Background: Slow degradation kinetics of long-chain fatty acids (LCFA) and their accumulation in anaerobic digesters disrupt methanogenic activity and biogas production at high loads of waste lipids. In this study, we evaluated the effect of effluent solids recirculation on microbial LCFA (oleate) degradation capacity in continuous stirred-tank sludge digesters, with the overall aim of providing operating conditions for efficient co-digestion of waste lipids. Furthermore, the impacts of LCFA feeding frequency and sulfide on process performance and microbial community dynamics were investigated, as parameters that were previously shown to be influential on LCFA conversion to biogas.
Results: Effluent solids recirculation to municipal sludge digesters enabled biogas production of up to 78% of the theoretical potential from 1.0 g oleate l day. In digesters without effluent recirculation, comparable conversion efficiency could only be reached at oleate loading rates up to 0.5 g l day. Pulse feeding of oleate (supplementation of 2.0 g oleate l every second day instead of 1.0 g oleate l every day) did not have a substantial impact on the degree of oleate conversion to biogas in the digesters that operated with effluent recirculation, while it marginally enhanced oleate conversion to biogas in the digesters without effluent recirculation. Next-generation sequencing of 16S rRNA gene amplicons of bacteria and archaea revealed that pulse feeding resulted in prevalence of fatty acid-degrading Smithella when effluent recirculation was applied, whereas Candidatus Cloacimonas prevailed after pulse feeding of oleate in the digesters without effluent recirculation. Combined oleate pulse feeding and elevated sulfide level contributed to increased relative abundance of LCFA-degrading Syntrophomonas and enhanced conversion efficiency of oleate, but only in the digesters without effluent recirculation.
Conclusions: Effluent solids recirculation improves microbial LCFA degradation capacity, providing possibilities for co-digestion of larger amounts of waste lipids with municipal sludge.
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http://dx.doi.org/10.1186/s13068-021-01913-1 | DOI Listing |
Membranes (Basel)
January 2025
Department of Civil, Environmental, Architectural Engineering and Mathematics, University of Brescia, Via Branze 43, 25123 Brescia, Italy.
The management of biological sludge from wastewater treatment plants (WWTPs) poses a significant environmental challenge due to increasing sludge production and the presence of emerging pollutants. This study investigates an innovative solution by integrating a thermophilic aerobic membrane reactor (TAMR) into the sludge treatment line of a medium-size WWTP, aiming to minimize biological sludge output while enhancing resource recovery. The study involved a six-month monitoring of an industrial-scale TAMR system, assessing the reduction in volatile solids (VSs) in thickened sludge and evaluating the compatibility of TAMR residues with conventional activated sludge (CAS) systems.
View Article and Find Full Text PDFJ Environ Manage
January 2025
Department of Ecology, Engineering Research Center for Tropical and Subtropical Aquatic Ecological Engineering, Ministry of Education, Jinan University, Guangzhou, 510632, PR China. Electronic address:
Pyrite is considered as an effective and environmentally friendly substrate in constructed wetlands (CW) for wastewater treatment, but its application in recirculation stacking hybrid constructed wetlands (RSHCW) has been scarcely studied. This study uses varying amounts of pyrite as the substrate in RSHCW, leveraging the recirculation of wastewater to alter microenvironments such as dissolved oxygen (DO) and pH, to explore the potential mechanisms of nitrogen (N) and phosphorus (P) removal in pyrite-based RSHCW. The results show that as the proportion of pyrite increases, the removal rate of total phosphorus (TP) in the effluent also increases (25%→58%), significantly enhancing the deposition of iron-bound phosphorus (Fe-P) on the substrate, thereby turning CW into a P reservoir.
View Article and Find Full Text PDFBioresour Technol
February 2025
NORCE Norwegian Research Centre AS, Thormøhlens Gate 53, 5006 Bergen, Norway; University of Bergen, Department of Biological Sciences, Thormøhlens Gate 53, 5006 Bergen, Norway.
Effluent water from recirculating aquaculture systems (RAS) contains nutrients from fish excrements and leftover feed. This study investigated the nutrient remediation potential from RAS effluent water through microalgae cultivation in 25 L tubular reactors. We compared nutrient uptake and biomass productivity in continuous and perfusion cultivation modes for freshwater, brackish water and saltwater.
View Article and Find Full Text PDFJ Environ Manage
December 2024
Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Fortaleza, Ceará, Brazil. Electronic address:
This work investigated the operational and microbiological aspects of the decolorization of the azo dye Reactive Black 5 in acidogenic reactors followed by aerobic granular sludge (AGS) reactors, evaluating the effect of the acidogenic hydraulic retention time (HRT) (3, 2, and 1 h), effluent recirculation in the AGS reactor (50 mL min), dye concentration (50 and 100 mg L), and the redox mediator sodium anthraquinone-2-disulfonate (AQS) (50 μM). The acidogenic reactors were mainly responsible for the dye decolorization, with AQS significantly improving its efficiency and enabling the use of a shorter HRT (2 h). The recirculation effect was not so evident, probably masked by the adaptation of the acidogenic microbiota.
View Article and Find Full Text PDFEnviron Monit Assess
October 2024
Research Group for Optimization of Analytical Technologies Applied to Environmental and Sanitary Samples (GOTAS), School of Technology, Universidade Estadual de Campinas, Limeira, SP, 13484-332, Brazil.
Sludge from water treatment plants (WTPs) is usually processed by physicochemical clarification followed by thickening, which results in the production of an effluent from dewatering/drying sludge processes that can potentially impact the environment. This paper assessed the viability of employing sludge dewatering water from a water treatment sludge plant (WTSP) in São Paulo State, Brazil, for reuse purposes. Water quality variables were monitored in the effluent and receiving stream.
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