The nitrogen cycle and mitigation strategies for nitrogen loss during organic waste composting: A review

Composting is a promising technology to decompose organic waste into humus-like high-quality compost, which can be used as organic fertilizer. However, greenhouse gases (N₂O, CO₂, CH₄) and odorous emissions (H₂S, NH₃) are major concerns as secondary pollutants, which may pose adverse environmental and health effects. During the composting process, nitrogen cycle plays an important role to the compost quality. This review aimed to (1) summarizes the nitrogen cycle of the composting, (2) examine the operational parameters, microbial activities, functions of enzymes and genes affecting the nitrogen cycle, and (3) discuss mitigation strategies for nitrogen loss. Operational parameters such as moisture, oxygen content, temperature, C/N ratio and pH play an essential role in the nitrogen cycle, and adjusting them is the most straightforward method to reduce nitrogen loss. Also, nitrification and denitrification are the most crucial processes of the nitrogen cycle, which strongly affect microbial community dynamics. The ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB), and heterotrophic and autotrophic denitrifiers play a vital role in nitrification and denitrification with the involvement of ammonia monooxygenase (amoA) gene, nitrate reductase genes (narG), and nitrous oxide reductase (nosZ). Furthermore, adding additives such as struvite salts (MgNH₄PO₄·6H₂O), biochar, and zeolites (clinoptilolite), and microbial inoculation, namely Bacillus cereus (ammonium strain), Pseudomonas donghuensis (nitrite strain), and Bacillus licheniformis (nitrogen fixer) can help control nitrogen loss. This review summarized critical issues of the nitrogen cycle and nitrogen loss in order to help future composting research with regard to compost quality and air pollution/odor control.

Protein nanofibrils as versatile and sustainable adsorbents for an effective removal of heavy metals from wastewater: A review

Water is a valuable natural resource, which plays a crucial role in ecological survival as well as economic progress. However, the water quality has deteriorated in recent years as a result of urbanization, industrialization and human activities due to the uncontrolled release of industrial wastes, which can be extremely carcinogenic and non-degradable, in air, water and soil bodies. Such wastes showed the presence of organic and inorganic pollutants in high dosages. Heavy metals are the most obstinate contaminants, and they can be harmful because of having a variety of detrimental consequences to the ecosystem. The existing water treatment methods in many situations may not be sustainable or effective because of their high energy requirements and ecological impacts. In this review, state-of-the-art water treatment methods for the elimination of heavy metals with the help of protein nanofibrils are covered featuring a discussion on the strategies and possibilities of developing protein nanofibrils for the active elimination of heavy metals using kitchen waste as well as residues from the cattle, agriculture, and dairy industries. Further, the emphasis has been given to their environmental sustainability and economical aspects are also discussed.

Microbial fuel cell systems; developments, designs, efficiencies, and trends: A comparative study between the conventional and innovative systems

The microbial fuel cell (MFC) technology has appeared in the late 20th century and received considerable attention over the last decade due to its multiple and unique potential in converting the substrates into electricity and valuable productions. Extensive efforts have been paid to improve the MFCs performance, leading to the publication of a massive amount of research that developed various aspects of these systems. Most of these improvements have focused on optimization parameters, which is currently inappropriate to provide an innovational developing vision for MFC systems. The convergent results in most of the previous conventional studies (12,643 studies according to the WOS database) have reduced the value of MFCs by drawing an incomplete image for the performance of the systems. Therefore, this paper aimed to provide a comprehensive comparison between the highly reliable studies that innovatively developed the MFC systems and the conventional MFCs studies. The current paper discusses the novel MFCs development history, designs, efficiency, and challenges compared to conventional MFCs. The discussion has displayed the high efficiency of the novel MFCs in removing over 90% of substrates and generating power of 800 mW m^-2. The paper also analyzed the literature trends, history and suggested recommendations for future studies. This is the first paper highlighting the substantial differences between the innovative and conventional MFC systems, nominating it to be a vital reference for novel MFCs studies in the future.

