Organic Contaminants In Water Research Articles

Geochemical and Geospatial Distribution of Organic Contaminants in the Flood Plain of Ekpetiama, Niger Delta Region of Nigeria

This study investigated the geochemical and geospatial distribution of organic contaminants in the floodplain water and sediments of Ekpetiama in the Niger Delta Region of Nigeria. This study is necessary because there are limited data on the level of organic contamination in this section of the Niger Delta Region of Nigeria. The extinction of planktons in Ekpetiama became a source of concern to the residents. This concern is because this section of the coastal plain provides fisher folks with livelihood. So, there was a need to track the source of contamination in this part of the Niger Delta region. Previous studies have suggested a high level of Total Petroleum Hydrocarbon and Total Hydrocarbon Content as possible sources of reduced dissolved oxygen in similar deltaic terrain. A total of 10 water and 10 sediment samples were collected and analyzed in triplicate at an interval of 100 m in the flood plain. A particle size analyzer was used to perform particle size analyses of air-dried sediments. The American Public Health Association method (APHA) was used to do the chemical analysis of the water samples. Here, a liquid-liquid extraction procedure was performed on sediment samples using 30 mL of Dichloromethane (DCM) as the extracting agent. The results were subjected to statistical validation. The mean grain size ranged from 2.37-4.83, kurtosis (1.94-0.49), and skewness (-0.8-0.71). The contaminant indicators (pH, biochemical oxygen demand, chemical oxygen demand, dissolved oxygen and Total Organic Carbon) point to the presence of organic contamination of the flood plain. The results indicated a total petroleum hydrocarbon range of 0.47-0.87 ppm in water and 0.69-0.96 ppm in sediments and a total hydrocarbon content range of 1.10-2.80 ppm in water and 2.56-3.90 ppm in sediment# samples. The results were above the permitted limits of the World Health Organisation. The source of ecological damage is the abnormal concentrations of organic contaminants in the flood plain. These results significantly caused ecosystem damage and human health effects in the food chain. This study provides information to the National Oil Spill Detection and Response Agency for a cleanup process.

Long-term removal of perfluoroalkyl substances via activated carbon process for general advanced treatment purposes

Granular or powdered activated carbon (GAC/PAC) processes are installed in full-scale drinking water treatment plants (DWTPs) to reduce disinfection byproduct precursors, odor, ammonia, and pesticides. This study investigated the ability of GAC/PAC processes in 23 DWTPs to remove per- and polyfluoroalkyl substances (PFASs). In the GAC process, filter breakthrough of perfluoroalkyl carboxylic acids (PFCAs) occurred faster as the PFCA chain length is decreased. During periods of high water temperatures (20−29 °C), the effluent concentration of two short-chain PFCAs (C4 and C5) surpassed that of the influent after the throughput reached 5,000−7,500 bed volumes (equivalent to 2−3 months) due to desorption. However, such desorption was not observed during periods of low water temperatures (5−19 °C). Meanwhile, long-chain PFCAs were consistently removed, as the GAC was replaced before breakthrough became noticeable. PFAS removal deteriorated at a remarkably fast rate after a partial breakthrough of several tens of percent. Biological activated carbon was proved ineffective in removing PFASs due to its diminished adsorption capacity after long-term use. The PAC process, however, exhibited a slight decrease in PFCA residual (10%) at higher water temperatures (15−30 °C). The PAC dose required for a certain residual ratio was lower with an increase in the hydrophobicity of PFAS; C8-PFCA only required 20 mg/L of PAC for 50% removal, while C4-PFCA required a significantly higher dose of 100−700 mg/L. Consequently, the activated carbon process, which removes organic contaminants in surface water, was inadequate in removing PFASs, particularly those with short chains. Thus, it is recommended that GAC filters be replaced more frequently (within two months) for short-chain PFAS removal. Further, the adsorption performance of PAC must be enhanced.

