Wastewater Treatment

A Complex Recycling Process

The City of Vassar's Wastewater Treatment Plant has been in existence since 1939, when the first plant - then located on Wyman Street at the foot of Ashman Street - treated up to 2 million gallons per day in a combined storm and sanitary sewer system.

Over the years, this system has been reconfigured and enhanced. Today, Vassar's Wastewater Treatment Plant is capable of treating up to 18 million gallons of wastewater a day, though on average, the plant treats 5 to 7 million gallons each day.

How the System Works

Wastewater from throughout the city travels through underground pipeline by way of both gravity and pressure. The pressure method involves pump stations, which convey water through force mains to the Wastewater Treatment Plant.

Once at the plant, the sewage undergoes a complex treatment process designed to filter out debris and clean the water according to State regulations before it is discharged to the Cass River.

Screen For Debris

The City's treatment facility is comprised of one building and a myriad of tanks and ponds that are used to screen out debris and settle out sludge and grit - such as coffee grinds - from the wastewater. This debris is dewatered and collected in holding containers and periodically hauled to the landfill for burial.


After the debris has been removed and the water flow has been measured, the water continues through a recycling process that involves chemical and biological treatments. During the biological treatment phase, microorganisms are used to break down organic materials in the wastewater, which further cleans the water.

The City of Vassar's treatment plant has two separate biological treatment systems, which is unique in Michigan. Most facilities usually have only one system. Sludge that settles out during and after these treatment phases is pumped to a digester system, which stabilizes the sludge. The resulting product is called biosolids, which are returned to the earth as nutrient-rich farmland fertilizer. Any bacteria that remain after the biological treatment phases are killed by chlorine gas that is injected into the water in the next phase of the treatment process.
In the last treatment phase, water is dechlorinated using sodium bisulfite. The final product is then discharged to the Cass River.

Process Monitoring

Along every step of the way, trained wastewater operators monitor the equipment that controls the treatment processes and perform tests on the water in compliance with State law. The wastewater plant staff also work to ensure that the system is working properly, efficiently and effectively.

The result of the above processes and the hard work of highly trained professionals at the treatment plant is effluent that is returned to nature without harm to humans, wildlife, lakes and other waters of Michigan.