A minimum monitoring program should be conducted to reduce the threat to public health and the environment when using reclaimed wastewater
With greater demands being placed on domestic water supplies for expanding populations, increased attention is being given to the use of reclaimed domestic wastewaters for irrigation of golf courses, parks, parkways and ornamental shrubbery. However, there is justifiable concern about residual pathogenic organisms and hazardous or otherwise deleterious chemicals present in many treated domestic wastewater discharges. The use of wastewater reclaimed by treatment approaches that do not truly disinfect for all human pathogenic organisms, residual organics, and other constituents typically present in secondary-treated effluents must be considered carefully.
At this time, regulatory agencies allow the use of reclaimed domestic wastewaters for ornamental shrubbery, park and golf course irrigation that has been treated to essentially only secondary treatment effluent levels. Such treatment falls short of providing a reclaimed effluent that can be considered safe for those who spend time on golf courses, play in parks or playgrounds, etc., that are irrigated with reclaimed wastewater treated to only this standard.
Further, there is concern that the residual potentially hazardous or otherwise deleterious chemicals and pathogenic organisms in secondary-treated wastewater could, through repeated applications to public and recreational facilities, result in a significant buildup of these chemicals and pathogens on vegetation and soil. This, in turn, could threaten the water bodies receiving stormwater runoff from the areas irrigated by the reclaimed wastewater. Yates (1994) has reviewed the information available on the pathogens in domestic wastewaters that are used in golf course irrigation.
A summary of recommendations for a minimum monitoring program that can be conducted to significantly reduce the threat to public health and the environment due to the presence of these undesirable residuals follows.
Reclaimed Domestic Wastewater Treatment Performance Standards
The performance standard that should be achieved in any domestic wastewater reuse project is one of treating the incoming wastestream to a sufficient degree to control waterborne pathogens so that those who use a golf course, park, playground, softball field, botanical garden or any area irrigated with treated and reclaimed effluent experience no increased risk of disease compared to the situation that would exist if the area was irrigated with typically treated public water supplies.
Today, the sanitary quality of domestic water supplies and reclaimed domestic wastewaters is judged by the fecal coliform standard. It has been recognized since the 1940s that this standard will not protect public health from enteroviruses and cyst-forming protozoans (Lee and Jones-Lee 1993). It also has been long known that about one million people become ill and about 1,000 people die every year in the US due to infections caused by these organisms in public water supplies that meet the fecal coliform standard. It was not until the Milwaukee Cryptosporidium outbreak in April of 1993 that sufficient attention has been given to what are inadequate treatment standards to judge the safety of public water supplies. This unfortunate episode, in which 400,000 people became ill and about 100 died, had its origins in a contaminated water supply that met fecal coliform standards.
As a result of this Milwaukee incident, it has now become well known that enteroviruses and Cryptosporidium are commonly present in water treated to meet the fecal coliform standard. Therefore, those who have contact with such water are exposed to part of the endemic pathogen problem that causes large numbers of people to become ill with diarrhea, vomiting, etc. and a few people, especially the very young, the elderly and those with system immune deficiencies, to die.
In March of this year, the Executive Committee of the American Water Works Association (AWWA) acknowledged that treated domestic water supplies that meet current standards are not sterile. This Committee advised water utilities to inform their customers that those in the sensitive populations should routinely boil their water, even though their utility-provided supply met the existing coliform standard.
The magnitude of public health problems associated with contact with inadequately treated reclaimed wastewaters that just meet the coliform standard is significantly greater than for those who have the same kind of contact with typical public water supplies that just meet fecal coliform standards. This arises from the fact that domestic wastewaters typically contain far greater concentrations of pathogenic enteroviruses and protozoan cysts than typical domestic water supplies.
While there are some who assert that high levels of treatment of domestic wastewaters are not needed if the effluents are to be used for irrigation of golf courses, parks, ornamental shrubbery, etc., such an approach is very short sighted and fails to recognize what is a very significant public health threat. In addition, the residual chemical constituents in reclaimed domestic wastewater can become a significant contaminant in stormwater runoff quality, especially where it is used for groundwater recharge as part of the development of groundwater-based domestic water supplies.
A variety of approaches can be used to treat and reclaim sanitary wastewater for irrigating parklands, playgrounds, etc. In California, these can range from minimum Department of Health Services treatment standards (which include disinfection to meet fecal coliform standards of an "oxidized" secondary effluent), to full treatment involving membrane filtration and/or reverse osmosis and activated carbon bed treatment of the effluent. The spraying of reclaimed domestic wastewater for irrigation must be conducted in such a way as to avoid contacting people, (e.g., golfers and others) who are in the area of application. Further, there must be no spraying of the reclaimed water on drinking fountains.
It is important to not assume that even treatment of domestic wastewater by the activated sludge or trickling filter processes, followed by secondary clarification with alum or iron/polymer addition, rapid sand filtration, chlorination and dechlorination will produce an end product that can be safely used for irrigation of publicly used areas. Remember, Milwaukee was practicing treatment that exceeded the standards typically associated with these processes when the Cryptosporidium outbreak occurred.
