LRWRP_Design_Report_Chapter_5.pdf

CHAPTER 5

METALS REMOVAL (TM 3)

5.1 Introduction

Brown and Caldwell held a brainstorming meeting with City staff on September 16,2004, to discuss liquid treatment processes for the Lompoc Regional Wastewater Reclamation Plant PRWRP) upgrade project. The purpose of the meeting was to further define concepts and criteria for liquid treatment processes, including metals removal, to be incorporated into the upgrade project. A copy of the meeting minutes is in Appendix A.

Subsequent to the brainstorming meeting, Brown and Caldwell attended a meeting between the City and the Central Coast Regional Water Quality Control Board (RWQCB) on October 4,2004. The purpose of this meeting was to discuss the City's planned treatment plant upgrade project. The City's efforts in complying with current and future effluent discharge limits for trace metals through source identification, influent and effluent monitoring, and bench-scale testing also were discussed.

A copy of the letter to the RWQCB sent following the meeting is attached.

The Lompoc Regional Wastewater Reclamation Plant Master Plan (Kennedy/Jenks Consultants, September 2002) included a discussion of trace metals issues. These issues were evaluated in more detail in a separate study as reported in the document entitled, Lompoc Regional Wastewater Reclamation Plant Metals Study (I<ennedy/Jenks Consultants, June 2004, Final Draft). This metals study concluded that of the ten trace metals included in the effluent discharge limits (i.e., antimony, beryllium, cadmium, lead, mercury, molybdenum, selenium, silver, and thallium) only two, copper and molybdenum, have the potential to exceed their respective limits. Copper is one of the constituents regulated in the California Toxics Rule (CTR). Molybdenum is a concern because of potential impacts if high-molybdenum water is used for irrigation of fodder crops for cattle feed.

Potable water system corrosion was identified as the likely major source of copper in the treatment plant influent. Potable water distribution system corrosion control was recommended to reduce the influent copper concentrations to LRWRP. Molybdenum occurs naturally in groundwater supplies within the LRWRP service area, so source control is not an option. The report recommended that the potential impacts from effluent molybdenum be reevaluated based on naturally occurring background concentrations in the Santa Ynez fiver and on actual receiving water uses downstream of LRWRP.

5.2 Recommended Investigations

While Brown and Caldwell recognize the City conducted a number of bench-scale tests and performed numerous analyses as part of the metals study, there are several additional investigations we recommend as they may simplify and/or eliminate the need for dehcated metals removal fachties as part of the upgrade project.

First, we recommend that the City analyze for soh& and total copper and molybdenum in the final effluent. The results of these analyses would indicate the efficacy of tertiary filtration alone in complying with final effluent discharge criteria for these two metals. Previous analyses analyzed

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Metals Removal (TM 3) 5-2 only for total recoverable copper and molybdenum, which includes both soluble and particulate species. The tertiary filters will remove most of the particulate species, so copper and/or molybdenum compliance may be achieved through filtration alone if particulate species comprise a significant portion of the total recoverable metals concentrations.

We recommend that the City use ultra-clean sampling and analytical techniques in the collection, preparation and analyses of these samples. Dr. Lewis, of the LRWRP laboratory, noted during the brainstorming meeting that these techniques were used previously by plant staff and yielded lower concentrations compared to standard techniques. The cost of ultra-clean sampling techniques and analysis may be greater, but lower reported concentrations could eliminate the need to construct metals removal facilities, saving the City millions of dollars.

Second, we recommend that the City evaluate the performance of IUarAid CDP450, a blended organic/inorganic coagulant manufactured by GE Infrastructure (formerly Betz Dearborn), for molybdenum removal. The properties of this coagulant result in selective removal of soluble oxyanions, such as molybdate. Previous studies reported by GE Infrastructure showed effective molybdenum removal from industrial wastewaters. We recommend the City conduct a se~ies of jar tests to investigate molybdenum removal with KlaAid CDP450 as it has several potential advantages over ferric chloride; for example, more effective molybdenum removal and lower dosage requirements.

