OpenUCT :: Browsing by Author "Marais, Gerrit van Rooyen"

Browsing by Author "Marais, Gerrit van Rooyen"

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Open Access
Acid fermentation of primary sludge at 20v C
(1990) Lilley, Ian David; Marais, Gerrit van Rooyen
Full scale studies on biological excess phosphrous removal plants have demonstrated the biological excess phosphorous removal can be increased by acid fermenting the settled sludge in the primary settling tank, and adding either the fermented sludge, or the acids elutriated from the sludge, to the influent of the biological phosphorous removal plant. Considerable uncertainty still exists, however, as to the mass of short chain fatty acids that can be generated and the degree of improvement in phosphorous removal that can be expected. This study was undertaken to (1) evaluate short chain fatty acid production in laboratory scale batch, single and in-series completely mixed reactor systems, (2) development of a model for acid fermentation, and (3) theoretically estimate the effect of acid addition on biological excess phosphorous removal.
Open Access
Biological excess phosphorus removal in activated sludge systems
(1988) Wentzel, Mark Charles; Marais, Gerrit van Rooyen
When this investigation was commenced in 1983 two activated sludge systems had been developed in South Africa that accomplish biological excess phosphorus (P) removal, the UCT and modified Bardenpho systems. To predict the P removal in these systems, an empirical model had been developed. In the empirical model, P removal was formulated in terms of some of the system parameters, such as anaerobic mass fraction, available readily biodegradable COD and active mass concentration. Organisms directly implicated in biological excess P removal (poly P organisms) did not feature in the model and the P removal was not linked to any basic biological or biochemical behaviour. Clearly, there was a need for a more fundamentally based model. The objective of this thesis was to develop such a model.
Open Access
Biological excess phosphorus removal in short sludge age activated sludge systems
(1986) Burke, Russell Armstrong; Marais, Gerrit van Rooyen
The objective of this investigation was to test, at laboratory-scale, the behaviour of short sludge age biological excess P removal systems, to assess the response of the systems under non-nitrifying and nitrifying conditions, to determine the optimal system configuration(s) and operational parameters, and to check the settling characteristics of the mixed liquor produced in the systems. A secondary objective was to use the observed response data to test the predictive qualities of both the general activated sludge model of Dold, Ekama. and Marais (1985) and the semi-empirical biological excess P removal model of Wentzel, Dold, Ekama and Marais (1984). The objectives were fulfilled by operating a number of laboratory scale anaerobic/aerobic and anaerobic/anoxic/aerobic systems with varying sludge ages, anaerobic, anoxic and aerobic mass fractions, mixed liquor recycle ratios and COD loading rates.
Open Access
Biological nitrogen and phosphorus removal on large plants.
(1983) Nicholls, Harold Arthur; Marais, Gerrit van Rooyen
Full scale implementation of biological excess phosphorus removal by means of the activated sludge process commenced in South Africa at the Johannesburg Alexandra Plant in 1974. Originally the plant was designed to operate in the nitrifying extended aeration mode; but by switching off some surface aerators around the common inlet point for the influent and underflow recycle, an anoxic zone was created to induce denitrification. This operational modification worked very successfully. Later additional aerators were switched off to create an anaerobic-anoxic zone at the head of the aeration basin, in this manner attempting to induce the prerequisite conditions for excess biological uptake of phosphorus as put forward by Barnard (i.e. by stimulating P release under anaerobic conditions). This revised operational procedure was not successful due to difficulties experienced in controlling mixing in the anaerobic - anoxic zone. However the experience gained from this investigation together with research findings at laboratory and pilot scale level at the National Institute for Water Research, the University of Cape Town, and Johannesburg instilled sufficient confidence into City Council staff to proceed with the' design of the 150 Ml/d Goudkoppie Plant, initially for nitrogen removal and to subsequently modify it to a 5 stage Phoredox process for both nitrogen and phosphorus removal. Before the plant was commissioned (1976) it was necessary to proceed with extensions to the Northern Works and these were also based on the 5 stage Phoredox process. All the Johannesburg activated sludge plants were comprehensively monitored to determine their performance under cyclic flow and load conditions, The data collected from the Goudkoppie plant were particularly comprehensive and exhaustive. Concomitant with the monitoring program extensive research into the single stage nitrification/denitrification/excess phosphorus removal process was being undertaken by the three agencies mentioned earlier. Of particular interest was the development by the University of Cape Town of a general kinetic model of the single sludge activated sludge process that described carbonaceous degradation, nitrification and denitrification behaviour under cyclic flow and load conditions. This dissertation critically evaluates the predictions of this model against the observed responses on the Goudkoppie and Northern Works.
