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Published in Chemical Papers. Full-text access:https://rdcu.be/cZGaK

The release of pharmaceuticals into the environment induces adverse effects on the metabolism of humans and other living species, calling for advanced remediation methods. Conventional removal methods are often non-selective and cause secondary contamination. These issues may be partly solved by the use of recently-developped adsorbents such as molecularly imprinted polymers. Here we review the synthesis and application of molecularly imprinted polymers for removing pharmaceuticals in water. Molecularly imprinted polymers are synthesized via several multiple-step polymerization methods. Molecularly imprinted polymers are potent adsorbents at the laboratory scale, yet their efficiency is limited by template leakage and polymer quality. Adsorption performance of multi-templated molecularly imprinted polymers depends on the design of wastewater treatment plants, pharmaceutical consumption patterns and the population serviced by these wastewater treatment plants.

Pure water will become a golden resource in the context of the rising pollution, climate change and the recycling economy, calling for advanced purification methods such as the use of nanostructured adsorbents. However, coming up with an ideal nanoadsorbent for micropollutant removal is a real challenge because nanoadsorbents, which demonstrate very good performances at laboratory scale, do not necessarily have suitable properties in in full-scale water purification and wastewater treatment systems. Here, magnetic nanoadsorbents appear promising because they can be easily separated from the slurry phase into a denser sludge phase by applying a magnetic field. Yet, there are only few examples of large-scale use of magnetic adsorbents for water purification and wastewater treatment. Here, we review magnetic nanoadsorbents for the removal of micropollutants, and we explain the integration of magnetic separation in the existing treatment plants. We found that the use of magnetic nanoadsorbents is an effective option in water treatment, but lacks maturity in full-scale water treatment facilities. The concentrations of magnetic nanoadsorbents in final effluents can be controlled by using magnetic separation, thus minimizing the ecotoxicicological impact. Academia and the water industry should better collaborate to integrate magnetic separation in full-scale water purification and wastewater treatment plants.

The access to clean water is a critical issue in the context of climate change and worldwide pollution, calling for advanced methods of purification. Recent advances in materials science, nanoscience, and analytical chemistry have led to the design of novel nanoadsorbents having a unique properties, structure, and adsorption performances. In particular, research has focused on all-inclusive adsorbents which can remove different contaminants simultaneously. Here, we review the adsorption dynamics of doped, ionic liquid-enhanced, bio-based, and chemically functionalized materials. We examine their characteristics, underlying principles of adsorption, and their potential limitations in adsorbing various metal ions and xenobiotics. We found that chemical functionalization with specific organic moieties is a preferred approach for enhancing the adsorption capacities and selectivity of raw materials. Moreover, doping can also modulate the morphology, electronic structure, and surface chemistry for higher performance. Ionic liquids are promising solvents for the synthesis of stable adsorbents, owing to ionic liquid ability to pull other molecules through hydrogen bonds or electrostatic forces.

This review discusses a fresh pool of research findings reported on the multiple roles played by metal-based, magnetic, graphene-type, chitosan-derived, and sonicated nanoparticles in the treatment of pharmaceutical- and agrochemical-contaminated waters. Some main points from this review are as follows: (i) there is an extensive number of nanoparticles with diverse physicochemical and morphological properties which have been synthesized and then assessed in their respective roles in the degradation and mineralization of many pharmaceuticals and agrochemicals, (ii) the exceptional removal efficiencies of graphene-based nanomaterials for different pharmaceuticals and agrochemicals molecules support arguably well a high potential of these nanomaterials for futuristic applications in remediating water pollution issues, (iii) the need for specific surface modifications and functionalization of parent nanostructures and the design of economically feasible production methods of such tunable nanomaterials tend to hinder their widespread applicability at this stage, (iv) supplementary research is also required to comprehensively elucidate the life cycle ecotoxicity characteristics and behaviors of each type of engineered nanostructures seeded for remediation of pharmaceuticals and agrochemicals in real contaminated media, and last but not the least, (v) real wastewaters are extremely complex in composition due to the mix of inorganic and organic species in different concentrations, and the presence of such mixed species have different radical scavenging effects on the sonocatalytic degradation and mineralization of pharmaceuticals and agrochemicals. Moreover, the formulation of viable full-scale implementation strategies and reactor configurations which can use multifunctional nanostructures for the effective remediation of pharmaceuticals and agrochemicals remains a major area of further research.

