Exploiting Of Integrated Membrane Combined Purification Processes For Rural Area

With the serious shortage of water resources and the pollution of source water, conventional processes have already hardly meet the severe standards for drinking water quality. Membrane filtration technology is recognized as"water treatment technology in the 21st century". Micro-filtration and ultra-filtration and their combined processes are hotspots in feed water treatment recently.This subject is on the support of important scientific research project in Zhejiang province—"the development and application of tubular micro-filtration technology for drinking water treatment in rural area (NO. 2006C13107)"and the achievement industrialization special project of research institutes and universities in Nanhu district, Jiaxing city—"the development of integrative drinking water security treatment technology". Mirco-polluted source water of typical rural area in Jiaxing city was chosen, hybrid process of pre-aeration followed with tubular microfiltration to treat iron contaminated underground water and membrane bioreactor (MBR) to treat high organic and high ammonia-nitrogen contaminated surface water for drinking water production. Pollutants removal efficiencies were investigated; membrane fouling and control measures were studied.(1) Perfect treatment performance was achieved when hybrid process of pre-aeration followed with tubular microfiltration was used to treat underground water for drinking water supply. The Fe removal efficiency was as high as over 90%, 40～60% higher than using MF alone. Poisonous and harmful trace pollutants characterized by UV₂₅₄ and UV₄₁₀ were removed 82.1% and 88.7%. The turbidity removal rate was above 95% no matter pre-aeration was used or not, keeping turbidity in the filtrated effluent always below 0.2 NTU.(2) According continuous operation, membrane fouling characteristics and membrane cleaning of hybrid process of pre-aeration followed with tubular microfiltration was investigated. Membrane resistance increased rapidly owing to all pollutants were accumulated in the tubular tank body. Inorganic matters such as Fe were found to be the primary membrane contaminants. Fe concentration and turbidity in the effluent were higher than that in the influent during worse fouling period and ferruginous active microbial contamination may exit at anaphase. So chemical cleaning with 2～3% HCl combined with fresh water backwash was proved to be a simple but effective way to remove membrane contamination.(3) Effective operation performance was achieved using MBR to treat high organic and high ammonia-nitrogen contaminated surface water for drinking water production. The CODMn,TOC,UV₂₅₄,UV₄₁₀ and SUVA removal rates on PAC-MBR process were 52%,52%,62%,93%and 32%, respectively. The average CODMn in the filtrated effluent was 4.2 mg/L, meeting the Drinking Water Sanitary Standard of 5 mg/L if the amount in the source water exceeds 6 mg/L. 93% NH3-N removal rate was obtained with the filtrated effluent concentration of 0.14 mg/L on account of biological effect in the mixture. Ultrafiltration membrane and cake layer ensured the removal efficiency of turbidity stabilized at above 90%, the filtrate turbidity kept below 0.5 NTU and showed no relationship with PAC addition and change of influent turbidity.(4) Organic molecular distribution in micro-polluted source water mainly distributed at 0.22～0.45μm and <1 k. The removal rates of TOC and UV₂₅₄ at 0.22～0.45μm were 94.0% and 85.7% due to synergistic effect of ultrafiltration and cake layer filtration. UV₂₅₄ at 5-30 k was negative increased for the reason of biologic metabolic products dissolved in the mixture. The effects of ultrafiltration,PAC adsorption and biodegradation for genotoxics could control effluent genotoxicity effectively.(5) According investigating membrane fouling characteristics and membrane cleaning of MBR for micro-polluted surface water, it suggested that there were no effect on mitigating membrane fouling by adding PAC. The total membrane resistance was 13.0×10¹² 1/m, membrane inherent resistance, cake layer resistance and adsorption and clogging resistance were accounted for 15%, 43% and 42%, respectively. Fouling membrane specific flux recovered to 58% after fresh water cleaning, then recovered to 76% after alkaline cleaning and last recovered to 85% after acid pickling. Cake layer clogging was suggested to be the primary membrane fouling and could be easily flushed by fresh water. Using NaClO and HCl solution intermittently could further control biological pollution, organic and inorganic pollution. (6) PAC-MBR could effectively remove BDOC, ADOC and A&BDOC. Active biomass in MBR presented the tendency of slow growth and high microbial activity.Membrane technology for micro-polluted surface water treatment was remarkable. According this subject, we hope to develop integral processes which suitable for rural areas to treat micro-polluted source water with several advantages on perfect filtrate, smaller footprint, convenient operation and management as well as low investment, and provide technical support for rebuilding or building water-purified station in the future.