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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
421

Removal of aquatic organic matter and humic substances by selected water treatment processes

Collins, Michael Robin January 1985 (has links)
The characteristics of dissolved aquatic organic matter present in four natural water sources, as well as corresponding treated waters derived from eight water treatment plants, is described. An assessment is made of the performance of direct filtration, conventional treatment, and lime softening in removing trihalomethane (THM) precursors from a diverse array of water sources. A comparison is made between conventional treatment and direct filtration in removing THM precursors from a common natural water source, the Colorado River. In addition, the effect of selected initial conditions and operating parameters on the direct filtration process are evaluated by using a synthetic water/bench-scale apparatus. Important characteristics of the organic matter, including molecular weight (MW) distribution, carboxylic acidity and humic substances content, appear to affect the removal of this organic material. As a general rule, THM reactivity or yield (ug THM/mg C) increases with MW. The <10,000 MW range was found to be the most consistent reactive fraction of aquatic organic matter. All of the various treatments preferentially removed the most reactive fraction of precursor present in each MW range. None of the various treatments proved to be very effective in removing precursor material below a MW of <500. Humic molecules, with the highest carboxylic acidity and hence highest charge density, are generally more difficult to remove by alum coagulation. All of the various treatment processes studied preferentially removed hydrophobic over hydrophilic aquatic organic matter. None of the source related conditions (fulvic acid, kaolinite, pH) nor process-related conditions (flocculation velocity gradient, mixing time, prechlorination, preozonation) evaluated under the same experimental conditions exerted a major impact upon the performance of the bench-scale direct filtration process. Larger sized particles may be easier to remove by bench-scale treatment, but removal of the smaller particles may result in better removals of organic matter as quantified by NVTOC and UV Absorbance.
422

The effects of activated carbon adsorption and ozonation on trihalomethane speciation

Tan, Lo, 1963- January 1989 (has links)
Two surface water sources in the southwestern United States, Colorado River Water (CRW) and California State Project Water (SPW), were studied in bench-scale experiments examining two Trihalomethane (THM) precursor removal processes, activated carbon adsorption and ozone oxidation. Both source water contained bromide (Br-) ion leading to brominated THMs upon chlorination. Activated carbon removed THM precursors, as measured by dissolved organic carbon (DOC), while having little effect on bromide. The net result was an increase in the ratio of Br-/DOC and an increase in the relative abundance of brominated THMs. Ozone oxidized higher molecular weight precursor molecules into lower molecular weight by-products which were less reactive with chlorine. Moreover, ozonation transformed Br- to hypobromous acid (an "in-situ" oxidant), leading to an increase in the percentage of brominated THMs.
423

The development and application of combined water and materials pinch analysis to a chlor-alkali plant.

