| By 2020,China have completed the building of a moderately prosperous society in all respects and achieved the first of the two centenary goals.With the comprehensive achievement of this goal,China's economic level and people's well-being index has also improved significantly.In the field of drinking water treatment and water supply industry,the water supply infrastructure in China has been improved,and the problem of insufficient water supply has been greatly improved,the main contradiction of drinking water supply began to change from water supply to water quality assurance.Therefore,the research and development of advanced drinking water treatment technology is urgent.Membrane process has many advantages such as simple and efficient,small footprint,flexible design water quantity,stable water quality,no generation of other harmful by-products,and resistance to pollutant impact.It is known as the"third generation"drinking water treatment process,and is a new and efficient drinking water treatment technology.In this study,on the basis of the existing conventional water treatment process and advanced treatment process in drinking water treatment plant,the nanofiltration process was added.The pilot test of conventional treatment?coagulation-sedimentation-sand filtration?+nanofiltration?NF?process and conventional treatment+advanced treatment?ozone-biological activated carbon,O3-BAC?+NF process were compared.A variety of water quality indexes were analyzed,combined with high performance size-exclusion chromatography?HPSEC?-molecular weight distribution detection,three-dimensional excitation emission matrix?3DEEM?-parallel factor analysis,atomic force microscopy?AFM?and scanning electron microscopy+energy spectrum?SEM+EDS?analysis.The performance of conventional treatment+NF and conventional treatment+advanced treatment+NF combined process were evaluated from various angles,including the improvement effect of water quality,the removal of organic substances with different characteristics,the response to sudden pollution of water,the operational stability of NF membranes,and membrane pollution.And from June2019 to January 2020,a seven-month pilot study was conducted in order to obtain a water treatment process suitable for the preparation of high-quality drinking water.The conclusions are attained as follows:?1?During the experiment,the water temperature,algae cell concentration,electrical conductivity and pH value of the Lake Tai changed regularly with the seasons.The molecular weight of dissolved organic matter?DOM?in Lake Tai is mainly distributed in 0.22-30kDa,and the source of DOM is mainly proteinaceous organic matter polluted by algae,plankton and aquatic organisms.?2?According to the improvement effect of the two processes on the conventional water quality index,the removal rate of UV254 and DOC by conventional+nanofiltration process reached 97.01%and 96.32%;the removal rate of conventional+advanced treatment+nanofiltration reached 98.57%and 97.62%.In addition,the removal rate of biodegradable organic carbon?BDOC?and trihalomethane generation potential?THMFP?in the two combined processes was higher than 90%.The above results indicate that both processes can effectively improve drinking water quality,and the treated drinking water fully achieves the high-quality drinking water quality standards.?3?According to HPSEC-UV-TOC analysis,it was found that the two processes can effectively remove all organic compounds of molecular weight in the influent,but due to the Concentration polarization phenomenon,the organic compounds with a molecular weight between 1kDa-5kDa in the influent will enter to the permeated water.EEM-PARAFAC can separate the organic matter in water into 4 components.Both processes can effectively reduce the maximum fluorescence intensity(Fmax)of the above 4 components.?4?The NF90 nanofiltration membrane showed a very perfect removal effect on 2-methyl isobenol?2-MIB?and terrestrial olfactory?GSM?,which are typically present in lake water,even if the concentration of the two odorants in the influent reaches 158.5 and205.4ng/L,respectively,the nanofiltration membrane can also reduce it below the threshold;In addition,nanofiltration membranes can also effectively respond to multiple incidents of sudden benzene series water pollution in recent years.The optimization results are based on the nonlinear surface fitting results of recovery rate,operating pressure and benzene series concentration in permeated water.When the recovery rate is less than 21.63%,the nanofiltration membrane can fully guarantee the concentration of 6 benzene series in the production water In line with national standards.?5?When the conventional+nanofiltration combined process was in operation,the nanofiltration membrane can only guarantee 25L/m2·h flux for 25 hours,and the transmembrane pressure difference?TMP?rises from 0.36MPa to 0.45MPa;During the operation of the conventional+O3-BAC+nanofiltration combined process,the nanofiltration membrane can be stably operated at a flux of 22.5L/m2·h for 432 hours.The operation stability of the conventional+advanced treatment+nanofiltration process is much higher than that of the conventional+nanofiltration combination process.?6?After analyzing the organic components in the alkaline washing solution of the nanofiltration membrane after the two processes were run,both polysaccharides and macromolecular proteins were found.Such substances are the main types of organic substances that cause membrane pollution.Secondly,the small and medium molecular organics produced by microbial metabolism in Region IV were also one of the main components that cause organic pollution of nanofiltration membranes,while protein organics in Region I contributed less pollution to nanofiltration membranes.Combined with AFM and SEM+EDS analysis of the surface of the nanofiltration membrane after pollution found that during the operation of the conventional+nanofiltration combination process,the nanofiltration membrane was biofouled,and a thick biological mucosa was formed on the membrane surface.,Sulfur and calcium.This indicated that when the conventional process was used as a pretreatment,the inorganic,organic and biological pollution on the surface of the nanofiltration membrane caused the TMP to rise rapidly.In this paper,a large number of data samples were collected,and various common mathematical analysis methods were used to analyze and study the operation effects of the two kinds of pretreatment+nanofiltration processes.Finally,combined with the above six conclusions,the following conclusion was made:,the conventional+O3-BAC+NF process can ensure the stable operation of the process and effectively improve the quality of drinking water.This combined water treatment process is more suitable for the treatment of high-quality drinking water. |
PDF Full Text Request