thinness of the surface coating, evaporation is extremelyrapid, the moisture being flashed off, literally, in seconds. Steam requirements are heavy for this drying method, as a pressure of at least 5 atm has to be maintained, and the volumetric capacity of the drum is high, some being 4.6m long by 1. 8m in diameter UELS Suitable fuels. therefore, are coal and oil for the indirect systems, and propane, butane or natural gas for the d irect systems. In no circumstance should the gases of combustion of coal or oil be used in the direct air stream when dehydrating food for human consumption Therisks of contamination by sulphur and carbon compounds are very considerable in these circumstances and, whilst this method has been used in the past for dehydrating certain food products, it should certainly be avoided in the context of modern practice EFFLUENT The subject of waste and industrial effluent disposal is too wide and tin plicatedtobe dealt with in depth in this volume.It hasbecome, in recent es, a problem of nationalsignificance and importance, and the dehydrator creening solids from liquid effluent in italythinness of the surface coating, evaporation is extremely rapid, the moisture being flashed off, literally, in seconds. Steam requirementsare heavy for this drying method, as a pressureof at least 5.4atm has to be maintained, and the volumetric capacity of the drum is high, some being 4.6m long by 1.8m in diameter. FUELS Suitable fuels, therefore, are coal and oil for the indirect systems, and propane, butane or natural gas for the d irectsystems. In no circumstances should the gases of combustion of coal or oil be used in the direct airstream when dehydrating food for human consumption. The risks of contamination by sulphur and carbon compounds are very considerable in these circumstances and, whilst this method has been used in the past for dehydrating certain food products, it should certainly be avoided in the context of modern practice. EFFLUENT The subject of waste and industrial effluent disposal is too wide and complicated tobe dealt with in depth in this volume. It has become, in recent times, a problem of national significanceand importance, and the dehydrator 1 Screening solids from liquid effluent in Italy 35