Yan Zheng is a chair professor at Southern University of Science and Technology. In 1983, at the age of 14, he was admitted to the Department of Earth and Space Sciences of the University of Science and Technology of China from Zunyi, Guizhou. Due to her continuous skipping in primary and secondary school, she was only 14 years old when she graduated from high school. With her dream of going to the moon, she chose Earth and Space Science as her major. After graduating from the University of Science and Technology of China, Yan Zheng went to the United States for further study and received a Ph.D. in marine geochemistry from Columbia University. At the age of 37, she became a tenured full professor at the City University of New York, where she served as Dean of the School of Earth and Environment. In 2016, Yan Zheng resigned from his tenured position in the United States and joined Southern University of Science and Technology as a chair professor, reorganizing the laboratory and carrying out new research projects. Her research interests include marine geochemistry, hydrogeology, methods of water chemistry, drinking water safety, environmental risks and human health, and sustainable development. She has led dozens of research projects funded by the Chinese and U.S. governments and has published more than 100 academic papers. He is currently or has served as an associate editor or editor-in-chief of an international journal (Environmental Health Perspective, Journal of Geochemical Exploration, Science of the Total Environment, Science Bulletin). In 2010, he was elected a Fellow of the Geological Society of America. Yan Zheng has held important positions in various academic institutions and international organizations, including Chair Professor at Peking University, Assistant Professor and Tenured Professor and Director of the School of Environmental and Earth Sciences at the City University of New York at Queens, tenured professor in the Division of Chemistry at the Graduate School of the City University of New York, tenured professor at the School of Public Health at the City University of New York, and UNICEF Water and Sanitation Programme Specialist in Bangladesh. During her tenure at the United Nations, she led a team of about 20 people who applied the results of her years of research to the development of groundwater resources in Bangladesh to address the drinking water security of 2 million people exposed to high arsenic. After the Science review, Nature Water is reissued: Pay attention to arsenic treatment in water! In nature, inorganic arsenic (iAs) in water, usually in the form of As(III), is a major public health concern of the World Health Organization in more than 70 countries. Long-term consumption of water containing more than 10 mcg/L iAs can lead to a variety of cancer and non-cancer health problems, increasing mortality and morbidity. Globally, an estimated 9.4 to 220 million people are at risk of arsenic contamination, mainly those in rural areas who depend on well water. High-income countries have reduced arsenic exposure through expensive home treatment of iron-based adsorbent media ($2,740 to install and maintain, or about $1 per day), but for low-income households, it is more economically feasible to use POU treatment (deep water purification treatment). POU technology, despite its limited success in reality, has significant advantages in treating drinking and cooking water. Studies have shown that the removal of As(III) by iron-based and titanium oxide filter media remains challenging, requiring prolonged exposure and slower flow rates, as well as pre-oxidation steps such as chloride and hydrogen peroxide to improve effectiveness.
在这里，南方科技大学郑焰教授课题组联合史蒂文斯理工学院Xiaoguang Meng教授报告了MnO2 改性活性炭被集成到以颗粒状纳米 TiO2 作为主要吸附剂的使用到POU系统，进行了两次实际测试，以低于 0.01 美元每升的价格提供 As 安全水。 一项为期 4 个月的部署处理（deployment treated）了 4,200 个床容积(bed volume，~2.1 m3) 的地下水，其中含有 69 ± 16 μg/L As (78 ± 5% As(III))。 另一项为期 28 个月的部署处理了 10,000 个床容积 (~5.0 m3) 的地下水，其中含有 42±21μg /L As (33±21% As(III)) (图1) 。 地下水基质和过滤介质之间的相互作用会影响性能，突出表明需要通过长期部署来验证家庭除砷技术。 相关成果以“MnO2-modified activated carbon and granular nano-TiO2 in tandem succeed in treating domestic well water arsenic at point of use”为题发表在《Nature Water》上，第一作者位Yanhua Duan。
Figure 1: Schematic diagram of the kitchen sink POU used for arsenic removal during the 28-month deployment and recording of the volume and water consumption of the treated water The long-term deployment of the POU was successful in the As treatment In the four-month deployment (NJ), the F3 treatment system treated about 2.1 cubic meters of well water with a total arsenic (As) concentration of more than 10 μg/L. The concentrations of total arsenic and As(III) in untreated water were 54-92 μg/L and 43-70 μg/L, respectively, with 78±5% arsenic being As(III) (Figure 1). During treatment, the removal rates of total arsenic, As(III), and As(V) were 96±3%, 97±4%, and 91±3%, respectively (Figure 2b). Mass balance calculations showed that the POU system removed 101 mg of As(III), 129 mg of total arsenic, and 2911 mg of iron, and released 454 mg of manganese. During the entire deployment, the system removed 134 mg of As(III), 170 mg of total arsenic and 4,379 mg of iron, and released 1,232 mg of manganese. In 28 months of deployment (YC), after the system treated about 5 cubic meters of water, the As(III) removal effect failed (Figure 2e). Over a period of 28 months, the system removed 64 mg of As(III), 281 mg of total arsenic, and 1,785 mg of iron, and released 2,535 mg of manganese. Prior to failure, phosphate and silicate were removed at 43% and 80%, respectively. The removal of As(III) by the POU filter was 86±10% in 3.12 cubic meters of influent water, but then decreased (Figure 2f). In comparison, the removal rate of As(V) in the first 5.53 cubic meters of influent water remained at 96±6%. After the water source switch, the total arsenic and As(III) concentrations in the treated water exceeded 10 μg/L, but the removal of As(V) was still as high as 97% (Figure 2f). During deployment, the system removed 64 mg of As(III), but only 27 mg was captured by the filter, indicating that 58% of As(III) was oxidized during or after adsorption.
