Sensory quality of drinking water produced by reverse osmosis membrane filtration followed by remineralisation

Membrane capacitive deionization (MCDI): A flexible and tunable technology for customized water softening

There is a growing demand for water treatment systems for which the quality of feedwater in and product water out are not necessarily fixed with "tunable" technologies essential in many instances to satisfy the unique requirements of particular end-users. For example, in household applications, the optimal water hardness differs for particular end uses of the supplied product (such as water for potable purposes, water for hydration, or water for coffee or tea brewing) with the inclusion of specific minerals enhancing the suitability of the product in each case. However, conventional softening technologies are not dynamically flexible or tunable and, typically, simply remove all hardness ions from the feedwater. Membrane capacitive deionization (MCDI) can potentially fill this gap with its process flexibility and tunability achieved by fine tuning different operational parameters. In this article, we demonstrate that constant-current MCDI can be operated flexibly by increasing or decreasing the current and flow rate simultaneously to achieve the same desalination performance but different productivity whilst maintaining high water recovery. This characteristic can be used to operate MCDI in an energy-efficient manner to produce treated water more slowly at times of normal demand but more rapidly at times of peak demand. We also highlight the "tunability" of MCDI enabling the control of effluent hardness over different desired ranges by correlating the rates of hardness and conductivity removal using a power function model. Using this model, it is possible to either i) soften water to the same hardness level regardless of the fluctuation in hardness of feed waters, or ii) precisely control the effluent hardness at different levels to avoid excessive or insufficient hardness removal.

The Role of Low Mineral Water Consumption in Reducing the Mineral Density of Bones and Teeth: A Narrative Review

Low mineral water has gained increasing attention due to its potential health implications concerning bone mineral density (BMD) and dental health. Reverse osmosis (RO) systems to purify water are in use extensively, and these systems, in addition to removing impurities from water, also remove 92-99% of beneficial minerals like calcium, lead, fluoride, magnesium, and iron. These minerals are essential for maintaining optimal mineral density of teeth and bones, thereby preserving bone and teeth health. Most of these mineral components are physically larger than water molecules and are trapped by the semi-permeable membrane of RO filters when drinking water is filtered through it. The resultant water is of very poor mineral content, and studies have shown that this water, when consumed, can absorb minerals from the body and eliminate the same through urine. The combined synergistic effect of consumption of low mineral water along with minerals being excreted has been shown to cause demineralization of bones and teeth, increasing the risk of osteoporosis and dental caries. This review tries to address the ill effects of consuming low mineral water along with preventive strategies to overcome its much-concealed adverse effects.

A Review of Pectin-Based Material for Applications in Water Treatment

Climate change and water are inseparably connected. Extreme weather events cause water to become more scarce, polluted, and erratic than ever. Therefore, we urgently need to develop solutions to reduce water contamination. This review intends to demonstrate that pectin-based materials are an excellent route to detect and mitigate pollutants from water, with several benefits. Pectin is a biodegradable polymer, extractable from vegetables, and contains several hydroxyl and carboxyl groups that can easily interact with the contaminant ions. In addition, pectin-based materials can be prepared in different forms (films, hydrogels, or beads) and cross-linked with several agents to change their molecular structure. Consequently, the pectin-based adsorbents can be tuned to remove diverse pollutants. Here, we will summarize the existing water remediation technologies highlighting adsorption as the ideal method. Then, the focus will be on the chemical structure of pectin and, from a historical perspective, on its structure after applying different cross-linking methods. Finally, we will review the application of pectin as an adsorbent of water pollutants considering the pectin of low degree methoxylation.

Calculation of the contribution of water to calcium intake in low- and middle-income countries

Dietary calcium intake is low in many countries, particularly in low- and middle-income countries (LMICs). Water is often overlooked as a source of dietary calcium despite it being universally consumed and providing good calcium bioavailability. Our objective was to assess water distribution systems in LMICs and to develop a formula to simulate the contribution of different water sources to calcium availability. We calculated the contribution of drinking water considering different calcium concentration levels to estimate total calcium availability. We consider a country's households' access to drinking water sources and the distribution of the country's population by age and gender. Calcium availability could be increased by an average of 49 mg of calcium per person per day in the 62 countries assessed if calcium in drinking water was considered. In 22 (31%) of the countries studied, 80% of households are supplied by water sources that could increase calcium availability. Improving calcium concentration in water could be considered as a strategy in LMICs to slightly improve calcium availability.

