Removal of Arsenic (III) from water with a combination of Graphene Oxide (GO) and Granular Ferric Hydroxide (GFH) at the optimum molecular ratio

The occurrence of arsenic in water is a global problem for public health. Several removal technologies have been developed for arsenic removal from water, and adsorption onto iron oxyhydroxides is the most widely used technique. Granular ferric hydroxide (GFH) has been used mainly for As(V) removal, but it has the disadvantage that it can create a problem with the residual concentration of iron in the water. Moreover, graphene oxide (GO), which contains a large amount of reactive oxygen, exhibits high adsorbing capacity. In this study, the combined use of GO and GFH as adsorbent materials in different molar ratios was investigated in order to achieve the maximum As(III) removal from aqueous solutions. The effect of the adsorbent’s dosage, pH value, contact time, initial As(III), and different molar ratios of GO/GFH was examined. As depicted, the presence of GFH enhances the use of GO. In particular, the molar ratio of GO/GFH 2:1 (i.e., 0.2 g/L GO and 0.1 g/L GFH) is chosen as optimal at pH value 7.0 ± 0.1, while the removal percentage increased from 10% (absence of GFH) to 90% with the simultaneous addition of GFH. Freundlich isotherm and pseudo-second-order kinetic models described the experimental data adequately and the highest adsorption capacity that was achieved was 22.62 µg/g

Applications of Up-flow Anaerobic Sludge Blanket (UASB) and characteristics of its microbial community: a review of bibliometric trend and recent findings

Interest of research on up-flow anaerobic sludge blanket (UASB) reactors is growing. The meta-analysis of bibliometric data highlighted the growing interest in four diverse topics: (i) energy recovery production; (ii) combination with other treatments; (iii) the study of processes for the removal of specific pollutants and, (iv) characterization of microbial community and granular sludge composition. In particular, the papers pub-lished in the first 6 months of 2021 on this process have been selected and critically re-viewed to highlight and discuss the results, the gaps in the literature and possible ideas for future research. Although the state of research on UASB is to be considered advanced, there are still several points that will be developed in future research such as the consoli-dation of the results obtained on a semi-industrial or real scale, the use of real matrices in-stead of synthetic ones and a more in-depth study of the effect of substances such as anti-biotics on the microbiota and microbiome of UASB granular biomass. To date, few, and conflicting data about environmental footprint of UASB are available and therefore other studies on this topic are strongly suggested

A mini review of recent findings in Cellulose-, Polymer- and Graphene-based membranes for Fluoride removal from drinking water

Effective fluoride removal from water is a persistent global concern both for drinking water and wastewater treatment. According to World Health Organization (WHO) standards the maximum contaminant level in drinking water cannot be higher than 1.5 mg F 12 L-1 since affects the skeletal and nervous systems of humans. Various technologies have been developed to decrease fluoride concentration from waters, such as adsorption, coagulation, precipitation and membrane separa-tion. Membrane technology found to be a very effective technology, significantly reducing fluo-ride to desired standards levels; however, has received less attention than other technologies because it is apparent as a costly process. This review aims to discuss the recent studies using modified membranes for fluoride removal. Emphasis is given on cellulose, polymer and gra-phene based membranes and is further discussing the modification of membranes with several metals that have been developed in the last years. It was observed that the main focus of the to-tal publications, has been on the use of polymer based membranes. Most of the membranes ap-plied for defluoridation exhibit greater efficiency at pH values close to that of drinking water (i.e., 6\u20138).and maximum treatment capacity was obtained with the use of a cellulose modified membrane Fe-Al-Mn@chitosan with a permeate flux of 2000 L m-2 h-1, following the carbon based amyloid fibril nano-ZrO2 composites (CAF-Zr) 1750 L m-2. A technical-economic comparison study of NF and RO is also referred, concluding that NF membrane is slightly less expensive

Recent Advances in Water and Wastewater Treatment with Emphasis in Membrane Treatment Operations

The present Special Issue brings together recent research findings from renowned scientists in the field of water treatment and assembled contributions on advanced technologies applied to the treatment of wastewater and drinking water, with emphasis on novel membrane treatment technologies. 12 research contributions have highlighted various processes and technologies, which can achieve effective treatment and purification of wastewater and of drinking water, aiming (occasionally) for water reuse. The main topics which are analyzed are the use of novel type membranes in bioreactors, the use of modified membranes, for example using vacuum membrane distillation, the fouling of membranes, the problem of arsenic, antimony and chromium contamination in groundwaters and its removal and the use of novel technologies for more efficient ozonation

