Water Treatment Plant Improvements Study

Transcription

1 Water Treatment Plant Improvements Study Prepared for City of Pittsburg, CA July 22, 2011 Prepared by: Erik Zalkin, P.E., Browv and Caldwell California LicensNo. C75392 Reviewed by: Williai K. Faisst, PhD, PE, Project Manager Brown and Caldwell California License No. C29146 Brown AND Caldwell 201 North Civt Drive, Suite 115 Walnut Creek, California 94596

2 Executive Summary The City of Pittsburg (City) Water Treatment Plant (WTP) is a 32-million-gallons-per-day (mgd) facility last expanded and upgraded in The WTP needs improvements to mitigate current operating problems and to prepare it to reliably handle higher flow rates and meet current and anticipated drinking water regulations in the foreseeable future. The City contracted with Brown and Caldwell to conduct a study to address the problems and evaluate improvement measures. The findings and recommendations are presented in this report. Key Areas of Concerns Based on previous studies and current operations, City staff has identified the following key areas of concern for WTP operations: Separate treatment trains - Sedimentation Basins 1 and 2, and Basins 3, 4 and 5, operate differently as two parallel treatment trains. This situation makes it difficult to optimize chemical coagulation and flocculation. The main water source for both trains is the Contra Costa Canal; however, Basins 1 and 2 receive recycled water (up to 10 percent of WTP flow) from the lower lagoon after coagulation (rapid mix), while Basins 3, 4 and 5 receive well water at up to 2,000 gallons per minute (gpm), also downstream of coagulation. The City cannot introduce the recycled water and well water into the rapid mix tank ahead of the canal pumps due to potential backflow to the Contra Costa Canal. Lack of sedimentation basin sludge removal - The sedimentation basins have no regular sludge removal capability. Sludge accumulation reduces volume for floc settling and creates an opportunity for manganese dioxide (Mn02) reduction and dissolution due to anaerobic conditions resulting from long-term sludge storage. At higher hydraulic loadings, the sludge could re-suspend and cause higher turbidity in water directed to the filters. WTP staff drains each basin annually to the lower lagoon, which introduces extensive solids into the lagoon. These solids settle slowly, thus increasing the turbidity of water pumped back to the sedimentation basins and recycling iron and manganese. Manganese recycling - Manganese coming from the wells and recycled water from the lower lagoon can pass through the sedimentation basins and filters. Anaerobic conditions lead to re-dissolving manganese from sludge stored in the lower lagoon. Manganese can also be re-dissolved in the sedimentation basins as mentioned above and pass through the filters. Manganese oxidation by chlorine is not very effective at ph lower than 9. Using potassium permanganate (KMn04) to oxidize iron and manganese exacerbates the overall manganese problem due to the formation of Mn02from the oxidant itself. This problem is considered the main cause of occasional finished water turbidity excursions. A previous mass balance investigation indicated that the KMnO4 addition contributed 80 percent of the total manganese loading to the WTP; therefore, ending KMn04addition dramatically decreases possible manganese recycling. Algae growth in the lower lagoon - Algae growth during warm weather has caused taste and odor problems in the recycled water. Staff attempted to control lagoon water ph, and hence algae growth, by adding caustic soda manually, but this creates risks for the operators. Last summer, staff added KMn04 to the lower lagoon, which succeeded in controlling algae growth; however, this measure added more Mn02 to the sludge, which exacerbated the problem of returning manganese in the recycled water. Brown /*in Caldwell ES-1 P:440000\14 V:_... PittSOurg VVTP Improvement St, -2. L. REPORT \Pittsiat.irg WTP Improv.Gments Study Final RepOrt.doex

