Browsing by Author "Wentzel, Mark C"

Now showing 1 - 11 of 11
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    Aerobic digestion of waste activated sludge from biological nutrient removal activated sludge systems
    (2007) Mebrahtu, Michael Kidane; Ekama, George A; Wentzel, Mark C
    Waste activated sludge (WAS) is a biological sludge that contains biodegradable and non-biodegradable volatile suspended solids (VSS) and non-volatile inorgainic suspended solids (ISS). Stabilization for safe disposal of the WAS is a process of paramount importance at wastewater treatment plants (WWTPs). Hence, aerobic digestion of the WAS from biological nutrient removal (BNR) activated sludge (AS) systems was carried out under batch conditions to (1) measure changes in nitrogen and phosphorus concentrations in solid and liquid phases during aerobic batch digestion tests (2) simulate the parent system with Activated Sludge Model No. 2 (ASM-2) in AQUASIM computer program to obtain the initial conditions for batch test simulation (3) simulate the batch aerobic digestion process with ASM-2 and compare with experimental data (4) develop VSS-based and total suspended solids (TSS) (with the addition of ISS to the VSS-based) batch reactor and steady state models for aerobic digestion of nitrification denitrification biological excess phosphorus removel (NDBEPR) WAS based on the individual biomass die-off rates of phosphorus accumulating organisms (PAOs) and ordinary heterotrophic organisms (OHOs), and (5) evaluate the ASM-2 simulation results with steady state aerobic batch digestion model.
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    Anaerobic digestion of Fischer-Tropsch reaction water : submerged membrane anaerobic reactor design, performance evaluation & modeling
    (2008) Van Zyl, Pierrie Jakobus; Ekama, George A; Wentzel, Mark C
    Includes abstract. Includes bibliographical references (p. 209-217).
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    Characterization of municipal waste waters
    (1995) Mbewe, Alfred; Mbewe, Alfred; Wentzel, Mark C
    Over the past 20 years there have been extensive developments in the activated sludge method of treating wastewater. The functions of the single sludge system have expanded from carbonaceous energy removal to include progressively nitrification, denitrification and phosphorus removal, all mediated biologically. Not only has the system configuration and its operation increased in complexity, but concomitantly the number of biological processes influencing the system performance and the number of compounds involved in these processes have increased. With such complexity, designs based on experience or semi-empirical methods no longer will give optimal performance; design procedures based on more fundamental behavioural patterns are required. Also, it is no longer possible to make a reliable quantitative, or sometimes even qualitative prediction as to the effluent quality to be expected from a design, or to assess the effect of a system or operational modification, without some model that simulates the system behaviour accurately. To address these problems, over a number of years design procedures and kinetic models of increasing complexity have been developed, to progressively include aerobic COD removal and nitrification (Marais and Ekama, 1976; Dold et al., 1980), anoxic denitrification ( van Haandel et al., 1981; WRC, 1984; Henze et al., 1987; Dold et al., 1991) and anaerobic, anoxic, aerobic biological excess phosphorus removal (Wentzel et al., 1990; Wentzel et al., 1992; Henze et al., 1995). In terms of the framework of these design procedures and kinetic models, the influent carbonaceous (C) material (measured in terms of the COD parameter) is subdivided into a number of fractions - this subdivision is specific to the structure of this group of models. The influent COD is subdivided into three main fractions, biodegradable, unbiodegradable and heterotrophic active biomass. The unbiodegradable COD is subdivided into particulate and soluble fractions based on whether the material will settle out in the settling tank (unbiodegradable particulate) or not (unbiodegradable soluble). The biodegradable material also has two subdivisions, slowly biodegradable (SB COD) and readily biodegradable (RBCOD); this subdivision is based wholly on the dynamic response observed in aerobic (Dold et al., 1980) and anoxic/aerobic (van Haandel et al., 1981) activated sludge systems, that is, the division is biokinetically based. Thus, as input to the design procedures and kinetic models, it is necessary to quantify five influent COD fractions, that is, to characterize the wastewater COD. From a review of the literature on existing tests to quantify the COD fractions, it was evident that the existing procedures are either too elaborate or approximate or sometimes not even available. This research project addresses these deficiencies. In this research project, the principal objective was to develop simple accurate procedures to quantify the influent wastewater COD fractions. A batch test method has been developed to quantify the five influent COD fractions; namely heterotrophic active biomass, readily biodegradable COD, slowly biodegradable COD, unbiodegradable particulate COD and unbiodegradable soluble COD. Also, the physical flocculation-filtration method of Mamais et al. (1993) to quantify RBCOD has been evaluated and refined.
