Water Reuse Via Dual Distribution Systems

Transcription

1 GEPA Unted States Envronmental Protecton Agency Water Reuse Va Dual Dstrbuton Systems May 1985 Po?-c^) o\%.., - 1 ' j -. '! '

2 Water Reuse Va Dual Dstrbuton Systems ntroducton Many communtes are experencng water supply shortages. n partcular, communtes wth rapdly growng populatons, n ard clmates, or wth partal water supply contamnaton, may have a demand for water that exceeds ther supply. One remedy to ths problem s development of a dual dstrbuton water reuse system. Dual dstrbuton water systems transport reclamed water from treatment plants to rrgaton or ndustral stes. n many areas, development of a wastewater reuse system would provde reclamed water at a lower cost than potable water. Substtuton of reclamed water for potable water can reduce demands on ground water supples and can reduce or elmnate the amount of wastewater treatment plant effluent dscharged to envronmentally stressed surface waters (See Fgure 1). - tt Fgure 1. Dual Dstrbuton System Schematc A look at four operatng dual dstrbuton systems shows a cross-secton of benefts avalable from operatng a wastewater reuse system. The experences of the wastewater reuse facltes n rvne, CA; Tucson, AZ; Colorado Sprngs, Co; and St Petersburg, FL clearly demonstrate the benefts of utlzngfhs knd of wse management of a scarce and vtal resource... our water. rvne, Calforna Nature ntended ths land to be brown; f you want t to be green, brng your own wafer. So go the openng lnes of a hstorcal artcle about Southern Calfoma, where Orange County s lrvne Ranch Water Dstrct (RWD) s located. Encompassng 70,000 acres, nearly one-sxth of the county, RWD mports water from the Feather Rver n north-central Calforna va the Calforna Aqueduct and from the Colorado Rver va the Colorado Rver Aqueduct. RWD s Plan for Water Reclamaton Once mported, the water used and dsposed of as sewage by the Dstrct s 35,000 customers s reclamed. Reclamed water, about 9 mgd n 1984, rrgates cropland, a regonal park, school grounds, street medans and edgeways, golf courses, resdental lawns, and greenbelt pathways. Wastewater s reclamed and recycled by the Dstrct at the Mchelson plant rather than dsposed of nto streams or the nearby Pacfc Ocean. RWD s Water Resources Master Plan of 1972 trggered the constructon of sutable treatment facltes and the requrement that any,new development nclude dual dstrbuton facltes fo; potable and reclamed water. The Treatment Process Sewage treatment at the Mchelson plant s farly typcal, consstng of conventonal prmary and actvated sludge treatment, wth a capacty of 15 mgd. The reclamed water facltes consst of the addton of coagulaton chemcals, drect fltraton (seven sandfne carbon gravty flters), and two-hour chlornaton. All effluent leavng the plant must meet strct water qualty crtera establshed by the Calforna Department of Health Servces. Strngent relablty features are ncluded throughout the plant and storage ponds are avalable to contan, and return to treatment, any plant effluent not meetng the crtera. Dual Dstrbuton System The dual dstrbuton system ncludes an extensve array of storage reservors, pump statons, and a transmsson/dstrbuton ppng system. Water n the dual dstrbuton system s avalable upon demand by customers. t s delvered through regular servce connectons and meter facltes. n most cases use of declamed water for landscape rrgaton must occur between the hours of 9 p.m. and 6 a.m. Automatc controllers are used throughout. Reclamed water s sold at 85% of the prce of domestc water. The reducton n prce s n recognton of the lmtatons upon use and as an ncentve for choosng reclamed water. The costs of reclamaton and operaton of a dual dstrbuton system are hgh. Under 1984 condtons, the RWD reclamed-water. system requred a small payment n leu of altematve dsposal costs from the users of the sewerage system. -

