Les procédés membranaires hybrides (PMH) allient la filtration membranaire basse pression à l’usage du charbon actif en poudre (CAP). Afin de diminuer les coûts opérationnels du procédé, il a été proposé de laisser vieillir le CAP dans le PMH et donc de minimiser le dosage de CAP frais. Peu d’information est disponible quant à la capacité résiduelle d’adsorption de suspensions de CAP âgées. L’importance relative de l’adsorption et de la biodégradation dans les réacteurs à CAP âgés sur le traitement des composés dissous est inconnue, ce qui empêche notamment l’optimisation du procédé. <p><p>Le principal objectif de ce projet de recherche est de décrire la performance du contacteur à CAP du PMH pour l’enlèvement de l’azote ammoniacal, du carbone organique dissous (COD), du COD biodégradable (CODB) et des micropolluants. Dans ce projet, l’emphase est placée sur l’opération du PMH avec de hauts temps de rétention de CAP. <p><p>La première phase de ce projet a consisté en une série de développements méthodologiques, base nécessaire à l’étude du CAP âgé. Des méthodes permettant la quantification de la biomasse hétérotrophe et nitrifiante colonisant le CAP âgé ont mis en évidence des densités de biomasse similaires à celle du charbon actif en grain en surface de filtre biologiques. L’irradiation aux rayons gamma a été démontrée comme une méthode adéquate pour produire des témoins abiotiques à partir de CAP de 10 et de 60 jours.<p><p>La seconde partie de cette étude s’est concentrée sur la démonstration de l’efficacité du PMH pour l’enlèvement de l’azote ammoniacal, du COD, ainsi que d’un mélange de micropolluants. Les cinétiques d’enlèvements ayant lieu au sein de des contacteurs à CAP ont été simulées en laboratoire sous diverses conditions (température, concentration en CAP, âge de CAP, matrice d’eau variable, temps de contact). Deux modèles cinétiques prédisant l’enlèvement de l’azote ammoniacal et du COD dans le PMH ont été développés sur base des simulations en laboratoire suivies sur CAP neuf, colonisé et abiotique. <p><p>De manière générale, les travaux réalisés au cours de ce doctorat ont mis en évidence le rôle majeur de l’adsorption résiduelle sur l’enlèvement de la contamination dissoute. Alors que l’enlèvement d’azote ammoniacal a majoritairement eu lieu par nitrification, le COD et les micropollutants sont principalement adsorbés sur le CAP colonisé. Il a aussi été montré que la capacité d’adsorption résiduelle des suspensions de CAP âgées peut agir en tampon, permettant de faire face à une augmentation soudaine de la concentration en azote ammoniacal, en COD ou en micropolluants. Le suivi des cinétiques d’enlèvement a permis de démontrer que la concentration, l’âge de CAP et le temps de rétention hydraulique (TRH) sont trois paramètres clefs pour l’optimisation du procédé. D’un point de vue économique, un TRH inférieur à 15 min est néanmoins désiré pour limiter les coûts du procédé. Par ailleurs, l’intérêt économique associé à l’augmentation de l’âge du CAP peut-être atténué par le besoin d’augmenter la concentration en CAP si l’adsorption est le mécanisme visé. De façon générale, ce projet démontre qu’une optimisation à l’échelle pilote du procédé est nécessaire car les objectifs de traitement, la qualité de l’eau à traiter et le fait que les 3 paramètres d’opération soient inter-reliés complexifient l’optimisation du PMH. Étant donné l’impact du TRH sur le coût du PMH, de futures recherches devraient viser à l’optimisation du mélange. <p>Hybrid membrane processes (HMPs) couple membrane filtration with powdered activated carbon (PAC). In HMPs, low-pressure membranes ensure an efficient particle removal, including protozoan parasites such as Cryptosporidium, while the PAC contactor is devoted to the removal of dissolved compounds. Such processes are emerging as a promising alternative to conventional treatment chains, which no longer allow the drinking water facilities to comply with increasingly stringent regulations on the treated water quality. To decrease the operating costs associated with virgin PAC consumption, it was suggested to let the PAC age in the PAC contactor of the process. Until now, the potential of using aged PAC in HMPs has been demonstrated for ammonia and DOC removal, but the potential to remove micropollutants remains unknown. It is suggested that the biological activity in aged PAC contactors contributes significantly to the removal of the dissolved compounds. Yet, neither the extent of the biomass on the aged PAC, nor the residual adsorption capacity, was quantified. No study focused on discriminating the mechanisms responsible for the treatment when using aged PAC suspensions. Most of the data published on HMPs using aged PAC were gathered at pilot scale under warm water conditions, yet the efficiency of the process is most likely sensitive to temperature changes. There is currently little information available on the efficiency of HMPs under cold water conditions. This lack of information hinders the optimization of the HMP, leading to sub-optimal usage of aged PAC.