Effect Of Dosing Powdered Activated Carbon On Operational Performances Of MBR

With the rapid development of modern industry and economics, the demands of water increase day by day. China is a country whose water resources are sparse. The average possession of water resources is about 2500 m3 per capita, and is only 1/4 in the world. China is one of 13 water-poor countries. And water pollution has been a severe problem in many areas. In this paper, removal effect and membrane fouling on treating stimulant domestic wastewater were carried out.2 MBR were run in parallel to treat stimulant domestic wastewater, of which reactor 2 was activated sludge MBR and reactor 1 was powdered activated sludge MBR. In reactor 1,1100mg/L powdered activated carbon was put into. The study containing removal effect and membrane fouling on treating stimulant domestic wastewater was carried out. And the results showed that 2 MBR had similar COD removal and the removal in reactor 1 was higher than reactor 2. The average removal of COD efficiency was 96.6% and 94.3% respectively, and membrane had an excellent stabilization for COD removal. Because of high efficient membrane clog and longer sludge retention time, the slow-growth nitrobacteria were retained in MBR and the concentration of these two bacteria in reactor increased. 2 MBR had high removal of NH4+-N. Removal of supernatant and effluent was 80.5%, 77.6% and 84.3%, 83% respectively. NH4+-N removal in MBR 1 was higher than MBR 2 because powdered activated carbon provides a good carrier for bacteria. The types of microorganism in MBR 1 were more than MBR 2. There was a certain mount of Heliozoan Vorticella, Epistylis, Rotaria, et al, meanwhile in MBR 1 Epistylis, Rotaria, et al can be seen. Whereas in MBR 2 the quantity of these species were relatively scarce, and activity of MBR 2 was stronger than MBR 1 because of the absorption of powdered activated carbon. Meanwhile the microorganism activity of MBR 1 was also higher than those of MBR 2, the activity of 2 MBR was (4.9±1.26)mgO2.g -1MLSS.h-1, (5.2±1.45)mgO2.g-1 MLSS.h-1 respectively.In order to investigate the membrane fouling of 2 MBR, the membrane flux was determined everyday, and the flux of 2 MBR was 2.38 L/(m2·h), 1.95 L/(m2·h) respectively. Adding powdered activated carbon changed the gel layer formed on membrane surface of MBR 1 whose porosity was high and density was low, and improved the filtration performance of mixed liquor of sludge. The decreasing rate of membrane flux of MBR 1 was much slower than those of MBR 2, and the stable membrane flux of MBR 1 was also higher than those of MBR 2. The difference was 0.8 L/(m2·h). Due to the absorption of powdered activated carbon, viscosity of MBR 1(v=2.65 mPa·s) was much lower than those of MBR 2(v=5.03 mPa·s). Meanwhile the sludge resistance of 2 MBR was 2.78×l013 (cm.g-1), 2.84×l013 (cm.g-1) respectively. The R value of MBR 2 was 1.3 times as that of MBR 1, and this showed that membrane 1 had been polluted severely. Using the same cleaning method, the recovery rate of 2 membrane was 10.5%~88.9% and 11.4%~81.8%. Irreversible pollution of membrane 2 was serious.For the absorption of powdered activated carbon and special characteristic of biological activated carbon which was different with conventional activated sludge and produce different quantity and content extracellular polymeric substances(EPS), the quantity EPS (containing soluble EPS and bound EPS in mixed liquor of sludge and low-speed centrifugation adhesive material)of MBR 2 was more than that of MBR 1. The ratio of protein/carbohydrate in soluble EPS was less than 1 mostly, but in bound EPS this ratio was larger than 2. With the runtime, the ratio became larger as the membrane had selective absorption of protein. The quantity of EPS on membrane 1 was lower than that of membrane 2, and the ratio of protein/carbohydrate on membrane 2 was larger than that of membrane 1. The correlation coefficients of EPS and viscosity with membrane flux were investigated by SPSS software. The results showed that ratio of protein/carbohydrate were the strongest influencing parameter for decreasing rate of membrane flux. For 2 MBR, the ratio of protein/carbohydrate in EPS which contains soluble EPS and bound EPS in mixed liquor and low-speed centrifugation adhesive material was 0.74, 0.68, 0.54, 0.46 and 0.68, 0.72, 0.58, 0.41.Adding powdered activated carbon advanced the removal of pollutant and alleviated the membrane fouling. So this technique had some practical application value.