Doctoral Degrees (Chemical Engineering)

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Analysis of a pilot-scale anaerobic baffled reactor treating domestic wastewater.
(2009) Foxon, Katherine Maria.; Buckley, Christopher Andrew.
This thesis presents a chemical, microbiological and mathematical analysis of an anaerobic baffled reactor (ABR) treating domestic wastewater. The purpose of this study was to gain an understanding of the mechanisms of treatment of domestic wastewater in an ABR at pilot-scale, and to use this understanding to develop some guidelines for the design of ABR technology for the anaerobic treatment or pre-treatment of domestic wastewater. Previous research has been undertaken on ABR technology, but no detailed studies of the performance of an ABR on domestic wastewater at pilot-scale have been reported. In this thesis, operating data from a 3 000 ℓ pilot-scale ABR are presented and analysed. Two hypotheses were proposed: that (i) the baffled design of the reactor would facilitate phase separation whereby acidogenic and methanogenic processes predominate in different physical locations in the reactor; and (ii) the critical design parameter is the applied hydraulic retention time. The principle findings of this research were: • The pilot-scale ABR functioned as a solids retention device. Particulate material was retained through settling in the first compartment, forming a gel-like matrix. Reduction of solids occurred through anaerobic conversion to CH4 and CO2. • Partial phase separation of acidogenic and methanogenic communities was observed. • The major factor that controlled biomass washout rate and therefore reactor performance was upflow velocity in each compartment. At higher upflow velocities, slow growing microorganisms failed to establish, resulting in increased solids accumulation rates, while at lower upflow velocities, stable digestion proceeded. • Relatively poor treatment rates were obtained due to the low inherent alkalinity of waters in eThekwini municipality resulting in low operating pH values. • Insufficient pathogen reduction was observed indicating that post-treatment of effluent would be required. It was concluded that the benefit of the baffled design was related to the system’s solids retention characteristics and that the critical design parameters for an ABR domestic wastewater treatment unit were compartment upflow velocity and applied hydraulic retention time.
The Chemical removal of sulphates using barium salts.
(1988) Trusler, Graham Errol.; Buckley, Christopher Andrew.; Edwards, R. I.; Brouckaert, Christopher John.
Abstract available in PDF copy.
The development of a method for the inclusion of salinity effects into environmental life cycle assessments.
(2003) Leske, Anthony.; Buckley, Christopher Andrew.
The work presented in this thesis stemmed out of the apparent lack of a method for incorporating salinity effects into environmental life cycle assessments. Salination of the water resources is a well-known problem in South Africa, and is of strategic concern. Any environmental decision support. tool that does not allow the evaluation of salinity effects therefore has limited applicability in the South African context. The starting-point for the work presented in this thesis was to evaluate existing impact categories, and the characterisation models used to calculate equivalency factors for these impact categories, in an attempt to incorporate salinity effects into existing categories and/or characterisation models. The types of effects that elevated (above normal background levels) dissolved salt concentrations have on the natural and man-made environment were evaluated, and it was concluded that, although there was some overlap with existing impact categories, some of the salinity effects could not be described by existing impact categories. It was also concluded that there are clear and quantifiable causal relationships between releases to the environment and salinity effects. A separate salinity impact category was therefore recommended that includes all salinity effects, including; aquatic ecotoxicity effects, damage to man-made environment, loss of agricultural production (livestock and crops), aesthetic effects and effects to terrestrial fauna and flora. Damage to the man-made environment is evaluated in terms of effects on equipment and structures, interference with processes, product quality and complexity of waste treatment, and is used as an indicator for the environmental consequences derived from the caused additional activity in the man-made environment. Once a conceptual model for a separate salinity impact category had been formulated, existing characterisation models were evaluated to determine their applicability for modelling salinity effects. Salination is a global problem, but generally restricted to local or regional areas, and in order to characterise salinity effects, an environmental fate model would be required in order to estimate salt concentrations in the various compartments, particularly surface and subsurface water. A well-known environmental fate and effect model was evaluated to determine if it could be used either as is, or in modified form to calculate salinity potentiaIs for LCA. It was however concluded that the model is not suitable for the calculation of salinity potentials, and it was therefore decided to develop an environmental fate model that would overcome the limitations of existing model, in terms of modelling the movement of salts in the environment. In terms of spatial differentiation, the same approach that was adopted in the existing model was adopted in developing an environmental fate model for South African conditions. This was done by defining a aunit South African catchmenta (including the air volume above the catchment), which consists of an urban surface; rural agricultural soil (and associated soil moisture); rural natural soil (and associated moisture), groundwater (natural and agricultural) and one river with a flow equal to the sum of the flows of all rivers in South Africa, and a concentration equal to the average concentration of each river in the country. A non steady-state environmental fate model (or, hydrosalinity model) was developed that can predict environmental concentrations at a daily time-step in all the compartments relevant to the calculation of salinity potentials. The environmental fate model includes all the major processes governing the distribution of common ions (sodium, calcium, magnesium, sulphate, chloride and bicarbonate) in the various compartments, and described as total dissolved salts. The effect factors used in the characterisation model were based on the target water quality ranges given by the South African Water Quality Guidelines in order to calculate salinity potentials. The total salinity potential is made up of a number of salinity effects potentials, including; damage to man-made environment, aquatic ecotoxicity effects, damage to man-made environment, loss of agricultural production (livestock and crops), aesthetic effects and effects to terrestrial fauna and flora. The total salinity potentials for emissions into the various initial release compartments are shown in the table below. Initial release compartment Atmosphere River Rural natural surface Rural agricultural surface Total salinity potential (kg TDS equJkg) 0.013 0.16 0.03 1.00 The salinity potentiaIs are only relevant to South African conditions, and their use in LeA in other countries may not be applicable. This, in effect, means that the life cycle activities that generate salts should be within the borders of South Africa. It has been recognised that the LCA methodology requires greater spatial