U.S. Environmental Protection Agency
Office of Wastewater Enforcement and Compliance
Washington, D.C.
Ultraviolet Disinfection Technology
Assessment
September, 1992
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NOTICE
This document has been reviewed by the U.S. Environmental
Protection Agency and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or
recommendation for use.
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ACKNOWLEDGEMENT
This report was prepared by O. Karl Scheible, with
assistance from Ashok Gupta and Denais Scannel, all of HydroQual,
Inc. Wendy Bell, OWEC, Washington, D.C. was the U.S.
Environmental Protection Agency Project Officer. The assistance
provided by the operators and owners of the plants described in
this report is acknowledged with appreciation.
The cooperation and assistance provided by the manufactures
of Ultraviolet equipment was helpful and appreciated.
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ACKNOWLEDGEMENT
This report was prepared by HydroQual, Inc. In fulfillment of Contract
68-08-0023. It was prepared by 0. Karl Scheible, with assistance from Ashok
Gupta and Dennis Scannell, all of HydroQual. Wendy Bell, OWEC, Washington,
D.C. was the Project Officer for the U.S. Environmental Protection Agency. The
assistance provided by the operators and owners of the plants described in this
report is acknowledged with appreciation.
The cooperation and assistance provided by the manufacturers of UV
equipment, in particular Trojan Technologies, Fisher and Porter, Katadyn,
.Aquionics and yitradynamics, wss helpful_jind_appreciated. __ ..._
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CONTENTS
Section '
FIGURES . . . . ....... .• . . . .......... -
TABLES . .................. .
•i
- ................... iv
EXECUTIVE SUMMARY ---- .......................................... E'
BACKGROUND AND OBJECTIVES . . .................. . ............ E- 1
FINDINGS .............. . ............................ • ..... •' E~ 2
CONCLUSIONS ................................ - ..... • ........ E- 3
RECOMMENDATIONS, ................................... • ...... E~ 6
1 ASSESSMENT OF THE UV DISINFECTION PROCESS ELEMENTS ............ 1-1
1.1 UV DISINFECTION .......................................... *- *
1.1.1 Source of UV Radiation ............................ 1- 1
1.1.2 UV Effectiveness ......................... . ........ 1- 4
1.1.3 ^Alternate Indicators . . ._._._•_•£• • • • • •_• .v_.v _*..•.• !.*.: .!...'..• ;_: __________ \~... 5.._.
•—•-•--- •-£ -^ -^ photoreactivation ... ------ . . . . — ...... ...... ..... - • ------ 1- _9...
1 . 2 HYDRAULIC DESIGN CONSIDERATIONS ........................... 1-H
1.3 ULTRAVIOLET DISINFECTION COSTS ............................ 1-12
1.3.1 Capital Costs ...................................... i'13
1.3.1.1 Equipment Costs ..................... . ..... 1-13
1.3.1.2 Construction Costs ........................ 1-1*
1.3.1.3 Total Installed Costs ..................... 1-14
1.3.2 O&M Costs .............. ............................ I'15
1.3.2.1 Parts Replacement ......................... 1-15
1.3.2.2 Power Costs ......... . ................... '-. 1-16
1.3.2.3 Labor Costs ..................... , ......... 1-16
1.3.2.4 Summary of O&M Costs ...................... 1-17
2 STATUS OF UV SYSTEMS AND EQUIPMENT CONFIGURATIONS ........ ..... 2-1
2 . 1 SYSTEM CONFIGURATIONS .................................... 2- 1
2.2 UV SYSTEMS IN THE UNITED STATES ................ . ......... 2- 5
2 . 3 TYPES OF SYSTEMS ......................................... 2- 5
3 EVALUATION OF SELECTED OPERATING UV DISINFECTION FACILITIES ... 3-1
3.1 DESIGN AND PERFORMANCE OF THE SELECTED PLANTS ............ 3-2
3.1.1 Description of the Selected Plants with Open-
Channel UV Systems ................ . ............ • • • 3" 2
3.1.2 Description of the UV Systems at the Selected
Plants ........................ . ................... 3' 8
3.1.3 Summary of Performance and Permit Requirements at
the Selected Plants ....... . ....................... 3-!4
3.1.4 Design Sizing and Performance Summary for the
Selected Plants ...... . ..................... ....... 3'20
3.2 EVALUATION OF THE OPERATION AND MAINTENANCE OF UV SYSTEMS 3-22
3.2.1 Summary of 0 and M Practices at Selected Plants ... 3-22
3.2.2 Summary of UV Cleaning Practices at Selected Plants 3-36
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Section
3.2.2.1 Frequency and Labor Requirements for
Cleaning
3.2.2.2 Summary Assessment of Cleaning Practices
REFERENCES
••"•"••••••••••••oe,
<&
APPENDIX A - SITE VISIT REPORTS
3-45
3-46
4- 1
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FIGURES
Figure
1-1
2-1
2-2
3-1
3-2
3-3
3-4
PERFORMANCE-LOADING CURVES DEVELOPED FOR REHOBOTH BEACH UV
SCHEMATIC OF OPEN CHANNEL, MODULAR UV SYSTEM USING HORIZONTALLY
mw-nTA«AT OTXT/-»T r1 r«AMKTT?T TT\7 nT<5TNFPrTTON EQUIPMENT LAYOUT
UV SYSTEM SIZING FOR SELECTED PLANTS AS A FUNCTION OF PEAK
LABOR REQUIREMENTS FOR REPLACEMENT OF LAMPS/BALLASTS/QUARTZ
SCHEMATIC OF UV CHANNEL SYSTEM SHOWING CLEANING TANK (COURTESY
Page
1- 8
2- 3
2- 4
3-15
3-31
r__ ..3 i3Si_ ..-=_-_ --:.-•
o /. o
TROJAN TECHNOLOGIES, INC. LONDON, ONTARIO)
ill
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TABLES
Table
1-1 WASTEWATER CHARACTERISTICS AT REHOBOTH BEACH DELAWARE
(REFERENCE 15)
............. * ..... • ---- • ........... ........... 1- 7
2-1 UV SYSTEMS IN THE UNITED STATES ...... . „ ,
•••"••"•• ........... ........ ... /- 5
2-2 STATUS OF UV APPLICATIONS TO WASTEWATER ................ ......... 2-8
3-1 DESCRIPTION OF SELECTED PLANTS WITH OPEN- CHANNEL UV SYSTEMS.... 3- 3
3-2 DESCRIPTION OF UV SYSTEMS AT SELECTED PLANTS ____ . . ____ ........ 3- 9
3-3 SUMMARY OF PERMIT REQUIREMENTS AND PERFORMANCE AT SELECTED
_ PLANTS . ._. ..£.... . ,r • v ••-,•• •..-. -,— •_:. • -,•„• •..: - - ; t • .- .... .r.. . ...:....... ...... . .... .. . ..... , ,.3-16 _
3-4 SUMMARY OF DESIGN SIZING/PERFORMANCE -CHARACTERISTICS FOR
SELECTED PLANTS
3-5 SUMMARY OF 0 AND M PRACTICES AT SELECTED PLANTS... ............ . 3.23
3-6 SUMMARY OF UV CLEANING PRACTICES AT SELECTED PLANTS ............ 3.38
3-7 SUMMARY OF GLEANING PRACTICES FOR THE .30 SELECTED PLANTS. ...... 3.47
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EXECUTIVE SUMMARY
BACKGROUND AND OBJECTIVES
Ultraviolet (UV) disinfection systems are being widely considered for
application to treated wastewaters, for both new plants and retrofitting
existing plants in lieu of conventional chlorination facilities. The
technology is relatively new, with most systems installed over the past three
to four years. It has generally been successful, although there had been many
problems with the systems installed in the early to mid-eighties. Subsequent
"second generation" designs have resolved many of the earlier issues, resulting
in a higher degree._.of^ reliability....and....a_ more .rapid...acceptance of __the_
technology. These use modular, open-channel configurations in place of the
fixed, closed shell arrangements typical of the earlier designs.
The USEPA Design Manual for Municipal Wastewater Disinfection (1) was
published in 1986; the evolution to the newer open-channel configurations began
only shortly before this. Although the Manual points to the advantages of the
open-channel configuration, it does not adequately address their design and
operation and maintenance (0 and M) aspects, since there was little direct
experience with the systems at the time. New design, performance, operation
and maintenance information is being developed from recent full-scale
i
applications. These data need to be disseminated to the engineering and
owner/operator communities.
This report provides an assessment of the UV process, focusing on the newer
designs that utilize open-channel, modular configurations. It is a part of the
Office of Wastewater Enforcement and Compliance's (OWEC) program to provide
technical assistance to reviewing agencies and local governments in the area of
municipal Wastewater treatment, by evaluating specific technologies and
reporting on their capabilities and limitations.
Information was compiled from the EPA, Regional and State offices,
literature, equipment manufacturers, and wastewater treatment plant personnel.
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The report presents an assessment of the status of the technology relative to
the type and size of UV facilities that are currently operating, and discusses
the trends in system design, configuration and operations. The design and
operation of selected plants are reviewed; this information and current
practices are then summarized to give a perspective of key considerations that
should be incorporated into the design of UV facilities. Finally, a review of
costs associated with the construction and operation, of UV systems is
presented, based on data generated from this assessment.
FINDINGS
Thirty plants, covering a range of design flow ratings and UV open-channel
configurations .were evaluated; All are'Toperating successfully: aria"^^ -In
compliance with their permits, which typically address fecal coliforms. A high
level of satisfaction with the system operation and performance was noted by
the facility operators.
All the plants accomplish nitrification, by design or by the circumstance
of low loading. Improved disinfection performance is influenced by this higher
degree of treatment. Minimal coliform densities are observed after UV in
wastewaters with BOD/TSS levels less than 10 mg/L. Elevated effluent densities
(but still well within permit) are noted at BOD/TSS levels greater than 10
mg/L.
Limited redundancy and system flexibility was noted for the majority of
plants. Most plants, in particular the small systems, had single channels,
precluding shutdown of a channel for repair/maintenance. Flexibility should be
incorporated to a greater degree, including multichannel, multibanking
configurations.
System control is kept simple. Automatic flow pacing is incorporated into
the larger multichannel, multibank systems; control is flow-paced on a manual
basis at several plants. The tendency at the smaller plant (average design
flow less than 1.0 mgd) is to have 100 percent' of the system in operation at
all times.
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A downstream mechanical level control gate is the preferred method to
maintain liquid level in the UV channel, and it is generally successful.
However, it has a specific operating range. Plants with very low flow periods
(or no flow) may best be served by using adjustable weirs/weir launders for
level control. This may be the case with small systems.
A screen/bar screen is an appropriate device to have immediately upstream.
This serves to remove debris and algal mats from the wastewater and prevent
them from catching onto the lamp modules.
Sizing of the UV system was somewhat consistent. This ranged between 0.5
and 1.5 Ktf (of UV output at 253.7 nm) per mgd of peak design flow, with a mean
of 1 KW/mgd. This is equivalent to approximately 37 long lamps or 74 short
:• lamps i- - ^Siis estimate should be applied only to advanced ^secondary effluents ,-
and to plants with a peak to average flow ratio less than 2.5.
Lamps show an extended operating life. Operation greater than 14,000 hours
can be expected. The criterion generally followed for lamp replacement is
increasing fecal coliform density, although some plants will replace the lamps
on a routine fixed time basis (7,500 to 10,000 hours).
Insufficient experience exists to assess replacement cycles for ballast and
quartz sleeves. A 10 year cycle has been suggested.
Cleaning the quartz surfaces is a key element of UV O&M. Removal of the
modules is appropriate and is practiced by most plants, particularly those
using the horizontal lamp modules. In-place chemical recirculation is
practiced less frequently, typically with vertical lamp module systems.
Dip tanks are a convenience and assist in cleaning modules removed from the
channel. At minimum, a hanging rack should be provided to hold removed
modules.
A variety of cleaning agents are used, typically site specific or provided
by the manufacturer. Citric acid and Lime-Away^ are used most frequently.
Commercial detergents and dilute acids are also used.
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The frequency of cleaning varies widely from weekly to yearly with a
median of monthly. This is site specific. Fecal coliform density is typically
used as the criterion for cleaning.
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The labor requirement for smaller plants is estimated at 180 hours/year/100
lamps. Approximately one- third of this is associated with cleaning activities
For larger plants (greater than 150 lamps) the O&M labor is approximately 115
hours/year/100 lamp, with about one-half attributable to cleaning tasks.
The installed costs for UV systems were estimated to be $48,800/UV KW for
systems with less than 100 lamps and $39,000/UV KW for larger systems (a UV KW
is the power output at 253. 7nm). These are screening estimates only and may
vary considerably on a site by site basis. When considered on the basis of
flow for advanced .secondary -plants,- l^e-~costs
per mgd of average design flow for larger (greater than 1.5 mgd) to smaller
plants.
Operation and maintenance costs are site specific and will vary regionally
vith respect to rates. For screening purposes, annual costs (exclusive of
amortization) are estimated to be $3,300 to $3,800/UV KW/yr This is
equivalent to $6,500 to $7 , 500/year/mgd of average design flow.
CONCLUSIONS
Ultraviolet disinfection is now being widely applied to wastewaters, with
greater than 500 operating facilities, as compared to an estimated 50
facilities in 1984. Whereas closed shell and pipe systems were typical in the
early to mid-eighties, the modular, gravity flow, open-channel systems now
comprise essentially all new installations. The configuration is found in
greater than two thirds of active plants, as compared to less than five percent
In 1985. It is comprised of horizontally or vertically placed lamp modules,
Placed in open, relatively narrow channels . with the lamps fully submerged in
the wastewater. Horizontal systems represent approximately 85 percent of the
open channel facilities.
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The UV source used with essentially all systems is the low pressure mercury
arc lamp. Alternate lamps are being actively investigated and are in use at
several operating plants. These include medium pressure lamps and
modifications of the conventional low pressure lamps. A recent advance has
been the introduction of an efficient electronic ballast, which is lighter and
is incorporated into the modules themselves.
UV is effective and has been demonstrated to be capable of meeting existing
disinfection criteria. This includes secondary fecal coliform limits (200
fecal coliforms/100 mL) and shellfish limits (14 fecal coliforms/100 mL). An
exception may be the California total coliform limit of 2.2 per 100 mL for
discharge to shellfish waters. Filtration is generally required if UV is to
meet the lower shellfish standards.
Alternate indicators have been incorporated into EPA disinfection
guidelines and are being written into permits in a number of states. These are
126 E. Coli per 100 mL or 33 enterococci per 100 mL for freshwater, and 35
enterococci per 100 mL for marine waters. Recent studies have indicated that
the design sizing requirements for these indicators is similar to those for
fecal coliforms. Caution should be used, however, particularly when modifying
permits for existing UV facilities. A plant that readily meets fecal coliform
requirements can have difficulty meeting enterococcus limits under similar
operating conditions.
Photoreactivation is a necessary factor to consider when sizing UV systems
on the basis of total or fecal coliforms and E. Coli. An average maximum level
of repair demonstrated from several studies is a 1.5 log increase. Enterococci
do not have the ability to repair.
