The waste water from the industrial production of the herbicide monosodium methyl arsenate was treated using coagulation. The coagulation process as developed in this research proved to be suitable for arsenic removal in aqueous media using chromium (III), calcium (II), and combination of calcium (II) and chromium (III), and magnesium (II). The results obtained suggest that the coagulation process can be used for the treatment of the waste water from the monosodium methyl arsenate production. Response surface methodology was used to study the effects of the various parameters, namely pH, mole ratios (Cr:As, Ca:As, and Mg:As), concentration of flocculent and initial arsenic concentration. To optimize the process conditions for the maximum removal of arsenic. Central composite and factorial designs were used to study the effects of these variables and to predict the effect of each. ANOVA was used to identify those factors which had significant effects on model quality and performance. The initial arsenic concentration appeared to be the only significant factor. These models were statistically tested and verified by confirmation experiments.

This research was directed at reducing arsenic levels in the effluents generated at the Canelands facility that manufactures monosodium methyl arsenate. Two effluent streams containing arsenic have to be considered, a raw water stream that is treated on site and a brine stream that is disposed of by sea outfall. Removal of arsenate from aqueous media by coagulation was investigated and models were developed describing selected variables that influence the removal of the arsenate. Three coagulant systems were investigated, namely aluminium(III) coagulation, iron(III) coagulation and binary mixtures of aluminium(III) and iron(III). Researchers have studied individual aluminium (III) sulphate and iron(III) chloride coagulation. No detailed research and modelling had, however, been carried out on the use of binary mixtures of aluminium (III) sulphate and iron (III) chloride coagulation of aqueous arsenate, nor had individual aluminium(III) sulphate and iron(III) chloride coagulation of arsenate been modelled at relatively high arsenate concentrations. The models that were generated were validated statistically and experimentally. The variables investigated in the aluminium(III) model included initial arsenate concentration, pH, polymeric flocculent concentration, aluminium(III) concentration and settling time. The variables modelled in the iron(III) coagulation were initial arsenate concentration, pH, polymeric flocculent concentration, and iron(III) to arsenic mole ratio. The modelling of the binary coagulant system included initial arsenate concentration, pH, iron (III) concentration, aluminium(III) concentration, and flocculent concentration as variables. The most efficient arsenic removal by coagulation was iron(III), followed by the binary mixture of aluminium(III) and iron(III) and the weakest coagulant was aluminium(III) sulphate. Scale-up coagulations performed on real raw water samples at a 50 litre volume showed that iron(III) was the most efficient coagulant (on a molar basis) followed closely by the binary mixture, while aluminium(III) coagulation was considerably weaker. The residual arsenic levels of the iron(III) and the binary coagulation systems met the effluent discharge criteria, but the aluminium coagulation system did not. Leaching tests showed that the iron(III) sludge was the most stable followed by the sludge of the binary mixture and the aluminium(III)-based sludge leached arsenic most readily. Settling rate studies showed that the flocs of the iron(III) coagulations settled the fastest, followed by binary mixture flocs and the aluminium flocs settled the slowest. The flocs of the binary mixture had the lowest volume, followed by the iron(III) flocs, while the aluminium(III) flocs were the most voluminous. Based on current operations of the raw water treatment plant the aluminium(III)-based coagulation is the most cost efficient. Given a relative costing of 1.00 for the aluminium(III) coagulation, the iron(III) chloride-based coagulation would be 2.67 times more expensive and the equimolar binary mixed aluminium(III)/iron(III) system would be 1.84 times the cost of aluminium(III) coagulation.

Arsenic contamination in drinking water is a severe problem worldwide. The best way to prevent hazardous diseases from chronic arsenic exposure is to remove the exposure. Efforts to remediate arsenic in drinking water have taken two tracks. One is to provide surface or shallow well water sources as an alternative to the arsenic contaminated deep wells. Another approach is to remove arsenic from the contaminated water. Different removal technologies like oxidation, chemical coagulation, precipitation, adsorption and others are available. There are problems and benefits associated with each of these approaches that can be related to cultural, socio-economic and engineering influences. The method proposed in this research is adsorption of arsenic to iron coated limestone. Different iron coated limestone samples were prepared. Standard solutions of 100ppb arsenic were prepared and batch and kinetic experiments were conducted. The final solution concentrations were analyzed by Graphite Furnace Atomic Adsorption Spectroscopy (GFAAs) and the results showed that iron coated limestone removed arsenic below 10ppb with 5 grams of material. Variations in iron coverage impacted efficiency of arsenic removal.