differentiation. Salination is a global problem, but generally restricted to local or regional areas on the globe, and it is foreseen that local or regional salinity potentials would need to be calculated for different areas of the earth where salinity is a problem. The LCA practitioner would then need to know something about the spatial distribution of LCA activities in order to apply the relevant salinity potentials. The LCA practitioner should also take care when applying the salinity potentials to prevent double accounting for certain impacts. Currently, this is simple because no equivalency factors exist for common ions, or for total dissolved salts as a lumped parameter. The distribution of salinity potentials, which make up the total salinity potential, appears to be supported by the environmental policies and legislation of South Africa, in which irrigation using saline water is listed as a controlled activity, and subject to certain conditions. The major recommendations regarding further work are focussed on the collection of data that will allow further refinement of the model, and to decrease the uncertainty and variability associated with the results. The values of the published equivalency factors are dependent on the mathematical definition of the local or regional environment, and these values have been calculated for Westem European conditions. Equivalency factors may vary by several orders of magnitude, depending on how the local or regional conditions have been defined. It is therefore recommended that the model developed in this work ultimately be included into a global nested model that can be used to calculate equivalency factors for other compounds, including heavy metals and organic compounds. This would result in equivalency factors for all compounds that are relevant to South Africa.
An environmental life cycle assessment of the provision of recycled water in Durban.
(2006) Pillay, Sarushen Dhanapalan.; Buckley, Christopher Andrew.; Friedrich, Elena.
This dissertation investigated the questions of sustainable development, in the context of water and sanitation provision, for the eThekwini Municipality. The Durban Water Recycling (DWR) plant, run by Veolia Water, was initially the focus of this investigation. The use of recycled water in Durban has freed potable water supplies for a potential 200 000 new consumers. Industry also benefits as the recycled water is supplied at a lower cost. In order to create a holistic picture of the effect of water recycling, a network incorporating the abstraction, use, re-use and disposal of water in the South Durban Region was investigated. This water supply network was identified consisting of the following units: Inanda Dam, Wiggins Waterworks, the pumping and reticulation network, Durban Southern Wastewater Treatment Works, Durban Water Recycling and the Durban Southern Deep Sea Outfall. For the environmental analysis the Life Cycle Assessment (LCA) tool was chosen. Life cycle assessment is a systematic way to evaluate the environmental impacts of products or processes by following a scientific methodology in which the impacts are quantified. LCA provides objective answers to environmental questions while suggesting more sustainable forms of production and consumption. It is the only tool which has a cradle-to-grave approach and by this it avoids positive ratings for measurements which only consist in the shifting of burdens. The objective of this LCA was twofold. The first was to quantify and evaluate the environmental performance of relevant processes and so help decision makers choose amongst options. The second objective was to provide a basis for assessing potential improvements in the environmental performance of the system. Once these areas and the contributors to the high burdens were identified, improvement options were investigated. One of the key outcomes of this analysis was the development of an electricity index as an indicator of environmental performance for water and wastewater systems. The GaBi 3 software package, which uses the CML (Centre for Environmental Science, University of Leiden, The Netherlands) LCA methodology, was used to compile environmental impact scores for each impact category. For the non standard systems such as Inanda Dam and the Durban Southern Deep Sea Outfall a new way of assessing the impacts was developed. There is an emerging trend to combine the LCA methodology with social issues so as to improve the decision making capability. The social analysis was carried out using an LCA type methodology. The impact categories selected were; job creation and health and health risks. During the course of the study the issue of land displacement arose when investigating the social issues surrounding the construction of a dam. This was then incorporated into the entire study. The system was broken up into sub-systems which were studied separately and then combined to create a holistic picture. Each sub-system was further divided into three stages for analysis; the construction, operation and decommissioning. This method of analysing the system allows for the detailed description of individual process units with the highest social and environmental burden. For example it was identified that the operation of the activated sludge systems at the wastewater treatment works had an environmental burden due to the electricity consumption during this stage. For the impact category of global warming it was discovered that 40% of the total environmental impact of the system could be attributed to the secondary treatment stage at the wastewater works. The construction of the dam had the largest social burden due to the displacement of the communities living in the dam area. The final part of the study was a scenario analysis. The aim of this analysis was to develop a sustainability framework for municipalities seeking to expand their provision of water and sanitation services. Different scenarios for increasing the water supply of a municipality were considered. The environmental impact of each scenario was also investigated. In this stage various options were considered to see how changes in the system affected the environmental profile. Improvements using new, modified or alternate technologies were suggested and their effects calculated. An operating procedure, for the current system, with the lowest environmental impact was also suggested. The results of this research will prove valuable to designers and planners looking to expand existing water supply networks in a sustainable manner. A sustainability framework was developed to complement the existing DWAF framework for municipalities expanding their provision of water and sanitation services. The key findings of this study were: • The quantification of the environmental burdens for the supply of water and sanitation in the eThekwini Municipality first for the individual units then for the system. • An improvement analysis which suggested ways of reducing the environmental burdens of the existing system. • The development of a sustainability framework for a municipality to increase its water and sanitation service levels. • The incorporation of social indicators into the LCA methodology. • The development of a technique that could be incorporated into the LCA methodology, for assessing the toxicity of complex effluents. • The development of a method of evaluating the environmental performance of a water and sanitation system using an electricity index. The thesis provides a holistic view of the abstraction, use, re-use and disposal of water in the eThekwini Municipality and provides a guideline for decision makers when assessing options for expansion or improvement in water supply networks.
