treatment of oilfield produced water for industrial reuse - WateReuse ...

TREATMENT OF OILFIELD PRODUCEDWATER FOR INDUSTRIAL REUSEUpdated September 09 |

Regulatory Framework• Trinidad & Tobago (T&T) EnvironmentalManagement Agency (EMA) enacted WaterPollution Amendment Rules in 2006• Water Pollution Rules require pollution“Source Registration” with limits for“parameters or substances…likely to causeharm to human health and the environment”

Regulatory Framework• Purpose is to “maintain an intelligentinventory or record of all water pollutantsources in the country”• EMA can monitor progress on pollution reductionplans• Well-informed communities can protectthemselves from risk• Industry can improve process, safety, and publicimage

Current Site ConditionsProducing WellsStorage Tanks andWash Tank

Current Treatment SystemWater from wash tank tooil/water separationOil/water separation inlet

Current Treatment SystemOil/water separation outletSurface water outfall

Project Background• Original plan – four produced watertreatment plants (WTPs)• "Sticker shock" changed scope to one largerWTP receiving produced water from 3 fields• Design is a subcontract to constructor, T.N.Ramnauth & Co., Ltd. (TNR)• TNR will build, own and operate the WTP forten years under contract to oil company

Influent Design Basis and Treatment GoalsParameter Units InfluentvalueIndustrialreusestandardNearshoredischargelimitFlow rate bpd 25,000 ≥ 12,500 ≤ 12,500Oil & grease mg/L 1,900 < 1.4 NAChloride mg/L 4,500 < 55 NIAA*Chemicaloxygen demandmg/L 4,000 250 250NIAA = no increase above ambient

Treatment Goals• Consideration of standards for reuse, inlandor nearshore discharge, or drinking water• Treated water splits 50/50, for industrialreuse and nearshore ocean discharge• Reuse quality standards must be met for“clean” stream, nearshore dischargestandards must be met for waste stream

Treatment Process Overview• Unit Operations• Oil/water separation• Equalization basin (1-day, ~1 million gallons)• Dissolved air floatation• Cooling• Aerobic biotreatment• Settling (1-day, ~1 million gallons)• Media filtration and reverse osmosis• RO permeate to industrial reuse (boiler feed)• RO concentrate to permitted nearshore ocean outfall

Treatment Overview - Secondary Streams• Oil/water separator – oil to storage tank,settled solids to waste basin• DAF float and settled solids to waste basin• Settling basin solids, mucked out as neededand “landfarmed” prior to offsite disposal• RO prefilter waste stream to waste basin• Waste basin – can be returned to process,mucked out as needed

Treatment Plant Site Plan

Pipeline Route for Nearshore Discharge• Typical vegetation encountered on 10 kmroute

Pipeline route for nearshore discharge• Dropoff to the beach• Pipeline and outfall design to be done locally

Bench Testing• Blended influent analytical baseline –samples from 3 tank farms, analyzed for fullsuite or organics, metals, common ions• Bulk samples collected for DAF coagulantand polymer dose determination through jartesting (7 batches over a period of months)• DAF-treated water then used forbiotreatment bench tests

DAF Bench Testing ResultsParameter Units Before DAFtreatmentAfter DAFtreatmentTotal suspended mg/L 41 - 593 33 – 104solids (

DAF Bench Testing Results• 7 batches processed with:• a range of coagulant and polymer doses;•varied polymer products (anionic/cationic)• Relatively consistent DAF effluent despitewider variation in influent water quality• Upstream equalization should help level“peaks and valleys”• DAF polymer options may be needed

Bench Testing for Biological Treatment• Immobilized Cell Bioreactor (ICB)• Smaller footprint than lagoons or CSTRs• Minimal production of secondary waste(biosolids stay in reactor)• Diverse, dense, long-lived microbialpopulation• Mechanical simplicity – aeration blowers andgravity flow in series reactor configuration

Bench Testing for Biological TreatmentBench scale ICBsMicrobial growth onmedium

Biological Treatment Bench Results• Individual source waters tested in enrichmentcolumns – aerated, fed N and P, pH adjusted• COD removal efficiency for one source was90%, considerably lower for the other two• Difference is attributed to secondaryrecovery techniques• Based on influent blend, a 50% CODremoval efficiency is predicted

Biological Treatment Bench Results• Flow-through bioreactors used primarily tooptimize hydraulic retention time (HRT)• Using DAF treated water as biotreatmentfeed, HRT was optimized at 18 hours• COD “endpoint” of ~250 mg/L was reachedregardless of COD influent concentration

Biotreatment Bench Testing ResultsAnalysis for BOD and COD reveals recalcitrant CODParameter Units BiotreatmentinfluentBiological oxygendemand (BOD)Chemical oxygendemand (COD)Biotreatmenteffluentmg/L 260 Non-detectablemg/L 640 240Crux of the challenge – 250 mg/L COD limit for both ROpermeate (reuse water) and RO concentrate (nearshoredischarge)

Supplemental Treatment for COD Reduction• Ideally, a COD concentration of ~100 mg/L isneeded prior to RO.• Supplemental treatments evaluated•Anaerobic/aerobic biotreatment•Adsorption on granular activated carbon•Electrocoagulation•Chemical oxidation•Filtration

Supplemental Treatment for COD Reduction• Marginal results for supplemental processes•Anaerobic/aerobic – same COD endpointas aerobic treatment alone•Carbon adsorption – high operating cost•Electrocoagulation – ineffective on COD•Chemical oxidation – costly, hazardous•Filtration – 0.02, 0.01 and 0.005 µmineffective

Now what??• Literature research•Treatment process(es) selected forproduced water•COD endpoint, characterization andtoxicity•COD analytical technique in presence ofchloride interference

Literature Research• Process selection• Bench testing for desalination of produced wateridentified an optimum process train includingoil/water separation, DAF, microfiltration, carbonadsorption, and RO• Biotreatment bench tests reached endpointconcentration for COD due to “recalcitrant organiccompounds” but is considered “cheap, effective andenvironmentally friendly” for COD reduction

Literature Research• COD in treated effluent• Multiple studies showed COD concentrations in therange of 200 to 300 mg/L• Extensive analytical program to identifycomponents of recalcitrant COD resulted inapproximately half “unknown”• One study reported 230 mg/L COD in treatedeffluent as “non-toxic to Artemia salina, which arevery frail organisms used to assess ecotoxicity”

Literature Research• Presence of chloride affects COD analysis –resulting in false high COD concentration• Various analytical methods are adapted tocorrect for this interference• New “modified method” shows bettercorrection than others, resulting in 90+percent accuracy• Independent method comparison is ongoing

Literature Research Impact• Unit operations selected are “state of the art”• Influent COD volatiles, insolubles, and solids –physical separation processes treat a highpercentage of influent COD• Soluble COD can be reduced to a concentration ofabout 200 mg/L through biotreatment• Modified analytical method could show actual CODconcentration is lower than previously reported

Conclusions• All insoluble COD and half of soluble COD will beeffectively removed, a 90 percent COD massreduction, influent to effluent• Modified analytical method may show that actualCOD after biotreatment is about 100 mg/L, andnearshore discharge COD limit for RO concentratewill be met• If a treated stream for industrial reuse was notneeded, all nearshore discharge limits would bemet as biotreated effluent

Thank you!Questions?Golder Associates Inc. - Peter Lemke, Kevin ConroyTN Ramnauth & Co. Ltd. – Isaac Jurawan