The Sheboygan Regional Wastewater Treatment Facility (WWTF) has served the City of Sheboygan, City of Sheboygan Falls, Village of Kohler, Town of Lima, Town of Sheboygan, Town of Sheboygan Falls, and Town of Wilson since 1980. Wastewater discharged through the sanitary sewers of these communities is treated, recovering the nutrients, and producing a natural, exceptional quality soil fertilizer. Sheboygan produces this product via a Huber Medium Temperature Belt Dryer that was installed in 2014 at a cost of $7,916,417.
The bio-solids dryer was selected as a remedy to the bio-solids storage shortage. The Sheboygan Regional WWTF did not meet 180 day bio-solids storage requirement and was under a 4-year Compliance Schedule. The sludge that is produced as a byproduct of the wastewater treatment processes is anaerobically digested, dewatered, and then dried to a moisture content of less than 10%. The dryer will utilize biogas produced in the anaerobic digestion process and the waste heat from the plant’s micro-turbines to heat the dryer to approximately 204 degrees Fahrenheit. The final product is a pellet sized dry product that is a high quality fertilizer that is safe to use on lawns, shrubs, trees, flowers, vegetables, and as a general soil treatment.
Sheboygan’s dryer is designed to dry approximately half of the bio-solids produced by the facility’s treatment process. By drying half of the liquid bio-solids produced, the Sheboygan Regional WWTF was able to diversify the bio-solids disposal and reuse options, while minimizing capital and construction cost. The liquid bio-solids are land applied via injection into agricultural fields as a natural and beneficial fertilizer. Land application of the liquid bio-solids is limited by season, weather conditions, and field availability. The dried bio-solids are an Exceptional Quality, Class A product that can be used in residential and agricultural applications, as well as, landfilled if necessary.
There are only two Huber Medium Temperature Belt dryers installed in the United States; the first installation is in North Carolina, the second installation is at the Sheboygan Regional WWTF. There are only two bio-solids dryers installed and operating in Wisconsin: one at the Milwaukee Metropolitan Sanitary District (MMSD) and one at the Sheboygan Regional WWTF. The MMSD dryer is a higher temperature, drum dryer, that was initially installed in 1926. This dryer allows the MMSD to sell a similar product known as Milorganite.
The Huber belt dryer allows the City to enter a contract with Sure Gro, LLC to haul and beneficially reuse the dried bio-solids. They will pay the City $10/dry ton of bio-solids. This allows the city to reduce the expense of applying fertilizer to farm fields by drying the sludge and selling it to a third party. This new process and the sale of bio-solids will save the Sheboygan Regional WWTF an estimated $135,200 per year in operating cost and meet the bio-solids compliance schedule.
The Sheboygan Regional WWTF, through a series of incremental improvements, regularly achieves Net Zero Energy status: going off the grid and selling renewable electricity to the electric utility. On an annual basis, the WWTF produces more than 85% of its required electrical energy and 90% of its required heat energy.
The relatively low user rates enjoyed by the Sheboygan ratepayers are largely attributed to sound day-to-day management practices, revenues generated from the high strength waste program, and low energy costs. The combined bottom-line benefit is roughly $1 million annually.