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M.Ing. (Civil Engineering) / The dissolved air flotation process can be used for different functions in the drinking waterand sewage treatment fields. The focus for this study was on thickening of activated sludge. At first literature was studied to identify all possible parameters. Then five plants were visited periodically and the physical layout and operating parameters were documented. With the examination of the data the different existing models were evaluated, and new relationships were investigated.

M.Sc. / The disinfection of drinking water is an important step in the water treatment process. However, toxic (unwanted) disinfection by-products (DBPs) are often produced during the disinfection of drinking water. One such group of DBPs are the nitrosamines such as N-Nitrosodimethylamine (NDMA). Nitrosamines, particularly NDMA, are highly carcinogenic, mutagenic and teratogenic. The US Environmental Protection Agency (USEPA) placed these compounds into the group B2, which indicates compounds of probable human carcinogens. The USEPA integrated risk information system (IRIS) database lists an estimated 10-6 lifetime cancer risk level for NDMA in drinking water of 0.7 ng/L. The formation of NDMA during drinking water disinfection, particularly chloramination, has been linked to the formation of NDMA through a reaction between monochloramine and organic nitrogen precursors via unsymmetrical dialkylhydrazine intermediates, such as unsymmetrical dimethylhydrazine (UDMH). UDMH is oxidized by dissolved oxygen to form NDMA. Therefore, it is also crucial to remove NDMA precursors (UDMH and dimethylamine (DMA)), before disinfection is carried out. Also, the chlorination of secondary wastewater can result in the formation of NDMA. In this research project, determination of nitrosamines, especially NDMA was done at four different water treatment plants in South Africa. Water samples collected from Midvaal, Sedibeng, Magalies (Vaalkop and Klipdrift) and Rand Water treatment plants were qualitatively analysed for the presence of NDMA. Also, the determination of possible NDMA precursors such as dimethylamine and UDMH was investigated in water samples collected from Sedibeng water treatment plant. The water samples were collected before and after each drinking water treatment process (coagulation, sedimentation, filtration, chlorination and chloramination or ozonation). Solid phase microextraction (SPME) was employed in the extraction of the water samples. Polydimethylsiloxane/divinylbenzene (PDMS/DVB) proved to be the most efficient fibre for the SPME extraction procedure. The water samples vi were then qualitatively analysed using gas chromatography-mass spectrometry (GC-MS). Very small amounts of NDMA were detected in water samples collected from Sedibeng water treatment plant. There was no detectable presence of NDMA or other nitrosamines in water samples collected from the other treatment plants. Water-insoluble cyclodextrin (CD) polyurethanes were then used to ascertain how much of the NDMA they would remove. The CD polymers showed capacity to remove NDMA and dimethylamine (which is a known NDMA precursor) in the water samples with 80% removal efficiency for NDMA (when comparing peak area before and after treatment with CD polymers) and approximately 98% removal rate for DMA.

Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Microorganisms show a tendency to accumulate on surfaces in aqueous environments to form biofilms. Microbial biofilms represent a significant problem in public health microbiology as the development of these microbial communities, especially in water distribution systems, may lead to (i) the enhanced growth of opportunistic pathogens, (ii) the development of organoleptic problems, (iii) the reduction in the flow rate and (iv) the regrowth of microorganisms. In this project, biofilm monitors were installed in a large water distribution system to study biofilm phenomena in drinking water systems, and to deduce the biological stability and quality of the potable water. Measurements of biofilm formation potential showed that biofilms did not reach a steady state after 100 to 150 days. The microbial cells in these biofilms were mostly non-culturable. The contribution of the heterotrophic colony count to active biomass, as determined with cell numbers based on ATP measurements were often < 1%, while the ratio of heterotrophic plate counts and direct acridine orange counts were also <1%. The ratio between cell numbers based on ATP measurements and direct acridine orange counts were often < 100%. Results also showed that under certain conditions, such as those investigated in the present study, 1 pg of ATP may not be equal to approximately 104 active bacteria/cells, as stipulated by previous investigations, and that the average ATP content per active bacterial cell is indeed less than 10-16 - 10-15 g. It was calculated that threshold values for assimilable, and dissolved organic carbon below -5 IJg Gil and -0.5 mg Gil, respectively, should be target values for the control of biofilm formation in this system. It was shown that polyethylene, polyvinylchloride, teflon, plexiglass, copper, zinc-coated steel and aluminium provide favourable attachment surfaces that allowed primary colonisation and subsequent biofilm formation. Significant (p < 0.05) differences in surface colonisation on the materials were observed, indicating that the composition of the material has a direct influence on microbial colonisation. The two grades of stainless steel evaluated in this study were the least favourable materials for biofilm formation. It was further demonstrated that the nature of the surface of these materials, flow conditions and water type all had a direct influence on biofilm formation. While modification of the attachment surface did not result in significant differences (p > 0.05) in disinfection efficiency of two commonly used biocides, the concentration of the biocide, as well as the material to which the biofilm is attached, greatly influenced biocidal efficiency. The results show that biofilm monitoring needs to be implemented at the water treatment plants in addition to common biostability measurements. / AFRIKAANSE OPSOMMING: Mikro-organismes neig om te akkumuleer aan oppervlaktes in akwatiese omgewings om biofilms te vorm. Mikrobiese biofilms verteenwoordig In betekenisvolle probleem in publieke gesondheidsmikrobiologie omdat die ontwikkeling van hierdie mikrobiese gemeenskappe in waterverspreidingsisteme mag lei tot (i) die verhoogde groei van opportunistiese patogene, (ii) ontwikkeling van organoleptiese probleme, (iii) die vermindering in die vloeitempo en (iv) die hergroei van mikro-organismes. In hierdie projek was biofilm monitors geïnstalleer in In groot waterverspreidingsisteem om biofilm fenomene in drinkwatersisteme to bestudeer, en om die biologiese stabiliteit en kwaliteit van drinkwater af te lei. Bepalings van biofilmvormingspotensiaal het aangetoon dat biofilms nie In stabiele stadium na 100 tot 150 dae bereik nie. Die mikrobiese selle in hierdie biofilms was meestal niekweekbaar. Die bydrae van die heterotrofiese kolonie tellings tot aktiewe biomassa, soos bepaal deur seltellings gebaseer op ATP metings was dikwels < 1%, terwyl die verhouding van die heterotrofiese plaatteIIings en direkte akridien oranje tellings ook < 1% was. Die verhouding tussen seltellings, gebaseer op ATP metings en direkte akridien oranje tellings was dikwels < 100%. Resultate het ook aangetoon dat onder sekere omstandighede, soos dié wat ondersoek was in die huidige studie, 1 pg ATP nie gelyk is aan min of meer 104 aktiewe bakterieë/selle soos gestipuleer deur vorige ondersoeke nie, en dat die gemiddelde ATP inhoud per aktiewe bakteriële sel inderdaad minder as 10-16 tot 10-15 g is. Dit was bereken dat die drempelwaardes vir assimileerbare en opgeloste organiese koolstof onder -51-1g C/l en -0.5 mg C/l, onderskeidelik, teikens moet wees vir die beheer van biofilmvorming in hierdie sisteem. Dit was aangetoon dat polyetileen, polyvinielchlroried, teflon, plexiglas, koper, sink-bedekte staal en aluminium gunstige aanhegtings oppervlaktes voorsien wat primêre kolonisering en daaropvolgende biofilmvorming toelaat. Betekinisvolle (p <0.05) verskille in oppervlak kolinisering op die materiale was waargeneem, wat aandui dat die samestelling van die materiaal In direkte invloed op mikrobiese kolonisering het. Die twee tipes vlekvryestaal wat geëvalueer was in hierdie studie, was die minder gunstige materiale vir biofilmvorming. Dit was verder gedemonstreer dat die aard van die oppervlak van hierdie materiale, vloeitoestande, en water tipe almal In direkte invloed het op biofilmvorming. Terwyl die aanpassing van aanhegtingsoppervlak nie die ontsrnettinqsdoeltreffendheid resultaat van die twee algemeen-gebruikte biosiede betekinisvol (p > 0.05) beïnvloed het nie, het die konsentrasie van die biosiede doeltreffendheid grootliks beïnvloed. asook die aanhegtings-materiaal, biosied Die resultate het aangetoon dat biofilm monitering geïmplementeer moet word by waterbehandelingsaanlegte as In alternatief vir algemene biostabiliteit metings.

M.Ing. / A number of distinctly different local and international media specifications are currently being used in South Africa. Along with some opposing requirements, these specifications all specify different testing procedures to be used in the evaluation of filter media. Furthermore the already confusing situation is being complicated by a lack of knowledge as to the general properties of South African filter media ...

