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Microplastic (MP) is considered as one of the emerging pollutants in marine environments. Because of low density and small particle size (

The depletion of fossil reserves and environmental challenges associated with fossil fuels are major drivers of the search for sustainable renewable energy sources. Bioethanol production from macroalgae is one of the promising alternatives to reduce use of fossil fuels and achieve energy security and ecological sustainability. The purpose of this review is to critically discuss the options to optimize the process parameters for steady production of bioethanol from macroalgae. A comprehensive literature review reveals that bioethanol production from macroalgae not only depends on the macroalgae type but also on the selection of pretreatment, hydrolysis, and fermentation options. Unlike the first- and second-generation feedstocks, macroalgae contains low concentrations of glucans. Thus high bioethanol concentration cannot be achieved by converting only glucans. Therefore, it is important to produce bioethanol from other carbohydrate components of macroalgae, such as alginate, sulphated polysaccharides, carrageenan, mannitol, and agar. The selection of the right hydrolysing agents (e.g., enzyme and/or acid) and steps to minimize formation of inhibitors during the process were found to be important factors affecting the efficiency of hydrolysis process. The hydrolysis enzymes currently used were developed for lignocellulosic and starch-based biomass, not for macroalgae, which is different in polysaccharide structure and composition. Also, the lack of appropriate fermenting microorganisms capable of converting heterogeneous monomeric sugars in macroalgae is a major factor limiting bioethanol yield during the fermentation process. This review systematically discusses the implications of selecting different macroalgae types. The optimization of process parameters of different bioethanol production steps such as pretreatments, hydrolysis, and fermentation is discussed. It can be concluded that high bioethanol yield can be achieved by considering macroalgae type and composition, selecting appropriate pretreatment, hydrolysis, and fermenting microbes, and with effective bioethanol purification.

Microplastics (MPs) pollution in the water environment is recognized as an important environmental risk. Among the diverse sources of MPs pollution, road dust is a major contributor via stormwater runoff. Roaddust mainly originates from degradation of vehicle tyres, road marking paints, polymer-modified bitumen and the broken plastics on the surface of the road. The objective of this study is to provide a comprehensive understanding of the fate and control of MPs in the open water environment. This review critically discusses the characteristics and pathways of road dust-associated MPs in stormwater and common stormwater treatment processes used for removing MPs, and provides insight into the technical challenges of these technologies. Constructed wetland is widely used for stormwater management; however, it is found that this process is only removing 28 % MPs as they usually remain suspended or settle down very slowly in the sedimentation basin of constructed wetlands. This is because of the low density of MP particles as well as the low retention time of the wetland. Thus, untreated stormwater, rich in MPs, is released into open waterbodies. This study concludes by providing an outlook of the future opportunities of installing membrane- or flotation-based technologies in the outlet of the constructed wetland for removing 90–95 % MPs and other remaining contaminants. Such a process can produce clean water either for use in households, for sanitation, and for industrial and agricultural usage, or alternatively, for safe discharge into open waterways.

Wastewater treatment is becoming increasingly important due to the potential shortage of pure drinking water in many parts of the world. Adsorption offers a potential technique for the uptake of contaminants and wastewater purification. In the last two decades, several efforts have been made to remove fast green (FG) dye from wastewater via different adsorbent materials. But adsorption capacity shown by these adsorbents is low and is time-consuming. Herein, we have synthesized for the first time a new powdered adsorbent ZnOS+C, modified Zinc peroxide with sulfur and activated carbon to effectively remove FG dye from wastewater. Results of batch adsorption experiments have suggested that ZnOS+C has the maximum adsorption capacity of 238.28 mg/g for FG dye within 120 minutes of adsorption equilibrium for a wide range of pH ranging from 2-10 pH. The adsorption process follows the Freundlich isotherm model, suggesting a multilayered adsorption process that occurs on the surface of ZnOS+C. The adsorption kinetics study indicates that the kinetics of the reaction is the intraparticle diffusion model. Briefly, this study shows the proof of application of ZnOS+C powder as a new eco-friendly adsorbent with extremely high efficiency and high surface area for removing FG dye.