Note that while CDP450 may not provide selective removal of soluble copper species, the floc that is formed likely will capture particulate copper that will result in additional copper removal. If the final effluent analyses recommended above show that copper lunits could not be met through particulate copper removal alone, GE Infrastructure manufactures a blended flocculant, MetClear MR2405, for selective removal of soluble copper. We have tested this, with success, for effluent copper compliance at the U.C. Davis Campus WWW.

5.3 Objectives

Table 5.3-1 lists the effluent trace metals discharge limits that are included in the City's current discharge permit, which was issued on May 18,2001. These limits are to be met by May 18,2006.

The RWQCB included interim limits that were to be met between May 2001 and May 2006.

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Metals Removal (TM 3) 5-3

Table 5.3-1. Discharge Permit Metals Limits

California Toxics Rule Metals Antimony Beryllium Cadmium Copper Lead Mercury Selenium Silver Thallium

Basin Plan Molybdenum

" ppb = parts per billion

I Ultimate limit, pg/L

Interim limit, Average month1 ppb" 1 y Instantaneous

Brown and Caldwell recommends that the City proceed with the corrosion control measures and receiving water investigations recommended in the final draft metals control study. However, we also recommend that metals removal facilities be included as part of the LRWRP upgrade project should copper source control and/or molybdenum receiving water investigation be unsuccessful.

The zero concentration average monthly Limits for beryllium and thallium given in Table 5.3-1 are a concern as they seem somewhat subjective and unreasonable. These were discussed during the meeting with RWQCB. Additional discussions with RWQCB concerning these limts are warranted.

5.4 Existing Facilities

There are no specific treatment facilities for metals removal at the existing treatment plant.

5.4.1 Influent and Effluent Metals Concentrations

A series of cumulative probability plots that show influent and effluent total metals concentrations using monthly analyses between July 2002 and June 2003 are included in this Chapter as an attachment. For some metals that were present at relatively low concentrations, some of the measured concentrations are below the method detection limit (MDL). Where concentrations are below the MDL, the data points are not included on the plot. (Therefore, there are no plots for beryllium and thallium, as all influent and effluent analyses were less than the MDL.) From these plots, the 50th percentde value represents the mean concentration and the slope of the dstribution represents the variability in the reported concentration data. For most of the metals, the existing wastewater treatment facilities provide some level of removal (i.e., the mean concentration between

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Metals Removal ('I'M 3) 5-4 influent and effluent is reduced) and the effluent concentration is more stable (i.e., the slope of the distribution is reduced). The lower effluent concentration variability decreases the risk that discharge permit limits would be exceeded. However, the existing effluent concentration of two metals - molybdenum and copper - exceeds the ultimate discharge knits.

5.5 Process Interactions

5.5.1 Upstream Processes

The LRWRP upgrade project will include new secondary treatment facilities consisting of oxidation ditches and secondary clarifiers as described in Chapter 4 (TM 2). These facilities will replace the existing primary clarifiers, trickling Hter, and t r i c h g filter pumping station, aeration tanks, aeration blowers, and secondary clarifiers to meet new final effluent nitrate lunits included in the 2001 permit. Provisions will be included to modify the nitrification/denitrification oxidation ditch operation should more stringent final effluent phosphorus and/or nitrogen limits be imposed in the future.

h portion of the alkalinity consumed for nitrification will be recovered in the new secondary treatment system through denitrification. This alkalinity recovery wdl likely increase the historical median effluent pH of 6.9 and will help offset downstream alkalinity consumption if ferric chloride (or alum) is added as part of the tertiary treatment facilities.

The secondary treatment facilities will be sized to handle peak dry weather flows at the 5.5 mgd design average dry weather flow (ADWF) condition. Peak influent flow greater than 9.5 mgd will be diverted from downstream of the new aerated grit tanks to the existing emergency holding basin.

These diverted flows will be pumped back for treatment when the wet weather event subsides and influent flow drops below 9.5 mgd.