<p><p>The main objective of this research project is to describe the performance of the PAC contactor of HMPs in removing ammonia, dissolved organic carbon (DOC), biodegradable DOC (BDOC) and micropollutants. In particular, emphasis was placed on the operation of the HMP under high PAC residence times. On a more detailed level, the objectives of this project were (1) to develop and compare methods to quantify the biomass developed on aged PAC, (2) to develop a method to produce an abiotic control for aged PAC, (3) to characterize the removal kinetics of ammonia, DOC, BDOC and micropollutants occurring in the carbon contactor of an HMP, (4) to evaluate the impact of water temperature on the performance of the carbon contactor of an HMP, (5) to discriminate the relative importance of adsorption versus biological oxidation as mechanisms responsible for ammonia, DOC and micropollutants removal in the PAC contactor of an HMP, and finally (6) to differentiate the relative importance of the hydraulic retention time (HRT), the PAC age and the PAC concentration as key operating parameters on the optimization of the performance of the PAC contactor of an HMP.<p><p><p>To set the basis on the study of aged PACs, the first part of this research project consisted in methodological developments i) to quantify the heterotrophic and nitrifying biomass colonizing aged PAC, and ii) to create a reliable abiotic control of the colonized PAC, which is required for discriminating the mechanisms occurring on aged PAC. Heterotrophic and nitrifying biomass quantifying methods developed for colonized granular activated carbon (GAC) were successfully adapted to the aged PAC. The preferred methods were the potential 14C-glucose respiration (PGR) rate and the potential nitrifying activity (PNA), as they quantify the active heterotrophic and nitrifying biomass, which is most likely responsible for the depletion of BDOC and ammonia. An alternative method to the PGR, the potential acetate uptake (PAU) rate, was developed to alleviate the logistical and budgetary issues associated with the utilization of radio-labeled glucose. The densities (per gram of dry PAC) of both active heterotrophic and nitrifying biomasses were found comparable to that of the GAC sampled from the surface of a biological GAC filter. The gamma-irradiation was demonstrated as a reliable method to produce abiotic samples from soils, and was therefore chosen to produce abiotic colonized PAC samples in this project. In order to determine the optimized dosage of gamma-rays, increased doses were applied on PAC samples. Heterotrophic plate counts and methylene blue adsorption kinetics were used to determine respectively the lowest gamma ray dose required to inhibit the bacterial activity, and the highest dose that could be applied without affecting the aged PAC adsorption capacity and kinetics. Refractory DOC (RDOC) adsorption kinetics confirmed the accuracy of the dose chosen as the adsorptive behavior of the aged PAC was not affected. PGR rates were decreased 83% at the optimized dose. The gamma-irradiation method was therefore proven efficient and used in the following work phases of this research.<p><p>The second part of this study focused on the removal of ammonia, DOC and a mixture of micropollutants. Firstly, the PAC contactor of an HMP was simulated at lab-scale to monitor ammonia removal kinetics. Three PAC concentrations (approximately 1-5-10 g/L) of three PAC ages (0-10-60 days) were tested at two temperatures (7-22°C), in settled water with ambient influent condition (100 µg N–NH4/L) as well as under a simulated peak pollution scenario (1000 µg N–NH4/L). The kinetics evidenced that ammonia flux at pilot scale limited biomass growth (HRT = 67 min). In contrast, PAC colonization was not limited by the available surface and thus, PAC concentration was not a key operating parameter under the colonizing conditions tested (5-10 g/L). Ammonia adsorption was significant onto virgin PAC but the ammonia nitrification was crucial to reach complete ammonia removal at 22°C. When using colonized PAC, the 60-d PAC offered a better resilience to temperature decreases (78% at 7°C) as well as lower operating costs than the 10-d PAC (<10% at 7°C). Significant ammonia adsorption was also evidenced on 60-d PAC suspension, most probably due to PAC and the presence of suspended solids, but not on 10-d PAC. Adsorption and nitrifying activity were superior on 60-d PAC than on 10-d PAC at 7°C. In case of peak pollution, the process was most probably phosphate-limited but a mixed adsorption/nitrification still allowed 50% ammonia removal on 10-d and 60-d PAC at 22°C. A kinetics based model was developed to predict ammonia removals and to determine the relative importance of the adsorption and nitrification on colonized PAC under the conditions tested. <p><p>DOC, BDOC and RDOC removals