Volatile Fatty Acids Production With Food Wastes And Excess Sludge Coupling Polyhydroxyalkanoate Production By Activated Sludge

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 (PHA) storage. The strategy not only achieves recovery energy from the organic solid waste, but also reduces the production cost of PHAs greatly. The study and results were shown as follows:(1) Acclimated efficient VFAs fermentation bacteria with co-substrate of food waste and dewatered excess sludge under semi-continuous technique. The results showed that the acclimatization system achieved steady-state condition after 20 days, when the VFAs concentration was 4000±150 mgCOD/1 and butyric acid content was the highest, followed by valeric acid, propionic acid and acetic acid content is relatively small.Study the effect of ratio of food waste and excess sludge in substrate on bio-production of VFAs. The ratio of food waste and excess sludge choose in accordance with VSS ratio of 100:0, 90:10, 70:30, 50:50, 30:70, 0:100. The results showed that soluble chemical oxygen demand (SCOD) deserved from the acidogenesis was proportional to the content of food waste. When the food waste versus excess sludge is 90:10, the most VFAs concentration achieved. When the substrate was all the food waste, the NH₄⁺-N and PO₄^3--P concentration in the fermentative liquid were so low that inhibited the activity of VFAs fermentation microbiology. At the same time, the ratio of food waste and excess sludge can also influence the distribution of the VFAs. The percentage of acetate acid in VFAs increased with the ratio of food waste and excess sludge decreased, and the percentage of butyrate acid in VFAs increased with the ratio of food waste and excess sludge increased.(2) Used response surface methodology (RSM) optimization of semi-continuous VFAs production with co-substrate of food waste and excess sludge. The effects of food waste composition in substrate, solid retention time (SRT), organic loading rate (OLR) and pH on the acidogenesis were evaluated individually and interactively. The optimum VFAs condition derived was food waste composition; 88.03%, HRT; 8.92 d, OLR; 8.31 gVSS/l d and pH; 6.99. The experimental VFAs concentration was 29099 mg/L, which was well in agreement with the predicted value of 28000 mg/l. And the optimum VFAs/SCOD condition was food waste composition; 92.12%, SRT; 6.26 d, OLR; 4.26 gVSS/l d, pH; 7.18. The experimental VFAs/SCOD 89.91% wse well in agreement with the predicted value 92.82%. The ratio of even C and odd C of the fermentative VFAs increased with increasing the food waste composition and increasing OLR, and the lowest value achieved when pH was around 6.7.(3) Acclimated activated sludge with high PHAs storage capacity under aerobic dynamic feeding (ADF) technique fed with the fermentative VFAs by gradually increasing organic load. It was demonstrated that the optimum organic load was 3600 mgCOD/l when the maximum PHA content in biomass achieved to 47.65% (on dry cell weight basis), and the maximum yield occurred when the organic load was 720 mg COD/l.Uniform design was utilized to find out relational models between C sources and PHA components. The data from the experiments analyzed and calculated by software SAS Version 9.0. The models derived were proved to be useful of predicting PHA components, and the experimental values well agreed with the predicted values.The batch production of PHA were operated by the magnetic field with 0mT, 7 mT, 21 mT fed with fermentative VFAs. We found that 7 mT magnetic field favored HB accumulation in biomass and 21 mT magnetic field favored HV accumulation in biomass. The yield of PHA from co-substrate of food waste and excess sludge achieved to 205 mgCODPHA/gVSS without magnetic field, which was 232 mgCOD PHA/gVSS by 7 mT magnetic field similar with the 21 mT. HA accumulation fed with fermentative VFAs were lager than fed with synthesized VFAs under any magnetic field.The no VFAs composition of the fermentative liquid was demonstrated mostly contributed to growing; meanwhile, it also contributed to PHA storage.