.





Plant performance has averaged 96 percent BOD removal, 76 percent



COD removal, 96 percent suspended solids reduction, 88 percent
                                145

-------
phosphorus removal, and chromium reduction of 96 percent (Figure 4 )






SPECIAL PROBLEMS - LOCATION/ODORS



Inclusion of tannery wastes in the new treatment plant created con-



ditions which required special consideration from the very first.






Because the hair, lime and grease in tannery wastes tend to clog



sewer lines unless there is adequate sewer dilution or primary



treatment prior to discharge into sewers, plant siting became a



crucial decision.  To minimize the anticipated difficulties in



moving tannery effluent over longer distances, the new treatment




plant was situated within the city limits of Grand Haven, immed-



iately sputh of the Eagle Ottawa plant.  The location is in a semi-



residential neighborhood, and special provisions for odor control



have had to be implemented.






In the original scheme, all usual odor-producing areas (grit and



screening building, decant tank, thickeners, vacuum filters) were




covered.  The areas are vented and odors drawn off to the inlet



of the aeration blowers and solubilized in the mixed liquor.






Because of equipment failures and the tannery contribution, how-



ever, odor problems unforeseen originally have required extraord-



inary odor control techniques.





TREATABILITY




Treatability of the tannery-domestic waste mixture was a second



important question.  Pilot studies verified the effectiveness of



the activated sludge method, provided the chromium content of pri-



mary effluent could be reduced to approximately 5 mg/1 to avoid
                                146

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toxicity in the biological phase.  This was achieved by blending



lime from the tannery's beamhouse to aid in the precipitation of



chromium hydroxide.  The addition of sodium hydroxide to the tan-



nery waste prior to its combination with the domestic flow is also



possible.  This has rarely been necessary, however, except for a




period during a strike when the tannery was operating with limited



staff and not using the beamhouse to full capacity.






Since the tannery wastes are discharged on a batch basis, with pH



ranging from 3 to 12, an equalization tank was incorporated into



the system to hold tannery efflyent and create an acceptable pH




level of 8.5 to 9.0.






In addition, the system is designed so that all tannery wastes



can be taken into one primary tank, exclusive of domestic wastes,



and treated separately, should that become necessary.






SIDESTREAM RECYCLE




A great deal has been said about the supernatant decant liquor



which is returned from thermally conditioned sludge to the treat-



ment plant.  Sidestream treatment should be studied in light of



purpose and design of the total solids handling system and the



fate of solids throughout.






Let us deal with solids first.  While thermal conditioning is high-



ly successful in making the difficult-to dewater sludge easily de-




waterable, it also solubilizes a portion of the raw suspended sol-



ids. At the same time, a relatively small amount, approximately 5



percent, of oxidation of volatile solids occurs, due to the addi-



tion of air in the thermal conditioning system.
                                148

-------
Supernatant recycle, of course, is another concern.  After condi-




tioning, the oxidized sludge flow enters the decant tank, where it



thickens before it is sent to the vacuum filter for dewatering.




The decant supernatant, a relatively clear liquid resulting from



the thickening process, is decanted and returned to the aeration



tanks for treatment.  While its suspended solids concentration is



only, 2460 mg/1, its COD, 8005, and P concentrations are 22, 320



mg/1, 9370 mg/1 and 45 mg/1 respectively, due to the solubilized



dissolved volatile solids.  It constitutes the major biological



solids handling sidestream load on the plant.  It also has some



phosphorus load.  Additional capacity and operational flexibility



were designed into our secondary system to allow for adequate




treatment of the solids handling recycle streams.






PHOSPHOROUS REMOVAL



A chemical mixing, feeding and distribution system was provided to



provide chemical removal of phosphorous in the wastewater stream.




It was planned that the chemicals used for phosphorous removal



would include ferric chloride and polymer.






Ferric chloride would be delivered by truck and transferred to two



10,000 gallon (37,850 1) storage tanks located adjacent to the chem-



ical feed room underground outside the control building.





Because the concentrations of ferric chloride delivered to the



plant would vary from 38 percent to 45 percent during winter and



summer months respectively,  the operator had flexibility as to how




to store and feed the ferric chloride.  A dilution system was in-




 stalled so that a constant  dilution could be fed throughout the
                                 149

-------
year if desired.  Non-potable water could be added to the storage



tank along with air mixing from the bubbler system to provide the



desired diluted concentration.  Should the operator not desire to



dilute the concentration, as is the case with waste pickle liquor




currently used, the solution can be fed directly from the storage



tanks to the plant.






A bubbler system was incorporated in the design to measure the




level in both ferric chloride tanks.






Positive displacement metering pumps were provided to meter the




iron solution to the various feed points which consisted of the




rapid mix tank, inlet and outlet of primaries and aeration tanks,



and inlet of the final settling tanks.  Metering pumps were elec-



tronically paced from the main plant master flow meter.  A stand-



by iron solution pump was also included.  The solution from the



pumps flows to a rotameter distribution panel where it can be




distributed throughout the plant.