Mechanism insights into photo–assisted peroxymonosulfate activation on oxygen vacancy–enriched nolanites via an electron transfer regime

The utilization of photo–assisted persulfate activation for the removal of organic contaminants in water has garnered significant research interest in recent times. However, there remains a lack of clarity regarding specific contributions of light irradiation and catalyst structure in this process. Herein, a photo–assisted peroxymonosulfate (PMS) activation system is designed for the highly efficient degradation of organic contaminants on oxygen vacancy–enriched nolanites (Vo–FVO). Results suggest that the degradation of bisphenol A (BPA) in this system is a nonradical–dominated process via an electron transfer regime, in which VO improves the local electron density and thus facilitates the electron shuttling between BPA and PMS. During BPA degradation, PMS adsorbed at the surface of FVO–180 withdraws electrons near VO and forms FVO–PMS* complexes. Upon light irradiation, photoelectrons effectively restore the electron density around VO, thereby enabling a sustainable electron transfer for the highly efficient degradation of BPA. Overall, this work provides new insights into the mechanism of persulfate activation based on defects engineering in nolanite minerals.

Green synthesis of a mesoporous hyper-cross-linked polyamide/polyamine 3D network through Michael addition for the treatment of heavy metals and organic dyes contaminated wastewater

Environmental pollution is the greatest challenge of the modern age due to unprecedented industrialization and urbanization that has led to the contamination of water resources with a wide range of pollutants. The release of untreated industrial and municipal wastewater to water bodies further intensifies the problem. The presence of heavy metals and organic contaminants in water poses significant threats to humans, aquatic life, and the environment. Adsorption is one of the famous water treatment technologies due to its simplicity, low cost, efficiency, and minimal secondary pollution. The selection or synthesis of an effective adsorbent is key to the success of the adsorptive removal of pollutants. In this work, we synthesized an adsorbent consisting of a mesoporous hyper-cross-linked polyamide/polyamine 3D network through a single-step Michael addition reaction. The adsorbent was characterized by FTIR, PXRD, TGA, SEM, and TEM to investigate its functional moieties, material nature, thermal, morphological, and internal structural features, respectively. Due to its mesoporous structure, presence of functional groups, and 3D hyper-cross-linked network, it efficiently removed heavy metals (Cd, Cr, and Pb) from aqueous media. The effect of various parameters such as sample pH, adsorbent dosage, contact time, and adsorbate concentrations was thoroughly investigated. The experimental data were analyzed by a variety of isotherm models wherein Langmuir was found to be the best fit for explaining the adsorption of all the metals. The adsorption kinetics was best explained by the pseudo-second-order model. The maximum adsorption capacities for Cd, Cr, and Pb were 60.98 mg g−1, 119 mg g−1, and 9.302 mg g−1, respectively. The synthesized adsorbent was also tested for removal of organic dyes, and it showed selective and fast removal of Eriochrome Black T. Polymeric resins can be promising materials for adsorptive remediation of pollutants in aqueous media.

Sensor with enhanced performance based on photonic crystal with a defect layer

We propose an improved structure of an optical biosensor based on a photonic crystal with a defect layer, which can detect the concentration of organic contaminants in water by defect mode shift. We investigated 4 types of defective photonic crystals with different arrangements of layers inside the perfect photonic crystals and their impact on the performance of the sensor. The sensitivity and amplitude of defect mode were examined as a function of defect layer thickness. Also, the peculiarities of edge modes in the presence of defect layer were investigated. Finally, we obtained a characteristic equation to determine the wavelengths of defect modes for an arbitrary 1D photonic crystal with an isotropic defect inside.

