2017 Wes Eckenfelder Lecture Series
Water Environment Association of Texas
Desmond F. Lawler
Dept. of Civil, Architectural and Environmental Engineering
University of Texas at Austin
[email protected] 512 471 4595
Re-Imagining Wastewater Treatment
for Direct Potable Reuse
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 1952-1965
• U. of Texas 1965-1970
• Vanderbilt Univ. 1970-1986
Impact of Manhattan College (1950-65) 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)
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). www.twdb.texas.gov/publications/reports/contracted_reports/doc/1248321508_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 www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/rw_dpr_criteria/app_a_ep_rpt.pdf
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.
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 12-10 - 10 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 25 – 40 mg/L of NH3-N• Industrial pretreatment to prevent significant metal concentrations (Zn, Cu, Pb, Cr, Cd, others)
Microbial Group
Criterion
(log10
reduction)
Possible
Surrogates
Source Used to Develop
Criteria
Enteric virus 12MS2
bacteriophage
SWTR (U.S. EPA, 1989a);
CDPH (2011); NRC (2012);
NRMMC–EPHC–NHMRC
(2008)
Cryptosporidium
spp.10
Latex
microspheres,
AC Fine Dust,
inactivated
Cryptosporidium
oocysts, aerobic
spores
Interim ESWTR (U.S. EPA,
1998); LT2 ESWTR (U.S. EPA,
2006); CDPH (2011); NRC
(2012); NRMMC–EPHC–
NHMRC (2008)
Total coliform
bacteria9 NA
Total Coliform Rule (U.S. EPA,
1989b); NRC (2012) risk
assessment for salmonella
NWRI Panel
Suggestions for
Microbial
Reductions in
Advanced
Treatment (post
WWTP)
Publication
Number NWRI-
2013-01, National
Water Research
Foundation,
Fountain Valley,
California
Constituent UnitUntreated
Wastewater
Range of Effluent Quality after Indicated Treatment
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 130 - 389 5 - 25 2 - 8 5 - 20 1 - 4 <1 - 5
Turbidity NTU 80 - 150 2 - 15 1 –5 1 - 5 1 - 5 <1 - 2
Total organic carbon (TOC) mg/L 109 - 328 20 - 40 15 - 30 10 - 20 1 - 5 <0.5 - 5
Ammonia nitrogen mg N/L 14 - 41 1 - 10 1 - 6 1 - 3 1 - 2 <1 - 5
Nitrate nitrogen mg N/L 0 - trace 5 - 30 5 - 30 <2 - 8 1 - 8 <8
Nitrite nitrogen mg N/L 0 - trace 0 - trace 0 - trace 0 - trace 0.001 - 0.1 0 - trace
Total nitrogen mg N/L 23 - 69 15 - 35 15 - 35 3 - 8 2 - 5 <10
Total phosphorus mg P/L 3.7 - 11 3 - 10 3 - 8 1 - 2 ≤2 <0.3 - 5
Volatile organics (VOCs) µg/L <100 – >400 10 – 40 10 - 40 10 – 20 10 - 20 10 - 20
Total dissolved solids (TDS) mg/L 374 - 1121 374 - 1121 374 - 1121 374 - 1121 374 - 1121 374 - 1121
Trace constituents g/L 10 - 50 5 to 40 5 - 30 5 - 30 5 - 30 0.5 - 20
Total coliform No./100 mL 106 – 1010 104 - 105 103 - 105 104 - 105 104 - 105 <100
Protozoan cysts/oocysts No./100 mL 101 – 105 101 - 102 0 -10 0 -10 0 -1 0 - 1
Viruses PFU/100 mL 101 – 104 101 - 103 101 - 103 101 - 103 101 - 103 100 - 103
Water
Treatment
Plant
Secondary or tertiary WW treatment
Ozone
Micro or Ultra-filtration
Reverse Osmosis
UV/AOP (Advanced Oxid. Proc.)
Stabilization
Storage (optional)
WTP (optional)
TWDB report Treatment Train 1
(the gold standard?)
