| In this dissertation, we explored the constructed wetlands used to treat agricultural or industrial wastewater containing 1,2-dichlorobenzene as a representative of Chlorobenzenes organic pollutants. Firstly, the adsorption properties of 1,2-dichlorobenzene in three soil substrates from constructed wetlands were studied, which provided theoretical basis for the adsorption of soil matrix in the construction of artificial wetland treating 1,2-dichlorobenzene wastewater. The research was focused on wastewater treatment effect of four pilot constructed wetlands under the optimal hydraulic retention time and pollutants loading, discussing the feasibility of constructed wetland technology treating wastewater. The 1,2-dichlorobenzene remained in the wetlands soil and of reeds tissue were detected, ensuring the security of constructed wetland technology.The adsorption characteristics of 1,2-dichlorobenzene in three soil substrates from pilot constructed wetlands were studied with the balanced oscillation. The results showed that o-DCB achieved adsorption equilibrium in 12 hours, educing the first-order adsorption rate constants of three soils by Lagergren equation that are 0.3338 h-1,0.2679 h-1 and 0.2537 h-1, respectively, which indicated the adsorption capacity of loam is higher than that of fine sand or coarse sand. The adsorption isothermal line on 30℃could be described by Freudlich or Langmuir equation, which was actually a transition state from physisorption to chemisorption, simultaneously considered the adsorption amount of o-DCB by loam firstly decreased then raised and decline finally with the increase of temperature. Being one of nonionic organic compounds with strong hydrophobicity, o-DCB adsorbed in soils intensified at acidic or alkaline conditions,indicating the partitioning effect played a key role.Considering the removal and economic efficiency of 1,2-dichlorobenzene wastewater, the optimal HRT was determined at 5 d and ALR was suggested on 150 mg·m-2d-1, when the o-DCB removal efficiencies of W-L, W-F, W-C and W-Z were 81.2%,71.1%,72.4% and 65.2% respectively. The four constructed wetlands carried out for four months from July to October,2009. The performance of systems during operation time was upmost in mid-August and decline in the evening of October, in order of W-L＞W-C＞W-Z＞W-F. As the substrate of constructed wetlands, loam and coarse sand showed respective advantage, while W-F system using of fine sand blocked up in the end and ran sluggishly. In order to investigate the pollutant removal and the influence of plants in the pilot-scale CWs, the concentration of o-DCB and DO were measured at various distances from the inflow and depths of the W-L and W-Z constructed wetlands, which revealed that oxygen concentration played an important role for 1,2-dichlorobenzene removal and the presence of reeds greatly improved the dissolved oxygen conditions for removing pollutants in the dominated aerobic biodegradation process.The quantity of 1,2-dichlorobenzene remained in wetland soil decreased along the flow direction and increased with the depth of soil layers. The residues in soils of four constructed wetlands were in order of W-L＜W-C＜W-F＜W-Z, all of which were less than 0.65 mg·kg-1. The quantity of 1,2-dichlorobenzene remained in the reeds tissue of root, stem and leaf were 30.28μg·g-1,14.85μg·g-1 and 6.18μg·g-1. The residues in the reeds body of three constructed wetlands were in order of W-L＞W-C＞W-Z, which revealed that the better growing of reeds, the more o-DCB absorbed and enriched in the plants. |
