Development of a production chain from vegetable biowaste to platform chemicals

Integrated biorefineries for repurposing of food wastes into value-added products

Food waste (FW) generated through various scenarios from farm to fork causes serious environmental problems when either incinerated or disposed inappropriately. The presence of significant amounts of carbohydrates, proteins, and lipids enable FW to serve as sustainable and renewable feedstock for the biorefineries. Implementation of multiple substrates and product biorefinery as a platform could pursue an immense potential of reducing costs for bio-based process and improving its commercial viability. The review focuses on conversion of surplus FW into range of value-added products including biosurfactants, biopolymers, diols, and bioenergy. The review includes in-depth description of various types of FW, their chemical and nutrient compositions, current valorization techniques and regulations. Further, it describes limitations of FW as feedstock for biorefineries. In the end, review discuss future scope to provide a clear path for sustainable and net-zero carbon biorefineries.

Electrostatic Fields Promote Methanogenesis More than Polarized Bioelectrodes in Anaerobic Reactors with Conductive Materials

Direct interspecies electron transfer (DIET) is a breakthrough that can surpass the limitations of anaerobic digestion. Conductive materials and polarized bioelectrodes are known to induce DIET for methane production but are still challenging to apply at a field scale. Herein, compared to polarized bioelectrodes, electrostatic fields that promote DIET were investigated in an anaerobic reactor with conductive materials. As a conductive material, activated carbon enriched its surface with electroactive microorganisms to induce DIET (cDIET). cDIET improved the methane yield to 254.6 mL/g COD_r, compared to the control. However, polarized bioelectrodes induced electrode-mediated DIET and biological DIET (bDIET), in addition to cDIET, improving the methane yield to 310.7 mL/g COD_r. Electrostatic fields selectively promoted bDIET and cDIET for further methane production compared to the polarized bioelectrodes. As the contribution of DIET increased, the methane yield increased, and the substrate residue decreased, resulting in a significant improvement in methane production.

Production of acetoin from renewable resources under heterotrophic and mixotrophic conditions

This study aimed to reveal whether Cupriavidus necator H16 is suited for the production of acetoin based on the carboxylic acids acetate, butyrate and propionate under heterotrophic and mixotrophic conditions. The chosen production strain, lacking the polyhydroxybutyrate synthases phaC1 and phaC2, was revealed to be beneficiary for autotrophic acetoin production. Proteomic analysis of the strain determined that the deletions do indeed have a significant impact on pyruvate formation and its subsequent direction towards the introduced acetoin-synthesis pathway. Moreover, the strain was tested for its ability to use typical dark fermentation products under hetero- and mixotrophic conditions. Growth with butyrate and acetate led to low efficiencies, while 46.54% ±0.78 of the added propionate was converted into acetoin. Interestingly, mixotrophic conditions led to simultaneous consumption of acetate and butyrate with the gaseous substrates and lowered efficiency. In contrast, mixotrophic propionate consumption led to diauxic behavior and high carbon efficiency of 71.2% ±0.64.

Integration of membrane filtration in two-stage anaerobic digestion system: Specific methane yield potentials of hydrolysate and permeate

Two-stage biogas systems consisting of a CSTR-acidification reactor (AR) and an anaerobic filter (AF) were frequently described for microbial conversion of food and agricultural wastes to biogas. The aim of this study is to investigate the integration of a membrane filtration step in two-stage systems to remove inert particles from hydrolysate produced in AR in order to increase the efficiency of the subsequent AF. Hydrolysates from vegetable waste (VW) and grass/maize silage (G/M) were treated in cross-flow ceramic membrane filtration system (pore size 0.2 µm). Organic acids were extracted efficiently through filtration of hydrolysate. For both the substrates, membrane permeability was stable and high (46.6-49.3 L m^-2 h^-1 bar^-1). Filtration process effectively improved the specific methane yield of permeate by 40% (VW) and 24.5% (G/M) compared to hydrolysate. It could be shown that, the filtration-step increased hydrolysate's degradability, which lead to higher conversion efficiency in the following AF.