Biofouling, the unwanted growth of microorganisms on submerged surfaces, has appeared as a significant impediment for underwater structures, water vessels, and medical devices. For fixing the biofouling issue, modification of the submerged surface is being experimented as a non-toxic approach worldwide. This technique necessitated altering the surface topography and roughness and developing a surface with a nano- to micro-structured pattern. The main objective of this study is to review the recent advancements in surface modification and hydrodynamic analysis concerning biofouling control. This study described the occurrence of the biofouling process, techniques suitable for biofouling control, and current state of research advancements comprehensively. Different biofilms under various hydrodynamic conditions have also been outlined in this study. Scenarios of biomimetic surfaces and underwater super-hydrophobicity, locomotion of microorganisms, nano- and micro-hydrodynamics on various surfaces around microorganisms, and material stiffness were explained thoroughly. The review also documented the approaches to inhibit the initial settlement of microorganisms and prolong the subsequent biofilm formation process for patterned surfaces. Though it is well documented that biofouling can be controlled to various degrees with different nano- and micro-structured patterned surfaces, the understanding of the underlying mechanism is still imprecise. Therefore, this review strived to present the possibilities of implementing the patterned surfaces as a physical deterrent against the settlement of fouling organisms and developing an active microfluidic environment to inhibit the initial bacterial settlement process. In general, microtopography equivalent to that of bacterial cells influences attachment via hydrodynamics, topography-induced cell placement, and air-entrapment, whereas nanotopography influences physicochemical forces through macromolecular conditioning.

Phosphorus is a critical non-renewable mineral essential for sustainable crop production. However, it is a primary cause of eutrophication in natural water bodies. Hence, a pragmatic approach that allows wastewater treatment plants to efficiently recover phosphorus from wastewater is needed. In this study, we investigated phosphorus recovery from municipal wastewater using an industrial waste product (steelmaking slag) as an adsorbent to selectively separate phosphorus from wastewater before its concentration by the forward osmosis (FO) process. Phosphorus adsorbed on slag was extracted, thereby regenerating the adsorbent medium. The resulting phosphorus-rich solution was further enriched by FO prior to chemical precipitation for phosphorus recovery. Batch test results showed that the equilibrium of phosphorus sorption on the slag medium was achieved within 45 min with an adsorption capacity of 3.8 mg g−1. In continuous-flow column tests, the slag exhibited a stable phosphorus removal efficiency of 82% from wastewater, following which approximately 88% of the phosphate could be extracted from the adsorbent medium. When the phosphorus-rich solution extracted from the adsorbent was passed through the FO membrane, FO could retain 98% of the phosphate. However, the water flux through the FO membrane declined gradually to approximately 20% of the initial value at a water recovery of 90%, which could be attributed to the increasingly concentrated feed solution. The enrichment of phosphate in the concentrated feed by the FO process provided a favorable condition for spontaneous precipitation of amorphous calcium phosphate. This study demonstrates that the proposed combined adsorption–FO process can effectively remove, and thus recover, phosphorus from municipal wastewater.

Laccase-catalysed degradation is a promising technology for the degradation of trace organic contaminants (TrOCs). However, depending on their physicochemical properties (e.g., chemical structures), non-phenolic TrOCs appear to be resistant to laccase-catalysed degradation, thus requiring an additional treatment process. In this study, the performance of an integrated laccase and persulfate (PS) mediated oxidation process was explored and elucidated for the first time. Compared to that achieved during treatment with laccase alone, the addition of PS at 1–10 mM concentration into batch enzymatic bioreactors showed concentration-dependent improvement in the degradation of the five TrOCs selected, namely diclofenac, sulfamethoxazole, carbamazepine, bisphenol A and oxybenzone. The results obtained from a series of batch tests also confirmed that the structural components (e.g., carbohydrate moieties in the enzyme) as well as the possibility of PS acting as a final acceptor of electrons from the type II and type III active sites of laccase may have led to PS activation. A continuous treatment system was developed by integrating a nanofiltration (NF) membrane with the laccase/PS process (NF-MBRlaccase/PS), which achieved TrOC-specific degradation. Importantly, the degradation of non-phenolic TrOCs (diclofenac, sulfamethoxazole and carbamazepine) further improved by 10 to 65% in the NF-MBRlaccase/PS system. This improvement could be attributed to: (i) the prolonged contact time between laccase/PS and TrOCs, which was possible due to their complete retention by the NF membrane; and (ii) retention of oxidative cross coupling agents or secondary radicals enhancing TrOC degradation. The NF membrane not only retained the moderately degraded carbamazepine and sulfamethoxazole effectively but also effectively removed toxic transformation products and residual estrogenicity of the final effluent as evaluated by cytotoxicity and estrogenicity assays, respectively. These observations indicate the significance of the high retention membrane in the NF-MBRlaccase/PS system for producing high quality permeate suitable for disposal and potentially for water reuse applications.