5.5.2 Downstream Processes

Tertiary filtration using cloth media disc filters and disinfection using ultraviolet (UV) irradation will be downstream of the metals removal process. These facilities, as well as the metals removal process, will be sized for equalized flow at the 5.5 mgd ADWF condition.

5.6 Process Recommendations

The metals removal facdities recommended at this time wdl be located east of the existing aeration tank and secondary clarifiers as shown on the site plan in Figure 1.12.1. These facilities include secondary effluent equalization (in the existing aeration tank), tertiary flocculation/clarification, chemical storage, and chemical feed. New tertiary, lamella clarifiers are recommended to reduce capital costs, compared to molfying the existing secondary clarifiers, by sirnplif$ng construction.

Dedcated faciltties for copper and molybdenum removal may not be necessary based on the results of on-going projects and d~scussions with the RWQCB, so we recommend that the tertiary

February 2005

Metals Removal (TM 3) 5-5 flocculation/clarification facilities and some of the chemical storage and feed facilities be designed as an additive bid item. With this approach, work can proceed on preliminary and detailed design of these fachties, and they may be deleted from the upgrade project any time up to the construction contract award if they are not needed.

The existing aeration tank will be modified for secondary effluent equalization for the upgraded facilities. New variable-speed vertical-turbine pumps will be constructed adjacent to the southeast corner of the equalization tank. The pump speed will be adjusted periodically so the total flow to the flocculation/ clarification facilities equals the current ADWF. This system will equake the flow rate for downstream treatment processes: metals removal, filtration, and UV disinfection. The pump speed will be set initially based on the ADWF when the plant upgrade project is complete, approximately 4.0 mgd. As influent flow increases over time, the pump speed will be adjusted periodically. At the design condition, the pump speed will be set so the total flow is 5.5 mgd. This pump speed adjustability is needed so that continuous flow throughout the day can be maintained to the downstream unit processes when the ADWF is less than 5.5 mgd.

Secondary effluent will flow from the new secondary clarifiers to the equalization tank. The equalization tank volume will vary throughout the day due to diurnal fluctuations. The equalization tank will be emptied daily in normal operation. Flexibility will be included to route the secondary effluent pump discharge directly to the fiters and UV disinfection should the metals removal facilities not be required.

As described below, three new above-grade tertiary clarifiers are recommended for metals removal.

The existing secondary clarifiers would not be used as a process unit in the upgrade project because of the capital costs associated with refurbishing the existing clarifiers for service as tertiary clarifiers and for a second lift station to pump clarified secondary effluent to the filters. The elevation of the above-grade tertiary clarifiers will be set to facilitate gravity flow between the tertiary clarifiers and the filters.

The existing secondary clarifiers will be available for emergency equalization storage, however. The existing aeration tank would be operated as an equalization basin by keeping the maximum water surface elevation (WSEL) below 60.20 feet. If the WSEL rises above an elevation of 60.20 feet, secondary effluent d flow over the weir between the four 304-1 diameter mixed liquor pipes and the mixed liquor channel to the existing secondary clarifiers. These tanks more than double the available equalization volume; however, they would only be used in an emergency as they would need to be drained through the plant drain pumping station.

Three duty secondary effluent pumps and one standby will be provided, as shown on the process schematic in Figure 5.6.1. Each duty pump will be routed directly to the influent of one of the three tertiary clarifiers, providing equal loading to each. This configuration eliminates the need for a separate splitter structure to divide the flow equally to the three tertiary clarifiers. Ferric chloride, caustic soda, and/or polymer will be added to the clarifier influent for metals removal. A mechanical flocculator will be included in each tank. The clarifiers include inclined-plate settlers (i.e., "lamellas") to minimize the tank footprint while limiting the maximum surface overflow rate (SOR) to 0.5 gpm/f? (i.e., 720 gpd/f?) at 5.5 mgd. If one of the tertiary clarifiers is taken out of service, one-third of the equalized secondary effluent flow will be bypassed to the filters. This may

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I .

