Browsing by Author "Wentzel, M C"

Now showing 1 - 7 of 7
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    The development of a kinetic model for biological sulphate reduction with primary sewage sludge as substrate
    (2007) Van Wageningen, Sonél; Wentzel, M C
    Central to this process is biological sulphate reduction (BSR) using primary sewage sludge (PSS) as the electron donor and organic carbon source, with the concomitant reduction of sulphate to sulphide and production of carbonate alkalinity. To optimise the design, operation and control of BSR with PSS, a mathematical kinetic model of this system would be an invaluable aid. This study describes the development of such a kinetic model, and its application to a series of experimental lab-scale BSR systems fed PSS and sulphate. The biological processes of importance require inclusion in a kinetic model for BSR. For the biologically mediated processes, the PSS first requires hydrolysis/solubilisation (usually the rate limiting step) and acidification, mediated by the acidogenic group of organisms, in common with sewage sludge methanogenic anaerobic digestion systems. The products of these processes, the Volatile Fatty Acids (VFA) then enter into the methanogenic or sulphate reduction processes, which operate in competition. The end product of sulphate reduction is sulphide, which is inhibitory to the methanogens, and this inhibition would have to be included in the model.
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    Fullscale implementation of external nitrification biological nutrient removal in the Daspoort Water Care Works
    (2004) Muller, A W; Wentzel, M C; Saayman, G B; Van de Merwe, S A; Esterhuyse, C M; Snyman, J S; Ekama, G A
    In the external nitrification (EN) biological nutrient removal (BNR) activated sludge (AS) system, the nitrification process is removed from the main BNRAS system to a fixed media system external to the AS system (Hu et al., 2003). The ENBNRAS system provides considerable advantages over the conventional BNRAS system, e.g. reduced bioreactor volumes, secondary settling tank surface area and oxygen demand. Further, the ENBNRAS system provides opportunity for substantial system intensification. The performance and characterization of the ENBNRAS system has been successfully demonstrated at lab-scale (Hu et al., 2000, Sötemann et al., 2002), but has not yet been tested in full-scale implementation. In collaboration between the City of Tshwane Metropolitan Municipality (CTMM) and the University of Cape Town, ENBNR activated sludge is being implemented at fullscale at the Daspoort Waste Water Treatment Works (DWWTW) in Central Pretoria, South Africa. This paper describes the preliminary design of this full-scale plant and initial implementation.
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    Integrated biological, chemical and physical processes kinetic model for the anaerobic digestion of primary sewage sludge
    (2001) Van Rensburg, Pierre; Wentzel, M C
    Despite its wide application, the design, operation and control of anaerobic digesters treating sewage sludges still is largely based on experience, or empirical guidelines. To aid the design, operation and control of (and research into) anaerobic digestion, a mathematical model would be an invaluable process evaluation tool.
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    Modelling organic material in activated sludge systems
    (2004) Ekama, G A; Wentzel, M C
    A simple predictive model for the activated sludge reactor inorganic suspended solids (ISS) concentration is presented. It is based on the accumulation of influent ISS in the reactor and an ordinary heterotrophic organism (OHO) ISS content (fiOHO) of 0.15 mg ISS/mgOHOVSS and a variable phosphate accumulating organism (PAO) ISS content (fiPAO) proportional to their P content (fXBGP). The model is validated with data from 21 investigations conducted over the past 15 years on 30 aerobic and anoxic-aerobic nitrification denitrification (ND) systems and 18 anaerobic-anoxic-aerobic ND biological excess P removal (BEPR) systems variously fed artificial and real wastewater and operated from 3 to 20 d sludge age. The predicted reactor VSS/TSS ratio reflects the observed relative sensitivity to sludge age, which is low, and to BEPR, which is high. For effective use of the model for design, two significant issues require attention: measurement of the influent ISS concentration, which is not commonly done in wastewater characterisation analyses; and estimating a priori the P content of PAOs (fXBGP), which can vary considerably depending on the extent of anoxic P uptake BEPR that takes place in the system. Some guidance on selection of the mixed liquor VSS/TSS ratio for design is given.
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    Organic and inorganic components of activated sludge mixed liquor
    (1997) Ubisi, Makumu Fani; Wentzel, M C
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    Sulphate measurement in organic-rich solutions: Carbonate fusion pretreatment to remove organic interferences
    (2005) Ristow, N E; Sotemann, S W; Wentzel, M C; Loewenthal, R E; Ekama, G A
    Sulphate measurement using a barium sulphate turbidimetric method in solutions with high concentrations of organic material is shown to be problematic. The organics give background colour, which introduces a positive error to the measured absorption, and inhibit the barium sulphate precipitate, which results in a negative error. A carbonate fusion pretreatment of the sample results in the removal of the organic matter and associated interferences. With this pretreatment, excellent sulphate recoveries were obtained (100%). Rigorous testing of the method shows that reproducible and accurate results are obtainable.
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    The effect of dosing unstabilized landfill leachate to a nutrient removal activated sludge system
    (1998) Sneyders, Michael James; Ekama, G A; Wentzel, M C