Wastewater Reclamation and Reuse

Mark D. SobseyENVR 890-2Spring 2009

Wastewater Reuse: An Attractive Option for Improved Water Resources Management

• Why do THIS?• When you can do THIS INSTEAD?

• ……Potable use?

• Other non-potable uses

• Industrial cooling

• Irrigation

• Beneficial reuse for:

• Further treat, then…

Direct/Directed Potable Reuse

• Singapore, Malta, Israel and Namibia now augment their source drinking water (10-20 %) with reclaimed wastewater

WHO Agricultural Reuse of Wastewater and Excreta

• WHO Guidelines focus on agricultural and aquacultural reuse of wastewater

• Promote beneficial use• Health risk-based• Considers different exposure groups

– Workers (farmers)– Children– Neighbors– Consumers

• Employs epidemiological and microbial data for diarrheal disease and ascariasis health risk estimates

Health Risk Contaminants of Reclaimed Water

• Microbiological quality: pathogens• Total mineral content (e.g., TDS)• Heavy metal toxicants• Toxic/biologically active organic compounds

– Disinfection by-products– Pharmaceutically active compounds

• Antibiotics• Estrogens• Psychotropic compounds• Caffeine• Etc.

Health Risks and Benefits of Wastewater and Excreta Reuse

Direct Health Effects• Waterborne disease outbreaks; hyperendemic disease• Contributes to background disease rates from helminths

and other pathogensIndirect Health Effects• Impacts on water safety for drinking recreation, food

preparation• Positive impacts on household food securityDriving Forces• Water Scarcity• Wastewater as a Resource• Population growth, urbanization

WHO Health Risk-Based Approach

• Establish tolerable (acceptable) risk• Zero is not achievable in the real world)• A national to local concern• WHO anchors risk level in its international

guidelines• Accepted point of reference for carcinogens in

drinking water: 1/100,000 lifetime excess risk of cancer

• US EPA 1/10000 risk of infection (Giardia)• DALYs: 10-6 DALYS per person per year (WHO)• Considers beneficial use; attempts to make norms

not overly stringent

Summary of Health Risks Associated with the Use of Wastewater in Irrigation

Risk Management Points for Agricultural Reuse

Human Exposure Control for WW Agricultural Irrigation

Four groups of people are at potential risk:• Agricultural field workers and their families• Crop handlers• Consumers (of crops, meat and milk)• Those living near the affected fields

Human Exposure Control for WW Agricultural Irrigation

• Agricultural field workers are at high risk of parasitic infections. • Exposure to hookworm infection can be reduced, even eliminated,

by the use of less contaminating irrigation methods and by the use of appropriate protective clothing (i.e. shoes for field workers and gloves for crop handlers).

• A rigorous health education program that targets consumers, farm workers, produce handlers and vendors is needed.

• Handwashing with soap is an important behavior that needs to be emphasized. – Handwashing with soap reduces diarrheal disease transmission

by 30-40%• Field workers should be provided with adequate sanitation facilities

and safe water for drinking and hygiene purposes to avoid the consumption of, and contact with, wastewater.

Human Exposure Control for WW Agricultural Irrigation

• Sanitation facilities and safe water should be provided at markets for washing and ‘‘freshening’’ produce. – Vendors need to practice good personal and food

hygiene. • Consumers can cook vegetables, meat and milk, and

practice good personal and domestic hygiene to protect their health.

• Meat should be inspected and carcasses infected with tapeworm larvae should be rejected

Steps in Agricultural WW Reuse Management: Waste Treatment to Remove or Inactivation of Pathogens

• Conventional wastewater treatment options (primary and secondary treatments) are effective at removing/inactivating pathogens

• These processes may be difficult and costly to operate properly in developing world situations.

• Waste stabilization ponds (WSP), properly designed and operated properly, are effective at reducing pathogens– They can be operated at low cost where inexpensive land is

available• A series of shallow ponds linked together maximizes

retention time • WSPs should be designed, operated and maintained in

such a way as to prevent disease vectors from breeding in the ponds.

Steps in Agricultural WW Reuse Management: Crop Restriction

• Water of poorer quality can be used to irrigate:– Non-vegetable crops such as cotton– Crops that will be cooked before consumption (e.g. potatoes)

• Crop restriction may protect the health of consumers but not farm workers and their families.

• Crop restriction is not an adequate single control measure

• It should be considered within an integrated system of control

• In Chile the use of crop restriction when implemented with a general hygiene education program significantly reduced the transmission of cholera from the consumption of raw vegetables

• It has also been used effectively in Mexico and Peru

Steps in Agricultural WW Reuse Management Irrigation Techniques

• Aerosols from spray/sprinkler irrigation have high potential to spread contamination on crop surfaces and affect nearby communities.

• Where WW spray/sprinkler irrigation is used, buffer zones (e.g. 50–100m from houses/roads) are recommended to prevent health risks to local communities

• Farm workers/families are at highest risk when flood or furrow irrigation techniques are used– Especially when protective clothing is not worn and earth is moved by

hand.• Localized irrigation techniques (e.g. bubbler, drip, trickle irrigators) offer farm

workers good health protection because WW is applied directly to the plants– Can be problematical if WW has suspended solids that clogs water

emitters.• Drip irrigation also improves crop yields and reduces water use.• Cessation of irrigation for 1–2 weeks prior to harvest can be effective in

reducing crop contamination. • Many vegetables need watering nearly until harvest to increase market value

– This option may be possible with some fodder crops that do not have to be harvested at the peak of their freshness.

