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Biomass can be a sustainable choice for bioenergy production worldwide. Biohydrogen production using fermentative conversion of biomass has gained great interest during the last decade. Besides being an efficient transportation fuel, biohydrogen can also be also be a low-carbon source of heat and electricity. Microbes assisted conversion (bioconversion) can be take place either in presence or absence of light. This is called photo-fermentation or dark-fermentation respectively. This review provides an overview of approaches of fermentative hydrogen production. This includes: dark, photo and integrated fermentative modes of hydrogen production; the molecular basis behind its production and diverse range of its applicability industrially. Mechanistic understanding of the metabolic pathways involved in biomass-based fermentative hydrogen production are also reviewed. Keywords: Hydrogen, Biomass, Fermentation, Dark and photo fermentation

The present study is designed to identify various bioactive flavonoid compounds from the methanolic fern extract (MFE) of Cheilanthes tenuifolia. Flavonoids derived from C. tenuifolia (fern) possess potent anti-cancerous, anti-bacterial, anti-oxidant activities that are responsible for their chemo-preventive potential against selected bacterial panel. A preparative column chromatography with a column Sephadex LH-20 was used to isolate and purify flavonoids from C. tenuifolia. Their structure and chemical bonds were identified by using Nuclear Magnetic Resonance (NMR) spectroscopy and Fourier Transform-Infra Red Spectroscopy (FTIR). Two flavonoids were identified as rutin (2.8 mg) and quercetin (3.34 mg) from 100 g of C. tenuifolia. The minimum inhibitory concentration (MIC) values of (2.25 and 0.45 µg/ml) were obtained in purified flavonoids against Staphylococcus aureus and Enterobacter sp., respectively. The two flavonoids (Rutin and quercetin) showed significant in vitro anti-oxidant activity; in this regard, the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) scavenging potential of quercetin (86.1%) was higher than that of rutin (73.2%). However, for human hepatoma HepG2 and human carcinoma HeLa cells, quercetin exhibited high anti-cancer activity than rutin. The purified compounds (rutin and quercetin) with having great potential of free radical inactivator in HepG2 cells. The results suggest that MFE of C. tenuifolia could potentially be employed in traditional medicine as they are rich in compounds with anti-oxidant, anti-microbial and anti-cancer properties. Keywords: Cheilanthes tenuifolia, Column chromatography, Rutin, Quercetin, Fourier Transform-Infra Red Spectroscopy, Nuclear Magnetic Resonance

Wastewater treatment and reduction of metal pollutants are potent applications of bioelectroactive fuel cells (BFC) to reduce waste and reuse otherwise unavailable resources. This method is considered to be much simpler and faster compared with the conventional wastewater treatment in treatment plants which requires a rigorous physical, chemical, and biological process. BFC-assisted treatment has been shown to treat a wide variety of wastewater and recover valuable resources whilst simultaneously producing bioelectricity. The present chapter highlights the use of the bioelectroactive systems in treating wastewater from different sources and theelectrochemical reduction of metals and nonmetals in bioelectrochemical systems (BES). The efficiency and recovery of energy from these wastes in BES are briefly discussed.

Heavy metals removal and recovery from wastewater is a sustainable approach for wastewater treatment and environmental sustainability. This is also helpful to meet the strict effluent discharge norms. Acknowledging that wastewater presents a useful resource and the value of precious, semiprecious, and heavy metals has made it interesting to recover metals from wastewater. This chapter describes the sources, importance, and toxicity of heavy metals and the need to remove them before discharging effluents. The popular physical and chemical technologies, such as isolation, immobilization, toxicity and/or mobility reduction, physical separation, and extraction, used for the removal of heavy metals have been discussed along with their limitations. Finally, the configuration and application of bioelectrochemical systems (BES)-based systems present a sustainable alternative for the removal and recovery of heavy metals. Therefore in this chapter a general account of the process, principle, and BES that have been used for heavy metal removal and recovery has been covered.

As a renewable energy carrier, hydrogen gains international recognition, with the ability to substitute fossil fuels. A state-of-the-art technology called a microbial electrolysis cell (MEC) can produce viable, clean hydrogen energy and also treat wastewater using various renewable carbon sources. The key substrates tested include wastewater, fermentable, and nonfermentable organic effluents. This chapter mainly discuss the scientific fundamentals of MEC technology, including its operating principles, thermodynamics, and electron transfer mechanisms. This chapter also discusses the nutrient, heavy metal removal, and integrated technologies used for higher hydrogen production.

