Micro-oxygen Process Improved Synthesis of PHAs with Undomesticated Excess Sludge

Abstract

Polyhydroxyalkanoates (PHAs) are a potential substitute for traditional plastics. Synthesis of PHAs using excess sludge without additional domestication as a mixed microbial culture can reduce production costs. PHAs were synthesized using excess sludge (R1) from a continuous flow system performing simultaneous nitrification/denitrification and phosphorus removal. Excess sludge (R2) from a A2O wastewater treatment plant was used as a mixed microflora culture (MMC) and the waste fermentation liquid was used as a carbon source. Results showed that with volatile fatty acid (VFA) concentrations of 430-520mg/L (COD of 650-750mg/L), when R1 and R2 were reacted under anaerobic conditions, the maximum generated concentrations of PHAs were 84.41mg/g and 30.8mg/g, respectively. When aeration volumes were 5, 10, 15, and 20L/h, the amounts of PHAs synthesized from R1 and R2 increased by varying degrees, with the highest amount generated at 10L/h (108.6mg/g and 58.58mg/g, respectively). In the process of PHA formation, ORP shows a decreasing trend. When the concentration of PHAs reaches a maximum level, ORP drops to a "valley point." Lower ORP valley points indicate a higher potential for synthesis of PHAs. Therefore, ORP can be used as a control parameter to reflect the reaction process in the micro-oxygen synthesis of PHAs.