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With ever increasing regulation of the quality of drinking water and wastewater treatment, there is a need to develop methods to remove nitrogenous compounds from water. These processes are mediated by a variety of micro-organisms that can oxidise ammonia to nitrate, and then reduced to gaseous nitrogen by another set of organisms. This two stage process involves the relatively slow oxidation of ammonia to nitrate followed a relatively fast reduction of nitrate to nitrogen. Nitrate reduction normally requires anaerobic environments and the addition of organic matter to provide reducing power (electrons) for nitrate reduction. In practical situations the nitrate reduction can be problematic in those precise quantities of organic matter to ensure that the process occurs while not leaving residual organic matter. The aim of this study was to investigate microbial denitrification using electrochemical sources to replace organic matter as a redactant. The work also involved developing a system that could be optimised for nitrate removal in applied situations such as water processing in fish farming or drinking water, where high nitrate levels represent a potential health problem. Consequently, the study examined a range of developments for the removal of nitrate from water based on the development of electrochemical biotransformation systems for nitrate removal. This also offers considerable scope for the potential application of these systems in broader bio-nanotechnology based processes (particularly in bioremediation). The first stage of the study was to investigate the complex interactions between medium parameters and their effects on the bacterial growth rates. The results proved that acetate is a good carbon source for bacterial growth, and therefore it was used as an organic substrate for the biological process. High nitrate removal rate of almost 87% was successfully achieved by using a microbial fuel cell (MFC) enriched with soil inocula with the cathodes cells fed with nitrate and the anode fed with acetate. The maximum power density obtained was 1.26 mW/m2 at a current density of 10.23 mA/m2. The effects of acetate, nitrate and external resistance on current generation and denitrification activity were investigated, and the results demonstrated that nitrate removal was greatly dependent on the magnitude of current production within the MFC. Increase of acetate (anode) and nitrate (cathode) concentrations improved the process, while increasing external resistance reduced the activity. Furthermore, for a clear understanding of the nitrate reduction process, the analysis of the associated bacteria was performed through biochemical tests and examination of morphological characteristics. A diversity of nitrate reducing bacteria was observed; however a few were able to deliver complete denitrification. Pure cultures in MFC were examined and the voltage output achieved was about 36% of that obtained by mixed cultures. The nitrate removal gained was 56.2%, and this is almost 31% lower than that obtained by the mixed bacterial experiment. In an attempt to improve the MFC, modifications to the electrochemical properties of the electrode were investigated through the use of a cyclic voltammetry using carbon nanomaterials to coat the graphite felts electrodes. Among all the nanomaterials used in this study, graphitised carbon nanofibres (GCNFs) was selected for further investigation as it offered the best electrochemical performance and was thought to provide the largest active surface area. The performance of the MFC system coupled with the GCNFs modified electrodes was evaluated and significant improvements were observed. The highest voltage output achieved was about 41 mV with over 95% nitrate removal. The work is discussed in the context of improved MFC performance, potential analytic applications and further innovations using a bio-nanotechnology approach to analyse cell-electrode interactions.

An activated unsaturated sand filter (AUSF) is one of only a few of the filtration technologies utilized to treat waters and wastewaters that use unsaturated filter media. AUSF employs sand coated with potassium permanganate and operates with an open chamber allowing free air flow into the column of sand. The AUSF also benefits from operation without the need for a sedimentation unit. Previous studies have demonstrated the efficient removal of iron and manganese using an AUSF, however, to date there are still very limited studies available that use AUSF technology for the removal of metals from waters and wastewaters. Thus, there is an urgent need and opportunity to exploit this technology further. This research was conducted in order to develop and study the characteristics and subsequent operational performance of a novel AUSF media. The study focuses on the removal of copper, manganese, zinc and nickel from a synthetic wastewater and extends current knowledge to a passive aeration process rather than the active aeration used in the previous study by Lee et. al. (2004). The characterisation involved the use of sieving, Brunauer- Fmmett-Teller (BET) analysis, water evaporation studies and scanning electron microscopy (SEM) for structural analysis such as particle size, surface area, porosity and topography. Energy dispersive X-ray analysis (EDX), acid/alkali resistance, isoelectric point determination and acid digestion analysis were used to determine the chemical constituency, chemical stability, electrical charge properties and the binding efficiency of the media. Finally, tracer studies were employed to determine the flow characteristics through the particle media. The manganese coated sand was proven effective for the removal of copper in both agitated tank batch studies and continuous column studies. The batch studies showed that the equilibrium sorption of copper followed a Langmuir isotherm and the sorption rate was best modelled using the pseudo-second-order kinetic model. This suggests that adsorption is taking place as a single homogeneous layer on the surface of the sand particle via the chemisorption method. The Weber-Morris and Bangham models were used to determine the rate-controlling mechanism and this was found to be predominantly intra-particle diffusion. This was confirmed for column studies using the Bohart-Adams model that demonstrated that liquid-film mass transfer was not significant. Several mechanisms of metal removal are proposed and these include precipitation, electrostatic attraction, adsorption, ion exchange and complex ion formation. The column studies demonstrated that dispersion was low under the operating conditions and plug flow performance could be inferred, thus justifying the use of the AUSF model employed. Copper was best removed when operating as an unsaturated particle bed and the removal capacity was increased by approximately 100% when compared to a saturated particle bed. Moreover, the pH increase that occurs on exposure of the process water to the unsaturated column further improves removal capacity. Thus, there is no requirement for an expensive pH adjustment as a pre-treatment process prior to this unit operation. In addition, the removal capacity of the AUSF was demonstrated to increase with lower metal concentrations, lower water flow rates, smaller sand particles, an increase in manganese to sand ratio and an increase in particle bed height. The AUSF performance in removing metals followed the order Cu > Mn > Zn > Ni for individual and mixed component solutions and Cu > Ni > Zn > Mn for a synthetic wastewater typical of the electroplating industries. In conclusion, the novel manganese coated AUSF developed is effective in the removal of metals from solution and offers the potential of a sustainable low cost treatment method for the purification of waters and wastewaters.