Recent advances in the role of biocatalyst in biofuel cells and its application: An overview

Biofuel cells have recently gained popularity as a green and renewable energy source. Biofuel cells are unique devices of energy and are capable of converting the stored chemical energy from waste materials such as pollutants, organics and wastewater into reliable, renewable, pollution-free energy sources through the action of biocatalysts such as various microorganisms and enzymes. It is a promising technological device to treat waste to compensate for global warming and the energy crisis through the green energy production process. Due to their unique properties, various potential biocatalysts are attracting researchers to apply them to various microbial biofuel cells for improving electricity and power. Recent research in biofuel cells is focusing on the exploitation of different biocatalysts and how they are enhancing power generation for various applications in the field of environmental technology, and biomedical fields such as implantable devices, testing kits, and biosensors. This review focusing the importance of microbial fuel cells (MFCs) and enzymatic fuel cells (ECFs) and role of different types of biocatalysts and their mechanisms for improving biofuel cell efficiency gathered from recent reports. Finally, its multifaceted applications with special emphasis on environmental technology and biomedical field will be described, along with future perspectives.

Sustainable microalgal cultivation in poultry slaughterhouse wastewater for biorefinery products and pollutant removal

Microalgae's ability to grow in poultry slaughterhouse wastewater (PSHWW) is attracting interest for low-cost biomass production and wastewater treatment. In this study, PSHWW is evaluated by the cultivation of Chlorella sp. andNeochloris sp. for biomass,bioproducts, and nutrient removal. Results showed that Neochloris sp.produced the maximum of 1.4 g L^-1 biomass and 38% lipids compared toChlorella sp. (1.3 g L^-1 and 36%). The maximum carotenoids, proteins, and carbohydrates obtained from Neochloris sp. are 38 mg/g DW, 41.7%, and 29%, respectively. COD, nitrite, and phosphate removal efficiencies of 96.8%, 95%, and 79%, respectively, by Neochloris sp. and 89%, 93.5%, and 64.5%, respectively, by Chlorella sp. FTIR confirms the role of functional groups in pollutant absorption by microalgae. The predominant fatty acids found were C16, C18, C18:1, C18:2, C18:3, C20:5, and C22:6. The research demonstrated that microalgae can be used for the treatment of wastewater, nutraceuticals, food additives, and biofuels.

Biomass production and phycoremediation of microalgae cultivated in polluted river water

The present study evaluated polluted river water as a medium for the growth of oleaginous microalgae under mixotrophic conditions. Microalgae grow in the medium and produce biomass, pigments, and lipids with the removal of pollution loads from wastewater. Selenastrum sp. SL7 produced maximum biomass and lipids of 660 mg L^-1 and 194.5 mg L^-1, respectively. Fatty acid profiling data showed that elevated saturated fatty acid production and major fatty acids found in lipid from these algae were palmitic acids, oleic acid, stearic acid, linolenic acid, and linoleic acid. The low percentage of polyunsaturated fatty acids of EPA was also detected. Water quality in terms of pH, DO, TDS, COD, and BOD was significantly improved. The use of this medium for microalgae cultivation not only improves the biomass and lipid yields but also serves as an excellent means of phycoremediation of pollutants in waste streams with value addition and environmental benefits.

Sustainable microalgal biomass production in food industry wastewater for low-cost biorefinery products: a review

Microalgae are recognized as cell factories enriched with biochemicals suitable as feedstock for bio-energy, food, feed, pharmaceuticals, and nutraceuticals applications. The industrial application of microalgae is challenging due to hurdles associated with mass cultivation and biomass recovery. The scale-up production of microalgal biomass in freshwater is not a sustainable solution due to the projected increase of freshwater demands in the coming years. Microalgae cultivation in wastewater is encouraged in recent years for sustainable bioeconomy from biorefinery processes. Wastewater from the food industry is a less-toxic growth medium for microalgal biomass production. Traditional wastewater treatment and management processes are expensive; hence it is highly relevant to use low-cost wastewater treatment processes with revenue generation through different products. Microalgae are accepted as potential biocatalysts for the bioremediation of wastewater. Microalgae based purification of wastewater technology could be a universal alternative solution for the recovery of resources from wastewater for low-cost biomass feedstock for industry. This review highlights the importance of microalgal biomass production in food processing wastewater, their characteristics, and different microalgal cultivation methods, followed by nutrient absorption mechanisms. Towards the end of the review, different microalgae biomass harvesting processes with biorefinery products, and void gaps that tend to hinder the biomass production with future perspectives will be intended. Thus, the review could claim to be valuable for sustainable microalgae biomass production for eco-friendly bioproduct conversions.

