| The synergistic effect of the substrates, plants and microorganisms of constructed wetlands have been widely applied to treat the agricultural, industrial and domestic sewage. Constructed wetlands have good application prospect due to the characteristics of low construction and management cost, high decontamination and landscape benefits. Based on the concept, classification, mechanism and research progress of constructed wetlands, hydraulics and aeration play important roles in the whole system, so the model experiments of hydraulic loading and aeration conditions were carried out, then a pilot-scale verification test went on.During the indoor model experiments, gravel, zeolite and slag were used as substrate. The surface flow constructed wetland (A) and subsurface flow constructed wetland (B) were designed to establish four kinds of two-stage series systems as AA, AB, BA, BB and one kind of three-stage series system as BBB. Synthetic wastewater (inferior Class V) was configured as influent water. In the hydraulic loading experiment, there were five gradients of hydraulic loadings:0.12,0.19,0.28,0.42 and 0.69 m3/(m2·d). The effect of hydraulic loadings, combination types and their interaction on the removal efficiency was studied in order to fit function relations between removal rate, amount of pollutant and hydraulic loadings so that the best hydraulic load ranges were determined. In the aeration experiment, aeration position was located in bottom, middle and surface of the wetland bed, and the air-water ratio was as 3:1,6:1 and 9:1. Also effect of aeration positions, aeration amount and their interactions were obtained through dualistic variance analysis.According to the model experiments, experimental work was carried out in a pilot-scale base with length of 1.1 km in Zhengzhou City. From December 2014 to April 2015, under the hydraulic loadings of 0.15,0.3 and 0.45 m3/(m2·d), the removal efficiency of each part of the pilot-scale base was monitoried. Effect of hydraulic loading on the decontamination was verificated, the changes of each part were better known.The main results of the research were as follows:(1) Combination types had significant influence on removal efficiency only under low hydraulic loadings (p<0.05), AA was the best, while BB worst. There was a significantly negative linear correlation between the removal rate of pollutants and the hydraulic loadings (p<0.01), so there was quadric relationship between the removal amount and the hydraulic loadings. Through the quadratic function, the best hydraulic loading ranges of COD, NH3-N and PO43--P were 0.31-0.33,0.33-0.36 and 0.36-0.42 m3/(m2·d), respectively. The interaction of combination types and the hydraulic loadings did’t show significant influence (p>0.05).(2) Aeration positions and aeration amount both showed obvious influence on removal efficiency (p<0.05). For COD, and NH3-N, aeration had both positive and negative effect. For PO43--P, aeration had aeration negative effect. For COD, NH3-N and PO43--P, considering the effect of aeration and economic benefits, the best air-water ratio was 6:1, and the best aeration position was bottom. For PO43--P, the larger air-water ratio we set, the worse decontamination we got. The interaction of aeration positions and aeration amount did’t show significant effect on removal efficiency (p>0.05).(3) In the lasting five months of the test base monitoring, when influent water was seriously polluted, as COD>100 mg/L, NH3-N>5 mg/L, TP<3 mg/L, the greater the hydraulic loading was, the worse decontamination we found. However, when influent water was relatively clean, as COD<100 mg/L, NH3-N<5 mg/L, TP<3 mg/Lthe hydraulic loadings had little effect on the removal efficiency.(4)In the first 6 months’operation of the base, the removal rate of COD of part 1 to 6 was 4.45%,5.42%,29.12%,6.79%,4.27%,4.44%, respectively. The removal rate of NH3-N of part 1 to 6 was 14.1%,10.44%,3.48%,3%,10%,9.72%, respectively. The removal rate of TP of part 1 to 6 was 4.78%,11.03%,3.68%, 13.82%,4.52%,5.72%, respectively. After nearly three years of operation, the removal rate of COD of part 1 to 6 was-10.67%,5.35%,10.01%,10.44%,22.89%, 7.55%, respectively. The removal rate of NH3-N of part 1 to 6 was-9.22%,7.7%, 9.84%,16.69%,24.04%,9.46%, respectively. The removal rate of TP of part 1 to 6 was-6.52%,10%,10.77%,13.53%,20.69%,6.13%, respectively. The decontamination ability of the front part of the test base decreased, and it might even become a source of pollution. |
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