Interestingly, if one compares aerobic units operated at the
same 2-day HRT (AR1, AR2, AR3 and AR4), VSS levels were consistently
higher (as well as specific oxygen supply rates) in the aerobic
second-stage units. This is further confirmation that inhibitory
compounds in the shampoo waste itself, possibly surfactants, impair
the first-stage, low-HRT aerobic treatment units. Therefore,
anaerobic pre-treatment appears to reduce inhibitor loadings on
the aerobic units, improves overall system performance and stability,
and as such, makes it possible to use less energy for aeration. In
summary, aerobic reactors can treat shampoo wastes, but high
HRTs and oxygen supply rates are needed to achieve adequate
COD removal rates, consistent with experience in the PCP industry
(Ahammad et al., 2012).