Water treatment residues (WTRs), which are by-products from the production of potable water, are chemically benign, inorganic materials which are suitable for disposal by land application. Their high phosphorus (P) sorption capacities have, however, generated some concern in an agronomic context where P is recognised as a growth limiting plant nutrient. The extent to which labile P pools are reduced or enhanced by WTR amendments is, therefore, a central issue with respect to their disposal by land application. Therefore, the aim of this study was, through the use of empirical adsorption isotherm equations and chemical fractionation of P within the residues, to investigate the chemical processes responsible for the retention and release of P from 15 South African WTRs. Chemical characterisation revealed considerable variation in residue properties relevant to P sorption-desorption processes. pH, exchangeable Ca and organic carbon content ranged from 4.77 to 8.37, 238 to 8 980 mg kg-1 and 0.50 to 11.6 %, respectively. Dithionate, oxalate and pyrophosphate extractable Al fractions ranged from 741 to 96 375, 1 980 to 82 947 and 130 to 37 200 mg kg-1, respectively. Dithionate, oxalate and pyrophosphate extractable Fe ranged from 441 to 15 288, 3 865 to 140 569 and 230 to 90 000 mg kg-1 respectively. Therefore mechanisms of retention were hypothesised to be residue specific, being dependent on the unique chemical properties of the sorbent. Elevated Ca and amorphous Al and Fe concentrations did, nevertheless, suggest that all residues had the capacity to adsorb high amounts of P and to retain this P in forms unavailable for plant uptake. These arguments were confirmed by the sorption study where labile P was, for all residues, found to constitute a small fraction of total applied P even at high application concentrations (128 mg P L-1). Sequential P fractionation revealed that most of the inherent P (which ranged from 1 149 to 1 727 mg P kg-1) and applied P were retained in highly resistant mineral phases or fixed within the organic component. Thus P replenishment capacities were restricted even though residual P concentrations were often within adequate ranges for plant growth. Phosphorus adsorption data was described by four empirical adsorption isotherm equations in an effort to determine possible mechanisms of retention. Sorption data was, for most of the WTRs, described by the Temkin isotherm while the Freundlich and linear models fitted data for two residues each. A key finding was that the distribution coefficient (Kd) tended to increase with the quantity of P adsorbed (S) as opposed to decrease or remain constant in accordance with model assumptions. Therefore, the models could not be used for mechanistic interpretation, even though they provided excellent descriptions of the data. The direct relationship between Kd and S suggested a mechanism of retention involving the activation of sorption sites. This notion was supported by the fractionation study which showed that P addition results in the transfer of an increasing quantity of organically bound P to resistant residual forms. Model affinity parameters were strongly correlated to dithionate and pyrophosphate extractable Al and Fe which suggested that P was adsorbed primarily through ligand exchange mechanisms. The mobility of P bound to organic fractions did indicate that P was retained through weaker forces of attraction such as monodentate ligand exchange, charge neutralisation or proton transfer. Evidence to support the notion that P is immobilised through the formation of Ca phosphates was lacking. Based on P fractionation data, it was suggested that strong chemisorption mechanisms and the diffusion of P into WTR micropores were largely responsible for the minimal quantity of P desorbed by disequilibria desorption processes. A greater quantity of P was desorbed in the presence of oxalate and citrate which suggested that plants may increase bio-available pools through the release of organic ligands. Phosphorus desorbed in the presence of these ligands did, however, decline with P addition which confirmed that the affinity of the WTR surface for P increases with P application. Therefore, it was concluded that the application of P to WTRs is an uneconomical process unless sorption sites are already saturated or immobilisation processes are inhibited. In light of these findings, it was suggested that the absence of plant P deficiencies under the field application of WTRs is due primarily to inhibited sorption. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Water treatment residue (WTR), a by-product of the water treatment process, consists primarily of precipitated hydroxides of the coagulants used in the water treatment process, along with sand, silt, clay, humic compounds, and dissolved organic matter. It is usually disposed of by landfill, a technology with numerous problems that include dwindling landfill capacity, extensive dewatering requirements for the WTRs, high costs of transportation, and potential liability for landfill clean-up. Therefore, land disposal (or land treatment) presents a popular alternative disposal method based on the principle that the physical, chemical, and microbial properties of the soil can be used to assimilate applied waste without inducing any negative effects on soil quality. The objective of this study was to investigate the effects of land disposal of the WTR generated by Umgeni Water, a local water treatment authority, on soil quality. These effects were investigated using depth samples from soil profiles of Westleigh and Hutton soil forms at field trials located at Ukulinga Research Farm, near Pietermartizburg and Brookdale Farm, Howick, KwaZulu-Natal, South Africa, respectively. Four rates of WTR (0, 80, 320, and 1280Mg ha-1 incorporated into the soil) were investigated at both trials, in addition to mulched treatments at rates of 320 and 1280Mg ha-1 at Brookdale only. Sampling of plots was carried out in September 2001 and May 2002, and all treatments were investigated under fallow and grassed cultivation. Laboratory measurements used to assess soil quality included pH, electrical conductivity (EC), organic carbon (QC), and microbial activity using f1uorescein diacetate (FDA) hydrolysis. At both trials in September 2001 WTR-amended plots displayed higher pH in the 0-200mm soil in comparison to the controls, whereas by May 2002 pH had returned to the condition of the controls. Addition of WTR at Ukulinga resulted in higher QC in September 2001, but in May 2002 this was similar to the controls. However, at Brookdale QC was unaffected by WTR. At Ukulinga and Brookdale the effect of WTR on EC was variable, and microbial activity in the soil profile was unaffected by WTR addition. Observations at Ukulinga and Brookdale reflected long term changes (3 and 5 years, respectively) to soil quality following WTR addition. To examine the initial changes in soil quality a laboratory experiment was set up using the field trial soils. Research objectives were also extended to include WTRs from Rand Water (Johannesburg), Midvaal Water Company (Stilfontein), Amatola Water (East London), and two samples from the Faure Water Treatment Plant (near Cape Town). The second Faure sample (Faure2 ) was collected when blue green algal problems were experienced at the plant. The measurements used to investigate these short term effects on soil quality were soil pH, EC, and microbial activity as indicated by respiration rate. Each of the WTRs added to the Hutton and Westleigh soils increased soil pH by varying increments, and the higher the WTR application rate, the higher was the pH recorded. With the exception of the Rand and Umgeni WTRs that clearly increased soil EC, the effect of the otherWTRs on EC was variable. The Faure1 and Amatola WTRs appeared to have no effect on microbial activity, whereas the Umgeni, Rand, Midvaal, and Faure2 WTRs stimulated microbial activity by Day 2 following the addition of WTR, but this had declined by Day 14. As for pH, higher microbial activity was recorded at higher WTR application rates. Changes in microbial community structure of the Hutton soil only, following the addition of WTR were examined using denaturing gradient gel electrophoresis (DGGE) analysis. Community profiles of the different WTRs proved to be markedly different. However, WTR-amended soil retained banding patterns consistent with the control soil indicating that dominant populations in the Hutton soil had been retained. The field trials indicated that long term effects of land disposal of WTR were not detrimental to the measured indicators of soil quality namely, pH, EC, QC, and microbial activity. The laboratory assessments of the short term response of the Hutton and Westleigh soil forms to WTR addition suggested that the tested variables were altered by WTR, but not significantly changed to the detriment of soil quality. Microbial community analysis indicated that the community structure of the Hutton soil was not significantly altered by WTR amendments. Present findings provide no evidence to suggest that land disposal of WTR is detrimental to soil quality. It is therefore regarded as a feasible disposal option although there are some aspects that should be investigated further. These include investigations into rhizosphere/microbial interactions and the feasibility of growing cash crops. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

