LRWRP_Design_Report_Chapter_7.pdf

CHAPTER 7

DISINFECTION (TM 5)

Introduction

The LRWRP currently discharges treated effluent to San Miguelito Creek about 400 yards upstream of its confluence with the Santa Ynez River. During dry periods, the treated effluent is the only flow in either stream. Disinfection is currently provided by use of sodium hypochlorite with ammonia, while calcium thiosulfate is used for dechlorination. Disinfection to achieve stringent bacterial standards is required to meet permit requirements. Brown and Caldwell held a workshop with LRWRP staff on September 16,2004, to discuss the concepts and criteria to be used for liquid phase treatment processes, including effluent disinfection. This technical memorandum is based on concepts discussed at the September 16th meeting and subsequent evaluations.

KennedyIJenks (K/J) prepared an update to the Master Plan for LRWRP, dated September 2002, that included the following recommendations relative to disinfection:

rn Install ultraviolet (UV) disinfection for primary disinfection process.

Retain existing sodium hypochlorite system for in-plant uses.

Filter secondary effluent upstream of UV disinfection.

The construction cost was estimated to be $2.5 d o n for the projected 13.5 d o n gallons per day (mgd) peak wet weather flow system.

Brown and Caldwell reviewed these recommendations during preparation of our response to the request for proposals (RFP) for this project. This technical memorandum provides details to address needed additions to the disinfection process.

Objectives

As stated in the scope of work and as discussed at the liquid process workshop, the following objectives are to be addressed in thls technical memorandum:

Evaluate disinfection recommendations and costs presented in the Master Plan.

Evaluate process requirements for UV disinfection.

Evaluate potential UV disinfection options and their performance characteristics.

Recommend the preferred UV disinfection alternative.

Provide design criteria, mechanical layout and site space requirements.

Estimate the cost of the recommended alternative.

February 2005

Disinfection (Thl 5) 7 -2

Flow and Water Quality Projections

The following sections discuss flow rates and water quality projected to impact the design of the disinfection facility.

7.3.1 Flow rates

The following design flow rates were established at the liquid process workshop:

Average dry weather flow rate Peak dry weather flow rate

5.5 mgd

9.5 mgd

Wet weather flows will be stored and equalized such that the listed flow rates will not be exceeded.

The flow rate to the filters and W disinfection system will be a maximum of 5.5 mgd, accomplished by equalizing the daily flow.

7.3.2 Permit Requirements

LRWRP discharge to San Miguelito Creek is regulated under the provisions of National Pollutant Discharge Elkrunation System Permit No. CA0048127/Waste Discharge Requirements Order No.

01-87, dated May 18,2001.

7.3.3 Disinfection Objectives

Disinfection is required to meet the effluent bacterial limits and to assure that residual chlorine is not present in the effluent. The following standard from the permit is required for disinfection:

'Eflz~ent discharged to the creek shall be adeptate4 disinfected so that the 7 - d q median mostprobable n~nzber fl1'1V) of total col$om o~anisms in the efll~ent does not exceed 23per 100 milliliters, shall not exceed a log mean of ZOO/ 100 m4 or shall more than 10% ofthe total samples dming any 30-dqperiod exceed 400/ 100 ml. "

The design of UV disinfection wdl be based on California Title 22 requirements for the production of reclaimed water. While the current project is not intended to produce reclaimed water, it is prudent to follow Title 22 requirements in the design and specification of UV disinfection so that water reclamation is an option available to the City of Lompoc (City) in the fuhlre. In adktion, following Title 22 requirements allows the system to be sized on the basis of validated criteria known to meet stringent performance requirements during test work following standardned procedures.

