Research On In-situ Adsorption And Oxidation Treatment Of Groundwater With High Concentration Of Iron,manganese And Ammonia-nitrogen

Groundwater is an important source of drinking water in China.With the rapid development of industry and agriculture,the problem of groundwater quality shortage and groundwater environmental pollution is particularly prominent.At the present stage,in the process of urbanization and industrialization in China,this outstanding problem must be solved in order to restore the ecological environment,protect human health and promote the construction of ecological civilization.With the promotion of relevant laws and regulations such as the National groundwater pollution Prevention and Control Plan?2011-2020?,the prevention and control of groundwater pollution has been promoted rapidly,aiming at the typical over-standard components and pollutants in groundwater.It is urgent to carry out the research and application of economic,efficient and ecologically safe groundwater pollution control and remediation technology.About 70%of the population in China uses groundwater as the source of drinking water.Iron,manganese and ammonia nitrogen are the main over-standard components of centralized drinking water source?groundwater?.The problem of iron,manganese,ammonia and nitrogen exceeding the standard generally exists in groundwater in Northeast China,because the layout of villages and towns is scattered,and its water supply mode is often based on small decentralized water supply mode.Because of the long winter time and low temperature in Northeast China,the traditional ectopic treatment project has some shortcomings in engineering cost and daily maintenance.The economical and efficient in-situ treatment project is suitable for decentralized water supply in villages and towns in Northeast China.It plays a positive role in promoting local social and economic development.Based on the above,relying on the national water pollution control and treatment science and technology major project"Key technologies and demonstration of water quality safety guarantee for water exploitation along Songhua River"?2014ZX07201-010?,this paper aims at the excessive components of iron,manganese and ammonia nitrogen in groundwater in Northeast China,and carries out the research on the technology of in-situ adsorption and oxidation of high iron,manganese and ammonia nitrogen in groundwater.Through stimulating groundwater environmental conditions,screening of iron-manganese ammonia nitrogen adsorption materials and oxidation functional bacteria,and analysis of their adsorption characteristics,in-situ adsorption and oxidation simulation experiments and site verification tests were carried out.This study provides a certain reference for the improvement and popularization of in-situ treatment technology of iron,manganese,ammonia and nitrogen exceeding the standard of groundwater.Through this study,the main conclusions are as follows:?1?Volcanic slag,zeolite,manganese sand,quartz sand and activated carbon were selected to screen iron-manganese ammonia nitrogen adsorption materials.The results show that volcanic slag has better removal effect on iron-manganese ammonia nitrogen.Combined with its light weight,wide range of sources,economic and other characteristics,volcanic slag is determined to be the best adsorption material.The adsorption equilibrium time of iron-manganese ammonia nitrogen by volcanic slag is6 h,10 h and 6 h,respectively.The adsorption of iron-manganese ammonia nitrogen by volcanic slag accords with the law of quasi-second-order kinetics.The pH value significantly affected the removal efficiency of manganese and ammonia nitrogen,alkaline environment was more conducive to the removal of manganese and ammonia nitrogen,hardness had no significant effect on the removal of iron and manganese,and had an inhibitory effect on the removal of ammonia nitrogen.The results of comprehensive characterization and analysis show that the volcanic slag is a silicate material rich in iron and aluminum,the pore size is rich,the pore size distribution range is 2.5-30 nm,and the specific surface area is 3.069 m²/g.?2?The iron-manganese ammonia nitrogen oxidizing bacteria suitable for groundwater environmental conditions were screened.Under the experimental conditions,the dynamic equilibrium time of iron and manganese removal by iron and manganese oxidizing bacteria was about 75 hours,and the removal rates of iron and manganese were between 80.4%-98.8%and 