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Author ORCID Identifier



Open Access Dissertation

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program

Civil Engineering

Year Degree Awarded


Month Degree Awarded


First Advisor

Chul Park

Subject Categories

Environmental Engineering


The main objective of this research was to evaluate the effects of effluent nitrogen from conventional activated sludge (CAS) and biological nutrient removal (BNR) processes on eutrophication in receiving estuaries. To investigate differences in effluent nitrogen from CAS and BNR processes, lab-scale wastewater treatment systems having identical influent were operated under controlled conditions. This reactor study showed that the BNR system decreased nitrogen discharge by removing dissolved inorganic nitrogen (DIN) from wastewater but generated more effluent dissolved organic nitrogen (DON) than did the CAS system. The transition of treatment conditions from anoxic to oxic within the BNR process facilitated the production of low molecular weight dissolved organic nitrogen (LMW DON), causing the BNR effluent to contain more DON than the CAS effluent. Moreover, analysis of data from a local full-scale plant (the Amherst WWTP) confirmed that when the wastewater treatment mode was converted from CAS to BNR, the effluent DIN decreased but effluent DON increased. Bioassays, incubated with effluent and natural estuary water (Long Island Sound water), were conducted to compare algal growth stimulated by CAS and BNR effluents. The results demonstrated that the BNR effluent, despite containing less dissolved total nitrogen (DTN), stimulated more algal biomass and higher nitrogen-based productivity than the CAS effluent. These unexpected outcomes were attributed to the greater potential of LMW DON to drive algal growth compared to DIN. Numerical analyses for algal growth yields for effluent nitrogen species illustrated that LMW DON had approximately 7 times higher yield than DIN. In conclusion, this research revealed that the BNR system generated more effluent LMW DON, which showed greater algal growth yield, supporting for more algal biomass generation in the bioassays than did the CAS system. These findings indicate that simply decreasing the amounts of effluent nitrogen cannot ensure alleviating algal blooms in receiving estuaries. To evaluate the actual influence of effluents on eutrophication, not only amounts but also compositions of effluent nitrogen should be considered.