Processes and prospects on valorizing solid waste for the production of valuable products employing bio-routes: A systematic review

Integrating advanced techniques and machine learning for landfill leachate treatment: Addressing limitations and environmental concerns

This review article explores the challenges associated with landfill leachate resulting from the increasing disposal of municipal solid waste in landfills and open areas. The composition of landfill leachate includes antibiotics (0.001-100 μg), heavy metals (0.001-1.4 g/L), dissolved organic and inorganic components, and xenobiotics including polyaromatic hydrocarbons (10-25 μg/L). Conventional treatment methods, such as biological (microbial and phytoremediation) and physicochemical (electrochemical and membrane-based) techniques, are available but face limitations in terms of cost, accuracy, and environmental risks. To surmount these challenges, this study advocates for the integration of artificial intelligence (AI) and machine learning (ML) to strengthen treatment efficacy through predictive analytics and optimized operational parameters. It critically evaluates the risks posed by recalcitrant leachate components and appraises the performance of various treatment modalities, both independently and in tandem with biological and physicochemical processes. Notably, physicochemical treatments have demonstrated pollutant removal rates of up to 90% for various contaminants, while integrated biological approaches have achieved over 95% removal efficiency. However, the heterogeneous nature of solid waste composition further complicates treatment methodologies. Consequently, the integration of advanced ML algorithms such as Support Vector Regression, Artificial Neural Networks, and Genetic Algorithms is proposed to refine leachate treatment processes. This review provides valuable insights for different stakeholders specifically researchers, policymakers and practitioners, seeking to fortify waste disposal infrastructure and foster sustainable landfill leachate management practices. By leveraging AI and ML tools in conjunction with a nuanced understanding of leachate complexities, a promising pathway emerges towards effectively addressing this environmental challenge while mitigating potential adverse impacts.

Nexus of food waste and climate change framework: Unravelling the links between impacts, projections, and emissions

This communication explores the intricate relationship between food waste and climate change, considering aspects such as impacts, projections, and emissions. It focuses on the pressing issue of waste generation and its potential consequences if current trends persist, and emphasises the importance of efficient solid waste management in improving environmental quality and fostering economic development. It also highlights the challenges faced by developing countries in waste collection and disposal, drawing comparisons with the waste utilisation methods used by developed nations. The review delves into the link between food waste and climate change, noting the paradoxical situation of food wastage against the backdrop of global hunger and malnutrition. It underscores the scientific evidence connecting food waste to climate change and its implications for food security and climate systems. Additionally, it examines the environmental burden imposed by food waste, including its contribution to greenhouse gas emissions and the depletion of resources such as energy, water, and land. Besides environmental concerns, this communication also highlights the ethical and socioeconomic dimensions of food waste, discussing its influence on Sustainable Development Goals, poverty, and social inequality. The communication concludes by advocating for collective action and the development of successful mitigation strategies, technological solutions, and policy interventions to address food waste and its climate impacts. It emphasises the need for collaboration, awareness, and informed decision-making to ensure a more sustainable and equitable future.

Advancements in biosurfactant production using agro-industrial waste for industrial and environmental applications

The adverse effects of waste generation on the environment and public health have raised global concerns. The utilization of waste as a raw material to develop products with enhanced value has opened up novel prospects for promoting environmental sustainability. Biosurfactants obtained from agro-industrial waste are noteworthy due to their sustainability and environmental friendliness. Microorganisms have been employed to generate biosurfactants as secondary metabolites by making use of waste streams. The utilization of garbage as a substrate significantly reduces the expenses associated with the process. Furthermore, apart from reducing waste and offering alternatives to artificial surfactants, they are extensively employed in bioremediation, food processing, agriculture, and various other industrial pursuits. Bioremediation of heavy metals and other metallic pollutants mitigated through the use of bacteria that produce biosurfactants which has been the more recent research area with the aim of improving its quality and environmental safety. Moreover, the production of biosurfactants utilizing agricultural waste as a raw material aligns with the principles of waste minimization, environmental sustainability, and the circular economy. This review primarily focuses on the production process and various types of biosurfactants obtained from waste biomass and feedstocks. The subsequent discourse entails the production of biosurfactants derived from various waste streams, specifically agro-industrial waste.

Application of biochar on soil bioelectrochemical remediation: behind roles, progress, and potential

Bioelectrochemical systems (BESs) that combine electrochemistry with biological methods have gained attention in the remediation of polluted environments, including wastewater, sludge, sediments, and soils. The most attractive advantage of BESs is that the solid electrode is used as an inexhaustible electron acceptor or donor, and biocurrent directly converted from organics can afford the reaction energy of contaminant breakdown, crossing the internal energy barrier of endothermic degradation, which achieves a continuous biodegradation process without the simultaneous use of exogenetic chemicals and bioelectricity recovery. However, soil BESs are hindered by expensive electrode materials, difficult pollutant and electron transfer, low microbial competitive activity, and biocompatibility in contamination remediation. Fortunately, introducing biochar into soil BESs could reveal a high potential in addressing these BES inadequacies. The characteristics of biochar, e.g., conductivity, transferability, high specific surface area, high porosity, large functional groups, and biocompatibility, can improve the performance of soil BESs. In fact, biochar not only carries electrons but also transfers nutrients, pollutants, and even bacteria by facilitating transmission in the bioelectric field of BESs. Consequently, the abilities of biochar make for better functionality of BESs. This review collates information on the roles, application, and progress of biochar in soil BESs, and future prospects are given. It is beneficial for environmental researchers and engineers to extend BES application in environmental remediation and to assist the progress of carbon sequestration and emission reduction based on the inertia of biochar and the blocking of electron flow to form methane.