It was designed for polymer to be delivered to the plant in dry



form.  An automatic mixer and dispenser were provided to meter the



polymer solution to the various feed points.  As in the case of



the iron solution, the feed pumps were paced from an SCR controller



which in turn was paced from the main plant master flow meter.  The



rotameter panel for polymer was also provided for distribution



throughout the plant.  This panel would split only the diluted poly-



mer.






Numerous programs of varying chemical concentration and feed points



for phosphorous removal were conducted  (Figure 5).  In March 1974
                                150

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ferric chloride was applied to the rapid mix tank, and polymer to



the final sedimentation tank influent.  Ferric chloride in the a-



mount of 8.01 nvg/1 as Fe and polymer in the amount of 0.21 mg/1



was applied at a cost of $1,181.  Influent phosphorous was 5.5 mg/1



and the final effluent 1.2 mg/1.





In April the polymer was again used in the influent to final sed-



imentation only, with the ferric chloride split, adding 60 percent



to the rapid mix tank and 40 percent to the final sedimentation



influent with no apparent improvement in phosphorus removal.  Ferric



chloride in the amount of 8.63 mg/1 as Fe and polymer in the amount



of 0.17 mg/1 was applied at a cost of $1,271.  Influent phosphorous



was 5.2 mg/1 and final effluent 1.3 mg/1.





This mode of operation was continued in May and again with no ap-



parent improvement in phosphorus removal.





In June both the polymer and ferric chloride were split with two-



thirds of the chemicals added to the rapid mix and one-third to the



influent to final sedimentation.  Although the final effluent phos-



phorous concentration was lower at 0.7 mg/1, it should be noted



that the influent phosphorus was also lower at 3.8 mg/1.  The a-



mount of ferric chloride used was 8.38 mg/1 as Fe and polymer ap-



plied was 0.21 for a total chemicals cost of $1,989.  The diluted



phosphorous concentration in the influent was due to heavy precip-



itaion and river water backflow.  This condition was corrected



shortly thereafter.  Perhaps the impact of the tannery coming on



line May 28, 1974 may also have helped in phosphorus removal.  How-



ever, the tannery was on limited operation at that time and were
                                 152

-------
buying some of the hides in the blue, which reduced beamhouse lime




waste.






It was apparent that neither split feed, nor chemicals added to the



final sedimentation influent were as effective as adding the total



iron solution to the rapid mix tank prior to primary sedimentation.



Removals were excellent either with or without polymer addition.




It would follow that polymer use was discontinued and the iron



solution added to the rapid mix tank.






After several months of operation with ferric chloride we were con-



tacted by several companies who were contracted to remove waste




pickle liquor from the steel mills in Gary, Indiana.  We were able



to purchase the waste pickle liquor for less than the cost of com-



mercial ferric chloride.  This has been used for over five years



to date.  It has been equally as effective in phosphorus removal



as was ferric chloride.






Also shown on the lower portion of Figure 5 is 1975 data for the



same months as reported in 1974 for comparison.  In March 1975



ferrous sulfate in the amount of 4.1 mg/1 as Fe at a cost of $381



was applied to the influent containing 4.6 mg/1 of phosphorus and



resulted in a final effluent phosphorus content of 0.9 mg/1.






In April $352 was spent to apply 4.3 mg/1 of ferrous sulfate as



Fe to an influent containing 5.2 mg/1 of phosphorous which resulted



in a final effluent containing 0.9 mg/1 of phosphorus.






In May $402 spent for 4.8 mg/1 of Fe applied to an influent con-



taining 5.8 mg/1 of phosphorus resulted in a final effluent of 1.1



mg/1 of phosphorus.






                                153

-------
In June $542 was spent for 6.4 mg/1 of Fe applied to an influent


containing 6.1 mg/1 of phosphorus resulting in an effluent con-


taining 0.9 mg/1 of phosphorus.



It would appear from the data shown in Figure 6 , which shows the


iron used for phosphorus removal, that waste pickle liquor was


actually more effective than ferric chloride in that the amount


applied in milligrams per liter went from 9.3 in 1974-1975 to 6.6


in 1975-1976.  We would propose/ however, that the increasing load


from the Eagle Ottawa Leather Co. resulted in much more lime from


their beamhouse operations being discharged to the treatment plant,


which aided in the decrease in the amount of iron required for phos-


phorus removal.
                             I


To support that theory, Figure  7  shows the amount of flow from


the tannery and the amount of iron applied for phosphorus removal


for the same period of time.  As the amount of tannery waste in-


creased, the amount of iron necessary to control phosphorus removal


decreased.  The tannery flow went form 190 mg  (719,150 cu m) in


1974-1975 to 307 mg  (1,161,995 cu m) in 1978-1979.  The iron ap-


plied to the total plant flow decreased from 9.3 mg/1 to 1.6 mg/1.



