To alleviate eutrophication in coastal waters, reducing nitrogen (N) discharge from wastewater treatment plants (WWTPs) by upgrading conventional activated sludge (CAS) to biological nutrient removal (BNR) processes is commonplace. However, despite numerous upgrades and successful reduction of N discharge from WWTPs, eutrophication problems persist. These unexpected observations raise the possibility that some aspects of BNR yield environmental responses as yet overlooked. Here, we report that one of the most common BNR processes, predenitrification, is prone to the production of low-molecular-weight dissolved organic N (LMW-DON), which is highly bioavailable and stimulates phytoplankton blooms. We found that in predenitrification BNR, LMW-DON is released during the post-aerobic step following the preanoxic step, which does not occur in CAS. Consequently, predenitrification systems produced larger amount of LMW-DON than CAS. In estuarine bioassays, predenitrification BNR effluents produced more phytoplankton biomass than CAS effluents despite lower N concentrations. This was also supported by stronger correlations found between phytoplankton biomass and LMW-DON than other N forms. These findings suggest that WWTPs upgraded to predenitrification BNR reduce inorganic N discharge but introduce larger quantities of potent LMW-DON into coastal systems. We suggest reassessing the N-removal strategy for WWTPs to minimize the eutrophication effects of effluents.

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The goal of this study was to evaluate the effect of effluents from conventional activated sludge (CAS) and biological nutrient removal (BNR) processes on algal bloom in receiving waters. We made multiple effluent sampling from one CAS and two BNR facilities, characterized their effluents, and conducted bioassay using river and ocean water. The bioassay results showed that CAS effluents brought similar productivity in both river and ocean water, while BNR effluents were more reactive and productive in ocean water. Unexpectedly, nitrogen-based biomass yields in ocean water were up to six times larger for BNR effluents than CAS effluent. These results indicated that nitrogen in BNR effluents, although its total concentration is lower than that of CAS effluent, is more reactive and productive in ocean water. The ocean water bioassay further revealed that effluents of BNR and CAS led to considerably different phytoplankton community, indicating that different characteristics of effluents could also result in different types of algal bloom in receiving waters. The present study suggests that effects of upgrading CAS to BNR processes on algal bloom in receiving waters, especially in estuary and ocean, should be further examined.

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The Springfield Water and Sewer Commission (SWSC) operates a 67-MGD, regional activated sludge wastewater treatment facility (SRWTF) located on Bondi Island in Agawam, Massachusetts. The facility began secondary treatment in 1977 and recently upgraded its mechanical, surface aeration system to fine bubble diffusion through a $10.8 million dollar SRF loan.Over the last few years the SWSC has been developing a more competitive operation at the SRWTF. One major component is cost reduction, especially for biosolids management which normally represents about 50% of a facility's budget. The new aeration system provides process flexibility to address secondary sludge production issues, which are an important part of the long-term solids management program. Secondary sludges dewater poorly; are unstable with respect to organics, oxygen demand, and odors; and are expensive to manage.As part of the short-term biosolids program, it was decided to examine cost reductions associated with lower waste activated sludge production levels and downstream solids handling. Equipment and process modifications were made to the secondary system to allow operation in the extended aeration range of organic and solids loadings. The presentation will discuss the following aspects of the two year field study: equipment modifications necessary for higher clarifier solids loading rates (SLR) changes in the microbiology at MLSS levels up to 5000 mg/l and solids retention time (SRT) values of 20 to 30 days operational procedures developed for high flow, wet weather operatioǹ significant reductions in waste activated sludge (WAS) volumes and associated savings in biosolids management costs dewatering improvements resulting from improved primary/secondary sludge ratios seasonal considerations and effects