7.3.4 Total Residual Chlorine

In the event that sodmm hypochlorite is retained for final effluent disinfection or related process uses, the following permit limitations on total residual chlorine (TRC) must be met:

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Disinfection (TM 5)

"Compliance determinations for total residt~al chlorine .hall be based on 99% con@liance. To determine 99% compliance with eflwent linzitationsfor total chlorine residwaL, the folioowing conditions shall be satig9ed.

a) The total time d~ring which the total chlorine residual valhes are above 0.02 mg/L (insfantaneozts maxinzzrm value) shall not exceed 7 hours and 26 nlinutes in a y calendar month.

b) No individual excursion from 0.02 m g / L sbaIl exceed 30 minwtes; and

No individual exct/rsion shall exceed 0. I mg/ L.

d) When continwows monitoring is not being wsea', standard compliance gr~idebnes shall be followed (i.6. below 0.02ppm at ad times, measwed once a d q according to standard provisions). "

Continued use of sodium hypochlorite would require costly improvements to meet these TRC standards on a continuous basis.

Effluent Disinfection

The following section discusses and evaluates options for UV disinfection of filtered plant effluent at the LRWRP.

0 7.4.1 Evaluation of UV Disinfection Technologies

LRWRP currently uses sodium hypochlorite as the primary disinfectant, so all UV disinfection facilities will be new. There are a number of options available for UV lsinfection based on lamp type and configuration, whch are discussed below. The response to the RFP assumes that a new UV disinfection system will be installed, inclulng equipment, structures, buildings and controls.

7.4.1.1 W Disinfection. UV disinfection is achieved by exposing water or wastewater that contains bacteria, viruses, and protozoa to light within wavelength bands of between 210 nanometers (nm) and 300 nm. Light within these wavelengths has germicidal properties, with optimum inactivation occurring at a wavelength near 260 nm. UV light is not visible to the human eye, and is a significant component of solar energy that reaches the earth. UV disinfection systems use specialized lamps designed to emit UV light within the desired germicidal band. The lamps are enclosed in quartz sleeves and submerged in the wastewater to prevent contact between the lamps and the water.

UV dsinfection is a physical process in which light energy or irradiance penetrates the cell walls and damages the nucleic acids of the cell, DNA and RNA. Microbes are inactivated by this damage to the nucleic acid molecules, which prevents or inhlbits replication and reduces or eliminates infectivity. The degree of inactivation is related to the amount of UV light applied to the wastewater, the wavelength lstribution of the applied UV light, the distance the light travels to

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Disinfection (TILI 5)

( I reach the microbes, the suspended solids concentration and the transmissivity of the effluent. Each of these parameters is discussed below. The most important initial decision is the type of UV lamp and system to be installed.

7.4.1.2 UV Lamp Types. The UV lamp types available for municipal wastewater applications are described below. Each of lamp type can be installed in different configurations, whch is covered in the next section.

Low-Pressure, Low-Intensity (LPLI) UV Lamps The lamp used in early technologies for UV disinfection of wastewater is the LPLI lamp, which has a nearly monochromatic output at a wavelength of 253.7 nm. The lamps are made of quartz glass and contain low-pressure mercury vapor when operating at temperatures of 40 to 50 degrees Celsius (C). A typical LPLI lamp has a power input of 85 watts (W) and a UV output of 26.7 W at 253.7 nm.

LPLI lamps typically have a life span of 12,000 hours. They also have a relatively long history of operation in wastewater disinfection and have proven to be reliable and effective. As a result of the low-energy output of the lamps, a much larger number of lamps are required for disinfection than with other lamp systems. LPLI lamp systems are not provided with variable output control, so pacing is accomplished by turning lamps or banks of lamps on or off in response to a control signal. The lamps also are not available with automatic cleaning systems to reduce maintenance, so operators are required to clean them by hand or in large acid dip tanks.

Manufacturers of LPLI UV systems include Trojan Technologies, Inc. (Trojan), Capital Controls, Sunlight Systems, and Infilco-Degremont (IDI). Brown and Caldwell recommends conventional low-pressure UV lamps only for systems less than 1 mgd.

