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.
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.
Additional information and numerous references on this subject can be obtained from the authors.