occurring in the PAC contactor of an HMP were also simulated at lab-scale. Similar conditions to that of the ammonia removal kinetics were tested. The initial ammonia concentration remained untouched in the water matrices (settled water and raw water) but the BDOC-to-DOC ratio was altered by pre-ozonation (0 to 1.5 g O3/g C). The 10-d and 60-d abiotic controls were used to discriminate DOC adsorption from biodegradation. DOC biodegradation contributed marginally to DOC removal in the investigated conditions and DOC adsorption was increased at higher temperature. An original model integrating the PAC age distribution was developed to predict DOC removal in aged PAC contactors operated at steady-state. At a mean PAC residence time of 60-d, the younger PAC fraction (25-d and less) was primarily responsible for DOC adsorption (> 80%). This fraction represents 34% of the mass of PAC in the contactor. When using a water matrix with a higher initial DOC concentration (raw water) or a lower affinity for PAC (pre-ozonated settled water), the residual adsorption capacity of that older fraction was proven useful. <p><p>Lastly, a mixture of micropollutants (atrazine, deethylatrazine (DEA), linuron, microcystin, caffeine, carbamazepine, sulfamethoxazole, diclofenac, progesterone and medroxyprogesterone) was spiked at environmentally relevant concentrations (from 130 ng/L to 33 µg/L) in settled water (0 and 0.85 gO3/gC). The micropollutants concentration depletion was monitored over a period of 7h to 48 h on 1 g/L of 0-d, 10-d, 60-d PAC and gamma-irradiated 60-d PAC. Even in presence of NOM, the spiked micropollutants were rapidly adsorbed on aged PAC. No biodegradation was observed. Removals superior to 95% were reached within 5 minutes, and direct competition with NOM did not impact the efficiency of the process when micropollutants were spiked at environmentally relevant concentrations. Therefore, HMPs operated to remove DOC and ammonia can control transient micropollutant pollution and comply with the World health Organization recommendations for atrazine (2 µg/L) and microcystin (1 µg/L). However, the stricter European regulations for atrazine and DEA (0.1 µg/L) could not be met with 10-d and 60-d PAC under the operating conditions tested. Reaching such strict treatment objective would require a specific optimization of the process. <p><p>In general, this PhD research evidenced the role of the residual adsorption of aged PAC suspensions for the treatment of dissolved compounds. From the results obtained in this project, the potential of HMPs using aged PAC to remove micropollutants was evidenced. Additional research is however required to validate this potential under varied operating conditions. The modeling work improved the understanding of aged PACs. Finally, this research work provides original information on the optimization of HMPs. The optimization of the operating parameters will vary with the water quality targeted and the quality of the influent water. The PAC concentration, PAC age and HRT are inter-related. Therefore, it is recommended to optimize the operation of HMPs at pilot scale. Seasonal variations should be accounted for. An HRT of at least 15 min is required when the biological activity is mandatory to reach the water quality objectives. Lower HRT might be applied if adsorption is favored. Finally, as the HRT has a strong impact on the total cost of the process (capital and operational expenditure), PAC contactors’ hydraulic should be the point of focus of future research.& / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

This study is a component of a research project on the economic costs of eutrophication in the Vaal River system. Its objective is to investigate the relationship between raw water quality and the chemical costs of producing potable water at two water treatment plants: Zuikerbosch Station #2 (owned by Rand Water) in the Upper Vaal Water Management Area (UVWMA), and Balkfontein (owned by Sedibeng Water) in the Middle Vaal Water Management Area (MVWMA). Time series data on raw water quality and chemical dosages used to treat raw water were obtained for Zuikerbosch Station #2 (hereafter referred to as Zuikerbosch) for the period November 2004 – October 2006 and for Balkfontein for the period January 2004 to December 2006. Descriptive statistics reveal that raw water in the Vaal River is of a poorer quality at Balkfontein compared to that at Zuikerbosch. Furthermore, the actual real chemical water treatment costs (measured in 2006 ZAR) averaged R89.90 per megalitre at Zuikerbosch and R126.31 at Balkfontein, indicating that the chemical water treatment costs of producing potable water tend to increase as raw water quality declines. Collinearity among water quality (WQ) variables at both water treatment plants was analysed using Principal Component Analysis (PCA). The dimensions of water quality identified in the analysis are similar to those reported in Pieterse and van Vuuren’s (1997) study of the Vaal River. For both water treatment plants, Ordinary Least Squares (OLS) regression was used to identify the relationship between real chemical costs of water treatment and the dimensions of water quality identified through the respective Principal Components Analyses. The estimated regression models account for over 50.2% and 34.7% of variation in real chemical water treatment costs at Zuikerbosch and Balkfontein, respectively. The coefficient estimated for PC1 at Zuikerbosch is statistically significant at the 1% level of probability with high negative loadings of total alkalinity and turbidity. Increases in the levels of total alkalinity and turbidity in raw water treated at Zuikerbosch is negatively related to the chemical costs of water treatment. An increased total alkalinity level was found to reduce the chemical costs of treating potable water. PC2 is statistically the most important variable in the estimated explanatory model for Balkfontein. The estimated regression coefficient for PC2 is statistically significant at the 5% level of probability. The estimated relationship between chemical water treatment costs and PC2 shows that there is a positive relationship between the raw water temperature and chemical water treatment costs. However, increases in the levels of chlorophyll and pH in raw water treated at Balkfontein is negatively related to the chemical costs of water treatment. Total hardness, magnesium, calcium, sulphate, conductivity, and chloride, being the highest positive loadings in PC1, relate negatively to the chemical cost of treating water. For predictive rather than explanatory purposes, a partial adjustment regression model was estimated for each of the two water treatment plants. Using this model, real chemical water treatment costs were specified as a function of real chemical water treatment costs in the previous time period, and of raw water quality variables in the current period. The R2 statistics for the two regression models were 61.4% using the data for Zuikerbosch and 59.9% using the data for Balkfontein, suggesting that both models have reasonable levels of predictive power. The chemical cost of water treatment for Zuikerbosch and Balkfontein are predicted at R96.25 and R90.74 per megalitre per day respectively. If raw water nitrate in the UVWMA increases by 1% per megalitre a day while other factors remain constant, chemical water treatment costs at Zuikerbosch can be expected to increase by 0.297% per megalitre and the cost accompanied this change is (R0.285*1998ML*365days) R207,841.95 provided that Zuikerbosch treats an average of 1998 megalitres per day. Likewise, if Zuikerbosch maintains its daily average operating capacity and is able to maintain an optimal level of total alkalinity in UVWMA, the estimated saving on chemical water treatment cost will be R150.063.78 per annum. At Balkfontein, chemical water treatment cost is expected to increase on average by 0.346% per megalitre per day for a 1% per megalitre per day increase in the level of chlorophyll-a, and the cost accompanied this change is R41,128.20 per annum. The prediction also shows a 2.077% per megalitre per day increase chemical water treatment cost for a 1% increase in turbidity and this accompanied with a chemical water treatment cost of R 249,003 per annum, provided that Balkfontein operates at its full capacity (i.e., 360 megalitres per day). / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

The Ceratium species occurring in the Vaal River since 2000, was identified as Ceratium hirundinella (O.F. Müller) Dujardin as proposed by Van Ginkel et al (2001). Ceratium hirundinella is known to cause problems in drinking water purification and has been penetrating into the final drinking water of Rand Water since 2006. Ceratium hirundinella is associated with many other water purification problems such as disrupting of the coagulation and flocculation processes, blocking of sand filters and algal penetration into the drinking water. Ceratium hirundinella also produce fishy taste and odorous compounds and causes discolouration of the water. The aims of this study were to determine the main environmental factors which are associated with the bloom formation of C. hirundinella in the source water and to investigate the influence of C. hirundinella on the production of potable water. In order to optimise treatment processes and resolve problems associated with high C. hirundinella concentrations during the production of potable water, jar testing and chlorine exposure experiments were performed. Multivariate statistical analyses were performed to determine the main environmental variables behind C. hirundinella blooms. Ten years data (2000 - 2009) from the sampling point C–VRB5T in the Vaal River, (5 km upstream from the Barrage weir) were used for this investigation, because C. hirundinella occurred there frequently during the ten year period. In this study, it was found that