Producing Bio-Polyhydroxyalkanoates (PHA) With Anaerobic Fermentation Slurry From Kitchen Waste By Microbial Fermentation

The fermentation slurry of kitchen waste commonly was known as biogas slurry. This project focused on the resource utilization of the fermentation slurry of kitchen waste. Based on the physical and chemical properties of typical fermentation slurry in China, some microbial strains were selected. These strains could survive in fermentation slurry properly and also can produce a great amount of PHA. PHA has complete biodegradability and broad application prospect in the aspects of biodegradable plastic. After adjusting its pH, nutrient contents and biological enzyme, the fermentation slurry was used as microbial culture. The orthogonal experiments of three factors and three levels, time, oxygen supplement and temperature was used to determine the optimum condition and in which condition microbial stains had the maximum production of PHA in this high-salinity fermentation slurry.The physico-chemical properties and environmental parameters of kitchen waste anaerobic fermentation liquor were analyzed. The biological organic matter content: protein 14.8 g/kg, fat 98.7g/kg, total sugar 17g/kg. Main pollutants indicators of fermented liquid:Total nitrogen:3660 mg/L, total phosphorus 584 mg/L, ammonia nitrogen 1286 mg/L, the COD 16500 mg/L, TS 2.71%,13.595‰ salinity, pH about 8.5 to 9.0.66 strains were screened out from the kitchen waste anaerobic fermentation liquor which included 61 bacteria strains and 5 fungus strains.3 strains produced PHA effectively were found by Nile blue staining method:13(Alcaligenes aquatilis),65(Bacillus methylotrophicus), and 2581 (Halomonas elongate). Adding three other bacteria strains which were bought from DSMZ, Germany, total 6 strains were screened by single factor experiment, Adjusting its pH, nutrient contents and biological enzyme, the fermentation slurry was used as microbial culture. Three strains grew well in this microbial culture were selected and screened by gas chromatography. Of which, the 65 strain can produce PHV, the 2581 strain can produce PHB and neither PHV nor PHB were produced by the 13 strain.Number 65 and 2581 strains were selected to optimization of fermentation conditions,the orthogonal experiments of three factors and three levels, time, oxygen supplement and temperature were used to determine the optimum condition and in which condition our microbial stains had the maximum production of PHA. By using the BBD method to optimize the fermentation conditions, the optimal fermentation conditions were founded to produce PHV by the 65 strain:temperature 35℃, intermittent oscillation, cultivating 108h, PHV production 0.95g/L and to produce PHB by the 2581 stain: temperature 35℃, intermittent oscillation, cultivating 72h, PHB production 0.114g/L. This research preliminary explored on producing PHA with high halt slurry from restaurant garbage digestion, provided scientific basis and development suggestion for the following application. It has important theoretical significance and practical value to the treatment and the resource utilization of restaurant garbage in our country.