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

Abstract

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°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 μg-N∙gblend–1∙h–1, 160.9 μg-N∙g-blend–1∙h–1, and 7.6 × 103 μg-O∙g-blend–1∙h–1, respectively. These results suggested that the PLA/starch blends may be an ideal packing material for nitrogen removal.