Evaluation of forward osmosis technology for the treatment of selected concentrated brines.
(2021) Sitabule, Namadzavho Enos.; Buckley, Christopher Andrew.
Abstract available in PDF.
An integrated computational fluid dynamics an kinetics study of ozonation in water treatment.
(2005) Huang, Tzu Hua.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
Computational fluid dynamic (CFO) modelling has been applied to examine the operation of the prc-ozonation system at Wiggins Waterworks, operated by Umgeni Water in Durban, South Africa. Ozonation is employed in water treatment process primarily to achieve the oxidation of iron and manganese, the destruction of micro-organisms and the removal of taste and odour causing compounds. It also aids in the reduction of the colour of the final water, enhancement of algae removal and possible reduction of coagulant demand. A hydrodynamic model has been satisfactorily verified by experimental tracer tests. The effect of the gas injection was modelled by increasing the level of turbulence intensity at the ozone contactor inlet. The model prediction of the overall tracer response corresponded closely to the experimental results. The framework of ozone reaction modelling was subsequently established using values of rate constants from the literature. An accurate prediction of the ozone concentration profile requires the application of the correct ozone kinetics involved. In raw waters, the depletion of ozone is influenced by the presence of natural organic matters (NOM). The observed ozone decay was found in good agreement using the pseudo first-order rate law. By measuring the total organic carbon (TOC) as a surrogate for NOM, the experimentally determined rate constants can be calculated to account for the effects of the ozone doses and the water quality. The characterisation study also aimed to provide sufficient information on ozone depletion and to be operated easily, without the lengthy and costly analyses ofa detailed kinetics study. The predicted profile of residual ozone concentration suggests the current operating strategy can be improved to optimise the ozone utilisation. The proposed monitoring point was suggested to be at the end of second companment where most ozone reactions have been completed. By coupling the transport equations of the target compounds with their chemical reaction rates, the concentration profile of these compounds such as ozone can be predicted in order to assist the understanding of an operation and to attain better interpretation of experimental results.
An investigation of advanced oxidation processes in water treatment.
(2001) Schwikkard, Gavin Wyatt.; Buckley, Christopher Andrew.
The deteriorating water quality in South Africa and changing legislation requiring the industrial implementation of waste minimisation and pollution prevention technologies has highlighted the need for the investigation of new effluent treatment technologies such as advanced oxidation processes. This investigation details the evaluation of ultrasound, an emerging advanced oxidation process, to degrade organic compounds during water treatment. The objectives of the investigation included the design of a suitable ultrasonic laboratory reactor to investigate ultrasound chemistry and the sub-processes occurring during sonication. Atrazine was used as a model compound to compare the performance of ultrasound with that of ozone and hydrogen peroxide, already established advanced oxidation processes. Recommendations have also been made for the scale-up of ultrasonic processes. A 500 mL ultrasonic cell containing an ultrasonic horn as an energy source was designed and constructed. The measurement of hydrogen peroxide concentration was used as a tool to indicate the process conditions under which the formation of free radical reactions during sonication are enhanced. These include the application of oxygen and air sparging or the addition of a commercial source of hydrogen peroxide. It was found that oxygen sparging and a high acoustic power input should be used in ultrasonic processes with a short retention time, and conversely, that air sparging and a lower acoustic energy source should be used in processes with a long retention time. A flow loop system should be considered to maximise oxidation both within and beyond the sonicated zone, gas sparging should only occur within the sonication zone else the degradation of hydrogen peroxide is encouraged. Ultrasound is most effectively applied in water treatment as a pretreatment stage in combination with other technologies and not as a stand-alone process. Atrazine was used. as a model compound to compare the performance of ultrasound with ozone because of its persistence in the environment and resistance to degradation. Atrazine was degraded during sonication and ozonation. degradation increased wim the addition of hydrogen peroxide. Ozone decomposition (and hence free radical reactions) was enhanced when ozone was combined with ultrasound or hydrogen peroxide. Enhanced ozone decomposition during ozonation combined with sonication is due to the conditions (high temperatures and pressures) as well as the free radical reactions occurring within the collapsing cavitation bubbles and at the gas-liquid interface. The enhancing effect of combining ultrasound with ozone was greatest at the low ozone concentrations typically applied during water treatment. Atrazine degradation during sonication and ozonation is predominantly due to the reaction with hydroxyl radicals. Atrazine degradation products identified using gas chromatography and mass spectrometry were deethylatrazine. hydroxyatrazine and deethyldeisopropylatrazine (tentatively identified).