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    The effect of high temperatures (30 degrees Celsius) on biological nutrient removal performance
    (1999) Mellin, Hannu Kaarlo Olavi; Ekama, George A; Wentzel, Mark C
    The main objective of this investigation was to evaluate activated sludge biological nutrient removal (BNR) performance at elevated temperatures for possible application of nitrification denitrification (ND) and ND biological excess phosphorus removal (NDBEPR) systems to municipal wastewater treatment in the equatorial and tropical regions or to combined treatment of municipal and anaerobically (thermophilic) pretreated paper and pulp industry wastewaters in the very cold northern forested regions. To accomplish this objective, a ND Modified Ludzack Ettinger (MLE) system and a NDBEPR University of Cape Town (UCT) system were operated at 30°C and 10 days sludge age for a period of 582 days. During the investigation 41 sewage batches, each lasting about two weeks, of real sewage from the Mitchells Plain municipal wastewater treatment plant (Western Cape, South Africa) were fed to the systems. The two systems were sampled and tested ,almost daily for Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), Free and Saline Ammonia (FSA), nitrate, nitrite, Total Phosphorus, Volatile Settleable Solids (VSS), Total Settleable Solids (TSS), pH, Oxygen Utilization Rate (OUR) and diluted sludge volume index (DSVI) in the influent, anaerobic, anoxic and aerobic reactors and effluent as appropriate. Also, in order to determine the kinetic rates of nitrification, denitrification and readily biodegradable COD (RBCOD) conversion to Volatile Fatty Acids (VF A), aerobic, anoxic and anaerobic batch tests were conducted at 30°C on sludge harvested from the two systems and microscopic examination of the sludges was undertaken every four weeks to identify the filamentous organisms in the systems.
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    Evaluation of batch test for measurement of active biomass in activated sludge mixed liquor
    (2001) Beeharry, Amal Oodhay; Wentzel, Mark C
    Over the past two decades significant advances have been made in the areas of engineering (design) and technology (implementation and operation) of the single sludge activated sludge system. Activated sludge systems have been successfully designed and implemented at full-scale for the biological removal of carbon (C), nitrogen (N) and phosphorus (P). This implementation has been aided by the development of a suite of steady state design models (e.g. WRC, 1984; Wentzel et aI., 1990; Maurer and Gujer, 1994) and kinetic simulation models (e.g. Dold et al., 1980, 1991; Van Haandel et aI., 1981; Henze et al. , 1987; Wentzel et aI., 1992; Henze et al., 1995).
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    External nitrification in biological nutrient removal activated sludge systems
    (1999) Moodley, Rajan; Ekama, George A; Wentzel, Mark C
    In conventional nitrification-denitrification biological excess phosphorous removal (NDBEPR) activated sludge systems, such as the UCT system for example, both nitrification and phosphorous uptake (P uptake) occur simultaneously in the, usually large, aerobic reactor. In the UCT system the nitrate load to the anoxic reactor is limited by the a-recycle (i.e. system constraint recycle from the aerobic to the anoxic reactor) and the internal aerobic nitrification performance. The latter process, is mediated by the nitrifiers having a slow growth rate of 0.45/d, governs the sludge age of the biological nutrient removal activated sludge (BNRAS) system and thus results in long (20 - 25 day) sludge ages and large aerobic mass fraction requirements to nitrify completely. However, if stable nitrification could be achieved outside the BNRAS external nitrification (EN) system then nitrification and the suspended solids sludge age become uncoupled allowing greater flexibility into the BNRAS system.
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    External nitrification in biological nutrient removal activated sludge systems
    (2000) Sötemann, Sven; Ekama, George A; Wentzel, Mark C
    Biological nutrient removal activated sludge (BNRAS) systems have become the preferred treatment system for advanced municipal wastewater treatment in South Africa. They have proven to be cost-effective systems that produce effluents of excellent quality that can be re-introduced to the receiving water bodies without a significant negative impact on the scarce surface water of South Africa. The widespread implementation of the BNRAS system has drawn attention to some of the weaknesses of the system, predominantly (i) the long sludge ages and resulting large biological reactor volumes required for nitrification, (ii) filamentous organism bulking of the sludge that develops in the system, (iii) treatment of the P rich waste sludge from the system and (iv) containment of the large mass of P in the sludge during a failure of the aeration in the system. In order to overcome the first two weaknesses of the system, it is proposed to separate the process of nitrification from the BNRAS mixed liquor and achieve nitrification externally to the BNRAS system.
