Evaluation And Analysis Of Efficiency Of Sulfur Autotrophic Constructed Wetland And Study On Nitrogen And Sulfur Cycle

Nitrogen pollutants produced by human activities are the crucial factors that cause eutrophication and the malodorous black water.The discharge of nitrogen pollutants without appropriate treatment results in the further loss of ecological functions and the gradual reduction of environmental capacity.It is vital to control water eutrophication and guarantee ecological and water security to deeply reduce the nitrogen pollution discharged into the environment from the source.Constructed wetland as an ecological treatment technology has been widely used in sewage treatment.However,in the treatment of low carbon/nitrogen ratio wastewater,it usually faces such problems as hindered denitrification process caused by lack of electron donor,will lead to low total nitrogen treatment capacity and substandard effluent.These issues can be solved by strengthening the autotrophic denitrification in constructed wetlands.Given these situations,this study introduced sulfur-based substrate into the vertical subsurface constructed wetlands.Compared with the traditional constructed wetlands,studied the denitrification efficiency of sulfur-based enhanced constructed wetlands in the treatment of low carbon/nitrogen ratio wastewater.Quantitative analysis of the nitrogen and sulfur cycling process in enhanced constructed wetlands.The main factors affecting the processing efficiency were studied.The quantitative contribution of each nitrogen removal path,the rule of product transformation and formation,and the microbial structure and groups were clarified.Besides,the composite constructed wetland system was constructed by improving the operation mode of process combination.In order to solve the problem of low ammonia nitrogen treatment efficiency in the operation of single stage flow sulfur-based enhanced constructed wetlands.The results showed that when the total inorganic nitrogen was 20.97±0.78 mg/L,nitrate 12.68±0.63 mg/L,and ammonia 8.28±0.92 mg/L,the total inorganic nitrogen was controlled at 6.58±2.19 mg/L,nitrate 2.16±1.3 mg/L and ammonia 4.34±1.01mg/L in outflow.The total inorganic nitrogen removal load was 1426.42±570.33 mg N·m^-2·d^-1,and the removal rate was 68.5±10.74%.The sulfur base substrate enhanced the removal of nitrate,about 428.03 mg N·m^-2·d^-1 nitrogen removal load was increased,but had a negative effect on the removal of ammonia nitrogen.The optimal hydraulic retention time was 2 d,taking into account the processing capacity and the generation of by-products.The denitrification pathways in the system were:59.26%for microorganisms,3.43%for plants,1.63%for substrates,and 35.67%for outflow.The mass ratio of nitrate removal to sulfate production was 1:9.92,the sulfate concentration was 124.22±38.13 mg/L in outflow.Sulfide was mainly derived from sulfate reduction,and concentration of sulfide was 0.7±0.57 mg/L in outflow.Thiobacillus was the main autotrophic bacteria,with a relative abundance of 2.64%.In order to further improve the removal of ammonia nitrogen and control the generation of by-products,the composite constructed wetlands systems A and B were constructed,and the effects of two different flow patterns on the denitrification efficiency of the composite system were compared.The results showed that the change of inflow state improved the dissolved oxygen level in the systems and enhanced the ammonia nitrogen removal capacity of the composite constructed wetlands systems.The difference of nitrogen removal between the two systems was mainly generated in the S2 denitrification system.Total inorganic nitrogen removal rate of system A was 70.35±4.63%,and total inorganic nitrogen removal rate of system B was 81.42±3.26%.The constructed wetlands systems are set up in a hierarchical way,with the front end running in aerobic state and the back end running in anaerobic?anoxic?alternately,which improves the removal capacity of the grading system for different nitrogen pollutants,thus greatly improving the nitrogen removal capacity of the composite constructed wetland system.The average effluent sulfide concentration of system A was lower than 0.1 mg/L,and that of system B was0.63±0.089 mg/L.The improved process form controls the generation of reaction by-products,improves the treatment effect and avoids the potential ecological risks of by-products.The form of sulfur autotrophic process introduced into the constructed wetlands systems are more suitable to be embedded in the form of terminal modularization.