Natural organic matter (NOM) is produced through metabolic reactions in water supply in drinking water sources and has been reported to cause several problems including objectionable taste and color ...of water, formation of disinfection by-products (DBPs) and reducing the amount of dissolved oxygen in water. The removal of NOM and its constituents from water is a challenging issue worldwide. Many technologies have been examined for this purpose. The properties and amount of NOM, however, can significantly affect the process efficiency. In the present work, an overview of the recent research studies dealing with adsorption method for the removal of NOM and related compounds from water is presented. A wide variety of conventional and non-conventional adsorbents have been reviewed for their potential in NOM removal from water. As revealed from the literature reviewed, modified adsorbents, composite materials and few nanomaterials have shown promising results for NOM removal from water. The main findings obtained for the removal of NOM using different adsorbents have been discussed in this review.
•Use of various adsorbents in NOM removal has been reviewed.•Influence of various parameters on NOM removal by adsorbents is discussed.•Mechanisms of NOM adsorption by different adsorbents are reviewed.
Wastewater treatment plants (WWTPs) are acting as routes of microplastics (MPs) to the environment, hence the urgent need to examine MPs in wastewaters and different types of sludge through sampling ...campaigns covering extended periods of time. In this study, the efficiency of a municipal WWTP to remove MPs from wastewater was studied by collecting wastewater and sludge samples once in every two weeks during a 3-month sampling campaign. The WWTP was operated based on the conventional activated sludge (CAS) process and a pilot-scale membrane bioreactor (MBR). The microplastic particles and fibers from both water and sludge samples were identified by using an optical microscope, Fourier Transform Infrared (FTIR) microscope and Raman microscope. Overall, the retention capacity of microplastics in the studied WWTP was found to be 98.3%. Most of the MP fraction was removed before the activated sludge process. The efficiency of an advanced membrane bioreactor (MBR) technology was also examined. The main related finding is that MBR permeate contained 0.4 MP/L in comparison with the final effluent of the CAS process (1.0 MP/L). According to this study, both microplastic fibers and particles are discharged from the WWTP to the aquatic environment.
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•Microplastic concentrations were studied in different stages of a municipal WWTP.•Microplastics were identified by visual identification, FTIR- and Raman-microscopy.•98.3% of microplastic load was removed during conventional WWTP processes.•MBR process had higher retention rate for microplastics than secondary CAS process.•Polyester fibers and polyethylene fragments were detected most frequently.
In recent decades, increased domestic, agricultural and industrial activities worldwide have led to the release of various pollutants, such as toxic heavy metals, inorganic anions, organics, ...micropollutants and nutrients into the aquatic environment. The removal of these wide varieties of pollutants for better quality of water for various activities is an emerging issue and a robust and eco-friendly treatment technology is needed for the purpose. It is well known that cellulosic materials can be obtained from various natural sources and can be employed as cheap adsorbents. Their adsorption capacities for heavy metal ions and other aquatic pollutants can be significantly affected upon chemical treatment. In general, chemically modified cellulose exhibits higher adsorption capacities for various aquatic pollutants than their unmodified forms. Numerous chemicals have been used for cellulose modifications which include mineral and organic acids, bases, oxidizing agent, organic compounds, etc. This paper reviews the current state of research on the use of cellulose, a naturally occurring material, its modified forms and their efficacy as adsorbents for the removal of various pollutants from waste streams. In this review, an extensive list of various cellulose-based adsorbents from literature has been compiled and their adsorption capacities under various conditions for the removal of various pollutants, as available in the literature, are presented along with highlighting and discussing the key advancement on the preparation of cellulose-based adsorbents. It is evident from the literature survey presented herein that modified cellulose-based adsorbents exhibit good potential for the removal of various aquatic pollutants. However, still there is a need to find out the practical utility of these adsorbents on a commercial scale, leading to the improvement of pollution control.
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•Various modification methods for cellulose-based adsorbents have been reviewed.•Potential of cellulose-based adsorbents in water treatment has been reviewed.•Current challenges and future perspectives in this direction have been presented.
Natural organic matter (NOM), a key component in aquatic environments, is a complex matrix of organic substances characterized by its fluctuating amounts in water and variable molecular and chemical ...properties, leading to various interaction schemes with the biogeosphere and hydrologic cycle. These factors, along with the increasing amounts of NOM in surface and ground waters, make the effort of removing naturally-occurring organics from drinking water supplies, and also from municipal wastewater effluents, a challenging task requiring the development of highly efficient and versatile water treatment technologies.
