Research Of Simultaneous Nitrification/Denitrification And Membrane Fouling In Carrier-type STMBR

Inorganic nitrogen is one of the main pollutants in the water environment, which is greatly harmful to the environment and human health. To overcome the shortcomings of traditional biological nitrogen removal, we added polyurethane sponge carrier to the submerged tubular membrane bioreactor(STMBR) in this study. We used synthetic wastewater to study the factors affecting the simultaneous nitrification and denitrification(SND) in carrier-type STMBR. And we studied the role of the polyurethane sponge carrier in membrane fouling mitigation.We studied the effects of dissolved oxygen(DO), hydraulic retention time(HRT), C/N and F/M on of SND in carrier-type STMBR by changing the influent water quality and operating conditions. High DO affected the denitrification process, low DO inhibited the nitrification process. When DO was 0.78~0.96 mg/L, it not only could guarantee nitrification, but also could guarantee denitrification, and SND could achieve good result. When HRT was too short, the removal of COD and ammonia nitrogen were not sufficient. When HRT was too long, it would affect the heterotrophic bacteria competition for organic carbon source, thus affecting the SND. When the HRT was 8.6 h in this system, SND obtained the best effect. C/N and F/M effected carbon source supply in the process of denitrification. In this system, the most suitable C/N and F/M were 8.0 and 0.38 kg COD/kg MLSS·d. Under optimal operating conditions, TN removal rate and SND rate of the carrier-type STMBR system could reach about 70% and 48% respectively. In carrier-type STMBR, formation of anoxic area in polyurethane sponge carrier and sludge flocs was the foundation of SND. Polyurethane sponge carrier was beneficial to form larger particle size sludge flocs, which promotes the SND. Not only full nitrification and denitrification exisited in carrier-type STMBR, but also short-nitrification and denitrification did.The time of carrier-type STMBR's TMP reaching 30 kPa was 105 h,which was 3.9 times of STMBR. Dosing polyurethane sponge carrier could retard membrane fouling and maintain the stability of the system. The analysis of membrane resistance and cake layer showed that the total resistance and cake layer of carrier-type STMBR were 19.70×1011 m-1and 8.84 g/m2 respectively, well below 36.54×1011 m-1 and 15.71 g/m2 of STMBR. Polyurethane sponge carrier was beneficial to promote the formation of loosely bound cake layer. Fourier infrared spectrum and EPS analysis showed that polyurethane sponge carrier could reduce the content of EPS and SMP in the system. The concentration of Polysaccharides and SMP was reduced by 25.2% and 37.1% respectively. The sludge particle size distribution results showed that polyurethane sponge carrier can reduce sludge floc breakage by adsorption and retard the shear force of aeration, and form larger particle size sludge flocs. Membrane fouling mitigation were implemented by a variety of function, the scouring effects on the membrane was the main reason.