Waste from fish-processing units have been customarily disposed of through dumping at landfill sites or water bodies. Disposing of fish waste can be considered unbefitting waste management practice because the fish waste represents a valuable source of nutrient and energy. This chapter aims to summarize the microbial fuel cell approaches used for the treatment of fish waste. The Malaysian National Green Technology Policy on fish-waste treatment and the characteristics of fish-processing wastewater, along with the physiochemical parameters that affect the treatment process, are discussed in this chapter.

Bioelectrochemical systems (BESs) convert chemical energy into electrical energy using metabolic activities of microorganisms. This technology has gained tremendous interest and it is evolving not only for bioremediation of different wastewaters but also for production of bioenergy. The main aim of this chapter is to introduce the principles of the BESs and discuss the role of BESs in the production of bioenergy and remediation of different pollutants. Here, an effort is made to discuss the various types of BESs and production of bioenergy using these systems. Moreover, bioremediation of different recalcitrant pollutants using BESs is discussed. Furthermore, sustainability of this technology is also elaborated. Also, an attempt is made to discuss the scale up of these technologies from lab scale to field scale. It is observed that it is challenging to implement directly these systems for full-scale applications due to challenges in technical, microbiological, and economic viability. Thus, it is revealed that diverse expertise is required to improve this technology for sustainable and large-scale applications. Finally, brief conclusions are highlighted in the area of BESs for remediation of wastewaters and bioenergy production.

The bioelectroactive fuel cells (BFC) or bioelectrochemical systems (BES) are regarded as a potent source for producing green and sustainable energy. The two major BFCs studied extensively are the enzymatic fuel cells and the microbial fuel cells. The main difference between them is the bioactive source that catalyzes the electrochemical reaction in the system. In recent times BES has gained tremendous publicity due to its unique technique for producing fuel, bioremediation, and many other applications. The BES differs from chemical fuel cells (CFC) in terms of catalysts, reaction mechanism, operational conditions, yield, and quantity of the product, etc. Although the BES has some limitations, it is considered to be advantageous over conventional CFC in several ways. However, the losses and the limitations present in BES are the main drawbacks. The present chapter highlights the working mechanism, operational condition, and other fundamental concepts of the BFC.

In an era of electronics, recovering the precious metal such as gold from ever increasing piles of electronic-wastes and metal-ion infested soil has become one of the prime concerns for researchers worldwide. Biological mining is an attractive, economical and non-hazardous to recover gold from the low-grade auriferous ore containing waste or soil. This review represents the recent major biological gold retrieval methods used to bio-mine gold. The biomining methods discussed in this review include, bioleaching, bio-oxidation, bio-precipitation, bio-flotation, bio-flocculation, bio-sorption, bio-reduction, bio-electrometallurgical technologies and bioaccumulation. The mechanism of gold biorecovery by microbes is explained in detail to explore its intracellular mechanistic, which help it withstand high concentrations of gold without causing any fatal consequences. Major challenges and future opportunities associated with each method and how they will dictate the fate of gold bio-metallurgy from metal wastes or metal infested soil bioremediation in the coming future are also discussed. With the help of concurrent advancements in high-throughput technologies, the gold bio-exploratory methods will speed up our ways to ensure maximum gold retrieval out of such low-grade ores containing sources, while keeping the gold mining clean and more sustainable.

In the current global scenario, the problems of the depletion of fossil reserves, increasing waste generation, climate change, and the need for energy security are matters of prime concern. All these issues are inevitable in any economy today due to the absolute reliance on fossil fuels for fulfilling energy requirements. A global movement toward creating sustainable circular bioeconomies has taken shape over the past decade to address these problems. The valorization of waste through different technologies like incineration, pyrolysis, gasification, anaerobic digestion, and MFCs and MECs offers a scope of providing an alternative source of energy and other value-added products with an added advantage of solving the problem of waste management and reducing the problem of climate change. However, there may be an increase in other indirect environmental impacts due to the process of energy production from waste and these need to be quantified to understand the sustainability of the waste-derived bioenergy economy. A life cycle assessment (LCA) is a significant instrument used to measure and evaluate the ecological impact of a given bioenergy system. This chapter aims to address the importance of life cycle thinking to understand the sustainability of waste-derived energy systems along with the key challenges and recommendations for future LCA studies.

