Investigation of the effect of nitrification inhibition on the performance and effluent quality of aerobic sequential batch reactors.

The use of nitrification inhibition as a concentrating step for ammonium (NH), for the purpose of increasing the potential for simultaneous recovery of phosphate (PO) and NH from effluent streams of an aerobic sequencing batch reactor (SBR) system, has never been investigated in the literature. Therefore, the present study aimed to determine the effect of the inhibition of nitrification on both the reactor performance and effluent quality in a laboratory scale aerobic SBR system. In order to compare the observed results, a separate reactor, where the inhibition was not applied, was operated as a control reactor (CR) under the identical operational conditions used for the inhibitory reactor (IR). Experimental results for the reactor performance showed that effluents with low total suspended solids (< 50 mg/L) and chemical oxygen demand concentrations (> 90% of removal efficiency based on the influent concentration of 500 mg/L) were achieved for both SBRs by obtaining an activated sludge with a sludge volume index < 60 mL/g after the acclimation period. In the same period, the effluent PO, NH, and nitrate (NO) concentrations were found to be 17.0 ± 4.0, 1.26 ± 0.84, and 21.5 ± 39 mg/L for the CR and 10.0 ± 4.4, 3.9 ± 2.4, and 9.2 ± 1.5 mg/L for the IR, respectively. During this period, 94% of the removed NH (NH) was converted to NO in the CR, indicating almost complete nitrification occurred in the reactor. However, only 47% of the NH was converted to NO in the IR as a result of the inhibition of nitrification, meaning a partial inhibition (53%) occurred due to the inhibition treatment. These results clearly demonstrated that the inhibition of nitrification allowed the effluent NH concentrations to increase by suppressing the formation of NO ions. Based on the results, it can be concluded that inhibition of nitrification in an aerobic SBR system creates a potential for conserving the effluent NH concentration and increasing consecutive recovery of PO together with NH from the effluent discharges.