Optimization of supercritical carbon dioxide explosion for sewage sludge pre-treatment using response surface methodology

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

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/(LReactor⋅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/(LReactor⋅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/(LReactor⋅day).

Bioethanol production from agricultural residues as lignocellulosic biomass feedstock's waste valorization approach: A comprehensive review

Bioenergy is becoming very popular, drawing attention as a renewable energy source that may assist in managing growing energy costs, besides possibly affording revenue to underprivileged farmers and rural populations worldwide. Bioethanol made from agricultural residual-biomass provides irreplaceable environmental, socioeconomic, and strategic benefits and can be considered as a safe and cleaner liquid fuel alternative to traditional fossil fuels. There is a significant advancement made at the bench scale towards fuel ethanol production from agricultural lignocellulosic materials (ALCM). These process technologies include pretreatment of ALCM biomass employment of cellulolytic enzymes for depolymerizing carbohydrate polymers into fermentable sugars to effectively achieve it by applying healthy fermentative microbes for bioethanol generation. Amongst all the available process methods, weak acid hydrolysis followed by enzymatic hydrolysis process technique. Recovering higher proficient celluloses is more attractive in terms of economic benefits and long-term environmental effects. Besides, the state of ALCM biomass based bioethanol production methods is discussed in detail, which could make it easier for the scientific and industrial communities to utilize agricultural leftovers properly.