Present 21st century world has started facing several challenges (such as waste management, bioresource scarcity, food/and energy security, climate change, global warming and health risks) as a heavy price of reckless usage/or exploitation of natural resource. In such a scenario, the implementation of circular economy model (based on use, produce, consume, waste recovery/or recycling, sharing, leasing, reusing, repairing, renovating, refurbishing and using waste feedstock to produce secondary products) emerged as the best sustainable option than linear economy model (based on use, produce, consume and waste discard). Inculcation of circularity in every aspect of our life (behavior, livelihood, economy, infrastructure) can help us in attaining long-term goals of sustainability and harmonizing human existence on planet Earth. Recent technological advancements have assisted in creating sustainable methods (incineration, pyrolysis, composting, anaerobic digestion) for treating or recycling the enormous solid waste, thereby enhancing valuable product recovery (such as heavy metals, biogases, bioelectricity, feedstock). So, it is necessary to develop more efficient sustainable waste-to-energy technologies capable of reutilizing solid wastes and helping to safeguard the environment from waste generated hazards. This chapter deals with sustainable ways to incorporate solid wastes into the circular loop of circular economy model. This chapter will present practical solutions for solid waste recycling and for fully realizing the potential of solid waste in circular economy in terms of more revenues.

With the depletion of fossil fuels, growing energy demands, and the issue of climate change, finding sustainable renewable sources of energy has become extremely important. Innovative approaches are being developed for the production of bioenergy, biomaterials, and chemicals from organic wastes so as to find an alternative to fossil fuels as well solve the problem of the dumping of organic wastes into landfills. One viable options of energy generation from organic wastes is biogas. An added advantage of biogas technology is the production of organic manure for crops. This chapter is intended to evaluate the current status of biogas production, the various feedstocks available, the technological advancements being made, and the barriers in the dissemination of these technologies.

Bioactive flavonoids derived from Asplenium nidus (fern) possess potent tumoricidal, anti-bacterial, anti-oxidant activities that are responsible for their chemo-preventive potential against multidrug-resistant (MDR) pathogens, Proteus mirabilis, Proteus vulgaris and Pseudomonas aeruginosa. Fractionation and recognition of the flavonoids were attained through gas chromatography and mass spectrometry (GC/MS). Twelve known and three unknown compounds were revealed by fractions 1 & 3, representing 13.12% and 2.61% out of the total composition (15.12%). Gliricidin7-O-hexoside was found 3.83% followed by quercetin-7-O-rutinoside (3.09%) keampferol-3-O-rutinoside (0.19%) and myricetin-3-O-rhamnoside (1.10%). The anti-bacterial and anti-oxidant activities of present fractions along with pure bioactive constituents were tested against three MDR pathogens through microbroth dilution: MIC50 ranges for amoxicillin, gliricidin7-O-hexoside and quercetin 7-O-rutinoside were 0.0003–0.06 μg/mL, 0.004–0.06 μg/mL and 0.005–6.0 μg/mL, respectively. Gliricidin-7-O-hexoside and quercetin-7-O-rutinoside’s inhibitory activities were comparable to standard antibiotic, amoxicillin (p > 0.05). Herein we report for the first time a number of flavonoids that may act as the source of therapeutically useful compounds against MDR pathogens. In addition, the most extracted flavonoids (gliricidin-7-O-hexoside (78.1%) and quercetin-7-O-rutinoside (69.2%) showed a significant in vitro antioxidant activity i.e. DPPH radical scavenging activity. Both fractions of A. nidus showed obvious cytotoxic effects on human hepatoma HepG2 and human carcinoma HeLa cells. Moreover, the anti-cancer activity generally enhanced with ameliorating antioxidant and antibacterial potential of fern’s flavonoids. These findings illustrate the potential of this fern as a probable source of bioactive constituents and provide a scientific basis for its folklore or ethno-medicinal uses for infectious diseases and cancers. Keywords: Asplenium nidus, Flavonoids, Anti-oxidant, Anti-cancer, Anti-bacterial

The purposes of this study were to investigate the effects of operating parameters, such as electrode material, current density, percentage of hydrogen peroxide and amount of polialuminum chloride (PAC) on chemical oxygen demand (COD) removal of palm oil mill effluent (POME). The current density was varied between 30–80 mA cm −2 , PAC (1–3 g L −1 ) as coagulant-aid and 1 and 2% of hydrogen peroxide as an oxidizing agent. As for the performance of electrode type, iron was more effective than aluminum. It appeared that the removal of COD increased with the increased of current density. When PAC and H 2 O 2 increased, the percent of COD removal was increasing as well. The overall results demonstrate that electrocoagulation is very efficient and able to achieve more than 70% COD removal in 180 min at current density 30–80 mA cm −2 reliant upon the concentration of H 2 O 2 and PAC.