Study On Quality Requirements Of Reclaimed Water For Vegetation Restoration And Technologies Of Moderate Wastewater Treatment In The Coal Base Of Northwest Desert Region

The coal base in the northwest desert region is dry and short of water.Reclaimed water?mine water and domestic sewage?is one of the main water sources available for vegetation restoration.In this study,the water quality requirements of reclaimed water for vegetation restoration in the coal base in the northwest desert region were firstly studied.According to the water quality requirements of reclaimed water,the composite system of activated sludge and biofilm and the nanofiltration membrane filtration technology were used to treat domestic sewage and mine drainage.In addition,the operation parameters of moderate treatment to meet the quality requirements of reclaimed water were studied,and the removal mechanism of pollutants was explored.Finally,the technical and economic estimates were given according to the treatment and utilization of reclaimed water in yangchangwan mining area.It is of profound significance to the conservation of soil and water vegetation,the establishment of vegetation diversity,the maintenance of ecological balance and the improvement of natural environment in the coal base in the northwest desert region.According to the quality of domestic sewage and mine water in northwest China,combined with the relevant national standards of reclaimed water and relevant literature on the use of reclaimed water in vegetation restoration,the quality of reclaimed water suitable for vegetation restoration in northwest desert areas was determined.The main pollutant control index of reclaimed water was:turbidity?10NTU,SS?30 mg/L,Total hardness?450 mg/L,Chloride?350 mg/L,TDS?1000 mg/L,COD?65mg/L,NH₄⁺-N?20 mg/L,TP?4 mg/L.In the moderate treatment of domestic sewage,sequence batch sludge membrane integrated hybrid bioreactor?HBR?was used to form a composite biological system of stable activated sludge and biofilm with strong pollutant removal capacity.Sequence batch composite reactor adopts the anaerobic-anoxic-aerobic mode.Suitable operating conditions to meet the requirements of moderate sewage treatment were:15 min of water inlet,90 min of anaerobic,90 min of anoxic,180 min of aerobic,30 min of sedimentation,15 min of drainage,10 days of sludge drainage,the best operating temperature was 25?,the best packing proportion was 1/4,the best carbon/nitrogen ratio was 7/1.HBR system stably operated for 5 months,and according to the results HBR had stronger ability to resist shock and decontamination,with an effluent COD concentration of 58 mg/L,NH₄⁺-N concentration of 9.4 mg/L of 14 mg/L,TN concentration of 14 mg/L,TP concentration of 2.8 mg/L,ensuring both the removal of organic matters in sewage and the right amount of nitrogen and phosphorus as nutrients for vegetation irrigation.Suspended matter and high salinity are the main problems of mine drainage in northwest coal base.The membrane filtration process based on nanofiltration was used to remove suspended solids in the water.The experimental results showed that the dosage of polyaluminum chloride in the coagulation-precipitation pretreatment process was 80 mg/L,and the removal of suspended solids and turbidity in the water was the best,with an effluent turbidity of 5.14 NTU and a suspended solid of 8.55mg/L.NF90 nanofiltration membrane filtration technology was selected in combination with mine drainage treatment effect and economic ratio.The appropriate operating pressure of NF90 film was 0.8MPa and the operating temperature is 25?.Cleaning with 2%citric acid and adjusting p H to 2.5-4with ammonia can significantly reduced membrane fouling and restored membrane flux.The treatment effect of this process on mine drainage in Yangchangwan Coal Mine is obvious,and the effluent total hardness was 14.64 mg/L,the chloride was 331.12 mg/L,and the TDS was 735 mg/L.At the same time,the treatment cost was saved.According to the vegetation restoration plan of the engineering site-yangchangwan mining area,the project estimation of the moderate treatment technology of reclaimed water in accordance with the vegetation restoration technology of yangchangwan mining area was given by using the sewage treatment facilities already built in yangchangwan mining area,combining with the process and optimized operation conditions proposed in this study.After the improvement of domestic sewage treatment technology,the efficiency was improved by 30%,the treatment cost was about 0.98 yuan/m³,and the annual average total domestic sewage treatment cost was 407,500 yuan.The cost of mine water treatment was 0.182 yuan/m³,and the annual average total cost of mine water treatment was 1.14478million yuan.