Protozoa grazing of nitrifiers is important process in activated sludge process that leads to decrease of mass of active bacteria. In classical models this process is included in decay processes. Such approach makes modelling of influence of protozoa grazing on nitrifiers impossible. https://safeersappliancers.shop/product-category/grundig-gkng1691dg-50-50-fridge-freezer-graphite/