Gianadda, Paolo. January 1989 (has links)
Pinch Analysis, in the broadest sense, is concerned with the optimal use of resources (material or energy) in a multi-process system. Pinch Analysis based techniques have emerged for water systems over the past decade. A major assumption that has been made in applying these techniques is that a process system can be segregated into a set of process streams and a set of water streams. With this distinction in place, only the water streams are considered in the Pinch Analysis with the process streams represented implicitly. This approach has obvious limitations in situations where a clear distinction between process streams and water streams cannot be made. The chlor-alkali process is an example of a system in which the clear distinction between process streams and water streams cannot be made. Water is intrinsically involved in the process, serving as a carrier medium for raw materials and eventually becoming part of the products produced by the complex. Hydrochloric acid and caustic soda are reagents which are both used within and produced by the complex. These reagents are required by the process at a range of concentrations and the concentrated reagent is diluted to the required concentrations using demineralised water. Within the chlor-alkali complex, a number of effluents containing the reagent species are available and are typically sent to drain. It is conceivable that these effluents might be recovered and used for dilution purposes instead of demineralised water. This would bring about a reduction in the amount of water and concentrated reagent used and the amount of effluent produced by the complex. Given the economic value of these reagents relative to water, their recovery, if feasible, is likely to dominate the optimal water-use and effluent generation strategy. Current Water Pinch Analysis theory relies on the distinction being made between process streams and water streams and does not consider the recovery of reagents or the presence of desirable species within the system. In addition, the assumption is made that species are non-reactive; reactive species such as hydrogen chloride and sodium hydroxide, fall outside the scope of the current theory. The objectives of this study have included the development of an approach which is able to address these limitations of the existing theory. This approach, termed Combined Water and Materials Pinch Analysis seeks to identify optimal use strategies for raw materials and reagents, in addition to water-use and effluent generation. The approach combines mathematical programming with conceptual insights from Water Pinch Analysis. The approach is based on the optimisation of a superstructure which represents the set of all possible flow configurations for water, reagents and raw materials between the various operations within the process system; this problem is solved as a nonlinear programming (NLP) problem using standard optimisation tools. The application of the developed approach to the Sasol Polymers chlor-alkali complex at Umbogintwini, south of Durban, has been a further objective of this study. Given the variety of process operations present within the complex, which differ both in terms of their physical structure and function, individual process models for these operations were required. These models were described in terms of four basic functional elements, namely, mixing, flow separation, component separation and reaction, and incorporated into the superstructure. Given the complexity of the problem, the process system was divided into three subsystems which were optimised in isolation from each other. These results were subsequently integrated to reflect the performance of the subsystems in combination with each other. The results showed a potential reduction of 14% in water-use and 42% in effluent production by the complex, relative to the existing operating configuration. Amongst other savings in material use, the results indicated a 0.2% reduction in the use of salt, a 1.6% reduction caustic soda use and an 8.3% reduction in the use of hydrochloric acid. Economically, the potential saving identified was R 945 727 per annum, based on operating costs in the year 2000. The final objective of this study was the interpretation of the pinch as it relates to the Combined Water and Materials Pinch Analysis problem. A general definition of the pinch was proposed; according to this definition, the pinch corresponds to that constraint or set of constraints which limits the performance of the system, that is, prevents it from further improvement. For the Combined Water and Materials Pinch Analysis problem, this performance is measured in terms of the operating cost. This definition is thus a departure from its usual thermodynamic interpretation of the pinch; in addition, the pinch is defined in terms of a constraint or a set of constraints instead of a point. These constraints are identified by an analysis of the marginal values provided by the optimisation algorithm. Marginal values are also used as a means of identifying process interventions which may be effected such that the performance of the system may be improved further. / Thesis (M.Sc.Eng.)-University of Natal, 1989.
424

Comparison of an anaerobic baffled reactor and a completely mixed reactor : start-up and organic loading tests.