NANO: and microplastic (NP/MP) is one of the most challenging types of micropollutants, coming from either direct release or degradation of plastic items into ecosystems. NP/MP can adsorb hazardous pollutants (such as heavy metals and pharmaceutical compounds) and pathogens onto their surface that are consumed by humans, animals, and aquatic living organisms. This paper presents the interaction of NP/MP with other pollutants in the water environment and mechanisms involved to enable the ultimate fate of NP/MP as well as the effectiveness of metal-organic frame (MOF)-based membrane over conventional membrane processes for NP/MP removal. It is found that conventional membranes could remove MPs when their size is usually more than 1000 nm, but they are ineffective in removing NPs. These NPs have potentially greater health impacts due to their greater surface area. MOF-based membrane could effectively remove both NP and MP due to its large porous structure, high adsorption capacity, and low density. This paper also discusses some challenges associated with MOF-based membranes for NP/MP removal. Finally, we conclude a specific MOF-based ultrafiltration membrane (ED-MIL-101 (Cr)) that can potentially remove both negative and positive charged NP/MP from wastewater by electrostatic attraction and repulsion force with efficient water permeability.

The skyrocketing demand and progressive technology have increased our dependency on electrical and electronic devices. However, the life span of these devices has been shortened because of rapid scientific expansions. Hence, massive volumes of electronic waste (e-waste) is generating day by day. Nevertheless, the ongoing management of e-waste has emerged as a major threat to sustainable economic development worldwide. In general, e-waste contains several toxic substances such as metals, plastics, and refractory oxides. Metals, particularly lead, mercury, nickel, cadmium, and copper along with some valuable metals such as rare earth metals, platinum group elements, alkaline and radioactive metal are very common; which can be extracted before disposing of the e-waste for reuse. In addition, many of these metals are hazardous. Therefore, e-waste management is an essential issue. In this study, we critically have reviewed the existing extraction processes and compared among different processes such as physical, biological, supercritical fluid technologies, pyro and hydrometallurgical, and hybrid methods used for metals extraction from e-waste. The review indicates that although each method has particular merits but hybrid methods are eco-friendlier with extraction efficiency 90%. This study also provides insight into the technical challenges to the practical realization of metals extraction from e-waste sources.

Heavy metals are one of the major chemical pollutant groups in urban runoff. The application of porous concrete is a potential alternative to conventional runoff management systems with the ability to remove heavy metals. Hence, a thorough understanding of the heavy metal removal mechanisms and constraints of conventional porous concrete opens a path for the development of effective modifications. This review critically discusses the major contributors in ordinary porous concrete which supports heavy metal removal. The effects of initial concentration, contact time and competing ions on heavy metal removal using porous concrete are also discussed. Additionally, the effect of decalcification, atmospheric carbonation, acid influent on heavy metal removal is reviewed. The major drawback of porous concrete is the high pH (8.5) of the effluent water, decalcification of the porous concrete and leaching of adsorbed pollutants. Overall, the addition of adsorbent materials to the porous concrete increases removal efficiencies (7% - 65% increase) without neutralizing the effluent pH. Meanwhile, the addition of Reduced Graphene Oxide is successful in reducing the leachability of the removed heavy metals. The addition of pozzolanic materials can lower the effluent pH while maintaining similar removal efficiencies to unmodified porous concrete. Therefore, developing a novel method of neutralizing the effluent pH must be prioritized in future studies. Additionally, the toxicity that can occur due to the abrasion of modified porous concrete requires study in future research. Further, advanced characterization methods should be used in future studies to understand the mechanisms of removal via the modified porous concrete materials.

