A review on biological biohydrogen production: Outlook on genetic strain enhancements, reactor model and techno-economics analysis.

Modernisation of industrial and transportation sector would have not imaginable without the help of fossil fuels, but constant usage has led to many environmental concerns. As a step forward, for safer next generation living we are forced to look into green fuels like bio­hydrogen and higher alcohols. This review mainly focuses on bio­hydrogen production via biological pathways, genetic improvements, knowledge gap, economics, and future directions. Dark and photo fermentation process with the factor influence the process (pH regulation, temperature, hydraulic retention time, organic loading rate, Maintenance, Nutrient) is studied. Integration of dark fermentation and microbial electrolysis cell is the most trending progression for sustainable bio­hydrogen production. Genetic improvement of microbe for biohydrogen production via inactivation of hydrogenase (H2ase) and improve oxygen tolerant H2ase. In future, bioaugmentation, multidisciplinary integrated process and microbial electrolysis needs to be experimented in industrial level scale for successful commercialization. About 41.47 mmol H2/g DCW h at 40 g/L of optimum biohydrogen production was obtained through glycerol fermentation. From the studies, the cost of biohydrogen production was found to high with respect to the direct bio photolysis it cost around $7.24 kg-1; for indirect bio photolysis it cost around $7.54 kg-1 and for fermentation it cost around $7.61 kg-1.

Bioprocessing of biowaste derived from food supply chain side-streams for extraction of value added bioproducts through biorefinery approach.

Food chain-based waste is generated in tonnes globally and this has led to release of greenhouse gases, poor air quality, land and water pollution. Food wastes are generated in tremendous quantity globally from local producer to international consumers and traders. Authors have used systematic literature review to identify the research gaps, thematic areas, methodology, sustainable techniques and future directions of processing food supply chain waste. Research is focused towards utilization of food waste as source for recovery of value-added compounds through sustainable technologies. Food waste can be utilized to synthesis platform chemicals, nutraceuticals, sugars, bio-fuels, bio-gas and bio-char via thermo-chemical conversion, anaerobic digestion and fermentation processes. This paper summarizes and provides technical insights on achieving circular bio-economy via technological advances in food waste processing for enhanced recovery of value-added compounds and future industrial scale operations. The state of art perspectives of food waste valorization and market outlook of platform chemicals and other products provides profitable economy for the food waste generator. Food security requires holistic approaches for effective usage of resources with inter linked global policies.

Technical insights into the production of green fuel from CO2 sequestered algal biomass: A conceptual review on green energy.

Algae a promising energy reserve due to its adaptability, cheap source, sustainability and it's growth ability in wastewater with efficient sequestration of industrial carbon dioxide. This review summarizes the pathways available for biofuel production from carbon sequestered algae biomass. In this regard, this review focuses on microalgae and its cultivation in wastewater with CO2 sequestration. Conversion of carbon sequestered biomass into bio-fuels via thermo-chemical routes and its engine emission properties. Energy perspective of green gaseous biofuels in near future. This review revealed that algae was the pre-dominant CO2 sequester than terrestrial plants in an eco-friendly and economical way with simultaneous wastewater remediation. Hydrothermal liquefaction of algae biomass was the most preferred mode for biofuel generation than pyrolysis due to high moisture content. The algae based fuels exhibit less greenhouse gases emission and higher energy value. This review helps the researchers, environmentalists and industrialists to evaluate the impact of algae based bio-energy towards green energy and environment.

Anaerobic digestate water for Chlorella pyrenoidosa cultivation and employed as co-substrate with cow dung and chicken manure for methane and hydrogen production: A closed loop approach.

In rural India, unpleasant atmosphere, anthropogenic gas emission, air and soil pollution are caused due to disposal of livestock's wastes (cow dung and chicken waste) in open environment. This study provides zero emission concept for waste disposal and value addition of these wastes for renewable green energy production. In this study, biogas production was carried out with varying proportion of cow dung to chicken waste (1:0, 0:1, 1:1, 2:1, 1:2, 3:1 and 1:3) for duration of 40 days. Chlorella pyrenoidosa was cultivated from digestate water and used as co-substrate in digester in varying proportions (2:1:1, 2:1:2 and 2:1:3) to study its role on biogas distribution. The effect of pH, feedstock ratio, time and C/N ratio for biogas production were evaluated. The maximum methane and hydrogen yield was 68% (30th day) and 29% (10th day) for 2:1:2 ratio respectively. The slurry possessed nitrogen (1.7%), phosphate (0.8%) and potassium (0.4%) respectively.

Recent advancements in the synthesis of novel thermostable biocatalysts and their applications in commercially important chemoenzymatic conversion processes.

Thermostable enzymes are a field of growing interest in bioremediation, pharmaceuticals, food industry etc., due to their ability to catalyze bio reactions at high temperatures. This review aims to provide an overview on extremophiles with a special focus on thermophiles and enzymes produced from extremophilic bacteria. Novel thermostable catalysts, used in producing commercially important chemicals, are discussed in this review. Various classes of enzymes produced by microbes, synthesis of thermozymes and comparison with enzymes produced at optimal conditions are critically discussed. A detailed discussion on immobilized enzymes in comparisons with free enzymes, produced by extremozymes, is included. Different parameters which affect enzyme production are also discussed. The current industrial trends along with the future of biocatalysts in the production of chemicals using efficient methods are also discussed.

Hydrothermal liquefaction of Scenedesmus obliquus using a novel catalyst derived from clam shells: Solid residue as catalyst for hydrogen production.

This study explores the catalytic application of waste clam shell in hydrothermal liquefaction (HTL) of microalgae (Scenedesmus obliquus) for liquid hydrocarbons production. Novel catalyst (calcium hydroxide) was derived from clam shells. Catalytic HTL was performed at varying temperature of 240-320 °C for catalyst load (0.2-1 wt%) at a reaction time of 60 min. Bio-oil yield was maximum (39.6 wt%) at a temperature of 300 °C for catalyst load of 0.6 wt% at a reaction time of 60 min with calorific value of 35.01 MJ/kg. Compounds like phenols, aromatic hydrocarbons, acids and aldehydes were detected in bio-oil through Gas Chromatography Mass Spectrophotometry (GC-MS). Gasification of microalgae with waste solid residue obtained from HTL was carried out for hydrogen production. Valuable hydrogen gas production was maximum (37 wt%) at a temperature of 400 °C for 3 wt% of solid residue. Water-gas shift, methanation and steam reforming reactions favoured the hydrogen gas production.

Co-liquefaction of Prosopis juliflora with polyolefin waste for production of high grade liquid hydrocarbons.

In this study, co-liquefaction (HTL) of Prosopis juliflora (PJ) biomass with polyolefin waste (PO) was performed to produce bio-oil. HTL on bio-oil yield was studied at varying PJ to PO ratios (0:1, 1:0, 1:1, 2:1, 3:1, 4:1 and 5:1) and temperatures from 340 to 440 °C. Bio-oil and HTL by-products were characterized by Mass Spectroscopy (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR) analysis. Bio-oil yield was around 61.23%wt at 420 °C for 3:1 blends with 3 wt% of HCl activated bentonite catalyst at 60 min holding time. HHV value was 46 MJ/Kg with 88.23% purity (petro-diesel). Additionally gas possessed 26.28% of Hydrogen gas, 45.59% of Carbon dioxide gas, 7.1% of Carbon monoxide gas, 8.12% of Methane gas and other elements. The energy recovery (78%) and carbon recovery (94%) was higher for 3:1 blends bio-oil than PO and PJ processed bio-oils. HTL wastewater possessed higher degree of reusability nature as HTL medium.