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During the water treatment process, chlorination and ultraviolet (UV) sterilization can modify microplastics (MPs) and alter their physicochemical properties, causing various changes between MPs and other pollutants. In this study, the impact of chlorination and UV modification on the physicochemical properties of polystyrene (PS) and polyvinyl chloride (PVC) were investigated, and the adsorption behavior of pefloxacin (PEF) before and after modification was examined. The effect of pH, ionic strength, dissolved organic matter, heavy metal ions and other water environmental conditions on adsorption behavior was revealed. The results showed that PS had a higher adsorption capacity of PEF than PVC, and the modification increased the presence of O-containing functional groups in the MPs, thereby enhancing the adsorption capacity of both materials. Chlorination had a more significant impact on the physicochemical properties of MPs compared to UV irradiation within the same time period, leading to better adsorption performance of chlorination. The optimal pH for adsorption was found to be 6, and NaCl, sodium alginate and Cu2+ would inhibit adsorption to varying degrees, among which the inhibition caused by pH was the strongest. Chlorination and UV modification would weaken the inhibitory effect of environmental factors on the adsorption of PEF by MPs. The main mechanisms of adsorption involved electrostatic interaction and hydrogen bonding. The study clarified the effects of modification on the physicochemical properties of MPs, providing reference for subsequent biotoxicity analysis and environmental protection studies.

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The chlorination of oxides of major concern in cassiterite concentrate with various chlorinating agents is investigated in light of their thermodynamic feasibilities to extract and recover their valuable metal components. Mechanisms responsible for the processes and their Gibbs free energy changes as a function of temperature to selectively separate and/or recover the metal(s) of interest and unwanted ones as their metallic chlorides are identified. Attention is given to gaseous (Cl2 and Cl2 + CO mixture) and solid (CaCl2 and MgCl2) chlorine sources, from which Cl2 + CO shows no reaction selectivity for any of the oxides but a feasible metal chloride formation for all. Chlorine gas (Cl2), on the other hand, could selectively form chlorides with metals of +2 oxidation state in their oxides, leaving those of high oxidation state unreacted. MgCl2, unlike CaCl2, is found capable of producing calcium, ferrous, and stannic chloride from their metallic oxides with enhanced reaction tendencies in the presence of silicon dioxide (SiO2). An overall study of the thermodynamic feasibility of all chlorine sources looked at alongside operational and environmental viabilities suitably suggests MgCl2 for a selective extraction of the valuable metal components in a cassiterite concentrate, in which case, moderate temperatures seem promising.

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Opioids are widely distributed, potent prescription analgesics that are known to be diverted for illicit use. Their prevalence of use is reflected by high concentrations of parent compounds and/or metabolites found in samples collected from wastewater treatment plants. Given that treatment byproducts enter the environment through several routes, the consequences of insufficient removal by treatment methods include unwanted environmental exposure and potential to disrupt ecosystems. Activated sludge treatment has been widely investigated for a large suite of prescription opioids but the same cannot be said for UV and chlorination. Additionally, the biosolid cycle of opioids has been overlooked previously. This study aimed to determine the extent to which secondary and tertiary wastewater treatment methods remove opioids from influent, and the associated environmental exposure for those persistent, as well as the fate of opioids in biosolids. Membrane bioreactor treatment proved effective for natural and semi-synthetic opioids while the effect of UV treatment was negligible. Chlorination was the most effective treatment method resulting in effluent with concentrations below theoretical predicted no-effect concentration. Biosolids are not subjected to any additional biological or chemical treatment after membrane bioreactor treatment and the levels detected in biosolid used as fertiliser had several opioids at potentially hazardous concentrations, indicated by a QSAR theoretical model. This data indicates a potential issue regarding the treatment process of biosolids and reliance on chlorination for effluent treatment that should be investigated in other treatment plants.

