Wastewater-nitrogen removal using polylactic acid/starch as carbon source: Optimization of operating parameters using response surface methodology

Nitrogen removal from ammonium-containing wastewater was conducted using polylactic acid (PLA)/starch blends as carbon source and carrier for functional bacteria. The exclusive and interactive influences of operating parameters (i.e., temperature, pH, stirring rate, and PLA-to-starch ratio (PLA proportion)) on nitrification (Y-1), denitrification (Y-2), and COD release rates (Y-3) were investigated through response surface methodology. Experimental results indicated that nitrogen removal could be successfully achieved in the PLA/starch blends through simultaneous nitrification and denitrification. The carbon release rate of the blends was controllable. The sensitivity of Y-1, Y-2, and Y-3 to different operating parameters also differed. The sequence for each response was as follows: for Y-1, pH > stirring rate > PLA proportion > temperature; for Y-2, pH > PLA proportion > temperature > stirring rate; and for Y-3, stirring rate > pH > PLA proportion > temperature. In this study, the following optimum conditions were observed: temperature, 32.0 degrees C; pH 7.7; stirring rate, 200.0 r .min(-1); and PLA proportion, 0.4. Under these conditions, Y-1, Y-2, and Y-3 were 134.0 mu g-N.g-blend(-1) .h(-1), 160.9 mu g-N.g-blend(-1).h(-1), and 7.6 x 10(3) mu g-O.g-blend(-1).h(-1), respectively. These results suggested that the PLA/starch blends may be an ideal packing material for nitrogen removal. (C) Higher Education Press and Springer-Verlag Berlin Heidelberg 2016