Biohydrogen production from various organic wastes, wastewaters and biomass has been widely studied due to the higher production rates and fundamentals and technologies have also been well developed and heavily documented through diverse laboratory-scale bioreactors. Recently, research has been geared to the concomitant production of biohydrogen and methane which is so called “biohythane”. One-stage and two-stage (bio-H2 + bio-CH4) methods are the main biohythane production methods and this field of research for probing into green biofuels is gradually gaining ground. In this paper, the salient aspects of biohythane research at the present time are revisited and the research success and latent promise of biohythane are highlighted based on the findings of the relatively few publications in this area.

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.

Endosulfan is a highly polluting and toxic pesticide which has been used in many areas globally to control pests in view to improve productivity. Concomitantly, endosulfan has also been associated with many cases of environmental pollution and various types of irreversible metabolic dysfunctions in living organisms both on lands and in waters. Subsequently, since over the last three decades, several endosulfan remediation methods have been studied and many are gradually bringing hope towards efficient clean-up. This article specifically reviews endosulfan degradation and endosulfan removal by discussing the recent findings reported and the trends observed in studies reporting bacterial and fungal bioremediation, photocatalytic degradation, adsorption and membrane separation processes. The salient observations from this review are: there are many bacterial species which degrade endosulfan isomers with relatively high efficiencies; many studies indicate the merits of plants in phytoextracting and accumulating endosulfan but the identification of endosulfan hyperaccumulators remains; photocatalytic systems involving one or two metals also bring about significant endosulfan degradation but issues related with variations in rates of reactions, catalyst deactivation due to fouling, intricacy of metal-based nanocatalyst structures and their complex fabrication methods and lack of control of morphology of the nanosized structures have to be addressed; and membrane retention systems specifically treating endosulfan-contaminated aqueous media are scanty and more analysis is also needed to optimize the shear force-membrane structural integrity-membrane stability rapport of the membranes being developed. In the end, a number of research and development avenues which need further attention and probing towards the development of suitable endosulfan-remediation routes are pointed out. Post-print / Final draft

The green approach of the one-pot enzyme-assisted biomass deconstruction for the production of biofuels and high-value added chemicals in the presence of combined ionic liquids with metal nanoparticles (CILMNPs) process is receiving more interest in biomass-to-energy research. This paper gives a succinct overview of the recent applications of CILMNPs in the pretreatment of lignin-based biomass for macrocellular deconstruction at the one-pot scale and then holistically addresses the multifarious research hurdles, challenges and prospects which have to be addressed to achieve the green merits on a larger scale of processing. Once the one-pot green metrics will be matched by their corresponding process metrics, the potential for pilot-scale production and eventually industrial utilization of CILMNPS will take good shape. Furthermore, such process scale-up campaigns using CILMNPS for biomass depolymerization will have to be robustly designed for an effective and efficient application by selecting bioprocesses involving enzymatic hydrolysis, saccharification and deoxygenation/hydrodeoxygenation routes operated under continuous regimes. These tasks will demand considerable applied research efforts in the form of process intensification and optimization both at the one-pot scale and for prospective large-scale bioprocessing units.

The release of recalcitrant dyes into the biosphere is a threat because of pollution and environmental health issues. Adsorption using commercial activated carbon has been effective in industrial dye-loaded effluent remediation to some acceptable extent. However, commercial activated carbon suffers from limitations related to cost, relatively lower adsorption capacity, fewer microporous and mesoporous networks in comparison with other competing adsorbents, and reduced adsorption efficiency after regeneration. Here we review the recent developments in applying microwave irradiation, ultrasonication, ionic liquids and nanoscience for the preparation, activation, and physical, chemical and biological functionalization of novel and more potent adsorbents such as metal, mineral, carbon and polymer-based nanoparticles for dye removal. We observed that microwave and ultrasound irradiation and the use of ionic liquids are highly beneficial for the preparation of adsorbent materials; those adsorbents display enhanced porous structures and morphologies that account for much larger surface areas for faster adsorption interactions. Graphene-based, magnetic, cellulose-based and nanocomposite adsorbents are more selective and thermally more stable, faster in dye adsorption kinetics, have higher adsorption capacities for many dyes and can be regenerated for reuse without significant decrease in adsorption capacity. The scales of fabrication of green adsorbents do not go beyond the kilogram scale.

