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

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 for the maximum contaminant level in drinking water cannot be higher than 1.5 mg F− 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 separation. Membrane technology has been found to be a very effective technology, significantly reducing fluoride to desired standards levels; however, it has received less attention than other technologies because it is a costly process. This review aims to discuss the recent studies using modified membranes for fluoride removal. Emphasis is given on cellulose-, polymer- and graphene-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 total publications has been on the use of polymer-based membranes. Most of the membranes applied for defluoridation exhibit greater efficiency at pH values close to that of drinking water (i.e., 6–8), 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

Graphene Oxide/Fe-Based Composite Pre-Polymerized Coagulants: Synthesis, Characterization, and Potential Application in Water Treatment

This study presents for the first time the synthesis and characterization of GO (graphene oxide), PFSiC (polyferric silicate chloride), and hybrid GO-PFSiC derivatives, aiming to enhance synergistically the performance of coagulation, when applied for the treatment of water. The structure and the morphology of composite GO-PFSiC coagulants were studied in detail by the application of FTIR, XRD, and SEM characterization techniques. Furthermore, the proposed coagulants were applied for the treatment of simulated turbid surface water. The effects of the reagent’s dosage, pH value, and experimental/operational conditions on the coagulation efficiency, applied mainly for the removal of turbidity, were examined. The results, obtained from the FTIR and XRD measurements, showed the presence of a bond between the PFSiC and the GO surface, indicating that the PFSiC particles are distributed uniformly on the surface of graphene, which was also confirmed by the SEM images. Especially, the composite compound GO-PFSiC1.5-15-0.5 presents the most uniform distribution of iron on the surface of graphene oxide and exhibits the optimum coagulation efficiency, while it significantly reduces the turbidity for doses above 3–5 mg/L, i.e., achieving the respective legislation limit as proposed by WHO. Specifically, at the alkaline pH values (>7.9), the removal of turbidity reaches 96%. Consequently, the results of this study render these materials as potential coagulant agents for further research and applications, aiming to also achieve the co-removal of other water components

Arsenic(III) and Arsenic(V) Removal from Water Sources by Molecularly Imprinted Polymers (MIPs): A Mini Review of Recent Developments

The present review article summarizes the recent findings reported in the literature with regard to the use of molecularly imprinted polymers for the removal of arsenic from water and wastewater. MIPs are polymers in which a template is employed in order to enable the formation of recognition sites during the covalent assembly of the bulk phase, via a polymerization or polycondensation process. The efficiency of both arsenic species and the mechanism of removal are highlighted. The results have shown that under certain conditions, MIPs demonstrated arsenic sorption capacities of up to 130 mg/g for As(V) and 151 mg/g for As(III), while the regeneration ability was found to reach up to more than 20 cycles. The overall results showed that further development of MIPs could result in the formation of promising adsorbents for arsenic removal from waters. The use of MIPs for the removal not only of arsenic but also other inorganic contaminants is considered a very important topic, with great potential in terms of future applications in water treatment. The main advantage of these materials is that they are very selective toward the contaminant of interest. This enhanced selectivity is attributed to the incorporation of specific templates, which can then adsorb the contaminant of interest almost exclusively. Therefore, the main problem in adsorption processes is the competition for adsorption sites by other water components, for example, phosphates, nitrates, carbonates, and sulfates, which can be circumvented by the use of MI-type adsorbents

Removal of Arsenic, Chromium and Uranium from Water Sources by Novel Nanostructured Materials Including Graphene-Based Modified Adsorbents: A Mini Review of Recent Developments

Groundwater is commonly used as a drinking water resource all over the world. Therefore, groundwater contamination by toxic metals is an important issue of utmost concern for public health, and several technologies are applied for their effective removal, such as coagulation, ion exchange, adsorption, and membrane applications like reverse osmosis. Adsorption is acknowledged as a simple, effective and economic technology, which has received increased interest recently, despite certain limitations regarding operational applications. The respective scientific efforts have been specifically focused on the development and implementation of novel nano-structured adsorbent materials, which may offer extensive specific surface areas, much higher than the conventional adsorbents, and hence, are expected to present higher removal efficiencies of pollutants. In this paper, the recent developments of nanomaterial applications for arsenic, chromium and uranium removal from groundwaters are critically reviewed. Particularly, the use of novel composite materials, based mainly on hybrid metallic oxide nanoparticles and on composites based on graphene oxide (GO) (i.e., graphene-based hybrids), showed promising evidences to achieve efficient removal of toxic metals from water sources, even in full scale applications

Biochar Derived from Rice by-Products for Arsenic and Chromium Removal by Adsorption: A Review

