Abstract
Diethylhexyl phthalate (DEHP) is a common plasticizer in industrial production. Recently, environmental problems caused by microplastics have drawn wide attention. As the microplastics have a large specific surface area, the release rate of the plasticizer from the microplastics to the environment is accelerated. The DEHP in the wastewater enters the wastewater treatment plants (WWTPs) along with the urban pipeline. After DEHP enters the WWTPs, it may affect the anaerobic fermentation with waste activated sludge (WAS) as raw material. So far, there has been no study on the effect of DEHP on anaerobic fermentation of WAS. Our study focused on the impact of exogenous DEHP on WAS anaerobic fermentation, and the results showed that DEHP mainly affects the solubilization stage of sludge anaerobic digestion, but has no significant effect on other stages. It does not affect the total yield and composition of short-chain fatty acids (SCFA). However, DEHP inhibited the solubilization process of WAS anaerobic fermentation, which was mainly manifested by the changes of soluble protein and soluble polysaccharide in the system. The results of the analysis of microbial communities revealed that the addition of DEHP did not change the diversity of microbial communities, but caused a change in the abundance of microbial organisms. DEHP reduced the abundance of acetogen bacteria and increased the abundance of methanogens. This work provides some insights into WAS fermentation systems in the presence of DEHP and helps to gain a better understanding of the potential environmental hazards of microplastics.
Highlights
Phthalate esters (PAEs) are one of the most widely used groups of industrial products [1,2,3]. ey are primarily used in the production of polyvinyl chloride to make it more gentle and flexible [3,4,5] and as plasticizers for building materials and furniture, food packaging, and mosquito repellents [5,6,7].e exceptional performance of PAEs has promoted them as plasticizers and additives in the plastic production industry for decades [8]
Sources of waste activated sludge (WAS) and Diethylhexyl phthalate (DEHP). e WAS used in this study was extracted from the secondary sedimentation tank of a municipal wastewater treatment plants (WWTPs) in Changsha, China. e fresh sludge was shaken evenly and passed through the stainless-steel filter steel mesh (0.45 mm). e filtered sludge was concentrated at 4°C for 24 h to gain the concentrated sludge used in the study. e relevant properties of concentrated sludge are as follows: pH 6.8 ± 0.1, total suspended solids (TSS) 17640 ± 510 mg/L, volatile suspended solids (VSS) 15340 ± 230 mg/L, total of chemical oxygen demand (COD) 16134 ± 540 mg/L, soluble chemical oxygen demand (SCOD) 480 ± 10 mg/L, total carbohydrate 1590 ± 270 mg COD/L, and total protein 10340 ± 460 mg COD/L
From the 1st day to the 5th day, the short-chain fatty acids (SCFA) content continues to rise and reached the maximum on the 5th day. en, the production of SCFA gradually decreased until day 8, and the total SCFA content in all reaction systems increased slightly and reached the second peak on day 9. en, the production of SCFA continued to decrease in the remaining time. e two increasing trends of SCFA production during anaerobic fermentation are inconsistent with the results of previous studies [47, 48]
Summary
Phthalate esters (PAEs) are one of the most widely used groups of industrial products [1,2,3]. E exceptional performance of PAEs has promoted them as plasticizers and additives in the plastic production industry for decades [8]. Some researches [25,26,27] have reported that industrial products such as microplastics and rubber release large amounts of PAEs, which enter WWTPs through raw wastewater. As the major by-product of sewage treatment, wasted sludge contains a large number of organic pollutants such as PAEs [28]. Lots of PAEs with high molecular weight, like DEHP, are adsorbed into the biological grease and remain in the sludge
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