3 Executive Summary Water Treatment Plant Improvements Study Recycled water turbidity - The maximum turbidity of the recycled water from the lower lagoon regularly exceeds 2.0 nephelometric turbidity unit (NTU), which is the turbidity goal recommended by the Cryptosporidium Action Plan (CAP) issued by California Department of Public Health (CDPH) to reduce the potential for reintroduction of pathogens from recycled flows. In a letter dated December 21, 2010, CDPH requested that the City seek solutions to mitigate the recycled water turbidity problem. Major Near-Term and Future Improvements Brown and Caldwell identified and evaluated near-term and future improvements for the WTP. Figures ES-1 and ES-2 show the existing WTP and proposed WTP schematic flow diagrams, respectively, for comparison. Figure ES-3 shows the new facilities integrated into the existing site plan. These facilities represent a preliminary plan for improvements and upgrades. The City will use detailed design to refine and optimize final facilities. The recommended improvements include the following: 1. Chlorine dioxide to replace KMn04 - chlorine dioxide would replace KMn04 to oxidize iron and manganese and to reduce taste-and-odor and disinfection-byproduct (DBP) formation potentials. Chlorine dioxide (CI02) is a desirable alternative oxidant to KMn04 as it does not add manganese loading to the sedimentation sludge, and the resulting low level chlorite residual from the C102 is beneficial in reducing nitrification in the distribution system. New facilities would include a chlorine dioxide generator and injection system installed in the existing chlorine storage room and a sodium chlorite storage tank in the chemical storage area. 2. Influent water blending and chlorine dioxide contact - a new 42-inch-diameter steel pipe would combine WTP influent flows from the existing 24-inch- and 30-inch-diameter influent pipes. New equipment would inject chlorine dioxide to the combined influent and mix the flow prior to entering a new concrete chlorine dioxide contact tank. Rapid mix (chemical coagulation) would occur after the contact tank. Coagulated water would re-enter the existing 24-inch- and 30-inch-diameter pipes that flow to the existing flocculation and sedimentation basins. 3. Ammonia feed relocation and dilution water softening - the WTP is currently using only chloramines to achieve required disinfectant contact time (CT). To have better operational control and flexibility, City staff would like to achieve required CT without depending on contact time in the finished reservoirs by using free chlorine contact between rapid mix and the end of flocculation. C102 use should help to limit DBP formation. The first ammonia feed point would be relocated, from the rapid mix tank to the end of flocculation, to provide a period of free chlorine contact, thereby increasing CT credit. A new softening system would soften the ammonia injection dilution water to prevent calcium carbonate precipitation in the injection piping. One uncertainty about the relocation of the ammonia feed relocation is the potential effect on DBP formation (trihalomethanes, ha loacetic acids, and N-Nitrosodimethylamine [NDMA1). Bench-top investigation should precede detailed design to address this potential issue. 4. Spent filter backwash management - two new packaged treatment systems (flocculation/plate settler, one initial and one future) would treat water from the lower lagoon - or later from a new equalization tank - to meet the 2.0 NTU turbidity goal of the CAP prior to recycling. Initially one settler would receive and treat flow diverted directly from the lower lagoon. A new recycle equalization tank, constructed after the first new settler is operating and flows through the WTP increase substantially, would store and continuously mix spent filter backwash (and miscellaneous flows from the new sludge management system) to prevent solids settling. The phased construction approach is necessary due to City's financial and budgetary constraints. C102 use in place of KMn04 makes construction and operation of the new equalization tank less urgent from a manganese re-dissolving point of view. ES -2 BrownANoCaldwell PIttsturg WTPimprovement Study 00 7: NAL REPORT \Pittsburg WTP improvements Study_

4 Water Treatment Plant lmprovements Study Executive Summary 5. Sedimentation basin mechanical sludge removal and thickening - one cable-drive submerged siphon sludge collection unit would be installed in each of the five sedimentation basins to regularly remove sludge. Sludge would flow to a sludge equalization tank with continuous mixing to prevent solids settling. The sludge equalization tank would also receive sludge from the spent filter backwash treatment system. Two new sludge thickeners would thicken the sludge prior to dewatering or drying in the sludge lagoons. Supernatant from the thickeners would flow by gravity to the recycle equalization tank. This approach is considered a longer term improvement as the use of C102 makes the mechanical sludge removal implementation less critical from the manganese re-dissolving point of view. 6. Sludge dewatering - for the foreseeable future, thickened sludge from the thickeners would be pumped to the upper lagoon for drying prior to landfill disposal. A new dike would convert the southern portion of the lower lagoon to a second sludge drying lagoon (approximately 0.5 acre). The rest of the lower lagoon would be used for stormwater and emergency overflow storage. In the future, when WTP annual average flow rate increases to a point when the drying lagoons have insufficient capacity (approximately 15 mgd average annual flow), the City could install mechanical dewatering facilities to supplement the sludge lagoons. Due to uncertain future energy costs and potential technology advancement, the City should conduct a more detailed evaluation near implementation time (approximately 3 to 5 years prior to the anticipated need) to determine the most appropriate technology. Brown.Caldwell ES-3 3 FINAL REPORT \Nasty,. Improvernts Study_fmal RepOrt.docA

5 5 Hovt, WII 5,,,0 qtr., Sea Easin II 1.,I1,1 Costa C..1.,1 Sod Su5in ilmr, Lhstritlaor Systr,rn 11, Pomp, 3 :400 on, pt,ch H 2, 6000 son, each o Pumps 2800 ori, I O Walor Resonoirs 5er0010 Ptary4.500 OM, 65v5 Pm, Urpti PROPOSED City of Pittsburg WTP Improvements Study Figure DRAW (0) Brown AND Caldwell Existing Process Flow Diagram E-1

