Acute Toxicity Identification Evaluation of Treated Wastewater
Tetra Tech provided an innovative effluent toxicity identification evaluation and examined and designed cost-effective treatment modifications to ensure compliance for a global food and beverage manufacturer’s discharge permit.
A global food and beverage manufacturer engaged Tetra Tech to develop and conduct studies to identify the cause of intermittent effluent toxicity that threatened future permit compliance at one of its facilities. The client believed that the overall dissolved solids content of the wastewater was the cause of toxicity, and available solutions would be prohibitively expensive. Tetra Tech quickly identified the cause of the observed toxicity and developed a more cost-effective solution to ensure long-term permit compliance.
Based on literature reviews and experience, Tetra Tech theorized that high concentrations of magnesium, due to the use of magnesium hydroxide as a treatment chemical, were causing the intermittent effluent toxicity. In less than four months, Tetra Tech’s Center for Ecological Studies used treatment performance information, chemical usage data, and previous toxicity testing results to develop several innovative laboratory testing approaches, including using synthetic effluents, to isolate the cause of toxicity. Our team then developed a cost-effective solution involving switching to an alternative treatment chemical to prevent the client from having to implement the previously proposed expensive and unnecessary modifications.
The collaborative effort between Tetra Tech’s wastewater process engineers and aquatic scientists quickly identified magnesium concentrations as the cause of toxicity. Toxicity due to excess magnesium from treatment chemicals is unusual and rarely seen in wastewater treatment, as the potential for magnesium to cause a toxic effect is typically counter-balanced by other constituents. However, our team identified that the nature of production processes and timing prevented this natural balancing effect from occurring continuously. Because toxicity was intermittent depending on specific production needs, our team used an innovative approach based on developing a synthetic effluent with non-toxic properties that allowed for rapid screening of the impact of magnesium concentrations. Once toxic samples were available from actual operations, our team confirmed that magnesium was the cause.
Tetra Tech’s efforts in executing the toxicity identification evaluation and identifying a less toxic chemical treatment strategy helped ensure that the facility will be compliant with its permit in the future. This allowed for a much more cost-effective solution based on a simple switch to an alternative chemical. The identification of the clear linkage between production operations and impacts on wastewater treatment operations also will be a critical factor in future plant operations, as it increased awareness between production operations and wastewater operations departments about the factors that can influence permit compliance.
Following approval of a conceptual design, Tetra Tech was asked to implement the proposed solutions using a turnkey design-build approach. The upgrades include switching to an alternative treatment chemical and significant modifications to wastewater treatment instrumentation and control systems. In addition to ensuring permit compliance, these changes also will improve the reliability of treatment operations in general, as well as increase resiliency in dealing with inevitable wastewater quality variability due to the ever-changing nature of production operations.