Immobilization of Photocatalytic ZnO Nanocaps on Planar and Curved Surfaces for the Photodegradation of Organic Contaminants in Water

Immobilization of Photocatalytic ZnO Nanocaps on Planar and Curved Surfaces for the Photodegradation of Organic Contaminants in Water

General analytical solution expressions for analyzing Langmuir-type kinetics of sonochemical degradation of nonvolatile organic contaminants in water

Detailed kinetic studies of the ultrasonic decomposition of contaminants in water are scarce. Most of the work has used a pseudo-first order kinetics law, which is unrealistic. The model based on a Langmuir-type mechanism has been shown to fit the sonolytic decomposition data well, especially by using the non-linear technique. To avoid unrealistic assumptions, general analytical solutions to a time-dependent non-linear Langmuir-type equation may be the appropriate method. In this work, the sonolytic oxidation of organic contaminants, i.e., naphthol blue black and furosemide, in water was analyzed using two general analytical solution expressions of the Langmuir-type kinetics model, which describe the pollutant concentration in water. The validity of the two general analytical solution expressions was tested under a diversity of operating conditions, such as initial substrate concentration and varying ultrasonication frequency and intensity. As the initial substrate concentration increased, the sonolytic oxidation kinetics decreased, while the initial ultrasonic decomposition rate increased and then plateaued. Consequently, a heterogeneous kinetics equation based on a Langmuir-type mechanism can be used to simulate the sono-decomposition process. The decomposition yield increased with increasing sonication intensity and decreasing frequency. The two analytical solution expressions seem to be in excellent agreement with the experimental results of the sonochemical decomposition of the nonvolatile organic contaminants tested for the different operating conditions examined. These expressions provide a valuable tool for the analysis and simulation of advanced sonochemical oxidation processes under various experimental conditions.

Facile, cost-effective, large-scale, reliable, and efficient fabrication of CuO as a potential catalyst for organic dyes removal from water

In recent decades, copper (II) oxide, also called cupric oxide (CuO) catalyst has shown promising results for decomposing organic water contaminants. This work aimed to optimize the different parameters linked with the fabrication of cupric oxide (CuO) to become feasible for industrial and commercial applications, meeting the technology-based treatment standards. The effects of calcination temperatures (CTs) and cooling rates (CRs) on the crystallographic properties were thoroughly studied employing Rietveld refinement and Statistical analysis. The phases are CuO > Cu2O > Cuo, with crystallite sizes <80 nm. The optimum conditions are 450 °C and air quench, yielding 98.5% cupric oxide [CuO] (54 nm) and 1.3% copper (I) oxide, also called cuprous oxide (Cu2O). The particle size distribution was found to follow the normal distribution at CT of 600 °C, indicating the maturity of the crystal system. The textural analysis exhibited Type-II adsorption. The preliminary catalytic activity results revealed high activity and room for enhancing process kinetics at mild conditions.

Greener Method for the Application of TiO2 Nanoparticles to Remove Herbicide in Water.

TiO2 nanoparticles have emerged as a great photocatalyst to degrade organic contaminants in water; however, the nanoparticles dispersed in water could be difficult to be recovered and potentially become contaminant. Herbicide like 2,4-dichlorophenoxyacetic acid (2,4-D) used in agriculture usually ends up with a large fraction remaining in water and sediment, which may cause potential risk to human health and the ecosystem. This study proposes a greener method to utilize TiO2 as photocatalyst to remove 2,4-D from water. Accordingly, TiO2 nanoparticles (10-45 nm) were synthesized and grafted on lightweight fired clay to generate a TiO2-based floating photocatalyst. Experimental testing revealed that 60.2% of 2,4-D (0.1 mM) can be decomposed in 250 min under UV light with TiO2-grafted lightweight fired clay floating on water. Degradation fits well into the pseudo-first-order kinetic model. The floating photocatalysts can degrade approximately 50% 2,4-D in 250 min under sunlight and the degradation efficiency is stable for cycles. The results revealed that the fabrication of floating photocatalyst could be a promising and greener way to remove herbicide contaminants in water using TiO2.