Hydraulic design is a key factor in the operation of UV systems. Plug flow
conditions with minimal dispersion must be maintained. This is best done by
using narrow channels relative to their length (to yield an aspect ratio
greater than 15), having two banks in series when using horizontal lamp systems
and a minimum of four banks in series with vertical lamp systems. Straightline
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approach and exit conditions should be maintained, with adequate upstream and
downstream distances from the lamp batteries.
Headlosses are relatively low through current system configurations under
normal design velocities. Care should be taken to account for upstream devices
such as stilling plates and screens, and the downstream level control device
when estimating overall headloss. The total headless through the UV lamp
portion of the reactor should be held to less than three inches at peak
instantaneous (hourly) flow.
Design sizing should be on the basis of peak requirements (e.g. maximum
daily, maximum 7-day, etc.) for disinfection. Hydraulic design is based on
peak hourly flow, reflecting diurnal variation. Wastewater parameters used for
design are the initial bacterial density; the UV transmittance--of the
wastewater (at 253.7 nm) and suspended solids. Design sizing should be based
on the assumption that the peak occurrences for these parameters and flow are
coincident.
RECOMMENDATIONS
There should be additional evaluation of the impact that alternate
indicators have on the design and performance of UV systems. In particular,
this should address plants that are or will be required to incorporate either
E. Coli or enterococcus into their discharge permit.
Application of open-channel, modular, gravity flow UV systems should be
encouraged for wastewater disinfection. The design implications of recent
advances in system design, in particular the high intensity lamps, should be
assessed. This would address potential applications and include a comparison
to the conventional systems.
Continued effort should be made to determine the impact of
photoreactivation on design and the degree to which this phenomenon affects
receiving waters. This would best be addressed in comparison to after growth
associated with chlorination/dechlorination.
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Page 1-1
SECTION I,
. ASSESSMENT OF THE UV DISINFECTION
PROCESS ELEMENTS
This section briefly describes the UV disinfection process and its
application to treated wastewaters. It then presents the equipment
configurations that have been and are being used for wastewater applications,
and addresses related process considerations and the design protocols currently
in use.
1.1 UV DISINFECTION
The inactivation of microorganisms by ultraviolet radiation is a physical
process, relying on the photochemical changes brought about when far-UV
radiation is absorbed by the genetic material of the cell (deoxyribonucleic
acid, or DNA). The wavelengths for optimum effectiveness correspond, as
expected, to the maximum absorption spectrum for nucleic acids, between 250 and
265 nanometers (nm).
The inactivation mechanism is well understood for UV radiation. The reader
is referred to other source material for more detailed discussions of the
mechanism (1,2,3,4,5). Specifically, the most common pathway involves the
dimerization of adjacent thymine monomers on a DNA strand. If many dimers are
formed by exposure to UV radiation, cell replication becomes very difficult.
Thus, although the cell is not "killed" by exposure to UV, it is effectively
inactivated because of its inability to replicate.
1.1.1 Source of UV Radiation
The low pressure mercury arc lamp is very efficient in generating UV light
within the optimal germicidal wavelength range. It is an electric discharge
lamp that generates light by transforming electrical energy into the kinetic
energy of moving electrons; this is converted to radiation by a collision
process. Mercury vapor, kept at an optimum pressure in the presence of a rare
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Page 1-2
gas (typically argon), is a very efficient emitter of light at 253.7 nm. The
lower the vapor pressure of mercury in an electric discharge, the greater the
intensity of the mercury resonance line at 253.7 nm. Exploiting this fact
construction of the low-pressure mercury arc lamp yields an output that is
nearly monochromatic in its radiation at 253.7 nm. Thirty-five to forty
percent of the input energy is converted' to light, and approximately eighty-
five percent of this light is at the wavelength of 253.7 nm.
These low-pressure lamps comprise the source of UV energy in effectively
all systems installed today. The lamps are long thin tubes, 1.5 to 2.0 cm in
diameter. Standard lengths are 91,4 cm_(36..inches) and 162,6 cm (64 inches),
with active mercury arc lengths of 76.2 cm (30 inches) 'and i^f"^^""
inches), respectively. The longer length lamps are typically used, except in
small systems. They are more cost effective than the shorter lamps; although
they have effectively twice the UV output, they are usually only 30 to 60
percent more in cost.
Some wastewater applications exist that use alternate UV sources, although
they all still rely on the basic mercury vapor electric discharge concept.
Medium to high pressure mercury lamps have significantly higher UV intensities
and have a broader spectrum of output than the low pressure units. A study by
Whitby and Engler (6) demonstrated that the germicidal effectiveness of a 2,000
watt (W) medium pressure lamp was 14.2 times that of a 60 W conventional'low
pressure lamp, based on the ability to achieve a 3-Log reduction in a primary
effluent. The single lamp experiments suggest that the total number of lamps
required for a given application can be reduced by a factor of up to 10 if
medium pressure lamps were used. This would result in potentially significant
savings in capital costs and area requirements, an important advantage for
large systems.
There are medium pressure lamp systems in the U.S. for the disinfection of
treated municipal effluents, including the Lewisburg (1 mgd) and Hillsboro (4
agd) Ohio plants (7). These systems are operated under pressure, which would
be impractical on a large scale. Uncertainties remain with the use of medium
pressure systems, reflecting the very limited direct experience with wastewater
applications. The costs of the lamps themselves are much higher than the low
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Page 1-3
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pressure lamps; they are also less efficient and thus, require more power. Heat
output is greater and can impose design problems relating to heat transfer.
Power supply requirements are more complex and because of their shorter length
and fractional second exposure times, hydraulic design becomes a critical issue
when attempting to maintain plug flow conditions.
Modifications of conventional low pressure lamps are being developed, with
some resultant in-field applications. A facility in Cuxhaven, Germany uses a
high intensity lamp similar to the medium pressure lamps. (8). Its energy
conversion is more efficient, however, similar to conventional low pressure
lamps. The lamps are u-shape, vertically oriented"in the water, with an ©pen-"'
channel layout. There is a heat dissipation contact spot with the quartz
enclosure that is used to remove the high heat load associated with these
lamps. Another alternate lamp is a conventional lamp that is flattened in
order to increase the emission from the mercury vapor, yielding higher
intensities (9). A plant in Baldwin, Florida was installed with these lamps,
although equipment problems have prevented an assessment of its performance.
A recent development has been the use of an alternate electronic ballast.
A ballast is required to counter the inherently unstable negative volt-ampere
characteristic of electric discharge arc lamps. In nearly all existing
installations conventional 2-lamp lead-lag type coil ballasts are used. The
electronic ballasts offer the advantage of being lighter and have the ability
to adjust the input voltage (dimming). Because of their lighter weight
(approximately one-third that of the coil ballasts), the ballasts are
incorporated into the lamp modules themselves, as opposed to the large cabinets
used for the coil ballasts. This has allowed a potentially significant cost
savings. .There is limited in-field experience with these modules; a full-scale
operating unit is located at Camp Quin-Mo-Lac in Ontario for beach water
control, with approximately three months operation. A 14.6 mgd wastewater
plant was commissioned in April 1991 at St. George de Beeauce, Quebec, and
several facilities in the design/bid/construct stage anticipate using these
modules with the electronic ballasts (10).
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*
• Overall, UV equipment for treated wastewater disinfection will likely
continue to be dominated by the conventional low pressure mercury arc lamps.
They are efficient, cost-effective, and are appropriate to a wide spectrum of
applications. The alternate lamps, particularly the medium pressure units,
continue to be investigated and applied on a limited basis. Their likely
application will be with large plants arid in cases of low-grade, high volume
waters such as combined sewer overflows' (CSO) and stormwaters.
1.1.2 UV Effectiveness
The effectiveness of UV in the inactivationof^microorganisms^i
documented. Generally, UV is the most effective of the standard disinfection
processes when applied to bacteria and viruses. Effectiveness increases with
decreasing complexity of the organism and with decreasing cell wall thickness.
Thus, viruses are particularly sensitive to UV, more so than to chlorine or
other oxidants. On the other hand, higher organisms are less sensitive; in
these cases chlorine is the preferred disinfecting agent. This is demonstrated
in recent research regarding the Safe Drinking Water Act rules on drinking
water disinfection. UV has limited cysticidal ability, and is not applicable
to Giardia Lambia disinfection (11,12).
Most National Pollutant Discharge Elimination Permits (NPDES) require
disinfection, with limits set on the basis of fecal coliform. There are
variations from state to state, relative to the requirement: for disinfection
(water use guidelines, seasonal disinfection, etc), indicators, and indicator
limits. UV disinfection is capable of meeting these standards in most cases:
Secondary Treatment Maximum 30-day Fecal coliform < 200 per 100 mL
Maximum 7-day Fecal Coliform < 400 per 100 mL
Shellfish Waters Maximum 30-day fecal coliform < 14 per 100 mL
These are geometric means. In some cases total coliform limits are
incorporated into the permit, such as 70 per 100 mL for shellfish waters. The
higher limits can be met by UV with adequate clarification prior to discharge.
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Page 1-5
Suspended solids concentrations that are consistently greater than 25 mg/L may
prevent the UV system from meeting the 200/400 fecal coliforms limits. Solids
tend to occlude bacteria from exposure to UV. California limits total coliform
to 2.2 per 100 mL for discharges to shellfish waters or impounded water bodies.
UV has not been demonstrated to be capable of meeting these levels on a
consistent basis in a treated wastewater matrix. The shellfish limits (14 per
100 mL) that are more typically used in various states can be met with tertiary
filtration prior to UV.
1.1.3 Alternate Indicators
~ : : A major policy change in disinfection regulationi haY been7the suggestedFuse7
of E. Coli and/or enterococcus as disinfection indicators in lieu of total or
fecal coliforms. The prevailing fecal coliform limits have been criticized
because available epidemiological evidence does not support their use, and
because the fecal coliform group can itself contain bacteria that are not
necessarily associated with fecal contamination. Studies have shown that E.
Coli and enterococci are better able to predict the incidence of swimming
related gastroenteritis than either total or fecal coliforms (13). The USEPA
"Ambient Water Quality Criteria for Bacteria" (14) recommends use of the E.
Coli and/or enterococcus as pathogen indicators in recreational waters.
EPA guidance states that E. Coli not exceed 126 per 100 mL (geometric mean)
in freshwater, or that enterococci not exceed 33 per 100 mL. Enterococcus
limits (35 per 100 mL) are recommended for marine waters. Several states are
moving toward the use of these standards, although all states that have
bacteriological standards continue to use fecal and/or total coliforms as
indicators. The state of New Jersey has begun to incorporate enterococci into
all permits, as they are renewed. The limits are 32.5 per 100 mL on a 7-day
average (GM) basis and 60 per 100 mL as a maximum value. Note that discharges
to shellfish waters still require compliance with U.S. Food and Drug
Administration (FDA) fecal coliform standards.
Movement to alternate indicators has raised concern over the adequacy of UV
design sizing criteria relative to standard fecal coliform requirements. If UV
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Page 1-6
facilities have been sized and installed on the basis of fecal coliform limits,
the question is weather the system would also be able to meet enterococcus
and/or E. Coli standards. Direct pilot studies have been conducted to address
this, including an EPA funded study (15) at the Rehoboth Beach Water Pollution
Control Plant (WPCP) in Delaware, and a recent pilot study (16) at the LOTT
WPCP in Olympia, Washington.
The Rehoboth Beach WPCP is an oxidation ditch facility with nitrification
and tertiary microscreens. The plant has an average design flow of 3.4 mgd;
during the 1989 study, the average flow was'1.7 mgd. Table 1-1 presents a
summary of effluent data representing the summer period in 1989. The plant
produces a nigh quality effluent"," with an averag¥"Bdb5""and fSS of "S^aaA^^l"
rag/L, respectively. The average and 95 percentile values are also reported for
total and fecal coliforms, E. coli, and enterococcus. Total coliforms were
typically 6.5 times the fecal coliforms in the treated effluent (before UV).
Enterococci and E.coli densities were significantly lower than the fecal
coliforms (at ratios of 0.04 and 0.13, respectively). These ratios increased
substantially after UV treatment, particularly for the. enterococci (1.3) and E.
Coli (0.7), suggesting a lower sensitivity to UV for these groups.
Figure 1-1 presents design curves developed from the Rehoboth Beach pilot
data that reflect this lower observed UV sensitivity. The log survival ratio
(N'/N0) is shown as a function of the system loading (liters per minute/UV
Watt, Lpm/UV W). From this figure one can estimate that the maximum allowable
loading to achieve a 4-log reduction of enterococcus or E. coli would be
approximately three-quarters the maximum allowable loading for a similar
reduction in fecal coliforms. The loading for total coliforms is approximately
1.15 times that of the fecal coliforms for a 4-log reduction. This means that
a larger size UV system would be necessary to accomplish equivalent reductions
for enterococcus and E. Coli. However, because the initial densities are
substantially lower than the fecal coliforms, the actual sizing requirements
are smaller.
At the LOTT wastewater treatment plant in Olympia, Washington, both fecal
coliforms and enterococcus were investigated as part of a pilot study for
design of the UV system. In this case the ratio of enterococcus to fecal
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Flow
1.74
2.56
fffluent
BODs (mg/L)
TSS (mg/L)
XTransmittance at 253.7 nm
XTransmittance at 253.7 nm
Total Coliform (100 mL'l)
Fecal Coliform (100 ..mL=-f)
Entercoccus (100 mL"1)
E. Coli (100 mL'1)
patio t
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0»
o
o
DC
o
p»
o
-6
./*• TOTAL COLIFORM
Horizontal Array
i = 100 tern/sec
2 Banks in Series
to
Lswding Q/Wh(|pm/ Watte, 253.7nm)
Q/Wn vs. Log Survival Ratio ( log N'/N )
Figure 1-1
Performance - Loading Curves Developed for
Rehoboth Beach UV System (15)
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Page 1-9
coliform averaged approximately 0.145, with mean values of 14000 and 96500 per
100 mL, respectively. This ratio increased to 0.95 after UV treatment, again
indicating a lower sensitivity to UV. When the design sizing requirements to
meet the 30-day limits of 200 fecal coliforms or 35 enterococci per 100 mL were
compared, the enterococci limits were found to be the controlling factor,
although the margin was rather narrow. A total of 1,030 lamps were estimated
for enterococci disinfection versus 943 lamps for the fecal coliforms. LOTT
will not have enterococci limits in their permit.
A third, most recent example of the enterococcus versus fecal coliform
issue can be found with the Northwest Bergen County Treatment Plant in
Waldwick7 New'Jersey "(17) . This is" a "retrofitted plant "that "was'•'•'designed" to™
meet fecal coliform limits (200/400). Its permit was recently changed to
include enterococcus at an average limit of 32.5 per 100 mL and a Eiaximum of 60
per 100 mL. Although the facility had been consistently meeting the fecal
coliform limits, even under design flow conditions (approximately 12 to 14 mgd)
extraordinary measures were needed to assure compliance with the enterococci
limits. This included replacement of the lamps with new lamps, a task that
will be done routinely after only 7,500 operating hours. This will
substantially increase the UV system's operating costs.