C. hirundinella was favoured by high pH, Chemical Oxygen Demand (COD), orthophoshapte (PO4), and silica concentrations, as well as low turbidity and low dissolved inorganic nitrogen (DIN) concentrations. No correlation was found between C. hirundinella and temperature, suggesting that this alga does not occur during periods of extreme warm or extreme cold conditions, but most probably during autumn and spring. The results of the multivariate statistical analysis performed with historical data from Vaalkop dam, indicate that the dinoflagellate C. hirundinella seems to be favoured by low temperature and turbidity, and high DIN, Fe, Methyl–orange alkalinity, Cd, PO4, Conductivity, pH, hardness and SO4 concentrations. In order to optimise treatment processes such as coagulation, flocculation and sedimentation, jar testing experiments were performed to investigate different coagulant chemicals namely: cationic poly–electrolyte only, cationic poly–electrolyte in combination with slaked lime (CaO) and CaO in combination with activated silica. Water from four different sampling localities were chosen to perform the different jar testing experiments: 1) sampling point M–FOREBAY (in the Forebay, connecting the canal to the Zuikerbosch Purification plant) near Vereeniging due to its proximity to the Zuikerbosch treatment plant, 2) M–CANAL_VD (upstream from the inflow of the recovered water from Panfontein) to determine the influence of (if any) the recovered water from Panfontein on Forebay source water, 3) source water from Vaalkop Dam (M–RAW_VAALKOP) and 4) source water from Rietvlei Dam (water from both Vaalkop and Rietvlei Dams contained high concentrations of C. hirundinella at that time of sampling) to determine which coagulant chemical is the most effective in removing high concentrations of C. hirundinella cells during the production of drinking water. The jar testing experiments with Vaalkop Dam and Rietvlei Dam source water (rich with C. hirundinella) indicated that using cationic poly–electrolyte alone did not remove high concentrations of C. hirundinella efficiently. However, when CaO (in combination with cationic poly–electrolyte or activated silica) were dosed to Vaalkop Dam source water a significant decrease of C. hirundinella concentration was observed. This indicates that the C. hirundinella cells were “shocked or stressed” when exposed to the high pH of the CaO, rendering it immobile and thereby enhancing the coagulation and flocculation process. However, when 10 mg/L CaO in combination with poly–electrolyte was dosed to Rietvlei Dam source water the turbidity and chlorophyll–665 results indicated that this coagulant chemical procedure was ineffective in removing algal material from the source water. The jar testing experiments using the cationic poly–electrolyte alone or cationic poly–electrolyte in combination with CaO on M–FOREBAY and M–CANAL_VD source water, showed a decrease in turbidity, chlorophyll–665 concentration, and total algal biomass, with an increase of coagulant chemical. When CaO in combination with activated silica was dosed, the inherent turbidity of the lime increased the turbidity of the Vaalkop Dam, M–FOREBAY and M–CANAL_VD source water to such an extent that it affected coagulation negatively, resulting in high turbidity values in the supernatant. Regardless of the turbidity values, the chlorophyll–665 concentration and total algal biomass (C. hirundinella specifically in Vaalkop Dam source water) decreased significantly when CaO was dosed in combination with activated silica. Therefore it was concluded that a cationic poly–electrolyte alone is a good coagulant chemical for the removal of turbidity, but when high algal biomass occur in the source water it is essential to add CaO to “stress” or “shock” the algae for the effective removal thereof. However, when CaO in combination with activated silica was dosed to Rietvlei Dam source water a decrease in turbidity and chlorophyll–665 concentration was found with an increasing coagulant chemical concentration. These results confirm the fact that coagulant chemicals may perform differently during different periods of the year when water chemistry changes and that certain coagulant chemicals may never be suitable to use for certain source waters. For the effective removal of algae during water purification, it is recommended that cationic poly–electrolyte in combination with CaO are used as coagulant chemical at the Zuikerbosch Water Purification Plant. Turbidity is not a good indication of algal removal efficiency during jar testing experiments. If problems with high algal concentrations in the source water are experienced it is advisable to also determine the chlorophyll–665 concentrations of the supernatant water during the regular jar testing experiments, since it will give a better indication of algal removal. Chlorine exposure experiments were performed on water from Vaalkop Dam (M–RAW_VAALKOP) and Rietvlei Dam source water, to