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This review analyses the relevant studies which focused on hydrogen synthesis by dark fermentation of galactose from macroalgal biomass by discussing the inoculum-related pretreatments, batch fermentation and inhibition, continuous fermentation systems, bioreactor designs for continuous operation and ionic liquid-assisted catalysis. The potential for process development is also revisited and the challenges towards suppressing glucose dominance over a galactose-based hydrogen production system are presented. The key challenges in the pretreatment process aiming to achieve a maximum recovery of upgradable (fermentable) sugars from the hydrolysates and promoting the concomitant detoxification of the hydrolysates have also been highlighted. The research avenues for bioprocess intensification connected to enhance selective sugar recovery and effective detoxification constitute the critical steps to develop future red macroalgae-derived galactose-based robust biohydrogen production system.

Three abundant coffee residues (green coffee powder, parchment and defatted cake) and sugarcane vinasse were co-digested under thermophilic anaerobic conditions. A pilot plant was set-up and operated under optimized conditions using mesophilic sludge seed to produce biohydrogen. The initial conditions were acidogenic regimes (pH 5.0–6.5) followed by methanogenic conditions (pH 6.5–8.0). Results indicated the concomitant generation of biohydrogen and biomethane (termed biohythane) from the coffee residues. The green coffee powder bioreactor produced a hydrogen-rich biohythane for the first 15 days with a maximum yield on day four (31.45% hydrogen). Results also suggested that start-up of the biosystem reached the methanogenic stage in only 20–25 days and produced methane yields as high as 0.14mlCH4/gVSadded. For the co-digestion of defatted cake and vinasse, the only gas of interest produced was biohydrogen 32% vol./vol. between the 9th and 32nd day. Anaerobic co-digestion of parchment and vinasse produced biohythane at an average yield of 0.21mlCH4/gVSadded.

The effects of microwave irradiation on the digestibility and biogas production of cauliflower (Brassica oleracea var. botrytis) and cabbage (Brassica oleracea var. capitata) leaves were investigated using biochemical methane potential (BMP) assays. Cow dung was utilised as inoculum. Different microwave powers (87.5, 175 and 350 W) were applied in a first set of runs for 15 min. The second set consisted of 20, 25 and 30 min irradiation at 350 W. Based on ANOVA analysis (α = 0.05), biogas production was significantly higher for the irradiated substrates compared to controls. The peak biogas production was 700 ml for 36 days HRT for 350 W/25 min. Peak COD, SCOD, volatile and total solids removals were 54.84%, 39.08%, 34.60% and 71.96%, respectively. Phosphate and total nitrogen increased significantly. Cumulative biogas production data fitted the modified Gompertz equation well. The highest biogas yield was 0.271 L/g VSremoved at a 350 W microwave irradiation for 30 min.

A sustainable expansion of corn-based and sugarcane-based ethanol production could induce food safety and also decrease the Southern Brazilian Amazon’s extensive cattle farming and deforestation of new pasture areas. The present work aims to evaluate a technological prospect regarding the strategies and market potential of bioenergy and bio-products generation for a corn-based production system. A ‘Strategic Foresight’ approach was formulated and thoroughly analyzed. Overall, it showed that productivity improvement of livestock could be accomplished, and light vehicles’ energy demand using anhydrous and hydrous ethanol could also be enhanced. The results demonstrated that greenhouse gas emissions from a ‘Corn-to-Ethanol’ production system are smaller than the conventional Mills. The Foresight analysis identified that the positive energy balance from ethanol provides more energy than its industrial consumption. ‘Corn Ethanol’ production processes are integrated in six (6) “Flex Mills” in Brazil by taking advantage of the existing installations for sugarcane processing with a production ranging from 250 to 500 million liters/year. The State of Mato Grosso shall have twelve (12) Ethanol Mills in “Full” operation until 2021. The SWOT analysis in this study revealed that: the economy's development could generate direct and indirect jobs, potentially supporting the energy transition to a low-carbon economy through the valorization of agricultural and livestock products, and thus allowing the expansion of confined livestock, pig, and fish farming. Finally, the Strategic Foresight showed the multi-tiered importance of technological application and cooperation in the agro-industrial sector.