Sulfate Radical Technologies as Tertiary Treatment for the Removal of Emerging Contaminants from Wastewater

International audienceWater scarcity and water pollution is a worldwide problem and has driven research into eco-friendly and low-energy cost efficient remediation. The reuse of wastewater for non-potable purpose after proper treatment is the only sustainable solution to the problem. Advanced oxidation processes (AOP) based on the in-situ generation of hydroxyl radicals have been intensively investigated for this purpose as a treatment step to achieve wastewater reuse. The main degradation mechanism of AOPs is based on the reaction of hydroxyl radicals with dissolved organic matter. However, hydroxyl radicals follow unselective multi-step pathways, limiting their efficiency in complex environmental matrices. To overcome such limitations, AOP treatment, based on generation of sulfate radicals, has been developed and widely investigated. This current mini-review will cover the most recent developments regarding emerging contaminant removal, i.e., organic micropollutants, using sulfate radicals generated by active persulfate or peroxymonosulfate, with a focus on an application to wastewater effluents for possible wastewater reuse

Innovative approaches for drinking and waste-water treatment: An editorial review summarizing and assessing the findings of the Special Issue

The present special issue collected articles that address the very important topic of innovative approaches in water and wastewater treatment technologies. Thirteen articles are published, ten research paper and three review articles. The papers can be divided in four major categories, namely, membrane treatment, adsorption studies, advanced oxidation processes and wastewater treatment optimization. In the editorial, a brief description of the findings of each paper is presented along with a critical assessment

Arsenic removal from groundwaters applying combined treatment methods

The problem of arsenic contamination of groundwaters has been under extensive discussion especially during the recent years, because of its adverse effects on human health. Several studies have reported that arsenic is a carcinogen and its effects are primarily due to consumption of arsenic contaminated drinking water at concentrations around 100 μg/L. As(V) can replace phosphate in several biochemical reactions, whereas As(III) may react with critical thiols in proteins and inhibit their activity. In Europe, several countries have to deal with the problem of arsenic contamination of groundwaters, used for drinking water, such as Greece, Finland, Italy, Hungary, etc., whereas in other countries, such as Bangladesh and India, arsenic has been reported to reach levels up to 1 mg/L. The Maximum Contaminant Level (MCL) of arsenic in drinking water has been recently revised by the European Commission. According to the new directive, by 2003 all drinking water supply systems within the European Union would have to comply with the new concentration limit, which has been reduced from 50 μg/L to 10 μg/L (EC, 1998). Recently, EPA decided to move forward in implementing the same standard for drinking water. This standard was also recommended by WHO. Therefore, the research on improving the established or developing novel treatment technologies for removing arsenic from contaminated groundwaters is an emerging issue. The distribution of arsenic species [As(III), As(V)] in natural waters is mainly dependent on redox potential and pH conditions (Tallman and Shaikh, 1980). Under oxidizing conditions such as those prevailing in surface waters, the predominant specie is pentavalent arsenic, which is mainly present with the oxyanionic forms (H2AsO4-, HAsO42-) with pKa= 2.19, pKb= 6.94 respectively. On the other hand, under mildly reducing conditions such as those prevailing in groundwaters, As(III) is the thermodynamically stable form, which at pH values of most natural waters is present as the non-ionic form of arsenious acid (H3AsO3, pKa=9.22). Thus, As(III) may interact in smaller extent with most solid surfaces, therefore, it is more difficult to be removed by the conventional treatment methods, such as adsorption, precipitation etc. Several treatment technologies have been applied for the removal of arsenic from groundwaters, such as coagulation/filtration, ion exchange, lime softening, adsorption on iron oxides or activated alumina, flotation and reverse osmosis. Most of these technologies are not efficient enough for the removal of As(III). Therefore, a pre-oxidation step is usually required to transform the trivalent form to pentavalent. The oxidation procedure is mainly performed by the addition of chemical reagents, such as potassium permanganate, chlorine, ozone, hydrogen peroxide or manganese oxides. Although these reagents are effective in oxidizing trivalent arsenic, they may cause several secondary problems arisen mainly by the presence of residuals or from by-products formation, inducing also a significant increase to operational costs of the methods. In the present study an alternative technology for the removal of both trivalent and pentavalent arsenic species was examined, based on the already established biological iron and manganese oxidation and removal from groundwaters. Iron oxidation is caused by several microorganisms, which are indigenous in most groundwaters, such as Gallionella ferruginea and Leptothrix ochracea. The main product of biological oxidation of iron is usually a mixture of poorly ordered iron oxides often containing significant amounts of organic matter. The intermixing of iron oxides, organic material and bacterial presence, produces complex multiple sorbing solids, which exhibit unique metal retention properties. Arsenic(V) can be removed by direct adsorption or co-precipitation on the preformed biogenic iron oxides, whereas As(III) oxidation by bacteria can take place, leading to improved overall removal efficiency. The objective of the present research was to study the mechanism of As(III) removal during biological iron and manganese oxidation, as well as to establish the optimum conditions for efficient arsenic (III & V) removal, in order to meet the new standard of 10 μg/L. Initially arsenic removal was examined using several filter media, which were previously modified by coating their surface by amorphous iron hydroxides. The method, termed “adsorptive filtration”, was examined under the variation of the major parameters. The pH value of water was found to be the most significant towards the removal of both inorganic forms of arsenic. The optimum pH value for As(V) removal was 5, whereas As(III) was removed more efficiently at pH values around 7. The removal of pentavalent arsenic was more satisfactory than trivalent arsenic, indicating the need for preoxidation. Other parameters were found to affect the treatment efficiency such as the linear velocity and the presence of competitive anions. Above all the choice of filter media was found to be the most significant parameter towards the overall performance efficiency of adsorptive filtration. The application of porous polymeric materials such as polyHIPE and alginate produced much better results than the commercially available polystyrene beads. The results were used to model the treatment operation using the “Bed Depth Service Time” and “Empty Bed Residence Time” models. The application of these models enabled the calculation of specific parameters of system performance. The maximum sorptive capacity for 20% breakthrough accounted for 7.79 μg As/g wet alginate bead, whereas the minimum residence time required to achieve effluent arsenic concentration below 10 μg/L, was found to be 76 sec. The further aim of this work was to apply a combined biological and physicochemical process for arsenic removal. The use of iron oxidizing bacteria was found to catalyze trivalent arsenic oxidation by dissolved oxygen and the total arsenic content was removed by sorption on biogenic iron and manganese oxides. Arsenic removal was more efficient by sorption on iron oxides than on manganese oxides. The method was examined under long-term operation. Approximately 70,000 bed volumes of ground water containing arsenic (60-80 μg/L) were treated, in an operation, which lasted around 10months. During this period, residual arsenic concentration was always below the maximum contaminant level and no problems were arisen, regarding treatment efficiency and operative conditions. The results were studied towards the kinetic of reactions of oxidation and adsorption. The rates of biological oxidation of iron, manganese and arsenic were faster than those reported for physicochemical oxidation, indicating the catalytic role of bacteria. The application of the specific treatment technology offers several advantages towards conventional physicochemical treatment methods. Efficient removal of inorganic arsenic can be achieved without the use of any chemicals for oxidative or sorptive processes. This renders the technique environmental friendly and more economical. The operation does not require monitoring of a breakthrough point, like in other column adsorption processes, as the sorbents (biogenic iron and manganese oxides) were produced continuously by the biological oxidation. This contributes to the combined removal of three major groundwater contaminants, iron, manganese and arsenic

