| Along with our country’s livestock and poultry industry to scale, intensive direction, large and medium-sized biogas project has been rapid development, livestock biogas engineering would has produced large quantity of organic wastewater with complex components and high concentration at the same time generating clean energy in the utilization of waste--biogas slurry, which has become the restricting factors of the development of large and medium-sized biogas project. At present, the biogas slurry disposal methods although cover cropland application or resource utilization, but they are restricted by many conditions, especially by the actual conditions of China’s crowded restrictions, so the process of industrialization is the inevitable choice processing large amounts of biogas slurry produced by livestock biogas engineering.In view of the fact that biogas slurry consists of the high nitrogen and phosphorus, low C/N ratio, so consider to change physicochemical properties of solution by the physical and chemical pretreatment method, remove or degradate refractory organic compounds, strengthen the subsequent biochemical treatment, so that discharge wastewater could achieve requirements of pollutant discharge standard in Discharge standard of pollutants for livestock and poultry breeding (GB18596-2001). Developing research treatment technology of biogas slurry, Their feasibilities of treatment biogas slurry were researched, including processing unit of micro-electrolysis with iron-carbon and electrolysis, biochemical treatment unit of SBBR and electrode-SBBR.The feasibility and efficiency of "three micro-electrolysis and electrolysis" and "micro-electrolysis-electrode-SBBR" were studied.1. micro-electrolysis experiments with iron-carbonAeration, initial pH value, iron-carbon volume ratio and the hydraulic retention time (HRT) were selected as the effective factors of micro-electrolysis experiments with iron-carbon, Through the single factor experiment to determine the reaction conditions recommended were as follows:aeration rate of15.0L/min·L, initial pH value of4, iron-carbon volume ration of1:1, HRT of2.5h., the removal of its COD, ammonia nitrogen,TN and TP respectively was37.22%-44.74%,18.47%～30.42%,20.32%～40.75%,66.01%～87.56%,. The orthogonal experiments showed that each factor on the order of COD removal rate was as follow:HRT> aeration> initial pH value> Fe/C, on the removal rate of ammonia nitrogen was as follow:Fe/C> HRT> initial pH value> aeration, on the removal rate of TP affects the degree of aeration> HRT> initial pH value> Fe/C. Through comprehensive analysis, the commendatory working conditions of micro-electrolysis with iron-carbon were as follows:aeration rate of15.0L/min·L, initial pH value of4, iron-carbon volume ration of2:1, HRT of2.5h. Tests showed that the multilevel series micro-electrolysis, the removal effect of3order reaction was the most reasonable. The parallel tests showed the stability of micro-electrolysis treatment effect.The SEM analysis showed that iron and carbon filler washed by water could restore its activity; The analysis of the XRD profiles of sediment showed that phosphorus was removed in the form of FePO4.2. electrolysis experimentsThe voltage, reaction time, initial pH value and electrode plate interval were selected as the influential factors of electrolysis experiments, the results showed that there were the best removal effect in the voltage of10V, reaction time of3.Oh, initial pH value of5and electrode plate interval of20mm conditions, COD, ammonia nitrogen and TP removal rates respectively were:30.77%～59.00%,6.34%～10.66%, and22.91%～44.04%. In the reaction conditions recommended, to change the electrode plates, transform three-dimensional electrode, aeration and increase the number of electrode plates, the results showed that aeration was the maximum effect of COD and ammonia nitrogen, and the effect of TP, increasing plate number to the maximum. So the aeration was selected as reaction to change conditions.3. the SBBR and the electrode-SBBR experimentLasted6weeks, the attaching biofilm and acclimation of activated sludg were completed on SBBR and electrode-SBBR reactor. The biofilm about1.2～1.5mm was formatted on the surface of soft filler at the end of the attaching biofilm, the microscopic examination showed that the system protozoa was the dominant microorganisms,such as Epistylis, rotifers, and a more dense zoogloea has formated. SBBR and the electrode-SBBR comparison test results showed that SBBR process after enhancing by electrode, could greatly improve the pollutant removal ability. Finally according to the test results,7.Oh was recommended as the running period of reaction, and its operating conditions were:adding wate→anaerobic processing (1.0h)→aeration (4.0h, electricity)→anoxic or anaerobic processing (2.0h,electricity)→effluent dewatering→idle.According to the operation condition detemined, voltage, concentration of DO and packing density were selected as the most factor of influencing the operation, the test results showed that it is better in the15V,4～5mg/L and30%conditions, the removal of COD, ammonia and TP was61.57%-69.81%,84.38%-90.69%and54.80%-65.26%respectively. Under the commendatory conditions, the electrode-SBBR stabilized run within30days, COD and ammonia have been better removal effect, the removal rate was maintained at above70%and80%, the effluent were stable, could reach discharge standard requirements of 《Discharge standard of pollutants for livestock and poultry breeding》, electrode-SBBR could stand up to a certain of impact load-The treatment effect on TP was also relatively stable, but the effect was not ideal, the average effluent concentration of8.86mg/L exceeded the limit requirements of8mg/L, so it was the need for strengthening treatment.4. process combinationBased on micro-electrolysis and electrolysis tests, and the physicochemical treatment combination technology" micro-electrolysis and electrolysis" were further researched. The process has obvious effect on COD, BOD5, ammonia, TP and SS removal. BOD5/COD increased from0.19of influent to0.53-0.57of effluent, the biodegradability of the effluent was significantly improved. The TP of effluent (3.95-7.17mg/L) could reach the standard requirements of GB18586-2001,then the rest could not reach standard requirements. The micro-electrolysis and electrolysis test showed that at the same time, the micro-electrolysis treatment effect was better than that of electrolysis according to their respective optimum reaction conditions, especially the effect on ammonia, TP and SS, the disparity of removal rate were very big, therrfore, the micro-electrolysis experiments with iron-carbon was seleted as a method of pretreatment of biogas slurry.On this basis, the combined process of "three micro-electrolysis-electrode-SBBR" were studied. The influent concentration of COD, ammonia, TP and SS was4400.00-6660.00,804.43～1675.95,89.87～175.41,5724～11462mg/L respectively, and pH value from4.3to5.1, after running,the results showed that the effluent concentration of each index was231.00～396.00,56.55～79.39,5.82-7.84and89.20～177.30mg/L respectively, pH value of4.3～5.1, reached the requirements specified in GB18586-2001400,8,8and200mg/L at the first eight days.Therrfore, eight days would be run as a cycle, the material absorbed on the iron-carbon filler surface was removed by backwashing way with tap water, and then continued processing.Based on the single process,a new system of micro-electrolysis-electrode-sequencing batch biofilm reactor(SBBR) technique was constructed for treating biogas slurry,its treatment effect was good,and the effluent could achieve requirements of pollutant discharge standard in Discharge standard of pollutants for livestock and poultry breeding (GB18596-2001),then has better stability. |
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