Modelling municipal wastewater treatment plants for industrial effluent discharge permitting: focusing on how modelling can be carried out in cases where measurements and resources are limited.
(2016) Mhlanga, Farai Tafangenyasha.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
Abstract available in PDF file.
Municipal wastewater characterization : application of denitrification batch tests.
(1999) Naidoo, Valerie.; Urbain, Vincent.; Ginestet, Philippe.; Buckley, Christopher Andrew.
The biological treatment of wastewater has evolved significantly from simple single sludge systems practicing organic carbon removal to ones which now include either nitrification/denitrification (N/DN) and / or phosphorus (P) removal. The inclusion of more biological processes have increased the complexity of current wastewater systems which has subsequently led to the development of more complex mathematical models. The operation of plants can be assessed and improved by the use of mathematical modelling tools which require accurate input data. Thus, knowledge of the wastewater characteristics is an important step towards the optimum modelling, design and operation of present and future plants. However, for these tools to be effective, the input data needs to be accurate which is dependent on the current methods used to determine them. Wastewater is a complex substrate consisting of compounds of differing biodegradability. Biokinetically, these compounds have been divided into readily biodegradable (RBCOD), slowly biodegradable (SBCOD) and unbiodegradable substrate groups. Compounds with intermediate biodegradability i.e. compounds which fall between the RBCOD and SBCOD groups, have been termed readily hydrolyzable organic substrates (RHCOD). The organic matter is discussed in terms of chemical oxygen demand (COD). The readily biodegradable and readily hydrolyzable COD fractions of wastewater can be determined by respirometric tests such as the oxygen utilization rate (OUR) and nitrate-N utilization rate (NUR) tests. The principal aim of this project was to investigate the NUR test as a tool for wastewater characterization and to study denitrification kinetics in batch reactors. In addition, an experimental readily biodegradable substrate, acetate, was used to determine the reliability of the NUR tests. Acetate was also used to ascertain utilization profiles and rates of a typical readily biodegradable substrate during denitrification. Biodegradable COD characterizations with enhanced biological phosphorus removal (EBPR) sludges were also investigated to determine the impact of anoxic phosphorus removal on NUR tests. The results obtained from the numerous NUR tests added to the undestanding of the NUR test. Samples from 22 wastewater treatment plants were tested, most of which were located in France. Four South African plants were also tested. Data obtained from the NUR tests were used to calculate the RBCOD and RHCOD fractions. The SBCOD, however, could not be determined directly from the 6 h NUR batch tests. The readily biodegradable COD (RBCOD) fractions ranged between 7 and 25 % of the total COD concentration of raw wastewater, with majority of those results falling within the 10-20 % (of the total COD) range. The results also showed that the initial rapid rate associated with readily biodegradable COD utilization was sometimes followed by a short intermediate phase (i.e. short duration, 2 to 3 h). The intermediate fraction was found to range between 5 and 29 % of the total COD concentration and was classed as a readily hydrolyzable COD component of raw wastewater since the magnitude of the RHCOD fraction was too small to be classed as slowly biodegradable COD which comprises approximately 30 to 60 % of the total COD found in raw wastewaters. The variability of the RHCOD fractions suggests that this fraction is either very variable or that the NUR test does adequately or accurately characterize it. Another possibility is that the RHCOD (or second biodegradable fraction) calculated from the NUR test is a component of the RBCOD of the influent wastewater. In this case, the bacteria may have used some of the RBCOD directly for energy and accumulated or stored the rest as part of a survival mechanism which allows them to be more competitive under dynamic operating conditions. Once the readily biodegradable COD becomes limiting, the bacteria will use the accumulated or stored compounds. This hypothesis is substantiated by tests done with acetate as substrate. An intermediate phase was also observed when acetate was the sole substrate. Thus, it was possible with the 3-phase profiles to calculate a second biodegradable fraction. Results suggest that a significant part of the added acetate (as COD) was stored and the second phase is in fact an 'apparent or residual' phase brought about by the consumption of the stored or accumulated acetate products. This is suggested in two ways: (1) the calculation of the yield coefficient is lower and closer to the 0.5 mg/l values, cited in the literature, when the COD calculated from phases 1 and 2 are considered, and (2) the acetate mass balances were found to be approximately 100 % when phases 1 and 2 were used to calculate the amount of acetate utilized under anoxic conditions. The results obtained with sodium acetate as a readily biodegradable substrate were used to formulate several conclusions on acetate utilization during denitrification. Firstly, from acetate mass balances it was found that acetate may be used exclusively for denitrification (100 % acetate was accounted for). In this case, the sludge contains a significant proportion of denitrifiers and little or no polyphosphate accumulating organisms. This observation was made only when non-EBPR (enhanced biological phosphorus removal) sludges were used. Secondly, acetate mass balances