2017 Wes Eckenfelder Lecture Series

Transcription

1 2017 Wes Eckenfelder Lecture Series Water Environment Association of Texas Re-Imagining Wastewater Treatment for Direct Potable Reuse Desmond F. Lawler Dept. of Civil, Architectural and Environmental Engineering University of Texas at Austin

2 Wes Eckenfelder a little history Born in NYC 1926; Died 2010 BS CE 1946, Manhattan College MS San Eng, 1948, Penn State MS CE, 1954, NYU Teaching Positions: Manhattan College U. of Texas Vanderbilt Univ

3 Impact of Manhattan College ( ) on Environmental Engineering (Eckenfelder, O Connor, and McCabe) Jim Morgan Aquatic Chemistry w W. Stumm; Cal Tech, NAE Charlie O Melia Coagulation/Filtration, UNC and Johns Hopkins, NAE Don Lauria; UNC, Developing Countries work with World Bank Joe Malina, long time faculty member at UT (RIP) Graduates were founders or partners in numerous northeast environmental consulting firms These graduates included John Lawler, 1954 and Patrick (Packy) Lawler, 1961 (my brothers and partners in Lawler, Matusky and Skelly Engrs)

4 A few major written resources on DPR National Research Council, 2012, Water Reuse: potential for expanding the nation s water supply through reuse of municipal wastewater Texas Water Development Board, 2015, Direct Potable Reuse Resource Document (Alan Plummer & Associates, esp.ellen McDonald) _Vol1.pdf Expert Panel for the California State Water Resources Control Board, 2016, Evaluation of the Feasibility of Developing Uniform Water Recycling Criteria for Direct Potable Reuse s/rw_dpr_criteria/app_a_ep_rpt.pdf

5 Terminology Potable Reuse of Wastewater: Transforming wastewater into drinking water de facto or inadvertent Reuse: occurs when a water supply (river, usually) is made up in whole or part of (treated) wastewater from an upstream city. Indirect Potable Reuse (IPR): Takes the effluent of a wastewater treatment plant, subjects it to advanced treatment, then puts it into an environmental buffer (reservoir or ground water storage) for some extended period before pulling it back out for reuse (after going through a drinking water treatment plant). Direct Potable Reuse (DPR): Similar to IPR but with no environmental buffer; the water stays within engineered systems from toilet to tap.

6 What are the concerns? Pathogens. o Protecting the public health is Job #1, so removing pathogens is critical. o Typically talked about in terms of log removals of viruses, cryptosporidium, and Giardia o California regulators and practitioners have agreed to a rule; the log removals of these three pathogenic MO s (based on wastewater treatment plant influent). These are much harder to disinfect than bacteria, so achieving these levels of disinfection will wipe out bacteria essentially completely. Emerging (unregulated) contaminants (PPCPs, EDCs, and others) Health effects are unknown but potentially substantial (in my opinion) Public concern is great, so for public acceptance of DPR, removing these contaminants is critical Organic Matter and Disinfection By-Products Not only NOM but Effluent derived Organic Matter (EfOM) WWTPs discharge DOC at several mg/l typically Creation and Effects of EfOM DBPs are not well-known but cannot be any simpler than with NOM Inorganics of concern: ammonia, nitrite, and nitrate (and perhaps others such as metals) Typical US WWTP receives mg/l of NH 3 -N Industrial pretreatment to prevent significant metal concentrations (Zn, Cu, Pb, Cr, Cd, others)

7 NWRI Panel Suggestions for Microbial Reductions in Advanced Treatment (post WWTP) Publication Number NWRI , National Water Research Foundation, Fountain Valley, California Microbial Group Criterion (log 10 reduction) Enteric virus 12 Cryptosporidium spp. Total coliform bacteria 10 9 NA Possible Surrogates MS2 bacteriophage Latex microspheres, AC Fine Dust, inactivated Cryptosporidium oocysts, aerobic spores Source Used to Develop Criteria SWTR (U.S. EPA, 1989a); CDPH (2011); NRC (2012); NRMMC EPHC NHMRC (2008) Interim ESWTR (U.S. EPA, 1998); LT2 ESWTR (U.S. EPA, 2006); CDPH (2011); NRC (2012); NRMMC EPHC NHMRC (2008) Total Coliform Rule (U.S. EPA, 1989b); NRC (2012) risk assessment for salmonella