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High quality, safe and sufficient drinking water is essential for public health and well-being. However, the war on Tigrai damaged the water sources of communities and pose people to health problems. Therefore, the aim of the present study was to assess the quality of water of the town of Abyi Adi, Tigrai, Northern Ethiopia using physicochemical and biological parameters and water quality indices. A total of 36 water samples were collected from four major water sources. The physicochemical and biological parameters were determined using standard analytical procedures for water analysis. The mean values of electrical conductivity and pH ranged from 273.63 to 881.27 µS/cm and 6.68 to 7.42, respectively. Moreover, the experimental results of major cations (Na+ = 3.70-14.77 mg/L and Ca2+ = 8.50-15.77 mg/L), and anions (HCO3 - = 21.52-40.77 mg/L, Cl- = 13.56-40.29 mg/L, NO3 - = 0.14-0.25 mg/L, NO2 - = 0.24-0.76 mg/L and PO4 3- = 0.34-1.32 mg/L) were recorded below the World Health Organization (WHO) permissible limits set for drinking water. The water quality index (WQI) that is determined using a weighted arithmetic water quality index method (WAWQIM) was also found in the range of 5.3-37.2. Subsequently, all groundwater sources except Adibakla are classified as excellent or "A" rating. However, the total coliform of Maylomin and Chiny water sources were found to be 6.33 MPN/100 mL and 3.67 MPN/100 mL, respectively. Both are higher than the WHO permissible limit set for drinking water. Considering the susceptibility of groundwater to pollution and its impact to human health, regular monitoring and supervision should be performed to keep the water safe for drinking. Accordingly, chlorination water treatment process is recommended to provide safe drinking water.

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We investigated the formation of nitrosamines from urine during electrochemical chlorination (EC) using dimensionally stable anodes. Short-term electrolysis (< 1 h) of urine at 25 mA cm-2 generated seven nitrosamines (0.1-7.4 µg L-1), where N-nitrosodimethylamine, N-nitrosomethylethylamine, and N-nitrosodiethylamine were predominant with concentrations ranging from 1.2 to 7.4 µg L-1. Mechanistic studies showed that the formation kinetics of nitrosamines was influenced by urine aging and composition, with fresh urine generating the highest levels (0.9-5.8 µg L-1) compared with aged, centrifuged, or filtered urine (0.2-4.1 µg L-1). Concurrently, studies on urine pretreatment through filtration and centrifugation underscored the significance of nitrogenous metabolites (such as protein-like products and urinary amino acids) and particle-associated humic fractions in nitrosamine formation during EC of urine. This finding was confirmed through chromatographic and spectroscopic studies utilizing LCOCD, Raman spectra, and 3DEEM fluorescence spectra. Parametric studies demonstrated that the ultimate [nitrosamines] increased at a pH range of 4.5-6.2, and with increasing [bromide], [ammonium], and current density. Conversely, sulfate and carbonate ions inhibited nitrosamine formation. Moreover, the implications of EC in urine-containing source waters were evaluated. The results indicate that regardless of the urine source (individual volunteers, septic tank, swimming pool, untreated municipal wastewater), high levels of nitrosamines (0.1-17.6 µg L-1) were generated, surpassing the potable reuse guideline of 10 ng L-1. Overall, this study provides insights to elucidate the mechanisms underlying nitrosamine formation and optimize the operating conditions. Such insights facilitate suppressing the generation of nitrosamine byproducts during electrochemical treatment of urine-containing wastewater.

