Browsing by Author "Ekama, G A"

Now showing 1 - 6 of 6
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    Biodegradability of wastewater and activated sludge organics in anaerobic digestion
    (2014) Ikumi, D S; Harding, T H; Ekama, G A
    The investigation provides experimental evidence that the unbiodegradable particulate organics fractions of primary sludge and waste activated sludge calculated from activated sludge models remain essentially unbiodegradable in anaerobic digestion. This was tested by feeding the waste activated sludge (WAS) from three different laboratory activated sludge (AS) systems to three separate anaerobic digesters (AD). Two of the AS systems were Modified Ludzack – Ettinger (MLE) nitrification-denitrification (ND) systems and the third was a membrane University of Cape Town (UCT) ND and enhanced biological P removal system. One of the MLE systems and the UCT system were fed the same real settled wastewater. The other MLE system was fed raw wastewater which was made by adding a measured constant flux (gCOD/d) of macerated primary sludge (PS) to the real settled wastewater. This PS was also fed to a fourth AD and a blend of PS and WAS from settled wastewater MLE system was fed to a fifth AD. The five ADs were each operated at five different sludge ages (10–60d). From the measured performance results of the AS systems, the unbiodegradable particulate organic (UPO) COD fractions of the raw and settled wastewaters, the PS and the WAS from the three AS systems were calculated with AS models. These AS model based UPO fractions of the PS and WAS were compared with the UPO fractions calculated from the performance results of the ADs fed these sludges. For the PS, the UPO fraction calculated from the AS and AD models matched closely, i.e. 0.30 and 0.31. Provided the UPO of heterotrophic (OHO, fE_OHO) and phosphorus accumulating (PAO, fE_PAO) biomass were accepted to be those associated with the death regeneration model of organism "decay", the UPO of the WAS calculated from the AS and AD models also matched well - if the steady state AS model fE_OHO = 0.20 and fE_PAO = 0.25 values were used, then the UPO fraction of the WAS calculated from the AS models deviated significantly from those calculated with the AD models. Therefore in plant wide wastewater treatment models the characterization of PS and WAS as defined by the AS models can be applied without modification in AD models. The observed rate limiting hydrolysis/acidogenesis rates of the sludges are listed.
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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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    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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    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
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    The effect of sewage sludge co-disposal and leachate recycling on refuse stabilization
    (1991) Chapman, Grant Campbell; Ekama, G A
    In the past sanitary landfill sites for solid waste disposal were regarded simply as containment sites so that the waste contents were isolated from the population. Various degrees of effort were made to reduce the impact of the waste in and around the site - in some cases none in other cases considerable but the prevailing attitude was that it was a disposal site - not a treatment site; consequently, the stabilization of waste in the site was largely disregarded and generally little effort was made to promote waste stabilization. Rapidly growing cities as a result of urbanization of the rural communities has placed management and operation of sanitary landfill sites under increasing pressure from two directions in that an increased metropolitan population not only produces more solid wastes but also makes the acquisition of appropriate landfill sites increasingly difficult and expensive. These problems are exacerbated by a heightened environmental awareness in large sectors of the public who are concerned that municipal wastes in general, but solids waste are properly managed so as to maximize safe disposal of the wastes and minimize the environmental impact of these operations. Such developments have considerably increased the responsibilities of the municipal engineers in waste treatment and disposal and has demanded alternative and innovative measures for these operations. As a result, sanitary landfills are becoming regarded as bioreactors in that much greater cognizance of the stabilization of the wastes in the landfill is being taken; also, greater efforts are being made to reduce the impact of the landfill on its surroundings by installing liners to reduce leachate contamination of surrounding groundwater and by burning methane gas to reduce air pollution.