The initial work at Rehoboth Beach suggested that imposition of the
alternate indicators would not adversely affect the sizing requirements of UV
systems to meet permit limits, nor would it compromise the ability of existing
facilities to meet permit limits. It appears, however, that this may be an
unknown, and one that is largely dependent on the specific site and its
wastewater characteristics. Caution must be used when sizing for enterococcus
(and/or E. coli) disinfection, or when modifying the permit requirements of
plants already designed to meet fecal coliform limits.
1.1.4 Fhotoreactivation
The damage caused by exposure to UV can, to a limited extent, be repaired,
depending on the environmental conditions and the specific organisms. The
phenomenon is well understood and documented by extensive research (1, 18,
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Page 1-10
19,). Two mechanisms are identified. The most dominant is a catalyzed
enzymatic repair requiring concurrent or subsequent exposure to light in the
visible range of 310 to 490 nm. The second is a dark repair involving cleavage
enzymes that clip out the dimerized nucleotides. Not all microbial organisms
exhibit the ability to accomplish this repair. Of the groups often addressed
by wastewater discharge permitting activities, the coliforms (total and fecal)
and the E. Coli will photorepair. Enterococcus will not! Viruses do not have
this ability, except when in a host cell that can repair.
Data on the photoreactivation of bacteria in treated wastewater have
generally been generated on the basis of the static bottle test In this
procedure, the UV exposed single is m^^
and is also split in to two bottles; one is opaque to visible light, while the
second is transparent to visible light. These are then exposed to sunlight for
one to two hours and the bacterial density is measured. The increased level
measured in the "light" bottle is attributed to the repair of UV damaged
organisms upon exposure to sunlight. Note that exposure to interior
fluorescent or incandescent light will yield lower results than when measured
with sunlight (16).
There are seasonal influences, likely due to light intensity, temperature
and cloud cover. Maximum repair occurs during summer months. The repair
mechanism has been shown, using the bottle technique, to result in a 1 to 2 5
log increase in fecal coliform, total coliform and E. coli (1,15,16) while the
enterococci do not repair (15,16). It is suggested that a mean repair level of
1.5 log should be anticipated as the maximum increase after UV exposure.
One should note that these are maximum levels, estimated under optimal
conditions for photoreactivation. These do not necessarily correspond to
conditions extant in the UV channel, the plant outfall and the receiving
stream. One has the discretion to consider partial photoreactivation when
d.ter»talng performance requirements for design sizing. Thus if a three-log
kill is necessary for system performance, one would conservatively design by
assuming maximum photoreactivation and size for a 4.5 log reduction
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Page 1-11
1.2 HYDRAULIC DESIGN CONSIDERATIONS
Considerable performance problems occurred with the older, closed shell
systems, often due to ineffective hydraulic design. The move to the open-
channel, modular system configuration has positively influenced good hydraulic
design. For UV disinfection this requires long, narrow channels with approach
and exit conditions that are conducive to the desired plug flow, minimal
dispersion behavior.
Two banks of horizontal lamp UV modules placed in series are typical of new
designs. The channel width should^ be kept low, such, that the .aspect._r.atio,.,is_
greater than 15 (ratio of the length to the hydraulic radius). Similar
calculations should be done in configuring the vertical lamp modules.
Retrofitting existing chlorine contact chambers often leads to excessively wide
channels; it is best to consider splitting the channel with narrow walls along
the length.
Straightline approach and exit conditions should be maintained. Upstream,
a perforated stilling plate can be installed, if there is sufficient head
available, to distribute the flow/velocity evenly along the cross-sectional
plane of the channel. General practice places this approximately four feet
upstream of the first lamp battery. Otherwise, the channel should have an
undisturbed Straightline approach two to three lamp lengths in distance. There
should be a sufficient distance between lamp banks (two to four feet) and two
to three lamp lengths between the last bank and the downstream level control
device.
Scheible(20) reported the hydraulic analysis of a UV system in West
Virginia that demonstrated the importance of channel hydraulic design. An
open-channel, horizontal lamp unit, it was designed with over-under-over
baffles in the approach channel to break the velocity of the pumped influent.
The system was unable to meet fecal coliform limits, however. A residence time
distribution (RTD) analysis showed very high dispersion, with an E estimate to
be greater than 2,000 cm2/sec (reference the EPA Design Manual, 1). The
Morrill Dispersion Index (the ratio of tgoAio) ranged between 2.2 and 6.4.
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Page 1-12
Ideally, the target for these two parameters should be an E less than 100
bm2/sec and a Morrill number less than 2.0. Mixing was occurring in the
reactor, preventing effective disinfection; this was found to be caused by the
disturbed flow in the approach section of the channel. The baffles were
removed and a stilling plate was installed. A subsequent RTD analysis showed
an E less than 100 cm2/sec and a Morrill Dispersion Index less than 2.0,
indicating that good plug flow hydraulic behavior had been achieved.
Good design practice should entail multichannel configuration, enabling the
flexibility of altering the number of channels in service as a function of
flow. The individual channels should be operated at a rate greater than 70
percent of its design flow; The channels :should also "be.'"hydrauliiiiiy"-'
independent; this can be accomplished with equivalent stilling plates at the
head of each channel, or with overflow weirs.
Headlosses are relatively low through current system configurations.
Design velocities are typically 1.0 to 2.0 fps and should not exceed 2.5 fps.
Care should be taken to account for upstream devices such as stilling plates
and screens and the downstream level control device when estimating overall
headloss. The total headloss through the UV lamp portion of reactor, inclusive
of all stages, should be held to less than three inches at the peak design
(hourly) flow.
1.3 ULTRAVIOLET DISINFECTION COSTS
Cost information was assembled from several sources: manufacturer's
equipment and major component replacement costs; bid quotes for specific
installations; and actual costs data from existing UV facilities. There were a
total of 35 plants for which cost information was available to some degree;
these do not correspond fully to the 30 plant survey presented in Section 3.
The following discussions present the capital and operational and maintenance
(O&M) cost estimates. Understand that these are meant for use In screening the
expected costs for a UV application. Site specific considerations are critical
and will affect any cost estimate for the installation and operation of a UV
disinfection system. The costs provided in the following discussions should be
-------
Page 1-13
assumed to have a range of plus or minus 35 percent. The estimates have been
normalized to 1990.
1.3.1 Capital Costs
1.3.1.1 Equipment Costs
The installed costs of UV systems are generally dominated by the equipment
costs. These include:
« UV modules with lamps and quartz sleeves;
• module support racks;
• level control device;
. • instrumentation and control panels;
• power supply distribution/ballasts;
• cables/cableways, and
• spare parts inventory.
There is an economy of scale, although this was found to be divided to two
distinct sizes: systems with less than 100 lamps and those with greater than
100 lamps.
The costs were normalized to the available power at 253.7 run. Thus,
standard 58 inch arc lamps have a rated UV output of 26.7 watts at 253.7 nm; if
a particularly system has 100 lamps, its total available UV output is 2,670
watts, or 2.67 KW. Conversely, one KW at 253.7 mn is equivalent to 37 standard
long lamps (58 inch arc) or 75 short lamps (30 inch are).
The average equipment cost (1990) for small systems (< 100 lamps) was found
to be $29,700 per UV KW. These are based on 18 plants ranging in sized from 24
to 76 lamps. The costs for systems greater in size than 100 lamps tended to
have a narrow range. Those systems with 100 to 500 lamps (2.67 to 13.35 KW)
had an average equipment cost of $23,500 per KW at 253.7 nm. This decreased to
an average of $20,500 per UV KW for systems having more than 500 lamps. The
mean cost of all systems with greater than 100 lamps was $22,000 per UV KW.
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Page 1-14
1.3.1.2 Construction Costs
Construction costs include the concrete open channel structures to support
the UV systems, influent and effluent channel structures, utilities, flow
diversion gates for each channel, grating, accessory equipment/structure, and
engineering. A building is not included in the installed costs. For small
systems (less than 100 lamps) the construction costs averaged $29,100 per UV
KW. This decreased to approximately $17,000 per UV KW for plants greater than
100 lamps in size. One should again note that these costs, exclusive of the UV
equipment, are very site dependent and can vary widely due to conditions unique
to a given site. - Overall, the construction costs, tend,:to.be ..equivalent, on
average, to 100 percent of the equipment cost for small systems and 75 percent
of the equipment cost for systems greater than 100 lamps.
1.3.1.3 Total Installed Cogt-g
The capital costs (1990) associated with the installation of UV systems are
summarized as follows:
System Size Equipment Construction __ Total
< 100 lamps $29,700/UV KW $29,100/UV KW $48,800/UV KW
> 100 lamps $22,000/UV KW $17,000/UV KW $39,000/0* KW
'The total available UV KW provided for a given plant is dependent upon the
Plant size, wastewater quality, performance requirements and degree of
redundancy. As such, it is difficult and not wholly appropriate to relate a
general cost to the size of the treatment plant. However, to gain a
perspective, Section 3 finds that the average design size of an open-channel,
modular UV system is approximately 1 KW at 253.7 nm/mgd peak design flow for
advanced secondary to tertiary plants having peak to average flow ratios less
than 2.5. This is equivalent to approximately 37 lamps per mgd of peak design
flow. If we were to assume a peak to average ratio of 2.0, the number of lamps
per 1 mgd of average design flow is 74; or an available UV output of 2 KW per
*gd of average design flow. Given the "small" versus "large" division of 100
lamps,^the small plant would have a design average flow of less than 1.5 mgd
with a total installed cost of $97,600 per mgd. "Larger" plants with a design
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Page 1-15
average flow greater than 1.5 mgd would have an installed cost of approximately
$78,000/mgd.
1.3.2 O&M Costs
The major elements in the costs for the operation and maintenance of UV
systems are parts replacement, power and labor. Experiences from 30 selected
plants are discussed in Section 3 for open channel, modular systems; these were
factored into the estimates of O&M costs. Again, as with the capital costs
estimates, the O&M costs are estimated for screening purposes; actual costs
„ _. __.
1.3.2.1 Farts Replacement
The key components that require periodic replacement are the lamps, quartz
sleeves, and ballasts. The cost of these items vary widely and from equipment
manufacturer to manufacturer. It is suggested that an owner pursue lamp
manufacturers and/or bidding in quantity, particularly with larger systems.
This will be especially effective in the purchase of lamps. For purposes of
this analysis, the following unit pricing is assumed (based on the use of
standard 58 inch arc length lamps):
I .amps $60
Quartz Sleeve $50
Ballast $80
The replacement cycle per lamp is presumed to be every 12,500 hours of
operation (1.4 years). System utilization is 40 percent; this means that an
average of 40 percent of the lamps in a system are on at a given time.
Furthermore, year-round operation is presumed. A life cycle of 10 years is
presumed for the quartz and ballasts. To account for miscellaneous parts
replacement/repair, an additional cost equivalent to two percent of the
equipment capital cost is assumed as an annual cost.
Normalizing this to available UV output at 253.7 nm:
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Page 1-16
Lamps: 37 lamps x . _ 0.4 x $60 - $592/UV KW/year
UV KW 1.5 years lamp
• Ballast (at one per two lamps):
- 37 lamps - x $80 x 1 - $148/UV KW/vear
UV KW x 2 lamps/ballast ballast 10 years ™/year
Quartz: 37 lamps x 1 x $50 - $185/UV KW/vear
UV KW 10 years quartz
• Miscellaneous Parts/Repair:
at 2 percent Equipment Cost/Year x $22,000/UV KW - $440/UV KW/year
The total annual (1990) parts replacement costs are thus estimated to be
$1,365/UV KW/year.
1-3.2.2 Power Costs
Power costs will obviously be dependent on the unit rate per KW/hr, a value
that is highly dependent on the regional location of the pla.nt. For purposes
of this analysis, an average rate of $0.08/KWhr is used. The power draw for a
UV system using the long standard lamp is typically between 90 and 100 W/lamp.
This accounts for the full draw of the system, including instrumentation,
control, lamps and ballast losses'. A value of 100 W/lamp is used for this
calculation, or 3.7 KW/KW at 254.7 nm. The annual system utilization assumed
for lamp replacement is then used to estimate the annual power costs:
TTTT? ' 7T ** - x fi*A_ x &L08 x 8.76Q hrs - $l,040/year/UV KW
UV KW power year KW hr year
Thus the annual power cost is estimated to be approximately $1,040/UV KW/year,
based on the operating assumptions and rates discussed earlier.
1.3.2.3 Labor Costs
The labor requirements will be site specific, focusing primarily on parts
replacement, general maintenance and monitoring, and cleaning. Estimates for
these labor elements are discussed in Section 3. The total O&M labor
requirement, exclusive of cleaning, was estimated to be 120 hrs/year/100 lamps
for smaller systems and 55 hrs/year/100 lamps for larger systems.
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Page 1-17
Cleaning requirements are highly site specific, both in frequency and the
level of effort required. For the 30 plants (Section 3) the median frequency
and hours per cycle were 12/year and 5 hours/cycle/100 lamps; this yields a
median of 60 hrs/year/100 lamps. Adding this to the labor estimates discussed
earlier, the total labor is 115 hrs/year/100 lamps to 180 hours/year/100 lamps
for large and small systems, respectively. When normalized to KW at 253.7 nm,
these values are 43 and 67 hours/year/KW.
A labor cost of $20/hr is assumed, encompassing direct salary, fringe
benefit costs and other related administrative costs. This too is a rate that
will vary regionally and must be adjusted accordingly for specific""site"
estimates. Based on these rates, however, the annual labor cost for operation
and maintenance of the UV system is $860 to $1,340/UV KW, depending on system
size.
1.3.2.4 Summary of O&M Costs
In summary, the annual costs (exclusive of capital cost amortization) for
operation and maintenance are:
Part Replacement $1,365/UV KW/year
Power $1,040/UV KW/year
Labor $860 to $1.340/UV KW/vear
Total $3,265 to $3,745/UV KW/year
The reader is cautioned, of course, that these are based on specific
assumptions regarding rates and operating conditions. These would necessarily
be adjusted by factors known for the site. Overall, these estimates are
sufficient for screening the annual costs associated with UV. Considering the
same assumptions used earlier in assessing capital costs (peak to average ratio
of 2.0 for an advanced secondary to tertiary facility), the annual costs
translate to $6,500 to $7,500/year/mgd of average design flow for large and
small systems, respectively.
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Page 2-1
SECTION 2.
STATUS OF UV SYSTEMS AND EQUIPMENT CONFIGURATIONS
This section presents a brief overview of the types of UV systems that are
being used for wastewater disinfection. The distribution of systems is then
given regarding size and type, location, and the trend in the types of systems
finding favor for wastewater applications.
2.1 SYSTEM CONFIGURATIONS
There are several ways in which UV reactors have been configured for the
disinfection of treated wastewaters. The design intent must be to minimize the
loss of UV energy and to maintain a minimum exposure time for all elements of
the wastewater passing through the reactor. This requires close contact of the
wastewater with the UV source, and plug flow conditions within the reactor
itself.
The configuration has evolved, depending during the first generation of
systems on the closed shell, fixed lamp systems. These gave way to open-
channel units that were modular in design, with open access to the lamp
assemblies. Closed shell reactors are arranged such that the lamps (within
their individual quartz enclosures) are held in a fixed position inside the
reactor, in full contact with the wastewater. The centerline spacing is
typically 8 to 12 cm for the lamps, with the flow directed parallel to the
lamps. The reactors are typically gravity flow, with piped inlet andsoutlet.