Water
Treatment
Plant
WW treatment w MBR achieving full nitrification
Reverse Osmosis
UV/AOP
Stabilization
Storage (optional)
WTP (NOT optional)
TWDB report Treatment Train 3
Water
Treatment
Plant
WW treatment including disinfection
Micro or Ultra-filtration
Ozone
Biologically active carbon
Chlorine
Storage (optional)
WTP (NOT optional)
TWDB report Treatment Train 5
Water
Treatment
Plant
Secondary WW treatment including nitrification
(Denitrification filters—considered but eliminated)
(Ozone was piloted but abandoned due to problems)
Chlorine/chloramine disinfection (membrane biofouling)
Micro or Ultra-filtration (remove particles)
Nanofiltration or Reverse Osmosis (remove both
organics and inorganics)
UV/AOP (oxidize remaining organics)
Carbon filtration to quench ozone
Chlorination and Direct entry to
distribution system
El Paso Proposed Treatment Train
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.
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
Idea 1A: Have an extensive industrial pre-treatment 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-, SO4
2-, K+, NH4+, NO3
-, Ca2+, Mg2+, …
• Metals (Cr3+, Cr2O7-, Cu2+, Zn2+, …
• 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.
www.ecospheretech.com
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.
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
www.4enveng.com
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 m3/d (~0.5 MGD)
• Used sinusoidal flow input, with amplitude of 0.3*Qave
• 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!)
Volume required for complete equalization
• � � = ���� 1 + �� 2��
= 2000 1 + 0.3�� 2��
• ����� ������ =2 0.3 2000 � sin 2�� ��
!."#
!
= −1200
2�%� 0.5� − %� 0
= −191 0 − 1 = 191�(
0
500
1000
1500
2000
2500
3000
0 0.2 0.4 0.6 0.8 1
Flo
w (
m3/d
)
Time of Day
Twice this area yields the required
volume for complete equalization
Flow Variation: with and without equalization
0
500
1000
1500
2000
2500
3000
7 7.5 8 8.5 9 9.5 10
Flo
w (
m3/d
)
Time (d)
Qin
Qout
No
Equalization
With
Equalization
Coef. Of Variation 0.21 0
Ratio: Max/Min 1.85 1
Suspended Solids Concentration (post primary)
0
10
20
30
40
50
60
7 7.5 8 8.5 9 9.5 10
TS
S (
mg
/L)
Time (d)
w no equalization
complete equalization
No
Equalization
With
Equalization
Coef. Of Variation 0.14 0
Ratio: Max/Min 1.49 1
BOD5 Concentration (post primary)
0
20
40
60
80
100
120
140
7 7.5 8 8.5 9 9.5 10
BO
D (
mg
/L)
Time (d)
complete equalization
w no equalization
No
Equalization
With
Equalization
Coef. Of Variation 0.034 0
Ratio: Max/Min 1.10 1
TKN concentration (post primary)
0
5
10
15
20
25
30
35
7 7.5 8 8.5 9 9.5 10
TK
N (
mg
/L)
Time (d)
w no equalization complete equalization
No
Equalization
With
Equalization
Coef. Of Variation 0.012 0
Ratio: Max/Min 1.04 1
Suspended Solids Loading to Activated Sludge
0
20
40
60
80
100
120
140
160
7 7.5 8 8.5 9 9.5 10
TS
S M
ass L
oa
din
g t
o A
ctiva
ted
Slu
dg
e (
kg/d
)
Time (d)
No
Equalization
With
Equalization
Coef. Of
Variation0.34 0
Ratio: Max/Min 2.70 1
BOD5 Mass Loading to Activated Sludge
0
50
100
150
200
250
300
350
7 7.5 8 8.5 9 9.5 10
BO
D M
ass L
oa
din
g t
o A
ctiva
ted
Slu
dg
e (
kg
/d)
Time (d)
No
Equalization
With
Equalization
Coef. Of Variation 0.24 0
Ratio: Max/Min 2.02 1
TKN Mass Loading to Activated Sludge
0
20
40
60
80
100
7 7.5 8 8.5 9 9.5 10
TK
N M
ass L
oad
ing
to
Activa
ted
Slu
dge
(kg
/d)
Time (d)
No
Equalization
With
Equalization
Coef. Of
Variation0.22 0
Ratio: Max/Min 1.90 1
El Paso Wastewater Treatment Plant Result—Nitrification
(Source: Arcadis; El Paso W/WW utility)
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!
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.)
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.
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
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?
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 regshave 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.
Thank you!
Questions?