3 Cty of Tucson, Arzona n Tucson, a Metropoltan Wastewater Reuse Assessment was completed n March of 1983 to assess the demand for reclamed water for turf rrgaton n the metropoltan area (See Fgure 2). The results of ths study were used to provde a basc plan,ar a reclamed water system provdng pretreatment by mssure fltraton of 8.2 mgd (expandable to 25 mgd). -he project was completely constructed wth local knds and was desgned and placed n operaton n dy eght months Year -gure 2. Projected Amual Reclamed Water Demand for Turf rrgston 4 demonst:aton recharge project s beng constructed '3 stcre up to 1.5 mgd of reclamed water underground durng low demand wnter months whch wll be pumpe:' lo the system durr;g peak summer demand. The Rr 'large Project wll be studed to evaluate the :reatmc t provded by the vadose (unsaturated sols) zone to assess the potental applcaton of ths treatment for future recharge projects. costs A 10-year captal drogram s n place to prqvde 24,000 acfe-feet per year of reclamed water to dentfed users gt a cost of $39 mllon. Operatng and manteoance costs are projected to be $70 per acre-foot whch ncludes $24 per acre-foot for pumpng. Users of the reclamed water pay 80% of!he applcable potable water rate, presently $348 per acre-foot. Effects on Potable Water System As turf rrgaton users shft from the potable system to reclamed water, overall utlrty revenues wll declne somewhat. Ths loss of revenue s generally offset by the reduced need for well capacty. More mportantly, the reclamed water system allows hgh qualty, potable ground water to be reserved for future use by Tuwn's. growng populaton. Publc Acceptance t would not have been possble for a project such as Tucson's to be constructed and nsttutonalzed n such a short tme wthout poltcal leadershp and wdespread publc acceptance. Publc offcals n Tucson are commtted to managng the regon's lmted water supp!y. The reuse of reclamed effluent s an mportant element n achevng the basnwde water balance mandated by state law. Colorado Sprngs, Colorado - Colorado Sprngs has reclamed wastewater for landscape rrgaton snce Secondary effluent from both an actvated sludge treatment plant and a trcklng flter plant s pplshed by seven gravty sandlanthracte dual meda flters and stored n uncovered reservo& pror to fna! chlorna'on and dstrbuton. The system fas a producton capacty of 10 mgd. Non-potable rrgaton water s delvered to users va a 13-mle dstrbuton system. Average daly summer rrgaton use s 5 mgd. Non-potable water s used tg rrgate approxmately 600 acres of landscapng n Colorado Sprngs ncludng the wastewater treatmmt faclty, muncpal parks, golf courses, cemetares, and prvate commercal establshments. Also, constructon frms purchase non-potable wa!er for constructon purposes and dust control. System Operaton The sand fltraton operaton s manned by wastewater treatment faclty personnel, whle the dstrbuton-system and storage lakes are mantaned by a sngle caretaker. Non-potable system customers own and operate the dstrbuton system on ther own stes n accordance wth a Use Polcy ssued and enforced by the Cty Wastewater Dvson n accordance wth gudelnes from the Colorado Department of Health. The Wastewater Dvson conducts an extensve samplng program of the rrgaton system to assure a hgh qualty product. c - COG&. The reclamed wastewater porton of the rrgaton system was put on lne n 1955 and expanded n The system s fnanced entrely by user charges. The non-potable water rate s set at $54 per hundred cubc feet as opposed to a potable water rate of $1.22 per hundred cubc feet. Snce Colorado water law operates on $e Lwropratons doctrne, the non-potable rrg n mportant element n the plan for the Colorado Sprngs water resources. Ths nhc economc beneft of securng the cty's. water.'{ghk'vady outweghs the ope

