Selective carboxylate production from detoxified lignocellulosic prehydrolysates through bioaugmented anaerobic...

Lignocellulosic residues often require pretreatments to modify their polymeric structure and facilitate subsequent upcycling. Steam explosion, a common pretreatment method, generates microbial inhibitors like furfural and 5-hydroxymethylfurfural, making detoxification essential to mitigate their adverse effects. This study investigated the novel application of anaerobic fermentation (AF) for converting prehydrolysates from steam-exploded municipal green residues (MGR) into carboxylates and assessed the effect of activated carbon (AC) as a detoxifying agent to promote lignocellulose valorization. Bioaugmentation of the AF was applied for the selective production of lactic and acetic acids. Continuous stirred-tank reactors were fed with detoxified prehydrolysates under identical conditions (15-days of hydraulic retention time (HRT), 1 g COD/Ld, pH 4.5), with one of them bioaugmented with 10% (v/v) Lactobacillus pentosus MAX2. Due to the heterolactic metabolism of this bacterium, the bioaugmented reactor selectively produced 56.8% w/w lactic acid and 40.5% w/w acetic acid, with a total bioconversion of 45.2%. The presence of L. pentosus MAX2 in the microbial community along the AF process was confirmed both by PCR and DNA sequencing. These results do not only establish AF as a viable route for the valorization of lignocellulosic hydrolysates into high value commodity chemicals, but also demonstrate that bioaugmentation can effectively steer metabolic selectivity in mixed cultures, even under conditions where washout could pose a challenge.