History

The original Mandan Wastewater Treatment System, constructed in 1967, consisted of two Aerated Stabilization Ponds each having a capacity of 16 million gallons. This system faithfully served the city for approximately 10 years.

The Clean Water Act of 1972 prompted improvements to meet specific discharge requirements. Other factors were a 40 percent population growth during the 1970s and the addition of several industries. Mandan’s existing plant was simply overwhelmed by the increased organic and hydraulic loadings. In 1977, the City added a third cell, increasing the volume by some 48 million gallons. To enhance algae removal (hence Total Suspended Solids reduction), three mixed media filters also were added in parallel with cell three. Finally, to enhance Biochemical Oxygen Demand (BOD₅) removal, 70 static tube aerators (helixors) were installed in cells one and two and 36 in cell three.

As years passed, the efficiency of the system became compromised. In early 1988, the dissolved oxygen (DO) in cell one was reduced to zero and noticeable odors occurred. The wastewater treatment plant was organically overloaded. In 1991, Mandan decided to remove sludge from all three cells and install 14 surface aeration chains. The filter media was replaced and multi-level draw-off points were installed in cell three. These multi-level draw-off points allowed for the removal of wastewater effluent from below the micro-algae layer.

Engineers were hired in 1994 to do a study of the City's immediate and future wastewater needs. Growth within the city couldn't continue without flexibility to handle any additional organic loading. The idea was to improve treatment so that all discharge requirements could be met. After reviewing nine different treatment options, the city decided to construct an Extended Aeration Activated Sludge Treatment System (EAASTS) with ultra-violet light for disinfection, designed by Parkson Corporation.