Low-Pressure, High Output (LPHO) UV Lamps LPHO lamps operate at higher temperatures than LPLI lamps and have hgher input and output energies. They operate at temperatures of between 60 and 100 degrees C, and produce light at a nearly monochromatic wavelength of 253.7 nrn.

Dependmg upon lamp design, these lamps consume between 200 W and 500 W each, and have a UV energy output between 75 and 125 W. The lamps are either mercury vapor or amalgam, containing mercury and iridium, in an inert gas. One LPHO lamp typically replaces three conventional LPLI lamps, making the total number of lamps required potentially much lower. Most manufacturers of LPHO output UV systems provide mechanical lamp sleeve cleaning as an option to reduce the labor required for maintenance. LPHO lamps have a lamp life of approximately 8,000 to 12,000 hours.

Disinfection (TM 5) 7-5

Manufacturers of LPHO lamp systems include IDI, US Filter (Ultraguard), WEDECO UV Systems (WEDECO), and Trojan. Several of these manufacturers have substantial experience in the application of LPHO lamps in wastewater disinfection applications.

Medium-Pressure, High-Intensity (MPHI) U V Lamps MPHI lamps are mercury vapor lamps that operate between temperatures of 600 and 900 degrees C and are enclosed within quartz sleeves. They are polychromatic, producing light output across the entire germicidal UV spectrum. Localized peak output of strong emissions near 254 nrn and 265 nrn provide for effective biocidal effects, but strong output bands elsewhere in the spectrum result in lower overall energy efficiency.

MPHI lamps are available for water and wastewater application in ratings of between 2,800 and 20,000 W. Far fewer lamps are required to achieve effective dsinfection, but the energy efficiency is much lower than LPLI or LPHO lamps. As a rule of thumb, one 2,800-W MPHI lamp will replace 16 LPLI lamps to disinfect the same amount of wastewater and use about twice as much power. The higher wattage lamps (20,000 W) are generally used only for drinking water disinfection or advanced oxidation.

MPHI lamps are always provided with mechanical sleeve cleaning systems, due to the higher temperatures at which they operate, which tends to increase their fouling tendencies. Mechanical cleaning is usually effective in maintaining MPHI lamps over the life of the system. Lamp life is approximately 3,000 to 7,000 hours.

Manufacturers of MPHI UV systems for wastewater include Aquionics, Inc. and Trojan.

Developing W Technologies A number of developing technologies are mentioned in technical literature, incluhg pulsed xenon lamps. These are not commercially available at this time for large systems and are not considered for this project.

7.4.1.3 System Configuration. The UV lamp types discussed above are available from manufacturers in a range of system configurations. The primary consideration for installation of UV equipment is the choice between in-vessel and open channel system arrangements. In-vessel systems are used for most water treatment applications and can be used for wastewater treatment.

They do not require elaborate hydraulic control systems but can produce higher head loss through the system at peak rates of flow.

Most LPLI and LPHO UV systems for wastewater applications are installed in open channel configurations. Open channel systems differ substantially based on whether the lamps are installed vertically or horizontally and parallel to flow. Level control is important in open channel lamp systems.

7.4.1.3.1 Installation. LRWRP disinfects secondary effluent by use of sodium hypochlorite, with contact time provided in concrete basins. UV disinfection equipment can be

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Disinfection (TM 5) 7-6 installed inside the existing chlorine contact basins, or in a separate structure constructed for the process. Installation inside of the chlorine contact basins is feasible, but would require substantial modification of the basins depending upon the equipment selected. Construction of a separate structure for the UV disinfection facility would leave the existing contact basins available for other potential uses. This is the recommended approach.

7.4.2 Design Considerations

Two major issues need to be considered for selection of design criteria for the UV disinfection process: water quality issues and ancillary equipment issues.

