Mar 30, 2017

Redefining Reuse

Researchers suggest water quality guidelines for reuse applications

Gyan Chhipi-Shrestha

The issue of water scarcity has caused many to explore the possibilities of water reuse. However, a globally agreed-upon set of health standards for reuse has yet to be established. A team of researchers at the University of British Columbia is attempting to change this, proposing guidelines based on the concentration of E. coli possibly present in the reused water. W&WD Associate Editor Michael Meyer asked study author Gyan Chhipi-Shrestha for insight into the proposed guidelines.

Michael Meyer: Please explain the guidelines your team has developed for water reuse.

Gyan Chhipi-Shrestha: Globally, no standard water quality guidelines exist for reclaimed water use. Indeed, the development of a practical guideline is complex.

Despite the Canadian federal government’s long-term goal to develop guidelines for many water reuse applications, guidelines have only been prescribed for reclaimed water use in toilet and urinal flushing in Canada. At the provincial level, British Columbia has promulgated guidelines for wide applications of reclaimed water, but only at broad class levels. Our team has investigated and then proposed suggested guideline values for microbial quality of reclaimed water in various non-potable urban reuses. The guidelines are based on probable risk. The non-potable water uses considered are lawn irrigation, public park irrigation, golf course irrigation, agricultural irrigation, vehicle washing, laundry machines, firefighting and non-potable urban uses.

The health risk was estimated by using quantitative microbial risk assessment technique, a common method. The proposed guidelines values are based on the indicator organism E. coli.

The guideline values were successfully applied to three wastewater treatment effluents in the Okanagan Valley in British Columbia. The health risks associated with other bacterial pathogens (Campylobacter jejuni and Salmonella spp.), virus (adenovirus, norovirus and rotavirus) and protozoa (Cryptosporidium parvum and Giardia spp.) were also estimated. The estimated risks indicate the effectiveness of the E. coli-based water quality guideline values. The ultimate guideline values are proposed and implemented by regulatory bodies in a country. These proposed guideline values would support the federal government in developing guidelines on reclaimed water quality for urban applications besides toilet and urinal flushing. The Canadian federal government already has implemented the guideline values for toilet and urinal flushing.

Meyer: Why did you use E. coli as an indicator of water quality?

Chhipi-Shrestha: Among the water microorganisms, E. coli is the best available indicator of water quality because it does not usually multiply in the environment, is easily detectable even in high dilution due to its excretion in feces in large numbers (approximately 1 billion cells per gram), and has a life span on the same order of magnitude as those of other enteric bacterial pathogens, according Health Canda. E. coli has widely been used as water quality indicator.

Meyer: What do you feel can be the impact of more widespread water reuse?

Chhipi-Shrestha: Our research is broadly on improving the sustainability of urban water systems using the water-energy-carbon nexus. Water reuse is an important component for urban water sustainability. Indeed, water reuse is a historic practice; however, water reuse has been increasing in the recent times.

Specifically, the effluent quality standards have progressively been made stringent due to public and environmental health issues. This will demand a higher level of wastewater treatment. This means higher cost, energy use and carbon emissions. Since the wastewater has to be treated to a higher degree, in some cases the quality resembles or is even better than freshwater or drinking water. In this case, with some degree of additional treatment, the treated wastewater can be reused safely. 

Creating Sustainable Communities

A hurdle facing those who wish to incorporate reclaimed water into their water systems is the lack of infrastructure designed to redistribute treated water to customers. Chhipi-Shrestha believes that when new construction projects are being planned, municipality and urban developers should consider the ways in which water in the community can be efficiently reused after proper treatment.

“As reclaimed water distribution infrastructure may be energy intensive and costly in an existing community, it is wise to consider it in the community planning and design stage,” he said.

In new communities, this depends several factors, primarily water availability and the location of source water. In some cases, it may make more sense not to engage in reuse.

“Depending on the water availability, location, climate and topography of a community, water reuse can be energy efficient and can also save carbon emissions,” Chhipi-Shrestha said. “For example, if the source water is very far from a community, the use of onsite wastewater after treatment could be energy efficient, as wastewater is to be treated in either case. If freshwater availability is very high and source is in the vicinity of a community, water reuse may be energy intensive, be costly and increase carbon emissions.”

Gyan Chhipi-Shrestha is a Ph.D. candidate at the University of British Columbia School of Engineering. He has a cross-disciplinary academic background in environmental science, engineering and sociology. His PhD research is on improving urban water sustainability using the water-energy-carbon nexus, and he has several publications in peer-reviewed journals and conference proceedings. His research focus is on sustainable water supply and wastewater management, environmental and human health risk assessment, environmental impact assessment, life cycle assessment, and green energy. Gyan Chhipi-Shrestha is a Ph.D. candidate at the University of British Columbia School of Engineering. He has a cross-disciplinary academic background in environmental science, engineering and sociology. His PhD research is on improving urban water sustainability using the water-energy-carbon nexus, and he has several publications in peer-reviewed journals and conference proceedings. His research focus is on sustainable water supply and wastewater management, environmental and human health risk assessment, environmental impact assessment, life cycle assessment, and green energy. Chhipi-Shrestha can be reached at [email protected].

About the author

Michael Meyer is associate editor for W&WD. Meyer can be reached at [email protected] or 847.954.7940.

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