Figure 2: Composition of influent and effluent water versus treated water MnO2-AC filter oxidizes Fe(II) and As(III) to help remove As The first MnO2-AC filter was designed to oxidize As(III), but reducing species in groundwater, such as Fe(II)), react with MnO2. At 2.1 m³, Mn failed at F3 and reached a few milligrams per liter after F1 (Figure 2d), indicating that MnO2 was reduced and dissolved by Fe(II) and that the iron content after F1 was low (Figure 2c). This is because arsenic-rich groundwater mainly contains ferrous iron. Most of the iron oxide in the YC deployment is captured by the medium in F1, and the HCl in F1 extracts Fe as Fe(III) (Fig. 3d, e). The tap water in YC is transported through village pipes, resulting in a very low concentration of Fe(II) in the influent (Figure 2g), but retains a modest and variable As(III) ratio (Figure 2e). Throughout NJ (Figure 2c) and YC (Figure 2g) deployments, Fe levels in effluent remained low, and Fe captured in F1 provided an additional As removal pathway. In NJ, F1 removed 39 mg of arsenic, accounting for 23% of the total POU retained arsenic (Figure 2a). In YC, 45 mg of arsenic accumulated on F1, accounting for 22% of the total cumulative arsenic (204 mg). The complexity of the interaction of Fe, Mn, and As in F1 suggests the importance of long-term deployment studies. Although the abundance of arsenic-associated microorganisms is too low to be detected, arsenic adsorption removal including MnO2 pre-oxidation may be abiotic. However, the relative abundance of iron-oxidizing bacteria in the three filters (Figure 4a) suggests that the Fe(II)-Fe(III) reaction may be microbial-mediated, involving a redox reaction involving N and S (Figure 4b, c).
Figure 3: Arsenic, iron, and manganese in 5 of the 3 filters treated media samples captured most of the As and MnGTO filters had two important functions: adsorbed most of the arsenic (As) and captured most of the manganese (Mn) released by F1. During the 28-month deployment of YC, nanoTiO2 captured approximately 157 mg of arsenic (77% of total arsenic removed), including 23 mg of As(III). During NJ's 4-month deployment, nanoTiO2 captured approximately 131 mg of arsenic (77% of total arsenic removed). The effluent of F1 contains As(V) and Mn(II) and is captured by the nanoTiO2 in F2, resulting in the highest As and Mn concentrations (Figure 3a,f). Nano TiO2 forms a highly stable composite structure with As. The tandem configuration of MnO2-AC and GTO prevents Mn from entering the treated water. Deployments in New Jersey and YC have demonstrated that the GTO is effective at capturing Mn, where 96±3% of Mn is removed by nanoTiO2 in F2. In YC, failure of Mn is observed at approximately 10,000 bed volumes (Figure 2h). The capture of Mn by nano-TiO2 in F2 may involve biological oxidation to form secondary Mn oxides.
Figure 4: Microbial-mediated Fe, N, and S reactions in YC POUs Discussion and Compact POU tandem configuration have three major advantages: First, the cartridge can be easily loaded into a standard POU filter, effectively removing As(III) and As(V) at a low cost. Secondly, maintenance is simple, only the filter element needs to be replaced. Third, where Mn and As fail at the same time (Fig. 2a, d, e, h), the health recommended level of Mn serves as a warning of As breakout. On-site colorimetric measurement of Mn is cheaper and easier than arsenic detection, and households can monitor Mn and test its levels in wastewater on their own. Long-term deployment under the kitchen sink of rural households, the small POU arsenic removal unit composed of MnO2-AC and GTO series successfully treated well water with high arsenic content, demonstrating its user-friendliness and competitive cost advantages. Overall, such installations have the potential to provide drinking and cooking water for low-income households, but they still need to be improved to protect the health of the rural population at large.
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Source: Frontiers of Polymer Science