A critical review on valorization of food processing wastes and by-products for pullulan production

Pullulan is a commercially available exopolymer biosynthesized by Aureobasidium pullulans supplemented with nitrogen, carbon and other vital components through submerged and solid-state fermentation. These nutrients are very expensive and it raises the cost for the production of pullulan. Hence, the need of alternative cost-effective raw materials for its production is a prerequisite. Owing to its unique physicochemical features, pullulan has various applications in the food, pharmacological, and biomedical domains. Food industrial wastes generate a considerable number of by-products which accumulates and has a negative influence on the environment. These by-products are made up of proteins, carbohydrates, and other components, can be employed as substrates for the production of pullulan. The present review briefs on the pullulan production using food processing waste and by-products and the elements that impact it. It provides an insight into versatile applications of pullulan in food industries. Various challenges and future prospects in the field of research on pullulan production have been uncovered.

Tricks and tracks in waste management with a special focus on municipal landfill leachate: Leads and obstacles

Landfilling is the most widely used disposal method for municipal solid waste around the world. The main disadvantage of this strategy is formation of leachate, among other aspects. Landfill leachate contains highly toxic and bio-refractory substances that are detrimental to the environment and human health. Hence, the risk(s) of discharging potentially harmful landfill leachate into the environment need to be assessed and measured in order to make effective choices about landfill leachate management and treatment. In view of this, the present review aims to investigate (a) how landfill leachate is perceived as an emerging concern, and (b) the stakeholders' mid- to long-term policy priorities for implementing technological and integrative solutions to reduce the harmful effects of landfill leachate. Because traditional methods alone have been reported ineffective, and in response to emerging contaminants and stringent regulations, new effective and integrated leachate treatments have been developed. This study gives a forward-thinking of the accomplishments and challenges in landfill leachate treatment during the last decade. It also provides a comprehensive compilation of the formation and characterization of landfill leachate, the geo-environmental challenges that it raises, as well as the resource recovery and industrial linkage associated with it in order to provide an insight into its sustainable management.

Bioremediation of petroleum hydrocarbon contaminated soil by microorganisms immobilized on sludge modified by non-ionic surfactant

The immobilization of microorganisms on high-quality and inexpensive carriers to remediate oil-contaminated soil is an effective strategy for contaminated soil remediation. Due to the abundance in nutrients, large specific surface area, and fewer pathogens, the composting sludge is considered a high-quality immobilized material. Herein, two non-ionic surfactants, TW-80 and sophorolipid, were used to modify composted sludge. High-efficiency petroleum hydrocarbon-degrading bacteria groups selected in the laboratory were fixed on the modified composting sludge under optimal conditions. The immobilized material was placed in the soil contaminated by petroleum hydrocarbons at an additive amount of 2wt/%, and a simulated remediation experiment was performed for 90 days. Both soil properties and microbial structure were characterized. Surfactant-modified compost sludge enhances the adsorption capacity to petroleum hydrocarbon. The immobilized microorganisms in the modified compost sludge showed a good effect on the remediation of soil contaminated by petroleum hydrocarbons. In addition, immobilized materials also increase the diversity of the microbial community structure in the soil. High-efficiency petroleum hydrocarbon-degrading bacteria immobilized on surfactant-modified compost can effectively promote the degradation of petroleum hydrocarbons in the soil and increase the abundance of microorganisms in the soil. It shows the feasibility of eco-friendly remediation of hydrocarbon-contaminated soil.

Numerical and experimental investigations on enhancement mixing performance of multi-blade stirring system for fluids with different viscosities

The poor mixing caused by zinc powder deposition in purification process is a serious problem which can’t be avoided in treatment of zinc-containing solid waste. Here, to enhance the purification efficiency of zinc-containing solid waste treatment reactor, two kinds of multi-blade combined stirring systems are compared with single layer four straight-blade and double-layer straight-blade (DFB) stirring systems which are traditionally chosen by industry. This study simulated and explored the flow field characteristics and purification effects of these four kinds of stirred-tank reactor, further proposes the unit ion purification energy (UIPE) as a criterion for purification energy consumption and effect evaluation. The results show that multi-blade combined (MBC) stirring system enhances axial flow by 12.56% in water. Meanwhile it effectively inhibits the growth of isolated mixing region which scope has decreased by 56.25%. In high viscosity Carboxymethylcellulose sodium solution, the fluid axial speed can be increased by up to 1407 times with MBC. MBC can increase the purification rate by 24.79% while the UIPE decreases by 29.45% compared with DFB which is used in industrial purification process. MBC paddle has exhibited a wide range of fluid viscosity applicability and axial velocity improvement effect. The improvement increases collisions between the impurity particles and the zinc powder particles, which increased rate of substitution reactions. The application of MBC solves the purification problem in the process of treating zinc-containing solid waste.