On May 18, 1978 the tannery discontinued the use of the million


gallon equalization tank that had been in use prior to that time


for equalizing the flow to the wastewater treatment plant.  Follow-


ing this, the tannery added more lime to their discharge during


periods of dump from the tanhouse portion of their operation.  In


the tanhouse operation, a pickling process brings the hides to an


acid condition in preparation for tanning.  This waste has a low pH.
                                 154

-------









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Further documentation in regard to the relationship between volume
of tannery flow and phosphorous removal at the treatment plant for
January and February of 1979 as compared to 1980 is as follows:  In
January 1979 the tannery flow was 24.65 mg and 2.21 mg/1 of Fe was
fed resulting in final effluent phosphorus of 0.6 mg/1.  To compare,
in January 1980 the tannery flow was only 13.857 and 6.65 mg/1 of
Fe resulted in final effluent phosphorus being 0.6 mg/1.  In Feb-
ruary 1979 the tannery flow was 27.424 mg, no Fe feed was required,
and the final effluent phosphorus was 0.5 mg/1.  However, in Feb-
reary 1980 the tannery flow was only 18.494 mg and 4.89 mg/1 of
Fe was applied which resulted in final effluent phosphorus concen-
tration of 0.7 mg/1.

SUMMARY
This domestic-industrial activated sludge wastewater plant with
approximately 18 percent of the total flow emanating from a chrome
tanner and 80 percent of the suspended solids and BOD, has achieved
excellent purification.  Suspended solids and BOD removals have con-
sistently been above 90 percent.  The final effluent phosphorus con-
centration has been under 1.0 mg/1 with removal over 80 percent.
This excellent phosphorus purification has been accomplished with
pickle liquor, all added prior to primary sedimentation, and without
a flocculating aid.  Although phosphorus removal was successful with
limited amounts of iron application when the tannery waste was pre-
sent in considerable amount, it was necessary to add much larger a-
mounts of iron solution when the tannery waste was limited or off
entirely.  Simple laboratory control has been practiced with analyses
made on the daily composite sewage samples, and iron feed adjusted
based on the prior day's operating results.
                                 157

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              THE PHOSTRIP PROCESS FOR  PHOSPHORUS  REMOVAL

                                    By

                            Mr.  Carl J.  Heim
                        Assistant Staff  Engineer
                        Union Carbide Corporation
                             Linde Division
                           Tonawanda, New  York
INTRODUCTION

     The PhoStrip process is a combined biological-chemical process for the

removal of phosphorus from wastewater.  The process works by concentrating

the phosphorus in the wastewater through biological means into a small sub-

stream, to which chemicals  are added for precipitation  of the concentrated

phosphorus.  Normally lime  is used for phosphorus precipitation  because the

quantity of lime required is proportional to the flow being treated rather than

the phosphorus concentration in that flow.  Thus, if the phosphorus in the

wastewater is concentrated into a substream that is 15% of the entering waste-

water flow, the amount of lime required would be only 15% of the  lime required

to treat the entire wastewater flow.

     In addition to drastically reducing the chemical requirement  for phosphorus

removal, the  PhoStrip process also produces relatively  small quantities of

chemical sludge. Phosphorus is precipitated in a separate reactor in the

process and the resulting chemical sludge does not contain.significant bio-

logical solids.  This sludge  is inert and stabilization (such as digestion) is

not required prior to disposal. When lime is used for phosphorus precipitation,

a very easily dewatered sludge is produced.  The net results are  very substantial

savings in  both chemical costs and sludge disposal costs.


                                159

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DESCRIPTION OF THE PHOSTRIP PROCESS




    A flow schematic of the PhoStrip process is shown in Figure 1.  In the




process, return sludge is mixed with plant influent and aerated exactly as in




a conventional activated sludge system.  While under aeration,  the micro-




organisms have the capability of removing essentially all of the soluble phos-




phorus from the wastewater because of special conditioning received in the




PhoStrip process.  The phosphorus removed in the  aeration  basin is incorporated




into the sludge in the form of stored polyphosphates.  The phosphorus content




of the sludge leaving the aeration basin can be more than twice  that of sludge




from a conventional system.  Removals of biological oxygen demand and sus-




pended solids in the aeration system are unaffected by PhoStrip.




    The phosphorus-laden sludge is separated from the phosphorus-free effluent in




the secondary clarifier.  The  sludge withdrawn with the clarifier underflow is then




either sent directly back to  the aeration basin, wasted from the system (excess




biological sludge quantities are not affected by the PhoStrip process) or sent to




a stripper tank, where it is held under anoxic conditions for several hours.




While under anoxic conditions, the microorganisms release their stored phospho-




rus in soluble form.  The released phosphorus is "washed" from the sludge blanket




by an elutriation stream and withdrawn as a supernatant from the stripper  tank.




