Thermal Hydrolysis Pretreatment Effects on Endocrine Disrupting Compounds and Microbial Communities in Wastewater Sludge from Anaerobic Digestion

Abstract

Concerns regarding endocrine disrupting compounds (EDCs) in wastewater treatment plant effluents have led to the need to better understand their fate during various treatment processes. The thermal hydrolysis process (THP) is a growing technology; this article aims to better understand the impacts of THP on EDCs. Serum bottles were used to understand how the THP of anaerobically digested wastewater influences concentrations of phthalic acid esters (PAEs) and antimicrobials. The succession of DNA-based microbial community was followed to assess conditions of contaminant biotransformation. Sludge samples were collected at different locations, placed in 250 mL serum bottles, and inoculated with samples collected from the anaerobic digestion solid recycle line to compare the influence of the THP pretreatment. Bottles were covered, kept at 37°C, and agitated for 22 days, with periodic destructive sampling for the chemical analysis of antimicrobials, PAEs, and transformation products, as well as the microbial community structure. Results demonstrated an increase in the concentrations of triclosan (TCS), triclocarban (TCC), and their transformation products with and without THP pretreatment. 2,4-Dichlorophenol increased at a significantly higher rate in pretreated sludge, while the TCC concentrations increased significantly faster in untreated sludge. Pretreatment did not significantly influence the formation rates of TCS and methyl triclosan. Pretreatment impacts on phthalate concentrations varied. Di(2-ethylhexyl) phthalate decreased and diisononyl phthalate concentrations were unchanged. Benzyl butyl phthalate increased in sludge that had undergone pretreatment and decreased in sludge without. PAE metabolites generally increased during the course of the experiments. Results demonstrate the potential for complex transformation processes and indicate the ability of THP to influence concentrations of certain compounds of concern. Analysis of the microbial community structure did not demonstrate any statistically significant difference between sludge with pretreatment and sludge without over the course of the experiment. These results indicate that changes in chemical concentrations could be due to other physicochemical mechanisms not examined.