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Polyhalogenated dibenzo-p-dioxins/dibenzofurans (PXDD/Fs) are commonly released into the environment as byproducts of combustion processes, accompanied by flue gases. Chlorinated (Cl) and brominated (Br) precursors play crucial roles in forming PXDD/Fs. However, the specific contributions of Cl-precursors and Br-precursors to PXDD/Fs formation have not been fully elucidated. Herein, we demonstrate that the formation of Br-precursors can increase the fraction of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) congeners substituted at specific positions, such as 1,2,3,4,6,7,8-HpCDD, OCDD, 2,3,4,7,8-PeCDF, and 2,3,4,6,7,8-HxCDF. This is attributed to the electrophilic chlorination reaction of the Br-precursors, which includes the Br-to-Cl transformation pathway, following the principle of regioselectivity. The observed formation of polybrominated/chlorinated dibenzo-p-dioxins/benzofurans (PBCDD/Fs) from 1,2-dibromobenzene (1,2-DiBBz) as a Br precursor provides direct evidence supporting the proposed Br-to-Cl transformation. Quantum chemical calculations are employed to discuss the principle of regioselectivity in the Br-to-Cl transformation, clarifying the priority of the position for electrophilic chlorination. Additionally, the concentration of PCDD/Fs formed from 1,2-DiBBz is 1.6 µg/kg, comparable to that of polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs) (2.4 µg/kg), highlighting the potential of brominated organic pollutants as precursors for PCDD/Fs formation. This study provides three potential pathways for PCDD/Fs formation from Br-precursors, establishing a theoretical foundation for elucidating the formation mechanism of PXDD/Fs in the coexistence of Cl and Br.

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Disinfection byproducts (DBPs) have been extensively investigated during the chlorination of water and wastewater. Although over 700 DBPs have been identified, more than 50% of the total organic halogen remains unknown. Solid phase extraction (SPE) has been emerged as a popular pretreatment approach for enrichment and desalting of unknown DBPs prior to the mass spectrometry analysis. However, the effects of SPE conditions on unknown DBPs in real wastewater have not yet been reported. Herein, three factors (acid types, pH values, and sorbent types) influencing the composition of DBPs in chlorinated municipal wastewater were systematically investigated by Fourier transform ion cyclotron resonance mass spectrometry and statistical analysis. The results indicated that the number of DBPs in different SPE conditions ranged from 280 to 706, and the majority ones were Br-DBPs and CHOX compounds. Compared with H2SO4, more common DBPs were found when using HCl and HCOOH to adjust the pH values of samples. The unique DBPs extracted at pH 1.0 and 2.0 generally owned higher modified aromaticity index (AImod) value and C number than at pH 3.0. The effect of acid types on the extracted DBPs was pH dependent, and the total number of extracted DBPs increased with the increasing of pH value. In terms of sorbent types, the unique DBPs in C18 sorbent possessed low O/C ratios (O/C < 0.6), whereas the unique ones in HLB sorbent owned high O/C ratios (O/C > 0.6). Compared with C18 and HLB sorbents, the unique DBPs extracted in PPL sorbent were characterized by relatively high AImod and DBE values. Based on mass difference analysis, 1496 precursors-DBPs pairs were identified in all extracted samples, with the highest number of bromine substitution reaction. Overall, the effects of SPE conditions on the composition of unknown DBPs should not be overlooked, and the amount and diversity of DBPs may be underestimated under a single SPE condition. This study provides new methodological references for the accurate identification of unknown DBPs with different characteristics in real wastewater.

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Chlorination is a common chemical modification process of soft wheat flour to prepare high-ratio cakes. Due to safety and labeling concerns of flour chlorination, alternatives to chlorination have been researched. Atmospheric Cold Plasma (ACP) is an emerging technology which is applicable for a wide range of food and biological components, including cereal grain products. The potential of ACP as an alternative to chlorination for high-ratio cakes has not been researched. Soft wheat flour was treated at 50 kV, 60 kV, and 70 kV each for 5, 6, and 7 min and compared to untreated and chlorinated wheat flour. High-ratio cakes were prepared from the chlorinated, treated, and untreated soft wheat flour and their properties were compared. Changes in the flour properties and the high-ratio cakes were observed at different treatment conditions. It was found that after 50 kV, 6 min, 50 kV, 7 min and 60 kV, 6 min had the better flour pasting properties, higher cake volume, and better texture properties as compared to untreated wheat flour and chlorinated wheat flour. This determines the potential of the application of ACP as an alternative to chlorination or to reduce the use of chlorination in soft wheat flour.