30.1%-83.5%,respectively.When the content of manganese was more than 15mg/L,the growth of manganese oxidizing bacteria was inhibited,and the dynamic equilibrium time of ammonia nitrogen removal by ammonia nitrogen oxidizing bacteria was about 65 hours,and the removal rate was between 80.1%-98.4%.The enriched iron-manganese ammonia-nitrogen oxidizing bacteria adapted to the low temperature environment and had little effect on their metabolic activity at room temperature,iron and ammonia-nitrogen oxidizing bacteria had little selectivity to organic carbon source,but manganese oxidizing bacteria showed certain selectivity to succinate.When C/N was 20-25,the activity of iron-manganese ammonia-nitrogen bacteria was the strongest.The ferric,manganese and ammonia mainly include Acinetobacter,Undibacterium,Pseudomonas,Bacillus,Arthrobacter,Brevundimonas etc in groundwater.?3?The simulation experimental study on the in-situ removal of ammonia nitrogen,iron and manganese showed that the removal effect of ammonia nitrogen,iron and manganese was better when the pH value was 7.5-8.5 and the DO value was more than 5.5mg/L.The flow rate significantly affected the removal efficiency of iron,manganese and ammonia nitrogen,and the change of flow rate had the most obvious effect on the removal of manganese,followed by ammonia nitrogen.The removal rate of iron,manganese and ammonia nitrogen increases with the increase of pH value,the pH value has the least effect on the removal of iron,and the effect on ammonia nitrogen is the most significant.The alkaline environment is beneficial to the formation of Fe-Mn oxides and increases the adsorption of NH₄⁺.Increasing the content of dissolved oxygen is helpful to the removal of iron,manganese and ammonia nitrogen.Fe²⁺has the strongest ability to compete for dissolved oxygen.The removal rate of iron,manganese and ammonia nitrogen is not significantly improved by increasing dissolved oxygen content under acidic conditions.When the hydraulic load of filter media is 0.71t/?h·m³?,there is a certain linear relationship between the removal rate of iron,manganese and ammonia nitrogen and the effluent flow rate,namely Y_Fe?%?=-0.1782Q+96.303,Y_Mn?%?=-0.4383Q+93.998,Y_NH4+-N?%?=-0.8866Q+87.408.The in-situ simulation experiment showed that the optimum backwashing time was 6 min,and the turbidity and concentration of iron,manganese and ammonia nitrogen of effluent after backwash were 37.4NTU,0.037mg/L,0.032 mg/L and 0.048mg/L,respectively.?4?Iron,manganese and ammonia nitrogen oxidizing bacteria can effectively enhance the removal efficiency of iron,manganese and ammonia nitrogen by volcanic slag.The removal of iron,manganese and ammonia nitrogen by simulated column depends not only on the adsorption and interception of volcanic slag in the column,but also on the further oxidation of low valence iron,manganese and ammonia nitrogen by bacteria.When the dissolved oxygen content is more than 4 mg/L,the enhancing effect of the oxidizing bacteria is obvious,and the oxidizing effect is stronger in alkaline environment.Iron,manganese and ammonia nitrogen oxidizing bacteria have a strong enzyme activity at 30?.Ca²⁺,Mg²⁺have a certain promoting effect on the activity of the oxidizing enzyme,while Pb²⁺,Ba²⁺have obvious inhibitory effect.These oxidizing bacteria mainly include:Curvibacter,Prosthecobacter and Brevundimonas,etc,which provide favorable conditions for oxidation of iron,manganese and ammonia nitrogen.?5?The site verification test shows that the in-situ treatment process designed in this paper has a good effect on the removal of iron ammonia nitrogen,and manganese in groundwater,and the process realizes the in-situ removal of iron ammonia nitrogen,and manganese in groundwater.The optimum parameters of in-situ treatment are as follows:Effluent volume 4.0 m³/h?Q?4.5 m³/h,3.5 m³/h?aeration volume?4.0 m³/h,7.5?pH?8.5.The in-situ treatment process has a significant effect on the microbial community in groundwater,and the abundance of each phylum,species and genus of microorganisms in groundwater has changed obviously.The comprehensive benefit analysis shows that compared with the traditional ectopic treatment,the in-situ treatment process can save 0.21 yuan/ton of treatment cost and water treatment cost by about 15%,and the in-situ treatment has the advantages of saving land resources and less affected by the change of environmental temperature.It is suitable for decentralized water supply in villages and towns in Northeast China.