Study On Micro-polluted Cellar Water Treated By Slow Biofiltration Filter Column With Different Filter Materials

The northwest part of China belongs to arid and semi-arid climates,which can be used by people with few water resources,and the remote rural areas often store rainwater in the water cellar and use it as drinking water.However,cellar water is easily contaminated by the surrounding environment(including domestic garbage,animal excreta,car exhaust,etc.),the contents of organic matter,microorganisms,heavy metal ions and other kinds of pollutants is too much,which can cause various diseases without water treatment for long-term drinking.Therefore,it is urgent to find water treatment technology which can be applied to small decentralized water supply systems in rural areas to make the local people's domestic water more clean and healthy.The slow biofiltration has the advantages of low cost,simple operation and no need for any potions,it has a good effect on removing excessive pollutants such as turbidity,chromaticity,organic matter,microorganism,heavy metal ions and so on,so the slow biofiltration can be used to treat cellar water and ensure the drinking water safety of local people.In this paper,the static and dynamic experiments of quartz sand,volcanic rock,and medical stone are used to study the feasibility of the application of volcanic rock and medical stone in the slow biofiltration,and selecting the filter material with the best treatment effect to cellar water.Firstly,the static adsorption experiment was used to study the ability of three filter materials to adsorb ammonia nitrogen and organic matter(including CODMn and UV254).Secondly,dynamic experiments were carried out to study the successful time of quartz sand filter column,volcanic rock filter column,medical stone filter column and the removal effect of pollutants in the cellar water during the biofilm formation.Thirdly,the factors that affect the effects of the three filter columns to remove pollutants were studied.Finally,the recovery time of the three filter columns and the removal effect of pollutants during the recovery period were studied in the case of intermittent operation.The static adsorption experiments of three filter materials showed that the adsorption capacity of ammonia nitrogen and organic matter from strong to weak was the volcanic rock > medical stone > quartz sand.This is because of the three filter materials,the surface roughness,porosity,and specific surface area of the volcanic rocks are the largest,and the contents of Fe,Mg,and Ca are the most,the adsorption capacity is also the strongest.The biofilm formation experiment showed that the successful time of quartz sand filter column,volcanic rock filter column and medical stone filter column were 43 days,29 days and 37 days respectively.The effluent water quality of three filter columns after the success of biofilm formation was up to standard,and the removal efficiency of all kinds of pollutants from the high to low was always the volcanic rock filter column > medical stone filter column > quartz sand filter column.This is because of the three filter materials,the physical properties of volcanic rocks are best,and microorganisms are more likely to attach to them for growth and reproduction.Therefore,volcanic rock filter column has the shortest time for biofilm formation and the best effect of removing pollutants.The influencing factors experiments showed that the three filter columns mainly removed pollutants in the upper part of the filter layer,and the removal rates were positively correlated with the thickness of the filter layer and the water temperature,and were negatively correlated with the filtration rate.The removal rates of ammonia nitrogen and CODMn were positively correlated with lower influent ammonia nitrogen concentrations(below 1.421 mg/L and 1.248 mg/L respectively),and were negatively correlated when they were exceeded.The removal rate of CODMn was positively correlated with the lower influent CODMn concentration(below 7.23 mg/L),and negatively correlated when it was exceeded.The removal rate of ammonia nitrogen was negatively correlated with the influent CODMn concentration.The intermittent operation experiments showed that when the water temperature was between 16.8 to 19.2°C and the shutdown days was within 3 days,the three filter columns only needed 1 day to restore the state before shutdown.When the shutdown days was 7 days,the recovery time of quartz sand filter columns was 2 days,the recovery time of the volcanic rock filter column and the medical stone filter column was 1 day;when the shutdown days was 15 days,the recovery time of the quartz sand filter column,the volcanic rock filter column and the medical stone filter column was 5 days,3 days and 4 days respectively.After the water was re-introduced,the effect of removing the pollutants from the three filter columns decreased significantly,and then gradually recovered with the increase of the intake days.The above experimental research shows that both volcanic rock and medical stone can be used as the filter material for slow biofiltration,and volcanic rock filter column has the best effect in treating cellar water among the three filter columns.Therefore,in the practical application of slow biofiltration in the future,the volcanic rocks can be considered as filter material in areas with high water quality requirements.