Inorganic arsenic exposure is a well-known toxicant of which we are still discovering harmful effects. People are exposed to inorganic arsenic in the environment through either drinking arsenic-contaminated groundwater or consuming arsenic-contaminated food. Regarding global public health, drinking water is still the most important source of inorganic arsenic exposure and is the main focus of this work. The overall goal of this dissertation is to answer some pointing epidemiological questions about exposure to inorganic arsenic: How much do we know about inorganic arsenic and non-malignant lung disease in the general population? To what extent are adolescents with lifetime arsenic exposure susceptible to the respiratory consequences seen in adults? And what actions can be taken to effectively reduce exposure from arsenic-contaminated drinking water? First, we conducted a systematic review of 29 peer-reviewed articles from various populations around the world. The review focused on the different ways in which arsenic is associated with respiratory health to help inform policy makers and public health researchers on the existing evidence. In short, associations between arsenic and respiratory health were noted throughout the lifespan: in infancy, there was growing evidence that in utero arsenic exposure was associated with increased frequency and severity of respiratory tract infections; in childhood, evidence of respiratory symptoms also began to appear; and in adulthood, there was consistent evidence that arsenic exposure was associated with deficits in lung function and increased reports of coughing and breathing problems. The review also uncovered some research gaps, including few studies with strong exposure history from early life and few studies examining respiratory effects during adolescence. Next, we used a life course epidemiological approach to create a more precise understanding of arsenic exposure and respiratory health during the teenage years. This study examined the relationship between lifetime arsenic exposure and lung function in 14-17 year olds, thus studying the period of maximal lung function before natural decline. Overall, higher arsenic exposure was associated with lower lung function levels; however, these associations were only observed in males. This study used a sensitive marker of lung function to investigate early signs of small airway disease. Incorporating this common marker of small airway disease and airflow limitation in future studies on arsenic and respiratory health may help clarify how inorganic arsenic contributes to the development of chronic respiratory disease. Lastly, we evaluated the effectiveness of arsenic removal filters at the household-level in rural Bangladesh. Identifying sustainable ways of reducing exposure to arsenic from naturally contaminated groundwater has been a major environmental health challenge. Although lab-approved arsenic removal water filters exist, there was limited evidence of their prolonged efficacy in the field. To our knowledge, this was the largest and longest deployment of filters accompanied by monitoring of urinary arsenic. Our results demonstrated that filters can temporarily reduce arsenic exposure for weeks to a few months, but should not be considered as a long-term arsenic mitigation option. This failed attempt to reduce exposure confirmed that alternative mitigation strategies need to be employed in Bangladesh, particularly among more vulnerable populations, including pregnant women and young children. This dissertation has important policy implications for future arsenic research and mitigation efforts and should be effectively communicated to policy makers, public health officials, and the general population. Given the pervasive nature of arsenic exposure and the growing evidence of health consequences at different stages throughout the life course, the continued integration of information on inorganic arsenic and research collaborations across disciplines is critical for the prevention and mitigation of arsenic-induced health consequences.