An overview of MXene-Based nanomaterials and their potential applications towards hazardous pollutant adsorption

With the massive development of industrialization, multiple ecological contaminants in gaseous, liquid, and solid forms are vented into habitats, which is currently at the forefront of worldwide attention. Because of the possible damage to public health and eco-diversity, high-efficiency clearance of these environmental contaminants is a serious concern. Improved nanomaterials (NMs) could perform a significant part in the exclusion of contaminants from the atmosphere. MXenes, a class of two-dimensional (2D) compounds that have got tremendous consideration from researchers for a broad array of applications in a variety of industries and are viewed as a potential route for innovative solutions to identify and prevent a variety of obstreperous hazardous pollutants from environmental compartments due to their exceptional innate physicochemical and mechanical features, including high specific surface area, physiological interoperability, sturdy electrodynamics, and elevated wettability. This paper discusses the recent progress in MXene-based nanomaterials' applications such as environmental remediation, with a focus on their adsorption-reduction characteristics. The removal of heavy metals, dyes, and radionuclides by MXenes and MXene-based nanomaterials is depicted in detail, with the adsorption mechanism and regeneration potential highlighted. Finally, suggestions for future research are provided to ensure that MXenes and MXene-based nanomaterials are synthesized and applied more effectively.

Recent advances of carbon-based nanomaterials (CBNMs) for wastewater treatment: Synthesis and application

Carbon-based nanomaterials (CBNMs) have attracted significant alert due to the affluent science underpinning their implementations associated with a novel mixture of high aspect proportions, greater thermal and electrical performance, outstanding optical features, and high exterior area. CBNMs not only bear assurance in a broad range of implementations in medication, nano and microelectronics, and ecological remedies but may also be utilized in practical laboratory determinations. More specifically, CBNMs perform as an outstanding adsorbent in terminating heavy metal ions (HMI) from wastewater. There is presently a deficiency of powerful threat inspection instruments owing to their complex detection and related deficit in the health risk database. Therefore, our present review concentrates on spreading CBNMs to release pollutants from wastewater. The article wraps the effect of these contaminants and photocatalytic strategies towards treating these mixtures in wastewater, along with their restrictions and challenges, convincing resolutions, and possibilities of these approaches.

Insights on synthesis and applications of graphene-based materials in wastewater treatment: A review

Graphene has excellent unique thermal, chemical, optical, and mechanical properties such as high thermal conductivity, high chemical stability, optical transmittance, high current density, higher surface area, etc. Due to their outstanding properties, the attention towards graphene-based materials and their derivatives in wastewater treatment has been increased in recent times. Different graphene-based materials such as graphene oxides, graphene quantum dots, graphene nanoplatelets, graphene nanoribbons and other graphene-based nanocomposites are synthesized through chemical vapor deposition, mechanical and electrochemical exfoliation of graphite. In this review, the specifics about the graphenes and their derivatives, the synthesis strategy of graphene-based materials are described. This review critically explained the applications of graphene-based materials in wastewater treatment. Graphene-based materials were utilized as adsorbents, electrodes, and photocatalysts for the efficient removal of toxic pollutants such as heavy metals, dyes, pharmaceutics, antibiotics, phenols, polycyclic aromatic hydrocarbons have been highlighted and discussed. Herein, the potential scope of graphene-based material in the field of wastewater treatment is critically reviewed. In addition, a brief perspective on future research directions and difficulties in the synthesis of graphene-based material are summarized.

Evaluate the role of biochar during the organic waste composting process: A critical review

Composting is very robust and efficient for the biodegradation of organic waste; however secondary pollutants, namely greenhouse gases (GHGs) and odorous emissions, are environmental concerns during this process. Biochar addition to compost has attracted the interest of scientists with a lot of publication in recent years because it has addressed this matter and enhanced the quality of compost mixture. This review aims to evaluate the role of biochar during organic waste composting and identify the gaps of knowledge in this field. Moreover, the research direction to fill knowledge gaps was proposed and highlighted. Results demonstrated the commonly referenced conditions during composting mixed biochar should be reached such as pH (6.5-7.5), moisture (50-60%), initial C/N ratio (20-25:1), biochar doses (1-20% w/w), improved oxygen content availability, enhanced the performance and humification, accelerating organic matter decomposition through faster microbial growth. Biochar significantly decreased GHGs and odorous emissions by adding a 5-10% dosage range due to its larger surface area and porosity. On the other hand, with high exchange capacity and interaction with organic matters, biochar enhanced the composting performance humification (e.g., formation humic and fulvic acid). Biochar could extend the thermophilic phase of composting, reduce the pH value, NH₃ emission, and prevent nitrogen losses through positive effects to nitrifying bacteria. The surfaces of the biochar particles are partly attributed to the presence of functional groups such as Si-O-Si, OH, COOH, CO, C-O, N for high cation exchange capacity and adsorption. Adding biochars could decrease NH₃ emissions in the highest range up to 98%, the removal efficiency of CH₄ emissions has been reported with a wide range greater than 80%. Biochar could absorb volatile organic compounds (VOCs) more than 50% in the experiment based on distribution mechanisms and surface adsorption and efficient reduction in metal bioaccessibilities for Pb, Ni, Cu, Zn, As, Cr and Cd. By applicating biochar improved the compost maturity by promoting enzymatic activity and germination index (>80%). However, physico-chemical properties of biochar such as particle size, pore size, pore volume should be clarified and its influence on the composting process evaluated in further studies.