6 3; -;, I (NHei AL UM POLYMER CI, (NH.I) I L.-7,, MECHANICAL SLUDGE REMOVAL INK+) RAPID FLOW L5,11.4,3 U IX INS 002 CONTACT TANK SPLIT CHAMBERS MECHANICAL SLUDGE REMOVAL SLUDGE 0. SLUDGE THICKENERS EQUALIZATION (2 gi TANK.4 TO UPPER LAGOON 5.12 r4e) OR CEWATERING EFFLUENT /INFLUENT SLUDGE PUMPS SLUDGE PUMPS PACKAGED INCLINED PLATE SETTLER (FLO0CLARIFICATION SYSTEM( 12 t5 NgdmicE1, 1 RECYCLED WATER PUMPS INFLUENT PUMPS EQUALIZATION TANK w pm (0.50 MG) NOTE: Gradly flow poselbla dooming on final packaged SLUDGE.11 PUMPS Brown AND Caldwell City of Pittsburg WTP Improvements Study Proposed Process Flow Diagram STATIC MIXER r - CK)2 555 EXISTING PROPOSED

7 NOT TO SCALE Figure E-3 sl.juzei c %lb, qv, EC UAL LTATION / NOTE: DETAILED DESIGN TALL CONSIDER ALTERNATIVE EQUIPMENT FOR SLUDGE EQuALIZA I ION AND THICKENING TI rickeners (2) EWATERING I %UR DING (FUTURE)] TO UPPER LAGOON City of Pittsburg WTP Improvements Study Proposed Site Plan qi"graiii0 ittatlik ib, met, FLOW SPLIT I 1111 IMF 11, M1 I sums II TO SLUDGE STORAGE EU TANK SLUDGE PUMP."' PACKAGED PLATE NFL)) SETTLERS (2) PUN RECYCI EQUALIZATION RECYCLED BASIN WATER PUMPS (IF REQUIRES) RECYCLE \ EQUALIZATION BASIN \ (FUTURE) Brown Arl3 Caldwell POSSIBLE AL TE RNA tivt LOCATIONS FOR PACKAGED PL An- SETTLERS rs

8 Water Treatment Plant Improvements Study Executive Summary Capital Cost and Preliminary Implementation Schedule Table ES-1 presents the opinion of probable capital cost for the improvement measures described above. The total opinion of probable cost, excluding the mechanical sludge dewatering system, is about $11.3M. Due to budget constraints the City may prioritize improvements implementation. Table ES-2 provides an initial phased construction plan with estimated capital by phase. Completing Phase 1 would address all CDPH issues described above. Figure ES-4 shows a preliminary implementation schedule, with firm dates only for Phases land 2. Table ES-1. Opinion of Probable Capital Costs of Improvement Measures Improvement Measure Estimated Costl (millions) 1. Influent blending and chlorine dioxide (C102) contact $ C102 generation and chemical storage and chlorinator modification $ Ammonia feed relocation $ Spent filter backwash management $ Sedimentation basin mechanical sludge removal and thickening $ Sludge dewatering (converting part of lower lagoon into a sludge lagoon) $ Sludge dewatering (add mechanical dewater in new building $1.95 TOTAL $13.23 lall costs are capital costs including allowances of 35 percent for contingency and 20 percent for engineering, legal, and administrative costs. Costs are in Winter 2011 dollars based on AACE1Class 4 construction cost estimates prepared for the San Francisco Bay Area when the ENR CCI was When the City implements projects, it should update estimated costs to the construction midpoint. Table ES-2. Project Phasing and Cost by Phase Preliminary Capital Cost (millions), Improvement Measure Phase 1 Phase 2 Phase 3 Phase 4 Influent blending and chlorine dioxide (CI02) contact $2.16 C102 generation and chemical storage and chlorinator modification $0.48 Ammonia feed relocation $0.12 Soent filter backwash management First treatment unit and piping $ i Second treatment unit $ MG Backwash basin $2.82 Sludge management Sedimentation basin mechanical sludge removal $1.22 Sludge thickening $1.90 Sludge dewatering (converting part of lower lagoon into a sludge lagoon) $0.48 Sludge dewatering with building $1.95 Total $4.16 $3.60 $2.82 $2.65 1A11 costs are capital costs including allowances of 35 percent for contingency and 20 percent for engineering, legal, and administrative costs. Costs are in Winter 2011 dollars based on AACEI Class 4 construction cost estimates prepared for the San Francisco Bay Area when the ENR CC/ was When the City implements projects, it should update estimated costs to the construction midpoint. Brown.D Caldwell ES-11 1.f:0000 \ Pittsburg VVTP improvement SluCy005.Delivereoies - \FINAL REPORT \Pittsburg WTP improvements Study_Final Rrmor..bocii

