This paper presents a new simple, rapid, and accurate method suitable for on-site measurement of volatile fatty acids (VFA) and carbonate alkalinity in anaerobic reactors. This titrimetric method involves eight pH observations, and typically, the full procedure takes approximately 15 min. An important feature of the method is a built-in quality control mechanism allowing the user a rapid means of assessing the reliability of the experimental procedure. To evaluate the accuracy of the method, both laboratory-made waters and industrial UASB effluent were tested. High accuracy for both VFA and carbonate alkalinity measurements (error within 2% and 1%, respectively) plus good repetition (average standard deviation of 6.7% and 1.45%, respectively) was obtained. The method takes into account the effects of the phosphate, ammonium, and sulfide weak acid subsystems. Appraisal of the effect of an input error in these subsystems revealed that VFA measurement is fairly insensitive to phosphate and ammonium concentrations. It is, however, sensitive to H2S loss during titration where the sulfide concentration is higher than approximately 10 mg/Las S. With regard to the carbonate alkalinity measurement, error in concentration of either phosphate or sulfide or H2S loss might result in a significant error. Short guidelines for correct execution of the method are given in an appendix.

Three biochemical models for biological excess phosphorus removal are critically analysed: the Comeau/Wentzel, Mino and modified Mino models. There is agreement between the models except in one respect, the generation of reducing equivalents (NADH2) required to convert acetate to poly-β-hydroxybutyrate under anaerobic conditions. In this regard a procedure is suggested to determine which of the models' premises are correct.

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Struvite precipitation is common in waste water systems containing high concentrations of dissolved orthophosphates, free and saline ammonia and magnesium ions, such as in anaerobic fermentation systems, often leading to severe fouling. It appears that a reduction of the partial pressure of CO2, ie. pCO2 is a trigger mechanism for struvite precipitation. An algorithm was developed, based on equilibrium chemistry, to quantitatively predict the struvite precipitation potential of the water in such a process. This was then extended, to predict the change in state together with precipitation potential due to chemical perturbations, particularly variations of pCO2. Experimental verification of the algorithms is presented.

Conventional characterisation of low alkalinity waters via pH measurement and titration of total alkalinity to a prescribed end-point invariably leads to large errors. These errors result from instability of the pH probe and an unknown titration end-point. In this paper two indirect methods (termed the "double Gran function" and the "blend" method) for the characterisation of such waters are evaluated critically. A blend composed of the raw water, sodium chloride (to increase conductivity), and standard bicarbonate (to increase buffering capacity) was titrated with standard strong acid in two pH regions: 6.3 < pH < 7.0, and 3.5 > pH < 4.0. In both methods, total alkalinity was determined using the latter set of points, and the first Gran function. In the double Gran function method the upper set of titration points was used to determine CO 2 acidity using the second Gran Function. In the "blend" method, equilibrium chemistry data were used to calculate total acidity for each point based on the known total alkalinity, pH reading, temperature and ionic strength. The two methods gave excellent results (in terms of both repetition and accuracy) as compared to characterisation based on total alkalinity and inorganic carbon analysis. A detailed procedure for the execution of the two approaches is given in an appendix.

The paper briefly reviews the development of the biological excess removal of phosphorus in the activated sludge process, from 1959 when it was first observed to the present. It concludes by proposing, tentatively, a biochemical mechanism whereby excess P uptake and release can be explained.

Corrosion and/or aggression are common problems arising in pipelines transporting terrestrial waters. The kinetics and severity of such events depend on both the quality of the water being transported and the material properties of the pipeline. Irrespective of the nature of the problem, its solution (or at least its minimisation) is strongly linked to control of pH, calcium concentration and carbonate chemistry of the water (stabilisation). However, application of such chemistry to water treatment problems is complex and time consuming. Various numerical, graphical and computer techniques have been developed to address this, but these are either of insufficient accuracy, too time consuming or lacking in generality. In this paper algorithms are presented for solving a broad spectrum of problems related to control of mineral precipitation/aggression, pH and chemical dosing in water treatment. These have been incorporated into a computer software package, STASOFT, which offers the requisite framework for use in water treatment. Various stabilisation problems pertinent to water supply are addressed.

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