| It's difficult to recycle manure by planting and breeding,for most dairy farms lacking of enough farmland in China.The effective wastewater treatment has become the key factor to restrict the sustainable development of dairy farms,it's particularly important to treat wastewater.In order to solve the problem of liquid waste disposal in dairy farms,the performance of membrane bioreactor treating wastewater from dairy farm was studied.It discussed the feasibility of using MBR for advanced treatment of high concentration dairy farm wastewater,and optimized its operating parameters.The main conclusions in this study were as follows:The membrane bioreactor with a volume of 10 m3 was designed for advanced treatment of dairy farm wastewater.The experiment was carried out according to the influent COD concentration,hydraulic retention time,dissolved oxygen and the addition of bacteria.After one month of sludge domestication,the experiment was carried out officially,and each combined process lasted for about one month.The results showed that membrane bioreactor had a high treatment performance to COD and NH4+-N.When the average concentration of COD and NH4+-N in the influent wastewater were 71357860 mg/L and181390 mg/L,with the condition of HRT was 4 days and the dissolved oxygen was 1.5 to 3 mg/L in winter which the average temperature is-3.4?,after adding some specific bacteria,the effluent were357±53 mg/L and 20±5 mg/L respectively,and the corresponding removal rate were 95±1%and 91±3%.Microorganism was the key factor for TN removal in MBR,the removal rate of TN was more than 80%from 54%after adding specific bacteria.During the operation,the removal of total phosphorus,total copper and total zinc was stable,the influent concentrations were 51.92±11.51 mg/L,3.46±0.63 mg/L and 3.08±0.68 mg/L,and the removal rate were 85±8%,95±2.9%and 97±0.7%,respectively.Analysis of microbial community showed that Proteobacteria,Bacteroidetes and Firmicutes were the most abundant phylogenetic group in the MBR.Besides,there was a very significant negative correlation between the content of Proteobacteria and Bacteroidetes during the five stages.Since the dry decontamination was adopted in most of dairy farms generally,the COD reached more than 20 000 mg/L in the wastewater after solid-liquid separation.In order to ensure the performance of MBR,the dairy farm wastewater was pretreated by chemical flocculation which was simple and efficient based on the results of the preliminary.A pretreatment experiment was designed to optimize the operational parameters of chemical flocculation.Poly aluminum chloride?PAC?and three types of ionic polyacrylamide?PAM?were used as flocculants.The results showed that the effect of PAM was better than that of PAC and PAM combination.The best flocculation effect was observed in adding 2.5 mL NPAM at the dosage of 1 g/L when 500 mL wastewater was treated.Under this condition,when the concentration of COD,NH4+-N and TP were 42 083±1 752 mg/L,531±7.17 mg/L,205±4.08 mg/L in the influent wastewater,the removal rates were 69.48±4.10%,13.11±8.59%and 85.05±1.27%,respectively.After the supernatant was treated with MBR,the average concentrations of COD,NH4+-N and TP in the effluent were 644.6 mg/L,41.58 mg/L and 4.65 mg/L,respectively.Based on the above results,it's proposed an advanced treatment for high concentration dairy farm wastewater by flocculation and MBR.A wastewater treatment system with capacity of 50 m3/d was designed for dairy farms.For dairy farm wastewater with COD of 25 000 mg/L and NH4+-N of 1 000mg/L,it can be discharged after treatment or used for flushing and reuse in dairy farms.,and the operating cost is 6.13 RMB/m3.The process is expected to provide a new technology to solve the problem of dairy farm wastewater. |
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