Nitrification toxicity evaluation using bench-scale testing

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Courtesy of Water Environment Federation (WEF)

The Camas Wastewater Treatment Facility experienced a prolonged period of poor ammonia removal (nitrification). A variety of “real-world” bench tests were developed and performed to determine if toxins were inhibiting the nitrification process. The focus of this paper is on the methodology used and conclusions drawn from the bench-testing.

Test were performed that compared toxicity of the wastewaters coming from each of the two main sewers – Joy and Adams. Tests were also performed on samples of wastewater originating from a major industry that discharges into the Camas Sewer (Joy Sewer), hereafter referred to as “Industry”. Because the potential existed for Camas’ wastewater to already be contaminated by a toxin, return activated sludge (RAS) was obtained from two wastewater plants that have a recent and steady record of good nitrification. These plants were Chehalis and Washougal, Washington. Tests were also performed using RAS and mixed liquor (MLSS) from the Camas secondary system. The evaluation utilized a large number of standard and not-so-standard “toxicity identifying tests.” There were six different tests utilized in this evaluation. The bench-top tests performed during this evaluation are shown below. The sources of the microorganisms used in the tests are shown in parenthesis.

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