Abstract
This study aims to investigate the performance and treatment capability of sequencing batch reactor and activated sludge systems under heavy metals shock loads. The combined effects of cadmium and zinc on both systems were studied. Two pilot plant units, one for each system were used to study the effect of gradually increasing both cadmium and zinc on the treatment process. Batch tests were also performed to study the effect of both cadmium and zinc shock loads on the acclimated sludge that collected from each pilot plants. The results of the pilot plant units showed that the efficiency of COD removal decreases under the gradual increase of heavy metals and that this efficiency was higher in the sequencing batch reactor pilot plant than the activated sludge pilot plant. Results of batch tests showed that the efficiency of COD removal of acclimated sludge collected from each pilot plant was higher than the normal sludge collected from both systems before adding metals. Similarly this efficiency was higher in the sequencing batch reactor pilot plant than the activated sludge pilot plant operated under the same conditions.