7.4.2.1 Water Quality. The performance and sizing of a W disinfection system is controlled by water quality considerations and the level of disinfection required. Important water quality considerations include:

UV transmittance (UVT) Total suspended solids (TSS) Temperature Dissolved constituents Initial bacterial concentration Variability of relevant water quality parameters Photoreactivation/dark repair

UVT is a measure of the ability of UV light at 254 nrn (or other wavelength) to pass through a sample of water over a defined path length. It is the ratio of the transmitted light to the incident light intensities, and is measured by use of a spectrophotometer. The spectrophotometer passes a collimated beam of light at a known wavelength through the water sample over a 1-centimeter distance. The spectrophotometer is initially calibrated to a sample of ultra-pure water, which is defined as having a UVT of 100 percent. The wastewater sample is then placed in the instrument to determine its W T ratio compared to the ultra-pure water.

The UVT at 254 nm of secondary effluent is generally between 55 and 65 percent. UVT is a site-specific value that must be determined by testing, and can vary diurnally and seasonally. It has a significant influence on the sizing of a UTT disinfection system.

UVT data have been collected during prior pilot plant investigations. It should be noted that changes to the liquid stream process made as part of k s upgrade may impact wastewater transrnittance. It is expected that the recommended liquid stream changes will increase UVT.

TSS is a measure of the particulate matter present in the wastewater and also is a significant design parameter due to the adverse impact of solids on UV disinfection. Suspended particulate matter reflects and absorbs UV light, and shields bacteria from irradiation. In addition to TSS, the particle

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Disinfection (TM 5) 7-7

I

I size distribution is an important design consideration. Larger particles have a more adverse impact on disinfection performance. Filtration of the secondary effluent w d control the impact of TSS on UV disinfection system sizing and performance.

Temperature has an impact on the UV output of LPLI lamps, but other types of lamps are not significantly water temperature-dependent. The UV inactivation of bacteria has been shown to be relatively independent of temperature. Temperature will not be a design consideration at LRWRP.

A number of dissolved organic and inorganic water constituents may impact disinfection by absorbing UV hght. Inorganic UV-absorbing compounds include aqueous ozone, ferric iron, permanganate, hypochlorite, hydrogen peroxide, ferrous iron, and sulfite in decreasing order of impact. Dyes and other complex organic compounds also absorb UV light. It is not expected that significant concentrations of these compounds w d be present at LRWRP.

UV disinfection is essentially independent of wastewater pH within the ranges normally encountered.

The metals removal process to be located immediately upstream of the filters and W disinfection process may use ferric chloride (FeClq as a coagulant. The dissolved iron remaining after metals removal has the potential of adsorbing UV light to lower UVT, and depositing on the lamp sleeves to cause fouling. If ~eC1" is used as a coagulant, it should be effectively removed in metals removed process and leave an insubstantial amount in the downstream flow. It is generally considered that soluble iron concentrations of 0.25 mg/L or less will not adversely impact the UV disinfection process. Brown and Caldwell has installed UV equipment downstream of iron addition processes for phosphorus removal without adverse performance impacts.

Photoreactivation is the process in which bacteria that are only partially inactivated during UV disinfection repair cellular damage and become viable again in the presence of sunlight.

Photoreactivation wdl be factored into the design by covering the UV channels and other structures to limit exposure to light downstream of disinfection. Also, the bacterial sample location should be located close to the exit from the UV disinfection channels so that photoreactivation is not a factor in sample collection. Title 22 requires that the dsinfection standards be met at one location in the treatment process, which is usually immediately downstream of disinfection.

Dark repair and regrowth is another mechanism by which bacteria that are not fully inactivated can repair cellular damage incurred during UV disinfection. Dark repair uses different cellular processes than photoreactivation and is usually only a problem if dsinfected water is stored in tanks or reservoirs for extended periods of time following disinfection.

7.4.2.2 Support Equipment. This section discusses common support elements required for UV disinfection systems.

Quartz Sleeves Quartz sleeves are used by all commercially available UV systems to isolate the lamps from the process flow.

