Effects of Grazers and Elevated Temperature on the Dynamics of a Wastewater Algal Treatment System

Wastewater algal treatment systems (ATS) have been shown to effectively remove excessive nutrients from wastewater and prevent eutrophication. However, the performance of ATS could be strongly affected by environmental factors. This study examined (1) the effect of grazers on nutrient removal rates and (2) the effect of 1.7 °C increase in temperature on algal biomass. The effect of grazers was assessed outdoors by analyzing dissolved and tissue nutrient concentrations in ATS with and without biological pesticide in two 20-day trials. The effect of elevated temperature was evaluated indoors by comparing algal biomass between heated and non-heated ATS for 20 days. Grazing had no consistent, detectable effect on nutrient removal rates or periphyton tissue nutrients. Furthermore elevated temperature had no detectable effect on algal growth rates. I conclude that the performance of recirculating ATS is unlikely to be affected by grazers or slight variations in temperature if harvesting regularly (days).