BIOLOGICAL NUTRIENT REMOVAL IN MUNICIPAL WASTEWATER TREATMENT: NEW DIRECTIONS IN SUSTAINABILITY
Zhirong Hu et al.

EnviroSim Associates Ltd, McMaster Innovation Park, 175 Longwood Rd South, Suite 114A,
Hamilton Ontario L8P 0A1, Canada.

ABSTRACT: To control eutrophication in receiving water bodies, biological nutrient removal (BNR) of nitrogen and phosphorus has been widely used in wastewater treatment practice, both for the upgrade
of existing wastewater treatment facilities and the design of new facilities. However, implementation of
BNRAS systems presents challenges due to the technical complexity of balancing influent COD for
both biological phosphorus and nitrogen removal. Sludge age and aerated/unaerated mass fractions
are identified as key parameters for process optimization. Other key features of selected BNR process
configurations are discussed. Emerging concerns about process sustainability and the reduction of
carbon footprint are introducing additional challenges in that influent COD, N and P are increasingly
being seen as resources that should be recovered, not simply removed. Energy recovery through
sludge digestion is one way of recovering energy from influent wastewater but which presents a
specific challenge for BNR: generation of sidestreams with high nutrient and low COD loads.
Technologies designed specifically to treat these sidestream loads are overviewed in this paper. Finally,
relatively high levels of nitrous oxide emissions, a powerful greenhouse gas, have been shown to occur
in the BNR process under certain conditions, particularly in the presence of high nitrite concentrations.
The advantages of using process modeling tools is discussed in view of optimizing BNR processes to
meet effluent requirements as well as meeting goals of sustainability and reducing carbon footprints.

 

Journal of Environmental Engineering. Submitted October 29, 2010; accepted July 14, 2011;
posted ahead of print July 16, 2011. doi:10.1061/(ASCE)EE.1943-7870.0000462