Biosorptive ascendency of plant based biosorbents in removing hexavalent chromium from aqueous solutions - Insights into isotherm and kinetic studies

Chromium is a toxic heavy metal prevalent in higher levels in aqueous matrices owing to industrial applications. Whilst being a key player in industries, the environmental issues caused by Cr(VI) are highly deleterious. Adsorptive remediation is found to be an effective method adopted by researchers in the past decades for Cr(VI) removal from water streams in which variety of naturally available biosorbents have been explored for handling Cr(VI). This review article briefly sketches up the biosorptive potential of plant-based biosorbents used in raw and chemically modified form for the optimum exclusion of Cr(VI) from aqueous sources. Mechanisms and kinetic behavior of the removal process are also discussed. pH of the solution and initial Cr(VI) concentration were found to be the key parameters in Cr removal. The mechanism of Cr removal from aqueous systems was elucidated to be either adsorption or adsorption-coupled-reduction. After precise discussion on various plant-based biosorbents with their maximum adsorption capacities, desorption and regeneration potential, it is perceived that plant-based biosorbents are superior options for Cr(VI) elimination from aqueous streams.

Applicability of bio-synthesized nanoparticles in fungal secondary metabolites products and plant extracts for eliminating antibiotic-resistant bacteria risks in non-clinical environments

The abundance of antibiotic-resistant bacteria in the prawn pond effluents can substantially impact the natural environment. The settlement ponds, which are the most common treatment method for farms wastewater, might effectively reduce the suspended solids and organic matter. However, the method is insufficient for bacterial inactivation. The current paper seeks to highlight the environmental issue associated with the distribution of antibiotic resistant bacteria (ARB) from prawn farm wastewater and their impact on the microbial complex community in the surface water which receiving these wastes. The inactivation of antibiotic-resistant bacteria in prawn wastewater is strongly recommended because the presence of antibiotic-resistant bacteria in the environment causes water pollution and public health issues. The nanoparticles are more efficient for bacterial inactivation. They are widely accepted due to their high chemical and mechanical stability, broad spectrum of radiation absorption, high catalytic activity, and high antimicrobial activity. Many studies have examined the use of fungi or plants extract to synthesis zinc oxide nanoparticles (ZnO NPs). It is evident from recent papers in the literature that green synthesized ZnO NPs from microbes and plant extracts are non-toxic and effective. ZnO NPs inactivate the bacterial cells as a function for releasing reactive oxygen species (ROS) and zinc ions. The inactivation of antibiotic-resistant bacteria tends to be more than 90% which exhibit strong antimicrobial behavior against bacterial species.

Prospects of MXenes in energy storage applications

The transition metal carbides/nitrides referred to as MXenes has emerged as a wonder material presenting newer opportunities owing to their unique properties such as high thermal and electrical conductivity, high negative zeta-potential and mechanical properties similar to the parent transition metal carbides/nitrides. These properties of MXenes can be utilized in various societal applications including for energy storage and energy conversion. In this focused review, we provide a ready glance into the evolutionary development of the MXene family and various efforts that are made globally towards property improvement and performance enhancement. Particular attention in this review is made to direct the attention of readers to the bright prospects of MXene in the energy storage and energy conversion process - which is extremely timely to tackle the current concern on climate change. The review concludes by offering fresh insights into the future research needs and challenges that need to be addressed to develop resilient energy solutions.