I

SECONDARY

EFFLUENT

PUMP (4)

v -

LOM SECONDARY - -

ARlFlERS

SECONDARY

EFFLUENT

EQUALIZATION

(TERTIARY CLARIFIER BYPASS) _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - - 7

( TERTIARY

LARlFlER (3)

FILTERS

TO DAFTS

TERTIARY SLUDGE

PUMP (4)

cl-d

POLYMER TOTE POLYMER

BLENDING AND

FEED SYSTEM

Figure 5.6.1. - RECOMMENDED PROCESS SCHEMATIC

FOR METAL REMOVAL

Metals Removal (TM 3) 5-7 increase the final effluent metals concentrations whde a tertiary clarifier is out of service; however, if the plant is meeting the "monthly average" metals limts, the increased effluent concentration with two tertiary clarifiers in service should be less than the "instantaneous" metals limits.

The tertiary clarifiers will be partially below grade to facihate gravity flow between the clarifiers and the filers to minimize pumping operations costs. The flocculated secondary effluent will flow through the above-grade plate settlers, where the solids settle to a below-grade concrete tank. A mechanical sludge mechanism collects the settled solids to a hopper in the tank bottom.

Periodically, settled solids are pumped to the new dissolved air flotation thickeners (DXFTs), where they will be co-thickened and routed to the anaerobic digesters. The clarifier effluent will flow from the tertiary clarifiers to the filters by gravity.

Chemical storage and feed facilities will be located south of the tertiary clarifiers as shown on Figure 1.12.1. Individual storage tanks will be provided for ferric chloride and caustic soda and will be sized to provide a 30-day supply. Ferric chloride is needed for metals removal. Caustic soda is needed to provide additional alkalinity and maintain a target pH during flocculation and clarification and for fmal effluent discharge. Each storage tank will be located in a concrete containment area.

Metering pumps will be located in the corner of each containment area for chemical feed to the tertiary clarifiers. Chemical-duty sump pumps will be included in each containment area to pump out rainwater and chemical should a leak occur. The arrangement of the chemical storage and feed facilities will provide for delivery truck access, mete&g pump access, and sump pump access without having to enter the containment area.

Polymer storage and feed facilities will be adjacent to the ferric chloride and caustic soda areas.

Pallet-sized totes will be used for polymer storage rather than a dedicated storage tank. The polymer storage area will be designed to accommodate forklift access for tote delivery and removal. A polymer blendmg and feed system will be used to dilute the concentrated polymer solution and meter the dilute polymer to the tertiary clarifiers.

If the City's on-going projects and discussions with the RWQCB elimtnate the need for metals removal facilities, the size of the chemical storage and feed facilities may be reduced. If metals removal is not needed, chemical addition is required only for secondary effluent conditioning prior to cloth disc media fdtration. Accordingly, alum storage and feed is recommended in place of the ferric chloride and caustic soda storage and feed facilities. Continuous alum addition may not be needed to meet effluent dscharge or recycled water criteria. When alum addition is needed, alum doses are no greater than approximately 10 mg/L for an in-line frltration configuration. There would be no change in the recommended polymer storage and feed facilities.

5.7 Design Criteria

Design criteria for the recommended facilities are summarized in Table 5.7-1. These design criteria include the tertiary clarifiers and ferric chloride and caustic soda facilities needed for metals removal.

Metals Removal (TM 3) 5-8

Secondary Effluent

Table 5.7-1. Design Criteria

Equalization

Equalization tank

Volume

Secondary effluent pumps

TJTe Number

Capacity, each

Tertiary Clarifiers

Type

Number

Sedimentation area

Number

Chemical Storage and Feed Ferric chloride storage tank

Number

Capacity

Caustic soda storage tank

Number

Capacity

Polymer storage

Type Number

Ferric chloride pumps

Type Number

Caustic soda pumps

Type Number ft' gal gal

Value

Surface overflow rate, max

Tertiary Sludge Pumps

Vertical turbine, variable speed

3 duty/ 1 standby gpm/ ft"

Inclined plate, above-ground w/flash mixer and flocculator

3,900

Progressing cavity

3 duty11 standby

Portable totes

1 duty11 standby

Diaphragm metering

1 duty/l standby

Diaphragm metering

1 duty11 standby

Metals Removal ('I'M 3) 5-9

5.8 Preliminary Cost Estimate

The preliminary estimate of probable construction const for the metals removal facilities is $4,364,088 as indicated for TM 03 in Table 2.1-2. A detailed breakdown of this estimate is provided in Appendix B.