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Strategies and advances in the pretreatment of microalgal biomass

Modification of structural components, especially the cell wall, through adequate pretreatment strategies is critical to the bioconversion efficiency of algal biomass to biorefinery products. Over the years, several physical, physicochemical, chemical and green pretreatment methods have been developed to achieve maximum productivity of desirable by-products to sustain a circular bioeconomy. The effectiveness of the pretreatment methods is however, species specific due to diversity in the innate nature of the microalgal cell wall. This review provides a comprehensive overview of the most notable and promising pretreatment strategies for several microalgae species. Methods including the application of stress, ultrasound, electromagnetic fields, pressure, heat as well as chemical solvents (ionic liquids, supercritical fluids, deep eutectic solvents etc.) have been detailed and analyzed. Enzyme and hydrolytic microorganism based green pretreatment methods have also been reviewed. Metabolic engineering of microorganisms for product specificity and lower inhibitors can be a future breakthrough in microalgal pretreatment.

Resource recovery through bioremediation of wastewaters and waste carbon by microalgae: a circular bioeconomy approach

Microalgal biomass-based biofuels are a promising alternative to fossil fuels. Microalgal biofuels' major obstacles are the water and carbon sources for their cultivation and biomass harvest from the liquid medium. To date, an economically viable process is not available for algal based biofuels. The circular bioeconomy is an attractive concept for reuse, reduce, and recycle resources. The recovery of nutrients from waste and effluents by microalgae could significantly impact the escalating demands of energy and nutraceutical source to the growing population. Wastewaters from different sources are enriched with nutrients and carbon, and these resources can be recovered and utilized for the circular bioeconomy approach. However, the utilization of wastewaters and waste seems to be an essential strategy for mass cultivation of microalgae to minimizing freshwater consumption, carbon, nutrients cost, nitrogen, phosphorus removal, and other pollutants loads from wastewater and generating sustainable biomass for value addition for either biofuels or other chemicals. Hence, the amalgamation of wastewater treatment with the mass cultivation of microalgae improved the conventional treatment process and environmental impacts. This review provides complete information on the latest progress and developments of microalgae as potential biocatalyst for the remediation of wastewaters and waste carbon to recover resources through biomass with metabolites for various industrial applications and large-scale cultivation in wastewaters, and future perspectives are discussed.

Recent trends in microbial nanoparticle synthesis and potential application in environmental technology: a comprehensive review

Microbial technology comprising environment in various aspects of pollution monitoring, treatment of pollutants, and energy generation has been put forth by the researchers worldwide in an eco-friendly manner. During the past few decades, this revolution has pronounced microbial cells in green nanotechnology, extending the scope, efficiency, and investment capita at research institutes, industries, and global markets. In the present review, initially, the source for the microbial synthesis of nanoparticles will be discussed involving bacteria, fungi, actinomycetes, microalgae, and viruses. Further, the mechanism and bio-components of microbial cells such as enzymes, proteins, peptides, amino-acids, exopolysaccharides, and others involved in the bio-reduction of metal ions to corresponding metal nanoparticles will be emphasized. The biosynthesized nanoparticles physicochemical properties and bio-reduction methods' advantages compared with synthetic methods will be detailed. To understand the suitability of biosynthesized nanoparticles in a wide range of applications, an overview of its blend of medicine, agriculture, and electronics will be discussed. This will be geared up with its applications specific to environmental aspects such as bioremediation, wastewater treatment, green-energy production, and pollution monitoring. Towards the end of the review, nano-waste management and limitations, i.e., void gaps that tend to impede the application of biosynthesized nanoparticles and microbial-based nanoparticles' prospects, will be deliberated. Thus, the review would claim to be worthy of unwrapping microorganisms sustainability in the emerging field of green nanotechnology.