Groundwater arsenic contamination is currently a global problem, and also a concern at numerous former industrial sites, agricultural sites, landfill sites and mining operations in the U.S. This dissertation aims to develop improved strategies of remediating these arsenic contaminated aquifers. It focuses on two distinct approaches of remediation: (1) mobilizing arsenic from contaminated aquifer sediments to decrease the quantity of arsenic at the source of contamination; and (2) immobilizing arsenic in situ, to decrease the mobility and bioavailability of this arsenic. Optimal remediation may well involve combinations of these two approaches. Arsenic mobilization using oxalic acid is effective because oxalic acid dissolves arsenic host minerals and competes for sorption sites on those minerals. In this dissertation, oxalic acid treatment was tested using sediments with contrasting iron mineralogies and arsenic contents from the Dover Municipal Landfill and the Vineland Chemical Company Superfund sites. Oxalic acid mobilized arsenic from both sites and the residual sediment arsenic was less vulnerable to microbial reduction than before the treatment. Oxalic acid thus could improve the efficiency of widely used pump-and-treat remediation. Oxalic acid did not remove all of the reactive iron(III) minerals in Vineland sediment samples, and thus released significant quantities of arsenic into solution under reducing conditions than the Dover samples. Therefore, the efficacy of pump-and-treat must consider iron mineralogy when evaluating its overall potential for remediating groundwater arsenic. Arsenic immobilization occurs by changing the chemical state, or speciation, of arsenic and other elements in the system. Arsenic is often assumed to be immobile in sulfidic environments. In this dissertation, sulfate reduction was stimulated in sediments from the Vineland Superfund site and the Coeur d'Alene mining district. Sulfate reduction in the Coeur d'Alene sediments was more effective at removing arsenic from solution than the Vineland sediments. The Vineland sediments initially contained abundant reactive ferrihydrite, and underwent extensive sulfur cycling during incubation. As a result, arsenic in the Vineland sediments could not be effectively converted to immobile arsenic-bearing sulfides, but instead a part of the arsenic was probably converted to soluble thioarsenates. Therefore, coupling between the iron and sulfur redox cycles must be fully understood for arsenic immobilization by sulfate reduction to be successful. Arsenic can also be immobilized by retention on magnetite (Fe3O4). Magnetite is stable under a wide range of aquifer conditions including both oxic and iron(III)-reducing environments. In this dissertation, a series of experiments were performed with sediments from the Dover and Vineland Superfund sites, to examine the potential of magnetite for use in arsenic immobilization. Our data suggest that the formation of magnetite can be achieved by the microbial oxidation of ferrous iron with nitrate. Magnetite can incorporate arsenic into its structure during formation, forming a stable arsenic sink. Magnetite, once formed, can also immobilize arsenic by surface adsorption, and thus serve as a reactive filter when contaminated groundwater migrates through the treatment zone. Reactive transport modeling is used for investigating the magnetite based arsenic immobilization strategy and for scaling laboratory results to field environments. Such modeling suggests that the ratio between iron(II) and nitrate in the injectant regulates the formations of magnetite and ferrihydrite, and thus regulates the long-term evolution of the effectiveness of the strategy. The results from field-scale models favor scenarios that rely on the chromatographic mixing of iron(II) and nitrate after injection. The studies in this dissertation demonstrate that the environmental fate of arsenic depends on the biogeochemical cycling of arsenic, iron, and to a lesser extent, sulfur. The development of effective groundwater arsenic remediation strategies depends on a good understanding of each of the involved processes, and their combinations.

PhD (Environmental Sciences) / Department of Ecology and Resource Management / The presence of arsenic in groundwater has drawn worldwide attention from researchers and public health officials due to its effects on human health such as, cancer, skin thickening, neurological disorders, muscular weakness, loss of appetite and nausea. World Health Organisation (WHO) has set the limit of 10 μg/L for arsenic in drinking water in trying to reduce the effects of arsenic. This was further adopted by South African National Standard (SANS). The present study aims at evaluating arsenic concentration in selected groundwater sources around Greater Giyani Municipality in Limpopo Province and further synthesize clay based adsorbents for arsenic removal using Fe3+ and Mn2+ oxides and hexadecylammonium bromide (HDTMA-Br) cationic surfactant as modifying agents. The first section of the work presented the hydrogeochemical characteristics of groundwater in the Greater Giyani Municipality. The results showed that the pH of the samples ranges from neutral to weakly alkaline. The dominance of major anionic and cationic species was found to be in the order: HCO3 ->Cl->SO4 2->NO3 - and Na+>Mg2+>Ca2+>K+>Si4+, respectively. Hydrogeochemical facies identified in the study area include CaHCO3 (90%) and mixed CaNaHCO3 (10%) which