After treatment by the integrated system, COD of the final effluent
was steadily reduced to about 100 mg l−1, which could meet the
requirement of the National Discharge Standard of China (GB8978-
1996). The COD change in the influent and the ZVI effluent was
shown in Fig. 3. The average COD removal efficiency of the integrated
system was 94.2% during the operation period, which was
much higher than that of the biofilm reactor system. In the single
biofilm reactor system, COD of the biological effluent wasmore than
200 mg l−1 and the maximal COD removal efficiency was 90.2% [20].
In the integrated system, the maximal COD removal efficiency was
up to 96.1% and COD of the final effluent was reduced to 76.2 mg l−1.
It is clear that ZVI process played an important role for organic
compounds removal as it was combined with the biofilm reactor
system.e