Study On The Removal Of Nh₄-N By Constructed Wetlands With Different Biochar Substrates

Constructed wetland is the most important tool in water ecological restoration project.The subsurface constructed wetland with several layers of substrates has the best decontamination effect,and has no odor and the risk of mosquitoes and flies breeding.Substrate is the key to subsurface wetland.In this paper,Biochar is used to replace gravel,a traditional matrix material.The study is about the effect of ammonia nitrogen removal by subsurface constructed wetlands with three kinds of substrates,which were Eichhornia Crassipes biochar,Cyperus Alternifolius biochar and waste wood biochar in this paper,and indoor simulation and field experiments were carried out.The research results can provide important parameters for the construction of a new type of high-efficiency biochar constructed wetland.It has practical significance for water environmental engineering,such as black and odorous water treatment,agricultural non-point source pollution control,rural scattered domestic sewage treatment,drinking water source protection,and provides important technical guarantee for water safety.The main research contents include:the effects of biomass type and pyrolysis temperature on the carbonization characteristics,surface functional groups and microstructure of biochar were compared and analyzed by physicochemical characterization.,isothermal adsorption of ammonia nitrogen and adsorption kinetics experiments were carried out to analyze the adsorption mechanism of biological carbon on ammonia nitrogen,microbial culture of biochar matrix was carried out to explore the effects of different biochar on wetland matrix,A laboratory experimental column device for biochar matrix in simulated constructed wetland was constructed to study the removal efficiency of ammonia nitrogen by biochar mixed matrix.an indoor simulated constructed wetland biochar matrix column was constructed to study the removal of ammonia nitrogen by biochar mixed matrix,a demonstration project of constructed wetland with biochar matrix was established.The main results are as follows:?1?With the increase of pyrolysis temperature,the biochar yield of the same raw material decreased,the pH value and specific surface area increased.The average pore size of Eichhornia Crassipes biochar increased with temperature?from 4.759 nm to 5.798 nm?,whereas that of Cyperus Alternifolius?from 5.392 nm to 4.598 nm?decreased.The specific surface area and average pore size of W950?the prefixes"S","H"and"W"are abbreviations of Eichhornia Crassipes,Cyperus Alternifolius and waste wood respectively,and the following figures indicate the pyrolysis temperature?are not large because of the high lignin content in the components,even if the preparation temperature is high.?2?The adsorption isotherm of biological carbon to ammonia nitrogen is more consistent with Langmuir model.The maximum adsorption capacity of ammonia nitrogen?mg/g?was2.962?W950?,2.929?S300?,3.538?S500?,3.436?H300?,2.811?H500?,respectively.The adsorption kinetics model is quasi-second-order kinetics model,and the adsorption kinetics of biological carbon to ammonia nitrogen is mainly controlled by chemical action.The best removal condition of ammonia nitrogen is weak acidity?pH=6-7?.?3?The addition of biochar is beneficial to the growth of microorganisms in the matrix,which provides a carrier and nutrients for the growth of microorganisms.The beneficial effects were S>H>W.In general,the removal efficiency of ammonia nitrogen by mixed substrates was H300>H500>A>S500>W950>S300,which is affected by the properties of biochar materials,adsorption capacity and microbial action.?4?The preliminary operation results of constructed wetlands with biochar matrix show that the addition of biochar has little effect on the pH of constructed wetlands.When the concentration of ammonia nitrogen in influent water is low,the removal efficiency of ammonia nitrogen in the constructed wetland with biological carbon matrix subsurface flow is not obvious?the highest removal rate of primary treatment is 12.0%?,and it is speculated that the amount of ammonia nitrogen produced by the strong ammoniation of influent nitrogen is larger.The maximum removal rate of ammonia nitrogen in tertiary wetlands was 51.0%.The maximum removal rates of total nitrogen in primary and tertiary wetlands were 92.3%and73.1%,and the total phosphorus was 70.2%and 80.7%(When COD_Cr content is more than 10mg/L,the removal rate can reach 94.9%).The results show that the addition of biological carbon improves the adsorption capacity of matrix,promotes the growth of matrix microorganisms,and enhances the physical,chemical and microbial functions of constructed wetlands.Thus,the removal effect of pollutants in constructed wetlands can be strengthened,and the ability of anti-impact load of constructed wetlands can also be improved.