| In view of the comprehensive factors such as the quantity and quality of rural domestic sewage in arid and semi-arid areas of northwest China and the shortage of farmland irrigation water,this subject proposes a combined process of high-efficiency(irregular corrugated plate)hydrolytic acidification and horizontal subsurface flow constructed wetland to treat rural domestic sewage,and the process has good removal effect on organic pollutants in sewage,and can retain nutrient elements required by crops such as nitrogen and phosphorus in sewage to a greater extent.Firstly,the static and dynamic experiments of nitrogen and phosphorus removal by filler adsorption were carried out to compare and select the filler with poor nitrogen and phosphorus adsorption capacity.Then,the removal effects and influencing factors of COD,ammonium nitrogen,TN and TP in rural domestic sewage by high-efficiency(corrugated plate)hydrolytic acidification treatment unit and horizontal subsurface flow constructed wetland unit were respectively studied through the establishment of simulation device,and confirm the best operation parameters for treatment unit,and inspect the removal rate of overall system for COD,TN,TP,ammonium nitrogen and SS.The test results show that:(1)Langmuir and Freundlich adsorption isotherm equations are used to fit adsorption isotherm curves for nitrogen and phosphorus removal characteristics of anthracite,zeolite,medical stone and magnetite.The study found that Langmuir isothermal adsorption equation is suitable to describe the characteristic changes of adsorption and phosphorus removal of Maifanitum,magnetite and anthracite fillers,and it is also suitable to describe the characteristic changes of adsorption and nitrogen removal of Maifanitum and zeolite.The Freundlich isothermal adsorption curve is suitable for describing the adsorption and phosphorus removal characteristics of zeolite fillers,and it is also suitable for describing the adsorption and nitrogen removal characteristics of anthracite and magnetite fillers.The theoretical saturated adsorption amount of phosphorus in the four fillers is anthracite,zeolite,magnetite and Maifanitum from large to small,and the theoretical saturated amount of nitrogen is zeolite,anthracite,magnetite and Maifanitum from large to small.The adsorption capacity of Maifanitum filler to nitrogen and phosphorus is weak.Selecting Maifanitum as the filler of constructed wetland can retain nitrogen,phosphorus and other nutrient elements needed by crops to a greater extent.(2)In the start-up phase,by comparing the COD removal effects of straight plate and high-efficiency(different corrugated plate)hydrolysis acidification tank,it can be found that the COD removal rates of both reach a stable value at about 74 d,and the start-up is completed.In the start-up phase,the average retention rate of ammonium nitrogen in domestic sewage in the high-efficiency(irregular corrugated plate)hydrolysis acidification tank increasing from 108.67% to 113.61%,and finally decreasing to 111.45%;The averageretention rate of TN in domestic sewage increased from 84.26% to 92.24% and finally to95.27%.The average retention rate of TP in domestic sewage increased from 71.64% to87.43%,and finally decreased to 77.82%.In the operation stage,by comparing the COD removal effects of straight plates with different hydraulic retention times(12 h,18 h and 24 h)and high efficiency(different corrugated plates)hydrolytic acidification tanks,it can be found that the COD removal rates of both increase with the extension of hydraulic retention time.The hydraulic retention time was 12 h.The average removal rate of COD in domestic sewage by straight-strip hydrolytic acidification tanks was 19.17%,while the average removal rate of COD in domestic sewage by high-efficiency(differential wave-folding)hydrolytic acidification tanks was 34.59%,an increase of 15.41%.At a hydraulic retention time of 18 h,the average removal rate of COD in domestic sewage by straight-strip hydrolytic acidification tanks was 22.75%,while the average removal rate of COD in domestic sewage by high-efficiency(different wave-folded plate)hydrolytic acidification tanks was 44.99%,an increase of 22.24%.The hydraulic retention time was 24 h.The average removal rate of COD in domestic sewage by straight-strip hydrolytic acidification tank was 34.35%,while the average removal rate of COD in domestic sewage by high-efficiency(different wave-folded plate)hydrolytic acidification tank