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 was more 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