ContentsCover: Separation of biotechnolgicaly syntesized product. Courtesy: Hoechst Aktiengesellschaft.Review: The degradation of organic compounds in water is the object of a number of fundamental and applied investigations. The aquasonolysis of organic compounds is an advanced technology for the purification of contaminated water. The process is based on phenomena of acoustic cavitation. The dominant reactions of volatile compounds are both cavitative hightemperature gas-phase reactions and thermal-oxidative decay in bubbles. This paper gives a state-of-the-art overview of ultrasound as a tool for the degradation of pollutants in wastewater. Communication: The selective biological elimination of hazardous substances from wastewater is of vital importance for production-integrated pollution control. It provides an opportunity to degrade otherwise persistent substances from wastewater mixtures. State-of-the-art industrial wastewater treatment plants cannot perform this task although the potential for an enzymatic degradation of most of these substances exists. This is due to the hydrodynamically determined mixing characteristics of the treatment plants. The aim of developing new technologies should be the adjustment of substrate-specific residence times at immobilized biomass. Communication: As has been confirmed by several studies reported in the literature, cavitation phenomena considerably contribute to droplet breakup during emulsification in high-pressure homogenizers. High-pressure homogenizers can be equipped with different homogenizing valves. The question, whether cavitation is also of importance for droplet breakup in orifice valves which have been proved very efficient for some emulsion systems, has not been investigated yet and is the subject of this contribution.

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Experimental and Theoretical Investigations on Hydrocarbons of the Formula C5H6: Pyrolysis of 1,3‐Cyclopentadiene The details of high temperature chemistry of the conversion of 1,3‐cyclopentadiene (CPD) are unknown. Therefore the pyrolysis of CPD was studied under various reaction conditions in labscale dimension. The attempt to interpret the composition of the reaction products only on the basis of convenient axiomes does not seem satisfactory. For that reason heats of formation and relative stabilities for 25 closed and open shell hydrocarbons of the formula C5H6 were calculated using the MINDO/3 procedure. These enthalpy values were used to estimate heats of reactions for selected start steps of the pyrolysis of CPD. The molecular‐assisted hydrogen transfer under formation of cyclopentadienyl and cyclopentenyl radicals ought to be one of the most important reaction steps.

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