was 58.89%,an increase of 24.54%.Compared with the straight plate hydrolytic acidification tank,the high-efficiency(isowave folding plate)hydrolytic acidification tank improves the removal rate of COD in domestic sewage.Compared with the straight plate hydrolytic acidification tank,the efficiency of the removal of COD in domestic sewage is different in the high-efficiency(different wave-folded plate)hydrolytic acidification tank under different hydraulic retention times.At the optimal hydraulic retention time of 24 h,the average removal rate of COD in the high-efficiency(heterocorrugated plate)hydrolysis acidification tank is 58.89%,and the average retention rates of ammonium nitrogen,TN and TP are 121.56%,85.49% and 75.00%,respectively.The high-efficiency hydrolysis acidification tank can remove COD to a greater extent,and can better retain nutrients required by crops such as nitrogen and phosphorus.In addition,with the increase of COD concentration(low,medium and high),the removal rate of COD in influent by high-efficiency(different corrugated plate)hydrolysis acidification tank increases,but the retention rates of TN,TP and ammonia nitrogen are not significantly affected.With the increase of reaction temperature(8-10?,10-20? and 20-25?),the removal rate of COD and the retention rates of TN and TP in influent by high-efficiency(corrugated plate)hydrolysis acidification tank decreased to different degrees,while the retention rate of ammonium nitrogen in influent increased.(3)The removal rate of COD in influent is generally not high in the horizontal subsurface flow constructed wetland of Maifanitum filler type during startup,ranging from19.88% to 61.08%.The retention rate of ammonium nitrogen in domestic sewage is relatively high,showing a trend of decreasing first and then stabilizing,ranging from 56.62% to 91.95%.The retention rate of TN in domestic sewage is relatively high,showing a trend of first decreasing,then increasing,then decreasing,and finally stabilizing,ranging from 74.17% to97.80%.The retention rate of TP in domestic sewage is relatively high,showing a trend of first increasing,then decreasing and finally stabilizing,ranging from 53.95% to 86.19%.The horizontal subsurface flow constructed wetland was started in 54 days.In the operation stage,the hydraulic retention time of sewage in the horizontal subsurface flow constructed wetland is controlled to be 12 h,18 h and 24 h,and the COD concentration(low,medium and high)and temperature(8-10?,10-20? and 20-25?)in the influent water.With the extension of hydraulic retention time,the removal rate of COD in the influent of horizontal subsurface flow constructed wetland increases,while the retention rates of ammonium nitrogen,TN and TP decrease to different degrees.At the optimum hydraulic retention time of 12 h,the average retention rates of COD,ammonium nitrogen,TN and TP in the influent of the horizontal subsurface flow constructed wetland reach 53.93%,57.99%,79.09% and 77.30% respectively.The removal of COD can meet the requirements,but it can better retain nutrients required by crops such as nitrogen and phosphorus.In addition,with the increase of COD concentration,the removal rate of COD in the influent of horizontal subsurface flow constructed wetland increases,but the retention rate of ammonium nitrogen,TN and TP has little effect.With the increase of reaction temperature,the removal rate of COD in influent by horizontal subsurface flow constructed wetland increased to different degrees,while the retention rate of ammonium nitrogen and TN decreased to different degrees,while the retention rate of TP in influent had little effect.(4)During stable operation,the removal rates of COD and SS are 76.87-82.56% and90.92-94.69% respectively,while the retention rates of ammonium nitrogen,TN and TP are53.11-60.69%,68.88-78.22% and 54.30-65.24% respectively.The high-efficiency(irregular corrugated plate)hydrolytic acidification-horizontal subsurface flow constructed wetland technology was used to treat rural domestic sewage.The average effluent concentration of COD and SS in the effluent water quality met the requirements of the "Water Quality Standard for Farmland Irrigation"(GB5084-2005),while the retention rate of ammonium nitrogen,TN and TP was high,and the average effluent concentration was high,which retained the nutrients required by crops such as nitrogen and phosphorus in domestic sewage to the greatest extent. |
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