Study On Under Ground River Reactor Dealing With Piggery Wastewater And Kinetic Model Developping

At present, the utilization and disposal of piggery wastewater is obtained much concern due to the serious environmental pollution caused by the breeding industry. The piggery wastewater is characteristic of high concentration of organic matters, nitrogen and phosphorus which threaten the quality of water and restricts the development of piggery breeding. Dealing with piggery wastewater has become an urgent problem which needs to be solved.In this paper, a new bio-reactor called underground river reactor is developed which changes the traditional vertical bio-reactor into horizontal structure. There are two characteristics:1) there is no need to supply extra power where the wastewater can flow from the inlet to outlet by gravity. It solves the key technology of feeding and discharging continually and the difficulty of discharging biogas residues; 2) there is also no need to supply an extra heat for the bio-reactor. The bio-reactor can be kept warm by the heat generated during the compost of the system which can guarantee the anaerobic digestion in the range of mesophilic fermentation. Meanwhile ,with the concern of instability of the anaerobic digestion, it analyzed the variation of a couple of parameters when the bioreactor was disturbance by an over-load and developed the most effective indicators for monitoring the anaerobic digestion process. The application of UR reactor will pave the way for the wastewater treatment and biogas production in a large scale. For the understanding of this technology, the following works were carried out in this thesis:(1) Analyzed the variation of temperature of bio-reactor in spring, summer, autumn and winter. The results showed that the bio-reactor could be well kept warm by the compost. The temperature of bio-reactor in four seasons can reach to 25.2?,34.6?,25.6? and 19.3? and even in the winter the lowest temperature of bio-reactor can reach 15.7?. At the same time, through the contrast with other kinds of heat technologies, the cost of compost was the lowest.(2) Studied the optimum conditions of bio-reactor and investigated the influence of inoculum ratio, organic loading rate and hydraulic retention time on the biogas yield, biogas composition and COD removal efficiency. Meanwhile, the variation of individual fatty acid, hydrogen and hydrogen sulphide were also studied. The results showed that with the increase of inoculums ratio and organic loading rate, there were inhibitions existing in the anaerobic digestion system which caused a decrease of biogas yield and COD removal efficiency. The optimum conditions were 35% of inoclum ratio, 5.3 g/L of OLR and 25 days HTR. Under the optimum conditions, daily average biogas yield could reach to 26.7 L and maximum biogas production rate vm could reach to 4.96 L/L-d. The organic removal efficiency can get high to 79.10%.(3) Developed a model to predict the degradation of organic matters, biogas production and the intermediate products based on the ADM1 considering the inhibition of pH, hydrogen and hydrogen sulphide. At the same time it also analyzed the sensitivity of COD, acetate, butyrate and propionate to the kinetic parameters and the influence of pH, hydrogen and hydrogen sulphide to the anaerobic digestion. The results showed that the model could be well used to predict the anaerobic process. And with the increase of OLR, there were existed inhibitions in the anaerobic digester which showed up in the increase of concentration of H2 and H2S. From the value of ka?kb and kp, it could be seen that the order of conversion rates of VFAs to methane was propionate> butyrate> acetate; From the value of fa?fb?and fP, it could be seen that the degradation order of VFAs were first converted into acetate acid, followed by butyrate acid and propionate acid. Through the sensitivity analysis, the initial concentration of COD was the most sensitive parameter which makes influence on the anaerobic digestion process.(4) Simulated the loading disturbance using glucose,peptone, lipids and actual piggery wastewater and analyzed the variation of biogas yield, biogas composition, TVFA, individual VFA, pH, hydrogen and hydrogen sulphide when an overload appeared. The determination of indicators followed the principles of sensitive and response speed. The results showed that, under statble operation, biogas production was 26.7±3.5 L/d, the content of methane was 62.1%±3.5%, the concentration of hydrogen and hydrogen sulfide were 5±1.5 ppm and 1000±50 ppm respectively, the concentration of acetate, propionate and butyrate were 5.1±1.5 mg/L,6.5±1.2 mg/L and 9.5±1.3 mg/L respectively, the concentration of was 4.8±1.5 mg/L, pH fluctated between 6.8-7.05. Once sufferred load disturbance, only biogas yield, hydrogen, hydrogen sulphide, TVFA and propionate showed positive response to the loading disturbance. The order of these parameters were hydrogen> hydrogen sulphide>propionate>TVFA> biogas yield. On the consideration of test methods and response speed, hydrogen and hydrogen sulphide were chosen as the indicators of anaerobic digestion.(5) Finally analyzed the environmental benefit, energy balance and economic benefit of UR bio-reactor. The results showed that the UR bio-reactor could save at least 5times energy compared with other heat mode due to the utilization of heat produced by the compost. Moreover, the economic produced by compost was also very considerable.