Presentation and evaluation of the zero-dimensional biofilm model 0DBFM.

A zero-dimensional biofilm model, i.e. 0DBFM, has been developed for dynamic simulation of moving bed bioreactors (MBBRs). This mini-review aims at presenting and evaluating 0DBFM. 0DBFM is presented in Petersen matrix format and is based on the activated sludge model ASM1, which is an explicit and quite complex model (eight processes, 13 state variables, and 19 parameters) that has found wide application in engineering practice. 0DBFM is thus based on existing knowledge in biological wastewater treatment. The ASM1 approach has been confirmed by respirometry since the resulting respirograms were successfully simulated with ASM1. 0DBFM distinguishes between attached and suspended biomass and incorporates attachment of suspended matter from the bulk liquid onto the biofilm and detachment of biofilm into the bulk liquid. Still, 0DBFM respects the golden rule of modelling, which says that 'models should be as simple as possible and as complex as needed' and resists Occam's razor. The practicability of 0DBFM has been shown on a pilot-scale plant since nine days of wastewater treatment were successfully simulated and effluent quality was dynamically predicted. Finally, 0DBFM can be inspiring and the applicability of 0DBFM to other biofilm systems can be tested.

Disequilibrium calorimetry for determination of ultrasonic power in sonochemistry.

The two most characteristic properties of an ultrasonic wave are the frequency and the power. It is therefore important to determine the power in a given reactor. This can be done by calorimetry, i.e. by measuring the temperature rise in the vessel during sonication starting at thermal equilibrium with the surroundings (classic calorimetry) [1-3]. However, the classic ultrasonic calorimetry has drawbacks. In particular it is difficult to evaluate the temperature rise at thermal equilibrium, because the relevant initial time and temperature intervals are small and measurement errors in the temperature readings are large. Also the initial temperature response of the probe is complex [4]. The authors propose to start the calorimetric measurement at thermal disequilibrium, i.e. with a lower temperature in the reaction vessel. During sonication the temperature in the reaction vessel rises faster than in the surrounding and passes thermal equilibrium. The acoustic power transferred to the vessel at thermal equilibrium can then be calculated. The method consists of: •Setting up the reaction vessel at lower temperature than the surroundings (ultrasonic bath or air).•Measuring temperature rise in the reaction vessel and the surroundings during sonication.•Determine the temperature rise at intercept by interpolation and calculate the ultrasonic power in the reaction vessel.

Purely ultrasonic enzyme extraction from activated sludge in an ultrasonic cleaning bath.

Enzymes are important in biological wastewater treatment systems, since they are responsible for breakdown of macro- and micropollutants, thereby making the pollutants available for metabolism. Enzyme activity has been investigated in particular in activated sludge processes, since the activated sludge technology is the most important and widely spread wastewater treatment technology used today. Various methods have been used to extract enzymes from activated sludge in order to measure their activity, these include stirring with additives like detergents and cation exchange resins, ultrasonication (with probes) and combinations of the three [1], [2], [3]. In this article we describe a method for purely ultrasonic enzyme extraction from activated sludge using low power ultrasound generated by an ultrasonic bath and no additives. The method essentially consists of: •Sonication of the sludge sample using a glass beaker and an ultrasonic bath.•Filtration of the sample in order to obtain the enzyme extract.•Measurement of enzyme activity by fluorescence spectrometry using a substrate that yields a fluorescent product.

Removal of tungsten oxyanions from industrial wastewater by precipitation, coagulation and flocculation processes.

Tungsten removal from industrial wastewater by precipitation, coagulation and flocculation processes using ferric chloride is reported. Suitable process conditions (pH, ferric chloride concentration) were established in jar tests performed with wastewater samples. Alkaline wastewater was treated with ferric chloride and pH was adjusted to various points using sulphuric acid. Tungsten removal was found to be most efficient (98-99%) in acidic conditions (pH<6). The process conditions were also found to be suitable for operation of an industrial scale wastewater treatment facility. More than 97% of tungsten were removed and the residual concentration was smaller than 10 ppm.

Sonovoltammetric studies on copper in buffered alkaline solution.

The effect of ultrasound on the voltammetry of copper in alkaline solution is reported. At pH 7 the electrode surface remains active after scanning to ca. +1.0 V (vs. SCE) and the effects of ultrasound show the expected substantial enhancement in limiting current due to improved mass transport under ultrasound. However at pH 9, whereas the silent scan is only slightly altered in gross detail from that obtained at pH 7, the sonicated scan is significantly different. This shows the expected current increase only up until ca. +0.6 V (vs. SCE), where there is a substantial loss of current showing a passivation phenomenon that is enhanced by ultrasound. In addition, during the reverse (reduction) scan under ultrasound an anodic peak appears. This suggests reactivation of the electrode during the cathodic sweep, possibly by reductive removal of a transient species from the electrode/(hydr)oxide interface at a potential where oxidation still occurs. Increasing the pH to 11 further shifts the cathodic peaks in the silent voltammogram.