The objective of this study was to evaluate the effects of sonication on the biogas production dynamics of sugarcane straw and vinasse in an anaerobic digestion. Two different ultrasound pretreatments were evaluated namely 180 W of ultrasonic power irradiated at 37 kHz for 30 min (PBU) and 800 W of ultrasonic power irradiated at 19 kHz for 15 min (PSU). Significant differences were observed in the biogas compositions of the PBU and PSU pretreatments and their respective controls. A continuous increase in methane concentration of the biohythane (biohydrogen and methane combined) was recorded in the PBU reactors (60–80% by volume). The main effect of ultrasound pretreatment was on the composition biohydrogen, methane and carbon dioxide (biohythane) produced.

This review summarizes the recent essential aspects of subcritical and supercritical water technology applied tothe extraction, hydrolysis, carbonization, and gasification processes. These are clean and fast technologies which do not need pretreatment, require less reaction time, generate less corrosion and residues, do not usetoxic solvents, and reduce the synthesis of degradation byproducts. The equipment design, process parameters, and types of biomass used for subcritical and supercritical water process are presented. The benefits of catalysis to improve process efficiency are addressed. Bioactive compounds, reducing sugars, hydrogen, biodiesel, and hydrothermal char are the final products of subcritical and supercritical water processes. The present review also revisits advances of the research trends in the development of subcriticaland supercritical water process technologies.

Hydrogen production from lignocellulosic biomass (LCB) using dark fermentation is an interesting research niche being developed over the last decade. This review analyses the relevant studies which focused on biohydrogen production from LCB using dark fermentation techniques in terms of substrate characterization, bottlenecks associated with the pretreatment and its subsequent utilization, possible remedies for the scale-up of the most adapted processes and finally the prospects and suggestions which may be envisaged. Studies dealing primarily with the utilization of raw and pretreated LCB have been assessed in terms of biohydrogen production performance for production rate and yield. Energy production analysis and prospecting of suitable cellulosic biomass and efficient cellulolytic microbes have been elucidated towards better cellulose hydrolysis and efficient conversion of LCB to H2 in addition to process economics.

Over the last couple of decades, academic research on adsorbents has been flourishing. The preparation, functionalization, and adsorption performance evaluation have grown explosively. Novel adsorbents have demonstrated excellent capabilities to remove metal ions and organic contaminants from aqueous environments having different physicochemical conditions. This article presents gaps and potential research possibilities related to economic assessment, benchmarking of synthetic real wastewaters, adsorptive (component) additivity, constraints of process scale-up, process intensification, and modeling, simulation and optimization of large-scale adsorption-based water remediation systems. These discussions foster fresh ideas and investigations in the cognate science and engineering disciplines so that industrial applications of novel adsorbents for innovative water treatment matures both technically and cost-effectively.

The aim of the study was to investigate the effects of carton in the composting process of mixed vegetable wastes using an experimental composter of capacity 80L. Three different mixes were set-up (Mixes 1, 2 and 3) which consisted of vegetable wastes, 2.0kg paper and bulking agents, vegetable wastes, 1.5kg carton and bulking agents, vegetable wastes, 4.5kg carton and bulking agents, respectively. Temperature evolution, pH trends, moisture levels, respiration rates, percentage volatile solids and electrical conductivity were monitored for a period of 50days. The system remained under thermophilic conditions for a very short period due to the small size of the reactor. The three mixes did not exceed a temperature of 55°C, where sanitization takes place by the destruction of pathogens. The highest peak of CO2 evolution was observed in Mix 2 indicating that maximum microbial degradation took place in that mix.

The agricultural and food industry sectors play essential roles in the global economy, but also generate significant amounts of wastes every year associated to their activities, which require an appropriate management. As an alternative, agro-industrial by-products can be used for obtaining valuable compounds such as amino acids, phenolic compounds, water-soluble sugars, organic acids, methane and oils, among others. Several processes have been developed for obtaining such compounds from by-products and residues, among of which the subcritical and supercritical water technologies are considered as green alternatives. This review presents a concise assessment of the research findings reported from 2001 to 2020 on the subcritical and supercritical water extraction and hydrolysis of protein-based substrates to obtain amino acids, addressing aspects such as: economic relevance of protein and amino acids, main routes for protein extraction, influence and interactions of the main reaction parameters and conditions. Protein aggregation-disaggregation and a comparison of selected extraction arrangements, reactor configurations, and finally, future research perspectives are also discussed.