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Site-selective functionalization of the heterobenzylic C(sp3)-H bonds of pyridines and related heteroaromatic compounds presents challenges associated with the basic nitrogen atom and the variable reactivity among different positions on the heteroaromatic ring. Methods for functionalization of 2- and 4-alkylpyridines are increasingly available through polar pathways that leverage resonance stabilization of charge build-up at these positions. In contrast, functionalization of 3-alkylpyridines is largely inaccessible. Here, we report a photochemically promoted method for chlorination of non-resonant heterobenzylic C(sp3)-H sites in 3-alkylpyridines and related alkylheteroaromatics. Density functional theory calculations show that the optimal reactivity reflects a balance between the energetics of the two radical-chain propagation steps, with the preferred reagent consisting of an N-chlorosulfonamide. The operationally simple chlorination protocol enables access to heterobenzylic chlorides which serve as versatile intermediates in C-H cross-coupling reactions between heteroaromatic building blocks and diverse oxidatively sensitive nucleophiles using high-throughput experimentation.

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The recycling of spent Li-ion batteries is urgent, and the effective recovery of valuable metals from spent cathode material is an economic and eco-friendly approach. In this study, Ni, Cu, Co, and Mn were extracted synchronously from spent LiNixCoyMn1-x-yO2 by chlorination and the complexation reaction of ammonium chloride at low temperatures. The kinetics of the chlorination process was investigated by nonisothermal thermal analysis to determine the rate equation of metal conversion, and the apparent activation energies were calculated to be 99.96 kJ·mol-1 for lithium and 146.70 kJ·mol-1 for nickel, cobalt, and manganese, respectively. The separation of valuable metals from polymetallic leaching solution and the regeneration of cathode materials were further investigated to promote the industrialization of the process. The recoveries of Ni, Co, Mn, and Li can reach 97.75, 99.99, 99.99, and 92.23%, respectively. The prepared LiNi0.8Co0.1Mn0.1O2 precursor is a multilayer spherical particle formed by stacking primary hexagonal nanosheets along the (010) crystal axis, the formation mechanism of which was discussed. The effect of temperature, time, and mixed lithium ratio on the performance of single crystal LiNi0.8Co0.1Mn0.1O2 cathode in the synthesis process was investigated to determine the optimum conditions. Compared with commercial materials, the prepared single crystal LiNi0.8Co0.1Mn0.1O2 cathode has a more regular crystal structure and higher initial discharge capacity (215.9 mAh·g-1 at 0.1 C).

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The coexistence of emerging pollutants and dissolved organic matter in wastewater complicates the transformation and generation of disinfection byproducts (DBPs) during chlorination treatment, which is essential for effective water quality evaluation and chlorination optimization. This study used fluoxetine (FLX) and humic acid (HA) as representative substances to analyze changes in their chemical characteristics and zebrafish embryonic developmental toxicity under different chlorination conditions. The analysis of the fluorescence characteristics and Fourier transform ion cyclotron resonance mass spectrometry indicated that chlorination treatment increased the aromatic compound content of the HA solution. FLX addition further increased the presence of aromatic ring structures and oxidized molecules, resulting in the formation of numerous Cl-DBPs with highly unsaturated and phenolic structures. Moreover, different responses in zebrafish embryo development and behavior were found with FLX, HA, and FLX + HA exposures. Cardiotoxicity was linked to changes in the concentration of cTn-I protein and expression of various genes. Prolonged chlorination conditions showed higher toxicities. Correlation analysis found a weak relation between chemical indicators and toxicity data, indicating that both analysis methods need to be considered when analyzing the impact of the chlorination. Further, a combination of chemical analyses and toxicity tests revealed that the FLX + HA solution with chlorination conditions of 3 mg/L for 30 min had lower chemical and toxic effects in this experiment. This study provides valuable scientific insights for the safe discharge of chlorinated water containing FLX and dissolved organic matter, as well as guidance for optimizing chlorination parameters in wastewater treatment.