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.

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 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.

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.

Biohydrogen production from lignocellulosic biomass (LCB) is an active research area. Several workers have tested a number of substrates under different operational conditions and brought forward the many positive process performance features and identified the main sources of inhibition. This review analyzes selected fermentative biohydrogen production processes by revisiting the core biohydrogen production performances in terms of gas production rates and yields and equally addresses the options for process enhancement by the application of through pretreatment methods and detoxification of process inhibitors. In addition, the issues related to continuous biohydrogen operation in different reactor configurations are highlighted. Lastly, future avenues of research which may be engendered and engineered to enhance the biohydrogen generation and process biokinetics are discussed. This review intends to provide the fundamental understanding of biohydrogen production and provides a perspective on future developments in this area of applied research.

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.

Excess consumption of energy by humans is compounded by environmental pollution, the greenhouse effect and climate change impacts. Current developments in the use of algae for bioenergy production offer several advantages. Algal biomass is hence considered a new bio-material which holds the promise to fulfil the rising demand for energy. Microalgae are used in effluents treatment, bioenergy production, high value added products synthesis and CO2 capture. This review summarizes the potential applications of algae in bioelectrochemically mediated oxidation reactions in fully biotic microbial fuel cells for power generation and removal of unwanted nutrients. In addition, this review highlights the recent developments directed towards developing different types of microalgae MFCs. The different process factors affecting the performance of microalgae MFC system and some technological bottlenecks are also addressed.

Textile effluents in natural waters pose environmental health problems if not treated to safe limits. Various bacterial species have the potential to degrade dyes. Here we studied the ability of Bacillus algicola to decolourise red, blue and yellow azo dyes. B. algicola was isolated from soil samples taken from a sanitary landfill site. Isolation and screening were performed using mineral salt medium. Dye-decolourising isolates were assessed in their capacity to decolourise dyes. Experiments were conducted at pH 6, 7 and 8, and 25, 35 and 45 °C. Phytotoxicity of the dyes and biodegradation products was assessed by seed germination tests. Results show that B. algicola gave the highest decolourisation at pH 8.0 and 25 °C in the presence of yeast extract as media supplement. B. algicola degraded the red and blue azo dyes by over 95%. The phytotoxicity results indicated that biodegradation products of the red and blue azo dyes were not toxic. Biodegradation products of the yellow dye were, however, toxic and considerably hindered germination. From these results, we infer that B. algicola has good potential for degrading and decolourising the red and blue test azo dyes.

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.

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 persistence and bioaccumulation of environmental pollutants in water bodies, soils and living tissues remain alarmingly related to environmental protection and ecosystem restoration. Adsorption-based techniques appear highly competent in sequestering several environmental pollutants. In this review, the recent research findings reported on the assessments of composts and compost-amended soils as adsorbents of heavy metal ions, dye molecules and xenobiotics have been appraised. This review demonstrates clearly the high adsorption capacities of composts for umpteen environmental pollutants at the lab-scale. The main inferences from this review are that utilization of composts for the removal of heavy metal ions, dye molecules and xenobiotics from aqueous environments and soils is particularly worthwhile and efficient at the laboratory scale, and the adsorption behaviors and effectiveness of compost-type adsorbents for agrochemicals (e.g. herbicides and insecticides) vary considerably because of variabilities in structure, topology, bond connectivity, distribution of functional groups and interactions of xenobiotics with the active humic substances in composts. Compost-based field-scale remediation of environmental pollutants is still sparse and arguably much challenging to implement if, furthermore, real-world soil and water contamination issues are to be addressed effectively. Hence, significant research and process development efforts should be promptly geared and intensified in this direction by extrapolating the lab-scale findings in a cost-effective manner.

