Effect of Cambi Thermal Hydrolysis Process-Anaerobic digestion treatment on concentrations on phthalate plasticisers in wastewater sludge

Authors: ARMSTRONG, DANA - University Of Maryland; HARTMAN, REBECCA - University Of Maryland; Rice, Clifford; RAMIREZ, MARK - District Of Columbia Water & Sewer Authority (DCWASA); TORRENTS, ALBA - University Of Maryland

Submitted to: Environmental Engineering Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Wastewater treatment plants (WWTPs) in the United States have been investing in upgrades to their processes to improve treatment and resource recovery. A local WWTP in the Washington DC area has implemented a new sludge treatment system involving thermal hydrolysis followed by anaerobic digestion treatment (TH-AD). This new system produces Class A biosolids, which allows for more options for the land-application of the treated sludge. Studies in the scientific literature have revealed that numerous organic contaminants of concern, that are not degraded during wastewater treatment, sorb to wastewater sludges – causing the land application of biosolids to act as an environmental source of these contaminants. Understanding how different treatment processes influence concentrations of pollutants is important in understanding the potential environmental impact of these biosolids. Concentrations of 4 phthalate plasticisers, referred to as DiNP, DiDP, DEHP and BBP, were determined in Class A biosoilds that were produced by the TH-AD process. These were compared to concentrations in Class B biosolids produced previously at the WWTP via the liming sludge. Results showed significantly higher concentrations of the phthalate plasticizers in the new Class A biosolids versus the Class B biosolids produced by lime stabilization. Analysis of samples from individual stages of the TH-AD treatment process revealed this increase occurs during anaerobic digestion. Calculations of predicted environmental concentrations for soil receiving these type A biosolids suggest that concentrations may be below levels where toxicity might occur. This information will be useful to scientists and policymakers dealing with waste treatment plants.

Technical Abstract: The impact of the recently implemented Cambi Thermal Hydrolysis Process™-Anaerobic Digestion (TH-AD) solids treatment method on concentrations of 4 phthalate plasticisers in wastewater sludge samples was explored in this study. Samples were analysed for diisononyl phthalate (DiNP), diisodecyl phthalate (DiDP), bis(2-ethylhexyl) phthalate (DEHP), and benzyl butyl phthalate (BBP) concentrations during individual stages of the TH-AD treatment process, in biosolids produced by the TH-AD process (Class A biosolids), and Class B biosolids from the same facility produced via the liming of sludges. Results showed significantly higher concentrations of all 4 compounds in Class A biosolids when compared to concentrations in Class B biosolids. For DEHP, DiNP, and DiDP, this increase occurred during the anaerobic stage of treatment. Calculations indicate that increases of the four study compounds in Class A biosolids when compared to Class B biosolids was not solely due to solids reduction during anaerobic digestion and dilution during liming, signifying the potential of another source of these compounds in wastewater sludge. Overall, implementation of the TH-AD process increased concentrations of phthalate plasticizers in biosolids.