Adsorptive removal of some Cl-VOC's as dangerous environmental pollutants using feather-like γ-Al2O3 derived from aluminium waste with life cycle analysis

Herein, we designed a cost-effective preparation method of nanocomposite γ-Al₂O₃ derived from Al-waste. The produced material has a feather-like morphology, and its adsorption of some chlorinated volatile organic compounds (Cl-VOC's) such as benzyl chloride, chloroform and carbon tetrachloride (C₇H₇Cl, CHCl₃ and CCl₄) was investigated due to their potential carcinogenic effect on humans. It showed a characteristic efficiency towards the adsorptive removal of these compounds over a long period, i.e., eight continuous weeks, at ambient temperature and atmospheric pressure. After 8-weeks, the adsorbed amounts of these compounds were determined as: 325.3 mg C₇H₇Cl, 247.6 mg CHCl₃ and 253.3 mg CCl₄ per g of γ-Al₂O_3, respectively. CCl₄ was also found to be dissociatively adsorbed on the surface of γ-Al₂O₃, whereas CHCl₃ and C₇H₇Cl were found to be associatively adsorbed. The prepared γ-Al₂O₃ has a relatively high surface area (i.e., 192.2 m². g^-1) and mesoporosity with different pore diameters in the range of 25-47 Å. Furthermore, environmental impacts of the nanocomposite γ-Al₂O₃ preparation were evaluated using life cycle assessment. For prepartion of adsorbent utilising 1 kg of scrap aluminium wire, it was observed that potential energy demand was 288 MJ, climate change potential was 19 kg CO₂ equivalent, acidification potential was 0.115 kg SO₂ equivalent and eutrophication potential was 0.018 kg PO₄^3- equivalent.

Effective mitigation of single-component and mixed textile dyes from aqueous media using recyclable graphene-based nanocomposite

The present study reported the synthesis and utilization of a graphene-based hybrid nanocomposite (MnFe₂O₄/G) to mitigate several synthetic dyes, including methylene blue, malachite green, crystal violet, and Rhodamine B. This adsorbent was structurally analyzed by several physicochemical techniques such as X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, N₂ adsorption-desorption isotherm measurement, point of zero charge, and Boehm titrations. BET surface area of MnFe₂O₄/G was measured at 382.98 m²/g, which was substantially higher than that of MnFe₂O₄. MnFe₂O₄/G possessed diverse surface chemistry properties with the presence of many functional groups such as carboxylic acid, phenolic, lactone, and basic groups. MnFe₂O₄/G was used to remove synthetic dyes in the aqueous media. The effect of many factors, e.g., concentration (5-50 mg/L), pH (4-10), dose (5-20 mg), and temperature (25-45 °C) on adsorption performance of MnFe₂O₄/G was conducted. Kinetic, isotherm, intraparticle, and thermodynamic models were adopted for investigating adsorption phenomenon of dyes on MnFe₂O₄/G. The maximum adsorption capacity of dyes over MnFe₂O₄/G was found as Rhodamine B (67.8 mg/g) < crystal violet (81.3 mg/g) < methylene blue (137.7 mg/g) < malachite green (394.5 mg/g). Some tests were performed to remove mixed dyes, and mixed dyes in the presence of antibiotics with total efficiencies of 65.8-87.9% after 120 min. Moreover, the major role of π-π stacking interaction was clarified to gain insight into the adsorption mechanism. MnFe₂O₄/G could recycle up to 4 cycles, which may be beneficial for further practical water treatment.

Effect of microwave/hydrothermal combined ionic liquid pretreatment on straw: Rumen anaerobic fermentation and enzyme hydrolysis

To explore green technology for wheat straw pretreatment, this study combined the microwave or hydrothermal with ionic liquid ([Bmim][OAc]) on wheat straw followed by rumen fermentation. The optimal conditions of microwave assisted ionic liquids pretreatment (M-I) and hydrothermal assisted ionic liquids pretreatment (H-I) treatment were 360 W and 200 °C, and the corresponding lignin removal rates reached 35.3% and 25.4%, respectively. Rumen fermentation showed that the highest volatile fatty acid (VFA) yield was found in M-I group, followed by H-I group at 234 and 180 mg/g, respectively. As for enzymatic hydrolysis, the saccharification rates at 3 days of M-I (360 W) and H-I (200 °C) were determined to be 393 and 320 mg/g. The optimal ionic liquid dosage was determined to be 30% in consideration of cost and VFA conversion rate. M-I pretreatment plus the rumen fermentation enjoyed the benefit of no enzyme addition and high product recovery, which was worth further investigating.

