Experimental Study On The Combined Treatment Of Snowmelt Water In Alpine Pastoral Area By Electrocoagulation-Electrobiological Slow Filtration Technology

In high-altitude and cold pastoral areas of China,the temperature is relatively low all year round,and herdsmen’s drinking water comes from surface runoff or underground runoff formed by melting snow.The way of drinking water for herders is usually direct drinking from nearby water bodies or drinking after simple filtration and sedimentation.At the same time,the surface layer of the alpine pastoral area has a certain thickness of soil humus layer,which contains a large amount of macromolecular organic compounds.Such organic compounds are easily infiltrated into nearby water bodies with rainfall and other factors,causing the water bodies to present intermittent and occasional pollutants exceeding the standard.In addition,herdsmen gather many livestock in nomadic residential areas,and the livestock often carry many pathogenic microorganisms.Such microorganisms would infiltrate into nearby water bodies with feces,causing many pathogenic microorganisms in the water bodies.This poses a potential threat to the safe drinking water of herdsmen.The experiment started with the investigation of snowmelt water quality in alpine pastoral areas,combined with the characteristics of regional water quality,an electro-flocculation pretreatment device and an electrobiological slow filtration core treatment device were designed,and the feasibility of using this technology to treat snowmelt water in alpine pastoral areas was explored by simulating water distribution in alpine pastoral areas in the laboratory.,and based on the experimental parameter optimization results,the actual application and verification are carried out in the field.The following research conclusions were obtained:（1）In order to explore the best working conditions of electro-flocculation for pretreatment of snowmelt water in alpine pastoral areas,the effects of electrode material（aluminum and iron）,current density,electrode spacing,and reaction time on the treatment efficiency of simulated water distribution were studied.The study found that when the current density was 12.35 A·m^-2,the distance between the plates was 10 mm,and the reaction time was 30 min,the removal rates of COD_Mn,UV₂₅₄,and NH₄⁺-N in the aluminum plate and iron plate water were the best.They were 56.91%,48.40%,62.82 and 44.63%,47.88%,51.06%,respectively.Combined with three-dimensional fluorescence spectrum,it can be seen that the main fluorescent organic substances in raw water were fulvic acid-like and humic acid-like humic substances.Under the action of electro-flocculation,electro-floating and electro-catalytic oxidation,the fluorescence intensity in the fluorescence peak region decreased to different degrees.And combined with the standard volume of regional integration,it was found that the fulvic acid-like and humic acid-like substances in the aluminum plate were removed by 46.06%and 49.13%,respectively,and the iron plate was removed by 15.09%and 24.70%,respectively.This showed that compared with the iron plate,the aluminum plate had a more significant removal effect of pollutants in the simulated distribution water.（2）In order to explore the effect of the electro-biological slow filtration device on the removal of pollutants in the snowmelt water in the alpine pastoral area,the conditions of the biological slow filtration membrane hanging under the same filtration rate with or without voltage were compared and analyzed,and the effect of voltage on the removal of pollutants in water by biological slow filtration device was investigated.It is found that under the condition of water temperature of 5～15℃and filtration rate of 0.2 m·h^-1,compared with the traditional biological slow filtration,the biofilm deposition time of the electro biological slow filtration（5 V）device is shortened by 7 days,which is mainly the result of the rapid growth of microorganisms promoted by the weak voltage.Under the optimal voltage（10 V）,the average removal rates of COD_Mn,NH₄⁺-N and UV₂₅₄in the water by the electro biological slow filtration device were 36.38%,39.63%and 38.20%higher than that of the biological slow filtration,The results showed that appropriate voltage was helpful for microorganisms to degrade pollutants in water efficiently.Combined with the three-dimensional fluorescence spectrum analysis,it was found that under the applied voltage,the degradation process of organic matter in each filter material layer changes to some extent.In the activated carbon layer,the electro biological slow filter device converts the refractory organic matter into tryptophan with good biodegradability through the leading role of electro oxidation.The effective degradation of dissolved organic matter was realized after the efficient microbial degradation of ceramsite layer and quartz sand layer,thus showed a high removal effect;The removal of organic matter by slow biofilter mainly depended on the biodegradation of activated carbon layer,while the ceramsite layer and quartz sand layer mainly played the role of physical interception.（3）The biofilm colony structure on the surface of each filter layer in the test device was analyzed by high-throughput sequencing technology.The study found that the external voltage had a significant effect on the bacterial and fungal community structure of the biofilm on the surface of the filter material.Under the influence of voltage,the microbial community diversity of the ceramsite layer in the electro-biological slow filtration device was better than that of the activated carbon layer,and the microbial community diversity of the activated carbon layer in the biological slow filtration device was better than that of the ceramsite layer,which further indicates that the appropriate voltage can Change the leading role of each filter material layer on the removal of pollutants in water.At the genus level,the dominant bacterial genera were Hydrogenophaga,Mycobacterium,Pseudonocardia,Erysipelothrix,SRB2＿norank,and Sulfuritalea.the dominant fungal genera were mainly Eukaryota＿norank,Fusarium,Scheffersomyces,Acaulopage.From the redundancy analysis,it can be seen that there was a positive correlation between the water quality physical and chemical indicators DO,NH₄⁺-N,and p H,and a negative correlation with UV₂₅₄.Among them,UV₂₅₄had the greatest impact on the bacterial community structure,and p H,DO,NH₄⁺-N had a greater impact on the fungal community structure.（4）The field test showed that the electro-flocculation combined with the electro-biological slow filtration device had a significant effect on the removal of pollutants in the snowmelt water in the alpine pastoral area.The average removal rates of turbidity,COD_Mn,NH₄⁺-N and UV₂₅₄by the device were 98.96%,64.89%,83.72%and 52.86%,respectively.The water quality and bacteriological indicators of the effluent after UV disinfection were in line with the requirements of"Drinking Water Sanitation Standard"（GB5749-2006）,and no"two insects"had been detected in the effluent.The removal rate of total Escherichia coli by the device can reach 99.99%,while the removal rate of total bacteria was only 15.15%.The experiment combined electrochemical technology with biological slow filtration technology.Compared with traditional biological slow filtration technology,the removal effect of pollutants in water was significantly improved,which was mainly due to the synergistic effect of microbial degradation and electrochemical oxidation.However,there are still shortcomings in the experiment,and further research can be done on the filter layer structure,filtration rate,electrode materials,and the mechanism of low-pressure and high-pressure regions,to provide new ideas for drinking water treatment.