Open Access
Calcium carbonate precipitation kinetics
(1975) Sturrock, Peter Lamond Knowling; Marais, Gerrit van Rooyen
A modified equation from that of Nancollas and Reddy is presented to describe the rate of calcium removed from water in CacO3; precipitation. The mass of CaCO3; precipitated at any moment was obtained by monitoring pH and utilizing this in the equilibrium equations for the Ca - H2CO3 system including ion pairing and ionic strength effects. Both batch and back mixing steady state conditions were studied. The precipitation rate constant was found to be independent of pH, and functionally related to the state of initial supersaturation in the batch tests and the state of supersaturation in the steady state tests. Both steady state and batch tests gave the same dependence of the precipitation rate constant with supersaturation.
Open Access
Carbonate chemistry in high salinity waters
(1983) Loewenthal, Richard Eric; Marais, Gerrit van Rooyen
The primary objective of this investigation was to develop phase equilibrium diagrams for the carbonate system in high salinity waters, i.e. for single aqueous phase, solid-aqueous phase, gasaqueous phase and solid-aqueous-gas phases. Such diagrams have been developed for low salinity waters, viz. Deffeyes and Caldwell-Lawrence diagrams and modifications of these.
Open Access
Chemical and biological phosphorus removal in the activated sludge process
(1980) Rabinowitz, Barry; Marais, Gerrit van Rooyen
This investigation set out to establish in what degree the phosphorus removal characteristics of the Modified Activated Sludge Process could be enhanced by the in-plant addition of iron salts. The motivation for the investigation was: 1. Due to the lack of understanding of the exact pre-requisites for inducing excess biological phosphorus removal (luxury uptake), such removal could not always be guaranteed in many activated sludge plants, even in those designed in accordance with the best available knowledge for inducing this removal mechanism. 2. There was evidence to suggest that even where excess biological phosphorus removal took place, the removal was limited by the process and the sewage characteristics. As a result, in plants where the specified phosphorus removal exceeded the possible biological removal, additional or alternative methods of removal had to be sought. In view of these factors it was concluded that only by chemical addition to the process, could a specified effluent quality be guaranteed. A laboratory scale Modified Activated Sludge (or Phoredox) Process, similar to that proposed by McLaren and Wood ( 1976), but without a secondary anoxic zone was set up and the process was evaluated with and without in-plant iron salt addition. Problems were encountered in predicting the biological removal as the removal tended to differ from one sewage batch to another, making it difficult to determine accurately the efficiency of the iron salt addition.
Open Access
The contact stabilization activated sludge process
(1979) Alexander, William Versfeld; Marais, Gerrit van Rooyen
In 1978 Ekama and Marais put forward a general model for the activated sludge process based on an energy requirement for adsorption of the nutrient onto the organisms. They briefly outlined an alternative bi-substrate hypothesis in which the energy requirement for adsorption fell away. No evidence in support of this alternative hypothesis was presented. The objective of this thesis was to investigate which of the two hypotheses gave the better description of the activated sludge process kinetics. When the adsorption hypothesis was replaced by the bi-substrate hypothesis in the general model and applied to the completely mixed activated sludge process and their predictions compared with experimental data, it was not possible to establish conclusively which hypothesis is to be preferred. As a consequence it was decided to test the two models under extreme conditions. The contact stabilization process was selected as the one presenting a most severe test of the predictive power of any hypothesis on activated sludge kinetics, and most likely therefore to establish the superiority of one hypothesis over the other. In order to obtain experimental data against which the hypotheses could be evaluated a series of laboratory scale tests on the contact stabilization process were conducted under time invariant and cyclic flow and load conditions at two temperatures, 12°C and 20°C. From a comparison of the experimentally observed and theoretically predicted data it was concluded that an additional factor had to be taken into account before a valid comparison could be made - whereas the general activated sludge theory accepted a rapid and complete enmeshment of influent particulate COD, in the contact reactor the experimental data indicated incomplete enmeshment in the short contact time available. When allowance was made for partial enmeshment in the predicted response of the system it was concluded that the bi-substrate hypothesis was superior to the adsorption one.
Open Access
Design and control of equalization tanks.
