An investigation program comprising 11 different phases
was performed. Each phase corresponded to a certain
volumetric loading rate (VLR), covering a wide range between
1.1 and 3.6 gCODT/(l day) to observe COD removal at various
conditions. In order to approximate steady state conditions, the
duration of each experiment was selected in such a way that the
reactor volume was at least four times exchanged by the feed to
the reactor. It should be noted, that due to the limited duration of
each experimental phase a complete steady state of the biomass
at high sludge ages might have not been reached.
At the beginning of the test period, the bioreactor was
inoculated with 5 g MLSS/l activated sludge from a pilot-scale
membrane bioreactor treating municipal wastewater. To let the
biomass adapt to the textile wastewater, a very low COD load,
VLR of 0.35 gCODT/(l day), was supplied to the MBR. As
shown in Fig. 4, after the adaptation phase a VLR of
3.1 gCODT/(l day) was applied which subsequently was
reduced stepwise to 1.1 gCODT/(l day). The sludge concentration
increased during the first phase from 5 to 10 g/l. For the rest
of MBR-operation it was kept between 10 and 15 g/l by
periodical sludge drawing.
In a part of the investigations, the influence of nutrient
addition was studied. During three phases (6–8) with VLRs
between 1.1 and 3.1 gCODT/(l day) the COD:N:P of the feed
was modified to 100:5:1 through supplementation with NaNO3
and an equimolar mixture of KH2PO4 and Na2HPO4 (dotted
line in Fig. 4). Finally, three additional experiments without
nutrient addition were performed, where VLR was again
stepwise increased from of 1.8 to 3.6 gCODT/(l day). In Table 2
the main operational parameters applied to the MBR are
summarised.