2017 wes eckenfelder lecture seriesftp.weat.org/presentations/2017_eck_lawler.pdf · wes...

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)


Water

Treatment

Plant

WW treatment including disinfection

Micro or Ultra-filtration

Ozone

Biologically active carbon

Chlorine

Storage (optional)

WTP (NOT optional)


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



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



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



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


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



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


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?

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