determine the possibility of implementing pre– or intermediate chlorination with the aim to render the cells immobile for more effective coagulation. The chlorine exposure experiments with Vaalkop Dam and Rietvlei Dam source water showed similar results. The chlorine concentration to be dosed as part of pre– or intermediate chlorination will differ for each type of source water as the chemical and biological composition of each water body are unique. When the effect of chlorine on the freshwater dinoflagellate C. hirundinella was investigated, it was found that the effective chlorine concentration where 50 % of Ceratium cells were rendered immobile (EC50) was approximately 1.16 mg/L for Vaalkop Dam source water. For the source water sampled from Rietvlei Dam, it was found that the EC50 was at approximately 0.87 mg/L. Results of analyses to determine the organic compounds in the water after chlorination revealed that an increase in chlorine concentration resulted in increase in total organic carbon concentration (TOC), as well as a slight increase in MIB and trihalomethanes (CHCl3). Pre– or intermediate chlorination seem to be an effective treatment option for the dinoflagellate C. hirundinella to be rendered immobile and thereby assisting in its coagulation process. The use of pre– or intermediate chlorination to effectively treat source waters containing high concentrations of C. hirundinella is a viable option to consider. However, the organic compounds in the water should be monitored and the EC50 value for each source water composition should be determined carefully as to restrict cell lysis and subsequent release of organic compounds into the water. / Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2012.

The Ceratium species occurring in the Vaal River since 2000, was identified as Ceratium hirundinella (O.F. Müller) Dujardin as proposed by Van Ginkel et al (2001). Ceratium hirundinella is known to cause problems in drinking water purification and has been penetrating into the final drinking water of Rand Water since 2006. Ceratium hirundinella is associated with many other water purification problems such as disrupting of the coagulation and flocculation processes, blocking of sand filters and algal penetration into the drinking water. Ceratium hirundinella also produce fishy taste and odorous compounds and causes discolouration of the water. The aims of this study were to determine the main environmental factors which are associated with the bloom formation of C. hirundinella in the source water and to investigate the influence of C. hirundinella on the production of potable water. In order to optimise treatment processes and resolve problems associated with high C. hirundinella concentrations during the production of potable water, jar testing and chlorine exposure experiments were performed. Multivariate statistical analyses were performed to determine the main environmental variables behind C. hirundinella blooms. Ten years data (2000 - 2009) from the sampling point C–VRB5T in the Vaal River, (5 km upstream from the Barrage weir) were used for this investigation, because C. hirundinella occurred there frequently during the ten year period. In this study, it was found that C. hirundinella was favoured by high pH, Chemical Oxygen Demand (COD), orthophoshapte (PO4), and silica concentrations, as well as low turbidity and low dissolved inorganic nitrogen (DIN) concentrations. No correlation was found between C. hirundinella and temperature, suggesting that this alga does not occur during periods of extreme warm or extreme cold conditions, but most probably during autumn and spring. The results of the multivariate statistical analysis performed with historical data from Vaalkop dam, indicate that the dinoflagellate C. hirundinella seems to be favoured by low temperature and turbidity, and high DIN, Fe, Methyl–orange alkalinity, Cd, PO4, Conductivity, pH, hardness and SO4 concentrations. In order to optimise treatment processes such as coagulation, flocculation and sedimentation, jar testing experiments were performed to investigate different coagulant chemicals namely: cationic poly–electrolyte only, cationic poly–electrolyte in combination with slaked lime (CaO) and CaO in combination with activated silica. Water from four different sampling localities were chosen to perform the different jar testing experiments: 1) sampling point M–FOREBAY (in the Forebay, connecting the canal to the Zuikerbosch Purification plant) near Vereeniging due to its proximity to the Zuikerbosch treatment plant, 2) M–CANAL_VD (upstream from the inflow of the recovered water from Panfontein) to determine the influence of (if any) the recovered water from Panfontein on Forebay source water, 3) source water from Vaalkop Dam (M–RAW_VAALKOP) and 4) source water from Rietvlei Dam (water from both Vaalkop and Rietvlei Dams contained high concentrations of C. hirundinella at that time of sampling) to determine which coagulant