Technological advancements in valorisation of industrial effluents employing hydrothermal liquefaction of biomass: Strategic innovations, barriers and perspectives

Hydrothermal liquefaction (HTL) is identified as a promising thermochemical technique to recover biofuels and bioenergy from waste biomass containing low energy and high moisture content. The wastewater generated during the HTL process (HTWW) are rich in nutrients and organics. The release of the nutrients and organics enriched HTWW would not only contaminate the water bodies but also lead to the loss of valued bioenergy sources, especially in the present time of the energy crisis. Thus, biotechnological as well as physicochemical treatment of HTWW for simultaneous extraction of valuable resources along with reduction in polluting substances has gained significant attention in recent times. Therefore, the treatment of wastewater generated during the HTL of biomass for reduced environmental emission and possible bioenergy recovery is highlighted in this paper. Various technologies for treatment and valorisation of HTWW are reviewed, including anaerobic digestion, microbial fuel cells (MFC), microbial electrolysis cell (MEC), and supercritical water gasification (SCWG). This review paper illustrates that the characteristics of biomass play a pivotal role in the selection process of appropriate technology for the treatment of HTWW. Several HTWW treatment technologies are weighed in terms of their benefits and drawbacks and are thoroughly examined. The integration of these technologies is also discussed. Overall, this study suggests that integrating different methods, techno-economic analysis, and nutrient recovery approaches would be advantageous to researchers in finding way for maximising HTWW valorisation along with reduced environmental pollution.

Bioconversion of biowaste into renewable energy and resources: A sustainable strategy

Due to its high amount of organic and biodegradable components that can be recycled, biowaste is not only a major cause of environmental contamination, but also a vast store of useful materials. The transformation of biowaste into energy and resources via biorefinery is an unavoidable trend, which could aid in reducing carbon emissions and alleviating the energy crisis in light of dwindling energy supplies and mounting environmental difficulties related with solid waste. In addition, the current pandemic and the difficult worldwide situation, with their effects on the economic, social, and environmental aspects of human life, have offered an opportunity to promote the transition to greener energy and sources. In this context, the current advancements and possible trends of utilizing widely available biowaste to produce key biofuels (such as biogas and biodiesel) and resources (such as organic acid, biodegradable plastic, protein product, biopesticide, bioflocculant, and compost) are studied in this review. To achieve the goal of circular bioeconomy, it is necessary to turn biowaste into high-value energy and resources utilizing biological processes. In addition, the usage of recycling technologies and the incorporation of bioconversion to enhance process performance are analyzed critically. Lastly, this work seeks to reduce a number of enduring obstacles to the recycling of biowaste for future use in the circular economy. Although it could alleviate the global energy issue, additional study, market analysis, and finance are necessary to commercialize alternative products and promote their future use. Utilization of biowaste should incorporate a comprehensive approach and a methodical style of thinking, which can facilitate product enhancement and decision optimization through multidisciplinary integration and data-driven techniques.

Gamma distribution function to understand anaerobic digestion kinetics: Kinetic constants are not constant

The Gamma model is a novel approach to characterise the complex degradation dynamics taking place during anaerobic digestion. This three parameters model results from combining the first-order kinetic model and the Gamma distribution function. In contrast to conventional models, where the kinetic constant is considered invariant, the Gamma model allows analysing the variability of the kinetic constant using a probability density function. The kinetic constant of mono-digestion and co-digestion batch tests of different wastes were modelled using the Gamma model and two common first-order models: one-step one-fraction model and one-step two-fraction model. The Gamma distribution function approximates three distinct probability density functions, i.e. exponential, log-normal, and delta Dirac. Specifically, (i) cattle paunch and pig manure approximated a log-normal distribution; (ii) cattle manure and microalgae approximated an exponential distribution, and (iii) primary sludge and cellulose approximated a delta Dirac distribution. The Gamma model was able to characterise two distinct waste activated sludge, one approximated to a log-normal distribution and the other to an exponential distribution. The same cellulose was tested with two different inocula; in both tests, the Gamma distribution function approximated a delta Dirac function but with a different kinetic value. The potential and consistency of Gamma model were also evident when analysing pig manure and microalgae co-digestion batch tests since (i) the mean k of the co-digestion tests were within the values of the mono-digestion tests, and (ii) the profile of the density function transitioned from log-normal to exponential distribution as the percentage of microalgae in the mixture increased.

