| Water environmental pollution and water shortage have become bottlenecks restricting China's social and economic development.There is an urgent need to develop efficient and low-consumption waste water recycling technology.Membrane separation technology,with its advantages of high efficiency,low consumption and good effluent quality,has become a research and application hotspot in the field of wastewater reuse.At present,organic membranes are widely used,which have short service life and susceptibility to acid-alkali corrosion,while inorganic ceramic membranes have shown irreplaceable advantages in environmental protection,chemical industry and bioengineering in recent years due to their good chemical stability and high mechanical strength.Aiming at the problems of unclear fouling mechanism,low cleaning efficiency and unclear service life of ceramic membrane in the process of using flat ceramic membrane,based on the research of water treatment characteristics of ceramic membrane itself,the key technologies of operation optimization control and efficient cleaning of flat ceramic membrane were developed,the service life prediction model of flat ceramic membrane was preliminarily established,and the control strategy of flat ceramic membrane aging was put forward.Finally,the key technology system of optimization control and efficient cleaning of ceramic membrane were formed.The fouling mechanism of ceramic membrane was effectively analyzed,and the operation control optimization and service life extension of ceramic membrane were realized,which provided technical support for the wide application of ceramic membrane technology in wastewater regeneration and reuse field.The water treatment characteristics of flat ceramic membranes showed that the water flux of flat ceramic membranes was positively correlated with the pressure of the membranes.When the pressure was 22 KPa,the water flux of the flat ceramic membranes could reach 736L/?m2·h?.The critical flux of municipal secondary effluent treated by flat ceramic membrane is 81 L/?m2·h?.Reduction of initial flux,intermittent operation and aeration can all play a role in controlling membrane flux attenuation.Four factors and three levels orthogonal experiments were designed with initial membrane flux?creeping pump speed?,intermittent time,filtration time and hydraulic backwash time as key control factors.The results showed that the four factors had significant effects on the average water yield of ceramic membrane in the following order:initial membrane flux?creeping pump speed?>intermittent time>filtration time>hydraulic backwash time;the optimal operation control conditions are determined as initial membrane flux 200 L/?m2·h?,filtration time 10 min,intermittent time 2 min,hydraulic backwash time 30 s,and the maximum average water yield of ceramic membrane is 43L/?m2·h?at this time.The EDS and FTIR of raw water and membrane fouling layer were compared and analyzed.The results showed that the main pollutants causing membrane fouling were aliphatic and amides,and inorganic metal ions were also important substances causing membrane fouling.According to Darcy's law,the resistance analysis of membrane fouling was carried out,which indicated that the resistance of gel layer was the most important factor to constitute membrane resistance,accounting for about 66%of total resistance.Research on high-efficiency cleaning technology of flat ceramic membrane was carried out.The effects of one-step cleaning of OP-10,SDBS,HCl,NaClO,EDTA-Na2 and NaOH and their compound cleaning with different chemicals were investigated.The test results showed that the effect of compound cleaning was better than that of one-step cleaning with single agent and based on the investigation of the stable operation period of the flat ceramic membrane after cleaning,the optimum chemical cleaning scheme was determined as follows:EDTA-Na2+OP-10,in which the concentration of EDTA-Na2 is 10mmol/L,the concentration of OP-10 is 4 CMC and the cleaning time is 2 hours.Atomic force microscopy,SEM-EDS and contact angle analysis were used to characterize the surface of the ceramic membrane.The results showed that the surface morphology,pore size,element composition and hydrophilicity of the ceramic membrane after optimum chemical cleaning could basically restore to the level of the new membrane.The long-term operation efficiency of plate ceramic membrane for municipal secondary effluent treatment was investigated.The results showed that the flat ceramic membrane has a good removal effect on turbidity and chroma of municipal secondary effluent.The turbidity of effluent is kept below 0.5 NTU and the chroma is kept below0.03A;the average removal rate of CODcr in raw water is maintained at about 40%;the average removal rate of UV254,ammonia nitrogen and total phosphorus in raw water is about 15%.Based on the relationship between the cumulative running time of flat ceramic membrane and the recovery rate of clean water flux,an empirical model for predicting the service life of flat ceramic membrane was established.:Y=-0.0025x+117.05.Among them,Y is the cumulative running time of flat ceramic membrane and X is the recovery rate of clear water flux.Based on the relationship between membrane fouling,membrane cleaning and membrane aging,the aging control strategies of flat ceramic membrane under the experimental conditions was put forward as follows:the optimal control of ceramic membrane operation was achieved by initial membrane flux 200 L/?m2·h?,filtration time10 min,intermittent time 2 min and hydraulic backwash time 30 s;physical cleaning,backwashing,EDTA-Na2?10mmol/L?+OP-10?4CMC?chemical cleaning were combined to achieve high efficiency cleaning of ceramic membrane. |
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