Additionally, small variations of ionic strength have a big effect on the structural properties, and therefore on the stability of sludge flocs. The flocs are first stabilized by an increasing ionic strength (64) before being destabilized at IS>0.1M . High ionic strengths have a negative effect on the dewatering behaviour of digested sludge . Another key process of wastewater treatment, nitrification/denitrification, is influenced by the salinity via the modification of the microbial community of the waste activated sludge (68, 69). The effect is positive at first, and negative for IS>0.1M . Such high ionic strength should only be encountered in WAS systems dealing with industrial, or very saline wastewater.