Exploring bacterial communities through metagenomics during bioremediation of polycyclic aromatic hydrocarbons from contaminated sediments

The goal of this study was to evaluate the degradation effectiveness of PAHs degrading bacteria at the mesocosm level, including Stenotrophomonas maltophilia (SC), mixed culture (MC), and enriched native microflora (EC) at the mesocosm level. Maximum degradation was found in the mesocosm MC (26.67 %), followed by SC (25.08 %) and EC (18.25 %) after 60 days. Thus, mixed culture and Stenotrophomonas maltophilia could be a game changer in the PAHs bioremediation at the chronically contaminated sites. MiSeq sequencing has revealed dominancy of γ-Proteobacteria, α-Proteobacteria, β-Proteobacteria at class level and Sphingomonadales, oceanospirillales, Rhodothermales at Order level. Families Alcanivoracaceae, Alteromonadaceae, Nocardiaceae, Rhodospirillaceae and genus Stenotrophomonas, Alcanivorax, Methylophaga, Fluviicola and Rhodoplanes were considerably increased which play key role in the PAHs degradation. Dominant bacterial communities have revealed resilience community to enable potential PAHs degradation process in all the mesocosms. To the best our knowledge this is the first ever attempt in PAHs biodegradation study conducted at the mesocosm level mimicking natural environmental conditions. Consequently, this study could be a benchmark against which future progress studies for the policy makers and stakeholders to design appropriate bioremediation study for the historically PAHs polluted contaminate sites.

Efficient removal of tar employing dolomite catalyst in gasification: Challenges and opportunities

Fossil fuels are currently the dominant source of electricity and energy production around the world. Biomass is one of the most referred renewable carbonaceous resource(s) that can be employed for the waste-to-energy concept. Syngas obtained from biomass gasification can be utilized for a variety of key industrial purposes, including internal gasification engine operation, power generation, and hydrocarbon compound production using the Fisher-Tropsch technique. However, the existence of impurities such as hydrogen sulfide, tar, and particulate matter along with other undesirable chemicals present in syngas are major disadvantages of biomass gasification. Tar is the most difficult among all the pollutants to be removed from syngas; it also causes serious problems in downstream syngas applications. For decades, studies have been performed with various catalysts to remove the tar. Dolomite has shown positive response for tar elimination and hydrogen-enriched gas production. Several studies have been carried out on dolomite for eliminating the tar from syngas. This review encompasses sources of solid waste, the mechanism of catalysis, and in-situ and ex-situ usage of dolomite in the gasification process. It addresses the key issues such as fragmentation and attrition, elutriation, and coke formation along with dolomite's usefulness in amalgamation with other catalysts, environmental consequences, and economic viability of dolomite applications. It also discusses the challenges and opportunities for tar removal using catalysts, with a specific focus on dolomite along with economic and environmental sustainability considerations.

Agri-Food Surplus, Waste and Loss as Sustainable Biobased Ingredients: A Review

Ensuring a sustainable supply of food for the world’s fast growing population is a major challenge in today’s economy, as modern lifestyle and increasing consumer concern with maintaining a balanced and nutritious diet is an important challenge for the agricultural sector worldwide. This market niche for healthier products, especially fruits and vegetables, has increased their production, consequently resulting in increased amounts of agri-food surplus, waste, and loss (SWL) generated during crop production, transportation, storage, and processing. Although many of these materials are not utilized, negatively affecting the environmental, economic, and social segments, they are a rich source of valuable compounds that could be used for different purposes, thus preventing the losses of natural resources and boosting a circular economy. This review aimed to give insights on the efficient management of agri-food SWL, considering conventional and emerging recovery and reuse techniques. Particularly, we explored and summarized the chemical composition of three worldwide cultivated and consumed vegetables (carrots, broccoli and lettuce) and evaluate the potential of their residues as a sustainable alternative for extracting value-added ingredients for the development of new biodynamic products.

Novel insight on ferric ions addition to mitigate recalcitrant formation during thermal-alkali hydrolysis to enhance biomethanation

Thermal-chemical pre-treatment has proven to facilitate the solubilization of organics and improvement in biogas generation from the organic fraction of municipal solid waste (OFMSW). However, the production of recalcitrant is inevitable when OFMSW is pretreated at high temperatures and alkali dosage. This study develops a strategy to use Fe³⁺ to reduce the formation of recalcitrant compounds, i.e., 5-HydroxyMethyl Furfural (5-HMF), furfurals, and humic acids (HA) during thermal-alkali pre-treatment. It was postulated that the formation of the recalcitrant compound during pre-treatment can be reduced by Fe³⁺ dosing to oxidize intermediates of Maillard reactions. A decrease in 5-HMF (45-49%) and furfurals (54-66%) was observed during Fe³⁺ (optimum dose: 10 mg/L) mediated thermal-alkali pre-treatment owing to the Lewis acid behavior of FeCl₃. The Fe³⁺ mediated assays show a substantial improvement in VS removal (28%) and biogas yield, i.e., 31% (292 mL/gVS_added) in 150 °C + 3 g/L NaOH, 34% (316 mL/gVS_added) in 175 °C + 3 g/L NaOH, and 36% (205 mL/gVS_added) in 200 °C + 3 g/L NaOH assays, over their respective controls (no Fe³⁺ dosing). The reducing property of Fe³⁺ rendered a low ORP (-345 mV) in the system than control, which is beneficial to the anaerobic microbiome. Electrical conductivity (EC) also shows a three-fold increase in Fe³⁺ mediated assays over control, promoting direct interspecies electron transfer (DIET) amongst microbes involved in the electrical syntrophy. The score plot and loading plots from principal component analysis (PCA) showed that the results obtained by supplementing 10 mg/L Fe³⁺ at 150, 175, and 200 °C were significantly different. The correlation of the operational parameters was also mutually correlated. This work provides a techno-economically and environmentally feasible option to mitigate the formation of recalcitrant compounds and enhance biogas production in downstream AD by improving the degradability of pretreated substrate.