Treatment of wastewater with high levels of fat, oil, and grease (FOG), produced by the growing number (annually 2%) of food service establishments (FSEs), is a major concern for water utilities. About 30-40% of sewer blockages are caused primarily by the formation of FOG deposits in sewer pipes, and an annual additional maintenance cost is required for sewer management. To manage FOG deposition, FSEs are required to recover the FOG at the point of generation by installing grease interceptors (GIs) before release to the sewer system. The successful control of FOG deposition is largely dependent on clear understanding of its complex properties, pre-treatment processes, deposition mechanism and public awareness. The objective of this study is to provide a comprehensive understanding of the physicochemical properties of FOG, including particle size distribution and their removal efficiencies by existing GIs. Nowadays, generation of FOG particles of ≤45 µm is increasing because of the increasing use of automatic dishwashers. Current hybrid processes which comprise pre-treatment prior to GI use are ineffective since they are unable to completely remove particle sizes of ≤45 µm. Hence, there is potential for these particles to be released into the sewer system and eventually cause blockages. This critical review discusses the characteristics of effluents, including the particle size distributions generated from automatic dishwashers and handwash sinks. It concludes by providing some case studies and a perspective of the future opportunities to develop a novel GI process integrated with pre-treatment to remove particles of all sizes, including colloidal particles.

Tailings storage facilities (TSFs) are the main source of pollution from mining operations. However, TSFs are increasingly being considered as the potential secondary sources of some critical minerals. Recovering the critical minerals from TSFs is important due to both environmental and economic implications. Yet, identification of the potential TSFs is the major challenge in this venture due to the lack of publicly available database of TSFs. The objective of this study was to identify the TSFs and document their status in the form of a database for Australia. Visual inspection and interpretation of satellite images in Google Earth were used to identify the TSFs in 6 states and the publicly available database of TSFs for Western Australia (WA) was validated in this study to incorporate into a national-level database. This study has identified 331 active and 759 inactive TSFs in Australia. Among the sites, 42 active and 56 inactive mine sites with TSFs were found within 2 km of urban centres in the studied states. Coal and gold were the major commodities of 27% of active mine sites with the TSFs and 38% of inactive mine sites with TSFs, respectively. Approximately 16% of active mine sites with TSFs and 28% of inactive mine sites with TSFs were found to process copper as a major commodity. Considering the companionability matrix, many of these TSFs could be explored for the possible recovery of critical minerals (e.g. rare earth elements, cobalt). This study has developed a national-level database of TSFs for Australia for the first time, and it could be used for a number of applications.

We investigated the effect of draw solution type on the forward osmosis (FO) performance for enriching nutrients from anaerobically treated dairy manure (ATDM) followed by chemical precipitation for phosphorus recovery as struvite crystal. The FO membrane significantly rejected COD (>97%) and phosphate (>98%) whereas there was only 70%–73% and 73%–76% rejection of ammonia-nitrogen and total nitrogen, respectively. The draw solution type had little impact on the retention of the aforementioned wastewater constituents by the FO membrane. At 60% water recovery, a water flux decline of 82%–96% was observed due to increasing contaminant concentration in the concentrated feed solution. Water flux decline was less for MgCl2 than EDTA-2Na and NaCl as draw solutes. On the contrary, the reverse solute flux was higher for NaCl than MgCl2, which in turn was higher than EDTA-2Na. Pre-concentration of ATDM by FO facilitated struvite precipitation. MgCl2 as the draw solute provided a higher purity of struvite than EDTA-2Na and NaCl. This is because when MgCl2 was used as the draw solute, the reverse salt flux of magnesium to the concentrated ATDM provided favourable conditions for struvite crystal formation. This study demonstrates the technical feasibility of phosphorus recovery from ATDM using the FO process.

