Evaluating the potential of nanofiltration membranes for removing ammonium, nitrate, and nitrite in drinking water sources.

Advanced drinking water treatment process using nanofiltration (NF) membranes has gained attention recently because it removes many challenging constituents in contaminated surface waters, such as dissolved organics and heavy metals. However, much literature has reported high variations and uncertainties of NF membranes for removing nitrogen compounds in the contaminated water-ammonium (NH4+), nitrates (NO3-), and nitrites (NO2-). This study aimed to identify the ability of commercial NF membranes to remove NH4+, NO2-, and NO3- and clarify the mechanisms underlying their transport through NF membranes. This was examined by evaluating their rejection by three commercial NF membranes using artificial and actual river waters under various conditions (variable permeate flux, temperature, pH, and ionic strength). Ammonium commonly showed the highest removal among the three nitrogen compounds, followed by nitrites and nitrates. Interestingly, ammonium removal varied considerably from 6% to 86%, depending on the membrane type and operating conditions. The results indicated that the selected nitrogen compounds (NH4+, NO2-, and NO3-) could be highly rejected depending on the clearance between their hydrated radius and the membrane's pore walls. Further, the rejection of the lowest molecular-weight nitrogen compound (NH4+) could be higher than NO2- and NO3- due to its highest energy barrier and larger hydrated radius. This study suggests that compliance with the drinking water regulations of NH4+, NO2-, and NO3- can be reliably achieved by selecting appropriate membrane types and predicting the range of their removal under various feed water quality and operating conditions.

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.