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    Mathematical modelling of integrated chemical, physical and biological treatment of wastewaters
    (1998) Musvoto, Eustina Vongai; Ekama, George A; Wentzel, Mark C; Loewenthal, Richard Eric
    The development of a kinetic-based model to simulate chemical, physical and biological processes in three phase (gaseous-aqueous-solid) mixed weak acid/base systems is described. The chemical processes are expressed in terms of the kinetics of the forward and reverse reactions for the dissociation of the weak acid/bases. In this approach the H⁺ and all the species of the weak acidfbases of interest are included and the pH is calculated directly from H⁺ via pH = -log (H⁺). The advantage of this approach over the alkalinity/equilibrium chemistry approach is that kinetics are used throughout. Also, the approach is general and can be applied to any combination of mixed weak acid/base systems. The kinetic expressions of the carbonate, phosphate, ammonia, acetate and water systems, including the kinetics of the three phase chemical processes viz. precipitation/dissolution of calcium and magnesium phosphates and carbonates and gas stripping/dissolution of O₂, CO₂ and NH₃, were programmed into the AQUASIM shell package to generate simulation results. The chemical processes part of the model was validated by comparing steady state model predictions with those obtained from equilibrium chemistry based models such as STASOFT I and III (Loewenthal et al., 1986, 1991). Virtually identical results were obtained. The kinetic approach allowed integration of the biological kinetic processes of the IAWQ activated sludge model No 1 (Henze et al., 1987), to extend application of the model to situations where precipitation of minerals, stripping of gasses and biological processes take place in an environment where the pH does not remain constant. Where required the interaction between the chemical species and biological processes was included, e.g. CO₂ uptake for autotrophic nitrifier growth and NH₄⁺ uptake for heterotrophic growth and nitrification. Also, literature information on the effect of pH on the maximum specific growth rates of nitrifiers was included.
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    Measurement of ordinary heterotroph organism anoxic yield in anoxic-aerobic activated sludge systems
    (2003) Muller, Ashley; Wentzel, Mark C
    The principal aim in this research is to investigate and quantify the ordinary heterotrophic organism (OHO) cell yield under anoxic conditions relative to its value under aerobic conditions for municipal sewage. In this regard, three primary objectives were identified: 1. Determine the ratio Y H,No: Y H,AE for real sewage in terms of electron acceptor (i.e. nitrate and oxygen respectively) utilization. 2. Measure Y H,NO and Y H,AE directly for known concentrations of readily biodegradable (RB)COD utilized. 3. Compare experimental results with other, independent studies on real sewage.
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    Water quality modelling of eutrophied reservoirs in South Africa
    (1996) Venter, Ansie; Marais, Gerrit van Rooyen; Wentzel, Mark C
    Governmental agencies in South Africa became concerned about the increase in eutrophication-related water quality problems during the early 1970's. The first step taken to control eutrophication was introduction of an effluent phosphate standard that limited the phosphorus concentration in effluents being discharged in certain sensitive catchments to a maximum of 1 mg P04-P 1-1. This standard applied only to point sources, because of an initial belief that the contribution from non-point sources was relatively minor, and the absence of practical economic measures to control phosphorus discharges from non-point sources. Subsequent to introduction of the 1 mg P Standard several modelling studies were undertaken, as there was a need to describe the response of eutrophic reservoirs to altered phosphate inputs. Most of the work was done on the hypertrophic Hartbeespoort Dam reservoir. The models utilised were empirical, zero-dimensional models that treated the reservoir as a completely mixed reactor. Usually these models considered only the steady state, or at most, annual changes. The models simulated annual mean phosphate-P concentrations with varying degrees of success, but a significant relationship between observed and simulated chlorophylla concentrations could not be obtained, i.e. these models could not be used to predict the response of eutrophic reservoirs to different management strategies aimed at alleviating eutrophication-related water quality problems. Consequently, a further study was initiated by the Water Research Commission to test the applicability of more sophisticated hydrodynamic and water quality models, developed in the USA and Australia, to stratified reservoirs under South African climatic conditions. Several models of varying complexity were available. From these four models were selected for study. The models that were tested were the one-dimensional models DYRESM (developed in Australia), and MINLAKE (developed in the USA) , and the two-dimensional models CE-QUAL and WASP (developed in the USA). The DYRESM model can simulate hydrodynamic behaviour only, whereas MINLAKE, CE-QUAL and WASP can simulate both hydrodynamic and water quality behaviour. This report covers the extensive study that conducted on the MINLAKE model. The study is justified in view of the potential of the MINLAKE model to evaluate different treatment options: of the four models selected, it is the only model that can simulate more than one algal class. Thus it is an ideal tool to assess the effect of a chosen treatment option on, for example, algal succession.