In this study, long-term performance of a persulfate (PS)-assisted direct contact membrane distillation (DCMD) process was examined for the treatment of secondary treated effluent spiked with a mixture of micropollutants including three pesticides and nine pharmaceuticals. A stand-alone DCMD (‘control’) was also operated under identical operating conditions for comparison. Depending on the micropollutant, the stand-alone DCMD achieved 86 to >99% removal. In comparison, removal by the PS-assisted DCMD was >99% for all investigated micropollutants. This was attributed to the fact that sulfate radicals (SO4– ) formed following the activation of PS at the DCMD operating temperature (i.e., 40 °C) achieved micropollutant-specific degradation, which reduced the accumulation of micropollutants in the feed. Chemical structures of the micropollutants governed their degradation by PS. Effective degradation (>90%) was achieved for micropollutants that contain strong electron-donating functional groups (EDGs) in their molecules (e.g., amitriptyline and trimethoprim). Micropollutants containing both strong electron-withdrawing functional groups (EWGs) and EDGs in their molecules were moderately degraded (60–80%). In addition to the micropollutants, activated PS significantly degraded total organic carbon (70%) and total nitrogen (40%) from the secondary treated wastewater. This helped to reduce the fouling layer on the membrane-surface in the PS-assisted DCMD system. PS-addition appears to slightly increase the toxicity of wastewater, but with effective retention of PS and degradation products, DCMD permeate (i.e., treated effluent) was not toxic. This is the first study demonstrating the performance of the persulfate oxidation process in a continuous-flow membrane system for micropollutant removal and membrane fouling control.

The forward osmosis (FO) membrane process has recently established its potential as an alternative option to traditional membrane processes for producing clean water and recovering nutrients from anaerobically treated wastewater streams. However, organic fouling of membrane leads to reduced flux, and, thus, reduced amount of the extractable resources. In this study, the impact of ultraviolet/persulfate (UV/PS) oxidation pre-treatment for the mitigation of organic fouling in the FO process during processing of anaerobically treated dairy effluent (ATDE) was determined using a multi-cycle filtration method. The UV/PS performance was compared with control pre-treatments such as stand-alone ultraviolet (UV) irradiation and potassium persulfate (PS) oxidation. Size exclusion chromatography confirmed that flux reduction over successive filtration cycles was due mainly to the humic substances and building blocks i.e., sub-units of humic substances in the feedwater. Although all investigated pre-treatment options mitigated membrane fouling, UV/PS achieved a greater enhancement in flux and decrease in both reversible and irreversible foulant deposition than stand-alone UV and PS pre-treatments. This was because UV/PS could generate sulfate and hydroxyl radicals, which were effective for decreasing the bulk organic content and fluorescent organic content, and particularly for breaking down the large molecular weight (MW) hydrophobic compounds to small MW hydrophilic components, resulting in less organics adhesion to the membrane. This research shows the applicability of UV/PS pre-treatment for the organic fouling mitigation of FO membrane during processing of ATDE for applications such as nutrient mining from ATDE.

The high demand for the rare earth elements (REEs) in the clean technological industries implies the increased demand to produce these elements from ores and REEs containing impaired water sources such as acid mine drainage (AMD). However, the presence of these elements in AMD has increased their toxic exposure to the water environment. Herein, we investigated the role of the orientation of the membrane (such as active layer facing feed solution (AL-FS) or active layer facing draw solution (AL-DS) mode), solution pH, and temperature variation on the flux performance and rejection of three REEs (e.g., lanthanum, cerium, and dysprosium) from a simulated AMD solution using the forward osmosis (FO) process. It was found that there was a greater water flux at high pH, AL-DS mode of the FO system and high feed and draw solution temperature. FO could effectively reject all three REEs in both AL-FS and AL-DS membrane orientations mode due to steric hindrance. The rejection of these REEs in the AL-DS mode was slightly lower (82–88%) than that in the AL-FS mode (86–96%). The rejection of all REEs was noticeably influenced by solution pH in both mode. This was due to the changes in membrane surface with pH variation. The rejection of REEs increased when the temperature of the feed and draw solution was 20 and 40 °C, respectively. However, the rejection of all REEs decreased markedly when the temperature of the feed and draw solution was 40 and 20 °C, respectively. The lower rejection of these REEs was due to the enhancement of their diffusivity at a higher temperature in the feed side.

