Co-fermenting lactic acid and glucose towards caproic acid production.

The functional role of lactate (HLac), as a co-substrate along with glucose (Glu) as well as an electron donor for the synthesis of caproic acid (HCa), a medium chain fatty acid (MCFAs) was studied. A varied HLac and Glu ratios were thus investigated in fed-batch anaerobic reactors (R1-R5) operated at pH 6 with a heat-treated anaerobic consortium. R1 and R5 were noted as controls and operated with sole Glu and HLac, respectively. Strategically, ethanol (HEth) was additionally supplemented as co-electron donor after the production of short chain carboxylic acids (SCCAs) for chain elongation in all the reactors. The reactor operated with HLac and Glu in a ratio of 0.25:0.75 (1.25 g/L (HLac) and 3.75 g/L (Glu)) showed the highest HCa production of 1.86 g/L. R5 operated with solely HLac yielded propionic acid (HPr) as the major product which further led to the higher valeric acid (HVa) production of 1.1 g/L within the reactor. Butyric acid (HBu) was observed in R1, which used Glu as carbon source alone indicating the importance of HLac as electron co-donor. Clostridium observed as the most dominant genera in shotgun metagenome sequencing in R2 and R3, the reactors that produced the highest HCa in comparison to other studied reactors. The study thus provided insight into the importance of substrate and electron donor and their supplementation strategies during the production of MCFAs.

Synergy of selective buffering, intermittent pH control and bioreactor configuration on acidogenic volatile fatty acid production from food waste.

The production of volatile fatty acids (VFAs) and biohydrogen (bio-H2) from food waste (FW) by acidogenic process is one of the promising strategies. The present study was performed to evaluate the role of initial (phase I) and intermittent pH (phase II) control strategies utilising combination of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) as buffering/neutralizing agents on VFAs and bio-H2 production from FW. The study was carried out in two bioreactor configurations (biofilm (UAFBB) and a suspended mode bioreactor (UASB)). Intermittent pH adjustment (phase II) increased hydrolysis and FW acidification compared to the initially adjusted pH (phase I), but had a detrimental influence on bio-H2 generation in both the studied bioreactor configurations. Combining NaOH and Na2CO3 resulted in higher buffering capacity and VFA production. The studied parameters in UAFBB aided in higher VFA (14.05 g/L; 48 h of cycle operation) and bio-H2 (56%; 12 h of cycle operation) production during phase II and phase I operation, respectively. Overall, the results showed a synergy between the examined parameters, resulting in increased VFA production from FW.

Critical factors influence on acidogenesis towards volatile fatty acid, biohydrogen and methane production from the molasses-spent wash.

The study explored the spent wash valorisation into value added biobased products viz. volatile fatty acids (VFAs), biohydrogen (bio-H2), methane (CH4) and biohythane (bio-H-CNG) based on eight selected parameters employing design of experiment (DOE) approach. Selectively enriched biocatalyst showed marked influence on the production of acidogenic products (bio-H2 and VFA) while untreated inoculum resulted in higher CH4 and bio-H-CNG generation. CaCO3 showed potential for butyric acid (HBu) production while Na2CO3 specifically yielded higher acetic acid (HAc) when supplemented as buffering agents. Higher degree of acidification (DOA; 49.8%) was observed at lower organic load (OL; 30 g/L). Biogas production and profile was influenced by OL, enrichment of biocatalyst and supplemented buffering agent. Higher OL related to higher bioproduct production, while yields of the respective products were higher at lower OL.

Renewable hydrogen production by dark-fermentation: Current status, challenges and perspectives.

Global urbanization has resulted in amplified energy and material consumption with simultaneous waste generation. Current energy demand is mostly fulfilled by finite fossil reserves, which has critical impact on the environment and thus, there is a need for carbon-neutral energy. In this view, biohydrogen (bio-H2) is considered suitable due to its potential as a green and dependable carbon-neutral energy source in the emerging 'Hydrogen Economy'. Bio-H2 production by dark fermentation of biowaste/biomass/wastewater is gaining significant attention. However, bio-H2production still holds critical challenges towards scale-up with reference to process limitations and economic viabilities. This review illustrates the status of dark-fermentation process in the context of process sustainability and achieving commercial success. The review also provides an insight on various process integrations for maximum resource recovery including closed loop biorefinery approach towards the accomplishment of carbon neutral H2 production.

Waste derived bioeconomy in India: A perspective.