While some communities adopt technology-based standards for developing processes domestic wastewater reclamation, the proper approach should be based on a performance standard. It is not the issue of just using disinfection to meet fecal coliform standards. It is disinfection to control pathogenic enteroviruses and protozoan cysts to very low levels not significantly different from those associated with the public water supplies delivered today. The key to public health protection from pathogenic organisms and residual chemical constituents is the development and operation of a reliable, intensive monitoring program of the effluent, as well as at the point of use of the reclaimed product.
Another important point is that in most treated wastewater reuse projects that receive only minimal treatment, the public normally does not come into direct contact with the wastewater stream. However, they can and frequently do come in contact with the residual pathogenic organisms and hazardous or otherwise deleterious chemicals present in the wastewater applied as reclaim. The monitoring program should be designed to determine whether there are any significant problems associated with such contact.
Monitoring Reclaimed Wastewater Reuse Activities
A monitoring program designed to protect public health and the environment from undesirable residual constituents should include intensive monitoring of the effluent source, as well as of the areas of application and the accompanying stormwater runoff.
- Effluent Monitoring: The reclaimed effluent should be monitored using state-of-the-science techniques for fecal coliforms, enteroviruses and protozoan cysts on a weekly basis. This monitoring should be done so that sampling of the effluent is variable during the seven-day week to be representative of the range of conditions that occur in effluent quality over the 24-hour day and seven-day week. Particular attention should also be given to monitoring during unusual situations such as a stormwater runoff event that leads to an increased hydraulic load on the wastewater treatment plant.
It may be possible to reduce the frequency of monitoring of the effluent for enteroviruses and protozoan cysts to every two weeks (except during unusual flow situations or plant upsets) once sufficient monitoring experience has been developed. Then, it should be possible to reliably predict the results of the next monitoring period based on past results. When such experience is gained, it then would be appropriate to reduce the frequency of monitoring, so long as previously gathered results provide a reliable indication of what the next monitoring of the effluent shows its characteristics to be.
- Reuse Area Monitoring: For the many types of publicly-used areas already described, where the public will have possible contact residual constituents, it is important to sample the turf, grass and other vegetation and soil for an accumulation of pathogenic organisms, such as protozoan cysts and enteroviruses. This monitoring is essential to evaluate the reliability of the effluent monitoring program, and to determine what the public is actually exposed to through the use of these areas as a result of applying the reclaimed domestic wastewaters. It should not be assumed that just because the effluent monitoring does not detect any problems, that there is not sufficient buildup of potentially hazardous situations that could be a threat to public health and the environment.
- Stormwater Runoff Monitoring: Specific sampling of the stormwater runoff from representative storms from irrigated areas should be conducted to determine whether the residual pathogenic organisms and hazardous or otherwise deleterious chemicals in the applied reclaimed water are detrimental to the designated beneficial uses of the receiving waters. Lee and Jones-Lee (1995d) recently described a stormwater runoff monitoring approach that can be used to assess whether chemical and organic contaminants in runoff are adversely affecting the designated beneficial uses of the runoff's receiving waters. Rather than mechanical end-of-the-pipe or receiving water monitoring, they advocate highly directed, site-specific studies that address whether constituents in the stormwater runoff are adverse to receiving water quality.
If runoff occurs from an area irrigated with reclaimed wastewater at times other than during storms, then monitoring of the associated runoff should be practiced on a routine basis, such as every two weeks to one month, when it occurs.
- Groundwater Monitoring: If there is significant potential for groundwater recharge associated with the reclaimed wastewater reuse areas, then monitoring of the unsaturated and saturated parts of the aquifer should be conducted to detect incipient pollution caused by wastewater-derived constituents. This groundwater monitoring should be conducted on a quarterly basis in order to detect seasonal influences of possible reclaim contaminants on any groundwater recharge action.
Using the Monitoring Program Data
The monitoring program should be supervised by an individual who is highly knowledgeable in sanitary wastewater and drinking water quality issues. The data should be critically examined as it is collected. If unexpected results occur, then additional sampling should be undertaken to confirm that the unexpected results are representative, and if so, explain why they are occurring.
Informing the Public of Potential Hazards
For those areas that either do not conduct a monitoring program of this type, or where such a program shows that the irrigated area contains potentially pathogenic enteroviruses and/or cyst-forming protozoans, the very least that should be done is to post large signs in the area irrigated with domestic reclaimed wastewater. These signs should state, "This area has been irrigated with reclaimed domestic wastewater that has not necessarily been adequately treated to protect public health and the environment. Persons using this area could experience illness, and possibly death due to the residual pathogenic organisms and hazardous chemicals in the reclaimed domestic wastewater used to irrigate the area."
Additional information and numerous references on this subject can be obtained from the authors.