Process optimization of volatile fatty acid production from lignocellulosic biomass wastes through acidogenic fermentation

With the global awareness and concerns on ecological negative effects such as climate change and increase in energy demand and pollution, there is a growing interest on sustainable management of wastes and renewable energy technologies. The valorization of biomass especially lignocellulosic wastes into high value added bio products has found prominence and of these products, volatile fatty acids (VFAs) are found to be important intermediate products in the biochemical conversion of organic wastes into liquid biofuels, chemicals, and biopolymers. This doctoral thesis presents of an integrated approach to optimizing with volatile fatty acid (VFA) production from lignocellulosic biomass, with a focus on Brewery Spent Grain (BSG) and Spent Mushroom Compost (SMC), through acidogenic fermentation in continuous stirred tank reactors (CSTRs). The research thoroughly addresses fundamental key challenges in relation to substrate complexity, pretreatment strategies, fermentation condition control, and also system integration toward scalable and sustainable VFA production. Initial investigations fully established the importance of nutrient balance using sucrose as a model substrate, identifying a carbon-to-nitrogen (C-N) ratio ranging from 5 - 20 as optimal for microbial activity as well as volatile fatty acid yield. It established a standard for future studies of biomass. Comparative studies of biological as well as chemical pretreatment revealed that white-rot fungal delignification, particularly through using Trametes versicolor, improved sugar availability along with VFA yields without the production of microbial inhibitors, while alkaline chemical pretreatment offered much faster processing, but that required trade-offs in respect to ecological effect. Fermentation parameter optimization identified near pH 6.5 and around 35 °C as optimal conditions. These conditions and an exact substrate-to-inoculum ratio of 3:1 were identified for maximizing VFA yield in CSTRs. The research finished specifically in an integrated cofermentation strategy combining BSG and SMC. This combination then resulted in the highest VFA productivity (58.92 g/L) under optimal organic loading and retention conditions. This work here shows further a viable and also ecologically conscious pathway for transforming agro-industrial residues into platform chemicals. These findings have certain implications for decentralized biorefinery development and contribute to wider sustainability goals through the valorization of waste streams in the circular bioeconomy.