Steps in Agricultural WW Reuse Management Chemotherapy and Vaccination

• Anti-helminthic treatment and immunization are not considered an adequate strategy to protect farm workers and their families.

• Immunization against helminthic infections and most diarrheal diseases is currently not feasible.

• For highly exposed groups or sensitive subpopulations (e.g. tourists), immunization against typhoid and hepatitis A may be worth considering.

• Anti-helminthic treatment of intense nematode infections in children and the control of anemia in both children and adults, especially women and post-menarche girls, is important.

• Treatments must be reapplied at regular intervals to be effective—several times a year for children living in endemic areas

Indicator Microbe Reductions by Conventional Sewage Rx: Log10 Reduction Efficacy

110

1001000

10000100000

100000010000000

100000000

110

1001000

10000100000

100000010000000

100000000

F. col. E. coli Ent. C. p. F+ phg.

Num

ber/

100

ml

RawTreated (geom. mean values of 24 biweekly samples)

Approx. Log10 Reductions: 5 5 4.5 2 2.5

Health Risk Basis of California Water Reclamation Program

• Initially, treatment performance-based on reducing viruses by 5 log10

– Specific treatment requirements: coagulate-floculate/filter/disinfect conventionally treated wastewater

– Effluent microbial quality• Later, health risk-based, but still targeting viruses • U.S. EPA Surface Water Treatment Rule (SWTR) (1989) defines

acceptable risk as ≤1 pathogen-derived infection/10,000 population/year from public water supplies

• If a 10-4 annual infection risk (≤1 infection/10,000 population/year) is set as the acceptable risk for recycled water, reliability can be calculated as the percent of time that infection risk due to exposure to enteric viruses in recycled water is less than this acceptable level of annual risk

Limitations of the California Reuse System• Preoccupied with viruses• Protozoan parasites respond differently to

disinfection process than viruses– Chlorine efficiently kills viruses and bacteria but is

much less effective against protozoan parasites

• UV radiation efficiently kills protozoan parasites and bacteria but is much less effective against enteric viruses– Adenoviruses a worst case

– >140 mJ/cm2 to inactivate 4 log10 of adenoviruses

Dual disinfection effective against ALL pathogens overcomes this limitation

Risk from One-time Consumption of 100 ml from the St. Petersburg, FL Reclamation Facility

(Rose et al., 1996) (assumed all microbes were viable and infectious; worst case)

OrganismConcentrations / 100LMean and Maximum

Estimated Risks

Rotavirus0.01 PFU 6 x 10-6

0.13 PFU 8 x 10-5

Echovirus 120.01 PFU 2 x 10-8

0.13 PFU 3 x 10-7

Cryptosporidium0.75 oocyst 4 x 10-6

5.35 oocysts 3 x 10-5

Giardia0.49 cyst 1 x 10-5

3.3 cysts 7 x 10-5

Estimated Risks of Virus Infection/Person/Year for Various Concentrations of E. coli by Use of Untreated or Treated Wastewater in Irrigation

Concentrations of E. coli in WW may not correspond to those of viruses in WW. (a) Risks are based on either consumption of irrigated raw vegetables (CV) or contact

with the wastewater during/after irrigation (WC) (b) Total coliforms in chlorinated secondary effluent used for unrestricted crop irrigation (c) Total coliforms in chlorinated tertiary effluent used for golf course irrigation

Management Strategies to Reduce Health Risks from Agricultural Reuse

• Treatment of Wastes

• Crop Restriction

• Waste Application Methods

• Control of Human Exposure

WHO Revised Microbiological Guidelines for Treated WW use in Agriculture

Category | Reuse Conditions | Exposed | Irrigation | Nematodes | FC | WW Treatment

Management Strategies - Crop Restriction

Management Strategies - Waste Application

Management Strategies - Control of Human Exposure

WHO Estimates of Log10Pathogen Reduction by Control Measures for Agricultural Reuse of Wastewater

• Wastewater treatment: 1-6 – Varies with degree of treatment

• Localized (drip) irrigation (low growing crops): 2• Localized (drip) irrigation (high-growing crops): 4• Spray drift control (spray irrigation): 1• Spray buffer zone (spray irrigation): 1• Pathogen die off: 0.5-2 per day• Produce washing with water: 1• Produce disinfection: 2• Produce peeling: 2• Produce cooking: 6-7

Existing Reclaimed Water Standards and Guidelines - Non-Potable Reuse

• CA: < 2 TC/100 ml; specified multi-Rx steps• US EPA: 200 FC/100 ml for less stringent uses• WHO guidelines: 1000 or 10,000 FC for

unrestricted agricultural use • State of NC wastewater reuse standards:

– Intermediate between extreme high level standards of California and lower level guidelines of US EPA and World Health Org.

– NC microbial requirement: geom. mean FC = 14/100 ml; single value max. = 25 per 100 ml)

– Proposed reg. would add log10 microbe reduction levels for bacteria (6) viruses (coliphages) (5) and bacterial spores (C. perfringens) as protozoan parasite indicator (4)

•

Indicator Microbe Concentration & Reductions by Conventional Sewage Rx: Proposed Log10 Reductions for NC Reclaimed Water

110

1001000

10000100000

100000010000000

100000000

110

1001000

10000100000

100000010000000

100000000

F. col. E. coli Ent. C. p. F+ phg.

Num

ber/

100

ml

RawTreated (geom. mean values of 24 biweekly samples)

Target Log10 Reductions: Bacteria = 6 Parasites = 4 Viruses = 5