Because of the higher velocities at the entrance and exit points, and the
change in direction required at each point, these units tend to exhibit a high
degree of dispersion, affecting disinfection performance. The closed shell
configuration also provides poor access to the lamps and quartz for maintenance
and repair. These types of units tended to dominate the market through the
mid-eighties, but very few are being currently specified.
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Page 2-2
A "non-contact" configuration uses Teflon pipes to carry the liquid. These
are thin-walled, and transparent to the 253.7 nm wavelength. The Teflon tubes
are surrounded by unsheathed lamps. The hydraulic behavior of these units is
good, simulating pipe flow. The energy utilization tends to be low, however,
when compared to the submerged quartz systems. Experience with these units was
generally difficult, due to serious fabrication problems, difficult
maintenance, and poor accessibility. These units are hot specified any longer
for wastewater applications.
The open-channel configuration relies on submerging the lamps in the
wastewater in, an open channel; An earlier, design used :a" fixed: lampr reactor :in "
which the entire lamp battery was installed in the channel, with the flow
perpendicular to the lamps. These too suffered problems with fabrication
difficulties, poor accessibility to the lamp battery, and poor maintenance.
These fixed open-channel systems are no longer used.
The newer "second-generation" open channel systems use modular designs in
which quartz-sheathed lamp assemblies are fabricated in multi-lamp modules;
these are then hung in an open-channel, using as many modules as is necessary
for the specific application. Multi-channel configurations can be used, often
with two or more banks of lamps placed in series within a channel. The open-
channel modular design is best suited 'to UV process design and represents
state-of-the-art for UV systems.
The lamp modules are designed such that they can be placed either
horizontally or vertically Into the channel. Figure 2-1 presents.a schematic
of a horizontally configured module. These typically have eight lamps per
module, although smaller systems may use modules with six of four lamps.
Package plant units are typically designed with 2-lamp modules. The Neuse
River Plant in North Carolina will use 16-lamp modules. Variations of the
module itself are provided by various manufactures, although each follows the
basic concept shown on Figure 2-1.
Vertical lamp modules typically contain 28 lamps. A schematic is provided
on Figure 2-2. The quartz sleeves are closed at the lower end and open in the
-------
System UV 2000
Uv Modules in
effluent enonnel.
System UV 2000
UV Module lifted
from effluent
channel.
Figure 2-1 Schematic of Open Channel, Modular UV System
Using Horizontally Placed Lamps
(Courtesy of Trojan Technologies, Inc. London, Ontario, Canada)
-------
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Page 2-5
' *•', -
access box at the top. The lamps can be slipped in and out of the quartz by
opening the box, and are either 36 inch or 64 inch; the majority of vertical
lamp systems used the longer lamps. The quartz are secured at the bottom by a
grid box with rubber grommets to hold the quartz sleeve in place.
2.2 UV SYSTEMS IN THE UNITED STATES
Table 2-1 presents the number of UV systems operating in the U.S. by region
and state. This list was complied from existing records and manufacturers
lists. It is not all-inclusive, although it is likely within 50 to 100 plants
of the total though 1990. The purpose is to show the extent of systems and the
trend of installation through the country, there are also as estimated TOO to
200 facilities in the planning, design/construct phase.
The total number of plants listed is 424; the actual number of facilities
under a complete census is likely between 500 and 600 facilities. UV systems
are noted for 42 of the 50 states. As indicated by Table 2-1 the major
fraction of operating facilities is in the eastern portion of the country.
Regions 1 through 5 comprise approximately 70 percent of the systems. Region 3
has the most facilities, dominated by Maryland, Virginia and West Virginia. UV
applications are least prevalent in the western regions of the country.
2.3 TYPES OF SYSTEMS
Table 2-2 gives the distribution of the various configurations operating
within the United States. This also shows a similar analysis conducted in
1984(1). In the 6 years since, the number of operating plants has increased
ten-fold.
In 1984, a survey identified 53 operating plants. Most were small; 80
percent had design flows less than 1 mgd. Nearly a third were the non-contact
teflon units and half were closed shell reactors. The remainder were open-
channel designs, but only one of these used a modular approach.
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-------
TABLE 2-1. UV SYSTEMS IN THE UNITED STATES
; Region 1; 23 facilities
Connecticut
Massachusetts
Maine
New Hampshire
Vermont
Region 2: 38 facilities
New Jersey
New York
Jlefion 3; 98 facilities
Delaware
Maryland
Pennsylvania
Virginia
West Virginia
Region 4: 44 facilities
Alabama
Florida
Georgia
Kentucky
Mississippi
North Carolina
South Carolina
Tennessee
Region 5: 86 facilities
Illinois
Indiana
Michigan
Minnesota
Ohio
Wisconsin
Region 6: 50 facilities
Arkansas
Louisiana
Oklahoma
Texas
Number of Operating Plants
5
3
4
4
7
12
26
4
30
13
21
30
11
1
3
6
5
12
3
3
2
15
22
6
20
19
19
10
9
2
-------
TABLE 2-1. UV SYSTEMS IN THE UNITED STATES
(Continued)
Number of
Replon 7: 44 facilities
Iowa
Kansas
Missouri
Nebraska
Region 8: 25 facilities
Colorado
Montana
Utah ;• •_ •••- -
Wyoming
Region 9: 7 facilities
Arizona
California
Region 10: 9 facilities
Alaska
Idaho
9
4
29
2
7
6
5
2
1
8
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Page 2-8
TABLE 2-2. STATUS OF UV APPLICATIONS
TO WASTEWATER
Year
Number of Plants
Flows < 1.0 mgd
1-20 mgd
> 20
Closed Shell
Teflon
Open Channel
Horizontal
Vertical
Other
1984
50 to 60
80%
20%
49%
35%
8%
(100%)
8%
1990
500 to 600
50%
47%
3%
-•• 25%
, . ... .. .7* - , .-_,
66%
(85%)
(15%)
2%
In 1990, with a ten-fold increase in plants, there were more larger plants.
Approximately half have design flows greater than 1 mgd, with several greater
than 20 mgd. No new Teflon systems are being installed; these represent only
approximately seven percent of the operating plants. Closed-shells systems are
being installed at a low rate, with very few being considered for new
applications. Approximately, 25 percent of operating systems are closed shell
configurations. A small number of plants (two percent) comprise other designs,
including the older fixed open-channel units and the new medium pressure (four
systems) or alternate lamp systems.
Ths field is now dominated by the modular open-channel designs, comprising
approximately two-thirds of operating systems. Nearly all new installations
use these configurations. Approximately 85 percent of these systems utilize
the horizontal lamp modules.
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Page 3-1
SECTION 3.
EVALUATION OF SELECTED OPERATING UV DISINFECTION FACILITIES
A total of 30 plants were selected for a detailed assessment of their
design, operation and maintenance. Only those with open-channel configurations
were chosen, in keeping with the focus of this evaluation. A random selection
was made, constrained by the desire to have plants of varying size, alternate
system designs, and representation by several manufacturers. The information
w.as. compiled through, .the summer of 199.0 on the basis of ..supplier djata--and-
direct contact with the plant owner, operator, and/or engineer. The thirty
plants are identified by their location:
Alabama
Colorado
Delaware
Indiana
Kansas
Kentucky
Maryland
Louisiana
New Hampshire
New Jersey
Oklahoma
Pennsylvania
Athens
Ozark
Waldron
Gunnison
Bridgewater
East Chicago
Olathe
Cave City
Edgewater
Jessup
Clearsprings
Abbeville
Olla
Hanover
New Providence
Okmulgee
Dewey
Owesso
Highspire
Willow Grove
Warminster
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Page 3-2
Tennessee Colllerville
Virginia Accomac
Stoney Creek
West Virginia Petersburg
White Sulphur Springs
Williamson
3.1 DESIGN AND PERFORMANCE OF THE SELECTED PLANTS
The following discussions present an overview of the selected plants with
respect to their size, the type of treatment processes they use, and a
description of the-, type arid -size"-oft"?He'UV"syst;emsT 't.^e^ac'ti^f^etfdi^n'c^.^
the plants relative to their permit requirements is then presented.
3'1-1 Description of the Selected Plants with Open-Channel UV Systems
Table 3-1 lists the selected plants, the facility contact, a summary of the
treatment plant unit operations, and the type of UV disinfection system used by
the facility. The flow rating is shown on the basis of peak design, average
design and current average flow. Note that UV systems are generally designed
on the basis of peak flow. The average design flow ranges from 0.2 mgd
(Clearsprlngs) to 15.0 mgd (East Chicago). The ratio of the peak design to
average design flow rate is typically between 1.5 and 3.0. The highest ratio
is at Olathe (4.0). Two plants (Dakota City and Jessup) have flow
equalization. The lower ratios are generally associated with the smaller
plants.
Eleven of the selected plants have design average flows of 1.0 mgd or less.
For convenience, these are separated to Group A:
Waldron Leadwood
Bridgeville Olla
Dakota City Dewey
Cave City Stoney Creek
Edgewater Petersburg
Clearsprings
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Page 3-6
All of these accomplish nitrification a minimum, with tertiary filtration
at three of the plants (Waldron, Bridgeville, and Clearsprings). Except for
two of these smaller plants, they use oxidation ditch/extended aeration
activated sludge treatment technologies. The two are the Edgewater plant
(wetlands) and Olla (aquaculture pond for water hyacinths). Except for the
Edgewater and Clearspring plants all practice some form of screening and grit
removal upstream of the biological system. Note that the Edgewater plant has
UV disinfection at an intermediate point and at the final effluent in the
constructed wetlands system.
The UV systems for these .smaller.plants.were j?tarted in l.?87_jQr later, with
the most recent startup in 1990 for the Cave City plant. Oniy onf ^TT
retrofit (Clearsprings). Two of the plants (Dakota City and Stoney Creak) use
the vertical lamp configuration, one of which (Dakota City) is equipped with a
mechanical wiper. The others use the horizontal lamp placement configuration
The Waldron plant has had problems with flooding due to high I/I input, well
above the design peak flow. Three of the plants are well under design capacity
at this point: Bridgeville (25 percent), Edgewater (16 percent), and Leadwood
(30 percent). Four are at approximately one-half their design capacity: Cave
City, Clearsprings, Dewey and Stoney Creek. The remainder (Waldron, Dakota
City, Olla and Petersburg) are at or near capacity.
Eleven of the selected plants have design average flows between 1 and 3.0
ngd (these are shown as Group B on Table 6-1):
Ozark
Jessup
Lebanon
Abbeville
Hanover
New Providence
Owasso
Highspire
Accosaae
White Sulphur Springs
Williamson
The facilities were constructed 1987 through 1989. Two were retrofits
(Lebanon and New Providence). The New Providence plant was originally equipped
with an Arlat system; this was replaced with equipment by Fisher and Porter in
1990. The plants all provide for nitrification; two are two-stage trickling
filter plants (Ozark and New Providence) and the rest are oxidation ditch
-------
Page 3-7
and/or extended aeration configurations of the activated sludge process. Two
of these have tertiary filtration (Jessup and Lebanon).
Three of the UV systems use the vertical lamp configuration (Ozark, Owasso
and Highspire). The Ozark units have hydraulic problems, vith flooding
occurring at flows greater than 3.5 mgd, which is still well below the peak
design flow of 5.25 mgd. The Lebanon plant had serious startup problems
relating to electrical and hydraulic design; the units were subsequently
rebuilt in late 1989. Except for the New Providence plant (25 percent) these
plants are at or above 50 percent of their average design flow capacity. Due
to high I/I conditions, the Abbeville plant experiences flow greater than
design.
The remaining eight plants (Group C) have design flows greater than 3.0
mgd, with the largest being East Chicago (15 mgd):
Athens Okmulgee
Gunnison Willow Grove
East Chicago Warminster
Olathe Collierville
The plants all have nitrification capabilities using extended aeration
activated sludge systems, except Athens, Olathe and Okmulgee which have two
stage fixed-film or fixed-film/activated sludge configurations. Five of the
eight UV systems are retrofitted into the old chlorine contact chambers. Three
(Athens, Gunnison and Okmulgee) are new systems. All were installed 1987
through 1989; three are vertical lamp units (Gunnison, Okmulgee and
Collierville). Note that in Gunnison a third channel had to be added when the
two existing channels were unable to meet effluent limits. There was a
problem with the level control gate at Olathe during startup; this was
corrected by adjustment of the weights on the mechanical gate. Two of these
plants are well below their design capacity: Gunnison and Olathe (approximately
25 percent), while three (East Chicago, Willow Grove, and Athens) are greater
than 90 percent of their design capacity. The remaining 3 are near the 50
percent capacity point.
-------
Page 3-8
Overall, of the 30 plants selected for evaluation, all are designed to
treat to nitrification levels at a minimum, and several have tertiary
filtration. These conditions suggest that, in general, the facilities using UV
have advanced secondary or tertiary processes, yielding effluents that are
especially conducive to the application of UV. Eight of the plants use the
vertical lamp configuration, somewhat higher in proportion to the horizontal
configuration than Is apparent in the overall census. Eight of the 30 are
facilities that have retrofitted their UV systems into existing chlorine
contact chambers, a procedure that is becoming popular with larger facilities,
and plants that are being upgraded.
Generally, the plants vary in their capacity relative to design. About a
third each are at approximately 25 percent, 50 percent, or 100 percent of their
design capacity.
3-1-2 Description of th*. TJV Systems at
elected p-)
Table 3-2 is a summary of the UV Installations at each of the selected
plants. This is divided into the same groupings as shown on Table 3-1. The
descriptors Include the type of configuration, the number of channels and banks
of lamps (that are placed in series in a given channel) , the design flow per
channel and the level of redundancy. The next three columns give the number
of modules and lamps per channel, the size lamps that are used, and the total
size of the system with respect to the number of lamps and the equivalent UV
output at 253.7 nm. The lamps are 1.47m (58 inch) or 0.76m (30 inch) in size.
Several ratios are then given to compare and assess the sizing characteristics
of each plant. These include the ratios of flow per lamp and the £lw per
killowatt (kW) In units of gpm and Lpm per kW, based on the peak design flow.
All of the smaller plants (Group A) are designed with one channel. Of the
two vertical lamp systems, the Dakota City plant has one bank of modules and
the Stoney Creek is divided into four banks in series. Three of the plants
with horizontal configurations have only one bank of lamps (Clearsprings ,
Leadwood, and Dewey) , effectively precluding standby and flexibility for
shutdowns and repair. The remaining six smaller plants have two banks in
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Page 3-12 J
series, three of which (Waldron, Olla, and Petersburg) are sized such that a
single bank will disinfect at peak flow (100 percent redundancy). Having at
least two banks allows for shutdown/repair of one bank, while still maintaining
disinfection capabilities. Channel repairs are not possible without bypassing,
given only one channel; disinfection .would not be possible under these
bypassing circumstances.
