The Effect Of PH On The Fermentation For VFAs With Food Waste And Excess Sludge And The Biosynthesis Of Polyhydroxyalkanoate With Fermentation Liquid

Food waste and excess sludge are the two kinds of representative organic solid waste, which are the source of decay, odor and toxic gas emission and groundwater and soil contamination due to their high-volatile solids and moisture content. Acidogenic fermentation of food waste in combination with excess sludge is an alternative strategy because volatile fatty acids (VFAs) can be harvested and used as carbon sources for polyhydroxyalkanoates (PHAs) storage. The strategy not only achieves recovery energy from the organic solid waste, but also reduces the production cost of PHAss greatly. The study and results were shown as follows:(1) Take food waste and dewatered excess sludge as substrates, and the acclimated efficient VFAs fermentation bacteria as inoculums, study the effect of pH on the the anaerobic fermentation production of VFAs. pH was controlled at 5,7,9 and 11,respectively, by adding 3 M NaOH or 3 M HCl, besides, pH was not controled and used as a blank test. On 35th day, the reactors reached steady state, at pH 9.0, the highest production of total VFAs was obtained,which was about 25934 mgCOD/L, the ratio of VFAs/SCOD was 0.61, the main components of the fermentation was VFAs.(2) Study the effect of pH on the percentage of individual VFAs and the consumption of protein and carbohydrate and the production of methane in reactors, and analyze the mechanism of pH affect the distruption of VFAs. After the steady state was reached, at pH 5.0 and blank test, the pH was kept about 4.55 and 3.12 respectively. The percentage of acetic acid was reached above 70%, but the total VFA was very low, so at pH 5.0, it can not be used for VFA production. At pH 7.0 and 9.0, the percentage of butyric acid was reached to 48.10 and 49.2% respectively, the fermentation was butyrate-type fermentation..Both protein and carbohydrates have effect on the production of volatile fatty acids, but because the composition of the carbohydrate was higher than soluble proteins, so carbohydrates have the significant effect on volatile fatty acids production.(3) With the pure acid that have the same components with VFAs, under aerobic dynamic feeding (ADF) technique feeding, the study revealed that the biosynthesis of PHAs was closed. Therefore, we can directly use VFAs as a carbon source to biosynthesis of PHAs, which can not only greatly reduce the cost of PHAs production, but also lay the foundation for the scale production.The effect of different feeding regimens on the production of PHAs was significant, one-pulse feeding, divides equally three times feeding pattern, divides equally three times feeding and draw off supernatant before every feeding regimens were obtained the highest at 330min. Continuous-feeding regimen have the highest synthesis rate, which was 64.5%.