This supernatant stream is then fed to a reactor-clarifier where the phosphorus




is precipitated with lime.  Typically,  the supernatant flow  is 10-20% of the influent




flow. Therefore, as explained previously, lime requirements are reduced by
                                     160

-------
Influent
                     Aeration
                      Basin
             Direct Recycle
                    Reactor-
                    Clarifier
                                 Supernatant
                                                                       Effluent
                                                        \
                                                                       Waste
                                                                       Sludge
                                                          Stripper Feed
 Anoxic
Stripper
  Tank
                            Elutriation Stream
                         Waste Chemical Sludge
                                Stripper Underflow
                 Figure 1.   Phostrip  System  Flow Schematic


                                      161

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80-90% and chemical sludge quantities are also reduced. The inert chemical




sludge is withdrawn from the bottom of the reactor-clarifier.  The overflow




from the reactor-clarifier, which has a relatively low phosphorus concentration,




is used as the elutriation stream.




     Sludge is withdrawn from the bottom of the anoxic stripper tank at the same




rate as it is fed to the tank to avoid solids  buildup.  This sludge is returned




to the aeration basin where phosphorus uptake is resumed.




     The PhoStrip process typically produces an effluent with a total phosphorus




concentration of 0.5-1.0 mg/1.  The effluent  soluble phosphorus concentration




normally ranges from 0.1-0.5 mg/1.  The PhoStrip process operates over the




normal range of activated sludge system operating conditions and can be used




with either air or oxygen activated sludge systems.








THEORY
    Biochemical Aspects




    The biochemical phenomemon responsible for the PhoStrip process has not




been fully defined.  Results of experimental work have led .to the formulation




of the following mechanisms for the observed phenomenon.




    Organisms containing high intracellular phosphate concentrations have




been isolated from wastewater treatment systems exhibiting high phosphorus




removal rates.  Typical of these  isolates are organisms of the genus Acineto-




bacter.    The  organisms  of this genus have demonstrated the ability to take
                                    162

-------
up and release phosphorus as a function of the aerobic-a noxic cycle, while


in pure culture form.  The interior of the cells have been characterized as


containing very large volutin (polyphosphate) granules while under aerobic


conditions. The  size of these granules diminished as the culture was main-


tained in an anoxic environment.  This indicates a transfer of phosphorus


from the volutin granules into solution.  These particular organisms are so


abundant in activated sludge systems that the Water Research Centre Labora-


tory at Stevenage, England, has utilized pure cultures to simulate activated


sludge systems.  These  organisms are also obligate aerboes preferring  Krebs


cycle  intermediates and acetates as substrates for metabolism.


    It is believed that the anoxic period  of the PhoStrip process forces these


strict aerobes to  undertake a sequential  series of reactions which result in


their forming polyphosphate granules while in the  aerobic period. This results


in a set of aerobic organisms that can compete more effectively with facultative


organisms in a cyclic aerobic-anoxic environment. The polyphosphate  granules


within the cell may provide phosphorus and energy to convert ADP to ATP during

                                                                     (2  3)
the anoxic period through the catalysis of the polyphosphokinase enzyme . '


Substitution of polyphosphate for ATP in biochemical reactions during anaero-

                       (4)
biosis is also possible.     (A third potential pathway of phosphorus release


utilizing the phosphatase enzyme has not yet been delineated.)


    In the first mechanism, conversion of ATP to ADP during the anoxic period


results in the  release of phosphorus from  the cell  as well as providing a source


of energy.  This energy is utilized by the obligate aerobes to continue  some of


their metabolic functions.  The fact that the addition of acetates increases the
                                     163

-------
rate of phosphorus release suggests an interaction between these organisms




and the facultative microbes present in activated sludge.  Under anoxic condi-




tions,  the facultative aerobes produce acetates which enhance the rate of phos-




phorus release by the oligate aerobes.  When the sludge leaves the  anoxic




environment and enters aerobic conditions, the ATP content within the cell




is low  because the reaction of ATP—>• ADP + P is a high rate reaction relative




to the formation of ATP from polyphosphates.




    In the  second, direct substitution mechanism,  the energy of the poly-




phosphate-phosphorus bond is utilized  in place of the ATP  bond energy. The




phosphorus would be directly released to solution from the polyphosphate




molecule.  If direct substitution is  the  major means of phosphorus release,




the above ATP to ADP reaction would also occur producing a low ATP/ADP




ratio in the cell.




    Under aerobic conditions, the  strict aerobes- oxidize stored metabolites




and other substrates to provide energy to increase  the ATP  content of the cell.




After a very short time, the ATP/ADP ratio in the cell becomes  high enough




to trigger the formation of polyphosphate via  the reversible polyphosphokinase




enzyme. This results in the formation of polyphosphate granules which are




stable  storage products in an aerobic environment.




    The performance of the  PhoStrip process  is consistent with the theory.




