Research On Polyhydroxyalkanoates Production By Waste Sludge

Petrochemical plastic is necessary in the daily life and industrial manufacture, but it causes serious "white polution" and increases the energy crisis. As a kind of fully biodegradable plastic, polyhydroxyalkanoates (PHAs) is a good substitute to the petrochemical plastic due to their similar characteristics. Industrial PHAs production is based on pure culture fermentation and has high operating costs which have impeded large-scal PHAs commercial development. The treatment and disposal of waste activated sludge (WAS) represents a major cost to municipal sewage plants. Volatile fatty acids (VFAs) production by fermentiton of WAS is widely applied as a means to convert organic waste into substrates for PHAs prodution. WAS is rich in microorganisms and organic carbon, so it could be utilised as a cheap but valuable resource for this bioprocess. In this study, PHAs-storing organisms were successfully enriched under aerobic dynamic feeding with a short feast length less than25%of the cycle and PHAs was produced from anaerobic fermentative liquid (AFL) of waste activated sludge. This study is aimed to reduce the production cost of PHAs and disposal amount of WAS simultaneously.PHAs accumulation and carbon consumption by Ralstonia eutropha H16were investigated in anaerobic fermentative liquid (AFL) of waste activated sludge (WAS). The WAS was fermented at52℃with a sludge retention time (SRT) of48hours in hydrolysis reactor to form AFL, in which the volatile fatty acids(VFAs) were feasible carbon source for PHAs synthesis. When acetic acid was the predominant component of VFAs in the AFL (C/N/P≈100/10/1,TOC=2881mg/L, acetic acid/total VFAs=48.9%), the maximum PHAs content detected in the cells was12.51%(dry weight) after40-hour reaction and the major monomer of PHAs was hydroxybutyrate (HB). When iso-valeric acid was the predominant VFAs in the AFL (C/N/P≈100/10/1, TOC=2358mg/L, iso-valeric acid/total VFAs=29.8%), the maximum PHAs content detected in the cells was up to32.14%(dry weight) and hydroxyvalerate(HV) was the major monomer of PHAs. Five methods for the recovery of PHAs from Ralstonia eutropha H16were used to optimize extraction conditions and the PHAs recovery of96.4%at the purity of97.3%was obtained when the cells were treated by SDS-NaCIO method.PHAs-synthesis mixed bacterial consortia were successfully enriched from WAS by aerobic dynamic feeding approach. Mixed bacterial consortium S-150(1) enriched by feast/famine (F/M) condition accumulated a maximum PHAs content of59.2%(dry weight). Effect of nitrogen and phosphrous limitation was not as significant as F/M for PHAs-storing organisms enrichment from WAS and the maximum PHAs content detected in cell was only7%(dry weight). The production of PHAs from WAS pre-treated by high-pressure thermal hydrolysis was18%(dry weight).Production of PHAs from anaerobic fermentative liquid was studied in batch and continous mode reacter system at a pilot scale fermentor. The final PHAs content was59.4%in batch culture and the highest dry cell weight was12g/L in continuous mode by mixed bacterial consortium S-150(1).