8 Range of Effluent Quality after Indicated Treatment Constituent Unit Untreated Wastewater Conventional Activated Sludge Conventional Activated Sludge with Filtration Activated Sludge with BNR Activated Sludge with BNR and Filtration Membrane Bioreactor Total suspended solids (TSS) mg/l <1-5 Turbidity NTU <1-2 Total organic carbon (TOC) mg/l <0.5-5 Ammonia nitrogen mg N/L <1-5 Nitrate nitrogen mg N/L 0 - trace < <8 Nitrite nitrogen mg N/L 0 - trace 0 - trace 0 - trace 0 - trace trace Total nitrogen mg N/L <10 Total phosphorus mg P/L <0.3-5 Volatile organics (VOCs) µg/l <100 > Total dissolved solids (TDS) mg/l Trace constituents g/l to Total coliform No./100 ml <100 Protozoan cysts/oocysts No./100 ml Viruses PFU/100 ml

9 TWDB report Treatment Train 1 (the gold standard?) Secondary or tertiary WW treatment Ozone Micro or Ultra-filtration Reverse Osmosis Water Treatment Plant UV/AOP (Advanced Oxid. Proc.) Stabilization Storage (optional) WTP (optional)

10 TWDB report Treatment Train 3 WW treatment w MBR achieving full nitrification Reverse Osmosis UV/AOP Stabilization Storage (optional) Water Treatment Plant WTP (NOT optional)

11 TWDB report Treatment Train 5 WW treatment including disinfection Micro or Ultra-filtration Ozone Water Treatment Biologically active carbon Plant Chlorine Storage (optional) WTP (NOT optional)

12 El Paso Proposed Treatment Train Secondary WW treatment including nitrification (Denitrification filters considered but eliminated) (Ozone was piloted but abandoned due to problems) Chlorine/chloramine disinfection (membrane biofouling) Water Treatment Micro or Ultra-filtration (remove particles) Plant Nanofiltrationor Reverse Osmosis (remove both organics and inorganics) UV/AOP (oxidize remaining organics) Carbon filtration to quench ozone Chlorination and Direct entry to distribution system

13 DPR has been conceived as a 3-part process 1. Conventional Wastewater Treatment (at least secondary plus filtration) 2. Advanced Treatment (Advanced oxidation processes and RO) 3. Conventional Drinking Water Treatment Most work to date has started with and focused on Step 2. My philosophy and the basis of this talk: We should start with Step 1.

14 Four ideas to re-design WWTPs for DPR 1. Change the influent characteristics (2 parts) 2. Do extensive flow equalization 3. Replace conventional primary treatment with micro- or ultrafiltration 4. Perform complete nitrification and denitrification

15 Idea 1A: Have an extensive industrial pretreatment program Conventional wastewater treatment is primarily designed for removal of suspended solids and biodegradable organics Industrial discharges often have other constituents: High dissolved solids (Na +, Cl -, SO 4 2-, K +, NH 4+, NO 3-, Ca 2+, Mg 2+, Metals (Cr 3+, Cr 2 O 7-, Cu 2+, Zn 2+, Recalcitrant organics (certain solvents, polymers, pharmaceuticals, ) Industrial discharges also can be sporadic, with dumps of batches with high flow and high concentrations For discharge to the environment, the fact is that we rely on dilution to mitigate effects, but this approach is inappropriate for human consumption.

16 Idea 1B: Have an extensive pollution prevention program for households For many years, the public was told to discard unused medicines by flushing them. Various evidence shows this is still widely practiced and is responsible for a significant portion of the PPCPs in our wastewater. Other liquid wastes are also discarded to the sewers (oils, paints, solvents, ). An extensive public education and an easy-to-use program for collection of these wastes is necessary for DPR.

17 Idea 2: Do extensive flow equalization Drinking water treatment plants operate with steady flow. Advanced treatment and DPR facilities will also run better with steady flow, and the place to start is at the start of the WWTP Of my four ideas, this is the only one for which I have done extensive (though still incomplete) modeling

18 Software Modeling to quantify a few of my ideas Used GPS-X software Used default values for essentially everything Influent characteristics Process design and operational variables Used very small plant 2000 m 3 /d (~0.5 MGD) Used sinusoidal flow input, with amplitude of 0.3*Q ave Ran non-steady state conditions for ten days; effect of initial conditions become insignificant after about five days, so I am showing results for days 7 through 10. (and, I am a novice at this modeling!)