The theory implies a temperature dependency. In fact, an Arrhenius  type




relationship has been established.  This theory also indicates that the rate




of phosphorus release per unit mass of organisms is a function of the duration
                                    164

-------
of the anoxic period, as well as the quantity and activity of facultative




organisms.  The activity of the facultative bacteria can be related to the




Food-to-Microorganism ratio  (F/M) of the activated sludge system,  while




quantity is related to the concentration of sludge in the stripper tank.  Since




strict aerobes are implicated in the above theory, too long an anoxic period




relative to the aerobic period could cause the organisms to cease phosphorus




uptake.  Experimentally determined operating limits for such a response do




exist. However,  there is a broad spectrum of conditions under which good




performance has been established.




     The  finite capacity of these organisms for phosphorus storage results




in a loading requirement which must not be exceeded if a high degree of




phosphorus removal is to be achieved.  Different activated sludge systems




have exhibited different maximum  levels of phosphorus per unit mass of




MLVSS.  This maximum  P/VSS  ratio has been observed to be a function




of the viable organism content of the volatile suspended solids.  The  P/




VSS ratio observed in efficiently operating PhoStrip Systems depends on the




phosphorus available in the feed,  the maximum  P/VSS   ratio attainable,




and the environmental conditions presented  earlier.




     Ideally,  all the  phosphorus in the feed would be incorporated into the




cell mass and wasted from the system  as biological sludge.  This mode of




operation would eliminate the need for chemical precipitation facilities and




significantly reduce  the operating cost of the process.  However,  there are




factors which prevent this from being realized in all but a few instances.
                                     165

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First, effluent quality is a function of the soluble and particulate phosphorus




content. Even if an effluent soluble  PQ^ level of ^^.01 mg/1 were achieved,




a 20 mg/1 VSS in the effluent would limit the phosphorus to VSS ratio to <0.05




in order to achieve an effluent  <^ 1.0 mg PO.-P/l.  Second, for a given P/




VSS level;, a specific quantity of sludge must be wasted as dictated by phos-




phorus mass balances  in order to remove enough phosphorus to achieve the




desired effluent.  The amount wasted generally depends on the F/M (SRT) of




the system.  In most cases a high degree of phosphorus removal could only be




achieved at very high F/M (low SRT)  values because of the low   P /VSS levels




necessary to satisfy effluent criteria as presented above.  Third, bio-chemical




sludges tend to release phosphorus when digested.  If high   P /VSS levels




are employed for phosphorus removal, large quantities of phosphorus could




return to the head end of the plant. This level of phosphorus return would




require a significant increase in sludge wasting unless some method of chemi-




cal precipitation were employed.




    The PhoStrip System is normally  designed for a phosphorus content of




0.03-0.04 Ib. P/lb.  VSS in the sludge in order to achieve  effluents of less




than 1.0 mg PO -P/l. • The phosphorus that is not removed through wasting is




precipitated from the supernatant  stream leaving the stripper tank. The




relative amounts of phosphorus removed through sludge wasting and precipi-




tation depend on the  F/M (SRT) of the activated sludge  system and the BOD5 /P




level in the wastewater. The ratio of phosphorus removal  by precipitation to
                                    166

-------
the overall phosphorus removal can range from 0 to 0.9+. Each wastewater




will result in different values of this ratio depending on the design conditions




of the activated sludge system and the method of waste sludge disposal.






     Chemical Precipitation of Phosphorus




     Lime was chosen as the  precipitant because of its pH functionality.




Unlike alum and ferric chloride,  the gross quantity of lime required for pre-




cipitation of phosphorus in water is dependent only on the amount and alkalinity




of the water not the concentration of phosphorus.  Further reduction in chemical




requirements  can be achieved by precipitating phosphorus at lower pH levels




(8.5 -  9.0).  At these pH levels, the stripper supernatant after lime addition




may typically contain 2-5 mg soluble PO^-P/l. A lowerphwillalsoresultin sub-




stantially less  chemical sludge to be handled because less calcium carbonate




and no magnesium hydroxide are formed.  The chemical sludge production will




be typically less than 50 percent of that produced at a pH = 10.5.  This material




could be used as an agricultural fertilizer because of  its high phosphate content.









FULL SCALE PERFORMANCE




     The PhoStrip system has  been demonstrated at two localities under full




scale conditions and 9 pilot plant locations.  These two full scale plants




were Seneca Falls, NY and Reno/Sparks,  Reno, Nevada.
                                    167

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SENECA FALLS. NY


    The wastewater treatment facility at Seneca Fall,  NY is an activated


sludge treatment plant with two trains and a total capacity of 3 .5 MGD

          3
(13,247 m /day).  The plant consists of a bar screen, comminutor, two cir-


cularprimary clarifiers, twocompletely mixed aeration basins with mechanical


aerators,  two rectangular secondary clarifiers and a  chlorine contact chamber.  The

The wastewater is largely domestic in character with a BOD  of approximately

160 mg/1; total dissolved solids of 680 mg/1 and total phosphorus of 6.3 mg/1.