MoSe2 nanoflakes decorated ZnO nanorods: An effective photoelectrode with S-scheme heterojunction for photoelectrocatalytic degradation of tetracycline and rhodamine B

Photoelectrocatalysis has been extensively used as one of the most widely known advanced oxidation processes (AOPs) owing to its superiority over photocatalytic systems with regards to the reduced recombination of charge carriers. ZnO demonstrates profound performance in PEC systems, and to overcome the obstacle of its limited visible light utilization, heterojunction formation of transition metal dichalcogenides (TMDs) with this classical semiconductor is proposed. Herein, MoSe2 was introduced onto ZnO nanorods to widen its visible light absorption and consequently boost the PEC ability of the proposed composite in omitting model organic contaminants in water. The as-synthesized nanocomposite was immobilized onto FTO by Electrophoretic deposition (EPD) technique which is then represented as the working electrode in the three-electrode PEC system. The characterization of the proposed nanocomposite was attained by techniques including: XRD, FESEM, FTIR, DRS and EDX. Moreover, electrochemical characterization was conducted to study its electrochemical properties. The PEC activity of the samples was studied by the degradation of Rhodamine B dye (62.3%) and tetracycline pharmaceutical (70.2%) under irradiation. The results indicated a much higher PEC ability for ZnO NR/MoSe2/FTO photoelectrode than its bare parent samples as well as its recyclability. To study the impact of the operational parameters, the electrolyte's concentration, initial pH, external bias voltage and initial concentration of the contaminant were investigated. By means of the scavenging tests, electrons and holes have the highest and the lowest importance in the PEC reaction, respectively. The S-scheme mechanism of degradation was proposed based on the cumulative experimental data.

Synthesis of TpTt/CdS Nanocomposite Structures for Methylene Blue Catalytic Degradation

The advancement of technology has resulted in severe issues in the natural environment, notably organic water contamination that poses a significant threat to living organisms. To mitigate such problems, various technological solutions have been developed to treat water pollution. The emergence of photocatalytic semiconductor technology has enabled the utilization of numerous novel semiconductor composites for pollution control due to their high efficacy and eco-friendliness. In this paper, TpTt/CdS composites were produced via a simple two-step process, and the resulting samples were characterized using X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, ultraviolet (UV)–visible and photodegradation experiments using methylene blue to simulate organic pollutants. The experimental findings reveal that the composite structure system enhances the radiation absorption capacity of CdS in the UV range, as well as the adsorption capability of organic pollutants. This introduces a fresh concept for modifying semiconductor composite structures and highlights the considerable potential of CdS in degrading organic contaminants.

Effective photodegradation of organic water pollutants by the facile synthesis of Ag2O nanoparticles

In this study, Ag2O nanoparticles were synthesized using a low-cost precipitation method. The synthesized nanomaterials are characterized by XRD, FTIR, XPS, Photoluminescence, and EDX. The shape and excellent size of incorporated Ag2O nanoparticles were exhibited utilizing SEM and XRD. XRD patterns of precipitated Ag2O powders indicated a cubic structure with crystallite diameters of 18.5 nm, respectively. The photocatalytic degradation of Rhodamine-B (Rh-B) gathered from the dyeing industry was used to examine the Ag2O nanoparticles. The photocatalytic activity of Rh-B degradation in an aqueous solution was also studied; this process resulted in a 76 % reduction of the dye in 60 minutes when exposed to UV-visible light. In the instance of pseudo first-order reaction kinetics, this corresponds to rate constants of 0.99804 min−1. As a result, precipitation was used to increase the photocatalytic activity of Ag2O nanostructures. The findings provide a pathway to developing advanced photocatalysts that may effectively remove organic contaminants in water using just visible light.

Overlooked Transformation of Nitrated Polycyclic Aromatic Hydrocarbons in Natural Waters: Role of Self-Photosensitization.

