In terms of COD removal efficiency a clear effect of the
nutrient addition was not obvious. However, when looking at
the COD concentration in the effluent (open circles, Fig. 6) it
can be seen that slightly lower values were achieved. These
findings are in line with results published by Ref. [9] who report
that addition of nutrients improved COD removal during
treatment of textile wastewater in a laboratory-scale sequencing
batch reactors. On the other hand nutrient addition had also
certain disadvantages. The addition of nutrients, in the form of
inorganic salts, significantly contributed to conductivity,
because salt concentration is not influenced by MBR treatment.
Elevated conductivity levels can be particularly disadvantageous
if reuse of MBR treated wastewater is intended,
especially when nanofiltration or reverse osmosis is used for
further effluent polishing as discussed later. Another disadvantage
was that severe foaming occurred with the addition of
nutrients. Foaming problems with MBRs treating textile
wastewater have been also reported by Ref. [7].