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Dehydrogenation of methanol (CH

Polyhydroxyalkanoates (PHAs) are group monomers/heteropolymers that are biodegradable and widely used in biomedical applications. They are considered as alternatives to fossil derived polymers and accumulated by microbes including extremophilic archaea as energy storage inclusions under nutrient limitations. The use of extremophilic archaea for PHA production is an economically viable option for conventional aerobic processes, but less is known about their pathways and PHA accumulation capacities. This review summarized: (a) specific adaptive mechanisms towards extreme environments by extremophiles and specific role of PHAs; (b) understanding of PHA synthesis/metabolism in archaea and specific functional genes; (c) genetic engineering and process engineering approaches required for high-rate PHA production using extremophilic archaea. To conclude, the future studies are suggested to understand the membrane lipids and PHAs accumulation to explain the adaptation mechanism of extremophiles and exploiting it for commercial production of PHAs.

The reliance of fossil fuel for industrial and energy sectors has resulted in its depletion. Therefore, enormous efforts have been considered to move-out from fossil fuels to renewable energy sources based industrial process developments. Recently, biohydrogen (bio-H2) has been recognised as a clean source of fuel with high-energy efficiency, which can be produced via different routes. Among them, biological fermentation processes are highly recommended due to eco-friendly and economically viable approaches compared to that of thermochemical processes. However, the low H2 yield and high production cost are major bottlenecks for commercial scale operations. Thus, this review proposed an integrated microalgae-based H2 production process, which will provides a possible route for commercialization in near future. Furthermore, process integration to improve efficiency and implementation of advanced strategies for the enhancement of bio-H2 production, economic viability, and future research needs are discussed.

Aerobic methane-oxidizing bacteria of the Alphaproteobacteria have been found to express a novel ribosomally synthesized post-translationally modified polypeptide (RiPP) termed methanobactin (MB). The primary function of MB in these microbes appears to be for copper uptake, but MB has been shown to have multiple capabilities, including oxidase, superoxide dismutase and hydrogen peroxide reductase activities, the ability to detoxify mercury species, as well as acting as an antimicrobial agent. Herein, we describe the diversity of known MBs as well as the genetics underlying MB biosynthesis. We further propose based on bioinformatics analyses that some methanotrophs may produce novel forms of MB that have yet to be characterized. We also discuss recent findings documenting that MBs play an important role in controlling copper availability to the broader microbial community, and as a result can strongly affect the activity of microbes that require copper for important enzymatic transformations, e.g. conversion of nitrous oxide to dinitrogen. Finally, we describe procedures for the detection/purification of MB, as well as potential medical and industrial applications of this intriguing RiPP.

Microbial fermentations are well recognized process for large-scale bioconversion of organic waste biomass into high-value organic acids. It requires processes optimization, i.e., that should reach at maximum productivity and no feedback inhibition, to reduce the cost of up- and down-stream processing for commercialization. To achieve this, triggered metabolic activities are often needed that maximize the conversion of organic carbon into organic acids under non-sterile conditions. By regulating the redox balance in-situ, the specific organic acid production could be tailored in fermentation systems under mixed/mono-culture conditions. In recent years, bio-electro-fermentations (BEF) has developed as a promising approach for organic waste conversion into value products due to its sustainable nature but yet required better understand for further development. In BEF, the fermentative metabolic pathways are enhanced with poising electrodes that facilitate effective electron transfers towards end-product recovery. It is expected to maintain the required redox conditions and buffer the system by regulating reducing equivalents e.g. NADH+ during fermentation. Moreover, microorganisms extract energy required to build biomass (anabolic process) from redox reactions (catabolism) through syntrophic interactions in BEF, while feedback inhibition of process could be overcome. In this chapter, we will elaborate the BEF process for organic acid production (mainly succinic, acetic, and muconic acids) and techno-economics of the process for commercialization.

Global industrial operations and commodity productions rely on fossil fuels that are non-renewable resources, projected to be exhausted by 2050. To mitigate and compensate for the high-end use of fossil fuel consumption, the use of renewable energy resources, i.e., biomass, wind, and solar energy is getting attention recently. Using photosynthetic organisms, algae is a viable alternative to produce food, feed, and fuels as algae are considered as one of the most robust species and commercially exploited for CO2 capturing or for water clean-up (i.e., remove pollutants and heavy metals at industrial settings). Very few produce high-value products using algae, e.g., carotenoids, vitamins, and pharmaceuticals that required extensive process integration and clean operations, but biohydrogen production using the algal platform was very scarce. Considering the future clean, green, and bio-circular economy, using algal technology to produce clean fuel hydrogen will be attractive and scalable. This chapter has summarized and culminated the literature about algal microbiology, mechanisms involved in the production of biohydrogen techniques, and the various secondary metabolites co-produced during the process of the algal hydrogen production platform. The chapter also listed and discussed the effect of various parameters on improving the biohydrogen yield and knowledge gaps to address shortly.