Bioremediation and biomass production of microalgae cultivation in river watercontaminated with pharmaceutical effluent

This work evaluated the potential of microalgae of Chlorella sp., SL7A, Chlorococcum sp., SL7B and Neochloris sp.,SK57 cultivated in river water contaminated with pharmaceutical effluent for biomass and lipid production. It has been observed that fast growing algae in this medium is Neochloris sp.SK57. Maximum biomass and lipid yield was obtained from Neochloris sp. SK57 (0.52 g/l) and Chlorococcum sp. SL7B (0.129 g/l)along with drycell weight of lipid was 28%.The increased in biomass and lipid in this media is could due to assimilation of organic nutrients and stress due to other components present in the river water. Fatty acid profile of algal biomass showed that saturated fatty acids production is enhanced in oils of Neochloris sp. SK57, and its suitability in food and fuel applications. Water quality of the river water was monitored before and after algal cultivation. Results showed that quality of river water was improved after algal cultivation.

Co-pyrolysis of phumdi and para grass biomass from Loktak Lake

In the present work, the pyrolysis of para grass (PG) and phumdi (PH) biomass samples was conducted in the temperature range of 300-500 °C to obtain the optimum temperature for obtaining the maximum yield of bio-oil. Further, co-pyrolysis experiments of PH and PG were also conducted at the same optimized temperature and varied compositions to investigate the synergistic effect. It was observed during the co-pyrolysis, that the maximum bio-oil yield of 37.80 wt% was obtained at the mass ratio of 1:1. The GC-MS, FT-IR and ¹H NMR analysis revealed that the bio-oils produced from all the processes were rich in functionalities. Phenolic compounds such as 2-methoxy-4-vinyl phenol, phenol, 2-methoxy, phenol 4-ethyl constituted a significant portion of bio-oils. The biochars obtained at the optimum pyrolytic conditions were analyzed by FT-IR and TOC analyzer.

Effect of dilute acid pretreatment of wild rice grass (Zizania latifolia) from Loktak Lake for enzymatic hydrolysis

Zizania latifolia commonly known as wild rice grass which is available in huge quantities in Loktak Lake is a major concern as it occupies a large area of the Lake and causing a several environmental problems. The investigation of present study was to evaluate possibilities of using Zizania latifolia as feed stock for bioethanol production. The method involved the pretreatment with dilute acid or alkali followed by enzymatic hydrolysis with commercial cellulase. Acid pretreatment was performed with 10% biomass loading with different concentration of acids (0.4-2% w/v) and alkali (0.25-1.5% w/v). Maximum sugar release of 457 mg/g was obtained from 10% biomass loading and 2% w/v of acids. Alkali pretreatment is not effective for this grass. Physicochemical characterization of untreated and treated biomass was carried out by XRD, FTIR, SEM and corresponding alterations in the chemical composition were also monitored. Results showed the feasibility of this grass as biofuel (bioethanol) feed stock and can be potential approach to address the sustainable utilization phumdis grasses of Loktak Lake for the production of value added product.

Applications of Microbial Enzymes in Food Industry

The use of enzymes or microorganisms in food preparations is an age-old process. With the advancement of technology, novel enzymes with wide range of applications and specificity have been developed and new application areas are still being explored. Microorganisms such as bacteria, yeast and fungi and their enzymes are widely used in several food preparations for improving the taste and texture and they offer huge economic benefits to industries. Microbial enzymes are the preferred source to plants or animals due to several advantages such as easy, cost-effective and consistent production. The present review discusses the recent advancement in enzyme technology for food industries. A comprehensive list of enzymes used in food processing, the microbial source of these enzymes and the wide range of their application are discussed.

