Biodigestion Program

Our Sanitary Service Area is growing. The Water Resource Recovery Facility (WRRF) is taking proactive steps to address increasing loads. The WRRF had three primary options to address these increases:

  1. Place greater regulations on surcharge customers
  2. Increase the capacity at WRRF through plant expansion
  3. Increase the capacity at WRRF by developing an alternative method to provide treatment services

The City moved forward with developing the following solutions:

WRFF local pipeline

We constructed a 2-mile-long, 10-inch waste transmission pipeline under Market Avenue SW. The pipeline allows surcharge customers to discharge concentrated waste. The waste flows into the WRRF at 1300 Market Ave. Currently, we hold waste from this pipeline until off peak hours. We then load balance the flow of the concentrated waste. This levels out current pollutant loading flow patterns at the WRRF.


We began construction of a biodigestion system in late 2017. When completed, this will manage municipal solids and higher strength wastes from the pipeline. We're planning to begin biodigester implementation in the summer of 2021. Biodigestion will allow us to recycle the available carbon (methane) that the biodigester produces and reduce the amount of solids we send to landfill.

Renewable Natural Gas (RNG) Conditioning System

RNG, or biomethane, is a high-quality gas that is interchangeable with natural gas. RNG can be used as vehicle fuel. Biogas that is produced during biodigestion can be refined to produce a higher quality product. The result is RNG. The sale of RNG produced by the biodigestion process will result in revenue. We expect this system to be functioning soon after the biodigestion system comes online.

Phosphorous Recovery

The City must recover phosphorous from the biodigestion process. This is essential to prevent the build up of struvite in the biodigestion system. Struvite is made up of magnesium, ammonium, and phosphate. Removing phosphorous from the system will prevent the build up of struvite. If struvite is allowed to grow, it will clog up the pipes at WRRF. Therefore we must have a phosphorous recovery system in place. 

Video Example

You can view a short video from Michigan State University. The City’s biodigester will not have manure going to it.

Odor Prevention

No, appropriate odor control is designed into the system. A properly designed system will not produce odors. Carbon filters and a biofilter are included as part of the design.

Biodigester Cost

The biodigesters are expected to be about 85 million dollars.

When calculating the cost, these are some of the factors we considered:

  • Adjusted timing of the revenue from the sale of RNG
  • Reductions from the value engineering
  • Operations & maintenance
  • Capital reprioritization

Municipal Bonds

It will be funded by issuing Municipal Bonds in 2018. The bonds will be repaid by the users of the sewer system.