The enzymatic hydrolysis of triglycerides with lipases (EC 3.1.1.3.) involves substrates from both water and oil phases, with the enzyme molecules adsorbed at the water-oil (w/o) interface. The reaction rate depends on lipase concentration at the interface and the available interfacial area in the emulsion. In emulsions with large drops, the reaction rate is limited by the surface area. This effect must be taken into account while modelling the reaction. However, determination of the interfacial saturation is not a trivial matter, as enzyme molecules have the tendency to unfold on the interface, and form multi-layer, rendering many enzyme molecules unavailable for the reaction. A multi-scale approach is needed to determine the saturation concentration with specific interfacial area so that it can be extrapolated to droplet swarms. This work explicitly highlights the correlation between interfacial adsorption and reaction kinetics, by integration of the adsorption kinetics into the enzymatic reaction. The rate constants were fitted globally against data from both single droplet and drop swarm experiments. The amount of adsorbed enzymes on the interface was measured in a single drop with a certain surface area, and the enzyme interfacial loading was estimated by Langmuir adsorption isotherm.

Membrane bioreactors (MBRs) are state of the art in municipal wastewater treatment. One of their main disadvantages is the high energy demand for air scour of the membrane. However, due to more stringent legal restrictions, sludge handling costs will increase and therefore they are becoming more and more signifi cant for the total operating cost of the MBR. In this study, a novel cost model approach for immersed MBRs treating municipal wastewater incorporating the energy demand for aeration and fouling prevention as well as the related sludge handling costs subject to local conditions is presented. The model is consciously kept simple to be easily applicable for end users and is based on a few easily accessible input parameters like operational (hydraulic retention time, sludge retention time) and bio-kinetic parameters (yield, decay coefficient) and feed conditions. Information on bio-kinetic parameters and oxygen transfer efficiency varies strongly in the literature; therefore, the correct choice of the...