L. T. J. van der Aa

Influence of natural organic matter on equilibrium adsorption of neutral and charged pharmaceuticals onto activated carbon

Natural organic matter (NOM) can influence pharmaceutical adsorption onto granular activated carbon (GAC) by direct adsorption competition and pore blocking. However, in the literature there is limited information on which of these mechanisms is more important and how this is related to NOM and pharmaceutical properties. Adsorption batch experiments were carried out in ultrapure, waste- and surface water and fresh and NOM preloaded GAC was used. Twenty-one pharmaceuticals were selected with varying hydrophobicity and with neutral, negative or positive charge. The influence of NOM competition and pore blocking could not be separated. However, while reduction in surface area was similar for both preloaded GACs, up to 50% lower pharmaceutical removal was observed on wastewater preloaded GAC. This was attributed to higher hydrophobicity of wastewater NOM, indicating that NOM competition may influence pharmaceutical removal more than pore blocking. Preloaded GAC was negatively charged, which influenced removal of charged pharmaceuticals significantly. At a GAC dose of 6.7 mg/L, negatively charged pharmaceuticals were removed for 0-58%, while removal of positively charged pharmaceuticals was between 32-98%. Charge effects were more pronounced in ultrapure water, as it contained no ions to shield the surface charge. Solutes with higher log D could compete better with NOM, resulting in higher removal.

Furfural degradation in a dilute acidic and saline solution in the presence of glucose

A kinetic study has been performed on the degradation of furfural in a dilute acidic and saline solution with and without the presence of glucose. Experiments have been performed in a stirred batch reactor. The degradation of furfural alone was accurately predicted both using a first- and a second-order kinetic model. It was shown that furfural is degrading significantly faster when glucose is present in the reaction mixture. In the series with glucose present distinct second-order reaction kinetics were observed. From experiments with varying concentrations of glucose it turned out that an additional (second-order) reaction had to be added to the reaction mechanism in order to satisfactorily predict the experimental data. This additional reaction incorporated the initial glucose concentration as a constant in the Arrhenius expression for the reaction rate constant. Furthermore, it has been argued that this second-order reaction could well be a Diels-Alder reaction.

Good modelling practice in drinking water treatment, applied to Weesperkarspel plant of Waternet

Good modelling practice increases the credibility and impact of the information and insight that modelling aims to generate. It is known to be crucial for model acceptance and it is a necessity to amass a long-term, systematic thorough knowledge base for both science and decision making. This paper shows how ten steps in model development and evaluation can also be applied to numerical modelling of drinking water treatment, using models of drinking water treatment processes of the Weesperkarspel treatment plant of Waternet. The Weesperkarspel plant consists of ozonation, pellet softening, biological activated carbon filtration and slow sand filtration. For the different processes models were developed that were used for operational improvements. The modelling resulted in new insights and knowledge about the treatment processes and improved operation of the processes. From scenario studies for the pellet softening it was concluded that chemical dosing can be diminished when by-pass ratio is increased and that pellet size can be controlled by measuring the difference in pressure guaranteeing fluidisation of the pellet bed. In addition, ozone dosage can be optimised by modelling ozone exposure, bromate formation and biologically degradable natural organic matter (NOM) under varying influent water quality.