Public Health Criteria for Direct Potable Reuse · Viruses Crypto Giardia Salmonella Raw WW...

transcript

Public Health Criteria for

Direct Potable Reuse

Brian Pecson, Ph.D., P.E.

Trussell Technologies

March 19th 2013

The Water

Environment

Structure of Indirect Potable Reuse Scenarios

Source Control Conventional

Wastewater Treatment

Potable

Water Treatment

Advanced

Wastewater

Treatment

Environmental

Buffer/blending

Consumers

•Indirect Paradigm

Distribution

System

The Water

Environment

Conventional

Potable

Water Treatment

Advanced

Wastewater

Treatment

Environmental

Buffer/blending

Consumers Distribution

System • IPR can be done safely!

– Numerous applications

• Groundwater Replenishment System

• Montebello Forebay

– Several studies demonstrating safety

– Various IPR regulations/guidelines

• CDPH Groundwater Recharge Regulations – 2013

The Water

Environment

Potable

Water Treatment

Advanced

Wastewater

Treatment

Environmental

Buffer/blending

Consumers

Distribution

System

The Water

Environment

Structure of Direct Potable Reuse Scenarios

Potable

Water Treatment

Advanced

Wastewater

Treatment

Environmental

Buffer/blending

Consumers

•Direct Paradigm

Distribution

System

Engineered

Storage

Buffer

Advanced

Wastewater

Treatment

Benefits

• No reliance on aquifer

• No WQ degradation

• Less costly

Benefits

• Less costly

Disadvantages

• Reduction in response time

• Reduction in contaminant

removal

• Reduction in dilution &

blending

Benefits

• Less costly

Disadvantages

• Reduction in response time

• Reduction in contaminant

removal

• Reduction in dilution &

blending

No regulations governing DPR!!!

No criteria to determine what is safe…or

what is equivalent to IPR….

Motivation

• What criteria must be met for us to say that direct

potable reuse provides an equivalent level of

treatment to indirect potable reuse?

• Significance: treatment trains meeting these

criteria are protective of human health

appropriate for municipal reuse projects

(both DPR & IPR)

• Focus of WateReuse Project #11-02

Public Health: The Principal Goal The minimum criterion that must be satisfied in DPR is

that water must not harm public health

Carbamazepine

Pathogens Toxic Chemicals

Ideal Criteria

1. Water is “free” of pathogens

2. Water is “free” of toxic chemicals

Carbamazepine

Pathogens Toxic Chemicals

Equivalency Criteria: Methodology

1. Develop and present draft Public Health Criteria

to Expert Panel (NWRI) – August 2012 workshop

2. Receive comments and refined criteria from

Expert Panel

3. Finalize and publish Public Health Criteria in 11-

02 State of the Science Report

Pathogen Criteria

Pathogens and Potable Reuse

• Pathogen removal: the most important aspect – “From a public health standpoint, provisions for adequate and reliable

disinfection are the most essential features of the advanced wastewater

treatment process” – UN 1992

– “Failures may cause a short-term risk to those exposed, particularly to acute

contaminants where even a single exposure can lead to an adverse effect” –

NRC 2012

• Why is this the case? – Pathogens (acute concern) immediate effect

– Chemicals (chronic concern) long-term effect

NRC 2012

Constant protection

NRC 2012

Constant protection

Brief exceedances less important than average

lifetime exposure

Free of Pathogens?

• What do we mean by “pathogen free”?

• Pathogens reduced no observable effect on consumers

• Can understand safety in terms of RISK:

– Since SWTR (1991), industry has accepted that when a risk is

reduced to a certain level “negligible”

– A consumer has 1 in 10,000 risk of infection from drinking water for

a year

De minimis risk: 10-4 annual risk of infection

Pathogens and de minimis risk

• Recommendation for PH Criteria:

– Use U.S. de minimis standard of 10-4 infections/y

– Logic: Potable Reuse projects must meet or

exceed the standard applied to local conventional

drinking water sources

Calculating Pathogen Removal

1. Identify target pathogenic organisms

2. Determine maximum concentrations in sewage

3. Define acceptable pathogen levels in drinking water

4. Determine removal goals based on difference

NOTE: Methodology used by CDPH to develop GRR; also used by US EPA for DW

standards

Calculating Pathogen Removal

1. Identify target pathogenic organisms

2. Determine maximum concentrations in sewage

3. Define acceptable pathogen levels in drinking water

4. Determine removal goals based on difference

Step 1: Identify Target Pathogens

• Focus: commonly present in sewage, causing illness

• Pathogens of interest – agree with CDPH IPR (+1)

– Enteric virus

– Cryptosporidium oocysts

– Giardia cysts

– Bacteria?

No. Pathogen Episodes Hospitalizations Deaths

1 Norovirus 20,796,079 55,825 569

2 Giardia intestinalis 1,121,864 3289 31 3 Salmonella spp. (non-typhoid) 1,095,079 20,608 403

4 Campylobacter spp. 1,058,387 10,599 95 5 Clostridium perfringens‡ 966,120 438 26

6 Cryptosporidium spp. 678,828 2473 42 7 Shigella spp. 421,048 4672 32

8 Staphylococcus aureus‡ 241,188 1063 6 9 Toxoplasma gondii 173,415 8859 654

10 STEC non–O157 138,063 331 0 11 Yersinia enterocolitica 108,490 592 32

12 STEC O157 93,094 3152 30 13 Bacillus cereus‡ 63411 20 0

14 Vibrio parahaemolyticus 40,309 116 4

15 Diarrheagenic E. coli other

than STEC and ETEC 39,739 26 0

From CDC (2011)

Step 2: Determine Concentrations in

Raw Sewage

• Literature review – journal publications, reports,

textbooks, etc.