chemical is the most effective in removing high concentrations of C. hirundinella cells during the production of drinking water. The jar testing experiments with Vaalkop Dam and Rietvlei Dam source water (rich with C. hirundinella) indicated that using cationic poly–electrolyte alone did not remove high concentrations of C. hirundinella efficiently. However, when CaO (in combination with cationic poly–electrolyte or activated silica) were dosed to Vaalkop Dam source water a significant decrease of C. hirundinella concentration was observed. This indicates that the C. hirundinella cells were “shocked or stressed” when exposed to the high pH of the CaO, rendering it immobile and thereby enhancing the coagulation and flocculation process. However, when 10 mg/L CaO in combination with poly–electrolyte was dosed to Rietvlei Dam source water the turbidity and chlorophyll–665 results indicated that this coagulant chemical procedure was ineffective in removing algal material from the source water. The jar testing experiments using the cationic poly–electrolyte alone or cationic poly–electrolyte in combination with CaO on M–FOREBAY and M–CANAL_VD source water, showed a decrease in turbidity, chlorophyll–665 concentration, and total algal biomass, with an increase of coagulant chemical. When CaO in combination with activated silica was dosed, the inherent turbidity of the lime increased the turbidity of the Vaalkop Dam, M–FOREBAY and M–CANAL_VD source water to such an extent that it affected coagulation negatively, resulting in high turbidity values in the supernatant. Regardless of the turbidity values, the chlorophyll–665 concentration and total algal biomass (C. hirundinella specifically in Vaalkop Dam source water) decreased significantly when CaO was dosed in combination with activated silica. Therefore it was concluded that a cationic poly–electrolyte alone is a good coagulant chemical for the removal of turbidity, but when high algal biomass occur in the source water it is essential to add CaO to “stress” or “shock” the algae for the effective removal thereof. However, when CaO in combination with activated silica was dosed to Rietvlei Dam source water a decrease in turbidity and chlorophyll–665 concentration was found with an increasing coagulant chemical concentration. These results confirm the fact that coagulant chemicals may perform differently during different periods of the year when water chemistry changes and that certain coagulant chemicals may never be suitable to use for certain source waters. For the effective removal of algae during water purification, it is recommended that cationic poly–electrolyte in combination with CaO are used as coagulant chemical at the Zuikerbosch Water Purification Plant. Turbidity is not a good indication of algal removal efficiency during jar testing experiments. If problems with high algal concentrations in the source water are experienced it is advisable to also determine the chlorophyll–665 concentrations of the supernatant water during the regular jar testing experiments, since it will give a better indication of algal removal. Chlorine exposure experiments were performed on water from Vaalkop Dam (M–RAW_VAALKOP) and Rietvlei Dam source water, to determine the possibility of implementing pre– or intermediate chlorination with the aim to render the cells immobile for more effective coagulation. The chlorine exposure experiments with Vaalkop Dam and Rietvlei Dam source water showed similar results. The chlorine concentration to be dosed as part of pre– or intermediate chlorination will differ for each type of source water as the chemical and biological composition of each water body are unique. When the effect of chlorine on the freshwater dinoflagellate C. hirundinella was investigated, it was found that the effective chlorine concentration where 50 % of Ceratium cells were rendered immobile (EC50) was approximately 1.16 mg/L for Vaalkop Dam source water. For the source water sampled from Rietvlei Dam, it was found that the EC50 was at approximately 0.87 mg/L. Results of analyses to determine the organic compounds in the water after chlorination revealed that an increase in chlorine concentration resulted in increase in total organic carbon concentration (TOC), as well as a slight increase in MIB and trihalomethanes (CHCl3). Pre– or intermediate chlorination seem to be an effective treatment option for the dinoflagellate C. hirundinella to be rendered immobile and thereby assisting in its coagulation process. The use of pre– or intermediate chlorination to effectively treat source waters containing high concentrations of C. hirundinella is a viable option to consider. However, the organic compounds in the water should be monitored and the EC50 value for each source water composition should be determined carefully as to restrict cell lysis and subsequent release of organic compounds into the water. / Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2012.