shows the dominance of water-rock interaction. About 60% of the tested samples contains arsenic concentration above 10 μg/L as recommended by SANS and WHO. Concentration of arsenic was found to be ranging between 0.1 to 172.53 μg/L with the average of 32.21 μg/L. In the second part of this work, arsenic removal efficiency of locally available smectite rich and kaolin clay was evaluated. Results showed that the percentage As(V) removal by kaolin clay was optimum at pH 2 while the percentage As(III) removal was greater than 60% at pH 2 to 12. For smectite rich clay soils, the percentage of As(III) and As(V) removal was found to be optimum at pH between 6 and 8. The adsorption isotherm data for As(III) and As(V) removal by both clays fitted better to Freundlich isotherm. Adsorption of both species of arsenic onto the clay mineral occurred via electrostatic attraction and ion exchange mechanisms. Both clay soils could be regenerated twice using Na2CO3 as a regenerant. Kaolin clay showed a better performance and was selected for further modification. In the third section of this work, Fe-Mn bimetal oxide modified kaolin clay was successfully synthesized by precipitating Fe3+ and Mn2+ metal oxides to the interlayer surface of kaolin clay. Modification of kaolin clay increased the surface area from 19.2 m2/g to 29.8 m2/g and further v decreased the pore diameter from 9.54 to 8.5 nm. The adsorption data fitted to the pseudo second order of reaction kinetics indicating that adsorption of As(III) and As(V) occurred via chemisorption. The adsorption isotherm data was described by Langmuir isotherm models showing a maximum As(III) and As(V) adsorption capacities of 2.16 and 1.56 mg/g, respectively at a temperature of 289 K. Synthesized adsorbent was successfully reused for 6 adsorptiondesorption cycles using K2SO4 as a regenerant. Column experiments showed that maximum breakthrough volume of ≈2 L could be treated after 6 hours using 5 g adsorbent dosage. Furthermore, the concentration of Fe and Mn were within the WHO permissible limit. In the fourth part of the work kaolin clay was functionalized with hexadecyltrimethylamonium bromide (HDTMA-Br) cationic surfactant and its application in arsenic removal from groundwater was investigated. The results revealed that adsorption of As(III) and As(V) is optimum at pH range 4-8. The maximum As(III) and As(V) adsorption capacities were found 2.33 and 2.88 mg/g, respectively after 60 min contact time. Pseudo first order model of reaction kinetics described the adsorption data for As(V) better while pseudo second order model described As(III) adsorption data. The adsorption isotherm data for As(III) and As(V) fitted well to Langmuir model indicating that adsorption of both species occurred on a mono-layered surface. Adsorption thermodynamics model revealed that adsorption of As(III) and As(V) was spontaneous and exothermic. The As(III)/As(V) adsorption mechanism was ascribed to electrostatic attraction and ion exchange. The regeneration study showed that synthesized adsorbent can be used for up to 5 times. In the firth part of the work inorgano-organo modified kaolin clay was successfully synthesized through intercalation of Fe3+ and Mn2+ metal oxides and HDTMA-Br surfactant onto the interlayers of the clay mineral. The batch experiments showed that As(III) removal was optimum at pH range of 4-6, while the As(V) removal was optimum at pH range 4-8. The adsorption data for both species of arsenic showed a better fit to pseudo second order of reaction kinetics which suggest that the dominant mechanism of adsorption was chemisorption. The isotherm studies showed better fit to Langmuir isotherm model as compared to Freundlich model. The maximum adsorption capacity As(III) and As(V) at room temperature as determined by Langmuir model were found to be 7.99 mg/g and 7.32 mg/g, respectively. The thermodynamic studies for sorption of As(III) and As(V) showed negative value of ΔGᴼ and ΔHᴼ indicating that adsorption process occurred spontaneously and is exothermic in nature. The regeneration study showed that the vi inorgano-organo modified kaolin clay can be reused for up 7 adsorption-regeneration cycles using 0.01 M HCl as a regenerant. Thomas kinetic model and Yoon-Nelson model showed that the rate of adsorption increases with increasing flow rate and initial concentration and decreases with increasing of the bed mass. In conclusions, adsorbents synthesized from this work showed a better performance as compared to other adsorbents available in the literature. Among the synthesized adsorbents, inorgano-organo modified clay showed highest adsorption capacity as compared to surfactant functionalized and Fe-Mn bimetal oxides modified kaolin clay. However, all adsorbents were recommended for use in arsenic remediation from groundwater. The following recommendations were made following the findings from this study: 1) routine monitoring of arsenic in groundwater of Greater Giyani Municipality, 2) evaluating the possible link between arsenic exposure and arsenic related diseases within Giyani in order to find the extent of the problem in order to establish the population at risk, 3) The toxicity assessment for HDTMA-Br modified kaolin clay should be carried out, 4) Materials developed in the present study should be modeled and tested at the point of use for arsenic removal, and lastly, 5) this study further encourage the development of other arsenic removal materials that can be used at household level. / NRF