Treatment Of Micro Polluted Pit Water In Northwest Villages And Towns By Nanofiltration Integrated Process

Northwest China is a typical dry and water shortage area where rainwater is used as drinking water source.Due to the collection mode of pit water and environmental factors,the turbidity,organic matter,ammonia nitrogen and other indicators in pit water exceed the standard,and the concentrations of ammonia nitrogen and Permanganate Index reach 0.18～1.14 and 2.74～6.83 mg/L respectively.Especially the existence of humic acid,fulvic acid and other natural organic matter,it is difficult to remove them effectively by conventional processes.This kind of water is a serious threat to human health for a long time.In this study,through the field investigation and detection of micro polluted cellar water in Northwest villages and towns,through the artificial simulation of water distribution,the pretreatment+membrane separation technology was used to optimize the process parameters,and the decontamination performance of the combined process of coagulation chlorine/ultraviolet advanced oxidation pretreatment and microfiltration nanofiltration dual membrane advanced treatment was studied,so as to provide reliable technology for the treatment of micro polluted cellar water in Northwest villages and towns support and improve the drinking water safety of residents in Northwest villages and towns.In this study,coagulation experiments were carried out for turbidity and macromolecular organic matter in pit water.The removal effects of different coagulant dosage on micro polluted pit water were investigated,and the optimal dosage of coagulant was determined.After coagulation,the removal effect of dissolved pollutants in water was general due to coagulation,especially for ammonia nitrogen pollution,coagulation had no removal effect Aiming at the harm of ammonia nitrogen pollution,chlorine/ultraviolet advanced oxidation pretreatment was set after the coagulation of ammonia nitrogen.The removal effect and transformation mechanism of ammonia nitrogen,chloramine and ammonia nitrogen in micro polluted pit water with different dosage of available chlorine and ultraviolet irradiation time were mainly investigated.The optimal dosage of available chlorine and ultraviolet irradiation time were determined.At this time,ammonia nitrogen pollution in outlet water was well removed.In order to improve the poor stability of effluent quality and ensure the safety of drinking water,the pretreated effluent was treated by composite microfiltration nanofiltration dual membrane process.The effects of composite microfiltration inlet pressure,nanofiltration inlet pressure,p H,temperature and other factors on membrane flux and pit water quality decontamination efficiency were analyzed.Finally,in order to verify the practical feasibility of the combined process,the overall treatment experiment of micro polluted pit water by component process was carried out under the best operating conditions,to explore whether the effluent index of the combined process can meet the standard of drinking water,and to analyze the removal effect of protein like and humus like fluorescent substances in pit water by various processes and combined processes.The research conclusions are as follows.In the experiment of coagulation treatment of micro polluted pit water,the influent turbidity,ammonia nitrogen,Permanganate Index and UV₂₅₄ organic matter content were3-15 NTU,0.5-1.2 mg/L,3.2-7.8 mg/L and 0.078-0.12/cm,respectively,which exceeded the standard.The molecular weight distribution of organic matter in raw water was seriously divided into two levels.Permanganate Index and UV₂₅₄ over 100 KDal accounted for 11.76%and 9.86%of the total organic matter,less than 3 KDal Permanganate Index and UV₂₅₄accounted for 78.3%and 67.75%of the total organic matter.When using separate coagulation to treat cellar water,under the optimal PAC dosage of 30 mg/L,the organic matter in each molecular weight distribution range of the coagulation effluent has a good removal rate,the removal rates of Permanganate Index and UV₂₅₄are about 50%-60%,and the removal rate of UV₂₅₄ is slightly higher than Permanganate Index,the turbidity removal effect is the highest,and the effluent turbidity is lower than 0.5 NTU,but the removal rate of ammonia nitrogen by coagulation is not high,only about 10%.In the experiment of treating micro polluted pit water with chlorine/UV,the best dosage of available chlorine is 6 mg/L,and the best time of UV irradiation is 8 min after 10 min reaction at 250 r/min Under the optimal conditions,the removal rate of ammonia nitrogen can reach 61.88%,the removal rate of organic matter can reach about 10%,and the molecular weight of organic matter in chlorine/UV effluent is less than 3 KDal and more than 100 KDal The organic matter content of KDal decreased.The results showed that the removal mechanism of pollutants in chlorine/UV treated micro polluted cellar water was mainly the reaction of chlorine and ammonia nitrogen to form monochloramine under low effective chlorine dosage,and monochloramine to 254 The UV light at nm has strong absorption capacity and can be photodegradated into chlorine free radical and amino free radical with strong oxidation.Chlorine free radical reacts with water molecule or hydroxyl to form hydroxyl free radical.Ammonia nitrogen,Permanganate Index and UV₂₅₄in water can be removed by oxidation.In the experiment of micro polluted cellar water treatment by composite microfiltration,the removal rates of turbidity,ammonia nitrogen,Permanganate Index and UV₂₅₄ in the chlorine/violet effluent treated by composite microfiltration were 86.93%,31.79%,54.97%and 79.12%respectively at the optimal inlet pressure of 0.1 MPa,and the contents of turbidity,ammonia nitrogen,Permanganate Index and UV₂₅₄ in the effluent were 0-0.3 NTU,0.14-0.33mg/L,0.65-1.58 mg/L and 0.006-0.01/cm respectively.In order to ensure the safety of drinking water,a nanofiltration device was added after pretreatment and microfiltration.The cross flow filtration method was adopted.Under the influent pressure,temperature and p H of 0.4 MPa,18℃and 7.5 respectively,the turbidity and UV₂₅₄of nanofiltration effluent could not be detected.The removal rates of ammonia nitrogen and Permanganate Index were 89.67%and 97.04%,respectively.The quality of nanofiltration effluent was stable.In this paper,through the optimization of various process parameters,the removal effect of pollutants by the combined process was improved.Then,the coagulation/advanced oxidation pretreatment of chlorine violet and the advanced treatment process of microfiltration nanofiltration were combined to treat the micro polluted pit water under the optimal conditions,and the removal of fluorescent substances was studied.The results show that the nanofiltration has a good removal rate for the conventional indicators,but also has a good effect on the water quality The total removal rate of fluorescent substances in the nanofiltration process also reached more than 90%,especially the content of humus fluorescent substances in the water was basically removed in the nanofiltration effluent,which ensured the safety of drinking water,and further demonstrated the practical application value of the process.