Novel synthesis methods and applications of MXene-based nanomaterials (MBNs) for hazardous pollutants degradation: Future perspectives

MXenes are a quickly growing and extended group of two-dimensional (2D) substances that have earned unbelievable analysis credits for various application areas within different manufacturing areas. Due to novel essential architectural and physicochemical properties shows good properties, such as elevated exterior area, living adaptability, strong electrochemistry, and great hydrophilicity. Given the fast progress within the structure and synthesis of MBNs for water treatment, quick updates on this research field are required to remove toxic substances, such as production approaches and characterization methods for the advantages and constraints of MXenes for pollutant degradation. MXenes are determined as a proposed road toward atmosphere-clean-up machinery to identify and decrease a pattern of hazardous resistant pollutants from environmental forms. Here, in this review article, we have been focused on describing the overview, novel synthesis methods, and characteristics of the MXene-based nanomaterials (MBNs) in the field for removing hazardous contaminants from environmental conditions. In the last, the utilizations of MBNs in water sanitization, organic solvent filtration, antibiotics degradation, pesticide degradation, heavy metals degradation, ions removal, bacterial pathogens degradation, along with the conclusion, challenges, and prospects in this field, have been discussed.

Inactivation of fungal spores from clinical environment by silver bio-nanoparticles; optimization, artificial neural network model and mechanism

The present study aimed to assess the efficiency of silver bio-nanoparticles (Ag-NPs) in inactivating of the Aspergillus fumigatus, A. parasiticus and A. flavus var. columnaris and A. aculeatus spores. The AgNPs were synthesized in secondary metabolic products of Penicillium pedernalens 604 EAN. The inactivation process was optimized by response surface methodology (RSM) as a function of Ag NPs volume (1-10 μL/mL); time (10-120 min); pH (5-8); initial fungal concentrations (log₁₀) (3-6). The artificial neural network (ANN) model was used to understand the behavior of spores for the factors affecting inactivation process. The best conditions to achieved SAL 10^-6 of the fungal spores were recorded with 3.46 μl/mL of AgNPs, after 120 min at pH 5 and with 6 log of initial fungal spore concentrations, at which 5.99 vs. 6.09 (SAL 10^-6) log reduction was recorded in actual and predicted results respectively with coefficient of 87.00%. The ANN revealed that the timehas major contribution in the inactivation process compare to Ag NPs volume. The fungal spores were totally inactivated (SAL 10^-6, 6 log reduction with 99.9999%) after 110 min of the inactivation process, 10 min more was required to insure the irreversible inactivation of the fungal spores. The absence of protease and cellulase enzymes production confirm the total inactivation of the fungal spores. FESEM analysis revealed that the AgNPs which penetrated the fungal spores leading to damage and deform the fungal spore morphology. The AFM analysis confirmed the total spore surface damage. The bands in the range of the Raman spectroscopy from 1300 to 1600 cm^-1 in the inactivated spores indicate the presence of CH_3, CH₂ and the deformation of lipids released outside the spore cytoplasm. These finding indicate that the AgNPs has high potential as a green alternative inactivation process for the airborne fungal spores.

MXenes based nano-heterojunctions and composites for advanced photocatalytic environmental detoxification and energy conversion: A review

Extensive research is being done to develop multifunctional advanced new materials for high performance photocatalytic applications in the field of energy production and environmental detoxification, MXenes have emerged as promising materials for enhancing photocatalytic performance owing to their excellent mechanical properties, appropriate Fermi levels, and adjustability of chemical composition. Numerous experimental and theoretical research works implied that the dimensions of MXenes have a significant impact on their performance. For photocatalysis to thrive in the future, we must understand the current state of the art for MXene in different dimensions. Using MXene co-catalysts in widely used in photocatalytic applications such as CO₂ reduction, hydrogen production and organic pollutant oxidation, this study focuses on the most recent developments in MXenes based materials, structural modifications, innovations in reaction and material engineering. It has been reported that using 5 mg of CdS-MoS₂-MXene researchers were able to generate as high as 9679 μmol/g/h hydrogen under visible light. The MXenes based heterojunction photocatalyst Co₃O₄/MXene was utilized to degrade 95% bisphenol A micro-pollutant in just 7 min. Numerous novel materials, their preparations and performances have been discussed. Depending upon the nature of MXene-based materials, the synthesis techniques and photocatalytic mechanism of MXenes as co-catalyst are also summarized. Finally, some final thoughts and prospects for developing highly efficient MXene-based photocatalysts are provided which will indeed motivate researchers to design novel hybrid materials based on MXenes for sustainable solutions to energy and pollution issues.

