Changes in dissolved and particulate copper following mixing of POTW effluents with Delaware River water

Effluents from publicly owned treatment works (POTWs) were mixed with Delaware River water at ratios of 1:1 or 1:2 effluent to Delaware River water. These mixing experiments were performed at pH 6, ambient pH and pH 8. In all mixing experiments, copper was released from effluent particulate matter when mixing was conducted at pH 6. No copper release was observed for mixing at the ambient pH of the samples. At pH 8, no copper was released when effluent from the Delcora or Camden POTWs was mixed with Delaware River water, but copper was released for Levittown, Philadelphia Northeast, Philadelphia Southwest and Gloucester effluents mixed with Delaware River water. The fraction dissolved of total recoverable copper was evaluated statistically at pH 6, ambient pH and pH 8. Because there was no copper released at ambient pH of mixing, we conclude that POTWs may be overregulated on the basis of total recoverable metal concentration as required by the National Pollutant Discharge Elimination System (NPDES). This is due to the fact that effluent particulate copper, which is the majority of the total recoverable copper, does not change to dissolved copper at the ambient pH of the river. Receiving water quality is evaluated on the basis of dissolved copper.