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:
- Reduce the discharge limits on surcharge customers.
- Increase the WRRF's capacity.
- Develop alternate methods 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 competed, this will manage municipal solids and higher strength wastes from the pipeline. We're planning to begin biodigester implementation in July 2020. Biodigestion will allow us to recycle the available carbon (methane) that the biodigester produces. We can use this to produce energy (electricity) to power and heat WRRF buildings and operations. We expect slight reductions in revenue requirements for the system.
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 estimate revenues of over $4 million annually when fully functional. We expect this system to be functioning soon after the biodigestion system comes online.
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.