Laboratory Investigation on the Influences of Field BNR and CAS Effluents on Algal Bloom in Connecticut River and Long Island Sound

The goal of this study was to quantify and evaluate the influences of conventional activated sludge (CAS) and biological nitrogen removal (BNR) effluents on algal bloom in same receiving waters, the Connecticut River and Long Island Sound. We made multiple effluent sampling from one CAS and two BNR wastewater treatment facilities, characterized the effluents, and conducted bioassay using the CT River water and LIS water. The bioassay results showed that CAS effluents resulted in similar reactivity for both river and ocean water while BNR effluents were more reactive and productive in the ocean water than river water. More importantly, overall COD yields for BNR effluents and ocean water were 2-4 times larger than the CAS effluent-ocean water set, indicating that BNR effluents, although their total nitrogen (TN) concentrations were much lower than those from CAS, were more reactive and productive in the LIS water. The results from the bioassay further revealed that BNR effluents and CAS effluents led to considerably different microalgal composition, although they were incubated in the same receiving waters. This suggests that different effluent characteristics could result in different algal bloom in receiving waters. The bioassay study further revealed that one BNR effluent set led to a bloom of filamentous cyanobaceria in LIS water. These cyanobacteria possessed the heterocysts, implying that they are able to fix atmospheric nitrogen into the water environment, which could complicate the N cycle in LIS. All these results suggest that reducing nitrogen concentration via BNR processes may not be the best solution to deal with the persistent eutrophication and algal bloom problems occurring in Long Island Sound.