Is anaerobic digestion effective for the removal of organic micropollutants and biological activities from sewage sludge?

Abstract

The occurrence of emerging organic micropollutants (OMPs) in sewage sludge has been widely reported; nevertheless, their fate during sludge treatment remains unclear. The objective of this work was to study the fate of OMPs during mesophilic and thermophilic anaerobic digestion (AD), the most common processes used for sludge stabilization, by using raw sewage sludge without spiking OMPs. Moreover, the results of analytical chemistry were complemented with biological assays in order to verify the possible adverse effects (estrogenic and genotoxic) on the environment and human health in view of an agricultural (re)use of digested sludge. Musk fragrances (AHTN, HHCB), ibuprofen (IBP) and triclosan (TCS) were the most abundant compounds detected in sewage sludge. In general, the efficiency of the AD process was not dependent on operational parameters but compound-specific: some OMPs were highly biotransformed (e.g. sulfamethoxazole and naproxen), while others were only slightly affected (e.g. IBP and TCS) or even unaltered (e.g. AHTN and HHCB). The MCF-7 assay evidenced that estrogenicity removal was driven by temperature. The Ames test did not show point mutation in Salmonella typhimurium while the Comet test exhibited a genotoxic effect on human leukocytes attenuated by AD. This study highlights the importance of combining chemical analysis and biological activities in order to establish appropriate operational strategies for a safer disposal of sewage sludge. Actually, it was demonstrated that temperature has an insignificant effect on the disappearance of the parent compounds while it is crucial to decrease estrogenicity.

Cometabolic Enzymatic Transformation of Organic Micropollutants under Methanogenic Conditions

“…Organic micropollutants. This study focuses on 20 compounds that are commonly detected in sewage sludge 3,4,8,9,[31][32][33] and whose chemical structures (Table S1), applications and physicochemical properties (Table S2) (Table S4), a pulse of the selected OMPs (100 µg L -1 except for the hormones, which were 10 µg L -1 , section S4) was added to each MRs, and their concentrations were followed in the liquid (17 samples) and solid (10 samples) phases for 10 d.…”

“…The supernatant was pre-filtered (AP4004705, Millipore) and filtered at 0.45 µm (HAWP04700, Millipore) before performing the SPE with mL samples and 60 mg OASIS HLB cartridges (Waters, Milford, MA, USA). 4,16 Samples from the enzymatic assays (50 mL)…”

“…5 Despite the environmental risks associated with biosolid-amended soils, 5 few studies have investigated the fate of OMPs during AD. 4,[6][7][8][9][10][11][12] They conclude that AD is able to biologically transform OMPs, but the degree of removal of some compounds is still controversial, and few transformation products (TPs) have been identified, which indicates the poor understanding of the microbial mechanisms and factors behind these biotransformations. 3 Therefore, to develop strategies that promote the complete elimination of OMPs and to predict the environmental risks of the TPs that are generated, it is essential to understand the biotransformation pathways involved in AD.…”

Towards better environmental performance of wastewater sludge treatment using endpoint approach in LCA methodology

“…Hospido et al (2010) showed that the digestion of the sludge, regardless of the operational conditions, was able to achieve up to one third reduction in human and terrestrial toxicity impacts. Gonzalez-Gil et al (2016) showed that the ability of anaerobic digestion to reduce organic micropollutants was not dependent on operational parameters but compound-specific (some organic micropollutats were highly bio-transformed while others were only slightly affected).…”

Occurrence of the Persistent Antimicrobial Triclosan in Microwave Pretreated and Anaerobically Digested Municipal Sludges under Various Process Conditions

“…Despite the prevalence of TCS in wastewater sludge, a few studies have explored its fate during conventional AD. According to these studies, it can be concluded that very limited (between 0-25%) TCS removal has been observed during the AD process [22,[42][43][44].…”