    Conversion of the plant to the PhoStrip process was facilitated by the

                                                                         3
fact that,  at the time of the study,  the raw wastewater flow was only 3800 m /G


(1 mgd).   This enabled the plant to handle the full plant flow through one of


the two reactor trains, thus freeing a primary clarifier to provide the anoxic


 environment required for the return sludge to release excess phosphorus.


The tank providing this anoxic  zone has been labelled the "stripper tank".


The use of a single train to treat the entire wastewater flow also permitted


the test to be run on a system that was  much nearer the design hydraulic loading


for the Seneca Falls plant.  The use of the primary  clarifier as the stripper tank


was expeditious; however, it was  significantly oversized relative  to the waste-


      flow entering the aeration basins.  Table  1 presents a  concise summary


of the data obtained during the first thirty days of operation at Seneca Falls.


It  is evident from this table that substantial savings have been demonstrated.


The amount  of lime has been greatly reduced  since  the supernatant from the
                                     168

-------
Table  1.   Results of Phosphorus Removal  Test
           at Seneca Falls,  N.Y.
 Plant Flow, m3/d (mgd)
 Return Flows, percent of raw flow:
     Sludge to Stripper
     Sludge to Aeration from Stripper
     Supernatant to Primary Clarifier
 Total Suspended Solids, mg/1:
     Mixed Liquor
     Sludge to Stripper
     Sludge to Aeration from Stripper
 Influent, mg/1:
    Total Phosphorus
Effluent, mg/1:
    BOD5
    Total Phosphorus
Plant Performance:
    BOD5 Removal, percent
    Total Phosphorus Removal,  percent
Lime Dose, Stripper Supernatant,  mg/1 of supernatant
                                         (as CaO)
Lime Dose, prorated to mg/1 of raw flow (as CaO)
                                                3400 (0.9)

                                                24
                                                10
                                                14

                                                1,440
                                                7,840
                                                15,910

                                                158
                                                6.3
                                                .6

                                                98
                                                91
                                                170
                                                24
                       169

-------
PhoStrip stripper is only fourteen percent of the incoming flow.  Calculated on


the basis of the incoming flow, the lime dose would be 24 mg/1 as CaO.


When compared to conventional lime requirements of 300-660 mg/1 for post


precipitation to obtain the same  total phosphorus effluent concentration of


less than 1 ppm (0.6 ppm), the savings are quite apparent.  This represents


the period of operation during which the performance of the process was inten-


sively monitored.  ,The recycle flow rates presented are typical of a system


utilizing sludge thickening in the stripper tank to produce  the phosphate-


enriched supernatant.  The data  on plant performance indicates that very high


removals of both BODS  and phosphorus were achieved. The lime dosage is


reflective of the chemical requirements anticipated  for many full scale systems.



RENO/SPARKS. RENO. NEVADA


    The Reno/Sparks  facility is  designed to process an average flow  of

        3
76,000 m /d (20 mgd) and discharges into the Truckee River.  The system con-


sists of an aerated grit chamber, three primary clarifiers, three activated sludge


trains and three secondary clarifiers. The PhoStrip System initially operated


by Kennedy Engineers, San Francisco, California,  on one third of the total av-

                         3
erage plant flow (25,000 m /d) by using the sludge recycle option of operation


(Figure 2).   In this option, the stripper is operated in a thickening mode and a


portion of the stripper underflow is recycled back to the stripper feed. The rea-


son for recycling the underflow is to increase the supernatant phosphorus by mix-


ing high P/low P streams.  (This mode of operation produced an elutriation effi-


ciency of approximately 38%, where elutriation efficiency,  E, is defined as the
                                     170

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Wastewater
Primary
Clarifier
              Lime
               Reactor
              Clarified
                 \| Waste
                   Sludge
                   Chemical
                                     Aeration
(Secondary
  Clarifier
                                                                           Effluent
                                         Direct Recycle
                               Stripper
                              Supernatant
                              Stripper
                                          Stripper
                                           Feed
                  Waste
                  Sludge
                                             Sludge
                                           Recycle
                                     Stripper Return
                  Figure 2.    Sludge Recycle Option
                                        171

-------
amount of phosphorus removed by the stripper overflow per day divided by the



amount of phosphorus released  in the stripper per day. )




      On June 25,  1975, Union  Carbide Corporation began its evaluation of the



 PhoStrip process  on the full scale plant at Reno/Sparks, Nevada.  A set of



 conditions was established  on the full scale (Table 2) -and the system was



 allowed to come to steady state.  After steady operating conditions were



 achieved, a period of intensive evaluation followed.  Table 3 presents  the



 results of analyses performed  at Reno/Sparks during this phase.  Figures  3  &



 4 present the influent and effluent phosphorus levels during the testing period



 and their variation with the  flow to the plant. The system demonstrated excel-



 lent effluent quality in all respects, and as evident in the figures, total phos-



 phorus levels were consistently 1 mg/1 or less.