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Level Controllers Level controllers provide a relatively constant water surface in the UV disinfection channel. Level control is provided by use of weirs or level control gates, and is an important issue in all open channel UV disinfection systems.

UV Intensity Monitors W intensity monitors are used in most UV systems to measure the intensity of UV light emitted by the lamps and produce a control signal to indicate when lamp output has decreased or sleeve f o u h g has increased to levels whch impact performance or require maintenance.

UV Transmittance Monitors UVT monitors are used in some installations to continuously measure and report the W T of the water being disinfected. UVT measurement may be used as a control signal to vary the input energy of the lamps. Continuous UVT monitoring is required for Title 22 systems in California. The costs and design criteria in this report are based on a UVT value of 55 percent as dictated by DHS guidelines as a default value. Use of a higher UVT will be investigated during design of the disinfection process.

Level Monitors Continuous monitoring of water level in open channel UV systems is important for several reasons. High water level in the channels may indicate that the lamps are submerged too deeply, creating poor disinfection and potential bypassing of un-dsinfected effluent. Conversely, low water level may indicate that the lamp sleeves are exposed to air, resulting in wasted energy and shortened lamp life.

Sleeve Cleaning Facilities

Vertical lamp UV equipment manufacturers recommend that an out-of-channel acid bath be used in adhtion to in-channel mechanical cleaning to assure adequate long-term performance. ID1 recommends that an acid-&p tank be used periodically for their vertical lamp modules. The horizontal tank manufacturers do not recommend an acid dip tank, and depend on the mechanical sleeve cleaning system. However, they do recommend that a washdown area be provided for the lamps.

Drains

Floor drains in the sleeve washdown area and bottom drains in each UV channel or tank would be provided for the UV system to assist in maintenance and operation.

7.4.3 Evaluation of UV System Options

The various UV dsinfection system alternatives offer benefits for specific applications, but may also have disadvantages that need to be considered. The systems evaluated are discussed below.

LPLI Lamps/Vertical or Horizontal

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Disinfection G M 5)

The LPLI lamp alternative is not considered in detail for the LRWRP project due to the larger number of lamps required and the lack of an available mechanical cleaning system for the quartz sleeves. These lamps are labor-intensive in larger systems.

LPHO Lamps/Vertical The LPHO vertical lamp system under consideration is manufactured by ID1 and is shown in Figure 7.4.1. The ID1 system uses a 165-W lamp installed vertically in multi-lamp modules. The layout is compact, and the system is furnished with a mechanical cleaning system that reduces the labor required for lamp sleeve cleaning.

Figure 7.4.l. IDI Vertical Lamp UV Sys tern

The advantage of the vertical lamp system is that the lamps are serviced from the top of the unit without removing the lamp sleeves from the effluent flow. It also uses the smallest amount of land area.

Two parallel channels would be provided with 11 modules of 40 lamps each per channel. There would be a total of 880 lamps that have a peak draw of 145.2 kilowatts (kW). Each channel would be 24.5 inches wide, 57 feet long and 72 inches deep. Nominal water depth would be 60 inches and head loss through the lamps would total 2.86 inches at peak flow capacity. The vertical lamp UV system delivers a W dose of 109.0 mJ/cm2 at 55 percent W T . The estimated equipment cost for this system is $850,000.

LPHO Larnps/Horizontal Two LPHO/horizontal systems were evaluated, the UV3000 Plus system from Trojan and the TAK55 system from WEDECO. Both systems provide automatic lamp sleeve cleaning.

Trojan proposes a two-channel system with five banks of lamps in series in each channel. Each bank would contain eight modules of eight lamps or 64 lamps total.

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Disinfection (TM 5) 7-1 0

The five banks would have a total of 320 lamps, with one bank redundant. The two channel system would have a total of six banks and 640 lamps. Since each lamp is rated at 275-W input power, the 640 lamps at full power would use 164 kW. Each channel would be 28 inches wide, 58 inches deep and 60 feet long. The design W dose would be 100 mJ/cm2 at 55 percent UVT. The estimated cost of the UV equipment is $1,200,000.

