The Dual Role of Indigenous <i>Trichoderma</i> in Sludge Anaerobic Digestion: Enhanced Hydrolysis versus Methanogenesis Inhibition

Trichoderma is a predominant fungal genus found in waste-activated sludge (WAS), yet its impact on WAS anaerobic digestion (AD) remains unclear. This study comprehensively investigated the impact of Trichoderma asperelloides on sludge solubilization, methanogenic performance, microbial availability, and functional gene traits, along with microbial resistance to inhibition. Results show that Trichoderma asperelloides promoted the solubilization of polysaccharides and proteins but also induced cell lysis and suppressed microbial metabolism. Storage further exacerbated the inhibitory effects, reducing methane yields by 25.58% (spores) and 37.19% (mycelia). Further investigation reveals that Trichoderma asperelloides damaged cell membranes, resulting in increased cell death by 18.52%–88.89%. Additionally, key microbes and functional genes related to acidogenesis and methanogenesis were generally down-regulated. In response, anaerobes counteracted inhibition by secreting extracellular protease to hydrolyze antimicrobial peptides (AMPs) and modifying cell membranes to block AMP entry. This study highlights the need to promote Trichoderma growth during the sludge hydrolysis stage while controlling its activities during methanogenesis to optimize bioenergy recovery from WAS during AD processes.