Mudunge, Reginald. January 2000 (has links)
The aim of the investigation was to compare the performance of an anaerobic baffled reactor (ABR) with a completely mixed anaerobic reactor (CMAR). The ABR was operated with a hydraulic retention time (HRT) of 20 h while the CMAR was operated at 20 d. A control experiment was conducted with a CMAR operated at a constant hydraulic retention time and substrate feed concentration. During the first phase, the start-up performance of the ABR and CMAR were compared. In the second phase of the study the steady state COD removals were compared. The laboratory completely mixed anaerobic reactor was a 20L glass vessel with a stirrer coming in through the neck. A second type of reactor, anaerobic baffled reactor (ABR) was also operated. The ABR was a rectangular perspex box with internal vertical baffles alternately hanging and standing. The baffles divide the reactor into eight compartments with a total working volume of 7.5 L. Each baffle is angled at about 45Q to distribute the flow towards the centre of the upcomer. The reactors were seeded with raw sewage and allowed to stand for 3 days after which a continous feed of sucrose and basal salts was commenced. The initial HRT for the ABR and the CMAR were 60 h and 30 days respectively. When the reactors reached steady state (pH, gas production, gas composition and alkalinity), the HRT was reduced in a stepwise fashion (ABR 60 h to 35 h to 20 h and CMAR 35 d to 30 d to 20 d). At the final HRT the COD removals were similar (67 %). The ABR took 120 d to attain final steady state while the CMAR took 200 d. The organic loading tests were undertaken with a stepwise increase (doubling) in the influent substrate concentration. The feeding commenced at an organic loading rate (OLR) of 4.8 kg/m(3).d for the ABR. The flow rate (HRT) into both reactors and other parameters were kept constant (HRT of 20 h and 20 d for ABR and CMAR respectively). The substrate concentration was increased from 4 gCOD/L (4.8 kg/m(3).d) to 64 gCOD/L (76.8 kg/m(3).d) for the ABR. For the CMAR it was increased from 4 gCOD/L (0.25 kg/m(3).d) to 32 gCOD/L (2 kg/m(3).d). The method used was to increase the organic loading rate until the reactors failed. Since the two reactors had different operating HRTs, the tests began when both had the same COD removal rate of about 60 % COD reduction. The same parameters as in the start-up period were monitored for both reactors. The CMAR had a COD removal efficiency ca. 70 %, which did not fluctuate when OLR was increased. The ABR reached a maximum COD removal of 80 %. An increase in the OLR led to an initial decrease in the COD removal until the biomass recovered and the high COD (80 %) removal rates resumed. The ABR reached a maximum OLR of 76.8 kg/m(3).d whilst the CMAR reached a maximum OLR of 2.0 kg/m(3).d. The investigations showed that the ABR could be operated at higher organic loads than the CMAR and give the same organic removal rate. This verified the importance of increasing the SRT/HRT ratio in anaerobic reactors. The CMAR, however, proved to be stable to changes in the influent feed strength, as there was no immediate noticeable changes in the gas production. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
425

Modelling of the tubular filter press process.

Mullan, David James. January 2000 (has links)
The objective of this project was to develop a suitable procedure for the design, control and optimisation of the Tubular Filter Press. To this end, the following objectives were defined for this study: • To extend or improve upon the constant pressure compressible cake filtration model, predictive solution procedure, and standard laboratory characterisation techniques requlred to obtain the empirical model parameters, presented in Rencken (1992). A new generalised area contact constant pressure compressible cake filtration model was developed for both the internal cylindrical and planar filtration geometries. The model utilises a heuristically developed area contact function which relates the interparticle contact area to the solids compressive pressure within the cake. If the area contact is zero, the model reduces to the conventional point contact model as presented in Rencken ( 1992). The sludge used in this investigation was found to exhibit a negligible degree of area contact. A new pseudo variable pressure solution procedure was developed, that is an extension of the constant pressure solution procedure, to account for the initial variable pressure stage of the Tubular Filter Press operation. The pseudo variable pressure solution procedure was found to account accurately for the initial filtration behaviour observed during the pressurisation period of the Tubular Filter Press. However for the normal operation of the Tubular Filter Press. the difference between the output of the pseudo variable pressure and constant pressure solution procedures, was found to be insignificant. Wall friction in compression-permeability (C-P) cell tests was identified as a main source of error. The significance of wall friction was investigated using a specially constructed C-P cell. that enabled the transmitted pressure through the cake sample to be measured. The accuracy of the characterisation which had been corrected for the effects of wall friction, was found to improve the prediction of the filtration behaviour of the sludge significantly. The direct shear test was identified and documented as a feasible experimental procedure to determine the coefficient of earth pressure at rest. The coefficient of earth pressure is unique to the non-planar filtration geometries. The coefficient of earth pressure at rest was determined for the sludge used in this investigation. • To incorporate the constant pressure compressible cake filtration model and the associated predictive solution procedures into a user-friendly computer programme that will facilitate the design and optimisation of full-scale plants. The predictive solution procedures were incorporated into the Windows 95 computer programme, COMPRESS, that can be used for any constant pressure compressible cake dead-end filtration application where the filtration geometry is planar or internal cylindrical. A control and optimisation strategy for the continuous operation of the Tubular Filter Press has been proposed. To develop a regressive solution procedure, and incorporate this procedure into a user-friendly computer progranune, that will enable the empirical model parameters. normally obtained from standard laboratory-scale tests, to be obtained from actual filtration data. A regressive solution procedure was developed that utilises a direct search optimisation technique that is an extension of the COMPLEX method. The regressive solution procedure was incorporated into the Windows 95 program, REGRESS. The program utilises filtration data from any dead-end constant pressure filtration application of either planar or internal cylindrical geometry. REGRESS provides an effective means for determining the true physical or plant specific filtration characteristics of the sludge. The regressive solution procedure also enables the parameters specific to the new area contact model to be determined. The sludge characterisation obtained from regressing on filtration data was found to be a significant improvement in predicting the filtration behaviour, than the characterisation obtained from the standard non-filtration laboratory-scale methods, even after the C-P cell data had been corrected for the effects of wall friction. The programs COMPRESS and REGRESS should greatly assist in the design. control and optimisation of the Tubular Filter Press process. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
426