The design loadings vary from 0.38 mgd per kW (Bridgeville) to 5.0 mgd per
kW (Leadwood). The higher value appears to be an aberration; the loading
values typically fall between 0.4 and 1.7. The average was 1.27 mgd per kW, or
0.91 mgd per ;.kW without _th.e jLeadwppd .Iplant;;~~- ;This AS : also-equivalent - to 1.1 --
kW/mgd. The last column lists the loading in terms of the rated flow per unit
UV watt; this averaged (without the Leadwood plant) approximately 2.4 Lpm per
UV Watt. Note that the power ratings are based on rated nominal UV (at 253.7
urn) output for low pressure mercury arc lamps; this is 26.7 watts per 1.47 m
lamp and 13.5 watts per 0.75 m lamp.
Several plants in this group experienced minor electrical problems,
primarily during startup, which were eventually corrected. The Bridgeville
operators complained of high costs associated with the lamps and quartz
replacements. This is a system installed by Arlat that requires shipment of
the modules back to the factory for replacement of the parts, effectively at a
rate of approximately $200 per lamp. This is excessive, and is not comparable
to any of the other manufacturers. The Cave City plant has a backup
chlorination unit in the case of UV failure; they have not had to use it to
date. Note that there were some difficulties with the quartz/lamp seals to the
module frames, resulting in leakage and kickout of the respective breaker.
This has been corrected by the manufacturer.
The moderate sized plants in Group B also are primarily limited to a single -
channel to handle peak flow. Three of the 11 have 2 or more channels (Ozark,
New Providence, and Owasso). Only Jessup has redundancy, whereby one of the
two banks is capable of handling the peak condition. Each plant except for
Accomac and Williamson has two or more banks within a channel that are operated
according to flow. The Accomac plant has equalization and is equipped with a
-------
Page 3-13
backup chlorination unit. The Williamson plant has a unit that allows for
variable water levels in the channel; with increasing flow (and level),
additional rows of lamps are activated. This unit had serious hydraulic
problems of mixing and shortcircuiting caused by improperly designed upstream
baffles. These were replaced by an upstream stilling plate that corrected the
problem and allowed the plant to be in compliance. The Lebanon plant had to be
rebuilt due to electrical problems and excessive lamp failures. The channel
was also modified to correct upstream flooding problems. Brought back on-line
in late 1989, it has since been operating successfully.
The system sizing for these plants appears to be moire consistent than
observed for the smaller plants. The range is between 6.7 and 1.65 mgd per kW,
with an average of 1.0 mgd/kW. This is equivalent to a loading of 2.6 Lpm/W.
The third grouping, comprising plants with design average flows of greater
than 3.0 mgd, have systems with one to three channels. Three of the plants
have only one channel. These are Athens, Willow Grove and Warminster; Athens
is designed to have one of its two lamp banks fully redundant under peak
loading. Note that Willow Grove and Warminster are both retrofits. The
remaining plants have two channels, except for Gunnison, which has three. The
horizontal lamp units all have two banks in series in each channel; the
vertical lamp units vary from two to four banks in series. Problems were noted
at two of the plants (Okmulgee and Warminster) relating to electrical and
hydraulic difficulties; these were corrected.
The size of the systems range between 0.5 and 1.68 mgd/kW, except for
Olathe which is designed at a loading of 3.25 mgd/kW. Similar to the Leadwood
plant in Group A, the Olathe plant is an outlier. Both plants have high peak
to average flow ratios (4.0 and 3.0 for Olathe and Leadwood, respectively),
which likely means that the systems were designed for a value less than peak
(e.g. 7-day average) for disinfection purposes. Without Olathe, the average
design loading is 1.0 mgd/kW. This is equivalent to 2.6 Lpm/W.
Overall, the selected plants show a certain consistency in their
configurations. One to three channels are used, with a single channel in the
-------
Page 3-14
smaller plants and the multiple channels found with the larger plants. Most of
the larger systems have some flexibility in operating banks of lamps within the
channel, although this is not always the case. Redundancy to any degree, is not
typical; only 5 of the 30 plants have redundant systems, and 4 of these are
with the smaller plants. Flexibility appears to be limited, with little
ability to isolate a portion of the system for repair or replacement. Bypasses
were not evident with most plants, suggesting a difficulty with
repairing/shutting down channels when only one channel exists.
Sizing of the units appears to be relatively consistent, falling between
0.5 and 1.7 mgd/ktf, with an average^.ssentially\equivalent to 1.0 mgd/kW. This,
is demonstrated in Figure 3-1, which presents the peak design flow of the plant
as a function of the total UV power (kW at 253.7 nm) of the UV system. There
is some scatter, particularly with the outliers discussed earlier (Leadwood and
Olathe), but the slope of the relationship closely approximates 1.0. Thus, a
rough sizing estimate can be made for a given plant by assuming 1 kW of UV
output for each mgd of peak design flow. This would be for advanced secondary
plants, and peak to average flow ratios less than 2.5. The 1.0 kW is the
nominal UV output, equivalent to approximately 37 long lamps (1.47 m or 58 inch
arc length) or 74 short lamps (0.75 m or 30 inch arc length). Such an
approximation should only be used in screening type assessments and should not
serve as a final design sizing parameter. Note also that redundancy or standby
capabilities would be added to this estimate.
3•1•3 .Summary of Performance and Permit Requirements at the Selected Plants
Table 3-3 presents permit and effluent data for each of the selected
plants. The UV system is first reiterated in terms of type, size, and year of
startup. The permit requirements are then summarized with respect to the BOD,
TSS, nitrogen, and bacterial limits. The current quality of the effluents is
then summarized, addressing these four parameters. Note that these data
reflect the six months prior to the summer of 1990. If appropriate, the permit
description includes seasonal requirements, particularly with respect to
nitrogen control and disinfection.
-------
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Page 3-19
The permit requirements vary widely, ranging from secondary levels of BOD
and TSS (i.e. 30/30) to advanced secondary with ammonia removal or some form of
nitrogen control, particularly on a seasonal basis. Eighteen of the plants
have requirements greater than secondary levels; almost all the plants
accomplish some degree of nitrification because they are low-loaded systems
(extended aeration, oxidation ditches, two-stage biosystems, etc.). This is
evident from the consistently low levels of BOD and TSS (and nitrogen in cases
where it is measured) in the treated effluents.
All except two plants have fecal coliforms as the primary indicator.
Waldron has no limitj .while the Hanover permit.is written on the basis^f total
coliforms. The Hanover plant has a not-to-exceed total coliform limit of
240/lOOmL, which is restrictive and somewhat analogous to the shellfish limit
of 14 fecal coliforms per 100 mL. The effluent has been close to this limit,
varying between 200 and 220/lOOmL. The plant is at approximately 60 percent
capacity and keeps both banks of lamps on in its single channel. It is not
clear that the facility will be able to stay in compliance as it approaches
design conditions.
The Lebanon plant must comply with a 30-day maximum average of 400 fecal
coliforms/100 mL and a single point maximum of 1000 FC/lOOmL. The facility is
meeting its requirements, and is currently at effectively full capacity.
Recall from Tables 3-1 and 3-2 that this was a retrofit that had to be rebuilt
in late 1989. Two plants, Edgewater and Olla, have low fecal coliform limits
of 14 and 25 FC/100 mL (30-d maximum average), respectively. Each is producing
a high quality effluent with fecal coliforms less than 2/100 mL.
The large majority of plants are required to meet standard secondary limits
of 200/400 on a 30-d/7-d basis. All are meeting their permit requirements,
although a number of plants tend to have significant effluent densities. The
Dakota City plant measures fecal coliform densities only slightly less than
permit, ranging between 160 and 180 FC/100 mL. It is at approximately 85
percent capacity and may require enhancement of its UV system. The New
Providence plant is at only 25 percent capacity, but is measuring higher and
variable levels in its effluent. Similarly, Dewey, Stoney Creek, Highspire,
-------
Page 3-20
and Williamson are measuring elevated levels (but within limits) in the
disinfected effluent.
Several plants have high permitted fecal coliforms levels. These are
Athens, Gunnison and Ozark; the 30-d limit for the Gunnison plant is 6 000
FC/100 mL. while it is 1000 FC/100 mL for the other two plants. In each case,
the UV systems are in compliance. At .Ozark, only seasonal nitrification is
required. Fecal Coliforms are.typically less than 100/lOOml when the plant is
nitrifying, but rise to 700 to 800 FC/lOOmL when the plant is not nitrifying.
This is due to the increased quality of the nitrified effluent, reflected by
higher UV transmittances and lower initial coliform densities. '
3>1*4 Design Sizing and Performance Summary for the Selected Plants
Table 3-4 is presented as a summary of the design sizing and performance
record for each of the selected plants. This information is drawn from Tables
3-1, 3-2 and 3-3, and presents the size of the treatment facility the
configuration of the UV system, its size, and the quality of the effluent
relative to BOD, TSS, nitrogen and coliforms. Each of the plants is generating
a quality effluent and is in compliance with its permit. Those that are
accomplishing a high degree of nitrification are also discharging minimal
levels of coliform. In cases where the BOD and TSS levels tend, to be at levels
greater than 10 mg/L, the effluent coliform levels also tend to be more
pronounced, with measureable densities between 10 and 200 FC/100 mL.
UV disinfection efficiency is very dependent upon the quality of the
effluent generated by the upstream processes. As higher levels of treatment
are accomplished, the UV process is more efficient, resulting in the need for
less hardware, or providing for a greater factor of safety Thus
nitrification, denitrification, filtration and other tertiary processes that
are added to conventional secondary treatment operations are particularly
conducive to assuring the success of the UV process. The impact on water
quality is generally represented by lower coliform densities, increased
sensitivity of the bacteria to UV, and increased UV transmissibility at 253.7nm
by the wastewater. An interesting observation made from this assessment was
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Page 3-22
the lack of any data regarding the incoming colifonn densities and the
transmissibility of the effluent. The plants did not measure these parameters
even in cases where there may have been difficulties and the data could be used
for troubleshooting.
3.2 EVALUATION OF THE OPERATION AND MAINTENANCE OF UV SYSTEMS
The review of the selected plants entailed an assessment of the 0 and M
practices associated with the disinfection system. This was based on
discussions with the plant operators and focused primarily on the routine
maintenance^ tasks ^ parts replacement and. system .cleaning. Some discussion
also addressed any difficulties encountered with the system, "the met*^s~ u^T
for system control, upstream screening devices, and routine safety practices
The first part of the following section will focus on operations; cleaning
practices will be addressed separately.
Table 3-5 presents a summary of information relating to 0 and M of the
selected UV systems, exclusive of cleaning activities. First the type of unit
and its Si2e are reiterated, including the startup year, for each of the thi
Plants. This Is the same Information from Tables 3-1 and 3-2. The next series
of columns presents the rate of replacement for the lamps, quartz and ballasts
the estimated labor associated with this task, and the criteria used to
Initiate lamp replacement. The replacement cycle could be estimated fairly
well for the lamps. It Is based on the operators criteria for replacement and
accounts for seasonal/year-round use of the system, and the probable system
utilization rate. Thus if the system is operated on the basis of flow the
utilization would be approximately 50 percent; this would increase up to 75 to
100 percent if the system was operated manually and was basically kept in full
operation as a matter of convenience or to assure compliance.
As shown on Table 3-5, the lamp replacement rate varies from 25 to 50
percent per year. Exceptions are the Williamson and Dakota City plants. These
replace the full Inventory of lamps after 7,500 hours operation, which is the
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Page 3-28
operating life generally stated by the lamp manufacturers. This is equivalent
to a rate of greater than 100 percent per year if year-round disinfection is
practiced. Olathe and Owasso replaced their lamps after 10,000 hours of
operation in order to improve performance. Ozark has a fixed 10,000 hour
replacement cycle. In general, however, one can expect to get greater than
12,000 hours of operation from the conventional low pressure lamps, when used
in the submerged, open-channel configuration. Gunnison has greater than 10,000
hours; Clearsprings, Dewey and Hanover each have greater than 14,000 hours
operation; and Highspire replaced their lamps after 17,000 hours operation, at
which point the coliform levels had begun to increase.
Three of the plants have units "supplied byT ^at. ^ ^ese Vr^r~r^~
level of effort to replace the lamps, using clips and heat-shririk seals; in
some cases it requires that the modules be returned to the factory for
replacement. This has been found to cause excessive costs, as cited by the
operators at Bridgeville, Abbeville, and Williamson. A fourth plant (New
Providence) had originally been using Arlat equipment; this was replaced with a
Fisher and Porter system in 1990.
The criterion for failure is generally lamp failure and or increasing
coliform densities (except at those plants with fixed operating cycles as
discussed earlier). Generally, its appears that the latter condition would be
the final trigger. The high operating life cycles that are being obtained
suggest that the lamps will not fail (i.e. electrode failure, shutoff); rather
their output will deteriorate to such a degree that there is insufficient
germicidal energy for effective disinfection. The lamps are replaced at this
point to restore the system efficiency. For design purposes, a reasonable
estimate of operating life would be 14,000 hours; thus the replacement rate in
a system with year-round disinfection, and an average 50 percent utilization,
would be approximately 30 percent per year:
((8,760 hours/year)/(14I000 hours/lamp)) x 50 percent - 31.2 percent
With the smaller systems, and to a lesser extent the larger plants, it
appears that the tendency is to operate the full system (75 to 100 percent
-------
Page 3-29
utilization) at all times instead of controlling it on the basis of flow. This
would increase the replacement rate for the above example to 50 to 60 percent
per year. If disinfection is required on a seasonal basis the replacement rate
is reduced to 25 to 30 percent per year.
Regarding the quartz sleeves and the ballasts, it is not possible to make a
direct assessment of their expected life cycle. The experience with full scale
systems, particularly with respect to the open channel submerged units, is
limited, covering a period of approximately five years. This is not sufficient
to evaluate in-field experience for long-term replacement rates of the quartz
and balTas ts. Many of -the replacements ~ curf eritly reported by operators have:
been due to breakage and electrical wiring failures, reasons ttiat do not speak
to the degradation or failure of the components themselves.
The quartz will degrade due to sol'arization of the quartz structure,
resulting in a cloudiness of the quartz and a loss of transmissibility.
Abrasion of the surface due to long-term exposure to the wastewater is also a
contributing factor to their deterioration. There is no current feedback on
replacement of the quartz for these reasons. At this point, an estimate that
may be appropriate is a replacement rate of 10 years, to account for minimal
breakage and for deterioration of the quartz.
Similarly, there Is little experience with ballast failures and replacement
rates. Earlier failures have been attributed to improper electrical design
and the lack of proper ventilation in the ballast cabinets. These difficulties
appear to have been corrected, although there are still reports of electrical
problems with a few installations upon startup. This was the case with the
Lebanon, Abbeville, Hanover, Williamson, and Athens systems. Ballasts are
expected to have long lives, particularly based on the experiences with those
found in normal fluorescent lighting fixtures. For purposes of life cycle
assessments with UV disinfection systems, a 10 year replacement period is
suggested.
