Study On The Characteristics And Application Of Food Waste Fermentation Liquid With High Lactic Acid

Nitrogen and phosphorus pollution has become a global problem since the 1980′s.High nitrogen, phosphorus and other nutrients discharged into waters damage the normal function of water body. However, the insufficience of carbon source in many operation process of sewage plants has become widespread, which leads to the low nutrients removal efficiecnes. Therefore, many researchers have proposed using additional carbon source to strengthen denitrification and PHB synthesis process to improve nitrogen and phosphorus removal. Some researchers have found that lots of rapid degradable organic matters including organic acids and VFAs in fermention liquid of wast food are the ideal carbon source. So in this thesis, food waste was utilized as substrate to produce lactic acid and then applied the fermentation liquid as additional carbon sources to strengthen nitrogen and phosphorus removal.Under the indoor temperature(25℃), the variations of SCOD, polysaccharide,protein, lactic acid and VFAs in different pH was detected to determine the optimal pH to produce lactic acid was 6. Under the conditions of the indoor temperature(25℃) and mesophilic temperature(37℃) fermentation, by comparing SCOD, polysaccharide,protein, lactic acid and VFAs with pH adjusted to 6 and a reactor without pH adjustment as a control, it showed that the optimal fermentation temperature to produce lactic acid was 37℃. In order to determine the denitrification potential, we used fermentation products under the optimum conditions for fermentation(pH=6, tem=37℃) in different periods to carry out the denitrification experiments. Then the author explored the denitrification characteristics of the fermentation liquid of food waste in different C/N ratios. It was concluded that the denitrifying effect was the best at C/N of 6. Then thefermentation liquid was applied to the step-feeding SBR, the removal rate of ammonia nitrogen, total nitrogen and phosphate reached 96%, 65% and 85%, respectively. It is indicated that the fermentation liquid of food waste as additional carbon source can obviously strengthen the nitrogen and phosphorus removal.Finally, the fermentation liquid fermented under the optimal conditions was applied to the A/O MBR reactor, the removal rate of ammonia nitrogen, total nitrogen and phosphate achieved over 96%, 65% and 85%, respectively. There was no negative effect on ammonia nitrogen removal(the removal rate was above 96%) and little effect on TN removal(the removal rate was about 70% to 75%) under the condition of regulating reflux ratio and SRT. The removal rate of phosphate was over 95% under the conditions of SRT of 30 d, and reflux ratio of 2 or 3. But increasing the SRT, the removal efficiency of phosphate quickly reduced, which showed that the influence of SRT on phosphorus is bigger. TP content in the sludge increased as a result of increasing reflux ratio, the extension of the SRT cannot effectively improve the effect of phosphorus removal.Food waste fermentation liquid as additional carbon source not only improves the nutrients removal from wastewater with insufficient carbon source, but also alleviates environment pollution, realizes the resource recycling. It obtains the social,environmental, and economic benefit unified win-win-win result.