Bioflocculation: An alternative strategy for harvesting of microalgae - An overview

Microalgae based research has been extensively progressed for the production of value added products and biofuels. Potential application of microalgae for biofuel is recently gained more attention for possibilities of biodiesel and other high value metabolites. However, high cost of production of biomass associated with harvesting technologies is one of the major bottleneck for commercialization of algae based industrial product. Based on the operation economics, harvesting efficiency, technological possibilities, flocculation of algal biomass is a superior method for harvesting microalgae from the growth medium. In this article, latest trends of microalgal cell harvesting through flocculation are reviewed with emphasis on current progress and prospect in environmental friendly bio-based flocculation approach. Bio-flocculation based microalgae harvesting technologies is a promising strategy for low cost microalgal biomass production for various applications.

Potential of Brachiaria mutica (Para grass) for bioethanol production from Loktak Lake

The aim of present study was to evaluate feasibility of using the Para grass as feedstock for production of bioethanol. Process involved the pretreatment with dilute acid or alkali and followed by enzymatic saccharification with commercial cellulase. Maximum sugar release of 696mg/g was obtained from 10% biomass loading and 0.5% w/v of alkali whereas in the case of acid pretreatment maximum sugar of 660mg/g was obtained from 20% biomass loading and 2% w/v acid loading. Results showed that Para grass utilization as a biorefinery feedstock can be a potential strategy to address the sustainable utilization of this invasive grass thereby keeping its population in check in the Loktak Lake.

Development of a novel ultrasound-assisted alkali pretreatment strategy for the production of bioethanol and xylanases from chili post harvest residue

A novel ultrasound-assisted alkali pretreatment strategy was developed which could effectively remove lignin and hemicelluloses and improve the sugar yield from chili post harvest residue. Operational parameters that affect the pretreatment efficiency were studied and optimized. Inhibitor analysis of the hydrolyzate revealed that major fermentation inhibitors like furfural, 5-hydroxymethyl furfural as well as organic acids like citric acid, succinic acid and propionic acid were absent. Hence fermentation can be carried out without detoxification of the hydrolyzate. Changes in structural properties of the biomass were studied in relation to the pretreatment process using Scanning Electron Microscopy (SEM) and the changes in chemical composition were also monitored. The biomass pretreated with the optimized novel method could yield 0.428g/g of reducing sugars upon enzymatic hydrolysis. The hydrolyzate obtained by this novel pretreatment strategy was found to be suitable for bioethanol and xylanase production.

Harvesting of microalgal biomass: Efficient method for flocculation through pH modulation

Harvesting of the micro alga Chlorococcum sp. R-AP13 through autoflocculation, chemical flocculants or by change in medium pH was evaluated. Surface charge of algal cells changed in response to the method used and affected flocculation efficiency. While aluminum sulfate and FeCl3 supported 87% and 92% efficiency, auto flocculation could recover 75% of biomass in 10min. Maximum efficiency (94%) was obtained with change in medium pH from 8.5 to 12.0 achieved through addition of 40mgl(-1) of NaOH. Since high concentrations of FeCl3 and AlSO4 were toxic to the cells, flocculation induced by pH change may be considered the most effective strategy. Residual medium after flocculation could be reused efficiently for algal cultivation, minimizing the demand for fresh water.

Cultivation of microalgae in dairy effluent for oil production and removal of organic pollution load

Dairy effluent (DE) was evaluated for cultivation of the oleaginous micro alga Chlorococcum sp. RAP13 under mixotrophic and heterotrophic modes. The alga grew better and accumulated more lipids under heterotrophic cultivation. Supplementation of biodiesel industry waste glycerol (BDWG) to DE enhanced the biomass production as well as lipid accumulation. While the biomass yield was 0.8g/L for mixotrophic cultivation, it was 1.48g/L and 1.94g/L respectively when cultivated with 4% or 6% BDWG. The cells accumulated 31% lipid when grown in mixotrophic mode, and heterotrophic cultivation with 4% or 6% BDWG resulted in a lipid accumulation of 39% and 42% respectively. Saturated fatty acids production was elevated in the DE, and the major fatty acid components of the algal oil were palmitic (16:0), oleic (18:1), stearic (18:0), linoleic (18:2) and linolenic (18:3) acids. DE quality improved with reduction in COD and BOD after algal cultivation.