Biotransformation of Nonylphenol Diethoxylate in anaerobic digesters: Accumulation of metabolites and their effects on digester performance

Nonylphenol(poly)ethoxylates (NPnEOs) have caused great concern over the last few decades due to their lipophilic, hydrophobic, and toxic properties. NPnEOs can be degraded to a certain extent in wastewater treatment plants; however since they accumulate in sludge, understanding their influence on digester performance and their fate become important, especially in regards to land application of biosolids. In this respect, the biotransformation of nonylphenol diethoxylate (NP2EO), an accumulative metabolite of NPnEOs, into degradation products was monitored in NP2EO-amended lab-scale semi-continuous anaerobic digesters. Determination and quantification of the degradation products, nonylphenol monoethoxylate (NP1EO), nonylphenol (NP) and nonylphenoxy acetic acid (NP1EC), was performed by gas chromatography-mass spectrometry (GC/MS). Results revealed that 90% of NP2EO was eliminated from the system within approximately 52 days following the spike. As biodegradation of NP2EO progressed, both NP1EO and NP accumulated in the sludge samples. NP1EC was not detected in any of the digesters. Methane production, solids reduction and COD removal were not affected by the spike of NP2EO or by the presence of biodegradation products (NP1EO and NP) in the digester system. The persistence and accumulation of NP and NP1EO verifies concerns about the potential danger for land application of biosolids. [Display omitted] •The biotransformation of NP2EO was monitored in semi-continuous anaerobic digesters.•NP2EO was quickly transformed into NP1EO and NP; no NP1EC was detected under anaerobic conditions.•The vast majority of all NP compounds were found in the solid phase, with very low aqueous concentrations.•Both NP1EO and NP were remarkably persistent and accumulated to high levels.•Digester performance was not negatively affected by NP2EO addition nor by NP and NP1EO accumulation.