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The highly reactive hypobromous acid (HOBr), which is generated after chlorination process of tap water, acts as a precursor of toxic brominated disinfection by-products (Br-DBPs) and further reacts with organic matter. In addition, HOBr produced from the oxidation of Br- during the degradation of pollutants by peroxymonosulfate (PMS, HSO5-) can be considered as the cause of the expedited degradation of pollutants. Therefore, it is particularly important to detect HOBr level in the water environment. Resazurin was selected as a fluorescent probe for selective recognition of HOBr in the water environment. The probe exhibited excellent spectral performance and showed high sensitivity to HOBr (LOD = 515 nM). This method has a relatively ideal recovery rate for HOBr detection in environmental water samples. Furthermore, the HOBr production during the chlorination disinfection process was simulated and the HOBr generated from this process was detected by the probe. Importantly, the process of HOBr recognition by the probe is accompanied by the change of color. Based on this, the relationship between the change of color B/G value and HOBr concentration was successfully constructed. The probe was loaded on the filter paper to make a test strip, which was utilized to the detection of HOBr. Collectively, this work provided a promising and powerful method for HOBr detection in the environment.

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Wastewater treatment plants and water reclamation facilities are reservoirs of antimicrobial resistance genes (ARGs). These ARGs are not limited solely to intracellular DNA (inARGs) but include extracellular DNA (exARGs) present in wastewater. The release of exARGs from cells can be exacerbated by treatment processes, including chlorine disinfection, which disrupts bacterial cells. Given the potential for exARGs to drive horizontal gene transfer and contribute to the proliferation of antimicrobial resistance, it is imperative to recognize these fractions as emerging environmental pollutants. In this study, we conducted a comprehensive year-long assessment of both inARGs and exARGs, further differentiating between dissolved exARGs (Dis_exARGs) and exARGs adsorbed onto particulate matter (Ads_exARGs), within a full-scale wastewater treatment and water reclamation facility. The results revealed that Ads_exARGs comprised up to 30 % of the total ARGs in raw sewage with high biomass content. Generally, treatments at low and high doses of chlorine increased the abundance of Dis_exARGs and Ads_exARGs. The fate of ARG levels that varied depending on the type of ARGs suggested variations in the susceptibility of the host bacteria to chlorination. Moreover, co-occurrence of several potential opportunistic pathogenic bacteria and ARGs were observed. Therefore, we propose higher doses of chlorination as a prerequisite for the effective removal of inARGs and exARGs.

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Biological activated carbon filter (BAC) is one of the most effective technologies for removing disinfection by-product (DBP) precursors from water. Biochar is a lower-cost medium that has the potential to replace granular activated carbon in BAC applications, thus leading to the development of biological biochar filter (BCF). This study compared BCF with BAC for the removal of DBP precursors using column experiments. Both BCF and BAC achieved the removal of DBP precursors, resulting in concentrations of all DBP formation potential below the World Health Organization guideline values for drinking water. Bromodichloromethane and unknown DBP precursor removal by BCF was comparable to that by BAC. However, BAC removed more chloroform and dichloroacetontrile precursors than BCF. For microbial community analysis, cell numbers in a bottom layer (inlet) of BCF and BAC columns were higher than those in the top layer. The abundances of Nordella and a microbial genus from Burkholderiaceae at the bottom layer showed a strong correlation to the number of DBP precursors removed and were comparable in BCF and BAC. This finding likely contributes to the similarities between DBPs species removed and the removal performances of some known and unknown DBP precursors by BCF and BAC. Overall results from this study revealed that biochar can be served as a low-cost and sustainable replacement of activated carbon in water filter for DBP precursor removal.