19 Volume required for complete equalization = = =!."# sin 2! Flow (m 3 /d) Twice this area yields the required volume for complete equalization = % 0.5 % Time of Day = =191 (

20 Flow Variation: with and without equalization Q in Flow (m 3 /d) Q out No Equalization With Equalization Coef. Of Variation Ratio: Max/Min Time (d)

21 Suspended Solids Concentration (post primary) TSS (mg/l) w no equalization complete equalization No Equalization With Equalization 10 Coef. Of Variation Ratio: Max/Min Time (d)

22 BOD 5 Concentration (post primary) BOD (mg/l) w no equalization complete equalization No Equalization With Equalization Coef. Of Variation Ratio: Max/Min Time (d)

23 TKN concentration (post primary) TKN (mg/l) w no equalization No Equalization With Equalization Coef. Of Variation Ratio: Max/Min complete equalization Time (d)

24 Suspended Solids Loading to Activated Sludge TSS Mass Loading to Activated Sludge (kg/d) No Equalization Time (d) With Equalization Coef. Of Variation Ratio: Max/Min

25 BOD 5 Mass Loading to Activated Sludge BOD Mass Loading to Activated Sludge (kg/d) No Equalization Time (d) With Equalization Coef. Of Variation Ratio: Max/Min

26 TKN Mass Loading to Activated Sludge TKN Mass Loading to Activated Sludge (kg/d) Coef. Of Variation No Equalization Time (d) With Equalization Ratio: Max/Min

27 El Paso Wastewater Treatment Plant Result Nitrification (Source: Arcadis; El Paso W/WW utility)

28 Idea 2: Do extensive equalization (summary) Flow variation leads to concentration variation after treatment Flow variation leads to even more extensive variation in loading rates for constituents that have both a solid and soluble makeup such as BOD and TKN. Presumably, this loading rate variation impacts both average effluent quality and the variation of effluent quality. Advanced treatment processes in DPR (e.g., advanced oxidation) will run better with minimal concentration variation and with constant flow. The earlier we start the constant flow, the better!

29 Idea 3: Replace primary sedimentation with microfiltration or ultrafiltration These membrane processes remove a very high fraction of suspended solids, and therefore leave only the soluble BOD and soluble TKN (ammonia). To the extent that recalcitrant organics and metals are adsorbed onto solids in the influent, these membrane processes would remove them as well. Not yet done sufficient modeling to quantify results well, but because degradation rates for soluble compounds are higher than for particulate BOD and TKN, effluent quality (post Activated Sludge) is improved. (Future work needed.)

30 Idea 4: Do complete nitrification and denitrification in the WWTP Nitrogen compounds are problematic in advanced treatment processes Ammonia is likely to cause biological growth so early and extensive oxidation and disinfection is required. Ammonia oxidation by ozone is quite slow. Bio-removal is better than RO for ammonia removal High nitrogen concentrations can limit recovery of RO.

31 Idea 4: Do complete nitrification and denitrification in the WWTP (cont d) Nitrification and denitrification are energy intensive, but not as much as RO El Paso pilot plant results showed occasional substantial post-ro concentrations of nitrate (e.g. ~5-7 mg/l as N; too close to the DW limit of 10 mg/l for comfort. And, most important to me, is the idea of multiple barriers RO should be the backup to biological nitrification and denitrification

32 Some Philosophical Thoughts about DPR Multiple barrier approach requires thinking far upstream of the Advanced Treatment Facilities Industrial pretreatment program and buy-in Public participation e.g., program to not flush prescription drugs The Wastewater Treatment needs to be optimized Conventional view is to remove carbonaceous materials and NBOD Nitrification and Denitrification seem to me to be critical nitrite is bad! Excursions and plant upsets need to be held to a minimum; the consequences are much worse in DPR WERF s One Water concept needs to become a reality why do we have water people and wastewater people?

33 Some Philosophical Thoughts about DPR (cont d) Failure of early designs would kill this movement, so conservative designs should be the only acceptable designs Only designs close to the gold standard should be considered For now, RO is critical in my opinion (for public acceptance as well as public health) Meeting the drinking water regulations is not sufficient; those regs have a built-in, unspoken assumption that the raw water supply is relatively clean natural water And, my main point today, DPR should start with the generation of wastewater, and not at the effluent of any wastewater treatment plant.

34 Thank you! Questions?