which were found to be < 100 % suggest that acetate could be used for denitrification and the production of storage products like polyhydroxyalkanoates (PHA's). These sludges probably contained a higher proportion of polyphosphate accumulating organisms which competed for the available acetate in the bulk liquid. This observation was made for both EBPR and non-EBPR sludges. Thirdly, acetate could be used for denitrification by denitrifiers and for polyhydroxyalkanoate synthesis by denitrifying polyphosphate accumulating organisms. The stored PHA's in the denitrifying polyphosphate accumulating organisms are subsequently utilized during denitrification. This secondary utilization is manifested in the second denitrification phase and is supported by the observation of phosphorus uptake. These results showed that wastewaters high in volatile fatty acids (VFA's) were also subject to denitrifying polyphosphate accumulating organism activity even though the sludge was sampled from non enhanced biological phosphorus removal systems (non EBPR). Several of the NOx profiles revealed either 2 or 3 rates due to the control of the substrate to biomass ratio (S/X: :<_0.1 mgO2 / mgO2). Majority of the samples (i.e. 85%) tested produced initial maximum specific denitrification rates (k1) between 3 and 6 mgN/gVSS.h. The intermediate denitrification rate (k2) was found to vary between 2 and 3 mgN/gVSS.h. Denitrification rates (k3) obtained from utilization of influent and. endogenous slowly biodegradable COD (SBCOD) varied between 1.0 and 1.5 mgN/gVSS.h. This latter rate is significantly higher than the endogenous denitrification rates cited in the literature. One of the reasons for these higher rates could be be linked to the the reuse of stored or accumulated products by the microorganisms. In addition, a comparative study on RBCOD determination of wastewaters with enhanced biological phosphorus removal and non-EBPR sludges. It was found that the RBCOD values derived by NUR tests with EBPR sludge were consistently lower (4 to 5 %) than those with non-EBPR sludge. Thus, the NUR tests with EBPR sludge resulted in a 4 to 5 % underestimation of the RBCOD fraction of raw wastewaters. This loss in RBCOD to polyphosphate accumulating organisms appears to be linked to the influent raw wastewater acetate concentration. These tests showed that the RBCOD fraction could be adequately characterized using the NUR method. The accuracy of the tests appears to be compromised when enhanced biological phosphorus removal sludges are used in the NUR tests. Moreover, it was found that non-EBPR sludges can also consume some of the acetate that is present in the system for the production and replenishment of storage compounds. Fortunately, for the wastewaters tested, the acetate component of the RBCOD fraction was small and therefore, did not significantly affect the results. Mechanisms such as substrate accumulation and storage may also impact on substrate removal and hence, the determination of the readily biodegradable COD concentration of municipal wastewaters. Thus, while the results showed that the NUR is a useful characterization tool for wastewaters, it will continue to be a more tedious characterization tool than the oxygen utilization rate test, until a suitable nitrate/nitrite electrode is developed to automate the test.
Performance studies of the tubular filter press.
(1992) Rencken, Gunter Eduard.; Buckley, Christopher Andrew.; Raal, Johan David.
The tubular filter press is a novel tubular configured filter press for the filtration or dewatering of sludges. The unique features of the filter press are: (i) during the cake deposition cycle, cake is deposited on the internal walls of a self-supporting array of horizontal collapsible porous fabric tubes; (ii) during the cake removal cycle, cake is dislodged from the tube walls by means of a roller cleaning device and the dislodged flakes of cake are hydraulically transported out of the tubes by the feed sludge which is simultaneously re-circulated at a high flow rate through the tubes. The two main problems experienced on a prototype tubular filter press, which was erected at a water treatment plant to dewater the sludge from the clarifier underflow, were: (i) tube blockage problems during the filtration cycle; (ii) low cake recoveries (high cake losses) during the cake removal cycle. The following objectives which were defined for this study, were regarded as fundamental prerequisites for any solution of the two main problems: (i) to develop a predictive dead-end internal cylindrical model for compressible cake filtration inside a porous tube; (ii) to investigate the cake losses during the cake removal cycle of the tubular filter press; (iii) to develop a predictive unsteady-state internal cylindrical cross-flow microfiltration model for a non-Newtonian sludge which, when filtered, produces a very compressible cake. (An alternative to dead-end filtration during the filtration cycle of a tubular filter press is low axial velocity cross-flow filtration). On the basis of the objectives the study was divided into three separate investigations. To date no one has developed a model which incorporates the cylindrical configuration of the filter medium for dead-end compressible cake filtration inside a porous tube. The most comprehensive model for dead-end external cylindrical compressible cake filtration is that of Tiller and Yeh (1985). This model was adapted for internal cylindrical compressible cake filtration. In essence the model by Tiller and Yeh (1985) requires the solution of a system of two ordinary differential equations in order to calculate the radial variation of solids compressive and liquid pressures in a compressible filter cake deposited externally on a cylindrical surface. The relevant equations were derived for internal cylindrical