Adsorption of Fluoride onto Acid-Modified Low-Cost Pyrolusite Ore: Adsorption Characteristics and Efficiencies.

Fluoride concentrations in the groundwater continue to be a major cause for concern in Thailand, particularly in the country's north and west. The process of removing fluoride through adsorption has captured the attention of the abundance of ore in the mining industry. For the purpose of this investigation, the utilization of the adsorbent pyrolusite, which is a manganese mineral largely composed of MnO2, was a major component. Lab-scale experiments were conducted to investigate the efficacy of original pyrolusite ore (PA-1) and acid-modification PA (PA-2) created as low-cost adsorption materials for fluoride removal. The results of the adsorption rate in both PAs showed a fast rate of adsorption within 60 min of reaching equilibrium. According to the results of the adsorption capacity (qe) tests, PA that had been treated with an acid solution (PA-2) had the capacity to contain more fluoride (qe = 0.58 mg/g) than the PA that had been used initially (PA-1) (qe = 0.11 mg/g). According to the findings of an isotherm, primary adsorption behavior is determined by the effect that surface components and chemical composition have on porous materials. This is the first current study that provides a comparison between pyrolusite from Thailand's mining industry and basic modified pyrolusite regarding their ability to remove a fluoride contaminant in synthetic groundwater by an adsorption process. Such an approach will be able to be used in the future to protect the community from excessive fluoride concentrations in household and drinking water treatment technology.

Efficiencies of O-MBR and A/O-MBR for Organic Matter Removal from and Trihalomethane Formation Potential Reduction in Domestic Wastewater.

Lab-scale anoxic/oxic membrane bioreactor (A/O-MBR) and oxic membrane bioreactor (O-MBR) systems using a submerged polysulfone hollow-fiber membrane module with a pore size of 0.01 µm and a total surface area of 1.50 m2 were used to treat domestic wastewater. The sludge retention time (SRT) of each system was examined by setting the SRT to 10, 20, and infinity (no sludge withdrawal). The results showed that the total nitrogen removal efficiency of the A/O-MBR was more significant than that of the O-MBR at a SRT of infinity, with figures of 72.3% and 33.1% being found, respectively. The COD removal efficiencies of the A/O-MBR system with a SRT of 10 days, 20 days, and infinity were 82.4%, 84.3%, and 91.5%, respectively. The COD removal efficiencies of the O-MBR system with a SRT of 10 days, 20 days, and infinity were 79.3%, 81.5%, and 89.8%, respectively. An increase in the SRT resulted in an increase in the COD removal efficiency. The FEEM peak of the influent tended to decrease after an increase in the SRT for both systems (A/O-MBR and O-MBR). For the A/O-MBR system, the trihalomethane formation potential (THMFP) was significantly reduced by 88.91% (at a SRT of infinity). The THMFP declined significantly by 85.39% for the O-MBR system at a SRT of infinity. The A/O-MBR system showed a slightly higher efficiency than the O-MBR system in terms of the COD removal and the THMFP reduction. These results indicated that the MBR process, and the A/O-MBR system, in particular, could be used as an effective wastewater treatment process for many developing countries that are troubled by the emerging contamination of water and wastewater.

Selective adsorption mechanisms of iodinated trihalomethanes onto thiol-functionalized HKUST-1s in a mixed solute.

The selective adsorption mechanisms involved in the competitive adsorption of five iodinated trihalomethanes (I-THMs) onto dithiolglycol and (3-mercaptopropyl)-trimethoxy functionalized HKUST-1 (HK-SH and HK-MPTS, respectively) were investigated by single- and mixed-batch adsorption. HK-SH had the highest adsorption rates and capacities for the five I-THMs, followed by HK-MPTS and pristine HKUST-1, even though the porosity and surface area decreased after modification. The primary adsorptive mechanism of HK-SH consists of ion-dipole interactions of I-THMs with the protonated hydroxyl and thiol groups at the metal (Cu) node, which is supported by Lewis acid-base reactions via Cu-Cu complex and π-π interactions. In a mixed solute, bromodiiodomethane, which was the most hydrophobic and had the smallest molecular size, exhibited the most competitive adsorption on HK-SH. In contrast, the selective adsorption of I-THMs onto HK-MPTS was affected by their log Kow values, causing hydrophobic partitioning onto the alkyl chain of the mercaptopropyl group. Iodinated haloforms tend to achieve a higher adsorption rate and capacity than chlorinated and brominated haloforms via hydrophobic partitioning. Moreover, dithiolglycol grafted onto HK-SH can better promote the excellent selective adsorption performance of iodoacetamide than dichloroiodomethane and iodoacetic acid in both single- and mixed-solute solutions due to hydrogen bonding via the -NH2 group of diiodoacetamide.

