| With the rapid development of the social economy and the urbanization process in China, urban water supply pressure has increased especially in small towns. Because of the limited capacity of groundwater, surface water has gradually become the major source of urban water supply in Shandong province. However, the deterioration pollution of surface water and limitations of traditional craft have brought serious challenges to urban water supply safety in Shandong province.Therefore this study examines the micro-polluted water(slightly polluted raw water) treatment effect and process characteristics of biological filtration unit with different puddings and low-voltage ceramic membrane unit by using the laboratory model test, according to the present problems in the existing technology and process which are used to treat slightly polluted raw water treatment. On this basis, exploring the treatment effectiveness, process features and microbial populations characteristics of BAF- low pressure ceramic membrane combination are treated slightly polluted raw water in order to build a kind of economic efficiency, easy operation and compact structure of the new water treatment process for treating slightly polluted raw water so as to provide technical reference for solving rural drinking water safety.The results show that the ceramist, volcanic rock and zeolite, three kinds of filter material for ammonia nitrogen adsorption performance have huge difference, the zeolite was most efficient, volcanic rock was less and the ceramist was lowest. The organic adsorption ability of three kinds of filter materials are low. Based on cost comparison analysis on the price, zeolite is cheapest, ceramist is cheaper and volcanic rock is the last while it is relatively easy to start successfully and they are suit to as aeration biological filter padding. The test results show that the BAF with ceramist, zeolite and volcanic are started successfully after 19, 16 and 13 days respectively, volcanic BAF uses the least amount of time.Under steady operating conditions that HRT, air-water and temperature ratio are 2:1, 30 min and 28 ℃.The ammonia nitrogen volume in effluent of ceramist filter, volcanic rock filter and zeolite filter are 0.33mg/L, 0.22mg/L and 0.10mg/L. The average removal rates are 82.9%, 88.5% and 95.7%. The average permanganate indexes of effluent are 3.26mg/L, 2.83mg/L and 2.60mg/L. The average removal rates are 25.3%, 34.9% and 40.5%. Turbidity in effluent are 1.92 NTU, 1.32 NTU and 1.05 NTU, which means the average removal rates are 66.9%, 77.1% and 81.9%.In addition to removing the UV245 there filters can achieve at 0.040cm-1, 0.036cm-1 and 0.038cm-1 in effluent and the average removal rates are 20.6%, 27.3% and 24.5%. In addition to the turbidity removal less, three kinds of filter paddings aeration biological filter show a good removal efficiency of pollutants. Among them, the BAF of volcanic rocks treatment effect is best and the activity of biofilm is higher.The results show that variation of operating temperature don’t have much interference on the removal efficiency of using BAF(biological aerated filter) with these three different paddings when treating slightly polluted raw water, and BAF stays available to remove pollutants even in low-temperature condition. By adjusting hydraulic retention time(HRT) and air-water ratio and investigating effluent quality with economic factors, the best HRT and the best air-water ratio are confirmed to be 30 min and 2:1. Inspect of the fact that BAF has a certain capability of surge withstand towards ammonia nitrogen. The haycite has relatively bad adsorption behavior, owing to the effluent of using BAF with haycite material not reaching drinking water sanitary standard when ammonia nitrogen concentration in influent is increasing to 9mg/L. The average removal ratio of COD in BAF effluent appears to be stable with the increase of organic load in the influent, which shows a relatively better capability of surge withstand towards organics, and the capability can handle problems deriving from changes of season and another factors.Microbial species abundance of BAF at room temperature is significantly higher than it which are in the low temperature. Microbial populations at low temperature are substantially reduced. At low temperature, volcanic diversity index is significantly higher than other two kinds of filter material, it means that at low temperature volcanic rocks in the filter material more conducive to the growth of microbial adhesion. At the same time, there are mainly microorganism which can remove pollutants effectively in the zeolite and volcanic rocks BAF, which guarantees the processing capacity at low temperature.At different HRT( 60 min, 30 min, 15 min) running conditions, microbial populations of different filter BAF have high similarity. The similarity degree of same filter material BAFs is relatively low under different operating conditions. Dominant populations in these systems are mainly Gammaproteobacteria, Betaproteobacteria and Deltaproteobacteria of Proteobacteria, Proteobacteria of Bacteroidetes, Nitrospirales of Nitrospirae and Nitrospira of Nitrospirae which can oxidize nitrite into nitrate.By using ceramic membrane of different pore sizes(200nm and 80 nm respectively) to filter micro-polluted source water under the condition of 0.1MPa pressure and average turbidity of raw water at 0.56 NTU, the turbidity of effluent of ceramic membrane with 200 nm pore size is under 0.1NTU, whose removal ratio arrives at 98.7%. But removal ratio of ammonia nitrogen and nitrate nitrogen are not high, which are 15.8% and 6.76% separately. The average removal ratio of permanganate index is 15.2% while UV254 at 9.8% and removal ratio of conductivity is 5.4%, average removal ratio of these indexes above by using ceramic membrane with 800 nm pore size are 97.95%, 9.72%, 5.02%, 13.6%, 8.78% and 4.83% respectively, which results demonstrate its removal efficiency is lower than ceramic membrane with 200 nm pore size. Ceramic membrane can be polluted partly while filtering slightly polluted raw water. The flux decreases 12.4% for ceramic membrane with 800 nm pore size and 26.7% for the 200 nm pore size.Dealing with micro-polluted source water by combining BAF with ceramic membrane can offset the deficiency of low turbidity removal efficiency while using BAF alone, and it can also act as pretreatment unit to remove organics, ammonia nitrogen and nitrate nitrogen effectively, finally improve effluent quality integrally. The treatment effects of respective combination of BAF with 200 nm and 800 nm pore-sized ceramic membranes are similar. The turbidity, ammonia nitrogen, nitrate nitrogen, permanganate index, UV254 and conductivity in the effluent of combined process are 0.08 NTU, 0.07mg/L, 0.01mg/L, 2.50mg/L, 0.037/cm-1 and 1252μm/cm respectively, which display an adorable effect. The water production rate of combined process with 800 nm pore size is lower than combined process with 200 nm pore size, but it still has a relatively higher capability of removal. Besides, its membrane flux is considerably higher than the other combined process. Seen from actual project operation, BAF-ceramic membrane(φ=800nm) combined process is preferable for treating slightly polluted raw water. When filtering raw water only using ceramic membrane equipment, flux decreased by 12.4% for 800 nm pore-sized ceramic membrane, and 26.7% for 200 nm pore-sized ceramic membrane while there are only 6.0% flux decreasing for 800 nm pore-sized ceramic membrane and only 14.3%flux decreasing 200 nm pore-sized ceramic membrane separately if combined with BAF. Consequently, pretreatment using BAF has the function to effectively slowing down the pollution to ceramic membrane. |
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