Understanding the health risks with reclaimed wastewater

Cyanobacteria

The potential presence of cyanobacteria and their toxins (e.g., microcystin) was raised as a concern by the regulatory stakeholders in relation to the wastewater storage pond. The only regulatory guidance for cyanobacterial toxins in water is for recreational waters such as swimming or bathing, or drinking water. No values were available for reclaimed water, wastewater, or agricultural irrigation water.

The presence of cyanobacteria or related toxins in the system is not related to the performance of the wastewater treatment plant. Their potential formation is related to a number of factors, including temperature, nutrient content of the storage water and dissolved oxygen concentration. A limited literature review was completed to identify the most relevant indicator organisms and trigger concentrations of relevance to the project.

For the Harmony project, potential formation of cyanobacteria is related to the proposed pre-irrigation storage pond rather than the treatment plant. A cyanobacterial management program had already been developed by Urban Systems. Intrinsik also recommended that the growth of cyanobacteria in the pond be evaluated, once the wastewater plant and storage pond are in operation. Also, an understanding of the characteristics of the storage pond water should be gained through data analysis and review.

As no guidelines for the management of cyanobacteria appear to exist for irrigation water or reclaimed water, the existing Alberta and federal recreational water quality criteria were suggested as alternative values for comparison.

With respect to microbial indicator organisms, the literature review concluded that the micro-organisms proposed to be monitored at the treatment plant (fecal coliform, E. coli, and thermotolerant coliforms) were generally consistent with other jurisdictions.

Evaluation of water in the post-treatment, outdoor storage pond was challenging with respect to turbidity and residual chlorine. The available reclaimed water guidelines did not appear to involve pre-irrigation storage, only reclaimed water used immediately for irrigation. Further, the water quality in the storage pond could be additionally impacted by factors such as precipitation, run-off, organic matter from aquatic birds or aerial deposition. To help mitigate these variables, regular monitoring will be incorporated into the project design.

Alberta Environment and Sustainable Resource Development issued a Wastewater Treatment Plant Approval for the Harmony development in October 2014. It contains some provisions for reducing potential human exposure through the use of access restrictions and irrigation times. The findings and related recommendations of the Intrinsik risk assessment contributed to the development of a monitoring plan and to the regulatory approval of the wastewater treatment plant.

Karen A. Phillipps, M.Sc, DABT, Nino Devdariani, M.Env.Sc., and Claire McAuley, M.Sc, M.Eng,, P.Eng., are with Intrinsik Environmental Sciences Inc. This article appeared in ES&E’s March/April 2015 issue.