Photochemical transformation is an important process that involves trace organic contaminants (TrOCs) in sunlit surface waters. However, the environmental implications of their self-photosensitization pathway have been largely overlooked. Here, we selected 1-nitronaphthalene (1NN), a representative nitrated polycyclic aromatic hydrocarbon, to study the self-photosensitization process. We investigated the excited-state properties and relaxation kinetics of 1NN after sunlight absorption. The intrinsic decay rate constants of triplet (31NN*) and singlet (11NN*) excited states were estimated to be 1.5 × 106 and 2.5 × 108 s-1, respectively. Our results provided quantitative evidence for the environmental relevance of 31NN* in waters. Possible reactions of 31NN* with various water components were evaluated. With the reduction and oxidation potentials of -0.37 and 1.95 V, 31NN* can be either oxidized or reduced by dissolved organic matter isolates and surrogates. We also showed that hydroxyl (•OH) and sulfate (SO4•-) radicals can be generated via the 31NN*-induced oxidation of inorganic ions (OH- and SO42-, respectively). We further investigated the reaction kinetics of 31NN* and OH- forming •OH, an important photoinduced reactive intermediate, through complementary experimental and theoretical approaches. The rate constants for the reactions of 31NN* with OH- and 1NN with •OH were determined to be 4.22 × 107 and 3.95 ± 0.01 × 109 M-1 s-1, respectively. These findings yield new insights into self-photosensitization as a pathway for TrOC attenuation and provide more mechanistic details into their environmental fate.

A review on the versatility of Carica papaya seed: an agrogenic waste for the removal of organic, inorganic and microbial contaminants in water

AbstractThe advent of civilization, coupled with growing industrialization in many countries, is placing more demand on the available water sources. At the same time, the daily surge in wastes generated by man's anthropogenic activities has led to microbial, organic and inorganic contamination of water sources. Based on available evidence, significant research efforts are being made into the use of low‐cost agricultural materials such as Carica papaya seed (CPS) in the removal of these contaminants from water sources in a bid to provide clean water. In the present review, the organic, inorganic and microbial contaminants in waters were elucidated. Furthermore, the chemical composition of the CPS was illustrated. The adsorption capacity and efficiency of CPS and their composites in the remediation of the selected contaminants were discussed while identifying the various factors affecting the adsorption efficiency. Finally, the reusability of this agricultural material was discussed. Solution pH was identified as a major factor influencing the sorption process. The high removal efficiency reported in the studies that adopted CPS showed its vast potential in the elimination of contaminants from water sources. Also, the regenerative potential of the adsorbent over several cycles indicated its long‐term use. The economic feasibility and environmental sustainability afforded by using CPS chart a path for further investigation into the use of other low‐cost agricultural materials in the elimination of environmental contaminants. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry (SCI).

Novel morphological mono-metallic substituted polyoxometalate immobilized 3-(aminopropyl)-imidazole photocatalysts for visible-light driven degradation: Anti-bacterial activity, membrane bacterial activity applications

A novel keggin-type tetra-metalates substituted polyoxometalate was functionalized by 3-(aminopropyl)-imidazole (3-API) supporting a ligand substitution method. In this paper, polyoxometalate (POMs) (NH4)3 [PMo12O40] and transition metal substituted of (NH4)3 [{PMIVMo11O40}.(H2O)] (M = Mn, V) are used as one of the adsorbents. The 3-API/POMs hybrid have been synthesized and used as adsorbent for the photo-catalysis of azo-dye molecule degradation after visible-light illumination as a simulated organic contaminant in water. The transition metal (M = MIV, VIV) substituted keggin-type anions (MPOMs) were synthesized, which reveals the degradation of methyl orange (MO) of about 94.0 % and 88.6 %. Immobilizing high redox ability POMs as an efficient acceptor of photo generated electron, on metal 3-API. In the presence of visible light irradiation result reveals that 3-API/POMs (89.9 %) have incredibly achieved after certain irradiation time and at specific conditions (3)-API/POMs; photo-catalysts dose = 5mg/100 ml, pH = 3 and MO dye concentration = 5 ppm). As the surface of POM catalyst has strong absorption of azo-dye MO molecule engaged as a molecular exploration through photo catalytic reactant. From the SEM images it is clear that the synthesized POMs based materials and POMs conjugated MO have varieties of morphological changes observed such as flakes, rods and spherical like structures. Anti-bacterial study reveals that the process of targeted microorganism occur higher activity against pathogenic bacterium for 180 min of visible-light irradiation is measured in terms of zone of the inhibition. Furthermore, the photo catalytic degradation mechanism of MO using POM, metaled POMs and 3-API/POMs also has been discussed.

