Treated wastewater residuals, or biosolids, are land applied to condition soil but are also known to contain persistent emerging contaminants. In 2014, a Mid-Atlantic region WWTP plant implemented thermal hydrolysis process (THP) and anaerobic digestion (AD) to produce biogas and highly stabilized biosolids suitable for increased agricultural applications. The THP-AD system replaces lime stabilization previously used at this WWTP. Previous research indicated that the total concentration of PBDEs is lower in THP-AD treated final biosolids samples than in historic lime-stabilized final biosolids samples. We will present research to determine if the THP-AD system causes biological and physical degradation of PBDE-contaminated biosolids during the treatment process.  The anaerobic digestion of sludge containing PBDEs was modeled using laboratory-scale batch reactors. Analysis of sludge from the AD mesocosms using quantitative polymerase chain reaction (qPCR) revealed growth of obligate dehalogenating bacteria <i>Dehalobacter </i>in mesocosms fed with both THP-treated and non-THP-treated sludge. Gel electrophoresis results also indicate the presence of <i>Dehalogenamonas</i> and several other know dehalogenating bacteria in the anaerobic sludge mesocosms This suggests that ADs fed with both THP and non-THP treated sludge have the potential to biodegrade halogenated PBDEs. We will present ongoing GC-MS work targeting the congener distribution of PBDEs occurring in the mesocosm experiment to assess whether dehalogenating bacteria selectively debrominate specific PBDEs. Both anaerobic treatments contained methanogenic and fermenting microbial community structures that could support reductive dehalogenation, as confirmed by 16s rRNA-based Illumina sequencing of mesocosms.  Additional work is being conducted to quantify PBDE concentrations in historical limed biosolids sampled from 2011 to 2013 when PBDEs were phased out of production in the U.S. These results will help discern whether the chemical phase-out or change to the THP-AD treatment is responsible for lower concentrations of PBDEs measured in full-scale THP-AD treated biosolids recycled to agricultural lands.

Distributions and degradation of brominated flame retardants (PBDEs) in limed and THP-AD treated wastewater biosolids

2019 Fall National Meeting

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