The effort required for replacement of these key components (largely the
lamps themselves) is relatively low. The estimates shown on Table 3-5 are
-------
Page 3-30
based on discussions with the plant operators and their estimate of time
reqUirements over specific
g amp^ ^ so^
allowance for occasional replacement of ballasts and quartz sleeves This is
• also shown on Figure 3-2, which presents the hours spent per year against the
number of lamps that would be replaced per year. The mean is 0.4 hours per
lamp or 24 minutes per year. There is significant variability, with the rate
ranging from approximately 10 minutes to 50 minutes per lamp. Note that this
is total labor, even if two people are engaged in the activity (which tends to
be typical).
This analysis can be used in screening the labor and parts replacement
costs for UV systemsV "One should be carefuT to acknowledge how the' sys^wSf
likely be operated in terms of utilization; recall that the tendency is to have
rauch of the system on at a given time, regardless of the flow. Also account
for the year-round versus seasonal disinfection requirements. Note also that
these charges could be incurred in discrete intervals, rather than be spread
out somewhat evenly over a period of time. This results from the lilcelihood
that the operators will replace all the lamps at once, triggered by the overall
operating time and a decrease in disinfection efficiency, as discussed earlier.
A second labor factor is presented on Table 3-5. This is an estimate of
the time required, on a yearly basis, for activities other than replacement of
the lamps/quartz/ballasts and cleaning. These would include system monitoring
and sampling, area maintenance, component repair/replacement, etc. This tends
to be a factor of two to six times the amount of time estimated for the
replacement of Key components. When added to the parts replacement activities,
the total time required outside of routine cleaning needs (discussed in a later
section is estimated. These data are shown on Table 3-5 and plotted on Figure
3-3, which presents the total hours per year as a function of the system size
There is some scatter, particularly with the smaller plants. For the 14 plants
with less than 150 lamps, the mean labor requirement was 120 hours per 100
lamps The equivalent mean for piants with more than 150 lamps was 55
hours/100 lamps.
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Lamps/Quartz/Ballast
Mean 0.4 hrs/Iamp/year
50 100 150 200 250
REPLACEMENT RATE (LAMPS/YEAR)
350 400 450
Rgure 3-2
Labor Requirements for Replacement of
Lamps/Ballasts/Quartz
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10
Total O&WI (w/o Gleaning)
<150 120hrs/100lamp/yr
>150 55 hrs/100 lamp/yr
20
0 60 100 200 400 600 1000
NO. OF LAMPS M UV SYSTEM
SDOO 4000 6000
Figure 3-3
Estimate of O&M Labor (Exclusive of Cleaning)
-------
Page 3-33
The next series of columns on Table 3-5 addresses upstream protection for
the lamps, level control devices, and the method used for system control.
Upstream devices such as screens are used to protect the lamp battery from
debris that may reach the UV system and cause damage to the quartz/lamp
assemblies. Other problems occur from algae sloughing off the clarifiers and
leaves falling into the channels; these catch on the lamp modules and
accumulate, creating additional head loss problems and maintenance tasks. From
Table 3-5, three of the plants are noted to have filters (Clearsprings, Jessup
and Lebanon); these are installed for tertiary solids removal and will also
effectively remove unwanted material from the flow-stream. The plants report
no difficulties with debris in the UV channel.
One plant (Accomac) has a grating placed upstream of the UV units. This is
effective in removing debris, but the operators do note that algal mats are
still able to pass through and cause problems with the UV units. Seven plants
have either bar or mesh screens, ranging in size from one-quarter inch to 2
inch openings (Cave City, Gunnison, Stoney Creek, Ozark, Owasso, Highspire, and
Okmulgee). These all report no problems with debris or sloughed material
fouling the UV modules. Okmulgee reports that the screen is very effective in
removing algal mats from the wastestream. All of these devices are cleaned
manually.
Of the remaining 19 of the 30 selected plants, 12 report that they have no
problems relating to debris or sloughed material. The other seven state that
they do, however. The Waldron plant has experienced breakage of the quartz
from debris entering the unit during periods of bypass. At both Olla and New
Providence, leaves tend to enter the channel and accumulate on the modules.
Olla is installing a screen. Abbeville receives excess debris during high flow
periods; this problem is also reported by the Williamson plant. Both the
Athens and Willow Grove facilities complain of algae sloughing from clarifier
and channel walls and accumulating on the lead module frames.
Overall it appears that the installation of an upstream screening device is
an option that most plants do not choose. From this assessment, however, it
also appears that it is most appropriate to have one in place. These can be
-------
Page 3-34
simple, large-mesh (0.5 Inch) screens (stainless steel), that can be slipped in
and out of the channel manually for cleaning on a frequent basis. This will
save considerable labor if the alternate is to clean the debris attached to the
individual modules. An alternate device that may be more convenient to the
operator would be a bar screen that can be raked (a moving mesh or bar screen
that is self-cleaning would not be cost-effective); this would still have to be
removed periodically for a thorough cleaning. Note that it is important to
remember that these devices, particularly as they accumulate material will
impose a headloss; this must be accounted for when considering the hydraulic
design of the facility.
A critical operating requirement is that the water" level in th7~ch«rneT
must be kept fairly constant. If it fluctuates widely (greater than plus or
minus one inch from the control level), several problems can occur In
horizontal systems the top row of lamps can either be exposed or the depth of
water above this row.can become so great that disinfecting effectiveness of the
unit is compromised. In vertical units this same problem occurs, except that
the top portion of each lamp is affected. In the Arlat systems, the water
level was allowed to vary, using a fixed dowstream weir; in this case a level
sensor would turn on successive horizontal rows of lamps (Bridgeville
Abbeville and Williamson). In this way the exposed lamps would not be
operating. Adjustable weirs have also been used, with motorized actuators that
respond to level sensors. These are used at Cave City. Manually adjustable
weirs are used at Ozark, Highspire, Accomac, Owasso, Gunnison, and
Collierville.
The remaining plants all use a mechanical level control gate to maintain
the desired level. These rely on field setting and adjustment of the counter-
weights to assure the proper level control over a range of flow rates. They
have generally been very successful and comprise the dominant method for level
control In open-channel systems. Problems are noted, however, at low flows and
at plants that have no flow at times. The gates will oscillate and cause wide
fluctuations in level. They are not designed to be watertight and will allow
the channel to drain during periods of, very low or no flow.
-------
Page 3-35
The method of level control should be carefully considered In the design of
a facility. The mechanical gates would be the preferred device in most cases,
particularly larger systems in which multiple channels are used and the channel
velocities can be maintained within a reasonable operating range. If there are
low flow periods (or no flow), fixed weirs may be more appropriate. Sufficient
weir length must be provided, however, to avoid excessive level fluctuation.
This can be accomplished by using serpentine weirs and weir launders. An
alternative is to use a motorized adjustable weir slaved to a level sensor.
System control has generally been kept simple with the newer open channel
Uy units. This_has been limited to pacing the operation of multiple channels
and banks to the flow rater This is 'typical of the larger plants. In this
evaluation, 11 of the plants practice automatic flow pacing (Olla, Ozark,
Abbeville, New Providence, Owasso, Highspire, Williamson, East Chicago, Olathe,
Warminster and Collierville). Except for Olla, all have design average flows
greater than 1.0 mgd. The Okmulgee plant has automatic flow pacing
capabilities, but prefers to keep the system on manual control.
Of the 19 plants that are controlled on a manual basis, only 11 of these
attempt to vary the number of lamps in operation as a function of the flow to
the lamps. Thus, as an example, Willow Grove will operate with one bank on
(there is only one channel), and bring the second bank into service when the
flow exceeds 7 mgd. The remaining 8 plants simply operate with 100 percent of
the lamps on at all times (Dakota City, Edgewater, Clearsprings, Leadwood,
Dewey, Petersburg, Hanover and White Sulfur Springs).
The manner in which the UV system is controlled should be a function of the
type and size of plant. Above all, it should be kept simple; the objective is
to conserve the operating life of the lamps (and the associated power
utilization). This becomes increasingly important with the larger plants
(greater than 150 to 200 lamp systems), and more practical. With the small
plants, it may be best to have the full system in operation, exclusive of the
redundant units incorporated into the design. Manual control and flexibility
should be available as the system increases in size, enabling the operator to
bring portions of the system (i.e. channels and banks) into and out of
-------
Page 3-36
operation as a function of flow and performance. Automating this activity
becomes advantageous as the system becomes larger, using multiple channels.
Safety is Important in the operation of UV systems, centering primarily on
protection from exposure to UV radiation. This affects the eyes with a
r::irc:°nT - *<~-- - —* M.. that can last
be -• "~ *» -" —
burned upon exposure to W at these wavelengths. Exposure risfc is generally
LH 'Jd " ** °PeratInS lmPS ^ SUblIerged »d - ^ ^"-J
are Shielded. The danger arises if the la.Ps are operated in air; this shou!d
'irT''"^'i^'"ii*>rti^'*ti^e~"^'^^-»^'«
with safety tnteriocks that shut off operating «odules If they are
Tt T C"almel- ElMtriCal ^^ ^ °Inl— ^ - '™^»»
ground fault interruption circuitry with each operating «odule. This feature
wlth
exposure to UV radiation are straightforward. UV
, with side shields, should be worn at all times In the general
fc ^ * that '
,
s for full protection. Exposure of skin should be Minimized, using long
sleeved shirts and buttoned »ects. as examples. Signs should also he p'os
"he u! r rent 8nd In *• £enerai a
"' " ' °lni^- °f
• =
s ricter rules after an eye injury had occurred. Signs are also ped
trainins i
00 startup, and this does not always
occur. At best, safety issues and training renting to the «V syste. shouid be
be incorporated into the plant's normal safety program.
oBerti Ca C— C ln ««-
operation and performance of the W process. This is a simple task, entaill^
-------
Page 3-37
routine cleaning of the quartz sleeves with a standard agent. It is one that
has at times been overlooked, however, resulting in apparent failure of the UV
process because the quartz surfaces have become fouled and have lost their
transmissibility. The fouling is most often due to the deposition of
inorganics such as calcium or magnesium carbonates and iron. Greases or
biological films can also adhere to the surface. The key task is to anticipate
this and to have a fixed protocol for maintenance of the quartz surfaces.
The key elements of cleaning open-channel systems entail isolation of the
modules (either in or out of the channel), selection of a cleaning agent,
development of a method, the time required to accomplish the task, and the
criteria that trigger the need for cleaning. These factors were reviewed-for~
each of the selected plants and are summarized on Table 3-6. The assessment
showed considerable variability among the plants, making each case somewhat
unique. Essentially all are successful, using methods that are relatively
simple, easily applied, and which fit specifically to the conditions of the
facility. This is a marked improvement from the earlier system configurations
using closed shell, fixed in-channel, and teflon pipe designs (20). These
systems suffered serious problems relating to the ability to keep the quartz or
teflon surfaces clean and the access to the quartz for such maintenance tasks.
In-place cleaning is practiced at four of the selected plants: Dakota
City, Ozark, Okmulgee, and Collierville. This involves isolating the UV system
within the channel by upstream and downstream slide gates, and recirculating a
cleaning solution within the UV system. Agitation is generally provided
through air diff users (perforated pipes) at the bottom of the channel. The
spent cleaning solution is typically discharged back to the head end of the
plant or to a tank for reuse. The in-place method is not common to the. open-
channel designs, except those that use the vertical lamp modules. Each of the
four plants in this assessment are vertical lamp systems; note that the Dakota
City plant also has a mechanical wiper.
Each of the four plants uses a citric acid solution as the cleaning agent.
At Ozark, the in-place cleaning is conducted approximately once every two to
three weeks (equivalent to about 21 cycles per year) by recirculating the
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solution for approximately four hours in each channel. The modules are removed
once per year to manually clean the individual quartz sleeves. The facility
has reported difficulties with grease deposits on the quartz, suggesting that
the citric acid may not be the most appropriate cleaner, or that an additional
detergent type cleaner should be used periodically. The frequency of cleaning
is dictated by rises in effluent coliform densities. This is the only plant,
of the thirty, that reported problems with the quartz, indicating that the
sleeves showed evidence of etching and frosting (solarization) after only two
years use. This is unusual, and there was no immediate explanation as to the
cause of this early quartz deterioration. The operators also complained of
"£nad¥quaterwbrkspacer ricT area was pfovided between the two channels, .making it:
difficult to access the modules.
A similar procedure is used at Okmulgee and Colliervile. At Okmulgee the
cleaning is done on a routine weekly basis (at 50 Ibs citric acid use per
cycle), while the recirulation is conducted once per six months at
Collierville. As mentioned earlier, the Dakota City system is fitted with a
mechanical wiper. This is not a commonly used device, particularly with the
open-channel systems. The plant is satisfied with the unit, and has not had to
conduct an in-place recirculation cleaning in the first eight months of
operation. The operators anticipate removing the modules and cleaning them
manually on a yearly basis.
Two plants use dip tanks: East Chicago and Highspire. These are also
vertical lamp module systems, in which the modules are removed from the channel
and placed in a tank containing a recirculating cleaning solution. In both
cases, citric acid is used as the cleaning agent. The modules are allowed to
soak for a period of time, then rinsed and placed back in the channel. At
Highspire this is done approximately once per month, generally on the basis of
rising effluent coliform densities. Note that the plant adds an iron salt for
phosphorous removal, which may add to the fouling effects on the quartz. This
is also the case at East Chicago, which anticipates a frequency of once per
year based on limited experience (it started in 1989), using the water quality
meter to determine when cleaning is necessary. The plant finds the procedure
to be efficient and effective; two people are used, handling five modules at a
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Page 3-42
poas
pounds) and access Is good.
earlier *"•" (15
Note that the use of dip tanks Is gaining favor
with «ost new system. Deluding those ^ horlzontal congura0
These can be In . fixed location or rolled on wheel, to each ban, of «odu LT
An example Is shown on Figure 3.4 whlch ls . sketch of . ^^ ^ ^
placTi JT"" m°dU1"' "0dUUS "" "^ ***«^** ««- •*• *«-l and
LTV ? r'°irOUlatinS bath' " IS th™ «— on the rao, above the tanK
to drain, where It can be physically wiped and/or rinsed with dean water In
certain ca5es,: a cage^ system Is being, devised .to enable removal .of, banks of
oTt T t/hamel (VIa a movins '^h^^^^f^^^T^s
«P tank ^s „ especlauy usefu! .t larger p!ants. At present this Is
Planned for the Nuese River p!ant In Ralelgh-Durh^, North Carolina, and th
LOTT plant in Olympia, Washington (10).
chanTl Tlnl"S " Sel"ted Pl'ntS "ly °n "°°Vil °£ the —I" *- *»
Channel and manually cleaning the.. F1ve of these plants have a rack to hang
the .odules on BhUe the operator cleans lt: Haldron, BrldgevlUe. Edgewater
Ubanon. and Abbeville. tte others lay the modules on th. flo r, rest U
r have a second person how
pl
people to llft the nodulM oney reekj ^
of the wastewater Is relatively high, requiring .onthly cleaning. The
freouency Is set by observation of rising confer, levels. This partlcuU
Plant uses .urlatlc acid to remove the lroM stains that deposit on tl ouart*
:i:c;:;echeAr:rial is appi;" to the *— - •*- — - --
are r± d f °""° * C°mer°lal '"^ '"-:*«• 1. used. The modules
InsltTesT ^ ^^ " ' "" °* — '" »°"th
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Page 3-44
Waldron uses a commercial tile and bowl cleaner, cleaning on a routine
twice per month frequency. They also hose down the channels each time the
modules are cleaned. The modules are hung on a rack, rinsed, sponged down with
the cleaner and then rinsed again. Similarly, Bridgeville and Edgewater use a
rack to hang the modules, apply the cleaner and then rinse with clean water.
