The response of the integrated system after receiving the shock
loading was shown in Fig. 8. After 24 h for high loading influent
operated, the concentrations of COD and NH3-N in the final effluent
of the integrated system were increased to more than 200 and
30 mg l−1, respectively. Although both COD and NH3-N removal effi-
ciencies were recovered rapidly after the shock loading, the former
seemed to be recovered faster than the latter. In the proposed system,
it took 3 days for recovery of COD removal but 5 days for NH3-N
removal. Since the autotrophic nitrifiers were more susceptible
to environmental changes than heterotrophic microorganisms, the
recovery of NH3-N removal efficiency was always slower. Moreover,
ZVI process could remove part of increased refractory organic compounds,
which could help the recovery of the integrated system for
removal of COD and NH3-N in short time. When the integrated system
returned to the normal situation, the concentrations of COD
and NH3-N were reduced to less than 150 and 10 mg l−1, which
indicated that the high performance for pollutants removal of the
system could not be weakened by sudden increase of the influent
loading. As a result, the integrated system, which combined the
biofilm reactors with ZVI process together, was more efficient in
actual application for coking wastewater treatment than the single
biological treatment process.