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ATTACHMENT A

LETTER FROM CITY TO RWQCB

October 15,2004

Mi-. Gerhardt Hubner California Regional Water Quality Control Board Central Coast Region 895 Aerovista Place, Suite 101 San Luis Obispo, California 9340 1-7906

Subject: City of Lompoc Regional Wastewater Facility

Thank you very much to you and Todd Stanley for taking time to meet with us on 4 October and allowing us to share with you our recent progress with our wastewater facility upgrades. As we mentioned, we have recently accomplished the following milestones.

Completed and submitted reports in 2002,2003, and 2004 as required by our Waste Discharge Requirements Order No. 01-87 which provide important information on the sources of to our system as well as the effectiveness of treatment options to achieve interim and final effluent limits contained in our permit.

Began bench scale testing to evaluate the effectiveness of treatment options to achieve interhn and final effluent limits contained in our permit.

Signed a $6 million contract with Brown and Caldwell to provide preliminary design, detailed design, and construction management services for major upgrades to our wastewater facility to assure compliance with final effluent limits.

Obtained Oty Council approval for increases to our IocaI wastewater service charges to support the ultimate construction of our wastewater facilityupgmdes.

Applied for $46 million in loans from the State Revolving Fund to support the ultimate construction of our facility upgrades.

Bonds for the Gty's portion of the costs for the plant upgrade project will be issued by the Gty in January 2005.

In addition, we shared with you our preliminary schedule for the wastewater facility upgrades which includes a construction start date of April, 2006 and a construction completion date of April, 2008.

As we discussed with you, we are confident we will be able to achieve compliance with the vast majority of find effluent limits for constituents for whth there are interim litnits by the deadline contained in our current permit. We have attached a series of cumulative probability plots that show influent and effluent total metals concentrations using monthly analyses between July 2002 and June

Mr. Gerhardt Hubner October 11,2004

2003. For some metals which were present at relatively low concentrations, some of the measured concentrations are below the method detection limit (MDL). For those concentrations below the MDL, the data points are not included on the plot. (There are no plots for bery&urn and thallium, as all influent and effluent analyses were less than the MDL.) The 50' percentile value represents the mean concentration and the slope of the distribution represent. the concentration variability.

For most metals, the existing wastewater treatment facilities provide some degree of removal (i.e., the mean concentration is reduced) and the effluent concentration is more stable (i.e., the slope of the distribution is reduced). However, the existing effluent concentrations of two metals -molybdenum and copper - exceed the final effluent limits. As we discussed, we have some concerns with our ability to achieve compliance with the final limits for the constituents discussed below and appreciate your willingness to work with us to address these concerns.

Molybdenum: Analysis of the different influent water supplies in our service area has revealed elevated, natural levels of molybdenum, which are, in fact, higher than the final effluent limit contained in our permit that will be effective May 18,2006. The molybdenum cumulative probabilityplot in the attachment shows the existing treatment facilities do not affect the influent molybdenum; the effluent molybdenum concentrations equal the influent concentrations. In addition, our preliminary bench testing does not provide us with a high degree of confidence that our proposed treatment facilities will reduce molybdenum below the final effluent limit. Additional facilities, such as reverse osmosis, may be the only means available to achieve the permit lirnit.

These facilities would be extremely expensive to build, operate, and maintain, particularly for the removal of only one constituent. Disposal of the reverse osmosis concentrate (also referred to as brine) is problematic given the proximity of Lompoc to the ocean.