© 2018 Elsevier B.V. This study evaluated the removal of diclofenac (DCF) in activated sludge and its long-term exposure effects on the function and structure of the microbial community. Activated sludge could remove

Microplastics (MP) have become a major emerging class of pollutants representing significant eco-toxicological risks for ecosystems and marine environments. The aim of this study was to identify, classify and quantify MP present in both road dust and stormwater samples. A significantly higher level of MPs within road dust samples was detected from industrial area (1130 particles/kg of dust) than from residential area (520 particles/kg of dust), while stormwater samples from industrial and residential sites yielded 26 particles/L and 17 particles/L, respectively. Fiber-like shape accounted for 53% and 74% in road dust and stormwater samples, respectively. The main polymeric materials collected for both road dust and stormwater samples were, in order of occurrence (i) low-density polyethylene, (ii) high-density polyethylene, (iii) polypropylene, (iv) polyethylene terephthalate, (v) polystyrene, (vi) polyester and (vii) poly (amide). Most of the MP had an average maximum dimension smaller than 2 mm for both road dust and stormwater samples. The results from this study demonstrates that road dust is a significant contributor to MP pollution through direct polymeric materials wear off and transfer through stormwater, which eventually will end up in open water ways and broader ecological niches.

The presence of cobalt(II) in wastewater is an emergent concern because of its toxicity at elevated concentration. Co(II) is a non-biodegradable, carcinogenic and mutagenic pollutant released from natural, industrial and manmade sources. In recent years, the control of water that has been polluted with Co(II) has been an emergent issue. The release of Co(II) into waterways is undesirable because ingestion of high levels of Co(II) may cause severe health issues including cancer. The current review discusses the different adsorbents such as carbonaceous and activated carbon materials, nanosized metal oxides, low-cost natural materials, clay minerals and nanocomposites employed by researchers to treat Co(II)-polluted water. The systems used have been assessed in terms of overall Co(II) sorption capacity. Special emphasis has been given to the environmental conditions such as contact time, solution pH, initial Co(II) concentration, temperature, and mineral dosage. Moreover, empirical and surface complexation modeling (SCM) of the sorption systems is summarized. Natural materials, agricultural waste materials, and bio sorbents exhibited outstanding Co(II) sorption performance. The current investigation provides an overview of the state of the Co(II) removal studies performed by using various adsorbents.

Nanosized aluminium oxides (NAOs) are an important class of minerals widely found in soil, sediment, aquifer, and aquatic environments. Over the decades, these minerals have been explored as sorbents for the removal of wastewater contaminated with metal ions, anions, organic dyes, humic substances, phenolic compounds, pesticides, and pharmaceuticals from contaminated wastewater. This review summarizes the reported research of NAOs as sorbents and provides details on their sorption capacities including maximum removal capacity under various experimental conditions. Information on the composition, synthesis, characterization and experimental parameters together with sorption mechanisms is provided. A compilation of such information is not currently available and so this review should enable workers in the area to make more informed choices on suitable sorbents for large-scale environmental samples and be able to develop more efficient processes for environmental pollutant clean-up.

Nano/microplastics (NPs/MPs), a tiny particle of plastic pollution, are known as one of the most important environmental threats to marine ecosystems. Wastewater treatment plants can act as entrance routes for NPs/MPs to the aquatic environment as they breakdown of larger fragments of the plastic component during the treatment process; therefore, it is necessary to remove NPs/MPs during the wastewater treatment process. In this study, understanding the effect of water shear force on the fragmentation of larger size MPs into smaller MPs and NPs and their removal by air flotation and nano-ferrofluid (i.e., magnetite and cobalt ferrite particle as a coagulant) and membrane processes were investigated as a proof-of-concept study. It is found that a two-blade mechanical impeller could fragment MPs from 75, 150 and 300 μm into mean size NPs/MPs of 0.74, 1.14 and 1.88 μm, respectively. Results showed that the maximum removal efficiency of polyethylene, polyvinyl chloride and polyester was 85, 82 and 69%, respectively, in the air flotation process. Increasing the dose of behentrimonium chloride surfactant from 2 to 10 mg/L improved the efficiency of the air flotation process for NPs/MPs removal. It is also found that the removal efficiency of NPs/MPs by the air flotation system depends on solution pH, size, and types of NPs/MPs. This study also found a less significant removal efficiency of NPs/MPs by both types of ferrofluid used in this study with an average removal of 43% for magnetite and 55% for cobalt ferrite. All three plastics tested had similar removal efficiency by the nano-ferrofluid particles, meaning that this removal technique does not rely on the plastic component type. Among all the process tested, both ultrafiltration and microfiltration membrane processes were highly effective, removing more than 90% of NPs/MPs fragment particles. Overall, this study has confirmed the effectiveness of using air flotation and the membrane process to remove NPs/MPs from wastewater.