compressible cake filtration and it was found that one of the differential equations changes from: dPl/dr = H1/2nrK (external cylindrical) to dPl/dr = H12nrK (internal cylindrical). The other differential equation remains unaltered for internal cylindrical compressible cake filtration. A batch of waterworks clarifier sludge from the prototype tubular filter press was used for experiments to evaluate the performance of the internal cylindrical filtration model. The cake produced by the filtration of this sludge had to be characterized for the model. Compression-permeability data were obtained over a wide solids compressive pressure range. A Compression-Permeability (C-P) cell was used for high solids compressive pressures (10 kPa<_ ps<_400 kPa) and settling tests were used for low solids compressive pressures (0,0065 Pa <_ ps < 525,6 Pa). The cake was found to be very compressible (compressibility coefficient = 0,989). Empirical equations of the form, K' = Fps - b and (1 - E) = B pbs , were derived from the C-P cell and settling tests to relate permeability and porosity to solids compressive pressure. The equations were slightly different to those proposed by Tiller and Cooper (1962). The predictions by the internal cylindrical compressible cake filtration model were compared to the results of constant pressure internal cylindrical filtration experiments, at filtration pressures of 100 kPa, 200 kPa and 300 kPa, using the waterworks clarifier sludge. The internal diameter of the filter tube which was used for the experiments was 26,25 mm. The model accurately described the results of the filtration experiments in terms of volume of filtrate, average cake dry solids concentration, filtrate flux and internal cake diameter. The differences between external cylindrical, internal cylindrical and planar compressible cake filtration were highlighted. Since the tubular filter press is a novel process, the cake losses during the cake removal cycle have not been investigated before. An investigation was therefore conducted into the cake losses which occur during the cake removal cycle. The same batch of clarifier sludge was also used for the investigation of cake losses during the cake removal cycle at filtration pressures of 100 kPa and 300 kPa. It was found that significant cake losses occurred due to: (i) the shear of the cleaning fluid prior to the action of the rollers (losses varied between 10 % to 20 % of the deposited cake dry solids); (ii) the combined action of the rollers when dislodging the cake and the hydraulic conveyance of the dislodged flakes of cake (losses varied between 30 % to 40 % of deposited cake dry solids). A new shear model, which was developed, accurately predicted the cake losses and increase in internal cake diameter and average cake dry solids concentration, which occurred due to the shear of the cleaning fluid. For the shear model the sludge (cake) rheology was determined using a capillary-tube viscometer. It was found that the sludges exhibited Bingham plastic behaviour in the solids concentration range: 3,58 % m/m <_Cs <_16,71 % m/m. The cake losses due to the action of the rollers and hydraulic conveyance of the dislodged flakesof cake decreased markedly as filtration pressure and filtration time were increased, while a decrease in path length for hydraulic conveyance of dislodged cake flakes resulted in a mild decrease in these cake losses. A literature review revealed that to date only one mathematical model (Pearson and Sherwood, 1988) is available for the unsteady-state cross-flow microfiltration of a non-Newtonian sludge which, when filtered, produces a compressible cake. A new unsteady-state internal cylindrical axial convection shear model (for laminar flow of the feed sludge) was developed for cross-flow microfiltration of a Bingham plastic sludge which, when filtered, produces a very compressible cake. Similar to the approach by Pearson and Sherwood (1988) this model is a combination of the dead-end internal cylindrical compressible cake filtration model and the "cleaning fluid" shear model. The major difference between the new model and the model by Pearson and Sherwood (1988) is that unlike the convection-diffusion model of Pearson and Sherwood (1988), diffusive and shear induced diffusive back-mixing of particles were assumed to be negligible. The existence of a shear plane within the cake forms the basis of the model. Those cake layers with a yield stress less than the shear stress exerted by the flowing feed sludge at the inner cake wall are convected along the shear plane. It was assumed that the axial convection of the solids in the moving cake layer along the shear plane is the sole mechanism for removal of solids deposited at the cake surface. The model was compared to the results of cross-flow microfiltration experiments at one filtration pressure (300 kPa) and cross-flow flow rates of 0,84 l / min; 1,58 l / min; 2,43 l / min and 4,44 l /min. The model accurately described the variation of filtrate flux, internal cake diameter and average cake dry solids concentration during the unsteady-state time period. The model, however, had to be "extended" by incorporating empirical equations for changes in permeability and porosity (due to further cake compaction) to obtain a good fit between the model and experimental results during the pseudo steady-state time period. The results of all three investigations provide a greater understanding of the cake deposition process (during both dead-end and cross-flow filtration modes) and the cake removal process for the tubular filter press. This should assist in finding solutions to the two main problems which were experienced on the prototype tubular filter press.
The recovery of sodium hydroxide from cotton scouring effluents.
(1994) Simpson, Alison Elizabeth.; Buckley, Christopher Andrew.
