Finanzierung: | Alexander Von Humboldt Stiftung |
Laufzeit: | 01.12.2024 – 30.11.2026 |
Projektbearbeitung: | |
Problemstellung: | The presence of high concentrations of ionic contaminants in groundwater reservoirs pose a serious threat to humans and environment. Amongst, selenium (Se) oxyanions have been recorded in groundwater because of mining, petroleum refining, fossil fuel combustion, and irrigation [2]. In accordance, high Se concentration i.e., 2103 μg/L, 800 μg/L, 2700 μg/L and 4475 μg/L have been found in Soan Sakesar Valley, Pakistan; Atacama Desert, Chile; Martin Creek Reservoir, Texas, USA; and Sirmaur district of Himachal Pradesh, India; respectively [3]. Nevertheless, Se is an essential mineral required by human body however it becomes noxious when found in greater concentrations in drinking water supplies. The oral intake of higher Se concentration (>400 μg/day) may cause serious health problems including reproductive anomalies and developmental abnormalities in foetus, hair loss, body pain, muscle damage, liver and kidney failure, cancer, and even death may occur. Therefore, German drinking water ordinance, World Health Organization (WHO) and U.S. Environmental Protection Agency has set Drinking Water Regulation Limit (DWRL) for Se as 10 μg/L, 40 μg/L and 50 μg/L, respectively [4,5]. To meet stringent Se guidelines and ensure public health safety, an efficient and technoeconomic feasible treatment approach is needed. Amongst, adsorption technology utilizing commercial iron-based adsorbents has shown promising performance for removing contaminants including metal oxyanions from a wide range of water matrices. However, eliminating Se from drinking water is challenging owing to its toxicity, solubility and varying oxidation states. It is commonly found in environment as selenate (Se(VI): HSeO4‾, SeO42-), selenite (Se(IV): H2SeO3, HSeO3‾, SeO32-), selenium (Se(0)) and selenide (Se(-II): H2Se, HSe‾) depending on pH and redox conditions [2]. Previous research [6–8] has shown wide applicability of commercially available iron-based adsorbent i.e., granular ferric hydroxide (GFH) for removal of other oxyanions including arsenic, phosphate, vanadium etc. from water. Therefore, it may be hypothesized that GFH may contain potential in eliminating toxic Se oxyanions from drinking water supplies. In addition, release of iron from poorly crystalline GFH structure into the solution particularly at low redox potential, leading to its higher residual content, has been rarely investigated. Therefore, it will be critical to examine the stability of GFH at long term operations along with its effectiveness in remediating targeted contaminants. In accordance, little is known on how Se oxyanions will behave and react with GFH in aqueous environment. It will therefore be worth exploring the mechanistic insights into the fate, mobility, transformation, and removal behavior of Se species under environmentally relevant conditions. In addition to commercial adsorbents, prior research has focused on utilization of iron-based sorbents for Se remediation from drinking water, however, all these studies only discussed in-depth understanding of batch mode operation [9]. Moreover, there always remains a research gap in utilizing adsorbent material in GEH® adsorbent unit for continuous mode Se treatment from drinking water supplies. Therefore, the planned project aims to address these research gaps and provide practical and sustainable solution to drinking water industries when dealing with toxic Se oxyanions. |
Vorgehensweise: | The goal of this research is to initially investigate the adsorption performance and iron leaching aspects of GFH upon its contact with toxic selenium (Se) oxyanions under a series of batch mode laboratory experiments in various solution chemistries (e.g., GFH dosage, solution pH, contact time, suspension temperature, initial Se(IV, VI) concentration, coexisting ions etc.). Mathematical models on experimental results and characterization techniques on virgin and spent GFH will be later employed to explore mechanistic insights into adsorption and transformation behavior of Se oxyanions in water. The research work will then be expanded to small-scale continuous mode GEH® adsorbent unit for Se removal from drinking water, where GFH loading rates and initial Se oxyanions level will be tested in synthetic test solutions as well as real raw waters at long term operations. To achieve the Se permitted value of 10 μg/L in drinking water and to optimize the Se removal process using GFH, a response surface approach will be employed. The spent GFH media will be examined for various physiochemical variations at different bed depths using analytical techniques. In conjunction with technical aspect, economic feasibility of GEH® adsorbent unit will also be evaluated.
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