(1982) Dold, Peter Lorimer; Marais, Gerrit van Rooyen
The objective of this investigation was to develop a control strategy for the operation of an equalization tank upstream of a waste water treatment plant which utilizes the available equalization hold-up volume in such a manner that it reduces, optimally, diurnal fluctuations in both influent flow and load rates. The influent to a wastewater treatment plant generally exhibits wide diurnal variations in both flow rate and concentration, and consequently in load rate (defined as the product of flow rate and concentration). Deviations of these parameters from steady state cause plant operating problems in areas such as aeration control (due to load rate fluctuations) settling tank overloading due to flow rate fluctuations) and/or over- or under-aeration which affects settling properties, and others.
Open Access
The development of an ancillary textile industry waste treatment process
(1971) Greenblau, Norman; Marais, Gerrit van Rooyen
The objective of this thesis is twofold - (1) to design the unit processes for treating the waste from a specific industrial plant using the best practicable technology, and (2) to critically examine the theory of these unit processes for utilization in design. The industrial waste was derived from a synthetic button and textile trimmings factory producing polyester and casein buttons. The effluent has a high pH and COD; contains metallic poisons; and is highly coloured. It exceeds the limitations for effluent quality promulgated by the Cape Town Municipality before discharge to the sewers. A certain measure of pretreatment before discharge to the sewers was therefore required. The treatment process eventually selected consists of neutralization; flocculation; sedimentation; sand filtration of the sludge; and atmospheric drying of the sludge.
Open Access
The effect of nitrite and nitrate concentrations on low F/M filament bulking in nitrogen removal activated sludge systems
(1994) De Villiers, M E; Ekama, George A; Marais, Gerrit van Rooyen
Filamentous bulking and its associated poor sludge settleability is a considerable problem in South African activated sludge plants, as indicated by the two surveys undertaken on these plants in 1985 and 1988 (Blackbeard et al., 1986, 1988). Amelioration of this problem would enable a greater daily flow and load of wastewater to be treated by these plants. From the surveys it is apparent that bulking in long sludge age activated sludge plants is mainly due to the proliferation of the group of so-called low F/M filaments (as classified by Jenkins et al., 1984). In the course of a 4-year research program investigating specific bulking control methods, Gabb et al. (1989) concluded that the selector effect, which was proposed as a method for controlling low F/M filament bulking, was ineffective. This research also indicated that in fully aerobic systems low F/M bulking was ameliorated, but in intermittently aerated anoxic-aerobic systems low F/M filament bulking was promoted. The research presented in this thesis forms part of a follow-up bulking research program into low F/M bulking which led to the formulation of a bulking hypothesis by Casey et al. (1992b) and focuses on the effect of different anoxic-aerobic conditions and their effect on the concentration of nitrate and nitrite entering the aerobic zone/reactor in single intermittently aerated and multi-reactor nitrification-denitrification systems.
Open Access
Engineering aspects of calcium carbonate and magnesium hydroxide precipitation in waste water reclamation
(1978) Wiechers, Hermannus Nikolaas Sybrandus; Marais, Gerrit van Rooyen
This thesis attempts to resolve some of the major problems associated with lime treatment in waste water reclamation. The contribution to knowledge is briefly outlined below. One of the major problems associated with lime treatment is the instability of lime-treated effluent, which may result in serious calcium carbonate scale formation problems. In the thesis this instability is attributed to two fundamental causes, (1) Incomplete precipitation, i.e. a kinetic problem. (2) The unintentional absorption of carbon dioxide from the air by the highly alkaline lime-treated effluent, i.e. a contamination problem. Calcium carbonate and magnesium hydroxide precipitation are time dependent. As a consequence of this time dependency unstable effluent may be produced under reaction conditions commonly encountered in practice. An exhaustive study identified the major factors affecting the precipitation kinetics. Reaction system conditions required for producing a stable effluent are, (1) Lime slurry and sludge, in that sequence, must be thoroughly mixed with the waste water, preferably by means of in-line static mixers, before discharge to a completely stirred tank reactor. (2) A completely stirred tank reactor with a minimum mean residence time of two minutes must be provided for the dissolution and precipitation reactions to go as near to completion as possible. (3) The reactor contents must have a sludge concentration of the order of 10 000 mg l⁻¹.
