Investigation of High BOD in Final Plant Effluent

The Detroit WWTP had experienced intermittent high BOD in the dechlorinated final plant effluent from September 2003 to October 2004 and was not related to wet weather events. No NPDES violations occurred. A short-term cost effective laboratory investigation was initiated during the months that the intermittent high BOD values were occurring to determine possible causes. The results of the laboratory study were as follows: 1. Sulfide will increase the BOD in the final effluent; 2. The synergistic effect of manganese (II) and oil & grease will increase BOD; 3. Manganese (II) or Cobalt (II) present with excess sulfur dioxide did not cause high BOD.