The ability of six types of granular activated carbon (GAC) to quench H2O2 was evaluated by bench-scale H2O2 decomposition kinetics tests and pilot-scale H2O2 breakthrough tests. Bench-scale studies showed that carbon ageing significantly reduced the performance of H2O2 quenching by the GAC, but that the greatest impacts occurred within the first 25 000 bed volumes of water treated, with performance tending to stabilize afterwards. Pilot-scale studies suggested that both H2O2 exposure and exposure to natural organic matter were important factors in GAC ageing, with exposure to oxygen also suspected of being important. A continuously stirred tank reactor (CSTR)-in-series model was proposed for the prediction of H2O2 breakthrough in a GAC column.

The ability of six types of granular activated carbon (GAC) to quench H2O2 was evaluated by bench-scale H2O2 decomposition kinetics tests and pilot-scale H2O2 breakthrough tests. Bench-scale studies showed that carbon ageing significantly reduced the performance of H2O2 quenching by the GAC, but that the greatest impacts occurred within the first 25 000 bed volumes of water treated, with performance tending to stabilize afterwards. Pilot-scale studies suggested that both H2O2 exposure and exposure to natural organic matter were important factors in GAC ageing, with exposure to oxygen also suspected of being important. A continuously stirred tank reactor (CSTR)-in-series model was proposed for the prediction of H2O2 breakthrough in a GAC column.