WEDECO recommends a two channel system with six banks of lamps in series.

Each bank would contain three modules of 18 lamps or 648 lamps total. Since each lamp is rated at 360 W input power, the 648 lamps at full power would use 223 kW.

Each channel would be approximately 28 inches wide, 56 inches deep and 75 feet long. Head loss across the W system at peak flow would be approximately 2.5 inches plus 6 inches across an effluent control weir. The recommended system would provide a W dose of 100 mJ/cm2 at 55 percent WT.

The estimated cost of the equipment is $1,045,000. A photograph of a larger LPHO UV system is shown in Figure 7.4.2.

Figure 7.4.2. LPHO Lamps

MPHI Lamps/Open Channel A MPHI system in either the open channel or closed vessel configuration is not considered for LRWRP. There is no specific benefit of this system for the project, and the annual power costs are estimated to be twice as high as for any of the LPHO lamp systems under consideration.

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7.4.4 Summary of W Equipment Information -

The information presented above is summarized in Table 7.4-1.

Table 7.4-1. Alternative UV Disinfection Systems Under Consideration

Lamp type

Number of channels/ modules (banks)/ lamps

2/22/880 2/10/648 2/6/480

Manufacturer

LPHO/vertical LPHO/horizontal LPHO/horizontal

ID1

WEDECO

Trojan

7.4.5 Design Criteria

Power input;

peak, kW

The recommended design criteria for the W Disinfection system are listed in Table 7.4-2.

Mechanical cleaning available

Yes Yes Yes

Table 7.4-2. W Disinfection System Design Criteria

Flow rate I med Criteria

UV transmittance 1 Dercent

Units

TSS, maximum

End of lamp Me I mg/L Temperature, min.

UV dose factor Sleeve f o u h g

F mw.sec/cm2 factor I Type of lamp I Channels number and size

Peak Dower draw I kW

Lamp modules number

Value I Remarks

Head loss

5.5 I Maximum

inches

109.0 90% output after

10,000 hours Loss of UV light

1 due to fouli&

22 with 40 lamps

880 1 80 redundant

One module per channel is

145.2 I All lamps on

redundant 40 redundant

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2.86

2 peak flow

7.5 Structure and Support Facilities

The UV disinfection equipment should be installed in a structure with support systems as discussed below. The equipment requires a room for electrical distribution and, for some manufacturers, ballast panels. Controls for the UV and filter system would be located in this room. The control panel would be linked to the plant SCADA system and integrated into the overall plant control system. A local control panel at the UV equipment area would be the main operating station, with remote monitoring and control available from SCADA.

UV Disinfection Equipment Layout

Figure 7.6.1 shows the proposed layout of the Filter/UV disinfection building. This is based on the use of LPHO lamps installed in a vertical configuration in an open channel structure. The recommended structure would house both the UV disinfection equipment and the effluent filters. It would be a pre-engineered building approximately 50 feet by 55 feet in size. The building would have ventilation but only the smaller interior electrical and control room would be heated and air conditioned. The building w d improve operability by sheltering the equipment from sun and rain as well as limiting the growth of algae in the tanks and basins.

Both the filters and UV disinfection equipment would have overhead monorail hoists for lifting components out of the tanks for maintenance. The components themselves are not extremely heavy, and removal will be infrequent, but adequate maintenance will be improved by limiting the amount of manual lifting associated with maintenance. Lamp sleeve cleaning tanks and a wash-down area would be provided as shown. A small blower is provided as part of the vendor package for agitation of the cleaning tanks and channels.

