| Biogas was well developed as one of the key technology for achiving a virtuous circular modern agriculture. However, large amount of improperly disposed biogas slurry may cause seriously environmental problomes. In this paper, slurry from pig feces biogas was choosen as the research object. Considering the nutrient of the product, bio-filtring. and membrane concentration technology were integrated to dispose the biogas slurry. Firstly, different combinations of three different bio-filtring materials and the methods to improve slurry properties for the continuous treatments were researched because the high concentration of suspended solids and highly viscous of sullury. Secondly, an orthogonal experiment was performed to optimize the parameter on ultrafiltration part for removing microbial and macromolecular organic compounds as well as reserving nutrient. At last, nanofiltration part was optimized and high quality liquid fertilizer was produced through the whole process.The results of this research were listed as following:(1) The ultimate operating pressure of corn straw filtration column can reach to0.12-0.14MPa, and the value of volcanic and silica sand were0.23-0.25MPa. The combination of multi-particle size corn stalk filtration column (JG50+JG20) performed well according to water treatment amount, removal rate of suspended solids (SS) and chemical oxygen demand (COD). The water treatment amount can reach8.49m3/m3in one cycle control, and the removal rate of SS and COD were60%and40%-50%, respectively.(2) FeCl3can break the steady state of biogas slurry, and make biogas slurry more easily to penetrate membrane. Membrane flux was improved with the addition of FeCl3, and the more FeCl3added in the biogas slurry the greater the membrane flux improved. The value of pH was the key factor affecting the amino acid retention rate in the biogas slurry. The retention rate of amino acid came to the minimum value when pH was6.5. The optimum operating destabilization condition was set as follows, the addition of FeCl3was0.005mol·L-1, and the value of pH was7.5.(3) Corn stalk was a convenient material to filtrate biogas slurry continuously and composting with corn stalk saturated with biogas slurry was feasible. The pile came into high temperature period in the second day, and this period lasted for about ten days. The average seed germination index (GI) was above80%during the whole period of composting. During the composting process, lignin and fiber were broken down in different degrees. The final decomposition rate of the material was52%.(4) In the cross-flow operation experiment, the pH value of feedstock, operating pressure, membrane material and the temperature of feedstock were the main affecting factors to the concentration of amino acid in the concentrated liquid, and the pecking order was as follows, pH value> operating pressure> membrane material> feedstock temperature. As for membrane flux, those factors above were in different pecking order, membrane material> operating pressure> feedstock temperature> pH value. When the concentration of amino acid and membrane flux were considered together, the final operating condition were set as follows, membrane material was PVDF, operating pressure was0.05MPa, feedstock temperature was40℃, and pH value was7.5. (5) For different pH levels, the effect of nanofiltration membrane module to amino acid concentration was most significant in pH7.5. The maximum concentration of amino acid was10535.7mg·L-1which wasconcentrated about6.2times.(6) The capital investment of a200m3·d-1bio-slurry plant was1712750yuan. Daily operation cost was2965.22yuan, but16800yuan,344yuan and580yuan can be obtained per day from liquid fertilizer, permeate liquid and compost, respectively. Investment pay-back period was about120days. |
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