Fundamental Research On Application Of Different Hybrid Constructed Wetland In Treating Domestic Sewage Of Rural Area

Insufficient oxygen supply and low temperature environment are the main reasons for the reduction of pollutant removal of domestic sewage in the conventional constructed wetlands?CW?.In addition,different combinations of CW also affect its removal effect of pollutants.In view of this,this paper studied the winter start-up characteristics of different combinations of hybrid constructed wetlands?HCW?for domestic sewage treatment with two sets of parallel operation of HCWs for HF-VF?HFCW and VFCW?and VF-HF?VFCW and HFCW?.Then,the effects of three important factors of aeration mode,hydraulic load ratio and aeration amount were studied on the treatment of actual domestic sewage by the HCWs.Based on this,the removal approach of nitrogen and phosphorus in the system was analyzed when HCW treats actual domestic sewage.Finally,the treatment effect of domestic sewage under low-temperature conditions was studied,and the strengthening strategy of HCW treatment of domestic sewage under low temperature environment was explored.The main results and conclusions are as follows:?1?During low-temperature start-up period,the continuous aeration of the first-stage in HCW with an air-water ratio of 6.5:1 can significantly increase the DO concentration in the system and quickly increase the system's capability to treat the pollution.The removal ratio of major pollutants such as SS and COD in both HCWs was tended to be stable after start-up of 16 days.The average removal ratio of SS was greater than 91.0%,and the average removal ratio of COD was greater than 72.0%.Moreover,the plant tillering did not stop and the plant height continued to increase when HCW started up at low temperature in winter.Therefore,low temperature had little effect on the start-up of the CW from the perspective of plant tillering and plant height change.In particular,the CW can quickly reach a certain treatment in a short time with the strengthen start-up by aeration,and effectively reduced the concentration of major pollutants such as SS,COD and NH₄⁺-N in the system.?2?During the five operating phases of aeration-enhanced in spring,summer,and autumn,the removal ratio of SS,COD,TN,NH₄⁺-N and TP were 96.1%,90.6%,61.6%,98.8%and 48.2%in HF-VF,respectively.The removal ratio of SS,COD,TN,NH₄⁺-N and TP were 96.9%,87.9%,75.8%,90.3%and 48.6%inVF-HF,respectively.The results showed that there has little difference in the removal of SS for both systems.The removal of COD and NH₄⁺-N in HF-VF was better than that in VF-HF.However,the removal of TN in VF-HF was better than that in HF-VF,which can ensure the effluent of SS,COD,TN,NH₄⁺-N meet the first A standard of"Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant"?GB18918-2002?.Therefore,VF-HF is the better combination when treating actual domestic sewage.?3?The removal ratios of COD and NH₄⁺-N were 91.1%and 98.7%when using continuous aeration,90.0%and 99.5%when using intermittent aeration with 1h interval time,91.5%and 99.6%when using intermittent aeration with 2h interval time in HF-VF under the same daily aeration,respectively.Correspondingly,the removal ratios of COD and NH₄⁺-N were 86.6%and 91.7%,86.4%and 89.8,87.9%and 94.4%in VF-HF under the corresponding three aeration modes,respectively.Therefore,the aeration mode had little effect on the removal of COD and NH₄⁺-N in the same HCW,but the removal ratios of COD and NH₄⁺-N of HF-VF were significantly greater than that of VF-HF in the same mode.In addition,the removal ratio of TN in HF-VF was increased by 5.6%and 8.4%,while the removal ratio of TN in VF-HF was increased by 11.7%and 14.4%,respectively when the aeration interval time was increased from 0h to 1hour and 2 hours.The results showed that increasing the aeration interval time can improve the removal ratio of TN by HCWs.?4?The microbial biomass,nitrification activity and denitrification activity on the surface of the filler near the plant rhizosphere were 1.6,1.8 and 1.2 times of those in the non-rhizosphere zones in HF-VF.Meanwhile the microbial biomass,nitrification activity and denitrification activity on the surface of the filler near the plant rhizosphere were 2.2,1.5 and 1.1 times of those in the non-rhizosphere zones in VF-HF.In addition,the microbial nitrification activity on the surface of the filler in VF-HF was 1.2 times that of HF-VF.Therefore,the microbial biomass and activity on the surface of the filler near the plant rhizosphere were significantly greater than those in the non-rhizosphere zones,and the effect of plant rhizosphere on the nitrification activity of microorganisms was significantly greater than that on denitrification activity in HCWs.?5?The average amounts of nitrogen and phosphorus absorbed by phragmites australis stems and leaves were 38.98g N/kg plant?dw?and 2.96g P/kg plant?dw?,and the uptake of nitrogen and phosphorus by the P.australis roots was 28.87g N/kg plant?dw?and 4.17g P/kg plant?dw?.The P.australis stems and leaves uptake contributed11.04%and 19.21%to TN and TP removal,and the P.australis roots uptake contributed1.58%and 5.12%to TN and TP removal in HF-VF.The P.australis stems and leaves uptake contributed 9.34%and 20.88%to TN and TP removal,and the P.australis roots uptake contributed 1.39%and 7.76%to TN and TP removal in VF-HF.Therefore,the uptake amount of TN by the unit dry weight of stems and leaves of P.australis was 1.35times that of the roots,while the uptake amount of TP by the latter was 1.41 times that of the former.?6?The Both systems were performed in the low-temperature environment with intermittent aeration at the first stage of HCW,where the time ratio of aeration and non-aeration ratio was 1:2 and the aeration interval is 2 hours under the same gas-water ratio of 6.5:1.The effluent concentrations of COD,TN and NH₄⁺-N were 23.12,28.08and 0.24mg/L,which was increased by 26.1%,31.6%and 71.5%in HF-VF,respectively when compared with non-aeration.In addition,the effluent concentrations of COD,TN and NH₄⁺-N were 26.49,15.13 and 6.79mg/L,which was increased by19.9%,44.4%and 55.9%in VF-HF,respectively when compared with non-aeration.Therefore,the aeration enhancement of HCW can make up for the shortcomings of the limited oxygen secretion ability of plants during the dormant period in winter,and significantly improve the removal effect of COD,TN,NH₄⁺-N in the system.