surfactants. Shampoo wastes have high levels of surfactants, which
are known to disperse and impair microbial floc formation, including
in AS processes. This leads to poorly formed, buoyant floc that
can be lost in reactor effluents (Gerardi, 2002). This is consistent
with more dispersed floc observed in AR4 relative to the other
HRT units. The negative influence of surfactants was probably lower
in the higher HRT aerobic reactors because surfactants are
known to be aerobically biodegradable given adequate exposure
time (Qin et al., 2005).