Resource recovery from fish waste: Prospects and the usage of intensified extraction technologies

Globally, the valorization of fish biowaste as a feedstock to recover valuable components is an emerging research and commercial interest area to achieve the SDG goals by 2030. Fish waste-derived biomolecules are increasingly finding diverse applications in food and other biotechnological fields due to their excellent chemical, structural and functional properties. The focus of this review is to highlight the conventional valorization routes and recent advancements in extraction technologies for resource recovery applications, primarily focusing on green processes. Biointensified processes involving ultrasound, microwave, sub- and supercritical fluids, pulsed electric field, high-pressure processing, and cold plasma are extensively explored as sustainable technologies for valorizing fish discards and found numerous applications in the production of functional and commercially important biomaterials. With challenges in recovering intracellular bioactive compounds, selectivity, and energy requirement concerns, conventional approaches are being relooked continuously in the quest for process intensification and sustainable production practices. Nonetheless, in the context of 'zero waste' and 'biorefinery for high-value compounds', there is immense scope for technological upgradation in these emerging alternative approaches. This work details such attempts, providing insights into the immense untapped potential in this sector.

Sustainable management of municipal solid waste through waste-to-energy technologies

Increasing municipal solid waste (MSW) generation and environmental concerns have sparked global interest in waste valorization through various waste-to-energy (WtE) to generate renewable energy sources and reduce dependency on fossil-derived fuels and chemicals. These technologies are vital for implementing the envisioned global "bioeconomy" through biorefineries. In light of that, a detailed overview of WtE technologies with their benefits and drawbacks is provided in this paper. Additionally, the biorefinery concept for waste management and sustainable energy generation is discussed. The identification of appropriate WtE technology for energy recovery continues to be a significant challenge. So, in order to effectively apply WtE technologies in the burgeoning bioeconomy, this review provides a comprehensive overview of the existing scenario for sustainable MSW management along with the bottlenecks and perspectives.

Biochar production with amelioration of microwave-assisted pyrolysis: Current scenario, drawbacks and perspectives

In recent years, biomass has been reported to obtain a wide range of value-added products. Biochar can be obtained by heating biomass, which aids in carbon sinks, soil amendments, resource recovery, and water retention. Microwave technology stands out among various biomass heating technologies not only for its effectiveness in biomass pyrolysis for the production of biochar and biofuel but also for its speed, volumetrics, selectivity, and efficiency. The features of microwave-assisted biomass pyrolysis and biochar are briefly reviewed in this paper. An informative comparison has been drawn between microwave-assisted pyrolysis and conventional pyrolysis. It focuses mainly on technological and economic scenario of biochar production and environmental impacts of using biochar. This source of knowledge would aid in the exploration of new possibilities and scope for employing microwave-assisted pyrolysis technology to produce biochar.

Carbon-based catalyst for environmental bioremediation and sustainability: Updates and perspectives on techno-economics and life cycle assessment

Global rise in the generation of waste has caused an enormous environmental concern and waste management problem. The untreated carbon rich waste serves as a breeding ground for pathogens and thus strategies for production of carbon rich biochar from waste by employing different thermochemical routes namely hydrothermal carbonization, hydrothermal liquefaction and pyrolysis has been of interest by researchers globally. Biochar has been globally produced due to its diverse applications from environmental bioremediation to energy storage. Also, several factors affect the production of biochar including feedstock/biomass type, moisture content, heating rate, and temperature. Recently the application of biochar has increased tremendously owing to the cost effectiveness and eco-friendly nature. Thus this communication summarized and highlights the preferred feedstock for optimized biochar yield along with the factor influencing the production. This review provides a close view on biochar activation approaches and synthesis techniques. The application of biochar in environmental remediation, composting, as a catalyst, and in energy storage has been reviewed. These informative findings were supported with an overview of lifecycle and techno-economical assessments in the production of these carbon based catalysts. Integrated closed loop approaches towards biochar generation with lesser/zero landfill waste for safeguarding the environment has also been discussed. Lastly the research gaps were identified and the future perspectives have been elucidated.

Mycoremediation of lignocellulosic biorefinery sludge: A reinvigorating approach for organic contaminants remediation with simultaneous production of lignocellulolytic enzyme cocktail

This research work aims to valorize lignocellulosic biorefinery sludge with genetically engineered Trichoderma atroviride for simultaneous removal of organic contaminants, fermentation inhibitors, and lignocellulolytic enzyme cocktail production. Upon analysis, three phenolic compounds (42.6 ± 3.6 μg/g), two polycyclic aromatic hydrocarbons (0.42 ± 0.06 μg/g) and five fermentation inhibitors (2.5 ± 0.3 mg/g) were detected in the sludge. Bioaugmentation of sludge with 72 h-old T. atroviride (5%) results in the production of cellulase (21 U/g), xylanase (84 U/g), laccase (20 U/g), lignin peroxidase (14 U/g) and aryl alcohol oxidase (116 U/g), along with the concomitant removal of organic contaminants (phenol, 2, 4-dinitrophenol, pentchlorophenol, phenanthrene, benzo(a)pyrene) and fermentation inhibitors (furfural, 5-hydroxymethylfurfural, levulinic acid, ferulic acid, and catechol). Subsequently, the enrichment of sludge with nutrients and rhamnolipids enhanced the enzyme production by 5-6-fold and resulted in the removal of 85-95% of organic contaminants and fermentation inhibitors, which constitutes an eco-friendly process.