      In an effort to improve the elutriation efficiency a  low phosphorus  elutria-



 tion (LPE) modification was  employed. The  cross sectional area requirement



 for the stripper as dictated by the  limiting-flux theory is reduced relative to the



 sludge recycle  system.  Since the primary clarifier (stripper tank) at the Reno/



 Sparks plant had  a fixed  cross-sectional area,the solids flux considerations


                                                   3
 indicated that two-thirds of the plant flow (50,000 m  /d)  could be treated



 with the available area.  As a result, the system was  modified according to



 Figure  1,  which was referred to earlier.  Table 4 presents  the operating condi-



 tions for this two week test period  (Jan.  18-30,  1977)  and Figure 5 graphically



 displays the influent and effluent phosphorus concentration.  Again, the efflu-



 ent total phosphorus levels were usually 1.0 mg/1 of phosphorus or under.
                                      172

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Table 2.  Operating Conditions for the Phostrip
          Sludge Recycle System - Full Scale Testing
          at Reno/Sparks, Nevada (9/13/75-9/27/75)
Parameter
Flow Rates (m3/day)
Feed, (Q)
Recycle to Stripper (R,)
Stripper Underflow (R^)
Stripper Supernatant *
Recirculation Rate (R2)
Waste Sludge Rate
Aeration Time, Hr. (based on Q)
Anoxic Period, Hr. (based on R3)
MLSS, mg/1
MLVSS, mg/1
RjSS, mg/1
RiVSS, mg/1
R3SS, mg/1
R3VSS, mg/1
-TSS Stripper Supernatant, mg/1
VSS Stripper Supernatant, mg/1
D.O., End of Aeration, mg/1
D.O. , Rj, mg/1
\ D.O., R3, mg/1
pH, End of Aeration Basin
PH, Ri
pH, RJJ/
pH, Stripper Supernatant
Temperature, "C
F/Ma (kg COD/day/kg MLVSS)
Clarifier Overflow Rate, m/day
Clarifier Blanket Level, m.%
Minimum

14, 690
5,180
2,330
2,850
4,230
639
10.2
16.
_
-
3,060
2,480
9,620
7,700
65
50
_
0.4
0.3
_
6.8
6.4
6.6
23
-
22.4
0.08
Time
Weighted
Maximum Mean

25,060
7,340
4,150
3,200
2,420
639
6.0
9.4
_
-
4,620
3,740
9,120
7,300
90
69
1.5 (0.7-2.2)
0.7
0.3
7.0
6.8
6.4
6.5
23
—
38.2
0.09

22,460
6,830
3,630
3,110
2,850
639
7.1
11.0
1,150
900
4,230
3,420
9,250
7,340
84
64
_
0.6
0.3
—
-
-
—
23
0.96
34.3
0.09
                         173

-------
        Table 3.  Analytical Results for  the Phostrip
                  Sludge  Recycle System Full Scale Testing
                  at  Reno/Sparks, Nevada  (9/13/75-9/27/75)
           Parameter
                                      Minimum    Maximum
                  Flow
                Weighted
                  Mean
COD, mg/1
 Influent
 Effluent
                       mg/1
Total Suspended Solids,
  Influent
  Effluent
Effluent Volatile Suspended Solids,mg/1

Total Phosphorus, mg P/l
  Influent
  Effluent (ortho)
  Stripper Supernatant
  Stripper Underflow
  Filtered Stripper Underflow
  Filtered Aeration Effluent (ortho)
  Secondary Clarifier Underflow

P/VSS
  Secondary Clarifier Underflow
  Stripper Underflow
                                        187
                                        40
                                       19
                                       13
                                       9.6
                                       1.0 (.
                                       44
                                       257
                                       67

                                       104
                                       0.042
                                       0.025
3)
      266
      37
      13
      10
9.1
0.8
41
240
55
-  (-
161
(.4)
          04)
     0.043
     0.025
            253
            37
            113
            13
            10
9.2
0.8 (.4)
42
247
58

113
           0.043
           0.025
                                 174

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=3
cr
o
X
Q.
05
O
X
Q.
      22-
      20 -
       8 J
       2 -
0 -
8 -
       6  -
      4  -J
      0
                       INFLUENT TOTAL = A
                       EFFLUENT  TOTAL = D
                       EFFLUENT  ORTHO= O
                             7  18 19 20 21 22 23 24 25  26 27
                            SEPTEMBER,  1975
    Figure 3.  Reno/Sparks  Full Scale Phosphorus Data  Obtained
              during Minimum  Flow Period (16% of the  Total
              Volume Treated  by the Phostrip System)
                               175

