The co-precipitation of Fe(III) (oxyhydr)oxides with arsenic (As) is one of the most widespread approaches to treat As-contaminated groundwater in both low- and high-income settings. Fe-based co-precipitation of As occurs in a variety of conventional and decentralized treatment schemes, including aeration and sand filtration, ferric chloride addition and technologies based on controlled corrosion of Fe(0) (i.e., electrocoagulation). Despite its ease of deployment, Fe-based co-precipitation of As entails a complex series of chemical reactions that often occur simultaneously, including electron-transfer reactions, mineral nucleation, crystal growth, and As sorption. In recent years, the growing use of sophisticated synchrotron-based characterization techniques in water treatment research has generated new detailed and mechanistic insights into the reactions that govern As removal efficiency. The purpose of this critical review is to synthesize the current understanding of the molecular-scale reaction pathways of As co-precipitation with Fe(III), where the source of Fe(III) can be ferric chloride solutions or oxidized Fe(II) sourced from natural Fe(II) in groundwater, ferrous salts or controlled Fe(0) corrosion. We draw primarily on the mechanistic knowledge gained from spectroscopic and nano-scale investigations. We begin by describing the least complex reactions relevant in these conditions (Fe(II) oxidation, Fe(III) polymerization, As sorption in single-solute systems) and build to multi-solute systems containing common groundwater ions that can alter the pathways of As uptake during Fe(III) co-precipitation (Ca, Mg bivalent cations; P, Si oxyanions). We conclude the review by providing a perspective on critical knowledge gaps remaining in this field and new research directions that can further improve the understanding of As removal via Fe(III) co-precipitation.

Industrial wastewater containing heavy metals, such as Cd and Pb, must be treated prior to discharge to meet increasingly stringent discharge guidelines and to limit the impact of toxic metals on ecosystems and human health. The application of olivine particles is a natural mineral-based solution to treat heavy metal-laden wastewaters, but little is known about the efficiency and mechanism of metal removal by this solid phase. In this work, we investigate the potential of olivine for heavy metal treatment by combining batch metal removal experiments with solid-phase characterization by synchrotron-based X-ray techniques and electron microscopy. We probed the removal behaviour of a variety of metal contaminants (Co, Ni, Cd, Zn, Cu, Pb; initial concentration = 1500 µg/L) and used Zn specifically to identify the metal removal pathway of olivine. We found that olivine in powdered (0.3 g/L) and granulated (0.5 g/L) forms was able to remove up to >90% of the initial metal, depending on the metal identity, with the efficiency increasing in order of Co ≤ Cd ≤ Ni <Zn<Cu<Pb. This order matches the well documented selectivity sequence of other common mineral sorbents (e.g., Fe(III) and Mn(IV) (oxyhydr)oxides). In addition, metal removal was intimately linked to increases in pH during reaction (e.g., from pH 7 to 10), due presumably to H+ consumption by SiO44− ions released during olivine dissolution. Molecular-scale characterization of the solid reaction products revealed that metal removal occurred via secondary precipitation of distinct metal carbonates and silicates, which was promoted by the increase in pH, although metal adsorption to olivine surfaces might also occur at lower pH. Overall, our study provides strong evidence for the potential of olivine minerals for treatment of heavy metal-laden industrial wastewaters.

Nanotechnology is one of the most rapidly developing areas of science, with great potential to solve the developmental challenges in a wide range of industries such as aerospace, agriculture, bioengineering, cosmetics, chemicals, electronics, energy, renewables, surface coatings, textiles, medicine, materials manufacturing, military equipment, etc. To compile this book, distinguished scientists, engineers, and industrial professionals from different parts of the world have been invited. An array of 17 high-quality science-based chapters covering recent advancements, challenges, and future trends in industrial applications of nanotechnology is presented. The book is aimed at industrial professionals and graduate-level students and researchers.

Geogenic contamination of groundwater due to elevated fluoride (F-) concentrations is a significant issue worldwide (including in Tanzania). The present study focussed to assess the adsorption capacity of thermally treated (calcined) bauxite to remove the F- from contaminated water. Characterization of bauxite by X-ray fluorescence spectroscopy (XRF) revealed Al2O3, Fe2O3, and SiO2 as the major oxides in both raw and calcined bauxite. The major mineral phase in the raw bauxite was gibbsite, which disappeared after calcination. The optimum calcination temperature, dosage and contact time for F- removal by calcined bauxite were 400 degrees C, 40 g/L and 8 min, respectively. The experimental data revealed Freundlich isotherm as the best model to fit the F -adsorption process with kF and 1/n being 0.1537 mg/g and 0.8607, respectively. The pseudo-second-order ki-netic and intra-particle diffusion models explained well the F- adsorption process with the rate constants of 115.43 g/mg min and 0.0025 mg/g min0.5, respectively. The values of Delta G, Delta H and Delta S indicate the F- adsorption on bauxite surface indicated that the adsorption process was spontaneous, endothermic and structural changes occurred during the adsorption process. The F- adsorption under optimum conditions lowered the pH and F -concentration to WHO and Tanzania Bureau of Standards (TBS) standards.