9 Executive Summary Water Treatment Plant Improvements Study Phase 1 Phase co. ca Cl3 Q4 Q1 42 Q Q cta Design and Permitting ' Bid and Award li Construction and Start-up Phase 2 Design and Permitting Bid and Award Construction and Start up Note: The City will schedule Phase 3 (Spent Filter Backwash Equalization Basin) and Phase 4 (Second Spent Filter Backwash Treatment Unit and Mechanical Sludge Dewatering) as funding becomes available and water demand increases. Figure ES-4. Preliminary Schedule of VVTP Improvement Measures Conclusions and Recommendations The City should upgrade the WTP on an accelerated schedule to mitigate current operating and regulatory compliance problems, starting with bench testing and design to satisfy regulators. Upgrades will also prepare the WTP to handle higher flow rates reliably while meeting anticipated future drinking water regulations. Implementing and operating the improvements recommended in this report will bring the City into compliance with pertinent policies and regulations. The City can prioritize the improvement measures and implement them on a phased schedule in accordance with available funding; however, the influent blending, C102 contact, spent filter backwash treatment unit and ammonia addition relocation recommendations have the highest priority. Prior to implementing the C102 injection and ammonia feed relocation improvements, the City should conduct bench-scale testing for C102 demand and for the effect of NDMA generation with C102 and free chlorine. The City can postpone mechanical sludge removal and thickening and sludge lagoon conversion by several years, if necessary. The WTP is not expected to require the backwash equalization tank, second filter backwash treatment unit, and mechanical dewatering system for several years, and can conduct a more detailed evaluation of alternative dewatering technologies when such a need arises. The use of C102 in place of KMn04 for iron and manganese oxidation makes it possible to postpone the implementation of the sludge management improvements because of the manganese re-dissolution issue. Using C102 has the added benefits of DBP reduction and distribution system nitrification minimization, and is highly recommended. ES-12 BrownanCaldwell

10 201 North Civic Drive, Suite 115 Walnut Creek, California Tel: Fax: August 19, 2011 Brown AND Caldwell Mr. Walter C. Pease Director of Water Utilities City of Pittsburg - Department of Public Works 65 Civic Avenue Pittsburg, California Subject: Phase 1 Budget Adjustment (Remove C102 Portion from Blending Component) Dear Walter: As you requested, we revisited the cost estimates for the water treatment plant influent blending and chlorine dioxide components. In the table below, we divided Phase 1 into two sub-phases: la and lb. Phase la includes the blending piping modifications, static mixer, rapid mixing tank, dual rapid mixers, chemical injection, and flow split structure. This accounted for about 75% of the original Influent blending component cost ($2.16M). Phase lb includes all facilities related to Chlorine dioxide (d02) generation, injection and the C102 contact tank. Note that doing the work in two separate steps might increase the total cost slightly (extra piping, knock out walls, etc.). Hence we increased the budget for Phase lb slightly. Thus the total cost for Phase 1 in two steps is slightly higher than the Master Plan cost. Please call or us with any questions. Very truly yours, Brown and Caldwell William K. Faisst Vice President WKF:EZ:ddt E51/---. ele44,44 Erik Zalki, 9.E. Project M6Wrager bcw01 \projects \ \ Pittsburg WIP Impiovem&nt Study \ 005-Deliverables \FINAL REPORT \Phase I Budget Adjustim,nt docx

11 Mr. Walter C. Pease Director of Water Utilities August 198, 2011 Page 2 Table ES-2. Project Phasing and Cost by Phase Preliminary Capital Cost (millions) 1 Improvement Measure Phase la Phase lb Phase 2 Phase 3 Phase 4 Influent blending, static mixer, rapid mixing and flow split $1.58 C102 contact tank, piping and equipment $0.65 C102 generation, chemical storage and chlorinator mods. $0.48 Ammonia feed relocation $0.12 Spentfilter backwash management Firsttreatment unit and piping $1.40 Second treatment unit $ MG Backwash basin $2.82 Sludge management Sedimentation basin mechanical sludge removal $1.22 Sludge thickening $1.90 Sludge dewatering (converting part of lower lagoon into a sludge lagoon) $0A8 Sludge dewatering with building $1.95 Total $3.10 $1.13 $3.60 $2.82 $2.65 1A11 costs are capital costs including allowances of 35 percent for cont ngency and 20 percent for engineering, legal, and administrative costs. Costs are in Winter 2011 dollars based on AACEI Class 4 construction cost estimates prepared for the San Francisco Bay Area when the ENR CCI was 10,120. When the City implements projects, it should update estimated costs to the construction midpoint. \\biliwcis.01 \projects \ \ Pitlsburg WIP Improvement Study \ 005-Deliverables \FINAL REPORT\ Phase 1 Budget Adjustment docx