The provision of clean drinking water typically involves treatment processes to remove contaminants. The conventional process involves coagulation with hydrolysing metal salts, typically of aluminium (‘alum’) or trivalent iron (‘ferric’). Along with the product water this also produces a waste by-product, or sludge. The fact of increasing sludge production — due to higher levels of treatment and greater volume of water supply — conflicts with modern demands for environmental best practice, leading to higher financial costs. A further issue is the significant quantity of water that is held up in the sludge, and wasted. / One means of dealing with these problems is to dewater the sludge further. This reduces the volume of waste to be disposed of. The consistency is also improved (e.g. for the purpose of landfilling). And a significant amount of water can be recovered. The efficiency, and efficacy, of this process depends on the dewaterability of the sludge.In fact, good dewaterability is vital to the operation of conventional drinking water treatment plants (WTP’s). The usual process of separating the particulates, formed from a blend of contaminants and coagulated precipitate, relies on ‘clarification’ and ‘thickening’, which are essentially settling operations of solid–liquid separation.WTP operators — and researchers — do attempt to measure sludge dewaterability, but usually rely on empirical characterisation techniques that do not tell the full story and can even mislead. Understanding of the physical and chemical nature of the sludge is also surprisingly rudimentary, considering the long history of these processes. / The present work begins by reviewing the current state of knowledge on raw water and sludge composition, with special focus on solid aluminium and iron phases and on fractal aggregate structure. Next the theory of dewatering is examined, with the adopted phenomenological theory contrasted with empirical techniques and other theories.The foundation for subsequent analyses is laid by experimental work which establishes the solid phase density of WTP sludges. Additionally, alum sludges are found to contain pseudoböhmite, while 2-line ferrihydrite and goethite are identified in ferric sludges. / A key hypothesis is that dewaterability is partly determined by the treatment conditions. To investigate this, numerous WTP sludges were studied that had been generated under diverse conditions: some plant samples were obtained, and the remainder were generated in the laboratory (results were consistent). Dewaterability was characterised for each sludge in concentration ranges relevant to settling, centrifugation and filtration using models developed by LANDMAN and WHITE inter alia; it is expressed in terms of both equilibrium and kinetic parameters, py(φ) and R(φ) respectively.This work confirmed that dewaterability is significantly influenced by treatment conditions.The strongest correlations were observed when varying coagulation pH and coagulant dose. At high doses precipitated coagulant controls the sludge behaviour, and dewaterability is poor. Dewaterability deteriorates as pH is increased for high-dose alum sludges; other sludges are less sensitive to pH. These findings can be linked to the faster coagulation dynamics prevailing at high coagulant and alkali dose.Alum and ferric sludges in general had comparable dewaterabilities, and the characteristics of a magnesium sludge were similar too.Small effects on dewaterability were observed in response to variations in raw water organic content and shearing. Polymer flocculation and conditioning appeared mainly to affect dewaterability at low sludge concentrations. Ageing did not produce clear changes in dewaterability.Dense, compact particles are known to dewater better than ‘fluffy’ aggregates or flocs usually encountered in drinking water treatment. This explains the superior dewaterability of a sludge containing powdered activated carbon (PAC). Even greater improvements were observed following a cycle of sludge freezing and thawing for a wide range of WTP sludges. / Further aspects considered in the present work include deviations from simplifying assumptions that are usually made. Specifically: investigation of long-time dewatering behaviour, wall effects, non-isotropic stresses, and reversibility of dewatering (or ‘elasticity’).Several other results and conclusions, of both theoretical and experimental nature, are presented on topics of subsidiary or peripheral interest that are nonetheless important for establishing a reliable basis for research in this area. / This work has proposed links between industrial drinking water coagulation conditions, sludge dewaterability from settling to filtration, and the microstructure of the aggregates making up that sludge. This information can be used when considering the operation or design of a WTP in order to optimise sludge dewaterability, within the constraints of producing drinking water of acceptable quality.