Significance of External Carbon Sources on Simultaneous Removal of Nutrients from Wastewater

Laboratory-scale studies were undertaken to examine the effects of easily-biodegradable organic substances upon the nutrient removal by a simulated sequencing batch reactor (SBR). The fill and react period of the SBR was 14 hours, including an instant fill, 7 hours aeration, 4 hours anoxic and 3 hours aeration period. Three kinds of commonly used carbon sources, namely methanol, glucose and sodium acetate, at the concentrations equivalent to theoretical COD values of 50, 100 and 150 mg O2 l-1 were added to each reactor prior to the anoxic stage. The results showed that the concentration of NH4+-N dropped from its initial 50 to 18 mg l-1 (64 % removal) during the first aeration period, with the NO3−-N content increased from 2 to 33 mg l−1. A 60% depletion of COD was also recorded in this period. Denitrification occurred during the anoxic period, higher amount of NO3−1-N was removed in the reactors supplemented with carbon substrates at the concentrations of 100 and 150 mg l-1. The final inorganic nitrogen content was less than 5 mg l-1 in the reactor supplemented with 150 mg l-1 sodium acetate. Simultaneous removal of phosphorus was reported in reactors supplied with high concentration of sodium acetate. In these reactors, large amount of P was released during the anoxic/anaerobic period but the released P was taken up by bacterial cells in the subsequent aeration stage, and the final P content was less than 1.5 mg l-1 (84 % removal was achieved). Among the three carbon sources used, sodium acetate was the most efficient and effective source in removing wastewater nutrients, followed by methanol, and glucose was the least reliable substrate.