A global systematic review of the concentrations of Malathion in water matrices: Meta-analysis, and probabilistic risk assessment

Pesticide applications and the proximity of land use to water matrices have resulted in discharges of pollutants including Malathion -one of the most widely used organophosphorus pesticides- to water resources such as marine, freshwater, and under groundwater. Exposure to malathion through consumption of contaminated water may cause deleterious health effects on consumers. Determining the amount of pesticides used on farms can play an important role in preventing potential toxicity and pollution of nearby aquatic ecosystems. Therefore, this systematic review and meta-analysis is focused on evaluating the concentrations of Malathion in water resources while considering probabilistic health risk assessment. The international databases of Scopus, Embase, and PubMed were investigated to evaluate the related articles from January 01, 1968 to March 25, 2021. Thirty-four articles containing 206 samples from 15 countries were included. A meta-analysis of carcinogenic and non-carcinogenic risk assessments for Malathion was also performed. To determine uncertainty intervals, a Monte-Carlo simulation was conducted. The results of the meta-analysis showed that the rankings of Malathion pollution (from the most to the least) were: drinking water > surface waters > groundwaters. Moreover, the results of the risk assessments confirm that there is no non-carcinogenic risk for any of the study areas. The carcinogenic risk assessment was within the limit for the countries under this study, except for Ethiopia that was slightly over the limit as well as Iran, and Mexico had high carcinogenic risk.

Sustainable approaches for nickel removal from wastewater using bacterial biomass and nanocomposite adsorbents: A review

In this article, the nickel (Ni²⁺) ions removal from the wastewater is reviewed. Adsorption is widely used to remove Ni²⁺ ions from waters and wastewaters. The usage of biomass is becoming more common for Ni²⁺ ions removal, while the commercial activated carbon from different agriculture wastes is preferred as an adsorbent for Ni²⁺ ion removal. The present review aimed to organise the available information regarding sustainable approaches for Ni²⁺ ions removal from water and wastewaters. These include adsorption by nanoparticles, bacterial biomass, and activated carbon from agriculture wastes, since they are the most common used for the Ni²⁺ ions removal. The bacterial and agricultural waste adsorbents exhibited high efficiency with a renewable source of biomass for Ni²⁺ ion removal. The biosorption capacity of the Ni²⁺ ions by the bacterial biomass range from 5.7 to 556 mg/g, while ranging from 5.8 to 150 mg/g by the activated carbon from different organic materials. The biosorption capacity of the nanocomposite adsorbents might reach to 400 mg/g. It appeared that the elimination of nickel ions need a selective biomass adsorbent such as the tolerant bacterial cells biomass which acts as a store for Ni²⁺ ion accumulations as a results for the active and passive transportation of the Ni²⁺ ions through the bacterial cell membrane.

Sustainable nanotechnology based wastewater treatment strategies: achievements, challenges and future perspectives

Nanotechnology is being an emerging science for wastewater treatment requires more research emphasis and depth knowledge. For wastewater treatment, different forms of nanomaterials are used based on the type of contaminants and treatment efficiency desired. With the development in the field of nanomaterials, novel and emerging nanomaterials are coming into existence. The nanomaterials used for wastewater treatment can be carbon, single-walled carbon nanotubes, multiple walled carbon nanotubes, covalent organic frameworks, metal and metal oxide- based nanoparticles. Graphene based nanoparticles, their oxides (GO) and reduced graphene oxide (rGO) find tremendous applicability to be used in wastewater treatment purposes. Due to the introduction of graphene oxide nanoparticles in the adsorbent materials, their adsorption capacities have get enhanced and such materials have also improved the mechanical stability of the adsorbent. Ferric oxide shows greater adsorption capacities for organic pollutants. Furthermore, magnetic nano-powder confers a low adsorption capacity for phenols. Pyrrolidone reduced graphene oxide (PVP-RGO) nanoparticles have been used as adsorbents for the elimination of inorganic target contaminant copper, with great adsorption (1698 mg/g). The present study comprehensively reviews nanotechnology as a wastewater treatment strategy besides enlightening its safety issues and efficiency. The novelty of this article is that it highlights the overview of recent applications of various types of nanomaterials and research works releated to it. Such an approach will be helpful to get insights into technological advances, applications and future challenges of nanotechnology implementation for wastewater treatment.