Parameter Units

Pathogens

Viruses Crypto Giardia Salmonella

Raw WW

concentration IU/L 105 105 105 105

Step 3: Define acceptable pathogen levels in

drinking water

• Select safe level of risk: 10-4 annual risk of infection

• Determine # of pathogens risk level

• Determine “safe” concentrations

drinking water

Step 4: Determine Removal Goals

Parameter Units

Pathogens

Raw WW

Drinking Water

Goal IU/L 2x10-7 3x10-5 7x10-6 2x10-5

Step 4: Determine Removal Goals

Parameter Units

Pathogens

Raw WW

Drinking Water

Goal IU/L 2x10-7 3x10-5 7x10-6 2x10-5

Ratio - 5x1011 3x109 2x1010 2x1010

Log removal - 12 10 10 10

Our Conclusions

• Methodology used by CDPH in IPR regulations and

EPA SWTR is rational and rigorous

• Large factors of safety conservative estimates

• Independent analysis supports use of pathogen

removal requirements chosen by CDPH

• Additional analysis: requirements also provide

protection from outbreaks

• Overall: came up with the same pathogen

requirements as the CDPH (+ Salmonella)

Triclosan

Bisphenol a

Caffeine

Carbamazepine

Chemical Criteria

De minimis vs. Acceptable Risk

Exposure

Daycare

More personal example

Exposure

Daycare

Risk level

De minimis More personal example

Exposure

Daycare

Risk level

De minimis More personal example

(avoiding risk via

homeschooling)

Exposure

Daycare

Risk level

De minimis

Risk level

Acceptable (> de minimis)

More personal example (avoiding risk via

homeschooling)

Exposure

Daycare

Risk level

De minimis

Risk level

More personal example (avoiding risk via

homeschooling)

Use daycare, but use

Extra care re. hygiene

De minimis vs. Acceptable Risk Exposure

Risk level

De minimis

Risk level

De minimis

Risk level

Pathogens: 10-4 infections/yr

Chemicals:

- MCLs: some set at de

minimis levels

Risk level

De minimis

Risk level

Pathogens: 10-4 infections/yr

Chemicals:

- MCLs: some set at de

minimis levels

Chemicals:

- MCLs: some set at

acceptable levels

- Cr(VI)?

Acceptable Risk Involves Compromise

• The process of establishing regulatory

limits is a process of balancing risk,

benefit and cost to determine an

acceptable level of risk

risk cost

Proposed Methodology

1. Meet all criteria where a judgment has

been made on acceptable risk

2. Where no judgment of acceptable risk

is available, seek de minimis risk

Toxic Chemicals

• Use all drinking water MCLs (acceptable risk)

• For unregulated compounds, use order of priority:

– 1st use guidelines that consider consequences beyond risk

– 2nd use measures of risk below regulatory concern published by recognized authorities

– 3rd use measures of risk developed for medical purposes

– 4th use guidelines published by earlier studies

EPA MCL

WHO DWG

State MCL

State provisional level {e.g. NL)

De minimis concentration? (HA or PNEC)

De minimis dose? (RfD, ADD, etc.)

Medical Benchmark? (MTD, MRTD, etc.)

De minimis benchmark from secondary source

Expert Panel Recommendations

and Final Equivalency Criteria

Final Pathogen Removal Goals

Parameter

Pathogens

Log removal 12 10 10 10

Original Criteria

Parameter

Pathogens

Modified Criteria

Parameter

Pathogens

Modified Criteria

- Crypto requirements address Giardia, other protozoa

Parameter

Pathogens

Viruses Crypto Giardia Total Coliform

Salmonella

Modified Criteria

- Crypto requirements address Giardia, other protozoa

- TC addresses pathogenic enteric bacteria, including Salmonella

Chemicals

• Meet all drinking water regs (MCLs, NLs, etc.)

• Three additional groups:

1. Disinfection by-products

2. Chemicals of potential interest (if present in

wastewater sources)

3. Chemicals used for evaluating effectiveness of

organics removal

Chemicals

• Three groups:

1. DBPs

2. Chemicals of potential

interest (if present in

wastewater sources)

3. Chemicals to evaluate

effectiveness of

organics removal

Occurrence Toxic

levels? Other uses?

Chemicals – Group 1

Occurrence Toxic

levels? Other uses?

✔ ✔

Occurrence Toxic

levels? Other uses?

• Rationale:

– Monitor for these chemicals

– If present at high levels, continue frequent monitoring

– If not present or below thresholds, less frequent

monitoring

Chemicals – Group 3 Occurrence

levels? Other uses?

✔ NO ✔

Chemical

Universe

Cat. 1

Cat. 2

Cat. 3

Cat. 4

Occurrence Toxic

levels? Other uses?

✔ ✔

Physical – Chemical

Properties

Cat. 1

Cat. 2

Cat. 3

Cat. 4

Occurrence Toxic

levels? Other uses?

✔ ✔

Physical – Chemical

Properties

Used as indicators of removal of broad range of

chemicals

Chemicals

• Three groups:

1. DBPs

2. Chemicals of potential

interest (if present in

wastewater sources)

3. Chemicals to evaluate

effectiveness of

organics removal

Occurrence Toxic

levels? Other uses?

✔ ✔

✔ NO ✔

What about specific concerns?

• What are safe levels for chemicals outside

of this list?

– Other pesticides?

– Pharmaceuticals?

Additional Frameworks

Conclusion

• Provided summary of process to determine

removal criteria

– Pathogens

– Chemicals

• For further detail see 11-02 SOS report

• But removal criteria are just the beginning…

finito

Public Health Criteria for Direct Potable Reuse · Viruses Crypto Giardia Salmonella Raw WW...

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