Study On The Treatment Of Micro-Polluted Laged Water By Electrocatalytic Oxidation Coupled With Multi-Media Biological Slow Filtration

The northwest of our country belongs to the arid and semi-arid climate,dry all year round,little rain,groundwater aquifer is deep,even in some areas no use of groundwater resources,rainwater is the only potential water resources,but in the process of collecting rainwater will be such as solid waste,atmospheric sedimentation,chemical fertilizers,pesticides and other man-made pollution.In addition,due to the different geological conditions and the difference in the material of the cellar,the water quality in the cellar water exceeds the standard seriously,and the seasonal pollutants change greatly.In order to ensure the safety of drinking water quality of residents in the remote arid areas in northwest China,it is necessary to study the effective and safe treatment methods of rainwater harvesting water according to the actual characteristics of local culture and economy.In this experiment,the electrocatalytic oxidation technology,biological slow filtration technology and electrobiological coupling technology are the core,combined with the actual water quality characteristics and the local cultural environment to design the electrocatalytic oxidation coupling multi-media biological slow filtration water treatment technology and device,through the laboratory simulation of water quality of the water to explore the feasibility of the technology applied in the treatment of rainwater storage water in the northwest arid area,and practical application in the field.The main research contents are as follows:（1）In order to explore the optimal operating parameters of the three-dimensional electrocatalytic oxidation device,the anode was Ti/Ru O₂-Ir O₂-Sn O₂,the cathode was Ti plate,and Fe₃O₄/Sn O₂-GO particle electrode and activated carbon particle electrode were made by hydrothermal method.The effects of plate spacing,current density and particle electrode addition on the removal of organic matter in simulated cellars were studied.It was found that the optimal current density of organic matter removal was0.75 m A/cm²,and the removal effect of organic matter was not significantly increased by increasing the current density,and energy loss was caused.The optimal plate spacing is 2 cm,too small plate spacing will lead to the reduction of hydroxyl radical production efficiency,and too large plate spacing will increase the ion transport distance and reduce the mass transfer effect.The removal rates of COD_Mn and UV₂₅₄ were increased by15.62%and 15.09%respectively after the mixed particle electrode was added,indicating that the addition of activated carbon particle electrode had a beneficial effect on the removal of organic matter in the system compared with the single FSG particle electrode.（2）In order to explore the selection of multi-media biological slow filtration medium layer and the removal effect of pollutants during the hanging period,the method of"continuous water intake,natural hanging film"was adopted,and the three filter materials with the best treatment effect on the water quality of the cellar were selected as the multi-media biological slow filtration medium layer from the four natural filter materials with different element contents and one modified filter material.The results show that volcanic rocks and Fe-modified zeolite with higher comprehensive content of Na,K,Ca,Mg,Al and Fe have better pollutant removal effect.When the filtration rate is 0.2 m/h,the membrane hanging time of micro-polluted water treated by multi-media biological slow filtration is 25 days.After successful and stable operation,the average removal rates of turbidity,NH₄⁺-N,COD_Mn and UV₂₅₄ were96.17%,93.57%,64.36%and 53.71%.（3）In order to explore the coupling effect in electrocatalytic oxidation coupled multi-media biological slow filtration,the removal effect of various pollutants in simulated laged water was studied by applying 0.75m A/cm² micro current.The results showed that,The average removal rates of turbidity,NH₄⁺-N,COD_Mn and UV₂₅₄ are96.40%,96.36%,73.21%and 70.99%,respectively,after 0.75m A/cm² micro current is applied in stable operation.The stability time of the system is 7 days shorter than that of the system without micro current applied.The average removal rates of NH₄⁺-N,COD_Mn and UV₂₅₄ increased by 2.79%,8.85%and 17.28%,respectively.The electrobiological coupling system composed of micro current has a positive effect on the removal of various pollutants,especially improving the removal effect of organic matter.Moreover,the stimulation of current promotes the growth and propagation of microorganisms in the biofilm and speeds up the film hanging speed.（4）In order to explore the influence of various factors on the treatment effect of micro-polluted water in electrocatalytic oxidation coupled multi-media biological slow filtration,the influence of changes in filtration rate,water temperature,NH₄⁺-N load and COD_Mn load on pollutant removal was studied.It was found that,The removal efficiency of turbidity,NH₄⁺-N and COD_Mn by electrocatalytic oxidation coupled multi-media biological slow filtration decreases with the increase of filtration rate.With the increase of NH₄⁺-N load,the overall removal effect of NH₄⁺-N and COD_Mn increases first and then decreases.With the increase of COD_Mn load,the removal effect of COD_Mnfirst increased and then decreased,and the removal effect of NH₄⁺-N showed a downward trend.The removal effect of turbidity,NH₄⁺-N and COD_Mn increased with the increase of water temperature.（5）The removal effects of activated carbon,volcanic rock,Fe-modified zeolite and quartz sand on various pollutants were studied.The results showed that after the treated water passed through activated carbon,volcanic rock,Fe-modified zeolite and quartz sand,the removal effects of turbidity,NH₄⁺-N and organic matter showed an upward trend and were mainly concentrated in activated carbon layer.After passing through the activated carbon layer,the removal rates of turbidity,NH₄⁺-N、COD_Mn and UV₂₅₄ are 92.71%、93.04%、73.31%and 65.33%.The content of nutrients and dissolved oxygen in the water of activated carbon layer is higher,and the activity of microorganisms is higher,and the ability of pollutant retention and biodegradation is stronger.（6）Relying on the electrocatalytic oxidation coupled multi-media biological slow filtration technology,the electrocatalytic oxidation coupled multi-media biological slow filter-ultrafilter-ultraviolet disinfection water treatment equipment was developed and demonstrated in Xichuan Middle School,Huan County,Qingyang City,Gansu Province,and the operation parameters were optimized on site.The results showed that the biological slow filtration speed was 0.2 m/h,and the ultrafiltration operation mode was cross-flow filtration.The recovery ratio of concentrated water and clean water is90%,the filtration cycle is 40min,the ultrafiltration backwash time is 60s,and the biological slow filtration backwash time is 5min.Through phased water quality analysis,The effluent turbidity,COD_Mn、NH₄⁺-N and total number of colonies were lower than0.4 NTU、0.8 mg/L、0.04 mg/L and 20 CFU/m L,respectively,for six consecutive months.The quality of the produced water was in line with the Sanitary Standard for Drinking Water（GB5749-2006）through third-party testing,and there was no endogenous pollution during the operation of the device.To sum up,it is concluded that micro-current has a more obvious promoting effect on the growth of biological slow filtration biofilm,and electrocatalytic oxidation coupled multi-media biological slow filtration has a more significant removing effect on organic matter.Although various factors have an impact on the removal effect of various pollutants,compared with conventional biological slow filtration,The effect of electrocatalytic oxidation coupled multi-media biological slow filtration on the treatment of lightly polluted water is more stable.It can adapt to the seasonal change of pollutants in rainwater harvesting and cellared water in northwest arid area,and has certain practical significance and popularization value for the treatment of micro-pollution rainwater harvesting and cellared water.