Browsing by Author "Shen, Junjie"

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Removal of fluoride from water using activated carbon fibres modified with zirconium by a drop-coating method.
(Elsevier Ltd, 2020-09-01) Pang, Tianting; Aye Chan, Thet Su; Shen, Junjie; Jande, Yusufu
Metal-modified carbon materials have been widely used for fluoride removal, but the traditional impregnation by soaking method suffers from low loading of metals and substantial use of chemicals. This study proposed a new approach to prepare zirconium modified activated carbon fibres (Zr-ACF) by a drop-coating method. Using the same amount of chemicals, the drop-coating method yielded a 5.5 times higher fluoride adsorption capacity than the soaking method due to more effective loading of Zr(IV) onto ACF. The effects of various preparation conditions, including the addition of a complexing agent (oxalic acid) and Zr/ACF mass ratio (0.2-1), were investigated. Zr-ACF prepared by drop-coating was characterised by SEM and BET, and the functional groups involved in the anchoring of Zr(IV) on ACF and the adsorption of fluoride onto Zr-ACF were identified by FTIR and XPS. Adsorption experiments at pH between 3 and 11 revealed that ion exchange and electrostatic attraction were the main adsorption mechanisms at different pH levels. Co-existing anions such as CO, HCO and Cl had an insignificant negative impact (<5%) on fluoride adsorption capacity while SO decreased fluoride adsorption capacity by 11.5%. The adsorption kinetics followed the pseudo-second-order model. The adsorption isotherms followed the Langmuir isotherm model with a maximum fluoride adsorption capacity of 28.50 mg/L at 25 °C, which was higher than other carbon-based materials in the literature. The remarkable improvement of adsorption capacity and reduced chemical consumption demonstrate that Zr-ACF prepared by drop-coating is a promising adsorbent for fluoride removal.
Renewable energy powered membrane technology: Case study of St. Dorcas borehole in Tanzania demonstrating fluoride removal via nanofiltration/reverse osmosis
(Elsevier, 2016-10-01) Shen, Junjie; Richards, Bryce; Schäfer, Andrea
A brackish borehole located at a rural school in northern Tanzania contains excessive salinity (TDS = 3632 mg/L) and fluoride concentration (F− = 47.6 mg/L). This field study evaluated the feasibility of a solar-powered nanofiltration/reverse osmosis (NF/RO) system in treating this brackish water to make it potable. Key performance parameters such as permeate productivity, fluoride retention and specific energy consumption (SEC) were compared among four different NF/RO membrane modules (BW30, BW30-LE, NF90, and NF270). The NF90 membrane exhibited the best overall performance, balancing permeate productivity and quality, with 1582 L of clean drinking water being produced with an average SEC of 1.6 kWh/m3 over a solar day, while the NF270 could not meet the guideline values for fluoride. Further, the impact of fluctuating solar energy on system performance was studied. Very brief periods of heavy cloud cover in the afternoon affected transmembrane pressure and feed flow, and thus caused the permeate quality to temporarily exceed the guideline values. However, when considering that the permeate was stored in a product tank and was produced over the whole solar day, the system equipped with the NF90 membrane was able to produce high-quality drinking water that, on average, easily meets the guideline values despite the energy fluctuations.
Renewable energy-powered membrane technology in Tanzanian communities
(Nature Research, 2018-12-03) Schäfer, Andrea; Shen, Junjie; Richards, Bryce
Dissolved contaminants such as ions or organic matter require advanced technology for effective removal. Technologies such as membrane processes are to date absent in remote areas of developing countries, in part due to the absence of a reliable electricity grid to power such technologies, but also due to the large distances to be served in remote areas. By directly coupling a nanofiltration system with solar energy, the energy provision and storage obstacle can be resolved. Here, two very challenging natural waters were treated to drinking water standard without requiring permanent infrastructure: both water samples had very high concentrations of fluoride (50–60 mg/L), while one of them also had a high total organic carbon content (255 mg/L). In both cases the WHO guideline value of 1.5 mg/L for fluoride was achieved with the chosen membrane. The solar irradiance provided an unsteady power source, which did not impact on water quality in a significant manner. Given the somewhat extreme characteristics of the source waters, making such waters potable effectively increased the available water quantity. The technical feasibility of such a solar-powered ultrafiltration and nanofiltration hybrid system was demonstrated in terms of produced drinking water quantity (1200 L per solar day), water quality and specific energy consumption. While such state-of-the-art technology offers great potential towards the provision of clean water in rural areas, the remaining obstacles for effective implementation of such technologies are predominantly non-technical.