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The difficulty of separating Li during pyrometallurgical smelting of spent lithium-ion batteries (LIBs) has limited the development of pyrometallurgical processes. Chlorination enables the conversion of Li from spent LIBs to the gas phase during the smelting process. In this paper, the effects of four solid chlorinating agents (KCl, NaCl, CaCl2 and MgCl2) on Li volatilization and metal (Co, Cu, Ni and Fe) recovery were investigated. The four solid chlorinating agents were systematically compared in terms of the direct chlorination capacities, indirect chlorination capacities, alloy physical losses and chemical losses in the slag. CaCl2 was better suited for use as a solid chlorinating agent to promote Li volatilization due to its excellent results in these indexes. The temperature required for the release of HCl from MgCl2, facilitated by CO2 and SiO2, was lower than 500 °C. The prematurely released HCl failed to participate in the chlorination reaction. This resulted in approximately 12 % less Li volatilization when MgCl2 was used as a chlorinating agent compared to when CaCl2 was used. In addition, the use of KCl as a chlorinating agent decreased the chemical dissolution loss of alloys in the slag. The performance of NaCl was mediocre. Finally, based on evaluations of the four indexes, recommendations for the selection and optimization of solid chlorinating agents were provided.

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The Tibetan Plateau, a typical high-altitude area, is less affected by human activities such as industrial development, and the external pollution to water sources is extremely low. Then it is also an important source of water samples for exploring the molecular characteristics of precursors in the dissolved organic matter (DOM) of disinfection byproducts (DBPs) in drinking water. Research data on DBPs in drinking water on the Tibet Plateau remains insufficient, leading to uncertainty about DBP contamination in the area. This study explores the formation potential of 35 typical DBPs, including 6 trihalomethanes (THMs), 9 haloacetic acids (HAAs), 2 halogenated ketones (HKs), 9 nitrosamines (NAs), and 9 aromatic DBPs, during chlorination and chloramination of typical source water samples in the Tibet Plateau of China. Moreover, in order to further investigate the characteristics of the generation of DBPs, the molecular composition of DOM in the collected water samples was characterized by Fourier transform ion cyclotron resonance mass spectrometry. The findings reveal that, for chlorination and chloramination, the average concentration of the five classes of DBPs was ranked as follows (chlorination, chloramination): HAAs (268.1 µg/L, 54.2 µg/L) > THMs (44.0 µg/L, 2.0 µg/L) > HKs (0.7 µg/L, 1.8 µg/L) > NAs (26.5 ng/L, 74.6 ng/L) > Aromatics (20.4 ng/L, 19.5 ng/L). The dominant compounds in THMs, HAAs, and NAs are trichloromethane, dichloroacetic acid, trichloroacetic acid, and nitrosopyrrolidine, respectively. This study highlights a significant positive correlation between DBP generation and UV254, SUV254, and the double bond equivalents of DOM in the source water. It systematically elucidates DOM molecular composition characteristics and DBP formation potential in high-altitude water sources, shedding light on key factors influencing DBP generation at the molecular level in high-altitude areas.

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As ubiquitous chemical substances in water bodies, nitrophenol compounds (NCs) can form chlorinated halonitromethanes (Cl-HNMs) in the chlorination process. This work chose six typical NCs to explore Cl-HNMs produced during the UV/post-chlorination process, and Cl-HNMs yields from these NCs followed the increasing order of 4-, 2-, 2-amino-3-, 2-methyl-3-, 3-, and 2-chloro-3-nitrophenol. The Cl-HNMs yields increased continually or increased firstly and declined with post-chlorination time. Increasing chlorine dosage favored Cl-HNMs formation, while excessive chlorine dosage decreased Cl-HNMs produced from 2- and 4-nitrophenol. Besides, appropriate UV radiation, acidic pH, and higher precursor concentrations facilitated Cl-HNMs formation. Then, the reaction mechanisms of Cl-HNMs generated from these different NCs were explored according to density functional theory calculation and identified transformation products (TPs), and the main reactions included chlorine substitution, benzoquinone compound formation, ring opening, and bond cleavage. Moreover, the Cl-HNMs generated from 2-chloro-3-nitrophenol were of the highest toxicity, and the six NCs and their TPs also presented ecotoxicity. Finally, two kinds of real waters were used to explore Cl-HNMs formation and toxicity, and they were significantly distinguishable compared to the phenomena observed in simulated waters. This work will give new insights into Cl-HNMs formation from different NCs in water disinfection processes and help better apply the UV/post-chlorination process to water treatments.