Different types of biomass are being examined for their optimum hydrogen production potentials and actual hydrogen yields in different experimental set-ups and through different chemical synthetic routes. In this review, the observations emanating from research findings on the assessment of hydrogen synthesis kinetics during fermentation and gasification of different types of biomass substrates have been concisely surveyed from selected publications. This review revisits the recent progress reported in biomass-based hydrogen synthesis in the associated disciplines of microbial cell immobilization, bioreactor design and analysis, ultrasound-assisted, microwave-assisted and ionic liquid-assisted biomass pretreatments, development of new microbial strains, integrated production schemes, applications of nanocatalysis, subcritical and supercritical water processing, use of algae-based substrates and lastly inhibitor detoxification. The main observations from this review are that cell immobilization assists in optimizing the biomass fermentation performance by enhancing bead size, providing for adequate cell loading and improving mass transfer; there are novel and more potent bacterial and fungal strains which improve the fermentation process and impact on hydrogen yields positively; application of microwave irradiation and sonication and the use of ionic liquids in biomass pretreatment bring about enhanced delignification, and that supercritical water biomass processing and dosing with metal-based nanoparticles also assist in enhancing the kinetics of hydrogen synthesis. The research areas discussed in this work and their respective impacts on hydrogen synthesis from biomass are arguably standalone. Thence, further work is still required to explore the possibilities and techno-economic implications of combining these areas for developing robust and integrated biomass-to-hydrogen synthetic schemes.

The hydrothermal pretreatment route is gaining research interest as a potentially green method for deconstructing lignocellusic biomass. Based on the relevant literature, the conversion of biomass into platform chemicals or energy carriers through hydrothermal processes has been found to be advantageous by reason of enhanced process performance, while being environmentally friendly and technologically innovative. In this review, an assessment has been made of recent research findings and reservations in regard to the synthesis of subcritical and supercritical hydrolysates and the production of platform chemicals namely ethanol, butanol, furfural, hydroxymethylfurfural, lactic acid, levulinic acid and its derivatives, succinic acid, sorbitol, and xylitol. This review also proposes a number of future research-oriented directions to harness the findings of primary research-oriented efforts for developing technically and economically feasible large-scale systems.

Heavy metals released from industrial activities pose a significant threat to the environment and public health due to their reported toxicity even at trace levels. Although there are several available methods to treat or remove heavy metals from water and wastewater, the research focuses on development of technological solutions which sound environmental friendly and economically feasible, able to reduce the costs and maximize the efficiency. In this framework, the biosorption process, which uses cheap and non-pollutant materials, may be considered as an alternative, viable and promising, technology for heavy metal and metalloid ions sequestration and ultimately removal technology in the waste water treatment. However, there is as yet little data on full-scale applications for the design and testing of adsorption units using single biosorbents and their combinations to sequester heavy metal ions from multi-metal systems. Immediate research and development is hence earnestly required in this specific direction to further make progress this blooming technology and widen its scope of application to real situations needing heavy metal pollution remediation. This review provides a comprehensive appraisal of the equilibrium modeling of a number of biosorption processes as well as the structural, chemical and morphological modifications and activation of biosorbents. Further the relative merits of the methods used to recover sequestered heavy metal ions and regenerate biosorbents through desorption routes and their future applications are discussed.

The kinetics, adsorption isotherms, thermodynamics and spectroscopic analyses of the removal of the anthraquinone dye, Alizarin Red S by adsorption onto mustard husk were studied. Batch adsorption experiments were conducted using synthetic aqueous solutions and the effects of initial dye concentration, initial pH of solution, adsorbent dose and temperature were investigated. The mustard husk adsorbent was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy and through the determination of pH zpc . The equilibrium adsorption data fitted very well to the Freundlich model and this provided evidence of multilayer adsorption of the dye molecules onto the active sites on the biosorbent. The kinetic studies showed that the process was quite rapid and 90% of equilibrium capacity was achieved within 80 min. The process followed the pseudo-second-order kinetic model with a k 2 value of 0.094 g/mg min for an Alizarin Red S concentration of 25 mg/L. Positive Δ H ° and negative Δ G ° were indicative of the endothermic and spontaneous nature, respectively, of Alizarin Red S removal by adsorption onto mustard husk biomass.

Due to the excellent chelating properties of aminopolycarboxylic acid (APCAs), they can be used for the removal of metals from contaminated waters. This paper reviews the research results obtained for both commercial and self-prepared adsorbents functionalized with four most common APCAs: iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). The structural characteristics and unique metal binding properties of these chelating adsorbents are presented. The theory of the adsorption phenomena is discussed based on the kinetics of adsorption, equilibrium adsorption isotherm models, and thermodynamic models. The most important applications of APCA-functionalized adsorbents are also described. APCA-functionalized adsorbents are found to be highly promising materials for metal removal from contaminated waters.