Grade 12 students conceptual understanding of chemical reactions: a case study of flouridation.

Mpofu, Nomathemba Victoria January 2006 (has links)
<p>The purpose of this study was to investigate grade 12 students conceptual understanding of chemical reaction using fluoridation of public water supply as a practical example of chemical reaction. The study also attempted to find out the effectiveness of concept mapping in facilitation the students understanding of chemical reaction, particularly redox reactions.</p>
427

Tio₂nanocatalysts: synthesis, layer-by-layer immobilisation on glass slides and their support on carbon-covered alumina (cca) for application in drinking water treatment

16 August 2012 (has links)
D.Phil. / Clean water (i.e. water that is free of toxic chemicals and pathogens) is essential to human health and in South Africa the demand is fast exceeding the supply. The prevalence of toxic contaminants in water remains a huge challenge for water supplying companies and municipalities. However, the presently used water treatment technologies either fail to remove these contaminants to acceptable levels or they transform them into more toxic substances (e.g., DBPs). Nanocatalysts, especially TiO2 (titania) have a proven potential to treat ‘difficult-to-remove’ contaminants and hence are expected to play an important role in solving many serious environmental and pollution challenges. In this study TiO2 nanocatalysts were used for the degradation of Rhodamine B dye both under UV and visible light irradiation. Two phases of titania, i.e. anatase and rutile phases, were compared for the degradation of Rhodamine B under UV light irradiation. The anatase titania was found to be more photocatalytically active for the degradation of Rhodamine B than the rutile phase. It completely degraded 100 mg ℓ–1 (100 mℓ) of Rhodamine B within 270 min and was two times more photocatalytically active than the rutile phase (Kapp of 0.017 min–1 compared to 0.0089 min–1). To extend the band edge of the titania nanocatalysts towards visible-light, TiO2 was doped with metal ions (Ag, Co, Ni and Pd). These metal-ion-doped titania nanocatalysts were photocatalytically active under visible-light illumination. The Pd-doped titania had the highest photodegradation efficiencies, followed by Ag-doped and Co-doped, while Ni-doped had the lowest. The optimum metal-ion loading percentage was found to be at 0.4%, with the exception of Co-doped titania as it had the highest efficiencies at 1% loadings. The free and metal-ion-doped titania nanocatalysts were embedded on carbon-covered alumina (CCA) supports. The CCA-supported TiO2 nanocatalysts were more photocatalytically active under visible light illumination than they were under UV-light irradiation. The CCA-supported metal-ion-doped titania nanocatalysts were more photocatalytically active under visible light than their unsupported counterparts. The CCA-supported Pd-TiO2 nanocatalysts were the most active while CCA-supported Ni-TiO2 catalysts were the least active. The improved photocatalytic activities observed were as a result of increased surface areas of the CCA-supported nanocatalysts. Also, supporting the nanocatalysts did not destroy the anatase phase of the titania while doping with metal ions and supporting on CCAs resulted in decreased band gap energies, hence the visible-light photocatalytic activities. Finally, the metal-ion-doped titania nanocatalysts were supported on glass slides using the layer-by-layer thin film self-assembly technique. This was to overcome the aggregation and post treatment problems associated with the use of TiO2 in suspension form. PAH and PSS were the polyelectrolytes used. These metal-ion-doped titania thin films were highly porous and strongly adhered by the polyelectrolytes onto the glass slides. The thin films were photocatalytically active for the degradation of Rhodamine B under visible light irradiation. The photocatalytic degradation efficiencies observed were similar for all four metal-ions (i.e. Ag, Co, Ni and Pd) with average degradation of 30%, 50%, 70% and 90% for 5 catalysts (5 glass slides) of 1, 3, 5 and 10 bi-layers, respectively, after 330 min. Although, these were less active than the suspended titania nanocatalysts, this study proved as a stepping stone towards large scale use of titania nanocatalysts using solar energy as the irradiation source. Also, catalyst reusability studies were performed and the PAH/PSS m-TiO2 thin films were found to be highly stable over the five cycles it was tested for.
428

