Sequential and consolidated bioprocessing of biogenic municipal solid waste: A strategic pairing of thermophilic anaerobe and mesophilic microaerobe for ethanol production

Emerging innovations for sustainable production of bioethanol and other mercantile products from circular economy perspective

Biogenic municipal solid waste (BMSW) and food waste (FW) with high energy density are ready to tap renewable resources for industrial scale ethanol refinery foreseen for establishing bio-based society. Circular economy has occupied limelight in the domain of renewable energy and sustainable chemicals production. The present review highlights the importance of BMSW/FW as newer feed reserves that can cater as parent molecules for an array of high-visibility industrial products along with bioethanol upon implementing a judicious closed-cascade mass-flow mechanism enabling ultimate feed and waste stream valorisation. Though these organics are attractive resources their true potential for energy production has not been quantified yet owing to their heterogeneous composition and associated technical challenges thus pushing waste refinery and industrial symbiosis concepts to backseat. To accelerate this industrial vision, the novel bioprocessing strategies for enhanced and low-cost production of bioethanol from BMSW/FW along with other commercially imperative product portfolio have been discussed.

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.

A new method for screening and culture of Clostridium from pit mud under non-anaerobic conditions

Strong-flavor Baijiu (SFB) is produced in complex fermentation in pits under ground. Clostridium producing hexanoic acid plays a key role in the flavor formation of SFB. The screening and culture for Clostridium are very difficult because of its strict anaerobic characteristics. In this study, electric field assisted screening (EFAS) was used to screen Clostridium from pit mud, and electric culture (EC) was used to cultivate Clostridium under non-anaerobic conditions. A strain with a high yield of hexanoic acid was screened and named as Clostridium sp. EFAS6. Under non-anaerobic conditions, it grew rapidly only near the cathode end in the EFAS device because of the low oxidation-reduction potential of that electrode. In the experiment of high-density culture in the EC device, the cell concentration reached 10⁶-10⁷. After energy consumption was calculated, the optimal loading voltage was found to be 10 V. In the application, the broth of Clostridium sp. EFAS6 increased the content of ethyl hexanoic in SFB. Under non-anaerobic conditions, the anaerobe was screened by EFAS and cultivated in high density by EC. The EFAS and EC could also be used for the screening and culture of other anaerobes under non-anaerobic conditions.

Biochemical biorefinery: A low-cost and non-waste concept for promoting sustainable circular bioeconomy

The transition from a fossil-based linear economy to a circular bioeconomy is no longer an option but rather imperative, given worldwide concerns about the depletion of fossil resources and the demand for innovative products that are ecocompatible. As a critical component of sustainable development, this discourse has attracted wide attention at the regional and international levels. Biorefinery is an indispensable technology to implement the blueprint of the circular bioeconomy. As a low-cost, non-waste innovative concept, the biorefinery concept will spur a myriad of new economic opportunities across a wide range of sectors. Consequently, scaling up biorefinery processes is of the essence. Despite several decades of research and development channeled into upscaling biorefinery processes, the commercialization of biorefinery technology appears unrealizable. In this review, challenges limiting the commercialization of biorefinery technologies are discussed, with a particular focus on biofuels, biochemicals, and biomaterials. To counteract these challenges, various process intensification strategies such as consolidated bioprocessing, integrated biorefinery configurations, the use of highly efficient bioreactors, simultaneous saccharification and fermentation, have been explored. This study also includes an overview of biomass pretreatment-generated inhibitory compounds as platform chemicals to produce other essential biocommodities. There is a detailed examination of the technological, economic, and environmental considerations of a sustainable biorefinery. Finally, the prospects for establishing a viable circular bioeconomy in Nigeria are briefly discussed.

Refining of vegetable waste to renewable sugars for ethanol production: Depolymerization andfermentation optimization

The study evaluates the potential of different vegetable wastes namely, composite vegetable waste (CVW), potato waste (PW), sweet potato waste (SPW) and yam waste (YW) as an alternative feedstock for the production of renewable sugars. Thermal assisted chemical pretreatment followed by enzymatic saccharification yielded maximum sugars (0.515 g/g CVW, 0.56 g/g PW, 0.57 g/g SPW and 0.56 g/g YW) with total carbohydrate depolymerization of 95.01%, 88.30%, 90.32% and 88.59% respectively. Obtained sugars were valorized into bioethanol through fermentation using S. cerevisiae by optimizing the pH and temperature. The highest ethanol yield of 251.85 mg/g was obtained from SPW at 35°C followed by YW (240.98 mg/g), PW (235.4 mg/g) and CVW (125.6 mg/g) at pH 5.0. Utilizing the abundantly available vegetable wastes as a renewable feedstock for reducing sugars and subsequent bioethanol production will influence the economics and sustainability of the process positively in circular biorefinery format.

Comparison of mesophilic and thermophilic dark fermentation with nickel ferrite nanoparticles supplementation for biohydrogen production

In this work, nickel ferrite nanoparticles (NiFe₂O₄ NPs) was prepared to improve hydrogen (H₂) production by dark fermentation. Moderate amounts (50-200 mg/L) promoted H₂ generation, while excess NiFe₂O₄ NPs (over 400 mg/L) lowered H₂ productivity. The highest H₂ yields of 222 and 130 mL/g glucose were obtained in the 100 mg/L (37 °C) and 200 mg/L NiFe₂O₄ NPs (55 °C) groups, respectively, and the values were 38.6% and 28.3% higher than those in the control groups (37 °C and 55 °C). Soluble metabolites showed that NiFe₂O₄ NPs enhanced the butyrate pathway, corresponding to the increased abundance of Clostridium butyricum in mesophilic fermentation. The endocytosis of NiFe₂O₄ NPs indicated that the released iron and nickel favored ferredoxin and hydrogenase synthesis and activity and that NiFe₂O₄ NPs could act as carriers in intracellular electron transfer. The NPs also optimized microbial community structure and increased the levels of extracellular polymeric substances, leading to increased H₂ production.