Simultaneous Removal of Arsenate and Chromate from Ground- and Surface- Waters by Iron-Based Redox Assisted Coagulation

Arsenic (As) and chromate (Cr(VI)) contamination of ground and surface waters is a major problem worldwide. Given that a new drinking water limit is anticipated for Cr(VI) and that the limit of arsenic in drinking water is quite low (10 μg/L), there is an urgent need for evaluating technologies that could be efficient for removal of both contaminants simultaneously. In this work, the use of Fe(II) redox assisted coagulation was investigated to simultaneously remove the contaminants of interest. The basic principle of this technology is that Fe(II) could react with Cr(VI) and form Fe(III)-hydroxides and insoluble Cr(III) species, while the freshly formed Fe(III) hydroxides are very efficient adsorbents for As(V). The effect of pH, the water matrix composition, Fe(II) dose, initial contaminant concentrations, NOM presence and phosphate concentration were the examined parameters. The results revealed that with a dose of 2 mg/L Fe(II), residual As(V) and Cr(VI) concentrations were both below 10 μg/L, from initial concentrations of 50 μg/L. Though, this is effective only at circumneutral pH values. This is however not a big obstacle, since most natural waters, especially groundwaters, have near neutral pH values. At these pH values, residual iron concentration was far below 200 μg/L. The presence of phosphate anions inhibited As(V) removal but had no effect on Cr(VI) removal. Increasing Fe(II) concentrations eliminated the effect of phosphate and provided simultaneous phosphate removal. Therefore, Fe(II) coagulation can be applied, with secured results, for simultaneous As(V), Cr(VI) and phosphate removal from waters