Firefighters responded to the facility located on Grand Haven's east side shortly before 6 p.m. when flames started to light up the sky over a sludge storage building.
Police evacuated nearby businesses as a precaution and kept pedestrians out of the area, Grand Haven Public Safety Director Jeff Hawke said. Beechtree Street between Franklin and Columbus avenues was closed to traffic.
The initial call for firefighters was made at 5:44 p.m.
Wastewater treatment plant Director John Stuparits said the rectangular building was about half full of sludge.
"It stores our bio solids," he said.
He said there was probably a half million gallons of sludge in the tank.
The open area above the sludge was full of methane gas, and somehow the gas ignited, with the flames shooting through the vent.
The cause of the fire has yet to be determined, said Lt. Joe Boyle of the GHDPS. But “preliminary reports indicate a possible electrical failure in the rooftop ventilation louvers caused methane gas inside the plant to ignite.”Stuparits said the building was made of cement block and there was really no where for the fire to go.
Firefighters remained on the scene after the fire was out, dousing the roof and vent with water to cool it down.
Assisting city firefighters at the scene were Grand Haven Township firefighters and the Ottawa County Hazardous Materials Team.
Officials cleared the scene at 8 p.m.