4 Publc Acceptance Colorado Sprngs' non-potable rrgaton system has a hstory of trouble-free operaton wth regard to communty health. An extensve epdemology study to assess the mpacts of the system on communv health has ndcated that there are no apparent dfferences n gastrontestnal llness rates between users of parks rrgated wth potable versus non -potable water. Publc acceptance of reuse technology n general, and the exstng rrgaton system n partcular, s hgh. Strong local partcpaton n the Areawde Water Qualty Management Plan (the 208 Plan) has resulted n repeated endorsement of wastewater reuse. St. Petersburg, Florda The cty of St. Petersburg operates the largest effluent spray rrgaton system n the Unted States. n response to PL and a state legslatve act that requred ether advanced treatment or zero dscharge to Tampa Bay, the Cty Councl adopted the concept of zero 'dscharge through wastewater reuse n Three cf the Cty's four wastewater plants currently supply water to the effluent dstrbuton system. When the fourth plant s ted to the system (scheduled for 1986). the recycled water potental wll ncrease to 66.4 mgd. Although current demand requrements are less than 20 mgd, the Cty's pragram for extendng the dual water system wll contnue to ncrease effluent usage. n addton, other nearby communtes may eventually use the Cty's effluent. System Desgn Each of the four wastewater plants s a standard Complete Mx Actvated Sludge plant wthout prmary clarfers. Complete Mx requres a shorter aeraton detenton tme for treatment, and therefore, a smaller aeraton basn. The shorter aeraton perod normally prevents ntrfcaton. The ntrogen and phosphorus n the effluent reduce lawn fertlzer requrements - a good sellng pont. A tregfed wastewater man tes all four plats together n a complete loop, dmhathg any problems n supply or pressure drops due to shut-down at any one plant. mllon gallons) provde the reservor for nghttme pumpng. The closed storage tanks elmnate algae problems, as well as mosqutoes, brd contamnaton, etc. Effluent Dsposal System Effluent dsposal s accomplshed through spray rrgaton or deep-well njecton. The spray rrgaton system conssts of a complete secondary water man of 100 mles, carryng effluent to the four quadrants of the Cty. Branches of the water man supply both large water users - golf courses, parks, school grounds - and also the crtcal water qualty (CWG) areas. CWQ areas (generally resdental users) are areas where wells produce salt water, whch s unacceptable for rrgaton and would therefore requre potable water for rrgaton. Excess effluent not used for rrgston s njected va deep wells nto a brtn_e zone a thcusand feet below the ground. An mpermeable layer of rock and clay over-layng the brne zone prevents vertcal mgraton of the effluent, elmnatng the possblty of contamnatng ground water. Reclamed Water Use Snce the program was ntated n 1977, the Cty has experenced a substantal declne n the ncreasng rate of potable water consumpton and attrbutes ths declne to the ntroducton of the Reclamed Water System (See Fgure 3). Reclamed water, on a lmted scale, s 8 Probably the most mportant process n meetng effluent qualty restrctons s fltraton. Preflter alum addton for enhanced solds capture s used at two of the plants. Suffcent chlornaton after the flters s also mportant n dsnfecton and vrus nactvaton. Wh the major percentage of reuse rrgaton at nght, a shft n effluent dscharge from the normal daly flow s requred. Four ground storage tanks (capacty Yen? Fgure 3. St. Petersburg Water Usage

5 avalable throughout the current system for fre protecton. The Cty s also engaged n a plot program utlzng the reclamed water as make-up water for coolng towers, llustratng the flexblty of the system. Charges for reclamed water are based on the area to be served, not on water volume. Currently, charges for the frst acre or less are $6.00 per month for unrestrcted use. Large users pay an addtonal $1.20 per half acre rrgated. These stes are not metered. The excepton to ths s the ndustral user, where the water s used for boler make-up or coolng water, etc. The charge for metered ndustral users s 25 cents per thousand gallons. For More nformaton: Colorado Sprngs Denns T. Cafaro Mgr. Wastewater Dvson P.O. Box Colorado Sprngs, CO (303) Tucson Water Krke Guld Cty of Tucson P.O. Box Tucson, AZ (602) lrvne Ranch Water Dstrct Joyce Wegner-Gwdt P.O. BOX D-1 mne, CA (714) St. Petersburg, FL J. Davd Shulmster Mgr.Wastewater Operatons Publc Utltes 1635 Thrd Avenue North St. Petersburg, FL (813) EPA-OMVH-595) 401 M street. SW Washnglon. DC (202)3@ PA-WERL (489) 26 West St. Clar Street Cncnnat, OH (513) EPARqlh 1 EPA Regon 6 Johp F. Kennedy Federal Buldng Elm Street Boston. MA Dallas. lx PA Regon 2 PA Regon 7 26 Federal Plaza 726 Mnnesota Avenue - New York NY 1M78 Kansas cty. KS EPA R egh Chwvt Street Phladelpha. PA EPA Reglon lem street Denver. CO EPA Regon 4 PA Regon Coumand Street. NE 21 5 Fmnl Street Atlanta. GA San Francsco. CA PA Regon SoUm Deaftom Street chgo. L EPA Ragh th Avenue Seattle, WA Prepared by Envronmental Resources Management, nc.