This dissertation describes the characterisation of, and development of a novel integrated waste management strategy for, hydroxide scouring effluents produced during cotton processing. Such effluents are typical of mineral salt-rich waste waters which are not significantly biodegradable in conventional treatment plants. The proposed strategy focuses on two complementary concepts: process-oriented waste minimisation adopts a systematic approach to identifying potential problems and solutions of waste reduction in the manufacturing process itself; while add-on controls reduce the impact of the waste after it has been generated, by recycling and treatment. The basic procedures for ensuring effective water and chemical management within the scouring process are described. Examples are given of factory surveys, which have resulted in significant chemical and water savings, reduced effluent discharge costs, maximum effluent concentration, and minimum pollutant loading and volume. Pilot-plant investigations demonstrate the technical and economic feasibility of a four stage treatment sequence of neutralisation (using carbon dioxide gas), cross-flow microfiltration, nanofiltration and electrochemical recovery to remove colour and impurities from the scouring effluent and produce directly reusable sodium hydroxide and water. Fouling and scaling of the cross-flow microfiltration, nanofiltration and electrochemical membranes are minimal and reversible if the operation is carried out under carefully selected conditions. A long anode coating life is predicted. Current efficiencies for the recovery of sodium hydroxide (up to 20 % concentration) are 70 to 80 % and the electrical power requirements are 3 500 to 4 000 kWh/tonne of 100 % NaOH. Pilot-plant trials are supplemented by extensive laboratory tests and semi-quantitative modelling to examine specific aspects of the nanofiltration and electrochemical stages in detail. Electromembrane fouling and cleaning techniques, and other anode materials are evaluated. The effects of solution speciation chemistry on the performance of the nanofiltration membrane is evaluated using a combination of speciation and membrane transport modelling and the predicted results are used to explain observed behaviour. Based on the results of pilot-plant trials and supplementary laboratory and theoretical work, a detailed design of an electrochemically-based treatment system and an economic analysis of the electrochemical recovery system are presented. The effects of rinsing variables, processing temperatures, and background rinse water concentrations on the plant size requirements and capital costs are determined. The implementation of the waste management concepts presented in this dissertation will have significant impact on water and sodium hydroxide consumption (decreasing these by up to 95 and 75 % respectively), as well as effluent volumes and pollutant loadings.
Scientific and management support for ventilated improved pit latrines (VIP) sludge content.
(2014) Bakare, Babatunde Femi.; Foxon, Katherine Maria.; Buckley, Christopher Andrew.
Providing adequate sanitation to all in the form of VIP latrines as proposed by the South African Government Strategic Framework for Water Services does not end with building toilets. All municipalities need to plan for maintenance during the operation and when these toilets reach their capacity. An understanding of the processes occurring in pit latrines will facilitate better management during their lifespan and identifying suitable options for dealing with the accumulated sludge when they eventually reach their capacity. This research aims at providing scientific support for decision making in management of accumulated sludge in ventilated improved pit latrines during their life span and when they reach their capacity under South African conditions. The approach to this research work was divided into two main thrusts: The first was to provide an understanding of the processes in VIP latrines and mechanism of sludge stabilization in pit latrines. The second approach was to provide management and disposal options for pit latrine sludge before and once it has been exhumed in the context of the eThekwini pit latrine emptying programme. Two options were used as case studies, namely: (i) deep row entrenchment of exhumed pit sludge for agroforestry and, (ii) in situ treatment of pit sludge using additives. Three hypotheses were proposed: that (i) significant biological stabilization occurs in a pit latrine with time, such that the disposal/treatment options depend on the inherent ability of the chosen option to accept the load of solids and organic material in the VIP sludge, the residual biodegradability of the VIP sludge, and the health risks, (ii) VIP latrine sludge can be used in deep row entrenchment for agroforestry since the sludge contains nutrients that are available to plants, and that the sludge is sufficiently stable not to cause a negative environmental impact, and (iii) that In situ treatment of VIP latrine sludge using pit additives had no significant effect on the rate of mass loss or volume loss of pit latrines contents. The methodological approach to this research was aimed at addressing the proposed research hypotheses. Thus to test the first hypothesis, two studies were conducted; the first study investigated sludge accumulation rate in pit latrines and the role of digestion processes on sludge accumulation rate in pit latrines. Direct measurement of sludge accumulation rate from selected pit latrines within a community in eThekwini municipality was performed and a laboratory investigation into the effect of moisture content and aerobic/anaerobic conditions on sludge accumulation rate was conducted. The second study investigated the chemical and biological characteristics of pit sludge at different depths within a pit latrine. Research into deep row entrenchment of VIP latrine sludge for agroforestry was conducted to test the second hypothesis. The effect of deep row entrenchment on sludge characteristics and surrounding groundwater at the site was investigated by monitoring changes in sludge characteristics and groundwater quality at the entrenchment site over time. An investigation into the effect of pit latrine additives on pit sludge was conducted to test the third hypothesis. Two sets of trials were conducted; the first was a laboratory trial conducted to investigate the effect of pit latrines additives on collected sludge samples from pit latrine in laboratory scale test units. The rate of mass loss that could arise from the effect of addition of pit additives to sludge in the test unit was determined. The second was a field trial in which pit additives were added to randomly selected pit latrines within a community in Durban and changes in amount of the sludge in the pit was investigated using a laser tape measure and a stereographic imaging technique. The main findings of this research were: • The sludge volume accumulation rate in pit latrines investigated was between 120 ℓ/year and 550 ℓ/year regardless of the number of pit users. The overall average sludge accumulation rate was 282 ± 46 ℓ/year. This converts to a per capita sludge accumulation rate of 56 ℓ/person∙year for an average of 5 number of pit users obtained in this study. Statistical analysis performed indicated that sludge accumulation rate on a per capita basis does not decrease with an increase in number of pit users. • In the laboratory batch experiments, it was observed that by increasing the moisture content