Enhanced Anaerobic Fermentation Of Swine Manure By PH Adjustment And Simultaneous Recovery Of Nitrogen And Phosphorus From The Fermentation Liquor

As the development of the agricultural modernization in China, the rural environmental problem in the form of non-pointed pollution has become more and more serious, mainly due to the tremendous amount of livestock waste discharge. The anaerobic fermentation is an effective way to treat livestock wastes, because it can not only eliminate the rural non-pointed pollution, but also obtain resource and energy from the livestock wastes, with significant environmental and economic benefits. As the world’s primary pig-breeding country, China discharges hundreds of millions of tons of swine manure annually with high level of organic components, which is the appropriate substrate for the production of volatile fatty acids (VFAs) through anaerobic fermentation. Based on the existed research, this study aimed at the VFAs production by enhancing the performance of hydrolysis and acidification of swine manure with different pH adjustment methods, and investigated the corresponding mechanism. After the anaerobic fermentation, the nitrogen and phosphorus in the fermentation liquor were recovered simultaneously by using the natural zeolite, and its efficiency, operation conditions and mechanism were discussed. The objective of this study was to maximize the resourceful treatment of carbon, nitrogen and phosphorus in the swine manure comprehensively.Firstly, the batch experiments were tested to investigate the enhancement of initial pH adjustment on the of hydrolysis and acidification performance of swine manure for 20 days, with the initial pH of the substrates setting at 3,5,1,9,10,11 and 12, respectively. The results revealed that the initial pH 10 was the best condition for the VFAs production, with the highest concentration of 13634mg-COD/L at 20th day, and 71.2% of them were acetic acid and propionic acid. Initial pH 5 was found to be advantageous for the production of butyric acid and its highest concentration was 2530 mg-COD/L, amounting for 24.6% of VFAs. In addition, the ammonium nitrogen (NH4-N) increased significantly with the fermentation progressing, and there was a positive correlation between the VFAs production and ammonium release. Based on the analysis of microbial community structures in the fermentation samples by PCR-DGGE, it was revealed that the initial pH adjustment had obvious influence on the microbial community:the halophilic and basophilic C. alkalicellum and C. humireducens became the dominant acid producing bacteria at initial pH 10 condition, while Butyricimonas sp was the primary butyric acid producing bacterium at initial pH 5 condition.Due to the initial pH 10 was beneficial for VFAs accumulation, the continual pH 10 adjustment by NaOH addition regularly was further tested to study the anaerobic fermentation performance of swine manure. The results showed that compared with the initial pH 10, the continual pH 10 adjustment increased 2.55 and 2.08 times of soluble protein and carbohydrates concentrations, respectively, but the productions of VFAs had no noticeable difference (11950mg-COD/L) at both pH adjustment conditions. The kinetic simulation of fermentation process demonstrated that, the VFAs productions at both pH adjustment conditions met the feature of the first-order kinetics, but the KVFAs value at continual pH 10 condition was lower than that of initial pH 10 condition. Thus it could be inferred that the continual pH 10 adjustment might inhibit the microbial metabolic activity at some extent, therefore the VFAs producing rate decreased. The high-throughput pyrosequencing of 16S rRNA was adopted to analyze the microbial community structure in the fermentation samples. Compared with the fresh swine manure, the diversity of microbial community in the substrate after anaerobic fermentation under alkaline condition (pH 10) decreased. The ratios of primary acid producing bacteria, like Clostridium sensu stricto and Clostridium XI decreased at the continual pH 10 adjustment condition, meanwhile some alkaline-resisting and tough bacteria, including Bacilli and Amphibacillus became the dominant ones.At last, this study used the natural zeolite to recover ammonium (NH4+) and phosphate (PO43-) simultaneously in the fermentation liquor, in order to realize the resourceful utilization of swine manure. Both static and dynamic experiments were tested to investigate the nitrogen and phosphorus removal performance and the corresponding mechanism by the natural zeolite. The static experiment results showed that:(1) about 50% of cations in the zeolite structure exchanging with NH4+ was Ca2+. (2) The effective pH range for simultaneous removal of NH4+ and PO43- was 9.0～10.0, because higher pH of solution (>9.0) was disadvantageous for NH4+ adsorption, but advantageous for PO43- removal. And more ammonium existed in the solution, higher removal rate of phosphate was reached. (3) The main mechanisms of ammonium and phosphate removal using the natural zeolite included the cation exchange (remove ammonium) and chemical sedimentation (remove phosphate). Compared with the performance of static experiments, the ammonium and phosphate removal capacities decreased at some extent in the dynamic experiments when treating the synthetic wastewater and the practical fermentation liquor. But this method had no obvious negative effect on VFAs concentration in the fermentation liquor. Therefore, using the natural zeolite to recover ammonium and phosphate from the fermentation liquor could not only realize the resourceful utilization of nitrogen and phosphorus, eliminating the nutrients loading for the subsequent treatment of fermentation liquor, but also guarantee the maximization of organic carbon utilization.