Bridgeville does this once every three weeks (based on coliform increase),
while Edgewater has a frequency of once a month (coliform kill efficiency).'
Bridgeville uses a dilute hydrochloric acid and Edgewater uses Lime-Away. Cave
City also uses a hydrochloric acid descaler (once/month) but: finds it difficult
to clean the quartz surfaces. They will be getting a dip tank to improve this
operation. - . ..
Clearsprings and Leadwood use Lime-Away on a frequency of once/month and
once per six weeks, respectively. They also report that the channels are hosed
down daily; at Leadwood debris tends to catch on the lamps, which is removed
(hosed downed) daily. Both plants would like to have hanging racks to make the
cleaning process more convenient. The Olla plant uses a dishwashing detergent
about once every two weeks on a routine basis, spraying the quartz with the
soap solution, wiping them with a towel, and then rinsing them with water. At
Dewey, Lime-Away is used about once every two months, based on coliform levels.
Petersburg uses a dilute phosphoric acid solution. This is done
approximately one every six months, generally based on effluent coliform
densities. This is set at a limit of 60 fecal coliforms per 100 mL. At
Jessup, a dilute acid is also used. One person holds the modules while a
second cleans and rinses it. This is done approximately once per month, based
on effluent coliform density and intensity readings.
At Hanover, the modules are tipped up, wiped and brushed with lime-away and
then returned. This wastewater is high in iron and manganese, such that the
modules require cleaning one per week. Twice each year the modules are removed
completely for a more rigorous cleaning. The Accomac plant uses both dilute
sulfuric acid and Windex to clean the quartz. This is done more frequently in
the summer because of algal growth through the plant, requiring a cleaning
approximately once per month. The frequency decreases to once per month during
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Page 3-45
the winter. At New Providence, a scouring pad (Brillo) is used with detergent
.to clean the quartz surfaces. The frequency is variable, ranging from once per
week to once per five weeks.
A 6 percent phosphoric acid solution is used approximately once per 6
months, based on coliform densities (when fecal coliforms exceed 40 per 100
mL). This frequency is once per three weeks at Williamson, which uses a mild
acid solution. Athens uses Lime-Away, cleaning at a frequency of three times
per year. This is based on coliform density. There is difficulty in accessing
the modules from these deep channels." Two operators are needed; one holds the
module, while the second cleans, it. The pperatprs..stated a,need,.for a hanging.
'rack".
Olathe, Willow Grove, and Warminster all use Lime-Away, at a frequency
based on intensity meter readings. This is once per six weeks, three months,
and six months respectively. Each removes the modules, applies the Lime-Away
with a soft cloth, and then rinses with clean water.
3.2.2.1 Frequency and Labor Requirements for Cleaning
The frequency of cleaning is highly variable, ranging froa-. once per week to
once per year. Table 3-6 presents the estimated time spent per year for
cleaning the quartz, based on input from the operators. It is not appropriate
to simply include this in the O&M labor requirement summarized on Figure 3-3.
Rather, the time required per 100 lamps is normalized to the cycles per year,
which is shown on Table 3-6.
There is no.clear trend in this value relative to plant type or size. The
labor requirement ranges from 0.7 to 26 hours/cycle/100 lamps. Eighty percent
(24 of the 30 plants) are less than or equal to 8.3 hours/cycle/100 lamps, with
a mean value of 4.3 hours/cycle/100 lamps. The remaining 6 plants range
between 10.4 and 26 hours/cycle/100 lamps, with an average of 17.4 hours/cycle
per 100 lamps. The overall 30 plant mean is 6.9 hours/cycle/100 lamps.
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Page 3-46 ,
Overall, a value to 5 to 10 hours/cycle/100 lamps would appear to be
appropriate for use in screening a facility labor requirement for cleaning.
Actual yearly requirements will then depend on the frequency. Of the 30
plants, the median frequency was approximately one per month or 12 times per
year. Using a median estimate of 5 hours/cycle/100 hours and 12 cycles per
year, the yearly requirement would be 60 hours /100 lamps. When compared to
the labor requirements on Figure 3-3, this is twice that of the large plants
and equivalent to that of the smaller plants. Thus, the cleaning activities
can comprise one-third to one-half the total labor requirement for (O&M).
3.2.2.2 Summary Assessment- of Cleaning Pract-ti
The cleaning practices, as presented in the preceding discussions is highly
variable. The principle points are summarized on Table 3-7, addressing the
equipment and methods used for cleaning; the cleaning agents; the criteria used
for cleaning; and the resultant frequency and labor use.
The dominant practice is to remove the modules from the channel, with or
without provision of a rack to hang the module. In-place recirculation or dip
tanks are more typically used for the vertical lamp module systems. The
standard practice for manually cleaning the units is to simply apply the
cleaner onto the quartz and then rinse the module with clean water.
Citric acid and Lime-Away are typically used as cleaning agents, although
several others are used including detergents and 'other dilute acids. There is
no strict criterion that sets the type of cleaner; the manufacturer will
generally recommend one or more. It becomes a matter of trial and error
specific to the plant site. This is also the case with frequency; as noted,
this varies widely and depends on the specific site requirements.
The criterion for cleaning is typically based on fecal coliform densities
This was the case for two-thirds of the selected plants. The remaining third
was split between using the intensity meter reading, or simply setting a
proscribed frequency.
-------
TABLE 3-7. SUMMARY OF CLEANING PRACTICES FOR THE
30 SELECTED PLANTS
A. Equipment Use for Cleaning Number of Plants Comments
(1) In-place Recirculation 4 All vertical lamp
modules; Remove
once/year
(2) Mechanical Wiper 1 One of four "in-
place" units
(3) Dip Tanks 2
(4) Remove modules onto a rack 5*
(5) Remove modules 19* No special
equipment to hold
.module .7." . _1I
*Method is to rinse, apply cleaning agent, rinse, and return to channel.
B. Cleaning Agents
(1) Citric Acid 9 Two dip tanks,
four in-place,
three external
modules
(2) Lime-Away 10 Commercial product
(3) Dilute HCI Acid 4
(4) Detergent 3 dishwashing
detergent; Windex;
a plant also uses
Brillo pads.
(5) Phosphoric Acid 2
(6) Sulfuric Acid 1
(7) Tile/Bowl Cleaner 1 Commercial product
-------
TABLE 3-7. SUMMARY OF CLEANING PRACTICES FOR THE
30 SELECTED PLANTS
(Continued)
C.Frequency (cycles)
(1) Weekly (52/year)
(2) Monthly to biweekly
(12 to 26/year)
(3) Six weeks to yearly
(1 to 9/year)
D. Labor per cvcle/per 100 lamps
(1) 1 to 10
(2) greater than 10
Criteria for Cleaning
(1) Fecal coliform
(2) Intensity meter
(3) Routine
14
14
24
20
5
5
Comments
mean, 4.3 hours/
.cycle/10.0, .lamps
mean, 17.4 hours/
cycle/100 lamps
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Page 3-49
In summary, the following observations are made:
• removal of the modules is appropriate and probably best for most
plants. Cages are suggested for larger plants for removing bundles of
lamp modules.
• moving hoists/cranes will facilitate removal of the module bundles or
vertical lamp modules,
• dip tanks provide a convenience and assist in cleaning modules removed
'"-"." ' -from the channel, ' '•-'"• -: :: """-".: :: "-;:-~":..-—.:~:~~:--
in-place recirculation is effective, particularly for vertical lamp
modules. Agitation should be provided during the recirculation cycle.
Plant should still plan to remove the modules once per year for a
rigorous cleaning.
the cleaning agent(s) that suits the facility is dependent upon the
nature of fouling. A trial and error series of test should be
conducted, using readily available, off-the-shelf commercial products,
frequency of cleaning will be, dependent on the specific site
requirements,
small-scale piloting would be very effective in establishing the
cleaning agents and frequency most suitable to a specific plant, and
monitoring fecal colifonns is an effective tool for determining the
need for cleaning lamps. Note that this is also used for triggering
lamp replacement.
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Page 4-1
SECTION 4.
REFERENCES
(1) U.S. Environmental Protection Agency, Design Manual; Municipal Wastewater
Disinfection. Center for Environmental Research Information,
EPA/625/1-86/021, Cincinnati, Ohio.
/
(2) Jagger, J. Introduction to Research in Ultraviolet PhotoblolOKY. Prentice-
Hall , Inc., Englewood Cliffs, NJ, 1967.
(3) Smith, K.C. and P.C Hanawalt, Molecular Photobiologv. Inactivation. and
Recovery. Academic Press, New York, NY, 1969
(4) Harm, W. Biological Effects of Ultraviolet Radiation. Cambridge,
England, 1980.
(5) Stanier, R., M. Doudoroff, and E. Adelburg, The Microbial World. Prentice-
Hall Inc., Englewood Cliffs, NJ, 1970.
(6) Whitby, G.E. and F. Engler, "A Preliminary Study to Determine the
Feasibility of Medium Pressure Lamps for Disinfecting Low Quality Waste-
waters." Prepared for the Research Management Office, Ontario Ministry of
the Environment, RAG Project No. 380C, Toronto, Ontario, 1988.
(7) Communication with Aquionics, Inc.
(8) Asea Brown Boveri, Sweden, Bulletin CH-ISU-4013E, North American licensee
is WaterGuard, Inc. Port Moody, B.C., Canada (D.F. Sommerville).
(9) Communication with Wedeco, Herford, Germany.
(10) Communication with Trojan Technologies, Inc., London, Ontario, Canada.
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Page 4-2
(11) Carlson. D.A.. R.w. Seabloom. F.B. DeWalle, T.F. Wetzler, J. Engeset R
Butler S. Wangsuphachart, and .. Wang. -uitravioUt *
. . ravot **, ,
Water for «1 Water Supplies.- U.S. Environmental Protectloj,
Office of Research and DeveUpment, EPA/600/2-85/092, Cincinnati, Ohio.
(12) National Sanitation Foundation, Standard 5,, Ultraviolet Disinfection
Systems, Aim Arbor, Michigan 1987.
(13) USEPA Kunicipal Wastewater Disinfection Development Document. Office of
Municipal Pollution c°«rol, DRAFT, jashl»gtonf,,D,C., 1989.
(14) USEPA. A^ient Water Quality for Bacteria - 1986. EPA 600/4-85/076.
at Rehoooth Beach.
K «-te»ater Treat^en
Foru. , 1990. U.S. EPA Office of Water. EPA 430/09-90- 015
Washington. D.C., September 1990.
(16) HydroQual Inc.. -nv Piiot Studies at the LOIT Bastewater Treatment
Facility.- Prepared under subcontract to Parametrix, tnc., Sumn.r
the LOIT
-P-intendent. „ Bergen WPCP,
(18) Har», „. , c.s. Rupert and „
Voe; Ut°r C° Ph"-h^S^ - ^-biology of Hucleic Acids,
Volume 2. Academic Press, inc., New York, HY, 1976.
(20) Scheme, „. Karl, m Dlslafect,m ^ ^^.^^..^^^ ^^
nfe"nC EPA/600/9-90/ 036,
n
, Ohio, August 1989.
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Page 4-3
(21) Fahey, Richard J. "The UV Effect on Wastewater," WATER/Engineering And
Management, December 1990.
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APPENDIX A
SITE VISIT REPORTS
o NW Bergen County, Waldwick, New Jersey
o Blytheville, Arkansas
o Piggott, Arkansas
o Wallkill, New York
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SITE VISIT
NORTHWEST BERGEN COUNTY WASTEWATER TREATMENT PLANT
March 2, 1990
The Town of Waldwick, New Jersey is approximately 20 miles due north of
Newark, New Jersey. Mr. Dave Alvarez, the operations supervisor who has been
at the plant for nine years, conducted the plant tour. It is a secondary
treatment facility which employs the activated sludge process. Preliminary
treatment is accomplished through screening and comminution. Primary settling
is provided by three primary settling tanks; a primary sludge degritter removes
inert material prior to on-site incineration. Oil and grease skimmed from the
surface of the primary clarifiers are also incinerated. The activated sludge
system is composed of three aeration basins, each- of jrtiich has two passes.^.
generating in the step aeration mode. Secondary clarification is provided
prior to disinfection and final discharge.
Disinfection is accomplished by ultraviolet radiation. The UV disinfection
system is a retrofit, with the UV equipment installed in an existing chlorine
contact chamber. As shown on Figure A-l, the rear half of the chlorine contact
chamber was utilized for the equipment installation. The front half provided a
long straight approach channel to the UV system. The chlorine contact chamber
walls were widened in order to decrease the channel width to the proper size
for accommodating the UV equipment. A structure was also built over the last
half of the chlorine contact chambers which fully encloses the UV equipment.
The decision to replace chlorination with ultraviolet disinfection was the
result of a study which investigated several disinfection alternatives,
including hydrogen peroxide, ozonation, chlorination and ultraviolet radiation.
The study was conducted due to growing concerns over safety issues involved
with continued use of chlorine for disinfection and the fact that
dechlorination would soon be required. The Rehoboth Beach, Warminster and
Willow Grove wastewater treatment plants were three of four treatment plants
using ultraviolet radiation that were visited as part of the disinfection
study. Ultimately UV disinfection was chosen on the basis of safety, cost and
maintenance.
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unit consists of two ^infection channels . wlth
. , c is an °pen oha"
and parallel to the ^.^ „ „„„
1
in series and Is rated for 12 mgd with both banks „ operatloil
contains 240 la^ps <„ inc. arc length) in 30 maul?s of .
the v
°' °*
the second bank ls brousht lnto
th , - S »» 1- *
the OT inlet to prevent floating debris ft. fouling the lmps. A
contro gate is Provided on. the. ef^nt _end. of .the disinf.ctJn chall
naintain adequate liquid level iff the' channel. ' ' --~~~- ~-.'.-~=-I^
-
for each bank of 1^.. The systeo controls include: . 1^ status
display and Upsed tine lndIcMor; and ^ ^ ^tor ^ a~
display consists of . pattem of indicator li^ts arranged identical to
la.p arra^ent in the channel. A lit la,p indicates that either power to
" " "— "«• - apsed
indict i reC°r ?Pera"ng ""* ^ "hedule -m-nance. one
indicator is provided for each barf= of lmps. tte Intenslty nonltor ^
•
the te - nS- " — — ding of
perfoLn°Pera °"al Parime"rS
performed three times per day.
-------
The plant design flow is 12 mgd; it currently averages around 10 mgd. The
plant's fecal coliform limit is 200 organisms/100 mL as a 30-day average and
400 organisms/100 mL as a 7-day average. Coliform sampling is performed four
days a week. The samples ^are generally taken during periods when the UV is
under its heaviest load. UV transmittance is run along with the coliform
testing. The operator reported that since the UV equipment has been installed
there have been no counts over 400 organisms/100 mL and only a few occasions
where the count exceeded 200 organisms/100 mL. He also added that the system
has gone over its design flow several times without problems.
