Modelling of ionic interactions with wastewater treatment biomass.

Titration data for samples of mixed salts with glycine, baker's yeast cell mass and anaerobic digester sludge were obtained and compared to a speciation model of weak acid-base interaction in aqueous solutions. The effect of glycine on the buffer intensity of the solution could be precisely described by the speciation model but did not represent the proton exchange characteristics of either baker's yeast or anaerobic sludge well. A model component, UKZiNe, consisting of carboxylic acids, phosphate and amine groups described the baker's yeast well, and a combination of UKZiNe and carbonate-yielding inorganic solids described anaerobic digester sludge. The effect of biomass on buffer intensity in the pH range 6.5 to 8 was small for the concentration ranges tested.

A critical review of experimental and predicted methane generation from anaerobic codigestion.

Anaerobic digestion is increasingly being considered as a treatment option for an extensive range of waste biomass, due to the potential for energy recovery, in the form of methane production, and lower sludge volumes relative to aerobic treatment processes. Furthermore, when two substrates are codigested (i.e. digested together), added benefits are foreseeable, such as increased methane production and detoxification of toxic compounds via cometabolic degradation pathways. The objectives of this study were to compare experimental and predicted methane production from codigestion literature studies in order to objectively evaluate digester performance. Two predictive methods were used, both assuming methane yields are additive: literature values for digestion of single substrates and a stoichiometric method using model substrates to represent different substrates. Waste sources included in the analysis were primary sewage sludge, waste activated sludge, cow manure, waste paper, grease trap sludge, fat oil and grease and algal sludge. It was found that methane production could approximately be predicted using both methods, with literature methane yields from the same study being the most accurate predictor. One important finding from this study was that the assumption that methane yields are additive is a reasonable one. Furthermore, both predictive methods may be usefully employed as a screening tool to compare methane yields between different types and blends of substrates.

A graphical technique for wastewater minimisation in batch processes.

Presented in this paper is a graphical technique for freshwater and wastewater minimisation in completely batch operations. Water minimisation is achieved through the exploitation of inter- and intra-process water reuse and recycle opportunities. In the context of this paper, a completely batch operation is one in which water reuse or recycle can only be effected either at the start or the end of the process. During the course of the operation, water reuse and recycle opportunities are completely nullified. The intrinsic two-dimensionally constrained nature of batch processes is taken into consideration. In the first instance, time dimension is taken as a primary constraint and concentration a secondary constraint. Subsequently, the priority of constraints is reversed so as to demonstrate the effect of the targeting procedure on the final design. Attention is brought to the fact that first and cyclic-state targeting are essential in completely batch operations. Moreover, the exploration and use of inherent storage in batch processes is demonstrated using a real-life case study. Like most graphical techniques, the presented methodology is limited to single contaminants.

The application of pinch analysis to water, reagent and effluent management in a chlor-alkali facility.

South African industry is coming under increasing pressure to reduce the amount of freshwater it uses and the amount of effluent it produces. Water pinch is a cleaner production technique aimed at reducing the freshwater consumption and effluent production within a chemical complex. The design of water-reuse or water pinch networks as applied to the case study of a chlor-alkali complex is considered. Insights are provided into the analysis and formulation of problems for large-scale industrial systems and the application of present techniques and tools to the formulated problem is illustrated. The features of the problem posed by the chlor-alkali facility are discussed and the limitations of the present theory in dealing with this problem highlighted. The concepts of utility-waterpinch analysis and process-water pinch analysis are introduced.

A computational fluid dynamic and experimental study of an ozone contactor.

A computational fluid dynamic (CFD) model of an ozone contacting chamber in the Umgeni Water Wiggins Waterworks in Durban, South Africa, has been set up and verified by experimental tracer tests, as part of an investigation to optimise the control and disinfection efficiency of the contactor. The effect of gas injection was modelled by increasing the turbulent intensity at the reactor inlet. Experimental tracer responses which were used as partial verification of the model correspond very closely to model predictions.

Modelling and control of potable water chlorination.

The Umgeni Water Wiggins water treatment plant feeds the southern areas of Durban in South Africa and has a maximum treatment capacity of about 350 Ml/d. Two interconnected reservoirs at this facility hold treated water before it enters the distribution network. Because of the variable demand, the reservoir levels and residence times undergo considerable variation. This has a strong influence on the free chlorine concentration in the water leaving the reservoir, which should be 0.8 to 1.2 mg/l, to ensure an adequate disinfection potential within the network. This paper describes a model which accounts for the observed variations of chlorine concentration, and will form the basis of a predictive controller for the chlorine concentration in the outlet.

Optimal operation of a potable water distribution network.

This paper presents an approach to an optimal operation of a potable water distribution network. The main control objective defined during the preliminary steps was to maximise the use of low-cost power, maintaining at the same time minimum emergency levels in all reservoirs. The combination of dynamic elements (e.g. reservoirs) and discrete elements (pumps, valves, routing) makes this a challenging predictive control and constrained optimisation problem, which is being solved by MINLP (Mixed Integer Non-linear Programming). Initial experimental results show the performance of this algorithm and its ability to control the water distribution process.