Genetic modifications associated with sustainability aspects for sustainable developments

Sustainable development serves as the foundation for a range of international and national policymaking. Traditional breeding methods have been used to modify plant genomes and production. Genetic engineering is the practice of assisting agricultural systems in adapting to rapidly changing global growth by hastening the breeding of new varieties. On the other hand, the development of genetic engineering has enabled more precise control over the genomic alterations made in recent decades. Genetic changes from one species can now be introduced into a completely unrelated species, increasing agricultural output or making certain elements easier to manufacture. Harvest plants and soil microorganisms are just a few of the more well-known genetically modified creatures. Researchers assess current studies and illustrate the possibility of genetically modified organisms (GMOs) from the perspectives of various stakeholders. GMOs increase yields, reduce costs, and reduce agriculture's terrestrial and ecological footprint. Modern technology benefits innovators, farmers, and consumers alike. Agricultural biotechnology has numerous applications, each with its own set of potential consequences. This will be able to reach its full potential if more people have access to technology and excessive regulation is avoided. This paper covers the regulations for genetically modified crops (GMCs) as well as the economic implications. It also includes sections on biodiversity and environmental impact, as well as GMCs applications. This recounts biotechnological interventions for long-term sustainability in the field of GMCs, as well as the challenges and opportunities in this field of research.Abbreviations: GMCs-Genetically modified crops; GMOs- Genetically modified organisms; GE- Genetic engineering; Bt- Bacillus thuringiensisNIH- National Institutes of Health; FDA- Food and Drug Administration; HGT- Horizontal gene transfer; GM- Genetically modified; rDNA- Ribosomal deoxyribonucleic acid; USDA- United States Department of Agriculture; NIH- National Institutes of Health.

Organic solid waste: Biorefinery approach as a sustainable strategy in circular bioeconomy

Waste generation is associated with numerous environmental consequences, making it a point of discussion in the environmental arena. Efforts have been made around the world to develop a systematic management approach coupled with a sustainable treatment technology to maximize resource utilization of organic solid waste. Biorefineries and bio-based products play a critical role in lowering total emissions and supporting energy systems. However, economic viability of biorefineries, on the other hand, is a stumbling hurdle to their commercialization. This communication provides a thorough study of the concept of biorefinery in waste management, as well as technological advancements in this field. In addition, the notion of techno-economic assessment, as well as challenges and future prospects have been covered. To find the most technologically and economically viable solution, further techno-economic study to the new context is required. Overall, this communication would assist decision-makers in identifying environmentally appropriate biorefinery solutions ahead of time.

Municipal solid waste management: Dynamics, risk assessment, ecological influence, advancements, constraints and perspectives

Global energy consumption has been increasing in tandem with economic growth, putting pressure on the world's supply of renewable energy sources. Municipal Solid waste (MSW) has been reported contributing immensely to the improvement of a secure environment and renewable sources. Energy scarcity and conventional MSW disposal methods in developing countries lead towards many environmental and economic issues. Scientists have been able to experiment with various waste-to-energy conversion technologies in light of this situation. This communication highlights and reviews WtE technologies to convert MSW and other feedstocks into electricity, hydrogen gas, bioethanol along with other value added products like fertilizer(s), platform chemicals as an environmentally friendly products. This review comprehensively summarized the dynamics, risk assessment, ecological influence, advancements, constraints and perspectives altogether in field of municipal solid waste management and treatment. Stare-of-the-art information on ecological influence and risk assessment in handling and transportation of municipal solid waste has been provided. Advanced trends involved in remediation of emerging pollutants and resources obtained from municipal solid wastes have been uncovered. Lastly, this paper comprises constraints and perspectives for uncovering MSW based circular bioeconomy aspects.

Microbiological insights into anaerobic digestion for biogas, hydrogen or volatile fatty acids (VFAs): a review

In the past decades, considerable attention has been directed toward anaerobic digestion (AD), which is an effective biological process for converting diverse organic wastes into biogas, volatile fatty acids (VFAs), biohydrogen, etc. The microbial bioprocessing takes part during AD is of substantial significance, and one of the crucial approaches for the deep and adequate understanding and manipulating it toward different products is process microbiology. Due to highly complexity of AD microbiome, it is critically important to study the involved microorganisms in AD. In recent years, in addition to traditional methods, novel molecular techniques and meta-omics approaches have been developed which provide accurate details about microbial communities involved AD. Better understanding of process microbiomes could guide us in identifying and controlling various factors in both improving the AD process and diverting metabolic pathway toward production of selective bio-products. This review covers various platforms of AD process that results in different final products from microbiological point of view. The review also highlights distinctive interactions occurring among microbial communities. Furthermore, assessment of these communities existing in the anaerobic digesters is discussed to provide more insights into their structure, dynamics, and metabolic pathways. Moreover, the important factors affecting microbial communities in each platform of AD are highlighted. Finally, the review provides some recent applications of AD for the production of novel bio-products and deals with challenges and future perspectives of AD.