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Disinfection (TM 5) 7-13

[Inlet Gates .", 4" Channel

Drain t

Level Control r",",:," f weirs

PLAN

Filter Hois'

SECTION

Figure 7.61. Effluent Filters and UV Disinf ction Building Layout

7.7 Estimated Costs

This section evaluates the capital and operating costs of the W disinfection systems considered for

LRWRP.

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7.7.1 Preliminary Construction Costs

This section presents the equipment, construction and operating costs for the W disinfection systems under consideration. Equipment costs are considered to be reliable, since they were provided by manufacturers based on preliminary design criteria provided to them. The estimated costs wiU change if the basic design criteria are revised.

The recommended W disinfection system is the LPHO lamp option installed in an open channel configuration with two parallel channels. The recommended configuration is the vertical lamp UV system installed in deeper channels that provide a better aspect ratio as the flow approaches the lamp modules and optimized plug flow conditions. This system also provides better use of the proposed building space.

The preliminary estimate of probable construction cost for the W system described above is $2,386,515 as indicated for TM 05 in Table 2.1-2. A detailed breakdown of this estimate is provided in Appendix B.

7.7.2 Operating Costs

The major operation and maintenance (O&M) costs associated with UV disinfection are power, lamp replacement, parts, chemicals, and labor. The cost for power is assumed to be $0.10 per kW-hour. Labor is estimated to be $30 per hour. Parts and chemicals are estimated to cost 5 percent of the total of the other operating costs per year. Lamp replacement costs are based on lamp prices and estimated lamp lives are provided by the manufacturers. Estimated operating costs are presented in Table 7.7-2.

Table 7.7-2. O&M Costs for Various UV Disinfection Systems

Alternative

Lamp replacement Labor

Manufacturer

ID1

Trojan per year per yeat ($) I ( $ )

Power cost per year

3 1,200 30,500

Parts and chemicals

A 2,250 2,860

Annual operating cost

47,250 60,060

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Conclusions and Recommendations

The following recommendations are made based on the evaluation of disinfection requirements for the LRWRP discussed in this technical memorandum. The information also considers the recommendations of the September 2002 Master Plan.

The existing sodium hypochlorite disinfection system for plant effluent should be replaced by UV disinfection.

The existing sodium hypochlorite feed system should be retained and upgraded for in plant use as recommended in the Master Plan. There is no plan to use s o & u hypochlorite for redundant disinfection.

LPHO lamps should be used for the new disinfection system. The use of a vertical lamp system is recommended due to lower equipment costs and better use of the available plant site area.

The UV system should be designed for a flow capacity of 5.5 mgd, with upstream flow equalization.

Plant effluent requires filtration prior to UV disinfection in order to meet permit limits. The filters should produce an effluent turbihty less than 2 NTU.

The UV disinfection system should be designed to meet California Title 22 requirements as laid-out in "Ultraviolet Disinfection Guidelines for Drinktng Water and Water Reuse" by the National Water Reuse Institute and the American Water Works Association Research Foundation (latest edition), and other related information.

Title 22 design criteria include:

UV dose of 100 mW.sec/cm2 following granular meha filters

b. UVT of 55 percent unless otherwise demonstrated to be higher. (Pilot study data support a UVT value of 60 to 65 percent.) Use of 60 percent UVT for design will be considered.

c. Filtration to 2 NTU or less upstream of Qsinfection.

d Continuous monitoring of UVT and UV intensity and dose.

e. A redundant bank of lamps is required.

The proposed UV dsinfection system would be a two channel system with 11 modules of vertical lamps for each channel. One bank in each channel would be redundant. A total of 880 lamps are required for the system.

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Disinfection (TM 5) 7-16

The UV disinfection equipment should be housed in a structure that also contains the effluent filters since these processes are so closely inter-related.

10. The Filter/UV Disinfection building should have a separated electrical and control room that is climate-conditioned and contains the power and control panels required for both systems.

11. While Title 22 treatment requires chemical coagulation upstream of filtration and disinfection, this requirement will be met by the upstream metals removal process.

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