Trihalomethanes in Water Supply System and Water Distribution Networks.

The formation of trihalomethanes (THMs) in natural and treated water from water supply systems is an urgent research area due to the carcinogenic risk they pose. Seasonal effects and pH have captured interest as potential factors affecting THM formation in the water supply and distribution systems. We investigated THM occurrence in the water supply chain, including raw and treated water from water treatment plants (coagulation, sedimentation, sand filtration, ClO2-disinfection processes, and distribution pipelines) in the Chiang Mai municipality, particularly the educational institute area. The effects of two seasons, rainy (September-November 2019) and dry (December 2019-February 2020), acted as surrogates for the water quality profile and THM occurrence. The results showed that humic acid was the main aromatic and organic compound in all the water samples. In the raw water sample, we found a correlation between surrogate organic compounds, including SUVA and dissolved organic carbon (DOC) (R2 = 0.9878). Four species of THMs were detected, including chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Chloroform was the dominant species among the THMs. The highest concentration of total THMs was 189.52 µg/L. The concentration of THMs tended to increase after chlorination when chlorine dioxide and organic compounds reacted in water. The effect of pH on the formation of TTHMs was also indicated during the study. TTHM concentrations trended lower with a pH ≤ 7 than with a pH ≥ 8 during the sampling periods. Finally, in terms of health concerns, the concentration of TTHMs was considered safe for consumption because it was below the standard (<1.0) of WHO's Guideline Values (GVs).

Evaluation of Fluoride Adsorption Mechanism and Capacity of Different Types of Bone Char.

The fluoride adsorption capacity of three types of bone char (BC), including cow BC (CBC), chicken BC (CKBC), and pig BC (PBC), was examined. At the optimum charring conditions (temperature and time), PBC had the highest hydroxyapatite (HAP) content (0.928 g-HAP/g-BC), while CBC had the highest specific surface area (103.11 m2/g-BC). CBC also had the maximum fluoride adsorption capacity (0.788 mg-F/g-HAP), suggesting that fluoride adsorption capacity depends more on the specific surface area of the BC than the HAP content. The adsorption data of CBC, CKBC, and PBC fit well with the pseudo-second-order model and the Langmuir isotherm. The maximum fluoride adsorption capacity of BC reached the maximum value when the solution had a pH of approximately 6.0. Lastly, the highest fluoride desorption occurred when the BCs were soaked in solutions with a pH higher than 11.0.

Adsorption of iodinated trihalomethanes onto thiol functionalized ZIF-8s: Active adsorption sites, adsorptive mechanisms, and dehalogenation by-products.

The adsorptive mechanisms operating in, and the effect of two different thiol modification methods on, the removal of five iodinated trihalomethanes (I-THMs) by the zeolite imidazolate framework (ZIF-8) were investigated in single and mixed solutions. The direct postgrafting of dithioglycol to the zinc complex node of ZIF-8 (ZF-SH) can increase the mesopore structures that enhance inner pore accessibility; this increase is a critical property required for excellent adsorption of I-THMs. The synergetic adsorptive interactions consist of Lewis acid-base interactions via the Zn-Zn complex, ion-dipole interactions involving the protonated hydroxyl and thiol groups, and hydrophobic interactions at the imidazole ring. In contrast to ZF-SH, the (3-mercaptopropyl)-trimethoxy functionalized silica coating on ZIF-8 (ZF-Si-SH) causes a lower thiol moiety and a steric effect that is reflected in its lower adsorption capacity. In both single and mixed solutions, the small molecular size and hydrophobic nature of I-THMs can promote better adsorption capacity on all thiol-modified ZIF-8, while the minus dipole charge distribution of the I-THMs structure plays a more critical role in selective adsorption on pristine ZIF-8. Interestingly, the dehalogenation of triiodomethane to diiodomethane due to a nucleophilic substitution (SN2) reaction can be accelerated by the thiol functionalized silica layer on ZIF-8.