Aluminum toxicity and ecological risk assessment of dried alum residual into surface water disposal

This paper presented a simplified ecological risk assessment of the toxicity of alum residuals from water treatment plants to surface water that is based on the framework recommended by United States Environmental Protection Agency (USEPA). Though few studies have investigated the potential for increased aluminum toxicity with discharge of alum residual streams to the aquatic environment, none have explored the use of ecological risk assessment methodologies to gain additional insight into the potential risk. This systematic approach has been used to elucidate the process of aluminum toxicity from oven-dried alum residuals on aquatic habitats. A laboratory experiment was performed to assess the leaching of dried alum residuals to five lake water samples. The tests were also done to evaluate the effect of pH levels (4, 5.5, and 7) and drying mechanism of alum residual (oven, air or freeze-thaw). Total inorganic aluminum leaching from laboratory analysis was used along with toxicity reference values to determine a risk quotient (RQ) for assessment of risk. Results revealed that alum residuals in surface water could reduce aluminum concentration or potential risk (RQ) for fish in some lake waters at natural pH levels. Surface water pH and drying mechanism of alum residuals did not have considerable effect on leachability of aluminum. Lake waters with and without the addition of alum residual showed a potential risk for chronic sub-lethal toxicity for trout species. Both chronic and acute lethal toxicity was observed in some tests depending on the initial aluminum concentrations in the lake water. A detailed review of toxicological effects of aluminum, its exposure and bioaccumulation was studied for appropriate risk assessment.