Carbon dioxide present in natural gas/biogas lowers the heating value of fuel and is associated with environmental pollution. In addition to this, bio-oil contains a significant amount of oxygenates, which limits its wide range of applications and reduces its performance as a fuel. The sulfur compounds in diesel, gasoline, and crude oil is another issue along with its rapid depletion. Therefore, an efficacious method is essential for the reduction or separation of impurities from gaseous and liquid fuels. The implication of ionic liquids (ILs) for the separation of carbon dioxide from biogas/natural gas and oxygenates from bio-oil can be a green and efficient treatment method because of no volatile organic compounds emission, some inherent advantages, and task-specific properties of ILs. The objective of this chapter is to analyze the previous research on the application of ionic liquid for the absorption of carbon dioxide and the removal of sulfur compounds and oxygenates. The paper outlines the research gap, application, and potential future of ionic liquids in the reduction of the impurities from gaseous and liquid fuels.

Wastewater contains only ∼ 1% impurities that are required to be separated precisely for water recycling and reuse applications, particularly in water scare regions. Membrane-based separation has been recognised as an environmentally-friendly and energy-efficient process for effective pollutant removal and clean water production. To further improve the selectivity and water flux of membranes, two-dimensional (2D) materials, such as graphene and those exhibiting graphene-like properties, have been intensively studied for nanoporous and lamellar membrane fabrication in the last decade. Herein, we critically review the progress in 2D membranes for water purification and uniquely discuss the performance governing factors and research gaps from the standpoint of environmental and material chemists, which are critical to realize 2D membrane commercialization. The major points of this review are: (1) among the six types of reviewed 2D membranes, graphene, graphene oxide and reduced graphene oxide membrane have been predominantly studied for water treatment. (2) atomically thin nanoporous membranes with a defined pore size can achieve excellent water permeance and selectivity but large-scale fabrication of nanoporous membranes with uniform shape and size of nanopores remains a challenge. (3) salt separation performance of the pressurized lamellar membranes may not be comparable to commercial nanofiltration membranes. (4) functionalization or crosslinking of 2D materials is inevitable to stabilize 2D membrane pore structure and/or improve molecule separation. (5) membranes fabricated using emerging 2D materials such as born nitride and MXene appear to show better stability than graphene oxide membranes. (6) several aspects, particularly membrane stability, long-term performance, and membrane fouling propensity need attention to realize commercial application of 2D membranes in water treatment.

While cleaning wastewater, biological wastewater treatment processes such as membrane bioreactors (MBR) produce a significant amount of sludge that requires costly management. In the oxic-settling-anoxic (OSA) process, sludge is retained for a temporary period in side-stream reactors with low oxygen and substrate, and then it is recirculated to the main reactor. In this way, excess sludge production is reduced. We studied the influence of the rate of sludge exchange between MBR and side-stream anoxic reactors on sludge yield reduction within MBR. Two MBRs, namely, MBROSA and MBRcontrol, each coupled with separate external anoxic side-stream reactors, were run in parallel for 350 days. Unlike MBRcontrol, MBROSA had sludge exchange with the external reactors connected to it. During the investigation over a sludge interchange rate (SIR) range of 0-22%, an SIR of 11% achieved the highest sludge reduction (58%). Greater volatile solids destruction i.e., bacterial cell lysis and extracellular polymeric substance (EPS) destruction occurred at the SIR of 11%, which helped to achieve the highest sludge reduction. The enhanced volatile solids destruction was evident by the release of nutrients in the external anoxic reactors. It was confirmed that the sludge yield reduction was achieved without compromising the wastewater treatment quality, sludge settleability and hydraulic performance of the membrane in MBR.