Microbial Dynamics during the Removal of Linear Alkylbenzenesulfonate (LAS) under Anaerobic and Microaerobic Conditions with Different Co-substrates

Abstract Linear alkylbenzenesulfonate (LAS) is the most widely used anionic surfactant and is commonly found in wastewater due to its extensive use in detergents and cleaning products. Although LAS is biodegradable, its degradation in anaerobic environments remains a challenge, often requiring the addition of co-substrates and optimized operating conditions. This pioneering study evaluates the microbiological pathways and metabolisms underlying LAS biodegradation in UASB reactors operated under microaerated conditions, compared with strictly anaerobic systems. Furthermore, the effects of different co-substrates (ethanol and sucrose) on LAS removal efficiency and biogas production were also evaluated. The results indicate that microaeration, combined with sucrose as a co-substrate, significantly improves LAS removal, increasing efficiency by 34.3%. The study also revealed that microaeration influenced methane production, reducing its purity but increasing overall volumetric biogas production. Microaeration significantly influenced the microbial structure and function of the systems, depending on the co-substrate used. In the presence of ethanol, both systems showed a predominance of fermentative and methanogenic communities, with no significant differences in LAS removal. In contrast, with sucrose, microaeration promoted greater removal efficiency, associated with the selection of a specialized consortium composed of Pleomorphomonas and Desulfovibrio, capable of partially oxidizing the benzene ring and desulfonating the surfactant. This condition activated oxidative and sulfur metabolism pathways, while maintaining functional methanogenesis, resulting in a less diverse but metabolically more targeted and efficient community in LAS degradation. These findings highlight the potential of microaeration and co-substrate selection to optimize anaerobic treatment of LAS-containing wastewater while maintaining stable reactor performance.