Food waste can be used as a potential feedstock for the generation of various fine biochemicals, such as aromatic compounds, pigments, essential oils, antibiotics, and biolubricants. The production of food waste-derived fine chemicals is an eco-friendly approach due to the subsequent reduction in waste generation and maximum utilization of the resource. These fine chemicals have high industrial value and more utility and are considered to be a sustainable resource for the future. This chapter gives an overview of the fine biochemicals that can be generated from various types of food waste for promoting sustainable management and its potential recovered commodities. In addition, a detail discussion of various extraction processes and reactors used for food waste management are provided. Economic considerations and the outlooks regarding commercial scale-up of fine chemical generation from food waste are also discussed. In addition, brief discussions of the limitations and challenges facing large-scale implementation of fine chemical production processes are also provided.

We assessed the suitability of various biogenic materials for development of a gradient packed bed bio-filter to mitigate the methane (CH4) emission from landfills. Five different biogenic materials (windrow compost-WC; vermicompost-VC; landfill top cover-LTC; landfill bottom soil-LBS; and river soil sediment-SS) were screened. Among these materials, the VC showed a better CH4 oxidation potential (MOP) of 12.6μg CH4 gdw(-1)h(-1). Subsequently, the VC was used as a packing material along with wood chips in proto-type bio-filters. Wood chips were mixed at 5-15% to form three distinct gradients in a test bio-filter. Under the three different CH4 loading rates of 33, 44 and 55 gCH4 m(-3)h(-1), the achieved MOPs were 31, 41, and 47gCH4 m(-3)h(-1), respectively. The gradient packed bed bio-filter is effective for landfill CH4 mitigation than the conventional bio-filter as the latter shows gas channeling effects with poor MOPs.

Food waste (FW) is a valuable resource which requires sustainable management avenues to reduce the hazardous environmental impacts and add-value for better economy. Anaerobic digestion (AD) is still reliable, cost-effective technology for waste management. Conventional AD was originally designed for sewer sludge digestion, is not effective for FW due to mainly high organics and volatile fatty acid (VFA) accumulation, hence better technical aptitudes and biochemical inputs are required for optimal biogas production. Besides, to overcome these challenges, FW co-digestion with complementary organic waste e.g. sewage sludge (SS) mixed which complement each other for better process design. The main aim of this article is to summarize the recent updates and review different holistic approaches for efficient anaerobic co-digestion (AcoD) of FW and SS to provide a comprehensive review on the topic. Moreover, to demonstrate the status and perspectives of AcoD at present scenario for Hong Kong and rest of the world.

The aim of this review was to elucidate the role of copper and iron in regulating methane (CH4) oxidation and subsequent biopolymer (i.e. polyhydroxyalkanoate [PHA]) accumulation in methanotrophic bacteria. Specifically, the review emphasizes the ―copper switch mechanism‖ which alters CH4 oxidizing enzyme activities, i.e. soluble- and particulate-methane monooxygenase, in type II methanotrophic bacteria. Both copper and iron are essential nutrients, and reports demonstrate that addition of either can improve PHA accumulation. However, based on analyses of available data, a major knowledge gap regarding a clear understanding of the interactive effects in regulating methane monooxygenase enzyme activities/gene expressions was identified in this review.

Anaerobic co-digestion of food waste with primary sewage sludge is beneficial for urban centers, while the optimized conditions reported in the literature are not locally suitable for Hong Kong. Therefore, the present study was aimed to develop an optimized mixing ratio of food waste to chemically enhanced primary-treated sewer sludge (CEPT) for co-digestion using batch tests under mesophilic (37°C) and thermophilic (55°C) conditions. The mixing ratios of 1:1, 1:2, 1:3, 2:1 and 3:1 (v v(-1)) of food waste to CEPT sludge was tested under the following conditions: temperature - 35°C and 55°C; pH - not regulated; agitation - 150 rpm and time - 20 days. The thermophilic incubations led a good hydrolysis rate and 2-12-fold higher enzyme activities than in mesophilic incubations for different mixing ratios. While the acidogenesis were found retarded that leading to 'sour and stuck' digestion for all mixing ratio of food waste to CEPT sludge from thermophilic incubations. The measured zeta potential was most favourable (-5 to -16.8 mV) for methane production under thermophilic incubations; however the CH4 recovery was less than that in mesophilic incubations. The results suggested that the quick hydrolysis and subsequent acid accumulation under thermophilic incubation lead to inhibited methanogenesis at the early stage than in mesophilic systems. It is concluded that buffer addition is therefore required for any mixing ratio of food waste to CEPT sludge for improved CH4 recovery for both mesophilic and thermophilic operations.