Advanced oxidation processes (AOPs) received an increasing amount of attention from researchers around the world, especially during the last decade. The related processes were frequently reported to be among the most suitable water treatment technologies to remove NOM from drinking water supplies and mitigate the formation of disinfection by products (DBPs). Thus, the present work overviews recent research and development studies conducted on the application of AOPs to degrade NOM including UV and/or ozone-based applications, different Fenton processes and various heterogeneous catalytic and photocatalytic oxidative processes. Other non-conventional AOPs such as ultrasonication, ionizing radiation and plasma technologies were also reported. Furthermore, since AOPs are unlikely to achieve complete oxidation of NOM, integration schemes with other water treatment technologies were presented including membrane filtration, adsorption and others processes.
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•O3, UV, Fenton-based processes and (photo)catalytic AOPs were overviewed.•AOPs are efficient to remove NOM from drinking water supplies.•Optimized AOPs helped reducing the formation potential of disinfection by-products.•Coupling AOPs with other water treatment processes improved NOM removal efficiency.
Over the past 10–20
years the amount of the natural organic matter (NOM) has been increased in raw water supplies on several areas. The presence of NOM causes many problems in drinking water ...treatment processes, including: (i) negative effect on water quality by colour, taste and odor problems, (ii) increased coagulant and disinfectant dose requirements (which in turn results increased sludge and potential harmful disinfection by-product formation), (iii) promoted biological growth in distribution system, and (iv) increased levels of complexed heavy metals and adsorbed organic pollutants. Thus, more efficient methods for the removal of NOM have emerged. Among these are advanced oxidation processes (AOPs). These include O
3/H
2O
2, O
3/UV, UV/H
2O
2, TiO
2/UV, H
2O
2/catalyst, Fenton and photo-Fenton prosesses as well as ultrasound. In the present work, an overview of the recent research studies dealing with AOP methods for the removal of NOM and related compounds from drinking water is presented.
Activated carbon refers to a wide range of carbonised materials of high degree of porosity and high surface area. Activated carbon has many applications in the environment and industry for the ...removal, retrieval, separation and modification of various compounds in liquid and gas phases. Selection of the chemical activator agent is a major step controlling the performance and applicability of activated carbon. Here, we review chemical activators used to produce activated carbon. We compare the impregnation method with the physical mixing method used in activating with alkali hydroxides. We selected 81 articles from Google Scholar, PubMed, Scopus, Science Direct, Embase and Medlin databases. Eighteen articles report the activation with potassium hydroxide, 17 with phosphoric acid, 15 with zinc chloride, 11 with potassium carbonate, nine with sodium hydroxide, and 11 with new activating agents. Activation with phosphoric acid is commonly used for lignocellulosic material and at lower temperatures. Zinc chloride generates more surface area than phosphoric acid but is used less due to environmental concerns. Potassium carbonate, in comparison with potassium hydroxide, produces higher yields and a higher surface area for the adsorption of large pollutant molecules such as dyes. Activating with potassium hydroxide in terms of surface area and efficiency shows better results than sodium hydroxide for various applications. Also, the comparison of the physical mixing method and the impregnation method in activation with alkali metals indicates that the activated carbon obtained through physical mixing had a higher porosity than the activated carbon produced by the impregnation method.
Being cost-effective, synthetic materials were initially used abundantly for the removal of oil. Gradually, however, awareness of the use of dispersants like Corexit, which makes water resources more ...toxic than oil, has changed the scenario for the treatment of spilled oil. The removal of spilled oil from water resources is still a very topical issue. An eco-friendly and sustainable approach towards the environment has introduced many low-cost, non-toxic and biodegradable materials along with different biomasses to make micro-to nano-sized materials, membranes, sponges/aerogel, etc. for the removal and recovery of oil from water resources. Additionally, the reusability of these materials after the recovery of oils has added one more step towards sustainability. This review comprises the work conducted by various researchers in the field of the removal and recovery of spilled oils using various biomasses and polymers, either in the form of sorbents or separators.
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•Low cost, non-toxic and biodegradable materials for oil spill treatment.•Stability of Pickering emulsions by particles is more than surfactants stabilized emulsions.•Mechanical removal of oil using gelators and aerogels.•Gravity-driven separation of oil and water from their mixtures.
