Advanced Treatment Of Domestic Sewage By Forward Osmosis Technology

The rapid development of membrane technology make it widely used in sewage deep, treatment sea water and brackish water desalination, electricity generation.forward osmosis as a kind of osmotic pressure driven membrane separation process,has the advantages of low energy consumption, low degree of membrane fouling,could be applied to secondary effluent deep treatment in urban wastewater treatment plant, has the wide development prospect.The research adopted a wastewater treatment plant secondary effluent as research object. Investigate the influences about draw solution concentration, secondary effluent temperature, aeration, draw solution flow rate on membrane separation performance and membrane fouling. Investigate the intercept rate of different pollutant in the deep treatment depending on forward osmosis On this basis, in light of membrane fouling caused by secondary effluent quality, study the feasibility of adopting aeration to wash on both sides of the active layers and control the feed solution temperature to reduce the membrane pollution.The main results show that:(Ⅰ)The study of key influence factors in forward osmosis separation process:The main factor order influencing membrane flux is draw solution concentration,draw solution flow rate, secondary effluent temperature, aeration. The best factor level conditions is draw solution concentration 4%; secondary effluent temperature 28°C,draw solution flow rate 4 L/min, aeration 4L/min. The TDS, PO43--P, TP, NO3--N and TN content intercept rate were 98.37%, 96.03%, 95.85%, 85.17%, 84.97%. When the concentration of TOC and Ammonia nitrogen is respectively 44.25mg/L and 17.06mg/L, the intercept rate of TOC and Ammonia nitrogen is 93.87%、 63.12% in the process of forward osmosis separating.(Ⅱ)The study of membrane pollution as to adopting two different pattern:From the point of pollutant quality distribution, had proved exist of membrane pollution. From the point of membrane flux change, in the measuring period of based line, the initiative membrane flux is 10.53L/m2·h. In the first period, the initiative membrane flux is 10.39L/m2·h, has decreased by 1.35% and proved that the membrane pollution have not occur or have little pollution. In the second period, the initiative membrane flux is 9.27L/m2·h, has decreased by 12.08% and the falling range is larger than the first period, concluded that the pollution has happened and is more serious.With the process of test, pollution continues, but slowly. After five periods, the initiative membrane flux has decreased to 8.89 L/m2·h, decreased by 18.44% compared with initiative membrane flux the based line.(Ⅲ)The effect of draw solution concentration and draw solution flow rate on membrane separation performance:With the increase of draw solution concentration, the membrane flux increase, the intercept rate of TN、NO3--N、TDS has a drop trend, the intercept rate of TP、PO43--P basically remain uncharged. with the increase of flow speed, the intercept rate of TDS、TN、NO3--N drop, the intercept rate of TP、PO43--P basically remain uncharged. The intercept rate of TDS is best, can reach 98%.(Ⅳ)the result of membrane pollution test show that:With the increase of secondary effluent temperature,the membrane flux increase,the intercept rate of TDS、TN、NO3--N、TDS、TP、PO43--P has a drop trend, the membrane pollution become more serious. At any temperature, the intercept rate of different pollution is TDS>TP≈PO43--P>TN>NO3--N.In the condition of continuous aeration on the membrane surface, with the increase of aeration, the flux increased at first and then decreased. When the aeration intensity is 4 L/min, the flux of continuous and interval aeration compared with no aeration increased by 5.5%, 2.4%, respectively. In the condition of no aeration, the membrane pollution is obvious. In the condition of continuous aeration, existed membrane pollution but the degree of pollution is small, the decrease of flux is notobvious. The aeration can decrease the membrane pollution and delay drop speed, but can not completely eradicate the pollution, and exaggerated aeration is not good for separation process.