Although drinking water is the main source of fluoride intake, recent studies reported that fluoride intake from foods could also be high, depending on cooking methods. In this study, we quantified the fluoride accumulation in foods soaked or boiled in fluoride-containing water and assessed the fluoride intake in different age groups from food and drinking water. We observed that, in the case of rice soaked in fluoride-containing water, more fluoride was accumulated in the rice than previously estimated. Fluoride interferes with the iodine staining process of rice, indicating fluoride adsorption. Fluoride accumulation in rice and vegetables increased when the soaking temperature was raised to 100 °C due to the gelatinization of rice grains and softening of vegetables. Ingesting foods boiled in fluoride-containing water increased the fluoride intake per body weight of infants more significantly than that in children and adults due to their low body weight. These results indicate that soaking and boiling foods in fluoride-containing water significantly increases fluoride intake compared to previous estimations. Therefore, it is necessary to re-evaluate the fluoride intake from food and drinking water considering the methods used for cooking food in each country and region.

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.

Fluoride intake from tap water supplied by fluoride-containing groundwater has been the primary cause of fluorosis among the residents of Buak Khang Subdistrict, Chiang Mai Province, Thailand. To reduce fluoride intake, bottled water treated using reverse-osmosis membranes has been made available by community-owned water treatment plants. This study aimed to assess the resultant reduction in fluoride intake from using bottled water for drinking and cooking. Water consumption surveys were conducted by providing bottled water to 183 individuals from 35 randomly selected households and recording the amount of water consumed for drinking and cooking. The mean drinking water consumption was 1.62-1.88 L/capita/day and the cooking water consumption on weekends (5.06 ± 3.04 L/household/day) was higher than that on weekdays (3.80 ± 1.90 L/household/day). The per capita drinking water consumption exhibited a positive correlation with body weight; however, the low-weight subjects consumed more drinking water per kilogram of body weight than the heavy subjects. Although sex and day of the week did not significantly affect drinking water consumption per capita, girls consumed less water in school possibly due to their group mentality. Drinking water consumption per kilogram of body weight was significantly higher among women, children, and the elderly because these groups generally have low body weights. The fluoride intake from using tap water for drinking and cooking was estimated to be 0.18 ± 0.10 mg/kg-body weight/day and 5.55 ± 3.52 mg/capita/day, respectively, whereas using bottled water for drinking and cooking reduced the fluoride intake to 0.002 ± 0.002 mg/kg-body weight/day and 0.07 ± 0.05 mg/capita/day, respectively. Despite the increased cost, 98% and 90% of the subjects selected bottled water over tap water for drinking and cooking, respectively; thus, bottled water delivery services could be used to mitigate fluoride intake in developing countries.

Iron and manganese in groundwater impair the quality of drinking water; however, the rates of iron and manganese removal with conventional aeration and rapid sand filtration (RSF) processes vary extensively. Five full-scale aeration–RSF processes in Nepal also showed varying efficiencies of iron and manganese removal; while the iron concentration was below the national standard (0.30 mg/L) in 31 out of the 37 treated waters, the manganese concentration was higher than the standard (0.20 mg/L) in all of the treated waters. Re-aeration and stirring of the treated water did not oxidize soluble manganese, and this caused the poor removal rates for manganese. Bench-scale dual-media filters comprising anthracite on top of sand/ceramic layers with dosages of poly aluminum chloride and chlorine worked well by removing coagulated iron in the anthracite layer and then removing manganese in the sand/ceramic layers. A manganese-oxide-coated ceramic filter provided the highest manganese removal from 1.10 mg/L to <0.01 mg/L, followed by manganese-oxide-coated sand and quartz sand. Increasing the pH from 7.5 to 9.0 stabilized the manganese removal. Therefore, we propose a re-design of the present treatment processes and the selection of suitable filter media for better removal of iron and manganese.

Bali Province, Indonesia, experiences serious water shortages and groundwater over-abstraction due to rapidly increasing water demand. Therefore, this study aimed to assess the potential for water reclamation and reuse in Bali Province, focusing on the operational performance of two wastewater treatment plants (WWTPs). Although the Suwung WWTP could increase its treatment capacity to produce reclaimed water for irrigation and landscape, there are multiple management issues to be addressed, including fluctuating water demand, limited customer base beyond hotels, concerns about water quality and safety, and cultural perceptions of reclaimed water. In addition, despite the organic loading rates being lower than the design value, the treatment performance of the Suwung WWTP was found to be significantly lower than that of the ITDC WWTP, which achieved high BOD, COD, and TSS removal rates by performing good maintenance of aerators and post-treatment based on dissolved air flotation (DAF). Causal loop analysis indicates that aerator malfunctioning causes multiple problems, such as low dissolved oxygen, poor BOD removal, sludge carryover, and low sludge concentrations. Therefore, regular maintenance of aerators, as well as the development of aerators robust against malfunctioning, are fundamental to producing effluents from stabilization ponds that meet the requirements for irrigation and landscape reuse.

Globally, scale deposition in water supply pipelines is one of the major problems faced by water utilities. This research aimed to determine the causes and effects of scale deposition in the water supply pipelines in Surakarta City, Indonesia. The total dissolved solids (TDS), hardness, manganese, and alkalinity in groundwater were higher than those in the surface water and spring water; thus, the supply areas from groundwater were identified using TDS at the taps. The three scaling indicators, i.e., the Langelier saturation index (LSI), the Ryznar stability index (RSI), and the Puckorius scaling index (PSI), indicated moderate calcium carbonate scaling. However, elemental analysis of eight scale samples using X-ray fluorescence (XRF) revealed that the major components of scale were either manganese (50.1–80.8%) or iron (45.6–63.8%), whereas calcium (3.0–7.8%) was a minor component. Because only five of twenty groundwater sources were chlorinated before distribution, it is estimated that dissolved manganese is oxidized by manganese-oxidizing bacteria. The manganese deposition rate in the networks was estimated to be 1660 kg/year using the manganese concentration at groundwater sources and in customers’ taps. These results suggest the importance of the elemental analysis of scale and avoidance of overreliance on scale indicators.