Open Access
An investigation into biological treatment of fruit cannery wastes
(1975) Law, Ian Beith; Marais, Gerrit van Rooyen
The production of canned fruits and vegetables in the Republic of South Africa is an important factor in the country's export trade. South Africa exported goods valued at R2 016m in 1972, of which R69m was accounted for by canned fruits and vegetables. (Bulletin of Statistics 1974 and Stats 1974). The major fruit and vegetable growing areas are in the Western Cape and the canneries are situated in those towns in close proximity to both the farms and railheads. The wastewaters generated by the numerous canneries vary greatly in composition - being dependent upon the particular fruit or vegetable being processed. The wastes generally have high BOD or COD concentrations (mainly due to sugars and starches) and low concentrations of the nutrients, nitrogen and phosphorus. In many towns the seasonal 'pollution' load from the canneries can exceed by several times the municipal load. Usually the municipal waste water treatment facilities are inadequate to handle the seasonal peak loads. This, in conjunction with the nutrient deficient nature of the cannery wastes, results in poor treatment efficiencies being recorded at the purification works.
Open Access
Kinetics of biological nitrogen removal in a single sludge activated sludge process
(1981) Sehayek, Ephraim; Marais, Gerrit van Rooyen
The objective of this investigation was to develop experimental set-ups and operational procedures for accurate and reliable evaluation of the kinetic constants and sewage characteristics that influence nitrification and denitrification in the single sludge nitrification-denitrification activated sludge process.
Open Access
Kinetics of enhanced phosphorus removal in the activated sludge process
(1975) Martin, Kevan A C; Marais, Gerrit van Rooyen
An investigation into the removal of phosphorus in the activated sludge process showed that: (1) Luxury uptake of phosphorus may be induced by the presence of an anoxic zone (2) If a primary and secondary anoxic reactor are present in the system, the actual retention time of the primary anoxic reactor will have the dominant effect on the degree of phosphorus removal. (3) In a system where only a primary anoxic reactor is present, there is an optimum actual anoxic retention time for obtaining maximum phosphorus removal. This optimum value appears to coincide with the condition where there is no nett release of phosphorus in the anoxic zone. Decreasing or increasing the actual anoxic retention time either side of the optimum value has a detrimental effect on phosphorus removal. (4) Increasing the influent ammonia-nitrogen and hence the reactor nitrate concentration, enhances phosphorus removal. (5) An increase in aeration reactor pH to between pH 7-8 enhances phosphorus removal. (6) The mechanism of removal does not appear to be precipitation. Although an increase in pH through the anoxic reactor was observed due to denitrification, phosphorus was released into solution. (7) The degree of phosphorus removal is independent of the influent phosphorus concentration. (8) Anoxic stripping of phosphorus is not a pre-requisite for luxury uptake of phosphorus to occur. (9) The concentration of phosphorus removed is a function of the COD utilized. The ratio of phosphorus removed to the COD utilized is constant at a particular sludge age, so that as the concentration of COD utilized increases, the concentration of phosphorus removed increases. (10) The concentration of phosphorus removed is a function of the sludge age. For a fixed biodegradable influent COD, the longer the sludge age, the less phosphorus removed.
Open Access
Kinetics of the activated sludge process
(1984) Marais, Gerrit van Rooyen
The writer decided to submit, for the purposes of the degree, a selection of the more important papers on the kinetics of the activated sludge process. These papers chronologically trace developments in the kinetic theory, from aerobic steady state behaviour to aerobic, nitrification and denitrification behaviour under cyclic flow and load conditions in multi-reactor systems including aerobic, anoxic and anaerobic reactors. Also included are papers reporting research, on biological excess phosphorus removal. Application of the research to design is illustrated by including a copy of a design manual written for the Water Research Commission of South Africa, to which the writer and his group made a major contribution. The reader will note that not a single contribution in the list selected was written by the writer alone, however, the research undertaken at the University of Cape Town in the fields described above was carried out under his direction. In this endeavour approximately 35 students participated, over a period of 14 years, to the common purpose of fulfilling the overall objectives set initially. The multiplicity of aspects to which attention had to be given is evident from the research reports listed in the Curriculum Vitae. In reading through the papers submitted one will notice that, due to the long time span over which they were written, ideas necessarily changed, and it may not be easy at times to see the common thread that passed through all. For this reason it was thought useful to give a review of the considerations that entered into setting up a model describing the kinetics of carbonaceous material degradation. This model forms the foundation on which denitrification and biological excess phosphorus removal are readily grafted; understanding of the carbonaceous degradation model facilitates understanding of the other two phenomena.
