Experimental Study On The Effect Of Treating Hospital Sewage By Iron Hydroxide In MBR

Hospital waste water, which contains a great deal of bacteria, virus and other toxic and harmful components, should be treated and disinfected properly before discharge. Otherwise, it will do great harm to human health and environment. After several public health incidents breaking out, such as the SARS and H1N1,more and more attentions have been attracted on the treatment of hospital sewage. However, it becomes a trend to develop new methods to treat hospital sewage, with the disadvantages of traditional methods being found. Membrane bioreactor(MBR), because of it's small footprint, high automation, excellent water quality, high disinfection efficiency, become the research focus for wastewater treatment in recent years.This experiment combined MBR with bioferric of conventional activated sludge, which adds hydrogen ferric oxide flocs to MBR to improve the performance of the sludge reduce membrane fouling and obtain better treatment results. This paper makes a research on the organic matter removal rate, sludge characteristic and the membrane fouling of the system. Besides, the mechanism is studied on the analysis of process operating conditions and parameters, sludge concentration, and microbiological characteristics. The following conclusions can be obtained:(1) On the dosage of ferric hydroxide sludge concentration of 1.5%,the removal rate of organic is studied under different aeration time. Following conclusions can be obtained:the removal rate of COD,NH3-N and so on, becomes stabilized after the aeration time of 6h-7h. In the comprehensive consideration of economic costs, the aeration time of 6h-7h is chosen.(2) Under certain conditions, the system of iron hydroxide-MBR showed good organic removal and long-term operation stability for the treatment of hospital wastewater. In continuous operation without sludge discharge condition, the COD degradation rate can reach 92.1%,the degradation rate of ammonia can reach 99.6%.The output water of this improved system can meet the "standards for medical water pollutants"(GB18466-2005).(3)Bioferric-MBR process has improved the quality of effluent to some extent. In this experiments, the iron hydroxide dosage of 3% of MLSS concentration is considered to be the best, on which condition, biological iron-MBR average effluent COD, total P, NH3-N were higher than the ordinary MBR by 9.13%,18%, and 4.2%.In this system, because of the membrane of MBR, the removal efficiency of E. coli is more than 98%.(4) For the biological iron-MBR process, the sludge with hydrogen ferric oxide dosage of 1.5%-3% sludge concentration have good structure, which reduces the membrane surface cake layer resistance and ease membrane pore blockage on the membrane fouling. However, when the dosage was increased to 5% sludge concentration, bio-sludge disintegrates to small particles, which reduce the adsorption ability of biological iron sludge. Thus, the organic matter removal rate is reduced. In addition, the high consumption of organic matter will encourage the growth of filamentous bacteria, which can release much more EPS, thus increasing membrane fouling and reducing membrane flux.(5) On the research of the effect of hydrogen ferric oxide dosage on the TMP and membrane flux, conclusions can got as follows:the first day of adding coagulant, TMP increased and flux suddenly decreased. The reason may be that activated sludge containing ferric floc is too small and adsorbed to the membrane pore to make a blocking resistance Rf.