The over-exploitation of non-renewable resources leads to the depletion of energy reserves, as well as a rise in the price of petroleum-based fuels. Thus, there is a need to find suitable and ...sustainable substitutes for conventional fuels. The main features required for an alternative fuel are availability and renewability, or lower dependence on restricted resources accompanied with no or lower pollution. Due to their eco-friendly and non-toxic nature, biodiesel has been attracting increasing interest. Biodiesel production can be accomplished using various raw materials, catalysts, and technologies. In recent years, nanocatalyst technology has been widely used for biodiesel production due to its numerous advantages, such as large surface area, reusability and high activity of the nanocatalyst. This review provides an overview of biodiesel production with a description of various kinds of feedstock used, their advantages and disadvantages. Further, it offers a detailed description of different classes of biodiesel, including a characterization, assessment of qualities and limitations, and quality analysis of each type. Various methodologies used for biodiesel production are also elucidated, focusing on the potential of nanocatalyst processes. The aspect of nanocatalyst regeneration and reuse is also considered. This review delivers a comprehensive overview of biodiesel synthesis by discussing recent trends and challenges in this field, which will further the development of economically sustainable biodiesel production.
Diclofenac (DCF) is a common anti-inflammatory pharmaceutical that is often detected in waste wasters, effluents and surface waters. Recently, DCF was included in the watch list of substances in EU ...that requires its environmental monitoring in the member states. DCF is also known to harmfully affect several environmental species already at concentrations of ≤1μg/l. This review focuses on the occurrence and fate of DCF in conventional wastewater treatment processes. Research done in this area was gathered and analyzed in order to find out the possibilities to enhance DCF elimination during biological wastewater treatment. More precisely, human metabolism, concentrations in wastewater influents and effluents, elimination rates in the treatment train, roles of sorption and biotransformation mechanisms during the treatment as well as formation of transformation products are reported. Additionally, the effect of process configuration, i.e. conventional activated sludge (CAS), biological nutrient removal (BNR), membrane bioreactor (MBR) and attached-growth bioreactor, and process parameters, i.e. solids retention time (SRT) and hydraulic retention time (HRT) are presented. Generally, DCF is poorly biodegradable which often translates into low elimination rates during biological wastewater treatment. Only a minor portion is sorbed to sludge. MBR and attached-growth bioreactors may result in higher elimination of DCF over CAS or BNR. Long SRTs (>150d) favor the DCF elimination due to sludge adaptation. Longer HRTs (>2–3d) could significantly increase the elimination of DCF during biological wastewater treatment. Bioaugmentation could be used to enhance DCF elimination, however, this requires more research on microbial communities that are able to degrade DCF. Also, further research is needed to gain more information about the deconjugation processes and biotic and abiotic transformation and the nature of transformation products.
•Diclofenac (DCF) is poorly biodegraded and sorbed into sludge.•Biotic elimination of DCF could be enhanced by the following techniques.•Use of MBR or attached-growth biomass process•Increase the hydraulic retention time to >2–3days•Enrich DCF degrading bacteria into the reactor (i.e. long SRTs or bioaugmentation)
Microplastics have recently been detected in the atmosphere of urban, suburban, and even remote areas far away from source regions of microplastics, suggesting the potential long-distance atmospheric ...transport for microplastics. There still exist questions regarding the occurrence, fate, transport, and effect of atmospheric microplastics. These questions arise due to limited physical analysis and understanding of atmospheric microplastic pollution in conjunction with a lack of standardized sampling and identification methods. This paper reviews the current status of knowledge on atmospheric microplastics, the methods for sample collection, analysis and detection. We review and compare the methods used in the previous studies and provide recommendations for atmospheric microplastic sampling and measurement. Furthermore, we summarize the findings related to atmospheric microplastic characteristics, including abundance, size, shapes, colours, and polymer types. Microplastics occur in the atmosphere from urban to remote areas, with an abundance/deposition spanning 1–3 orders of magnitude across different sites. Fibres and fragments are the most frequently reported shapes and the types of plastic which generally aligns with world plastic demand. We conclude that atmospheric microplastics require further research and greater understanding to identify its global distributions and potential exposure to human health through further field sampling and implementation of standardized analytical protocols.
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