| This research studied the effect of calcium addition on the performance and membrane fouling of membrane bio-reactor(MBR) at low temperature(8℃) with the concentration of 20 mg/1. Two parallel reactors were applied, one of which was synthetic domestic wastewater with calcium addition (Ca-MBR), namely the experimental reactor, the other was without calcium addition, namely the control reactor. The synthetic wastewater was prepared with deionized water (DIW) in order to avoid the effect of calcium in the water. The analyses of effluent quality, sludge particle size distribution (PSD), soluble microbial product (SMP) and extracellular polymeric substances and scanning electron microscope (SEM) pictures as well as energy disperse spectroscopy (EDS) were conducted to represent the impact of calcium addition on the MBR at low temperature.The results showed that, the removal efficiency of COD, NH3-N, TN and TP of MBR with calcium addition were 92.28%.95.73%,72.73% and 54.94% respectively, while the MBR without calcium addition were 84.72%,81.81%,44.26% and 30.63%. Besides, membrane fouling of the MBR with calcium addition was much slighter than the MBR without calcium addition, the increasing rate of transmembrane pressure (TMP) was much lower than the control, during the period of 65 days, TMP of the experimental reactor increased from 7 kPa to 31 kPa, while the control reactor increased from 7 kPa to 45 kPa, which might be a result of increased particle size. Sludge of the experimental reactor increased from 46μm to 158μm, while the control increased merely from 46μm to 104μm. Larger particle could alleviate the inhibitory impact of low temperature on the microorganisms in the sludge floc, leading to micro-anoxic environment in the inner floc, which might improve the removal of nitrogen and thus improve the effluent characteristics. It could be seen that from the picture of SEM cake layer formed by sludge with calcium addition was much more loose than the control which was net added with calcium. As is known that sludge particle as well as SMP and EPS are closely related to membrane fouling, where SMP may lead to pore blocking and loosely bound EPS (LB-EPS) may form gel layer on the surface of membrane. It’s known that protein and polysaccharides are the main composition of SMP and EPS. Compared with the control MBR, protein polysaccharides decreased from 37.34 mg/1 to 21.36mg/l and polysaccharides decreased from 38.08 mg/1 to 20.40 mg/1 of SMP, while protein decreased from 3.02 mg/gVSS to 1.27mg/gVSS and polysaccharides decreased from 2.9 mg/gVSS to 1.17 mg/gVSS respectively, of which reason was the bridging of SMP and LB-EPS to the tightly bound EPS (TB-EPS) by the calcium ion. leading to the increase of protein and polysaccharides from 36.26 mg/gVSS and 24.37 mg/gVSS to 45.9 mg/gVSS and 31.81 mg/gVSS respectively. Analysis of SEM and EDS showed that with the calcium interaction with the bulk solution, the experimental reactor formed more loose cake layer, which was also revealed by the resistance analysis that cake layer resistance was the main composition of resistance. The weak adsorption resistance decreased from 45.3×1010 m-1 to 36.0×1010 m-1 compared with the control. As it can be concluded, calcium addition at low temperature can increase the performance of MBR and alleviate the membrane fouling. |
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