Drinking Water Quality and Public Health in the Kathmandu Valley, Nepal: Coliform Bacteria, Chemical Contaminants, and Health Status of Consumers

Residents of Nepal’s Kathmandu Valley draw drinking water from tube wells, dug wells, and stone spouts, all of which have been reported to have serious water quality issues. In this study, we analyzed drinking water samples from 35 tube wells, dug wells, stone spouts, and municipal tap water for bacterial and chemical contaminants, including total and fecal coliform, aluminum, arsenic, barium, beryllium, boron, cadmium, cobalt, chromium, copper, fluoride, iron, mercury, manganese, molybdenum, nickel, lead, antimony, selenium, thallium, uranium, vanadium, and zinc. We also asked a sampling of households who used these specific water sources to rate the taste of their water, list any waterborne diseases they were aware of, and share basic health information about household members. This survey provided us with information from 146 households and 603 individuals. We found widespread bacterial contamination of water sources, with 94% of sources having detectable total or fecal coliform. Nepal Drinking Water Quality Standards and World Health Organization (WHO) Drinking-Water Guidelines or health-based values were exceeded for aluminum (max = 0.53 mg/L), arsenic (max = 0.071 mg/L), iron (max = 7.22 mg/L), and manganese (max = 3.229 mg/L). The distribution of water sources with high arsenic, iron, and manganese appeared to be associated with floodplain deposits. Mixed effects logistic regression models were used to examine the interactions between social factors and water contaminants and their effects on household members’ health. Consumers of water sources with both high and low concentrations of manganese were less likely to have a positive attitude towards school than those whose water sources had moderate concentrations of manganese. Social factors, especially education, played a large role in predicting individual health outcomes. Household taste ratings of drinking water were not correlated with iron or manganese concentrations, suggesting that WHO’s reliance on aesthetic criteria for these contaminants instead of formal drinking-water guidelines may not be sufficient to protect public health.

Evaluation of Performance of Existing RO Drinking Water Stations in the North Central Province, Sri Lanka

Reverse osmosis (RO) drinking water stations have been introduced to provide safe drinking water for areas with prevailing chronic kidney disease with unknown (CKDu) etiology in the dry zone of Sri Lanka. In this investigation, RO drinking water stations established by community-based organizations (CBO) in the North Central Province (NCP) were examined. Water samples were collected from source, permeate, and concentrate in each station to determine water quality and performance. Furthermore, the operators of the systems were interviewed to evaluate operational and maintenance practices to identify major issues related to the RO systems. Results show that the majority (>93%) of RO systems had higher salt rejection rates (>92%), while water recovery varied from 19.4% to 64%. The removal efficiencies of hardness and alkalinity were averaged at 95.8% and 86.6%, respectively. Most dominant ions such as Ca²⁺, Mg²⁺, K⁺, Na⁺, Ba²⁺, Sr²⁺ Cl⁻, F⁻, and SO₄²⁻ showed higher rejections at averaged values of 93.5%, 97.4%, 86.6%, 90.8%, 95.4%, 96.3%, 95.7%, 96.6%, and 99.0%, respectively. Low recovery rates, lower fluoride levels in product water, and membrane fouling were the main challenges. Lack of knowledge and training were the major issues that could shorten the lifespan of RO systems.

Nutrient Effect on the Taste of Mineral Waters: Evidence from Europe

In this study, 15 selected bottled mineral waters from chosen European countries were tested for their mineral nutrient contents. In particular, six important nutrients (Ca2+, Mg2+, Na+, K+, HCO3-, Cl-) were measured using atomic absorption spectroscopy. The content of mineral nutrients in all sampled mineral waters were compared to their expected content based on the label. Consequently, their taste was evaluated by 60 trained panelists who participated in the sensory analysis. The results from both the atomic absorption spectroscopy and sensory analysis were analyzed using the regression framework. On the basis of the results from the regression analysis, we determined to what extent the individual mineral nutrients determined the taste of the mineral water. According to the regression results, four out of six analyzed nutrients had a measurable impact on taste. These findings can help producers to provide ideal, health-improving nutrients for mineral water buyers.

Multi-parametric assessment of biological stability of drinking water produced from groundwater: Reverse osmosis vs. conventional treatment

Although water produced by reverse osmosis (RO) filtration has low bacterial growth potential (BGP), post-treatment of RO permeate, which is necessary prior to distribution and human consumption, needs to be examined because of the potential re-introduction of nutrients/contaminants. In this study, drinking water produced from anaerobic groundwater by RO and post-treatment (ion exchange, calcite contactors, and aeration) was compared with that produced by conventional treatment comprising (dry) sand filtration, pellet softening, rapid sand filtration, activated carbon filtration, and UV disinfection. The multi-parametric assessment of biological stability included bacterial quantification, nutrient concentration and composition as well as bacterial community composition and diversity. Results showed that RO permeate remineralised in the laboratory has an extremely low BGP (50 ± 12 × 10³ ICC/mL), which increased to 130 ± 10 × 10³ ICC/mL after site post-treatment. Despite the negative impact of post-treatment, the BGP of the finished RO-treated water was >75% lower than that of conventionally treated water. Organic carbon limited bacterial growth in both RO-treated and conventionally treated waters. The increased BGP in RO-treated water was caused by the re-introduction of nutrients during post-treatment. Similarly, OTUs introduced during post-treatment, assigned to the phyla of Proteobacteria and Bacteroidetes (75-85%), were not present in the source groundwater. Conversely, conventionally treated water shared some OTUs with the source groundwater. It is clear that RO-based treatment achieved an extremely low BGP, which can be further improved by optimising post-treatment, such as using high purity calcite. The multi-parametric approach adopted in this study can offer insights into growth characteristics including limiting nutrients (why) and dominating genera growing (who), which is essential to manage microbiological water quality in water treatment and distribution systems.