The contribution and insights of the immobilization technology in the recent years with regards to the generation of (bio)hydrogen via dark fermentation have been reviewed. The types of immobilization practices, such as entrapment, encapsulation and adsorption, are discussed. Materials and carriers used for cell immobilization are also comprehensively surveyed. New development of nano-based immobilization and nano-materials has been highlighted pertaining to the specific subject of this review. The microorganisms and the type of carbon sources applied in the dark hydrogen fermentation are also discussed and summarized. In addition, the essential components of process operation and reactor configuration using immobilized microbial cultures in the design of varieties of bioreactors (such as fixed bed reactor, CSTR and UASB) are spotlighted. Finally, suggestions and future directions of this field are provided to assist the development of efficient, economical and sustainable hydrogen production technologies.

In pursuit of a green and sustainable world, wastewater remediation and sludge treatment have equally become a growing global environmental concern. Several innovative treatment processes have been designed throughout the last few decades for treating wastewaters and sludges but many of them are very costly and operate at low efficiencies. In view to find novel treatment processes, active research is being conducted globally. Microwave irradiation technology is gradually making a modest but promising mark of its own in enhancing to significant extents the ease, fastness, and efficiency of certain treatment processes involved in wastewater and sludge management. The authors focus on and appraise the budding use and application of microwave irradiation in chemical research undertaken for sludge and wastewater treatment. The related aspects of microwave-assisted heavy metal stabilization, pathogen inactivation, wastewater parameter analysis, and wastewater treatment polymers synthesis are also discussed.

Arsenic is a toxic element and has been responsible for many accidental, occupational, deliberate, and therapeutic poisonings since its discovery in 1250. It occurs in natural waters as the arsenite (As3+) and arsenate (As5+) ions. The solubility of arsenite and arsenate compounds is relatively high so that these ions are readily transported through aqueous routes into the environment. Arsenic can be transferred from soils to crops and accumulates in various food crops and aquatic plants. The fascinating chemistry and toxicity potential make arsenic and its compounds of particular scientific interest and environmental concern. The conventional removal of heavy metals from wastewater, natural waters, and drinking water has only limited effects on arsenic removal. In this review, the main engineering and medical applications, salient health and environmental concerns, novel research on treatment for arsenic poisoning, and removal technologies for arsenic and their derivatives are discussed and enumerated wi...

Sustainable development requires the development and promotion of environmental management and a constant search for green technologies to treat a wide range of aquatic and terrestrial habitats contaminated by increasing anthropogenic activities. Bioremediation is an increasingly popular alternative to conventional methods for treating waste compounds and media with the possibility to degrade contaminants using natural microbial activity mediated by different consortia of microbial strains. Many studies about bioremediation have been reported and the scientific literature has revealed the progressive emergence of various bioremediation techniques. In this review, we discuss the various in situ and ex situ bioremediation techniques and elaborate on the anaerobic digestion technology, phytoremediation, hyperaccumulation, composting and biosorption for their effectiveness in the biotreatment, stabilization and eventually overall remediation of contaminated strata and environments. The review ends with a note on the recent advances genetic engineering and nanotechnology have had in improving bioremediation. Case studies have also been extensively revisited to support the discussions on biosorption of heavy metals, gene probes used in molecular diagnostics, bioremediation studies of contaminants in vadose soils, bioremediation of oil contaminated soils, bioremediation of contaminants from mining sites, air sparging, slurry phase bioremediation, phytoremediation studies for pollutants and heavy metal hyperaccumulators, and vermicomposting.

This study investigates the potential of incorporating inorganic amendments such as coal and bagasse ashes in different composting mixes. 10 different composting mixes were assessed as follows: A-20% bagasse ash (BA) with unsorted municipal solid wastes (UMSW); B-40% BA with UMSW; C-UMSW; D-20% BA with sorted municipal solid wastes (SMSW); E-40% BA with SMSW; F-SMSW; G-20% coal ash (CA) with UMSW; H-40% CA with UMSW; I-20% CA with SMSW and J-40% CA with SMSW. The composting processes were carried out in rotary drum composters. Composting mixes D, F, G and I achieved a temperature above 55 °C for at least 3 days, with the following peak temperatures: D-62 °C, F-57 °C, G-62 °C and I-58 °C. D resulted in the highest average net Volatile solids (VS) degradation of 68.6% and yielded the highest average volume reduction of 66.0%. The final compost from D, G, I, C and F were within range for electrical conductivities (EC) (794–1770 μS/cm) and pH (6.69–7.12). The ashes also helped in maintaining high average water holding capacities within the range of 183–217%. The C/N ratio of sorted wastes was improved by the addition of 20% coal ash and bagasse ash. Higher germination indices, above 0.8 were obtained for the ash-amended compost (D, G, I), indicating the feasibility and enhancement of using bagasse and coal ash as inorganic amendment in the composting process. Regarding heavy metals content, the chromium concentration for the composting mix G was found to be the highest whereas mixes D and I showed compliance with the MS (Mauritian Standards) 164 standards.

