Research On Biological Pretreatment Coupled With Ultrafiltration Process For Purification Of South China Reservoir Water

The safety of drinking water in rural areas has been of great concern for our country in recent years.Because of the lack of drinking water treatment facilities,most of the people use and dink untreated raw water directly in some areas.On account of the outdated technology of rural drinking water treatment and backward management level of water supply systems,the drinking water quality is still a serious problem in other regions where water treatment facilities has been built.Conventional potable or drinking water treatment system is complicated and the operation and maintenance of the system is difficult.What's more,the addition of chemical agents changed the properties of the drinking water and may have harmful effect on human health.So,the conventional system is not suitable for rural areas.In the course of designing the water treatment process,we should take into full account the high quality characteristics of the raw water and techno-economic level of the district in order to seek more simple and green drinking water treatment technology.In this research,the biological pretreatment coupled with ultrafiltration processes(BAC-UF and BAF-UF)were developed to treat the reservoir water in South China.By means of investigating the effluent quality of the two processes compared with the direct ultrafiltration(UF)process,the performance of the three processes were studied and the advantanges and disadvantages were also discussed Moreover,the effect of biological pretreatment on membrane fouling alleviation was evaluated.In order to provide technical support for membrane fouling control,the machanisms of membrane fouling were analysed and the foulants were also recognized.The results of the purification performance study showed that the average removal efficiency of turbidity,UV254,CODMn,ammonium nitrogen and DOC of UF was 98.94%?20%?22.32%?20.87%?28.9%,respectively,of BAF-UF was 98.94%?20%?26.48%?81.58%(later period 92.71%)?34.43% respectively and of BAC-UF was 99.1%?40%?35.27%?95.72%?49.74% respectively.With the biological pretreatment,the removal rate of organic matter and ammonia nitrogen was improved,and the water treatment performance of BAC-UF was better than that of BAF-UF.The increase of the removal rate of organic matter was not significant for the reason that the nutrient condition of this water was a oligotrophic type and not conducive to the growth of microorganisms.The ammonia nitrogen removal efficiency was greatly improved and without of biological pretreatment,the ammonia nitrogen in effluent could not meet the drinking water standard.The BAC-UF and BAF-UF processes can achieve high quality water supply and ensure the safety of drinking water in the test conditions.The results of the membrane fouling analysis showed that the specific flux of the UF with biological pretreatment decreased slower than the direct UF by 20% indicating that the biological pretreatment effectively alleviated the membrane fouling.The membrane fouling model fitting demonstrated that standard clogging and cake filtration were the dominantfouling machanisms of the three processes under the experimental conditions.The foulants identification indicated that when the biological pretreatment(BAC)The major irreversible foulants were the protein-like components produced by the metabolism of microorganisms and the humic-like substances in the raw water when the biological pretreatment(BAC)was adopted However,the membrane fouling in the absence of biological pretreatment is mainly composed of humus substances.In this experiment,the main membrane fouling was formed by humic-like components for the biological pretreatment effect of BAF was poor and the biomass was less of BAF-UF process.These results are expected to provide important implications for monitoring and controlling UF membrane fouling.The operating costs of the three processes were: UF process: 0.2582 yuan/t,BAC-UF process: 0.2954 yuan/t,BAF-UF process: 0.4218 yuan/t.The study showed that the BAC-UF and BAF-UF processes can achieve high quality water supply and ensure the safety of drinking water in rural areas.It is recommended the two processes above can be adopted for applying water with better quality when the superb source water like reservoir water is available.