the rate of degradation of sludge samples decreases. Over a period of 230 days, mass loss was inversely proportional to total moisture content, and it was found that the mass of solids have been reduced to somewhere between 17 and 64 % of the original sludge mass. This effect was attributed to the exposure of sludge samples in the test units to oxygen, since sludge samples with higher total moisture content in the test units appeared as increased depth of free liquid between sludge sample and air. The calculated mass loss rates observed is expected to be higher than that which will be observed in a pit because the laboratory test had continuous air exposure but pit contents are usually covered over by new materials added to the pit. • Natural stabilization of sludge within the pit does occur if the pit is managed and maintained properly thus providing a long service life for the pit. It was found that the volume of materials have been reduced to between 50 and 75 % of the volume of material added over the 3 years since the pits investigated were last emptied, based on the observed per capita sludge accumulation rate and an estimate of the material added to the pit per person/year. Thus, by comparing the calculated mass reduction in the batch laboratory experiment with the volume reduction in the field investigation of sludge accumulation rate, it can be infered that sludge densification/compaction could play an important role on the stabilization processes in a pit. • The nature of sludge in pit latrines varied significantly within the pit and between different pits. It was observed that below the surface layer in a pit, additional stabilization of sludge does occur and the degree of stabilization within a pit increases with increasing depth from the surface down to the bottom layer of the pit. Sludge samples from the bottom of the pit were well stabilized. • It was also observed from the investigation into deep row entrenchment of pit sludge for agroforestry that further stabilization of pit sludge does occur and as a result of that, nutrients (nitrogen, phosphorus and potassium) locked up in the buried sludge are released as fertilizers. Trees planted near buried VIP sludge showed better growth rate compared to those buried only on soil without VIP latrine sludge and no profound effect on groundwater was observed for the duration in which monitoring was carried out. Further research is needed to develop models for implementing this method cost effectively across a range of conditions. • Neither laboratory trials nor field trials provided any evidence that the use of pit additives have any beneficial effect on VIP latrine sludge. There were no systematic and statistically significant changes in the rate of mass loss on sludge samples in the laboratory test units as well as changes in sludge content of the pit latrines used for the field trials as a result of pit latrine additives. Although, it was observed that there was significant reduction in sludge height in pit latrines in which only water was added compared to those in which additives were added and those in which nothing was added (control) using the infrared distance measure, this effect can probably not be explained completely to be as a result of increasing biodegradation rate caused by higher moisture content, since this explanation would have been observed in the laboratory trials as well as in measurement taking using the stereographic imaging techniques. Instead, flattening of the surface of sludge content in the pit by the addition of water onto the highest part of the pile may play a part in the apparent reduction of sludge height observed. It is therefore concluded from the investigation conducted in this research, that sludge content in pit latrines has naturally undergone significant degradation and that the options for disposal of pit latrine sludge would be limited by the characteristics of the sludge. Therefore disposal options involving biological treatment such as disposal into wastewater treatment plants and anaerobic digestion are not appropriate because the residual biodegradability of VIP latrine sludge obtained was very low (about 30 %) and as such would only result in accumulation of undigested solid; of the options considered in this research, deep row entrenchment of VIP latrine sludge for agroforestry seems to be an appropriate option for the disposal of VIP latrine sludge. There was no evidence to suggest that pit latrine additives have any effect in reducing sludge content in pit latrines.
Treatment of dye wastewaters in the anaerobic baffled reactor and characterisation of the associated microbial populations.
(2002) Bell, Joanne.; Buckley, Christopher Andrew.
There is potential for the anaerobic baffled reactor (ABR) to be implemented on-site for pre-treatment of coloured wastewaters. The implementation of waste minimisation and cleaner production strategies in industry will result in the production of smaller volumes of concentrated wastewaters. With implementation of the ABR, the concentrated waste stream could be pre-treated, with an acclimated biomass, which should facilitate sufficient degradation such that the effluent could be discharged to sewer for further treatment. The ABR is a high-rate compartmentalised anaerobic bioreactor, the design of which promotes the spatial separation of microorganisms. The use of molecular teclmiques to characterise the microbial populations and the dynamics of these populations with time and/or changing operating conditions will add to the current understanding of the process, which is based on the biochemical pathways and chemical analyses. This knowledge will allow for optimisation of the design of the ABR. The hypothesis of the horizontal separation of acidogenesis and methanogenesis through the ABR was proven. Changes in the HRT affected the operation of the reactor, however, recovery from these upsets was almost immediate and operation of the reactor was stable. Two synthetic dye waste streams, one food dye (tartrazine) and one textile dye (Cl Reactive Red 141), and a real industrial dye wastewater, were treated in separate laboratory-scale ABRs. These investigations showed that successful treatment of a highly coloured wastewater is possible in the ABR. The design of the ABR facilitates efficient treatment of concentrated dye wastewaters by protecting the sensitive methanogens from the inhibitory dye molecules and promoting efficient colour and COD reduction. The molecular-based method, fluorescent in situ hybridisation, allowed the direct identification and enumeration of microbial populations active in the ABR. In all of the reported investigations, there was a definite shift in the microbial populations through the ABR, with a predominance of eubacteria in the first compartments (acidogenesis) and archaea (methanogenesis) in the later compartments. The number of compartments involved in each depended on the strength of the substrate (organic loading rate - OLR). A combination of FISH probing, and the analysis of 98 archaeal l6S rDNA clone inserts provided useful descriptions of the methanogens actively involved within each compartment. These showed a predominance of the Methanosaeta spp., particularly in the last compartments of the reactor. Methanogens present in the first four compartments consisted of species of Methanobacterium and Methanospirillum, a relatively unstudied methanogen Methanomethylovorans hollandica, and an unidentified short filamentous species.

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