From garbage to product and service systems: A longitudinal Finnish case study of waste management evolution

This longitudinal case study analyses the development of the pioneering waste management (WM) system in the Vaasa region of Western Finland, since the late 1980s to the present. It reflects the general features of the evolving WM from the one-bag system and throwaway culture towards today's circular economy and product service systems. The Vaasa region is an excellent example of how WM has evolved in Finland, which also follows the main direction of travel in Europe. The main features have been: (1) closing of dumping sites, minimizing dumping of waste and concentrating dumping to well-organized and environmentally managed sites; (2) development of comprehensive source separation systems for reuse of materials and energy; (3) building of waste treatment systems, consisting of different technical solutions connected with reuse and energy generation solutions. This evolution has resulted in expanding regional collaboration, where large investments are integrated within larger areas and consortia. The share of reused materials has grown significantly and dumping has decreased to close to zero. The practices of the circular economy are emerging and partly established. In this evolution, praxis does not immediately follow after "a brilliant idea", but only after the societal structuring process, including paradigmatic changes in attitudes, social norms, policies and regulation, customer behaviour, economic structures, and separate and systemic technological solutions and value chains. This research can add value both in terms of knowledge and science, and in being a change agents more practically. In the future, a strategic shift from WM to material management, and from public service to feasible businesses will be the next steps.

Anaerobic biobutanol production from black strap molasses using Clostridium acetobutylicum MTCC11274: Media engineering and kinetic analysis

Microbial reduction of black strap molasses (BSM) by Clostridium acetobutylicum MTCC 11,274 was performed for the production of biobutanol. The optimum fermentation conditions were predicted using one factor at a time (OFAT) method. The identification of significant parameters was performed using Plackett-Burman Design (PBD). Furthermore the fermentation conditions were optimized using central composite design (CCD). The kinetics of substrate utilization and product formation were investigated. Initial pH, yeast extract concentration (g/L) and total reducing sugar concentration (g/L) were found as significant parameters affecting butanol production using C. acetobutylicum MTCC11274. The maximum butanol production under optimal condition was 10.27 + 0.82 g/L after 24 h. The waste black strap molasses obtained from sugar industry could be used as promising substrate for the production of next generation biofuel.

Production of biosurfactants from agro-industrial waste and waste cooking oil in a circular bioeconomy: An overview

Waste generation is becoming a global concern owing to its adverse effects on environment and human health. The utilization of waste as a feedstock for production of value-added products has opened new avenues contributing to environmental sustainability. Microorganisms have been employed for production of biosurfactants as secondary metabolites by utilizing waste streams. Utilization of waste as a substrate significantly reduces the cost of overall process. Biosurfactant(s) derived from these processes can be utilized in environmental and different industrial sectors. This review focuses on global market of biosurfactants followed by discussion on production of biosurfactants from waste streams such as agro-industrial waste and waste cooking oil. The need for waste stream derived circular bioeconomy and scale up of biosurfactant production have been narrated with applications of biosurfactants in environment and industrial sectors. Road blocks and future directions for research have also been discussed.

Valorization of agro-industrial wastes for biorefinery process and circular bioeconomy: A critical review

Energy recovery from waste resources is a promising approach towards environmental consequences. In the prospect of environmental sustainability, utilization of agro-industrial waste residues as feedstock for biorefinery processes have gained widespread attention. In the agro-industry, various biomasses are exposed to different unit processes for offering value to various agro-industrial waste materials. Agro-industrial wastes can generate a substantial amount of valuable products such as fuels, chemicals, energy, electricity, and by-products. This paper reviews the methodologies for valorization of agro-industrial wastes and their exploitation for generation of renewable energy products. In addition, management of agro-industrial wastes and products from agro-industrial wastes have been elaborated. The waste biorefinery process using agro-industrial wastes does not only offer energy, it also offers environmentally sustainable modes, which address effective management of waste streams. This review aims to highlight the cascading use of biomass from agro-industrial wastes into the systemic approach for economic development.

A review on integrated approaches for municipal solid waste for environmental and economical relevance: Monitoring tools, technologies, and strategic innovations

Rapid population growth, combined with increased industrialization, has exacerbated the issue of solid waste management. Poor management of municipal solid waste (MSW) not only has detrimental environmental consequences but also puts public health at risk and introduces several other socioeconomic problems. Many developing countries are grappling with the problem of safe disposing of large amounts of produced municipal solid waste. Unmanaged municipal solid waste pollutes the environment, so its use as a potential renewable energy source would aid in meeting both increased energy needs and waste management. This review investigates emerging strategies and monitoring tools for municipal solid waste management. Waste monitoring using high-end technologies and energy recovery from MSW has been discussed. It comprehensively covers environmental and economic relevance of waste management technologies based on innovations achieved through the integration of approaches.

