Hydrolysis reaction was carried out at varying NaOH concentrations of 0.008, 0.016 and 0.024 M, variable temperature of 6 and 21 °C, and constant initial crystal violet (CV) concentration of 2.6 × 10–5 M. Kinetic data of the reaction were generated using UV–Vis Spectrophotometer. Analysis of the reaction kinetics shows that the overall rate order of the hydrolysis reaction was 1st order. The individual rate order of the reaction with respect to NaOH and CV was temperature dependent. At 21 °C the rate order with respect to NaOH and CV were 0.24th and 0.76th, respectively. While at 6 °C the individual rate order were 0.38th and 0.62th with respect to NaOH and CV, respectively. Values of the reaction rate constant (k) at 21 and 6 °C were 7.2 and 1.9 $$\left( {\frac{{{\text{mol}}}}{{\text{L}}}} \right)^{{ - 0.9}} min^{-1}$$ mol L - 0.9 m i n - 1 , respectively. The activation energy of the reaction was determined as 60.57 kJ/mol. The reaction was an endothermic reaction having enthalpy values of 58.13 and 58.29 kJ/mol at 21 and 6 °C, respectively. The entropy and Gibbs free energy of the hydrolysis reaction at ambient temperature of 21 °C were − 64.72 J/mol K and 77.15 kJ/K, respectively. At 6 °C the entropy and Gibbs free energy of the reaction were − 64.29 J/mol K and 76.19 kJ/K, respectively.

5A systematic experimental study of the effect of hydraulic residence time (HRT) and 6 solids residence time (SRT) on conventional suspended-growth biological wastewater 7 treatment processes was carried out. The aim of this study was to identify the 8 conditions that minimise the reactor volume, i.e. maximise the organic load rate (OLR), 9 and minimise the oxygen consumption. Lab-scale sequencing batch reactors (SBRs) 10 were operated with glucose or ethanol as only carbon sources, with HRT in the range 11 0.25-4 day and SRT in the range 1-71 day. The highest OLR values which gave 12 satisfactory performance were 4.28 and 4.14 gCOD/l.day for glucose and ethanol, 13 respectively, which are among the highest reported for conventional aerobic 14 suspended-growth processes. The highest OLR values were obtained with HRT=0.25 15 day, SRT=3.1 day for glucose and HRT=0.5 day, SRT=4.9 day for ethanol. The minimum 16 oxygen consumption was 0.36 and 0.69 kg O2/kg COD removed for glucose and 17 ethanol, respectively. In disagreement with conventional theories, it was found that 18 biomass production also depended on the OLR as well as on the SRT, higher OLRs 19 giving lower biomass production for the same SRT. From the kinetic analysis of the 20 experimental data, this behaviour, which has important consequences for the design 21 of biological wastewater treatment processes, was explained with a higher rate of 22 endogenous metabolism at higher OLRs. 23The aim of aerobic biological wastewater treatment processes is to treat the influent 30 wastewater with the highest possible reduction of the COD and BOD, with the 31 minimum possible size of the reaction tank and the minimum possible oxygen 32 consumption. A high COD reduction is required to maintain the high environmental 33 quality of the receiving water body, a small volume of the reaction tank decreases the 34 capital costs and the land usage by the plant, low oxygen consumption minimises the 35 energy costs and the environmental footprint of the plant. In addition, the production 36 of waste sludge needs also to be taken into account in the design of biological 37 treatment processes. Usually, waste sludge is considered a liability which needs to be 38 minimised, but the increasing use of anaerobic digestion to convert sludge into 39 methane is showing that waste sludge can rather be seen as a resource (McCarty et al., 40 2011). 41As far as the reactor volume is concerned, for a given flow rate and composition of the 42 influent wastewater, smaller reactor volumes correspond to lower values of the 43 hydraulic residence time (HRT) and, correspondingly, to higher values of the 44 volumetric organic load rate (OLR). In conventional suspended-growth activated 45 sludge processes, the OLR is typically in the range 0.5-1.5 kg COD/m 3 .day (WEF, 2012). 46 Various technologies have been investigated to increase the OLR and therefore 47 decrease the reactor volume, e.g. air-bubble or jet-loop bioreactors, membrane 48 bioreactors or granular sludge. For example, Petruc...

This paper summarizes the experience gained at Syngenta and at University of Aberdeen on visualization of gas–liquid mass transfer in agitated vessels. The aim is to show how simple experiments can be used to directly visualize the effect of vessel size, air flow rate, and agitation speed on the rate of mass transfer for gas–liquid reactions without the need for sophisticated probes or indirect calculations. The reaction used for visualization purposes is the “blue bottle” reaction, that is, the oxidation by oxygen of leucomethylene blue to methylene blue. This reaction produces a distinctive blue color, and its rate depends on the rate of oxygen mass transfer from the gas to the liquid phase. Therefore, this reaction can be used to visualize the rate of mass transfer and how this rate is affected by geometrical and operating parameters of agitated vessels. The described demonstration is furthermore highly convenient for educational purposes. This is the first demonstration visually illustrating scale-up effects in chemical processes.

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