The development of functionalized membranes with tunable pores and catalytic properties provides us an opportunity to manipulate the membrane pore structure, selectivity and reactivity. By introducing the functional groups into membrane pores, dissolved metal ions and reactive particles can be effectively immobilized within the polymer matrix for toxic chloro-organic and heavy metal remediation in water. A polyelectrolyte functionalized membrane platform with tunable pore size and ion exchange capacity has been developed for iron/iron oxide nano-catalyst synthesis and chlorinated organic compound (trichloroethylene, TCE and polychlorinated biphenyls, PCBs) degradation. Highly robust polyvinylidene fluoride (PVDF) microfiltration membranes are used as the support with cross-linked polyacrylic acid (PAA) filled in the pores. By varying the environmental pH, PAA hydrogels have either swelling or collapsing behavior, resulting in different effective membrane pore sizes for different separation purposes. Cation exchange groups (i.e. carboxyl groups) in PAA chains prevent the aggregation and leaching of nanoparticles (NPs) during in-situ synthesis and reaction. Depending on the catalyst loading and residence time, TCE and PCBs can be completely degraded by reduction of zero-valent iron and bimetallic iron/palladium NPs, or iron oxide catalyzed free radical oxidation at near-neutral pH. Biphenyl from PCB dechlorination can be further oxidized by hydroxyl radicals (OH•) generated from hydrogen peroxide (H2O2) decomposition. Hydroxybiphenyls and benzoic acid are identified as oxidation products. Line scan and elemental mapping in transmission electron microscopy (TEM) and X-ray photo electron spectroscopy (XPS) characterizations are conducted to understand the effect of iron surface transformation on NP reactivity, and to optimize the membrane functionalization. The same platform can also be used to remove toxic metal selenium in the scrubber water of coal-fired power plants. By reducing the salt concentration in water or increasing the residence time and temperature, the concentration of selenium oxyanions in functionalized membrane permeate can be reduced to less than 10 µg/L. Selenium is captured in membranes by both iron reduction to metallic selenium and iron oxide adsorption. The full-scale flat sheet functionalized membrane and spiral wound modules have also been developed. Iron NPs with alterable loadings are successfully synthesized inside the membrane module for real water applications.

Nitrosamines have garnered increasing attention from researchers and policy makers in recent years due to potential human health implications associated with their unintentional formation in water and wastewater treatment facilities. This work addresses a crucial nitrosamine formation pathway concerning the catalysis of amine nitrosation by activated carbon materials whose use is widespread in municipal and industrial systems. Experimental results show that this catalysis is highly pH dependent, with maximum formation achieved near the pKa value for each of the secondary amines tested. This result suggests that the overall formation potential is governed by individual amine properties and their interactions with carbon surfaces, rather than solely nitrite speciation as previously reported. Formation of the most commonly studied nitrosamine, N-nitrosodimethylamine, was shown to be highly dependent on initial dimethylamine (DMA) solution concentration, with yields of approximately 0.11% of the spiked secondary amine at pH 7.5. Morpholine and dibutylamine, larger and bulkier secondary amines, formed their corresponding nitrosamines at higher yields than DMA (0.21% and 1.69%, respectively). Additionally, select tertiary amines were shown to be capable of undergoing nitrosation on the same order of magnitude as the secondary amines under neutral conditions in the presence of activated carbons. The magnitude of these results indicates that greater attention should be paid to this previously overlooked mechanism for nitrosamine formation.

The objective of this study was to provide a technique, based on the residence time distribution of a process, for modelling, assessing and improving flow in the processes of water and waste water treatment works. The technique should be accessible to the staff managing and operating the works. From a review of the literature, a preference was given for the experimental method used for determination of the tracer response, including choice of tracer and tracer addition and monitoring. Data analysis techniques were reviewed, and the method of time domain fitting was developed into a computer program, IMPULSE. IMPULSE provided a tool for analysis of residence time data, and removed the constraint of numerical complexity. Using the building blocks of IMPULSE, a realistic flow model can be constructed from tracer data and evaluated. IMPULSE allows a quantitative comparison of models proposed for a process, and provides the parameters of the models. These parameters quantify the non-idealities in a process. A knowledge of the non-idealities provides a basis for decision-making when modifying a process. The results of tracer experiments performed on some water and waste water treatment processes were analysed using IMPULSE. The results showed that collection of good experimental data was critical to the success of the analysis. It is proposed that a guide be produced which draws out the main points raised in the study, including collection of tracer data and use of IMPULSE. The guide should be accessible and easily understandable to the staff managing and operating water and waste water treatment works. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 1995.

