The Munising Wastewater Treatment Plant in Munising, Mich., sits on the shores of rugged and picturesque Lake Superior in the state’s Upper Peninsula. When the city needed to replace an aging system, they chose the Tri-Oval oxidation ditch system for its overall costs savings, process control and operational flexibility.
Until February of this year, the city was using two conventional activated sludge package plants consisting of a circular clarifier surrounded by an outer ring containing an aerobic digestor section, a section for aerobic treatment and a chlorine contact chamber section. The plant needed to expand to meet increasing flows and loads. Also, the package plant equipment was experiencing high levels of corrosion in the steel tank and piping and had to be replaced. The new plant would need to stand up to the rigors of tough winters on the shores of Lake Superior, be operator friendly, produce a high-quality effluent and meet an installed cost within the city’s budget.
The city’s engineer, Mead & Hunt, selected an oxidation ditch as the activated sludge process that would satisfy all of these requirements. The 0.9-million-gal-per-day design flow of the plant is split evenly between two ditches operating in parallel. To keep costs low, the city’s engineer competitively bid the oxidation ditch to two major wastewater treatment system manufacturers using the same overall ditch footprint but offering radically different technologies for process control and operation in the oxidation ditches as dictated by the type of aeration and mixing equipment offered by each company.