| The large-scale and intensive development of pig breeding industry leads to a large number of pig manure.As an effective measure to deal with pig manure,anaerobic digestion technology can not only eliminate pollution,but also recover energy and reduce production cost,so it has attracted more and more attention and application.However,the traditional biogas project in large-scale pig farm has the following problems in operation:（1）high organic load and low biogas output;（2）the solid substance of pig manure will produce precipitation or scum crust in the biogas digester,which will affect the normal operation of the biogas digester;（3）due to high moisture content,odors will be released under long-term anaerobic conditions.The new process of combined biogas fermentation（LBR-CSTR）is to leach and soak the soluble organic matter in pig manure through biogas slurry circulation.The insoluble solid material is retained in the leachate bed,and the leachate enters the methane reactor.The construction cost of the whole system is lower than the composting process,and the batch anaerobic digestion process has no release of odor,and the biogas production rate of pig manure is high.In this study,a stainless steel leaching bed reactor（LBR-CSTR）coupled continuous stirred tank reactor（LBR-CSTR）with a hot water sandwich was used to control the reaction temperature.The volume of LBR was 15 L,and the effective volume was 4 L.The volume of CSTR was 40 L and the effective volume of the test was 32 L.Three sets of the same equipment were started at the same time for each test,and the physicochemical properties such as p H,COD,VFA and NH3-N in the leachate and biogas slurry were sampled and analyzed every day,and the dynamic changes of microbial community in the anaerobic digestion process were analyzed by Hiseq high-throughput sequencing technology.At the end of batch anaerobic digestion,pig manure leachate residue was dried by biological blower,and two kinds of vegetables,rape and cabbage,were tested.The main test contents are as follows:1)the influence of three filtration media on the anaerobic digestion performance of LBR-CSTR.2)influence of three biogas slurry reflux ratios on the anaerobic digestion performance of LBR-CSTR.3)influence of three biogas slurry reflux times on the anaerobic digestion performance of LBR-CSTR.4)study on the fertilizer efficiency of pig manure leachate residue as vegetable cultivation substrate instead of peat soil.The results show that:（1）The LBR-CSTR anaerobic digestion system with filtration medium not only prevents blockage in the percolation bed,but also improves the effect of fully mixed anaerobic fermentation through daily biogas slurry circulation.The LBR-CSTR with ceramsite as the filtration medium had the best digestibility（biogas yield was 24.05%higher than CK）,the VFA cumulative yield of LBR（C）was large（188.75ml/g VS）,and the methane yield of pig manure was high（137.39ml/g VS）.The final effluent COD,nh3-n and TN of CSTR were 553.82 mg/L,370.59 mg/L and 576.04 mg/L,respectively,which were 92.12%,36.16%and 49.20%lower than CK.At the end of batch anaerobic digestion,the weight of pig manure leachate residue decreased from 2.4kg to 0.1kg after biological drying,with a reduction of 95.83%.（2）The effluent reflux of methane reactor was inoculated into acidification reactor.The cumulative yield of VFA in LBR with reflux ratio of 100%was 10.63 g/L,which was acetic acid type fermentation.The methane yield of the whole system was as high as 167.44m L/g VS,higher than the estimated methane yield of Asian pig manure（131.4 m L/g VS）.（3）The optimal reflux times of LBR-CSTR were 2 times per day,with the maximum methane production rate（282.84 m L/g VS）and methane production rate（167.6 m L/g VS）,with a reduction of 97.35%.The microbial community dynamics of sludge in CSTR indicated that the diversity of methanogenic archaea increased by 27.08%,with Firmicutes and Bacteroidetes as the main species and Clostridium as the dominant bacteria.（4）Proper slurry infiltration filter residue replace peat soil make nursery substrates have the function of the growth of vegetables,including slurry infiltration filter residue and peat soil volume ratio of 1:1,the growth of rape and Chinese cabbage best（aboveground biomass were 169.20%and 265.08%higher than that of CK respectively,underground biomass than that of CK respectively increased by 55.1%and 216.00%）,high nutrient content,and CK have significant differences,rape and Chinese cabbage aboveground ratio CK increased by 62.27%and 61.40%,respectively.To sum up,the methane production rate of pig manure was high（167.6ml/g VS）and the reduction effect was good（97.35%）when the filtration medium was ceramsite,the reflux ratio of biogas slurry was 100%and the reflux times were twice a day.In addition,the bio-air drying product of pig manure leachate residue can replace 50%of the volume of peat soil as seedling substrate,which has obvious promoting effect on vegetable growth.The LBR-CSTR anaerobic digestion system developed in this project can not only produce clean energy methane,but also further treatment of pig manure leachate residue can alleviate the problem of peat soil resource shortage.There is no odor and biogas slurry release in the whole production process,and it has a certain application prospect in large-scale pig farms. |
