Tertiary Anammox for Sustainable Nitrogen Removal

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WRRI Project;20-02-U

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NC Water Resources Research Institute


Concentrated discharges of nitrogen into our waterways have led to serious environmental impacts, such as eutrophication and algae blooms. Due to these discharges, stringent total nitrogen (TN) discharge limits have been placed on Water Reclamation Facilities (WRFs). Mainstream deammonification offers a novel approach for improving nitrogen removal at these facilities by harnessing anaerobic ammonia oxidizing bacteria (Anammox). However, the success of this process has been limited. Previous research at NC State explored the conversion of tertiary filters to mainstream deammonification filters which were shown to be capable of an average total inorganic nitrogen (TIN) removal rate of 91%, with effluent TIN reaching below 2 mg/L-N. However, this research suggested that nitrate loading concentrations were the limiting factor in meeting 2 mg/L-N TIN effluent limits. Incorporating partial denitrification (PdN), the conversion of nitrate to nitrite for subsequent use in Anammox, offers a promising solution. The goal of this research was to explore the TIN removal capability and feasibility of a PdN-Anammox (PdNA) filter under typical filter loading conditions, in comparison to a conventional denitrification (FdN) filter. Different carbon loading strategies in pilot scale filters confirmed that maintaining a nitrate residual of >1.5 mg-N/L allowed for the highest PdN conversion efficiencies and in turn increased Anammox activity. Furthermore, the carbon requirement (C/N ratio) of 5.1 g COD/g TIN in pilot scale FdN was higher than the 2.08 g COD/g TIN achieved in the PdNA filters, demonstrating the cost benefits associated with mainstream deammonification and the application of PdNA. In addition to greater than 50% reduction in supplemental carbon, other benefits include nearly 38% reduction in oxygen demand and reduction in excess sludge in comparison to conventional BNR processes. Through this pilot study, PdNA was demonstrated to provide TIN removal efficiencies of greater than 80%. With further research, stable TN removal at WRFs at typical filter loading rates can be achieved, and with that, the possibility for substantial operational expenditure (OPEX) savings.