Study On Distribution And Removal Efficiencies Of Phthalic Acid Esters In Sewage Treatment Process

Phthalic acid esters (PAEs) are a class of widely used synthetic organic compounds. They can be used as cosmetics, plastic plasticizers, pesticides, lubricants and other raw materials. The most commonly used of PAEs is as plasticizers. In recent years, with the extensive use of plastic products, PAEs has become the most common organic pollutants in the environment. In many countries, PAEs has be listed it as priority pollutants.Urban sewage discharge is an important way of PAEs entering the environment. It has great significance to study on distribution and removal efficiencies of PAEs in sewage treatment process. Six kinds of phthalic acid esters (DMP, DEP, DBP, DEHP, DOP, BBP) had been studied on the effluent and sludge of each process of the main sewage treatment plants in Jinan, which were the first and second Everbright water treatment plants. And the distribution and removal efficiencies of PAEs were analyzed. The main research contents and conclusions were as follows.(1) By comparing the extraction efficiency of PAEs in sewage of the liquid-liquid extraction (LLE) and solid phase extraction (SPE), SPE was selected to extract the six PAEs. This study uses American Supelco company’s C18(3mL,500mg) reversed phase extraction column to extract water samples. The optimized conditions of SPE was followed:SPE was carried out by using1000mL samples, which was loaded onto the extraction column at a flow rate of5mL/min. The PH was adjusted to2.5. The eluant was dichloromethane and its optimum dosage is4mL. Using soxhlet extraction extract the PAEs in sludge. Then anhydrous sodium sulfate-silica gel-alumina column chromatography were used for further purification.(2) The six kinds of PAEs were measured by gas chromatography-mass spectrometry (GC-MS) analysis. Under the optimized conditions, the six kinds of PAEs can be effectively separated, quantitative standard curve has a good linear correlation, the lowest detection limits between0.003to0.007μg/L. The evaluation on qualification control and qualification assurance of the analysis methods indicated that the recoveries of PAEs by SPE-GC-MS method were between83.20and111.78percent, and the relative standard deviations were in the range of2.92～8.99percent, with good reproducibility.(3)The removal efficiencies of the conventional pollution and PAEs were studied on the first and second Everbright water treatment plants. The removal efficiencies of the conventional pollution indicators in the two sewage treatment plant were better, and water quality can meet the first A grade standard of "Urban sewage treatment plant pollutant discharge standard"(GB18918-2002), but PAEs had been detected existing in each process. The five kinds of PAEs (DMP, DEP, DBP, BBP, DEHP) were all detected except DOP. The content of BBP was the highest in all influent and effluent of the two plants, and was much higher than other kinds of PAEs. Contrast with the PAEs distribution situation of the sewage treatment process in October than in August, found that the total content of PAEs was higher in October than in August, and the content of BBP increased the most. Although the concent of PAEs changed in the sewage treatment process, but the distribution trends of each PAEs was roughly consistent along the process. The content of PAEs which is higher in influent, is higher in effluent.The removal of PAEs material mainly occurred in the main process of A2/O. The removal of PAEs by advanced treatment process is not obvious. A2/O process for the removal of PAEs material show a certain regularity:The higher the molecular weight is, and the longer alkyl chains is, and the bigger the n-octanol-water partition coefficient (Kow) is, the lower the removal efficiency is.The content of DMP and DEP was not high in the sludge, and their distribution variation was ont obvious. While most of DBP, BBP and DEHP were adsorbed to sludge, their content was much higher in sludge than in sewage. The distribution pattern of PAEs in the sludge was the same as their in sewage. The concentration of BBP in the sludge is still the highest, and its content is higher in October than in August.