Nitrogen & Phosphorous Removal via Anaerobic / Anoxic-Aerobic Processes and Struvite Formation in Mall Wastewater: Performance of Retrofitted Full-Scale Plants

With the new standards on nitrogen (N) and phosphorous (P) in wastewater discharges from industrial, commercial and municipal wastewater, there is a need for better wastewater treatment systems. Moreover, with the presence of such N and P in wastewater, struvite formation leading to clogging of pipes has also been a problem in wastewater treatment systems. This study aimed to improve N and P removal from mall wastewater through retrofitting with the inclusion of anaerobic/anoxic process prior to the existing aerobic process and recirculation of part of the effluent from aerobic process to anoxic tank in order to achieve ammonification of organic nitrogen, nitrification and denitrification in the whole system. The recovery of struvite, which is magnesium ammonium phosphate (MgNH4PO4), is also expected to be another pathway via which N and P can be removed from the wastewater. Seven mall wastewater treatment plants were monitored. Both the previous and new system include chlorination as a final treatment. The treatment performance with respect to the removal of N and P of the new retrofitted system is better than the system where the biological treatment process was mainly aerobic. Better levels of organic matter, oil and grease, total suspended solids (TSS), surfactant and fecal coliform were also achieved. The levels of N and P in the effluents of the anaerobic/anoxic process has become so low that precipitation of struvite via magnesium dosing is not feasible. Struvite formation already occurs at the mixing tank after anaerobic/anoxic tank. The new wastewater treatment system, with reduced aeration requirements, where N and P were removed by nature based bacteria and without the use of large dose of chemicals becomes a cost-effective solution for a cleaner environment.