Open Access
Nitrification and denitrification kinetics in the activated sludge process
(1981) Van Haandel, Adrianus Cornelius; Marais, Gerrit van Rooyen
The bi-substrate active-site death regeneration model, developed by Dold, Ekama and Marais (1980), to describe the aerobic activated sludge process, was extended to provide a reliable description of the behaviour of the nitrification-denitrification single sludge activated sludge process under constant, cyclic or unsteady conditions of flow and load. The extended model applies to series reactor systems containing aerated and non-aerated reactors and to single reactor systems having alternating aerated and non-aerated periods. The extension describing the behaviour in the anoxic state required no change in the basic equations describing the aerobic state. The numerical values of the kinetic constants in the anoxic state equations were found to be the same as those in the aerobic state equations, except for one: The value of the utilization rate constant for slowly biodegradable material in an anoxic environment is a fraction of approximately 0,38 of the value of this constant in an aerobic environment. Nitrification is affected in so far that growth of nitrifiers takes place in an aerobic environment, whereas death of nitrifiers takes place in both aerobic and anoxic environments. The existing empirical denitrification models (valid for constant flow and load conditions) could be deduced from the solutions of the basic equations. The empirical denitrification rate constants could be interpreted in terms of the expressions for utilization of easily and slowly biodegradable organic substrates in an anoxic environment. These constants were shown to have no fundamental kinetic significance; they are only apparent constants, the result of kinetic reactions which, fortuitously, show little variation under normal operational conditions.
Open Access
Pelletization in the upflow anaerobic sludge bed (UASB) reactor
(1989) Sam-Soon, Paul Alan Li Nai Sing; Marais, Gerrit van Rooyen; Loewenthal, Richard Eric
This investigation was prompted by a study into the feasibility of treating an apple juicing waste water in an upflow anaerobic sludge bed (UASB) reactor system. Past experience with this system suggested that a pelletized sludge would be produced due to the nature of the waste water. This indeed was observed but the system exhibited an unusual feature, a high removal of nitrogen far in excess of that normally found in normal anaerobic processes. This observation stimulated a far reaching investigation into, the behaviour of the pelletized sludge bed, the causes giving rise to pelletization, a biochemical model explaining pellet formation, verification of the biochemical model, criteria for pellet formation, pH control in the pelletized sludge bed, and a kinetic model for the UASB process.
Open Access
Phosphorus transport in the Berg River, Western Cape
(1989) Bath, Andrew John; Marais, Gerrit van Rooyen
The objective of this investigation was to develop a dynamic phosphorus export model that describes the transportation of phosphorus through the Berg River drainage basin. Such a model had to consider (1) export of phosphorus from nonpoint (diffuse) sources via surface and subsurface drainage, and from point sources such as wastewater treatment discharges, (2) transportation of phosphorus in the water prism along the river channel, taking account of removal and remobilization of phosphorus from and to the water column, and transportation of phosphorus in the bed load.
Open Access
Verification of the bisubstrate concept in modelling of the activated sludge process
(1986) Bagg, Wayne Kendall; Marais, Gerrit van Rooyen
This investigation was concerned with two problems: (1) verification of the bisubstrate concept proposed by Dold, Ekama and Marais (1980), in which the biodegradable component of wastewater consists of readily and slowly biodegradable fractions, and (2) physical separation techniques for estimating the readily biodegradable fraction. Intensive research, since 1970, into the behaviour of activated sludge systems at the University of Cape Town has culminated in the formulation of a general kinetic model, by Dold and Marais (1986). The model is highly complex, incorporating a number of different processes; however extensive simulation studies have shown that the model simulates the behaviour of activated sludge systems very closely. A crucial concept incorporated in the general model is that the biodegradable fraction of a wastewater can be subdivided into two fractions with sharply different characteristics (bisubstrate concept), a readily biodegradable fraction which is directly utilized by the organism mass at a high rate and a slowly biodegradable fraction which requires to be solubilized extracellularly to readily biodegradable material for subsequent use by .. the organism. Solubilization is hypothesized to be a relatively slow process. These characteristics were inferred from the oxygen utilization rate response of a system fed in a cyclic square wave fashion. No work has been done to verify if substrates of specific chemical structures can be allocated to one or the other of the fractions. One of the objectives of this investigation was to check if pure and mixtures of specific selected substrates reflected these fractions when fed to activated sludge systems. Glucose and maize starch were selected as representative of readily biodegradable and slowly biodegradable substrate respectively. Systems were run under steady state and square wave cyclic state with glucose only, starch only and glucose/starch mixtures. From the steady state response the specific yield values could be determined and the reliability of the data checked by doing mass balances on the COD. From the cyclic response the specific rate constants for growth and solubilization respectively could be determined by trial simulation using the general model and specifying the concentrations of readily and slowly biodegradable fractions equal to the stoichiometric concentrations of glucose and starch in the feed. The constants thus determined were compared with the "standard" constants for municipal wastewaters.