Denitrifying activity measurements using an anoxic titration (pHstat) bioassay.

An anoxic titrimetric test was investigated for measuring denitrifying activity in an activated sludge system. The method measures the amount of acid that is required to maintain the pH set-point value in a batch denitrification experiment. An iterative algorithm was implemented to extract nitrate uptake rate (NUR) data from titration data, since the accumulation and depletion (stripping) of reaction by-products HCO3- and CO2 affects the direct calculation of denitrifying activity from titration data. This method was performed using an automatic pH-stat acid dosing system, and the data were analysed using the simulation software package, AQUASIM.

Pilot-scale study of an anaerobic baffled reactor for the treatment of domestic wastewater.

Large proportions of South Africans live in areas with inadequate sanitation and a poor infrastructure for waterborne sanitation. Service providers are looking for alternative wastewater treatment options. The anaerobic baffled reactor is being considered as a decentralised sanitation option in these areas. A 3,200 L reactor was built and is currently being evaluated at a wastewater treatment works. The reactor was built based on experiences gained from working with a laboratory reactor (10 L) and predicted flow patterns observed on a computational fluid dynamics model. The design and construction of the reactor will be discussed in this paper. The feed to the reactor consists of screen degritted sewage and the flow to the reactor is maintained by means of a programmable logic controller. The pilot-plant layout is discussed in this paper. Samples are analysed for chemical oxygen demand, pH, alkalinity, ammonia, phosphorus, solids and ash content. Reductions of between 70 and 80% are obtained for COD and the pH values for the effluent samples are within the discharge limits.

Morphometric analysis to detect suspected myocardial disease. A pilot study.

Myofibres in the normal left ventricle (LVs) of 24 healthy young accident victims and the diseased LVs of 10 subjects who died from constrictive pericarditis or congestive (African) cardiomyopathy were subjected to morphometric evaluation. Each myofibre was represented by a pair of measurements: cross-nuclear fibre (FD) and nuclear (ND) diameters. Using a VIDS image analyser interfaced with a light microscope, 150 paired measurements were determined for each of the 34 specimens. The bivariate relationship between FD and ND for each group of specimens were expressed as linear regressions. The limits for the group distribution of normal specimen FD/ND means were calculated and graphically depicted in the form of an ellipse. Disease specimens were plotted for comparison. Of the normal specimens, 23/24 FD/ND coordinates fell within the "normal' ellipse whereas the altered relationship between FD and ND in pathological myocardia caused all 10 specimen means to be plotted outside the ellipse and their regression lines to be displaced from normal. It is suggested that the normal data define the morphometric parameters of LV myofibres in healthy hearts and create a graphic standard by which myofibre pathology in hearts suspected of disease can be detected.

Perspective graphics as a means of portraying the distribution of radiolabelled ligands in the spinal cord--a pilot study using intrathecally administered 3H morphine.

Tritium-labelled morphine sulphate was injected into the lumbar (L4-5) subarachnoid space of an adult male baboon. Three hours after injection, the animal was sacrificed. Using quantitative light microscopic autoradiographic mapping techniques, contour and perspective diagrams were prepared that described the position of radiolabel and by inference the distribution of morphine binding sites within the spinal cord. High concentrations of 3H was found in the medial regions of laminae I, II (substantia gelatinosa) and III of the dorsal horns. Smaller, but significant levels were seen bilaterally in the spinal anterolateral quadrant. Minimal 3H activity was seen in the remainder of the spinal cord with the lowest level being recorded in the spinal canal. Perspective graphics proved a precise and attractive method for locating the position and quantifying the concentration of radiolabel in baboon spinal cord.

Characterisation of normal human myocardium by means of morphometric analysis.

A morphometric analysis of ventricular myofibres, in specimens taken at necropsy from ten normal hearts, was performed to determine the distribution of fibre and nuclear diameters and their dependence on sampling position within the heart (group a). To assess the significance of the findings, two control groups of specimens were subjected to the same analysis: b) specimens from the hearts of four patients who had died of African cardiomyopathy; c) biopsies taken from the left ventricles of two hearts undergoing surgical repair of atrial septal defects (ASD), in which the myocardium is considered normal. Although mean values for the left ventricle were 13% greater on average than those for the right, a linear correlation, independent of sampling position, was found between nuclear and fibre diameter. Mean fibre and nuclear diameters for specimens from the normal and ASD control groups followed the same correlation as for individual normal fibres, whereas there was a significant deviation in the case of the cardiomyopathy specimens. The relationship between nuclear and fibre diameters was found to distinguish between normal and pathological specimens more clearly than the mean values of either dimension considered separately. It is suggested that this relationship is a more sensitive criterion of ventricular fibre normality or pathology than the parameters used in previous studies of this nature.