Arsenic (As) removal studies were carried out through batch experiments to investigate the performance of the locally available calcined magnesite mineral rocks from Tanzania. Natural water from a stream source in Tanzania and the prepared synthetic water at the laboratory were used for the studies. Parameters such as initial As concentration, calcined magnesite dosage, contact time and pH were evaluated for As removal using an overhead rea×2 shaker. Arsenic concentration was reduced from 5.3 to 1.1 mg/L As(V) at 180 min when 0.5 g/L calcined magnesite was applied to a synthetic water sample, whereas the concentration of 117 μg/L As(V) and 5.2 μg/L As(III) was reduced to below 0.1 μg/L in natural water. An increase in calcined magnesite dosage resulted in increased As removal up to below 0.01 mg/L. The calcined magnesite raised the pH of the water sample from 6.8 to 10 when the applied dosage increased between 0.002 g/L and 0.05 g/L. The pH was constant at around 10 even when the amount of 0.05 g/L was added 2000 times. Despite the high pH, the amount of magnesium released in water was low. The calcination of magnesite at 500 ◦C increased surface area by 4 times as compared to the natural magnesite and X-ray diffraction showed presence of MgCO3 phase as the dominant phase at this temperature. The reaction kinetics of As removal on 0.5 g/L calcined magnesite fitted with the pseudo-second-order (R2 = 0.96). Reaction isotherm was strongly fitted with Freundlich isotherm (R2 = 0.98). Linear regression and artificial intelligence neural network showed the As removal was influenced by both contact time and pH. Arsenic can be removed from As water using calcined magnesite and will be suitable for water treatment around gold mining areas. 

Rapid sand filtration is a widely used technology to remove suspended solids in drinking water and wastewater treatment plants. One of the challenges of the rapid sand filtration is to reliably predict the removal efficiency of suspended solids and pressure drop as a function of filtration time. In this study we put forward a novel CFD model to simultaneously predict the solids concentration in the effluent and hydraulic resistence build-up in rapid sand filters. The CFD model is assessed against lab scale filtration data at different filter media grain sizes and filtration velocities. Our results show an overall satisfactory agreement with the observations. Finally, we highlight the complexity and need for further work in developing general CFD models for rapid sand filtration.

In the past two decades, several studies on arsenic (As) occurrence in the environment, particularly in surface and groundwater systems have reported high levels of As in some African countries. Arsenic concentrations up to 10,000 mu g/L have been reported in surface water systems, caused by human activities such as mining, industrial effluents, and municipal solid waste disposals. Similarly, concentrations up to 1760 mu g/L have been reported in many groundwater systems which account for approximately 60% of drinking water demand in rural Africa. Naturally, As is mobilized in groundwater systems through weathering processes and dissolution of As bearing minerals such as sulfides (pyrite, arsenopyrite, and chalcopyrite), iron oxides, other mineralized granitic and gneissic rocks, and climate change factors triggering As release in groundwater. Recently, public health studies in some African countries such as Tanzania and Ethiopia have reported high levels of As in human tissues such as toenails as well as in urine among pregnant women exposed to As contaminated groundwater, respectively. In urine, concentrations up to 150 mu g/L were reported among pregnant women depending on As contaminated drinking water within Geita gold mining areas in the north-western part of Tanzania. However, the studies on As occurrence, and mobilization in African water systems, as well as related health effects are limited, due to the lack of awareness. The current study aims to gather information on the occurrence of As in different environmental compartments, its spatial variability, public health problems and the potential remediation options of As in water sources. The study also aims at creating awareness of As contamination in Africa and its removal using locally available materials.

Groundwater contamination from geogenic sources paces challenges to many countries, especially in the developing world. In Tanzania, the elevated fluoride (F-) concentration and related chronic fluorosis associated with drinking F- rich water arc common in the Fast African Rift Valley regions. In these regions, F- concentration is space dependence which poses much uncertainty when targeting safe source for drinking water. To account for the spatial effects, integrated exploratory spatial data analysis, regression analysis, and geographical information systems tools were used to associate the distribution of F- in groundwater with spatial variability in terrain slopes, volcanic deposits, recharge water/vadose materials contact time, groundwater resource development for irrigated agriculture in the Sanya alluvial plain (SAP) of northern Tanzania. The F- concentration increased with distance from steep slopes where the high scale of variation was recorded in the gentle sloping and flat grounds within the SAP. The areas covered with debris avalanche deposits in the gentle sloping and flat grounds correlated with the high spatial variability in F- concentration. Furthermore, the high spatial variability in F- correlated positively with depth to groundwater in the Sanya flood plain. In contrast, a negative correlation between F- and borehole depth was observed. The current irrigation practices in the Sanya alluvial plain contribute to the high spatial variability in F- concentration, particularly within the perched shallow aquifers in the volcanic river valleys. The findings of this study arc important to the overall chain of safe water supply process in historically fluorotic regions. They provide new insights into the well-known F- contamination through the use of modern geospatial methods and technologies. In Tanzania's context, the findings can improve the current process of drilling permits issuance by the authority and guide the local borehole drillers to be precise in siting safe source for drinking water.