Textile wastewaters contain refractory dyes that cause pollution and socio-economic issues, thus calling for efficient remediation techniques such as photocatalysis. We review the fabrication, functionalization, performance and limitations of doped catalysts for degrading and mineralizing dyes. We present developments in photocatalyst immobilization and photocatalytic reactor design. Methods such as microwave irradiation, sonication and use of ionic liquids are emerging for the preparation of doped photocatalysts. Whilst single-dye systems have been extensively studied, there is limited knowledge on multiple-dye systems. Immobilization of photocatalysts is gaining popularity for large-scale application, but faces issues of erosion, corrosion, mechanical strength and structure integrity. Ecotoxicological studies are required in real environments to validate the potential applications of nanostructured doped photocatalysts.

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.

International audience; This review provides the alternative routes towards the valorization of dark H-2 fermentation effluents that are mainly rich in volatile fatty acids such as acetate and butyrate. Various enhancement and alternative routes such as photo fermentation, anaerobic digestion, utilization of microbial electrochemical systems, and algal system towards the generation of bioenergy and electricity and also for efficient organic matter utilization are highlighted. What is more, various integration schemes and two-stage fermentation for the possible scale up are reviewed. Moreover, recent progress for enhanced performance towards waste stabilization and overall utilization of useful and higher COD present in the organic source into value-added products are extensively 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 implementation of cleaner waste treatment technologies in developing countries is accompanied by myriads of limitations and obstacles. This study reports that greenhouse gas (GHG) emission reductions that would not have happened with business-as-usual scenarios are achievable in the waste management system under the Clean Development Mechanism (CDM). The grounds for CDM failures and successes were reviewed by reflecting on the past and current episodes in developing countries. It was found that economic development was directly proportional to increase in waste generation rate and influenced waste composition. The need to decouple waste production from Gross Domestic Product (GDP) and linking the prevalence of more low-carbon emissions waste treatment options were found essential to ensure sustainable development and mitigate climate change. Based on the present evaluation, Brazil and Thailand have had the largest number of CDM projects and mostly small-scale projects with the highest maximum emission reductions in Brazil (751, 148 Mt CO2e) followed by Vietnam (158, 727 Mt CO2e) and India (158, 077 Mt CO2e). It was found that small-scale projects were more feasible as technology transfer and financial status were hindering the implementation of large-scale CDM projects. Moreover, emissions trading through CDM were accompanied by technical obstructions in terms of carbon leakage, permit allowances and unfair carbon price with irregular international policies and regulations to control GHGs. This study highlights the potential of a carbon trading scheme through CDM waste management projects designed to aid highly polluting developed countries achieve their target baselines for carbon emissions. The increasing GHG emissions in developing and least developed countries could be tackled at the early stages of economic growth through financial and technological assistance from industrialized countries.

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.

There is increased interest in reducing our reliance on fossil fuels and increasing the share of renewable raw materials in our energy supply chain due to environmental and economic concerns. Ethanol is emerging as a potential alternative to liquid fuels due to its eco-friendly characteristics and relatively low production costs. As ethanol is currently produced from commodities also used for human and animal consumption, there is an urgent need of identifying renewable raw materials that do not pose a competitive problem. Lignocellulosic agricultural residues are an ideal choice since they can be effectively hydrolyzed to fermentable sugars and integrated in the context of a biorefinery without competing with the food supply chain. However, the conventional hydrolysis methods still have major issues that need to be addressed. These issues are related to the processing rate and generation of fermentation inhibitors, which can compromise the quality of the product and the cost of the process. As the knowledge of the processes taking place during hydrolysis of agricultural residues is increasing, new techniques are being exploited to overcome these drawbacks. This review gives an overview of the state-of-the-art of hydrolysis with subcritical and supercritical water in the context of reusing agricultural residues for the production of suitable substrates to be processed during the fermentative production of bioethanol. Presently, subcritical and/or supercritical water hydrolysis has been found to yield low sugar contents mainly due to concurrent competing degradation of sugars during the hydrothermal processes. In this line of thinking, the present review also revisits the recent applications and advances to provide an insight of future research trends to optimize on the subcritical and supercritical process kinetics.

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.

