BP Whiting refinery running at 75 pct capacity -sources

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HOUSTON, Aug 10 (Reuters) - BP Plc's Whiting, Indiana refinery was operating at about 75 percent of its 413,500 barrel per day (bpd) capacity on Wednesday due to reduced production at the refinery's wastewater treatment plant, sources familiar with plant operations said.

A BP spokesman declined on Wednesday to discuss operations at the refinery.

BP is carefully restoring the wastewater treatment plant's production in order to avoid a malfunction like one last week, which led to greater than permitted releases of sediments into Lake Michigan, the sources said.

"Water flow dictates production flow," one of the sources said.

The wastewater plant utilizes microbes to consume hydrocarbons before the wastewater is discharged into Lake Michigan. Those microbes grew out of control over the weekend of July 30-31, overwhelming the plant's system for controlling the solids like the sediment, the sources said.

The careful increase in wastewater plant production is to make sure the microbes grow in a controlled manner, the sources said.

During the same weekend at the end of July, a 60,000 bpd reformer, called Ultraformer 4, and a blending oil unit were shut due to a malfunction. The reformer and blending oil unit restarted last week.

(Reporting by Erwin Seba; Editing by Phil Berlowitz)