Variation of chemical and microbial parameters in collection and storage tanks for source separated human urine

To investigate if variations in concentrations occur at different levels wi thin urine tanks and to evaluate possible consequences thereof, urine sampl es were collected from four collection tanks and one storage tank of differ ent urine separating sewerage systems. Plant nutrients and metals were foun d to concentrate in the sediment at the bottom of the tanks. Also, densitie s of indicator bacteria were higher in the bottom layer, probably due to ad sorption to sedimented particles. The differences in concentration at diffe rent levels became more apparent during storage of the urine mixture. After four months storage concentrations of the investigated indicator bacteria, except clostridia, were below detection limits at all levels. Considering the variability in nutrient concentration, samples from the middle level co rrespond well to the average composition in the tanks and can be used to ca lculate urine application rates. When estimating hygienic risks with the re use of human urine the concentration variability also needs to be considere d.