Adsorption and desorption of polychlorinated biphenyls on biochar colloids with different pyrolysis temperatures: the effect of solution chemistry.

Biochar releases colloidal particles into the environment during applications and aging which can become carriers of pollutants and influence on the environmental risk of pollutants due to the excellent adsorption and migration properties of biochar colloids (BCCs). The adsorption and desorption behaviors of BCCs can be different from their bulk ones due to the colloidal size, which merits specific studies. Herein, the adsorption and desorption of 2,4,4'-trichlorobiphenyl (PCB28) as a representative on BCCs released from bulk biochars prepared from bamboo chips at 300, 500, and 700C and the effects of solution properties were specifically investigated. Results show that the adsorption was dominated by pore filling and π-π interaction, and thus, BCCs prepared at higher temperature with greater pore volume and aromaticity had higher adsorption of PCB28. Results show that the adsorption was dominated by pore filling and π-π interaction, and thus, BCCs prepared at higher temperature with greater pore volume and aromaticity had higher adsorption of PCB28. The saturation adsorption amounts of PCB28 on BCC300, BCC500, and BCC700 were 21.9, 40.3, and 62.4mg/g, respectively. It is noteworthy that PCB28 possessed a significant desorption hysteresis from BCCs, with the hysteresis index (Ce = 80μg/L) increased from 0.380 to 0.661 as the preparation temperature of BCCs rising from 300 to 700℃. High concentration of NaCl (100mmol/L) was unfavorable for the adsorption and desorption. The presence of humic acid or fulvic acid (FA), especially the smaller FA, could inhibit the adsorption and desorption of PCB28 on BCCs due to micropore blocking. In seawater, groundwater, surface water, and soil solution samples, the PCB28 adsorption of BCCs was inhibited to varying degrees in comparison with that in deionized water, and the desorption was noticeably inhibited in the groundwater sample. These findings provide valuable information for the understanding of interactions between BCCs and organic contaminants in natural waters and for the environmental application of biochars as well.

Avoiding Interferences in Advance: Cyclodextrin Polymers to Enhance Selectivity in Extraction of Organic Micropollutants for Carbon Isotope Analysis

Compound-specific isotope analysis (CSIA) of organic water contaminants can provide important information about their sources and fate in the environment. Analyte enrichment from water remains nonetheless a critical yet inevitable step before measurement. Commercially available solid-phase extraction (SPE) sorbents are inherently nonselective leading to co-extraction of concurrent dissolved organic matter (DOM) and in turn to analytical interferences, especially for low-occurring contaminants. Here, we (i) increased extraction selectivity by synthesizing cyclodextrin polymers (α-, β-, γ-CDP) as SPE sorbents, (ii) assessed their applicability to carbon isotope analysis for a selection of pesticides, and (iii) compared them with commonly used commercial sorbents. Extraction with β-CDP significantly reduced backgrounds in gas chromatography-isotope ratio mass spectrometry (GC-IRMS) and enhanced sensitivity by a factor of 7.5, which was further confirmed by lower carbon-normalized CDOM/Canalyte ratios in corresponding extracts as derived from dissolved organic carbon (DOC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Gibbs free energies of adsorption demonstrated weak competition between DOM and analyte on the three CDPs. No isotopic fractionation (Δδ13C within ± 0.3‰) was observed for the investigated pesticides after using β-CDP as an SPE sorbent covering a range of concentrations (5-500 μg L-1), flow velocities (5-40 cm min-1), and sorbent regeneration (up to six times). The present study highlights the benefit of selecting innovative extraction sorbents to avoid interferences in advance. This strategy in combination with existing cleanup approaches offers new prospects for CSIA at field concentrations of tens to hundreds of nanograms per liter.