Flocculants are commonly used in industrial settings where solid-liquid separations are desired including industrial and municipal wastewater management and potable water production facilities. Conventional flocculants include inorganic metal salts and synthetic organic polymers. The cost, availability, and harmful effects of the non-biodegradable nature of these flocculants have led to the widespread study of natural flocculants. Current natural flocculants being studied include polysaccharides cultivated from microbial extracellular matrix products and plant based materials. In this study, the mucilage of Opuntia ficus-indica cactus was evaluated as a natural flocculant for sediments and bacteria. The O. ficus-indica cactus is also known as the nopal or prickly pear and is commonly used as a food source in Mexico and Latin America. Using simple extraction techniques non-gelling (NE) and gelling (GE) mucilage extracts were isolated from fresh cactus pads. Column tests were used to evaluate the flocculation and removal of suspended sediment and bacteria caused by mucilage addition. Throughout this work the mucilage's ability as a flocculant was evaluated by varying mucilage type and concentration, suspended contaminant type and concentration, and cation type and concentration. Many of the results are explained in terms of the morphology and chemical composition of the GE and NE mucilage extracts. The extracts consist primarily of polysaccharides and differences in physical structure between mucilage types were seen using atomic force microscopy and transition electron microscopy. A variety of suspended particles were used to evaluate the mucilage as a flocculant including kaolin, acid-washed kaolin, and bacteria. The bacteria employed in this study include Bacillus cereus, Escherichia coli HB101 K12, and fully attenuated Bacillus anthracis Sterne strain. The addition of monovalent (Na+ and K+), divalent (Ca2+ and Mg2+), and trivalent (Al3+ and Fe3+) cations was studied alone and in combination with mucilage. In cation studies Ca2+ had the most profound effect on flocculation efficiency; therefore its efficacy was further explored. Mucilage was most effective with dosages between 5 and 50 mg/L for the contaminants studied. Using these optimal concentrations, 20 to 200 L of water could be treated with only 1 g of mucilage powder. Based on the extraction method used in this work, 1 g of mucilage can be obtained from a cactus pad weighing approximately 250 g (wet weight). Mucilage remained an effective flocculant over a wide range of suspended contaminant concentrations showing that mucilage is a versatile flocculant that can be tailored for a variety of applications. Overall, this work shows that the O. ficus-indica cactus is an effective flocculant for suspended sediments and bacteria. The cactus' low cost, abundance, and current use in many areas make it an attractive alternative to traditionally used flocculants. Additionally, this work builds upon existing knowledge pertaining to natural flocculants and could offer insight into their general behaviors for water treatment applications.

The aim of this study was to investigate the efficacy of purification processes at the Rand Water Zuikerbosch treatment plant near Vereeniging. Raw water is abstracted via a canal and gravity pipeline from the Vaal Dam (in the upper Vaal River) and purified to ensure it meets the stringent standards set for drinkable water. The first step was to determine the ecological status of the raw water and it was done by measuring chemical, physical and biological variables as well as to identify and enumerate the different algal groups that occur in the raw water. The turbidity of the raw water was low but the phosphorous and ortho–phosphate levels were high. The Cyanophyceae (blue–green bacteria) especially Anabaena species were dominant in the raw water for the duration of the study. Potential problems such as relatively high alkalinity, chemical oxygen demand (COD) and total dissolved solids (TDS) as well as potentially hazardous chemicals such as cadmium and lead were observed in the raw water. The Zuikerbosch Water Treatment Plant (ZWTP) is a conventional water treatment plant which involves the following stages: coagulation, flocculation, sedimentation, sand filtration and chlorination. The use of pre–treatment chemicals ensures better water quality and effective removal of particles from the water. Only five of the variables (methylisoborneol (MIB); geosmin; chlorophyll–a; chlorophyll–665 and total organic carbon (TOC) were measured before filtration, after filtration and in the final water. Samples from the raw water, before and after filtration, as well as final water were collected weekly for a period of two years to measure the environmental variables as well as to do algal identification and enumeration. The purification processes at ZWTP were not able to remove MIB, geosmin, chlorophyll–a and TOC from the final water. Algal concentration was reduced but not totally removed by the purification processes. Although some variables were not totally removed by the purification processes, ZWTP produce potable water that complies with the Rand Water guidelines. / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2011.

South Africa's water resources are, in global terms, scarce and extremely limited (DWAF, 2004). Groundwater is a valuable source of potable water in South Africa. It was found that most of the health facilities in the Limpopo Province depend on groundwater as sole source of potable water. Groundwater quality is to a great extent influenced by the dominant land use in the vicinity of an aquifer. It is therefore important to carefully manage possible pollution sources of anthropogenic origin. This may be seen as pro–active water quality management that may result in significant saving on water treatment. This aim of this study is to obtain a regional view of the water quality situation at clinics and other health facilities in the Limpopo Province. It was found that the general water quality at health facilities in the Province is questionable. It is of concern to note that 56% of health facilities use water that is unacceptable for human consumption. Water quality may be managed by introducing appropriate treatment options to treat the water to ideal water quality standards. This dissertation explores some treatment options used at health facilities in the Province. The efficiency of these treatment systems is also investigated. / Thesis (M.Sc. (Geography and Environmental Studies))--North-West University, Potchefstroom Campus, 2011.