Experimental Study On High-solid Anaerobic Digestion Of Dewatered Sludge

With the emphasis on the improvement of sludge treatment, industry emission standards are more stringent, a large number of sludge from sewage treatment need to be disposed reasonably, otherwise it will cause secondary pollution. High-solid anaerobic digestion can not only meet the requirements of stabilization, harmless, reduction, resource utilization of sludge treatment, the idea of energy recycled can meet the general requirements for implementation of the strategy of energy saving and emission reduction in china.This paper is mainly concerned with the experimental study on high-solid anaerobic digestion of dewatered sludge. Firstly, a series of batch experiments were carried out to analysis the feasibility of the reactors customized in this study, then another series of batch experiments were carried out to optimize the loading height. Finally, a group of continuous tests were carried out in127days to optimize process parameters under mesophilic condition. The digestion effect under mesophilic and thermophilic condition were compared at the same time. In the course of the experiments, the samples of three stages were conserved to research the key bacteria. The main conclusions are as follows:(1) The daily gas production in high-solid anaerobic digestion process under mesophilic condition went through peak stage, stable stage and end stage, respectively. Biogas production of effective volume was increased by high-solid anaerobic digestion process, and the content of VS was significantly decreased. The average effective volumetric gas production rate reached0.538L/(Ld) at peak stage. VS removal rate reached41.9%.(2) The concentration of ammonia nitrogen of mesophilic high-solid anaerobic digestion was higher than the value of the traditional low-solid anaerobic digestion. Although the highest concentration of ammonia nitrogen reached3685mg/L, however, the biogas production was not inhibited. pH remained stable in the process of anaerobic digestion, and the digestion environment was weak alkaline.(3) Mesophilic high-solid anaerobic digestion can withstand high organic load. The initial loading height should be70%～80%under high organic load conditions. The degradation rate of VS was effected by different loading height. When the height was60%, organic matter content was low, the VS removal was not ideal. When height was more than70%, VS removal was improved. However, the height increase more than70%, VS removal was not affected.(4) When the reactors were started in sequencing batch mode, inoculation start could quickly achieve the higher gas production efficiency and greatly shorten the boot time. The gas production was easily inhibited in virtue of too high concentration of ammonia nitrogen. Vaccination could ease the accumulation of the concentration of ammonia nitrogen.(5) Mixing12h and stirring for6times a day, SRT=20d were considered as the best technique route of mesophilic high-solid anaerobic digestion by comprehensively contrasting and analysing of the effect of parameters on system performance.(6) Anaerobic microbial acclimation time under thermophilic temperature was visibly longer than mesophilic anaerobic digestion. When the reactors were operated with the optimum parameters of mesophilic anaerobic digestion process, mesophilic digestion is better than thermophilic digestion.(7) When the residence time was shorten and the organic load was increased, the organic matter removal rate of thermophilic anaerobic digestion was better than mesophilic anaerobic digestion. Thermophilic anaerobic digestion could bear higher organic load.(8)Compared with the mesophilic anaerobic digestion, solid organic matter under thermophilic condition was propitious to be hydrolyzed and acidulated, which would cause SCOD, VFA concentrations were higher than mesophilic anaerobic digestion. Thermophilic anaerobic digestion could withstand higher ammonia nitrogen and free ammonia concentration, especially when the concentrations were more than severe inhibition threshold of mesophilic anaerobic digestion of conditions, the gas production was still high.(9) DGGE spectra revealed, mesophilic anaerobic digestion processed more abundant microbial population structure in this test. And, the number of dominant bacteria was more, as the system was more stable.