Facile synthesis of ZIF‐67@PVA/CA nanofibrous aerogel as efficient and recyclable catalyst for the degradation of organic pollutants through peroxymonosulfate activation

AbstractMetal–organic frameworks (MOFs) are one of the most promising advanced heterogeneous catalysts for the activation of peroxymonosulfate (PMS) to degrade organic contaminants in water, and have been extensively studied. However, MOFs in powder form usually have the disadvantage of poor separation and regeneration, making it significantly challenging for practical applications. In this study, ultralight zeolitic imidazolate framework‐67@poly(vinyl alcohol)/citric acid nanofibrous aerogel (ZIF‐67@PVA/CA NFA) was prepared by a convenient and facile in‐situ growth method and it had excellent catalytic efficiency and recyclability. The factors affecting the activation of PMS by ZIF‐67@PVA/CA NFA, such as PMS concentration, reaction temperature, solution pH, and organic pollutant concentration, were investigated. Taking advantage of the distinctive structural characteristics of MOF and nanofibrous aerogels, the obtained ZIF‐67@PVA/CA NFA exhibited ultralow density, hierarchical porosity, remarkably high catalytic activity for activation of PMS for the degradation of organic pollutants. Furthermore, ZIF‐67@PVA/CA NFA also displayed excellent recyclability along with retention of high catalytic stability. The present study provides a new strategy for the efficient fabrication of three‐dimensional heterogeneous catalyst for the activation of PMS, with great potential in wastewater treatment.

A Review on Cassava Residues as Adsorbents for Removal of Organic and Inorganic Contaminants in Water and Wastewater

An increase in water demand for drinking, agriculture, and industries necessitates the treatment of water and wastewater. Among various conventional treatment techniques available, adsorption is found to be one of the most economical and feasible methods. Adsorbents from plant biomass are effective for the removal of organic and inorganic pollutants. Cassava has gained attention among researchers during the past decades due to its plentiful availability and resilient characteristics. Even though cassava contains cyanogenic glucosides as toxins, it is used in industries for development of various products. Cassava stem, rhizome, peel, and bagasse are industrial residues that are generated in abundance. The present review focusses on factors affecting adsorption using cassava residues, adsorbent preparation and activation methods, equilibrium, mass transfer, kinetics, and thermodynamic studies of adsorption.

A Review of Traditional and Emerging Residual Chlorine Quenchers on Disinfection By-Products: Impact and Mechanisms.

Disinfection by-products (DBPs) are the most common organic contaminants in tap water and are of wide concern because of their highly developmental toxic, cytotoxic, and carcinogenic properties. Typically, to control the proliferation of pathogenic microorganisms, a certain concentration of residual chlorine is retained in the factory water, which reacts with the natural organic matter and the disinfection by-products that have been formed, thus affecting the determination of DBPs. Therefore, to obtain an accurate concentration, residual chlorine in tap water needs to be quenched prior to treatment. Currently, the most commonly used quenching agents are ascorbic acid, sodium thiosulfate, ammonium chloride, sodium sulfite, and sodium arsenite, but these quenching agents can cause varying degrees of DBPs degradation. Therefore, in recent years, researchers have attempted to find emerging chlorine quenchers. However, no studies have been conducted to systematically review the effects of traditional quenchers and new ones on DBPs, as well as their advantages, disadvantages, and scope of application. For inorganic DBPs (bromate, chlorate, and chlorite), sodium sulfite has been proven to be the ideal chlorine quencher. For organic DBPs, although ascorbic acid caused the degradation of some DBPs, it remains the ideal quenching agent for most known DBPs. Among the studied emerging chlorine quenchers, n-acetylcysteine (NAC), glutathione (GSH), and 1,3,5-trimethoxybenzene are promising for their application as the ideal chlorine quencher of organic DBPs. The dehalogenation of trichloronitromethane, trichloroacetonitrile, trichloroacetamide, and bromochlorophenol by sodium sulfite is caused by nucleophilic substitution reaction. This paper takes the understanding of DBPs and traditional and emerging chlorine quenchers as a starting point to comprehensively summarize their effects on different types of DBPs, and to provide assistance in understanding and selecting the most suitable residual chlorine quenchers during DBPs research.