Abstract
The removal efficiencies (REs) of twenty-seven pharmaceutically active compounds (PhACs) (eight analgesic/anti-inflammatories, six antibiotics, four β-blockers, two antihypertensives/diuretics, three lipid regulators and four psychiatric drugs) were evaluated in a pilot-scale two-stage mesophilic anaerobic digestion (MAD) system treating thickened sewage sludge from a pilot-scale A2O™ wastewater treatment plant (WWTP) which was fed with wastewater from the pre-treatment of the full-scale WWTP Murcia Este (Murcia, Spain). The MAD system was long-term operated using two different sets of sludge retention times (SRTs) for the acidogenic (AcD) and methanogenic (MD) digesters (phase I, 2 and 12 days; and phase II, 5 and 24 days, in AcD and MD, respectively). Quantitative PCR (qPCR) and Illumina MiSeq sequencing were used to estimate the absolute abundance of Bacteria, Archaea, and Fungi and investigate the structure, diversity and population dynamics of their communities in the AcD and MD effluents. The extension of the SRT from 12 (phase I) to 24 days (phase II) in the MD was significantly linked with an improved removal of carbamazepine, clarithromycin, codeine, gemfibrozil, ibuprofen, lorazepam, and propranolol. The absolute abundances of total Bacteria and Archaea were higher in the MD regardless of the phase, while the diversity of bacterial and archaeal communities was lower in phase II, in both digesters. Non-metric multidimensional scaling (MDS) plots showed strong negative correlations among phyla Proteobacteria and Firmicutes and between genera Methanosaeta and Methanosarcina throughout the full experimental period. Strong positive correlations were revealed between the relative abundances of Methanospirillum and Methanoculleus and the methanogenesis performance parameters (volatile solids removal, CH4 recovery rate and %CH4 in the biogas), which were also related to longer SRT. The REs of several PhACs (naproxen, ketoprofen, ofloxacin, fenofibrate, trimethoprim, and atenolol) correlated positively (r > 0.75) with the relative abundances of specific bacterial and archaeal groups, suggesting their participation in biodegradation/biotransformation pathways.
Highlights
Urban wastewater is the main sink of pharmaceutically active compounds (PhACs) after their consumption by human populations
For a given PhAC, the concentrations detected in sewage sludge usually range from tens to several hundred μg kg−1 dry weight, and are often related to those measured in the raw wastewater; other factors influence the amounts occurring in this complex matrix, such as the physical-chemical properties of each particular compound, their resistance to biodegradation, or the sludge characteristics and operating parameters of each wastewater treatment plant (WWTP) (Carballa et al, 2008; Dubey et al, 2021; Radjenović et al, 2009; Samaras et al, 2014; Stasinakis, 2012)
The two-stage Anaerobic digestion (AD) configuration, which relies on the separation of the hydrolysis/acidification and acetogenesis/methanogenesis processes in two different bioreactors, in order to provide optimal conditions for the main microbial groups involved in each of these processes, offers some advantages for the stabilization of sewage sludge compared to the single-stage AD configuration, such as improved biogas production, pH self-adjusting capacity, reduction of pathogens and chemical oxygen demand (COD) concentrations, ability to work at shorter sludge retention times (SRT), and improved microbiota stabilization, among others (Maspolim et al, 2015a; Wang et al, 2018)
Summary
Urban wastewater is the main sink of pharmaceutically active compounds (PhACs) after their consumption by human populations. Some of these substances are efficiently removed from raw wastewater, but most of them remain in the treated water, sewage sludge, or both (Angeles et al, 2020; Jelić et al, 2012; Martín et al, 2012; Radjenović et al, 2009; Tran et al, 2018; ValdezCarrillo et al, 2020; Yan et al, 2014). For a given PhAC, the concentrations detected in sewage sludge usually range from tens to several hundred μg kg−1 dry weight (dw), and are often related to those measured in the raw wastewater; other factors influence the amounts occurring in this complex matrix, such as the physical-chemical properties of each particular compound, their resistance to biodegradation, or the sludge characteristics and operating parameters of each wastewater treatment plant (WWTP) (Carballa et al, 2008; Dubey et al, 2021; Radjenović et al, 2009; Samaras et al, 2014; Stasinakis, 2012). The two-stage AD configuration, which relies on the separation of the hydrolysis/acidification and acetogenesis/methanogenesis processes in two different bioreactors, in order to provide optimal conditions for the main microbial groups involved in each of these processes (acid-producing bacteria and methanogenic archaea, respectively), offers some advantages for the stabilization of sewage sludge compared to the single-stage AD configuration, such as improved biogas production, pH self-adjusting capacity, reduction of pathogens and chemical oxygen demand (COD) concentrations, ability to work at shorter sludge retention times (SRT), and improved microbiota stabilization, among others (Maspolim et al, 2015a; Wang et al, 2018)
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