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en
OL
O
m
Q.
CO
O
IE
Q_
      22-
      20-
       8 -
       6 -I
       4 -
       2 -
0 -
8 -
       6 ~
       4 -I
       2 H
                        INFLUENT  TOTAL =
                 EFFLUEN'T TOTAL «D

                 EFFLUENT ORTHO =O
             2 13 14  15  16 17 IS 19 20 2! 22  23 24 25 26 27

                           SEPTEMBER, 1975
     Figure  4.  Reno/Sparks  Full Scale Phosphorus Data Obtained
               during Maximum Flow Period (84% of the Total
               Volume Treated by the Phostrip System)
                               176

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      12-,
       I-
      10-
       9-
       8-
       7-
    cc
    o
    X
    O
    I
    a.
       6-
       5-
      4-
      3-
      2-
       1-
                      INFLUENT=A
   EFFLUENTS =B

   EFFLUENT*2 =O
               X>
O- - _ _
                           	O
            I    I    \    II    1    I    I    I   Till

            18  |9  20  21  22 23  24  25  26  27 28 29  30

                          JANUARY, 1977
Figure  5.  Reno/Sparks  Full Scale Phosphorus Data for  LPE System
                             177

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    A comparison between the LPE and sludge recycle system indicates that the




LPE System was capable of producing the same quality effluent while utilizing




the same stripper,  but handling twice the flow.




    The main reason for this is an improvement in elutriation efficiency with




the LPE System ( £ = 0.59 vs.  £ = 0.38).  This improvement translates to a




decrease in the initial capital cost due to the decrease in tankage.
                                    178

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                          ECONOMIC EVALUATION








 COMPARISON OF OPERATING COSTS FOR PHOSPHORUS REMOVAL SYSTEMS




     Table 4 shows a comparison of operating costs for various phosphorus




 removal systems.  Included in the  comparison are conventional chemical pre-




 cipitation with lime, alum, ferric chloride and pickle liquor, as well as the




 PhoStrip process with lime or pickle liquor addition.  The costs  are based on




 an alkalinity of 250 mg/1, and an influent phosphorus concentration of 1 mg/i.




 Chemical  requirements and costs for the conventional phosphorus removal




 systems were taken from the EPA Process Design Manual for Phosphorus




 Removal (1976) and have been adjusted to  1st quarter 1980. Chemical sludge




 disposal costs were assumed to be $100/ton of dry solids.




     It is apparent from inspection  of Table 5 that the use of the PhoStrip process




 drastically reduces the operating costs for phosphorus removal. For the example




 case shown, operating costs are reduced by approximately 40-55% compared




 to a conventional system using pickle liquor, which has the lowest operating




 cost of the conventional systems.






 CASE STUDY



     The following economic study  has been taken verbatim from the EPA Bio-




 logical-Chemical Process for Removing Phosphorus at Reno/Sparks, NV




publication,  and is for  illustrative purposes only.
                                    179

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          Table 4.    Operating Conditions  for  Full  Scale
                       Testing  at  Reno/Sparks, Nevada
                       Phostrip LPE  System  (January 18-30, 1977)
     PARAMETER
                                    MINIMUM
                                  TRAIN I/TRAIN 2
  MAXIMUM*
TRAIN I/TRAIN 2
     FLOW
WEIGHTED MEAN
 TRAIN I/TRAIN 2
Flow Rates, m /day
  Feed 0. (each train)                 17280/17280      29380/29380      22460/22460
  Recycle to Stripper. RI              1987/2160        3200/3370        2510/2680
  Stripper Underflow, R3              1210/1470        2250/2250        1640/1810
  Stripper Supernatant, S              6570             7000             6740
  Elutrlatlon, EL                     5270             5620             5440
  Total Aerobic Recycle, Rj + Rdirect    -                ~                4490/5530
  Sludge Wasting                     -                -                331/418

Aeration Time, Hrs.  (based on Q)       9.0/9.0          5.1/5.1          6.8/6.8
Anoxic Period, Hrs.  (based on R$)      11.6             7.0              9.5

MLSS, mg/1                         1230/1280        1110/1140        1170/1220
  VSS/TSS                           0.8              0.8              0.8
RlSS, mg/1                         5750/5460        6770/6720        6210/6030
  VSS/TSS                           0.78             0.78             0.78
R3SS, mg/1                         8930             8310             8650
R3VSS, mg/1                         7360             6590             7010
TSS Stripper Supernatant, mg/1                                           59
VSS Stripper Supernatant, mg/1                                           54

pH, Mixed Liquor, mg/1              7.1/7.0          7.0/7.0

Temperature (Influent), *C             13               13               13
F/Ma (kg BODs/dayAg MLVSS)         0.45             0.88             0.62

                                                    44.8/44.8        34.3/34.3
                                                                     <0.2
Secondary Clarifier Overflow Rate,m/day 26.4/26.4
Clarifier Blanket Level,  m.
            duration at max. flow y 11 hrs/day
                                         180