Pretreatment Optimization of Fiberglass Manufacturing Industrial Wastewater

Dragoo, Ron 12 1900 (has links)
Wastewater effluent produced in the fiberglass manufacturing industry contains a significant amount of total suspended solids. Environmental regulations require pretreatment of effluent before it is discharged to the municipal wastewater treatment plant. Chemical precipitation by coagulation and flocculation is the method of pretreatment used at the Vetrotex CertainTeed Corporation (VCT). A treatability study was conducted to determine conditions at which the VCT Wastewater Pretreatment Plant could operate to consistently achieve a total suspended solids concentration ≤ 200-mg/L. Jar tests varied pH, polymer dosage, and ferric sulfate dosage. Total suspended solids and turbidity were measured to evaluate treatment performance. The data were used to determine an optimum set of conditions under project guidelines. Of twelve polymers screened, BPL 594 was selected as the most effective polymer. For cost efficiency in the wastewater pretreatment operation, recommendations suggested that treatment chemical injection be electronically controlled according to turbidity of the treated effluent.
429

Microbiological Studies of Biological Activated Carbon Filters Used in Water Treatment

Chang, Eichin 12 1900 (has links)
A collaborative pilot study of the microflora on biological activated charcoal (BAC) filters employed in the tertiary treatment of drinking water revealed the principle bacterial genera to be Pseudomonas, Alcaligenes, Achromobacter, Bacillus, Micrococcus, Corynebacterium, Chromobacterium, Microcyclus and Paracoccus. The microbial population of the filters paralleled seasonal carbon dioxide production. Of particular interest were the effects of the BAC miroorganisms upon precursors of trihalomethanes (THMs). Mixed populations of BAC microorganisms were cultivated for 50 days in a mineral salts-humic acid medium. It was concluded that (1) the BAC microflora enhances the absorptive capacity of the filters; (2) chemico-physical and biological processes operate in concert to lower the concentration of precursors of THMs; and (3) few bacterial pathogens establish themselves on the filters.
430

Activated carbon and ozone as supplementary water treatment options at Rietvlei Dam

16 August 2012 (has links)
M.Ing. / Rietvlei Dam was completed in 1933, and has been utilized as a drinking water source for the City of Pretoria since then. The original process configuration operated for almost 50 years before being upgraded in 1988. This upgrading was mainly due to the eutrophication of the impoundment. The new plant worked excellently under normal conditions but certain serious problems did occur and full production could not be maintained at all times. Activated Carbon and Ozone are two possible solutions to these problems. This study was directed at investigating the possible implementation of Preozonation, Granular Activated Carbon, and Ozone and Granular Activated Carbon in combination (case study), and it was shown that: All these processes are beneficial to the final water quality. Pre-ozonation proved to be the most cost effective process, but the least effective process in improvement of the water quality. Ozone and Granular Activated Carbon in combination proved to be the least cost effective process, but should be the most effective in improvement of the water quality. Granular Activated Carbon proved to be the optimun process with regard to cost and water quality improvement. The final recommendation is the implementation of Granular Activated Carbon with an empty bed contact time of 10 minutes.

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