Additionally, we are aware of no reported historical evidence that existing natural levels of molybdenum in our mter supply have caused any impairments of the downstream agricultural water supply. The 10 pg/L limit cited for agricultural beneficial reuse in the Basin Plan, which was the basis for the discharge permit limit, is based on a document published in 1972. We have contacted agricultural water quality specialists at UC Davis regarding subsequent research on the impacts of molybdenum on agricultural water use. This research may indicate no impairment at concentrations exceeding 10 ,ug/L, especially in areas with naturally occurring elevated molybdenum levels. We will keep you apprised of any information we obtain.

We understand from your comments that over the next few months, you will investigate the Board's original rationale for the molybdenum limit which supported a Basin Plan ag r i cu ld water quality objective and determine whether that rationale continues to be appropriate for the mter body receiving our wastewater treatment plant effluent. We also understand you will determine the appropriateness of the existing effluent molybdenum limit in light of the fact that the CitJI's influent water supply has naturally elevated levels; you will also review other facilities molybdenum limits for consistency with the Citfs limit. We understand you may consider a revised effluent limit during our permit reissuance in 2006 and/or an extension to our compliance time schedule for this constituent.

Copper: Based on our bench-scale testing, we are optimistic we wiU be able to achieve compliance with the monthly average final effluent limit contained in our permit for copper of 8.9 &L.

Mr. Gerhardt Hubner October 11,2004

However, due to a lack of extensive data at this time, we are still not able to say with complete confidence we will be able to meet this limit 100 percent of the time. We anticipate additional data collection to more confidently answer this question. For example, we wiU analyze some effluent samples for both total and soluble (43.45 copper to determine if more efficient effluent suspended solids removal will allow us to meet the pennit final limit. We understand from your comments you would be willing to consider this issue as a part of our permit reissuance in 2006 and may consider a revised effluent limit for this constituent or an extension to our compliance time schedule.

Beryllium and Thallium: We wanted to make you amre also of o w concerns of the zero limits for these two constituents. There is a foot note in our permit stating limits of zero wiU be equivalent to the method detection limit of the constituent in question. Our concerns are that the limit will change each time a detection limit changes, that there is an unclear basis for these limits being either water quality based or technologically based.

TDS: Although we didn't have time for an in-depth discussion of total dissolved solids ('IDS), as you know, future discharges from our facility will likely exceed o w current pemit level for this constituent. As with molybdenum, analyses of the different influent water supplies in our service area have revealed elevated concentrations of TDS. Also like molybdenum, consistent removal of TDS would require very expensive treatment technologies, such as reverse osmosis. We request to have more in-depth discussion of TDS prior to our permit reissuance in 2006 and look forward to any suggestions you may have on how we should address this challenging issue.

Water Reclamation: Water rights issues have prevented the City of Lompoc from reclaiming wastewater treatment plant effluent for non-potable reclaimed water use. However, downstream agricultural users rely upon groundwater recharge from the Santa Ynez River for their supply and are, in essence, reclaiming the Civs effluent. We believe this groundwater recharge is consistent with the Board's interest in water reclamation throughout its region.

Thank you very much for your assistance with and continued discussion of these issues. The City of Lompoc is committed to protect and enhance it. local environment which includes compliance with our NF'DES permit. We appreciate the opportunity to work with you to assure our effluent limits are protective of our environment and appropriate for our local conditions. We look forward to the upcoming permit reissuance process and welcome any suggestions you may have in the interim on how we may best address our concerns.

Please contact me at 805-875-8405 or shalpin@ci.lompoc.ca.us if I may answer any questions.

Susan Halpin Wastewater Division Superintendent

ATTACHMENT B

CUMULATIVE PROBABILITY PLOTS OF

INFLUENT AND EFFLUENT METALS CONCENTRATIONS

4 Sb (Effluent)

Plant data (7102-6103)

Percent

4 CU (Effluent)

- Pb (Effluent)

4 Hg (Effluent)

4 Mo (Effluent)

Plant data (7102-6103)

---- Ag (Influent) G I

-E!- Se (Effluent)

Figure A. Potable water copper concentration.

reated mtable VAFB - Gmundwaler VAFB - Surface water WCSD - Gmundwd

Figut- -. - otable water molybdenum concentration.