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A study was conducted on two types of plastic materials, Mater-Bi Novamont (MB) and Environmental Product Inc. (EPI), to assess their biodegradability under aerobic and anaerobic conditions. For aerobic conditions, organic fractions of municipal solid wastes were composted. For the anaerobic process, anaerobic inoculum from a wastewater treatment plant was used. Cellulose filter papers (CFP) were used as a positive control for both mediums. The composting process was monitored in terms of temperature, moisture and volatile solids and the biodegradation of the samples were monitored in terms of mass loss. Monitoring results showed a biodegradation of 27.1% on a dry basis for MB plastic within a period of 72 days of composting. Biodegradability under an anaerobic environment was monitored in terms of biogas production. A cumulative methane gas production of 245 ml was obtained for MB, which showed good degradation as compared to CFP (246.8 ml). However, EPI plastic showed a cumulative methane value of 7.6 ml for a period of 32 days, which was close to the blank (4.0 ml). The EPI plastic did not biodegrade under either condition. The cumulative carbon dioxide evolution after 32 days was as follows: CFP 4.406 cm3, MB 2.198 cm3 and EPI 1.328 cm3. The cumulative level of CO2 varying with time fitted sigmoid type curves with R2 values of 0.996, 0.996 and 0.995 for CFP, MB and EPI, respectively.

Samples of textile effluents were subjected to physico-chemical treatment using alum, Polyaluminium Chloride (PAC), and different anionic and cationic acrylamide copolymers. Except for alum, all chemicals were tested individually. Combinations of alum and PAC with different anionic and cationic polyelectrolytes were also tested. Results indicated the anionic polyelectrolyte to be the best polymer when used in combination with inorganic coagulants. 30-40 mg/L PAC and 0.75 mg/L of anionic polymer resulted in the best removals of Chemical Oxygen Demand (COD), Total Suspended Solids (TSS) and Turbidity of 32.0-38.2%, 80.0-85.0% and 25.3-47.0%, respectively. This study indicated that dye-loaded textile wastewater could be treated with blends of inorganic?organic coagulants to reduce the organic load. However, the colour of the wastewater could not be removed.

The co-composting of shredded waste office paper with Broiler Litter (BL) in windrows was analysed in this study. Two compost mixes were monitored for five weeks; Mix 1 comprised 322kg BL, 117 kg shredded paper and 310L water and Mix 2 consisted of 112 kg BL, 265 kg shredded paper and 290 L water. The initial wet moisture content, initial porosity and initial wet bulk density for Mix 1 were 54.6%, 74.7% and 337kg/m?, respectively. The respective parameters for Mix 2 were 48.6%, 87.7% and 185 kg/m?. The initial C:N ratio was kept at 20.8 in both mixes. Peak temperatures recorded for Mix 1 and Mix 2 at day 5 were 71.4?C and 62.7?C, respectively. Temperatures remained above 60?C for more than 10 days in both windrows. The pH for both mixes varied between 7.2 and 8.8. An increase in wet bulk density of 47.6% for Mix 1 and 150% for Mix 2 was obtained. The net decrease in Volatile Solids (VS) was of 57.1% (Mix 1) and 56.3% (Mix 2) at the end of week 5. The respiration rate peaked at 33.7 mg CO2.C/day.gVS on day 3 for Mix 1 and decreased to 0.98 mg CO2.C/day.gVS on day 37. The concentrations of lead, cadmium, total chromium and zinc were 612 mg/kg, 60.8 mg/kg 103.2 mg/kg and 5760 mg/kg, respectively, in the final compost of Mix 1. NPK content of the final compost from Mix 1 was 5-5-10 (dry matter basis) with a level of phosphorous of 20,817 ppm.