Plant personnel are very pleased with the system, and felt that they made
the right choice by moving to UV. To this point the following benefits were
reported: less, intensive maintenance; no chemical costs; less, safety training
is required and it is less of a liability from a safety standpoint than
chlorine disinfection. It was noted that a screen would be a benefit, placed
upstream of the first bank of lamps. Debris tends to accumulate on the lead
end of the modules.
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UV Wastewater Disinfection
Process Flow Diagram
LMieonmi
Sine* only • taw aacond* of ultraviolet axpoaura are raqutrad to tr»at affluent, there to
no need for tar-fl* oontect tank*. R to posclbt* to ratraftt mo«t UV cystem* wtthln
•xlctlng chlorin* contact tanks, We* thto on* at North»t»t B*rg«n County^ WMtawator
plant
Figure A-1 Layout of Retrofit at NW Bergen Plant
(Reference 21)
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SITE VISIT
BLYTHEVILLE WASTEWATER TREATMENT PLANT TRIP REPORT
November 16, 1989
A visit was made Co the Blytheville Sewer District which owns and operates
three wastewater treatment plants: the Blytheville North WWTP, South WWTP and
the West WWTP. Blytheville, Arkansas is located in Mississippi County and is
55 miles due north of Memphis, Tennessee. The wastewater flow to the plants is
primarily domestic; all three plants process trains are essentially identical.
They are extended aeration activated sludge plants. Preliminary treatment
utilizes an Aquaguard Traveling Screen screenings are shredded by grinder pumps
prior to disposal. The Bioiac-R extended aeration activated sludge "system
manufactured by the Parkson Corporation, Fort Lauderdale, Florida is used for
secondary treatment.
The North plant is the smallest of the three and is designed for a flow of
0.8 mgd and a BOD loading of 1,134 Ibs/day. The South and West plants handle
1.40 mgd and 1.50 mgd average flow, and BOD loadings of 3,552 Ibs/day and 3,253
Ibs/day, respectively. All three plants have the same discharge limits. The
BOD and TSS limits are 30 mg/1 as a 30-day average and 45 mg/L as a 7 day
average. Coliform limits are seasonal; between October and April the limits
are 1,000 fecal coliform per lOOmL as a 30-day geometric mean, and 2,000 fecal
coliforms per 100 mL as a 7-day geometric mean. Between May and September the
limits are 200 fecal coliforms/100 mL as a 30-day geometric mean and 400 as a
7-day geometric mean.
All three plants went on-line in April, 1989. Each plant is operating at
approximately half its design flow, with average effluent BODs under 15 mg/L,
and average TSS levels less than 20 mg/L. There have been coliform excursions,
with 7-day averages exceeding 1,000 fecal coliforms/100 mL. Plant personnel
reported no major problems with the disinfection systems.
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The disinfection system in each plant consists of one channel. The
equipment was furnished by Ultraviolet Purification Systems (UVPS) Bedford
Hills, New York (now Katadyn Ultraviolet Systems). The North plant utilizes 64
lamps (58 inch arc length). The South and West plants each use 96 lamps (58
inch arc length). Each system is eight lamps deep and arranged in 4 banks.
Bank 1 consists of the bottom 5 horizontal levels of lamps, which remain on
continuously. Banks 2 through 4 represent lamp levels 6, 7 and 8 respectively.
These banks come on individually as the liquid level in the channel increases.
The,system controls are housed in a steel cabinet adjacent to the
disinfection channels. The system controls include: a lamp status display;
elapsed time Indicators; an analog Intensity monitor and hand switches for
manual control of-power to each rack :of lamps, - The-. lamp status display;dLs,^
clearly labeled pattern of Indicator lights which matches the pattern of lamps
in the disinfection channel. The indicator lights remain lit when power is
being delivered to the lamp and the lamp is on. The Indicator light goes out
when power to a lamp is interrupted or a lamp has burned out. Elapsed time
indicators are provided to record operating time and schedule maintenance for
each bank .of lamps. The analog intensity monitor relates the intensity of the
radiation to existing wastewater conditions. It is calibrated to read 100
percent with a new lamp and clean effluent. Beneath the intensity monitor are
3 Indicator lights; the red light indicates system failure; the yellow light
Indicates low Intensity and the green light indicates safe operation. Still
'further below the indicator lights, there are intensity test buttons. They
test the analog reading 0, 50 and 100 percent intensity.
Log books are kept at all plants; all maintenance performed and any
observations made from visual inspections are recorded. Visual inspections of
the UV disinfection system are made at least daily. The lamps are cleaned
weekly using a soft brush and a product called Simple Green™. This product is
sold In auto parts stores as a general purpose detergent and degreaser. The
district had recently acquired a lamp rack tester which checks on the lamp
status display.
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The system should have multiple channels. As it stands now, there is no
backup system to put on-line during lamp cleaning or repair and maintenance
tasks. The cause of the high effluent coliform counts had not been identified.
Upstream protection of the disinfection system in the form of screens may also
be appropriate.
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SITE VISIT
¥ALLKILL WASTEWATER TREATMENT PLANT
March 1, 1990
The Town of Wallkill, New York is approximately 50 miles northwest of New
York City. Preliminary treatment is accomplished by comminution followed by
automatic bar screening (by-pass to manual screening as a backup) and grit
removal using a cyclone degritter. Primary settling tanks .are not provided.
Effluent from the cyclone degritter is biologically treated in oxidation
ditches which operate in the extended aeration mode of the activated sludge
process. Stationary surface impellar type mechanical aerators are employed for
aeration requirements. Secondary settling is achieved in two secondary
clarifiers. Secondary, effluent flows to three-UV disinfection units priQr--;tQ-:
final discharge to a nearby river.
The plant is designed for a peak flow of 10 mgd and a daily average flow of
4.0 mgd. Space is provided in all structures for additional equipment needed
for expansion to 6.0 mgd. There were two permits written, both of which meet
or exceed standard secondary treatment limitations. The plant was designed for
nitrification and is limited to 8.1 and 5.0 mg/L of NHs-N in the effluent for
winter and summer seasons, respectively. The disinfection season runs from May
15 through October 15, limiting fecal coliform discharge to 200 organisms/100
mL as a daily average, with a maximum daily of 400 organisms/100 mL.
The plant went on-line November 16, 1989. Since startup, the average plant
flow has been 2.2 mgd with a peak flow of 3.6 to 3.7 mgd. The plant has
performed well in general, achieving average removals of 90 percent and 96 to
97 percent for BOD and TSS, respectively. It had experienced some problems
with nitrification. The operator due to the record cold weather throughout the
month of December 1989.
The UV disinfection system consists of three channels in parallel. The
equipment was furnished by Arlat Technology, Bramalea, Ontario, Canada. Arlat
Technology has since sold the rights of their UV disinfection business to
-------
Fisher and Porter. !nc. Arlat, hoBever, „ responslbu £or
the eq» p.ent and any warranty clalms .^^ be
Each unit contains 208 taps <58 Inch .„ l.ngth) and is rated for 6 0
». system is an open channel design with a horizontal tap arrangement s
gates located at the head of each chan™l are provided for now control t.
rr — — z «—-—•—
r >— rr,
the channel (rows 1 through 4 are on continuously).
Plasc i
Plastic _™?P_grip tube ctaps Which are riveted .to the. steel- tap
Removal of a tap rac* automatically shutfd^»- i power to"that~r.c
* — —
power supply and control panels are contained in stainless steel housings h
are set at grade level above the units. housings which
control
control panel consists of 2 sections-
voltaee »ow« , sect*°ns.
:;:—=
•«*
i
a iower section containi u
rr -
be manually
of the
^v,,,.*, j -—fo WAJ.X oe cleaned with a soft
brush and a cleaning solution provided with the equipment. Cleaning frequency
2
-------
has not yet been established since the disinfection system had not been put on-
line as yet.
UV was not originally chosen to accomplish disinfection. The original
designs called for chlorination. Before formal review of the designs by the
governing agency, the municipality was told the plans would not be reviewed if
chlorination was specified. At that point UV was incorporated into the
facility plan.
The UV system as previously mentioned has not yet been started up. The
plant plans to start up the system one month prior to the beginning of the
disinfection season which begins May 15, 1990. This is being done to assure
the system is fully operational prior to May 15. Performance testing of the
system by the contractor is scheduled "for the beginriihg" of April T The systemT:
will be tested for one month. A follow up call to the plant revealed that the
testing had begun during the first week of April. The tests were being
conducted on one channel with full plant flow (-2 to 2 1/2) with influent and
effluent samples being taken twice daily.
Plant personnel were generally displeased with the UV system. The chief
operator felt that the use of UV disinfection was forced upon him and he thinks
the system will be difficult to maintain. He envisioned maintenance personnel
involved in lamp cleaning on a daily basis. He also commented that the UV
system was one of the most expensive pieces of equipment on the site
($400,000). His perception of lamp cleaning was greatly influenced by a nearby
plant that was experiencing problems with their UV system.
General comments regarding the design and operation of the system are as
follows:
1. The system should be enclosed. An enclosure would provide
protection against adverse weather conditions.
2. There should be upstream protection of the UV system in the form
of screens.
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3. The design and construction materials used for the lamp rack are
poor. *
Plastic material used for electrical connections and lamp holders
is not well suited for its intended purposes. Lamp replacement
would be more difficult than the manufacturer's literature would
lead one to believe.
4. Baffles are not provided prior to the DV lamps. Considering the
nature of the influent structure, high turbulence may result.
5. Performance testing as it was briefly described, may not be
representative of the performance^ specifications. At 90 percent
BOD removal and 96 to 97 percent TSS rem^vaTr the ~ plant
» ~•"• t»j-«*Mt- J.B mosc
likely achieving far better than a 30/30 effluent which the UV
performance is written on. The flow of 2 to 2 1/2 Is also only 30
to 40 percent of its rated flow.
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SITE VISIT
PIGGOTT WASTEWATER TREATMENT PLANT (WWTP)
November 15, 1989
A visit was made to the Piggott WWTP, Piggott, Arkansas on November 15,
1989. The plant was designed by Hildson Engineering which is located in the
Memphis, Tennessee area. Piggott, Arkansas is approximately 85 miles north of
Memphis, Tennessee. The plant waste flow is characterized as 100 domestic.
Although the sewer district has separate sanitary and storm sewers, the plant
receives significant peak flows during storm periods due to
inflow/infiltration. The plant is located adjacent to a lagoon which was
previously used as the sewer district's treatment facility. A section of this
lagoon "Is" used"'for."'storage during high flows. .'""". — - -.-.-
The facility is an extended aeration activated sludge plant. Preliminary
treatment consists solely of screening by an Aqua-Guard™ Traveling Screen.
After screening, the influent flow is measured by a parshall flume prior to
biological treatment. Biological treatment is accomplished by the Biolac-R
Extended Aeration System manufactured by the Parkson Corporation, Fort
Lauderdale, Florida.
The plant is designed for an average daily flow of 0.6, a loading of 1,000
Ibs/day for BOD and TSS and an ammonia loading 75 Ibs/day. A review of the
plant's discharge monitoring report reveals a discharge limit of 30 mg/L as a
daily average and 45 mg/L as a daily maximum for both BOD and TSS. Ammonia is
limited to 4 mg/L and 6 mg/L May through October and 7 mg/L and 11 mg/L
November through April for daily average and daily maximum limits,
respectively. Seasonal limits are also written for fecal coliforms; 200 FC/L
and 400 FC/L from April through September for daily average and maximum daily,
respectively. October through March the daily average is 1,000 FC/L while the
daily maximum is limited to 2,000 FC/L.
The plant went on-line in April 1989. Since startup the plant flow has
averaged approximately 3.0 mgd. A review of recent plant data (June through
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October) operating shows some problem. Mthough the plant met its effluent
BOO Umit throughout this period (averaging 21 mg/L), the effluent TSS levels
.re consistently above permitted levels. The average effluent TSS was 35 mg/L
The Pla»t superintendent believes the plant effluent will Improve onee lt *L
up to Its operating MLSS. *
The -disinfection system perforce has been poor. Monthly daily maximum
effluent fecal coliform counts are all above 10.000/100 *. while L dai™
averages for these months ranged fro. about 4,000 to 18,000/100 «L This is
attributed to the high effluent suspended solids, and to the inability to
maintain a full complement of bulbs in operation. Although the system appeared
to be fully operation! at the time of the visit, the low intensity warning
ight was lit. The plant superintendent reported that the problems with the
system have nevar been satlsfactorlly:resolved.- - -~ -= ~ ~ --:.. ,,i. ::r_._^..
The UV disinfection system consists of one channel, without a backup The
.ouipment (Hodel 70OV2000) was furnished by Fisher and Porter Company
P°1Vanla- "" *«*
t f - " ** «— - I-* * 'nch arc length
rated for 0.6 md. The system is a horizontal, open channel design. The
paraiiei to
.
.Zt z rranEed paraiiei to the directio11 °f £i°- ^ «• ™* - i»
eight Modules across, and eight la^,s deep. The system is equipped with an
"
cont K, -lt' SyS"» "»«°ls « housed In a stainless steel
control cabinet. System control included: a lamp status display; cabinet
eiapsed
8 - ^
status display system consists of a series of indicator lights arranged in !
pattern Identical to that of the UV lamps in the channel. A dim light
"* aes
has burned out and must be replace and an unlit light indicates that the
lamp is not powered and Is off (this means either the main power is off or the
ballast is not functioning properly). An elapsed time meter is provided for
ievei °f
i
and is used to record and schedule maintenance as well as lamp
2
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replacement. This Is an important feature since different controlled levels
receive varied use. The cabinet temperature monitor displays the operating
temperature and will actuate a common user-accessible alarm contact when the
temperature within the cabinet exceeds a user-adjustable setting. Maintenance
of adequate cabinet temperature is essential to prevent electrical component
damage due to overheating. A UV intensity monitor is located on the cabinet
face, it consists of a digital meter which indicates the intensity of the
radiation being emitted by the lamps. The intensity probe can be positioned in
various locations. The intensity monitor output is a measure of the lamps
output given the wastewater clarity at that time. A loss of intensity at
similar wastewater conditions indicates that the lamp should be checked and/or
cleaned.
The flow to the disinfection unit is discharged over the effluent weir of
the polishing basin. The liquid drops 8 to 12 inches into a long straight
channel which directs the flow past the UV lamps. The long straight trough
allows for little turbulence and therefore the dispersion factor should be low.
The lamps are cleaned weekly with water and a soft brush. An operations
manual provided by Fisher and Porter recommends a cleaning solution of citric
acid or a mild detergent and water. The manual also recommends treating the
lamps, after they have been cleaned, and dried, with a protective coating of an
anti-fouling solution.
The system should have multiple channels. The system as it stands now has
no backup system to put on-line during lamp cleaning or repair and maintenance
tasks. The electrical problems responsible for preventing the system from
being fully operational on a full-time basis need to be corrected. There
should also be an upstream protection of the UV system in the form of screens.
Government Printing Office : 1992 - 312-014/40170
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