In this study, estimates of greenhouse gas (GHG) emissions (for methane, carbon monoxide and nitrous oxide) following the potential installation of an aerated bioreactor landfill system at the Mare Chicose landfill in Mauritius have been determined based on procedures outlined in the Approved Baseline and Monitoring Methodology AM0083, "Avoidance of landfill gas emissions by in-situ aeration of landfills" from the UNFCCC/CCNUCC CDM, and compared to the baseline emissions (flaring method) for a credit period of 10 years to compute emissions reductions (ERs). The second part of this study has employed a combined multi-parameter sensitivity analysis (MPSA) and response surface methodology (RSM) approach to assess the relative importance of 5 selected parameters in influencing the amount of ERs. This technique of data analysis is reportedly novel in this field of research in environmental engineering for GHG emissions quantification. The parameters tested were the monitored methane content in venting well/header k during in-situ aeration in the year y (MC CH4,v,k.q ), monitored methane content from surface emissions during in-situ aeration in zone i in the quarter q (MC CH4,s,i,q ), total volume of surface emissions in zone i in quarter q (SG s,i,q ), potential methane generation capacity (L o,i ) of the waste in landfill zone i as determined by sampling and lab analysis and fraction of degradable waste (f dg , i ) in landfill zone i. Results from the MPSA and mesh plots from the RSM showed that L o , i had the most influence on the ERs. The largest ERs amounted to 835,104.61 tCO 2e obtained from the variations in L o,i whereas 189,343.30 tCO 2e was the lowest predicted ERs. The best working values for the five parameters with respect to a better environmental performance for minimal GHG emissions and maximum ERs were: 0.077-0.134 ton CH 4 /ton waste for L o,i , 0.713-0.8 for f dg,i , 688,829.30-972,916.67 m 3 for SG s,i,q , 1.01 × 10 - 5 to 1.75 × 10 ―5 tCH 4/ m 3 for MC CH4,v,k,q and 6.70× 10 ―8 to 5.16 × 10 ―7 tCH 4 /m 3 for MC CH4,s,i,q . The results of this study present a novel tool of optimized parameter values and ERs data which can be used to decide on how to better design and operate the landfill in Mauritius under the Clean Development Mechanism.

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.

This paper reports the potential of chemically treated wood chips to remove copper (II) ions from aqueous solution a function of pH, adsorbent dose, initial copper (II) concentration and contact time by batch technique. The wood chips were treated with (a) boiling, (b) formaldehyde and (c) concentrated sulphuric acid and characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive analysis X-ray. pH 5.0 was optimum with 86.1, 88.5 and 93.9 % copper (II) removal by boiled, formaldehyde-treated and concentrated sulphuric acid-treated wood chips, respectively, for dilute solutions at 20 g L−1 adsorbent dose. The experimental data were analysed using Freundlich, Langmuir, Dubinin–Radushkevich and Temkin isotherm models. It was found that Freundlich and Langmuir models fitted better the equilibrium adsorption data and the adsorption process followed pseudo-second-order reaction kinetics. The results showed that the copper (II) is considerably adsorbed on wood chips and it could be an economical option for the removal of copper from aqueous systems.

Heavy metals affect the biochemical reactions that take place during anaerobic digestion processes of organic matter. In this review, the different effects observed in anaerobic digestion processes and during the production of biomethane and biohydrogen from several substrates contaminated with and/or inheriting heavy metals from the substrates themselves were discussed. It has been found that heavy metals exert important roles in biochemical reactions. Heavy metals like copper, nickel, zinc, cadmium, chromium and lead have been overwhelmingly reported to be inhibitory and under certain conditions toxic in biochemical reactions depending on their concentrations. Heavy metals like iron may also exhibit stimulatory effects, but these effects have been scantily observed. This review also concludes that the severity of heavy metal inhibition depends upon factors like metal concentration in a soluble, ionic form in the solution, type of metal species, and amount and distribution of biomass in the digester or chain of biochemical reactions which constitute the anaerobic digestion process. A majority of studies have demonstrated that the toxic effect of heavy metals like chromium, cadmium and nickel is attributable to a disruption of enzyme function and structure by binding of the metal ions with thiol and other groups on protein molecules or by replacing naturally occurring metals in enzyme prosthetic groups. This review has not found published data on the effects of heavy metals on the hydrolysis stage of anaerobic digestion process chemistry, and hence further studies are required to depict any changes.

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.