A state-of-the-art review on microbial desalination cells

The rapid growth in population has increased the demand for potable water. Available technologies for its generation are the desalination of sea water through reverse osmosis, electrodialysis etc., which are energy and cost intensive. In this context, microbial desalination cell (MDC) presents a low-cost and sustainable option which can simultaneously treat wastewater, desalinate saline water, produce electrical energy and recover nutrients from wastewater. This review paper is focussed on presenting a detailed analysis of MDCs starting from the principle of operation, microbial community analysis, basic architecture, evolution in design, operational challenges, effect of process parameters, scale-up studies, application in multiple arenas and future prospects. After thorough review, it can be inferred that MDCs can be used as a stand-alone option or pre-treatment step for conventional desalination techniques without the application of external energy. MDCs have been used in multiple applications ranging from desalination, remediation of contaminated water, recovery of energy and nutrients from wastewater, softening of hardwater, biohydrogen production to degradation of waste engine oil. Although, MDCs have been used for multiple applications, still a number of operational challenges have been reported viz., interference of co-existing ions during desalination, membrane fouling, pH imbalance and limited potential of exoelectrogens. However, the re-circulation of anolytes with electrodialysis chamber has led to the maintenance of optimal pH for favourable microbial growth leading to improvement in the overall performance of MDCs. In future, genetic engineering may be used for improving the electrogenic activity of microbial community, next generation materials may be used as anode and cathode, varied sources of wastewater may be explored as anolytes, life cycle analysis and exergy analysis may be carried out to study the impact on environment and detailed pilot scale studies have to be carried out for assessing the feasibility of operation at large scale.

Promotion of methane production by magnetite via increasing acetogenesis revealed by metagenome-assembled genomes

Metal oxides are wildly studied to enhance anaerobic digestion and the methanogenic process, which is generally interpreted by increased direct interspecies electron transfer (DIET). Yet microbial mechanisms involved are under debate. Herein, methane production dynamics were analyzed, and acceleration on biogas accumulation was presented. Complementing previous findings, Fe₃O₄ nanoparticles stimulated bacterial fermentation rather than methanogenesis or syntropy between electro-microorganism and methanogen. More importantly, metagenome-assembled genomes proved that Fe₃O₄ nanoparticles increased acetogenesis by Parabacteroides chartae, which provided abundant substrates for acetoclastic methanogenesis. Interestingly, the weakly conductive V₃O₇·H₂O nanowires increased potential hydrogen-producing bacteria, Brevundimonas, and electro-microorganisms, Clostridium and Rhodoferax, which is convenient for conducting DIET. Collectively, conductivity may not be a critical factor in mediating DIET and distinct strategies of metal oxides on methane production propose more possibilities, such as fermentation process.

A comprehensive review on the removal of noxious pollutants using carrageenan based advanced adsorbents

Rapid industrial development is associated with high discharge of toxic pollutants into the environment. The industries discharge their wastewater containing organic pollutants directly into the water system without treating them that has posed many serious threats to environmental protection. The use of bioadsorbents for the removal of such toxic pollutants from the waste water due to its simple synthesis, easy operation, effectiveness, and economic viability have emerged a new dimension in the wastewater treatment approaches. Various adsorbents have been prepared to examine their adsorption capacity against different adsorbates, but, to attain sustainability, biocompatibility, and biodegradation, bio-adsorbents have been found to won the battle. Seaweed derived polysaccharide; Carrageenan (CR) has been proven to be an excellent adsorbent for the wastewater treatment. It has been successfully modified with various components to form CR based-magnetic composites, hydrogels, nanoparticle modified CR composites and many others to enrich and diversify its properties. In this review, we have explained the adsorption behaviour of various carrageenan based adsorbents for the removal of different dyes. The influence of various parameters such as the effect of initial concentration, adsorbent dosage, contact time, pH, temperature, and ion concentration on dye adsorption is well explained. This paper also summarizes the structure, morphology, swelling ability, and thermal stability of carrageenan. The data also expounds on the adsorption capacity, kinetic model, isotherm model, and nature of the adsorption process. Different types of solvents are used for the regeneration and reusability of carrageenan adsorbents and their regeneration studies and desorption efficiency is well-explained. The adsorption mechanism of dyes onto carrageenan based adsorbents has been well described in this review. This review provides a deep insight about the use of carrageenan based adsorbents for the wastewater treatment.