Effect of carbon source feed regimen on polyhydroxyalkanoates production by activated sludge

• Main Authors: Ya-Lan Fang, 方雅嵐
• Other Authors: Wei-Chin Chang
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/31157908572166487326

碩士 === 雲林科技大學 === 環境與安全工程系碩士班 === 98 === Production of polyhydroxyalkanoates (PHAs) from waste activated sludge, which can obtain an effective to treat wastewater, and also is the more economical and environmental method than the production by the way of pure culture, has become one of the focuses in the PHA biosynthesis field. However, commercial applications and wide use of PHA is hampered due to its high price and low yield than the general petroleum-derived plastics. Therefore, to reduce their production cost, a great deal of effort has been devoted to develop focused on the optimization of PHA production by mixed cultures. In the present study, we operated anaerobic-oxic (A/O) activated sludge system fed with propionate. Then, sludge from the aerobic zone of the system was harvested to perform the aerobic batch experiments for PHAs production by feeding propionate in pulses (CODprop = 4000 mg/L、6000 mg/L). All experiments were utilized to explore the capability of PHAs production from changes in the way of carbon source feed regimen on PHAs production by activated sludge. Experimental results indicated that regardless of carbon source concentration CODprop = 4000 or 6000 mg/L, when the external carbon source fed by way of pulse (two pulses, three pulses or four pulses), their PHAs content and the yield of PHAs (YP/S) were significantly higher than the one pulse, and the yield of active biomass (YX/S) was relatively high in one pulse. The results showed that the carbon source fed by pulses can reduced microorganisms in carbon converted into cell proliferation, and then get a better PHAs production, and reduce the impact of inhibition production of PHAs from high concentrations carbon sources. In addition, from the batch experiments for PHAs production by feeding propionate in pulses under the pH controlled or not controlled, the results indicated that carbon source concentration CODprop = 4000 and 6000 mg/L has a better performance in PHAs production under the conditions of pH non-controlling. Therefore, this study further investigates the effect of pH on PHAs production by performing bath experiments with pH control at 7.5 and pH without control. When the system under the conditions of pH without control, the PHAs production indexes including PHAs content, specific PHAs production rate (qp) and the yield of PHAs (YP/S), were significantly better than when pH was controlled at 7.5. Furthermore, under the situation of batch experiments without pH control, the pH value changed to 9 ± 0.2 from the initial 7.5, then, maintained a constant in system. When further PHAs production was evaluated by performing experiment with pH controlled at 9, the PHAs production targets similar for the results of pH without controlled. The results showed that the system in pH without control had better capability of PHAs production with relation to control pH at 9. In addition, PHAs production by activated sludge system operated under aerobic dynamic substrate feeding (ADF) has drawn a most attention. In this study, the further experimental for the construction of into the flow matrix of the ADF (Acid-ADF) system of sludge with different concentrations of acetate and propionate as the sole carbon source for PHAs production in aerobic batch experiments and compare the best carbon source concentration. The results showed that the maximum attainable yield of PHAs was obtained under the two carbon sources feed in the COD = 6000 mg/L; besides, comparison with acetate and propionate for the effect on the PHAs production, when the use of acetate as carbon sources, PHAs with high yield as a main composition of 3HB, when usage propionate as carbon sources, PHAs yield was lower and its main composition as 3HV. Therefore, this study also operated the above experimental by using the ratio of acetate and propionate with 50:50 mixture (total carbon concentration in control as COD = 6000 mg/L) for PHAs production. The results show that t specific substrate uptake rate (-qS), specific PHAs production rate (qp) and the yield of PHAs (YP/S) and other PHAs production targets were higher than the single carbon source, but PHAs yield was slightly lower than the use of acetate as a single carbon source, it may be caused by easier processing of P(3HB-co-3HV) copolymer structure type, indicating a mixed carbon source with the production potential of producing PHAs. From the reported researches, the major cost in the PHAs production was distribution in the substrate to account for about 40% of the total production costs. Therefore, this study attempted to develop the production of alternative carbon sources, which was taken waste milk from a food processing plant in Douliu, through the pretreatment-anaerobic fermentation, then converted the various organic compounds into volatile fatty acids (VFAs), as an alternative carbon source for PHAs production, and to explore the process feasibility of producing PHAs by using a waste milk and the impact of VFAs composition on PHAs production. After fermentation of the effluent, 50% of the soluble COD was present as VFAs (acetate, propionate, butyrate, valerate and lactic acid) and the resulting PHA after batch accumulation can be achieved the P(3HB-co-3HV) copolymer structure types of PHAs.