Biomolecules Production from Greenhouse Gases by Methanotrophs

Harmful effects on living organisms and the environment are on the rise due to a significant increase in greenhouse gas (GHG) emissions through human activities. Therefore, various research initiatives have been carried out in several directions in relation to the utilization of GHGs via physicochemical or biological routes. An environmentally friendly approach to reduce the burden of significant emissions and their harmful effects is the bioconversion of GHGs, including methane (CH4) and carbon dioxide (CO2), into value-added products. Methanotrophs have enormous potential for the efficient biotransformation of CH4 to various bioactive molecules, including biofuels, polyhydroxyalkanoates, and fatty acids. This review highlights the recent developments in methanotroph-based systems for methanol production from GHGs and proposes future perspectives to improve process sustainability via biorefinery approaches.

Detection and removal of poly and perfluoroalkyl polluting substances for sustainable environment

PFAs (poly and perfluoroalkyl compounds) are hazardous and bioaccumulative chemicals that do not readily biodegrade or neutralize under normal environmental conditions. They have various industrial, commercial, domestic and defence applications. According to the Organization for Economic Co-operation and Development, there are around 4700 PFAs registered to date. They are present in every stream of life, and they are often emerging and are even difficult to be detected by the standard chemical methods. This review aims to focus on the sources of various PFAs and the toxicities they impose on the environment and especially on humankind. Drinking water, food packaging, industrial areas and commercial household products are the primary PFAs sources. Some of the well-known treatment methods for remediation of PFAs presented in the literature are activated carbon, filtration, reverse osmosis, nano filtration, oxidation processes etc. The crucial stage of handling the PFAs occurs in determining and analysing the type of PFA and its remedy. This paper provides a state-of-the-art review of determination & tools, and techniques for remediation of PFAs in the environment. Improving new treatment methodologies that are economical and sustainable are essential for excluding the PFAs from the environment.

Nutrient removal from domestic wastewater: A comprehensive review on conventional and advanced technologies

Nitrogen and phosphorous are indispensable for growth and vitality of living beings, hence termed as nutrients. However, discharge of nutrient rich waste streams to aquatic ecosystems results in eutrophication. Therefore, nutrient removal from wastewater is crucial to meet the strict nutrient discharge standards. Similarly, nutrient recovery from waste streams is vital for the realization of a circular economy by avoiding the depletion of finite resources. This manuscript presents analysis of existing information on different conventional as well as advanced treatment technologies that are commonly practiced for the removal of nutrient from domestic wastewater. First, the information pertaining to the biological nutrient removal technologies are discussed. Second, onsite passive nutrient removal technologies are reviewed comprehensively. Third, advanced nutrient removal technologies are summarized briefly. The mechanisms, advantages, and disadvantages of these technologies along with their efficiencies and limitations are discussed. An integrated approach for simultaneous nutrient removal and recovery is recommended. The fifth section of the review highlights bottlenecks and potential solutions for successful implementation of the nutrient removal technologies. It is anticipated that the review will offer an instructive overview of the progress in nutrient removal and recovery technologies and will illustrate necessity of further investigations for development of efficient nutrient removal and recovery processes.

Agricultural Waste and Wastewater as Feedstock for Bioelectricity Generation Using Microbial Fuel Cells: Recent Advances

In recent years, there has been a significant accumulation of waste in the environment, and it is expected that this accumulation may increase in the years to come. Waste disposal has massive effects on the environment and can cause serious environmental problems. Thus, the development of a waste treatment system is of major importance. Agro-industrial wastewater and waste residues are mainly rich in organic substances, lignocellulose, hemicellulose, lignin, and they have a relatively high amount of energy. As a result, an effective agro-waste treatment system has several benefits, including energy recovery and waste stabilization. To reduce the impact of the consumption of fossil energy sources on our planet, the exploitation of renewable sources has been relaunched. All over the world, efforts have been made to recover energy from agricultural waste, considering global energy security as the final goal. To attain this objective, several technologies and recovery methods have been developed in recent years. The microbial fuel cell (MFC) is one of them. This review describes the power generation using various types of agro-industrial wastewaters and agricultural residues utilizing MFC. It also highlights the techno-economics and lifecycle assessment of MFC, its commercialization, along with challenges.

A critical review on various feedstocks as sustainable substrates for biosurfactants production: a way towards cleaner production

The quest for a chemical surfactant substitute has been fuelled by increased environmental awareness. The benefits that biosurfactants present like biodegradability, and biocompatibility over their chemical and synthetic counterparts has contributed immensely to their popularity and use in various industries such as petrochemicals, mining, metallurgy, agrochemicals, fertilizers, beverages, cosmetics, etc. With the growing demand for biosurfactants, researchers are looking for low-cost waste materials to use them as substrates, which will lower the manufacturing costs while providing waste management services as an add-on benefit. The use of low-cost substrates will significantly reduce the cost of producing biosurfactants. This paper discusses the use of various feedstocks in the production of biosurfactants, which not only reduces the cost of waste treatment but also provides an opportunity to profit from the sale of the biosurfactant. Furthermore, it includes state-of-the-art information about employing municipal solid waste as a sustainable feedstock for biosurfactant production, which has not been simultaneously covered in many published literatures on biosurfactant production from different feedstocks. It also addresses the myriad of other issues associated with the processing of biosurfactants, as well as the methods used to address these issues and perspectives, which will move society towards cleaner production.