Environmental and climatic change issues, population explosion, rapid urbanisation, depletion of fossil reserves, need for energy security, huge waste generation, etc. are some of the inherent issues associated with the fossil based linear economy which need greater attention. In this context, the world is gradually transforming from fossil-based economy to a sustainable circular bio-economy. The biogenic waste which is generated in enormous quanties in India can be considered as potential feedstock for structuring the bio-based economy. This communication depicts the need for developing waste derived bioeconomy in the Indian perspective. Waste is now being perceived as a resource with value and believed to supplement petroleum feedstock to a great extent if properly utilized. The necessity to introduce waste as the core element for the future economic models which also allows sustainable development is discussed. The review also establishes drivers for the bioeconomy and structures the waste derived bioeconomy in a sustainable format to address the futuristic needs, scope and opportunities envisaged in the business and economic realm. The enabling technologies/processes that can be applied for biogenic wastes valorisation are elaborated. Circularizing the economy in a waste biorefinery model for the production of biobased products including bioenergy is discussed.

Food waste biorefinery: Sustainable strategy for circular bioeconomy.

Enormous quantity of food waste (FW) is becoming a global concern. To address this persistent problem, sustainable interventions with green technologies are essential. FW can be used as potential feedstock in biological processes for the generation of various biobased products along with its remediation. Enabling bioprocesses like acidogenesis, fermentation, methanogenesis, solventogenesis, photosynthesis, oleaginous process, bio-electrogenesis, etc., that yields various products like biofuels, platform chemicals, bioelectricity, biomaterial, biofertilizers, animal feed, etc can be utilized for FW valorisation. Integrating these bioprocesses further enhances the process efficiency and resource recovery sustainably. Adapting biorefinery strategy with integrated approach can lead to the development of circular bioeconomy. The present review highlights the various enabling bioprocesses that can be employed for the generation of energy and various commodity chemicals in an integrated approach addressing sustainability. The waste biorefinery approach for FW needs optimization of the cascade of the individual bioprocesses for the transformation of linear economy to circular bioeconomy.

Impact of selectively enriched microbial communities on long-term fermentative biohydrogen production.

The effect of selectively enriched inoculum for biohydrogen production and shifts in microbial communities was observed using anaerobic sequencing batch reactor (AnSBR). Significantly, combined pretreatment using acid and iodopropane resulted 3 fold increase in H2 production (8.65mol/kgCODR) over untreated control (2.63mol/kgCODR). Pretreatment showed significant shifts in the microbial communities which are thus accounted for enhanced H2 production. The high-throughput pyrosequence analysis depicted shifts in phylum Firmicutes and Proteobacteria. In the case of Proteobacteria, there was an increase in Betaproteobacterial, decrease in Epsilonproteobacterial and compositional variation in Alphaproteobacterial species. The decreased OTU number after pretreatment indicate, reduction of undesirable microbial populations while favouring conditions for microbiome that are involved in acidogenic, acetogenic and H2 production.

Waste Biorefinery: A New Paradigm for a Sustainable Bioelectro Economy.

A waste biorefinery is a means to valorize waste as a renewable feedstock to recover biobased materials and energy through sustainable biotechnology. This approach holistically integrates remediation and resource recovery. Here we discuss the various technologies employable to construct a waste biorefinery platform and its place in a biobased economy.

High rate biomethanation technology for solid waste management and rapid biogas production: An emphasis on reactor design parameters.

A high rate biomethanation digester was designed and fabricated to study its real field treatment efficiency and simultaneous biogas generation. The major design parameters like self mixing, delinking hydraulic retention time and solid retention time etc. were considered for efficient performance. It was operated with an organic loading rate (OLR) of 1.5kg/m(3)d(-1) with composite food waste for about one year. The maximum treatment efficiency achieved with respect to total solid (TS) reduction and volatile solids (VS) reduction was 94.5% and 89.7%, respectively. Annual mean biogas of about 0.16m(3)/kgVSd(-1) was observed with methane content varying from 56% to 60% (v/v). The high competence of high rate digester is attributed to its specific design features and intermittent mixing of the digester contents and also due to the hydrodynamic principles involved in its operation.

Acidogenic fermentation of food waste for volatile fatty acid production with co-generation of biohydrogen.

Fermentation experiments were designed to elucidate the functional role of the redox microenvironment on volatile fatty acid (VFA, short chain carboxylic acid) production and co-generation of biohydrogen (H2). Higher VFA productivity was observed at pH 10 operation (6.3g/l) followed by pH 9, pH 6, pH 5, pH 7, pH 8 and pH 11 (3.5 g/l). High degree of acidification, good system buffering capacity along with co-generation of higher H2 production from food waste was also noticed at alkaline condition. Experiments illustrated the role of initial pH on carboxylic acids synthesis. Alkaline redox conditions assist solubilization of carbohydrates, protein and fats and also suppress the growth of methanogens. Among the carboxylic acids, acetate fraction was higher at alkaline condition than corresponding neutral or acidic operations. Integrated process of VFA production from waste with co-generation of H2 can be considered as a green and sustainable platform for value-addition.