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The reaction mechanism for the chlorination and bromination of 2-naphthol with PIDA or PIFA and AlX3 (X = Cl, Br), previously reported by our group, was elucidated via quantum chemical calculations using density functional theory. The chlorination mechanism using PIFA and AlCl3 demonstrated a better experimental and theoretical yield compared to using PIDA. Additionally, the lowest-energy chlorinating species was characterized by an equilibrium of Cl-I(Ph)-OTFA-AlCl3 and [Cl-I(Ph)][OTFA-AlCl3], rather than PhICl2 being the active species. On the other hand, bromination using PIDA and AlBr3 was more efficient, wherein the intermediate Br-I(Ph)-OAc-AlBr3 was formed as active brominating species. Similarly, PhIBr2 was higher in energy than our proposed species. The reaction mechanisms are described in detail in this work and were found to be in excellent agreement with the experimental yield. These initial results confirmed that our proposed mechanism was energetically favored and therefore more plausible compared to halogenation via PhIX2.

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Reverse osmosis (RO) membrane fouling and biological contamination problems faced by seawater desalination systems are microbiologically related. We used full-length 16S rRNA gene sequencing to assess the bacterial community structure and chlorine-resistant bacteria (CRB) associated with biofilm growth in different treatment processes under the winter mode of a chlorinated seawater desalination system in China. At the outset of the winter mode, certain CRB, such as Acinetobacter, Pseudomonas, and Bacillus held sway over the bacterial community structure, playing a pivotal role in biofouling. At the mode's end, Deinococcus and Paracoccus predominated, with Pseudomonas and Roseovarius following suit, while certain CRB genera still maintained their dominance. RO and chlorination are pivotal factors in shaping the bacterial community structure and diversity, and increases in total heterotrophic bacterial counts and community diversity in safety filters may adversely affect the effectiveness of subsequent RO systems. Besides, the bacterial diversity and culturable biomass in the water produced by the RO system remain high, and some conditionally pathogenic CRBs pose a certain microbial risk as a source of drinking water. Targeted removal of these CRBs will be an important area of research for advancing control over membrane clogging and ensuring water quality safety in the future.

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This review details both the conventional and emerging methods of extracting tin from cassiterite. The emerging methods reviewed include sulphuric acid leaching of SnO, cooling crystallization of SnO, sulphide leaching, alkaline leaching, and dry chlorination. From these methods, the conventional approach (direct reduction smelting) stands out as the sole method that is suitable for industrial application, with none of the emerging ones being promising enough to be a contender. The thermodynamics involved in the hydrometallurgical extraction of tin from the mineral are also discussed. ΔGo values calculated at 25 °C for the reduction-dissolution of SnO2 using reducing gases revealed feasibility only when carbon monoxide was used. An indication of the possible species produced during the hydrolysis of the oxide of the metal (SnO2 and SnO) as a function of pH (ranging from -2 to 14 and 0 to 14 for SnO2 and SnO, respectively) was noted and highlighted to link a Pourbaix diagram generated from literature data. This diagram suggests that the solubility of SnO2 in both strongly acidic and alkaline media is possible, but with a small dissolution window in each. The purification and recovery routes of the various processing techniques were then envisaged.