Evaluation of the optimal sewage sludge pre-treatment technology through continuous reactor operation: Process performance and microbial community insights

Georgia-Christina Mitraka; Konstantinos N Kontogiannopoulos; Anastasios I Zouboulis; Panagiotis G Kougias

doi:10.1016/j.watres.2024.121662

Evaluation of the optimal sewage sludge pre-treatment technology through continuous reactor operation: Process performance and microbial community insights

Water Res. 2024 Apr 22:257:121662. doi: 10.1016/j.watres.2024.121662. Online ahead of print.

Authors

Georgia-Christina Mitraka¹, Konstantinos N Kontogiannopoulos², Anastasios I Zouboulis³, Panagiotis G Kougias⁴

Affiliations

¹ Laboratory of Chemical & Environmental Technology, Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece; Soil and Water Resources Institute, Hellenic Agricultural Organisation Dimitra, Thermi, P.O. Box 60458, Thessaloniki GR-57001, Greece.
² Soil and Water Resources Institute, Hellenic Agricultural Organisation Dimitra, Thermi, P.O. Box 60458, Thessaloniki GR-57001, Greece.
³ Laboratory of Chemical & Environmental Technology, Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece.
⁴ Soil and Water Resources Institute, Hellenic Agricultural Organisation Dimitra, Thermi, P.O. Box 60458, Thessaloniki GR-57001, Greece. Electronic address: p.kougias@swri.gr.

PMID: 38678834
DOI: 10.1016/j.watres.2024.121662

Abstract

This study investigated the impact of two low-temperature thermal pre-treatments on continuous anaerobic reactors' performance, sequentially fed with sludge of different total solids content (∼3 % and ∼6 %) and subjected to progressively increasing Organic Loading Rates (OLR) from 1.0 to 2.5 g volatile solids/(L_Reactor⋅day). Assessing pre-treatments' influence on influent sludge characteristics revealed enhanced organic matter hydrolysis, facilitating sludge solubilization and methanogenesis; volatile fatty acids concentration also increased, particularly in pre-treated sludge of ∼6 % total solids, indicating improved heating efficiency under increased solids content. The reactor fed with sludge pre-treated at 45 °C for 48 h and 55 °C for an extra 48 h exhibited the highest methane yield under all applied OLRs, peaking at 240 ± 3.0 mL/g volatile solids at the OLR of 2.5 g volatile solids/(L_Reactor⋅day). 16S rRNA gene sequencing demonstrated differences in the reactors' microbiomes as evidence of sludge thickening and the different pre-treatments applied, which promoted the release of organic matter in diverse concentrations and compositions. Finally, the microbial analysis revealed that specific foam-related genera increased in abundance in the foam layer of reactors' effluent bottles, dictating their association with the sludge foaming incidents that occurred inside the reactors during their operation at 2.0 g volatile solids/(L_Reactor⋅day).

Keywords: Anaerobic digestion; Foaming; Microbial analysis; Pre-treatment methods; Sewage sludge.