Study On Removal Of Organic Micropollutants Phthalic Acid Esters In Constructed Wetland Treating Sewage Wastewater

Constructed wetland systems (CWs) especially subsurface constructed wetlands (SSFCW) are widely used to remove pollutants in sewage in the world as an efficient technology. At present, the constructed wetlands are satisfied to remove regular pollutants, but very few studies are available on the removal of organic micropollutants utilizing constructed wetlands. Although organic micropollutants present in the environment at low concentration, they are harmful to the ecology and human. Phthalic acid esters have potential danger to human health as the most ubiquitous organic micropollutants. The phthalic acid asters were selected as model substances to investigate the removal of organic micropollutants in the constructed wetland. The main contents are as follows: (1) the removal efficiency of organic micropollutants in domestic sewage in a subsurface constructed wetland; (2) the main mechanism of micropollutants removal for the subsurface constructed wetland; (3) the factors afflecting the removal efficiency of organic micropollutants in the subsurface constructed wetland.The results are as follows:1. In the subsurface constructed wetland system, 4 PAEs, namely, DEP,DBP,BBP and DEHP were detected in the influent, and∑PAEs was 12.17μg L^-1; 3 PAEs,namely, DEP,DBP and DEHP were detected in effluent water with average∑PAEs of 9.75μg L^-1 The concentration of DEHP was the highest, which exceeded 80% of∑PAEs, followed by DBP. Detection frequency of DEHP and DBP were 100% both in influent and effluents, followed by DEP; BBP was found only in the influent water occasionally.2. The removal efficiency of DEP was about 50%, which was higher than that of DBP and DEHP, which was less than 30%. From upper to the bottom and along the flow of the subsurface constructed wetland, the concentration of PAEs reduced gradually. 3. The mechanism of organic micropllutants PAEs removal in the constructed wetland was controlled by microbial, adsorption on granular, and so on. The microbial activity played an important role in removing of PAEs; the removal of TOC had significant effect on PAEs removal. During the experimental period, the low oxygen level in the constructed wetland reveals the predominance of anaerobic conditions; and low ORP in the wetland beds (the average was below -300mv) indicated the reduced conditions in the wetland beds. Under anaerobic and reduced conditions, methanogenisis was of major biochemical process to remove organic matters. The removal of PAEs increased significantly with the increasing removal of volatile fatty acids. The removal of PAEs was significantly related to that of TN, showing that denitrification played an important role in PAEs removal. The ratio of C to N had positive relation to the removal of PAEs. PAEs could be also removed by granular sorption, especially for the PAEs with higher logK_ow.4. No significant differences were observed between the bed aspect ratio for the removal of PAEs, and a similar result was observed between granular medium sizes. The beds with water depth of 0.7 m had higher removal efficiency for organic micropollutan PAEs than that of 0.5 m. the operational parameters such as temperature and HRT could affect the PAEs removal. The removal of DEP, DBP and DEHP increased with the temperature. However, better performance was found for the three PAEs removal under lower HRT (0.5d), and the PAEs removal decreased when HRT was longer.