Environmental pollution by arsenic (As) and hexavalent chromium (Cr(VI)) has been one of the most serious environmental problems in recent years around the world. Their presence in water is a result of both natural and anthropogenic activities, and poses serious risks to human health due to their high toxicity. Adsorption is a leading method used to remove arsenic and chromium, with biochar, a carbonaceous pyrolytic product made from various types of biomass, under low oxygen conditions, being one of the most common adsorbents due to its high surface area. Although biochar’s ability to immobilize and remove As and Cr(VI) is high, in order to increase the adsorption capacity and nutrient release potential of rice husk biochar, it is essential to select an appropriate pyrolysis and biochar modification technique. Physical or biological activation, steam/gas activation, UV irradiation, magnetization, alkali/acid treatment, and nano-modification are the main modification methods that will be discussed in this review. These modifications have led to multi-fold enhancement in adsorption/reduction capacity of As and Cr(VI), compared with plain biochar. This review provides a recent literature overview of the different biochar modification methods, as well as the factors that influence their capacity to successfully remove As and Cr(VI), along with regeneration potentials

Biochar Derived from Rice by-Products for Arsenic and Chromium Removal by Adsorption: A Review

Environmental pollution by arsenic (As) and hexavalent chromium (Cr(VI)) has been one of the most serious environmental problems in recent years around the world. Their presence in water is a result of both natural and anthropogenic activities, and poses serious risks to human health due to their high toxicity. Adsorption is a leading method used to remove arsenic and chromium, with biochar, a carbonaceous pyrolytic product made from various types of biomass, under low oxygen conditions, being one of the most common adsorbents due to its high surface area. Although biochar’s ability to immobilize and remove As and Cr(VI) is high, in order to increase the adsorption capacity and nutrient release potential of rice husk biochar, it is essential to select an appropriate pyrolysis and biochar modification technique. Physical or biological activation, steam/gas activation, UV irradiation, magnetization, alkali/acid treatment, and nano-modification are the main modification methods that will be discussed in this review. These modifications have led to multi-fold enhancement in adsorption/reduction capacity of As and Cr(VI), compared with plain biochar. This review provides a recent literature overview of the different biochar modification methods, as well as the factors that influence their capacity to successfully remove As and Cr(VI), along with regeneration potentials

Composite Activated Carbon Modified with AlCl₃ for the Effective Removal of Reactive Black 5 Dye from Wastewaters

Many industries use huge amounts of synthetic dyes which may release into the wastewater in dyeing processes causing serious damage to aquatic life as they are recalcitrant, nonbiodegradable, stable to oxidizing agents, and toxic. Adsorption on activated carbon has been found to be a very efficient treatment method. In this work, a new adsorbent material composed of activated carbon and aluminum chloride (AC-Al) was prepared for the removal of a commercial anionic and anthraquinonic reactive dye, i.e., Reactive Black 5 (RB5) under various experimental conditions. Several parameters, such as the adsorbent’s dosage, initial RB5 concentration, pH, and contact time, were studied in order to determine the feasibility of AC-Al. According to the results, it was found that there was an increase in RB5 removal as the adsorbent’s dosage increased, especially, in pH 2 ± 0.1, where the removal rate increased, and reaching 100% by 1.0 g/L of AC-Al. Freundlich isotherm and pseudo-second-order kinetic models adequately fit the experimental data, indicating that favorable and heterogeneous adsorption occurred, closer to chemisorption. According to thermodynamics, it was found that the adsorption procedure was endothermic in nature (∆H0 = 62.621 kJ/mol) and spontaneous (∆G0 0 0.0293 (kJ/mol∙K), there is an increase in random interaction between solid and liquid interfaces. Finally, the AC-Al adsorbent was successfully regenerated and reused for four cycles

Novel and Conventional Technologies for Landfill Leachates Treatment: A Review

Municipal solid waste final disposal represents an environmental burden worldwide since landfilling, or open dumping, is still the preferred solution for the end of life of solid discarded materials. This study aims to review the technological innovations applied for landfill leachate treatment, taking into consideration the experiences obtained during the past years and the solutions which have been implemented. The review showed that both biological and physiochemical treatments are not able to achieve the requested water quality level, according to the limits established by regulations, whether applied in a single treatment or multiple treatments. In order to respect sustainable release limits to guarantee environmental protection, the construction of depuration systems and combining biological and physiochemical treatment methods is considered of the utmost importance. The review looks at possible joint applications of different treatment techniques reviewed by other studies and considers the state of the art of current research. Combined technical solutions suggested within the 2016 peer-reviewed papers are presented and discussed as a sustainable way to effectively treat landfill leachate, giving particular attention to feasible solutions for developing countries