Municipal Treatment of Industrial Wastewater

CHALLENGE

In 1988, Marshalltown Water Pollution Control Plant was faced with a problem of increased ammonia loads in the wastewater discharge from a large industrial contributor and more restrictive ammonia discharge limits from IDNR to protect the Iowa River. Construction space was limited and high groundwater made deep construction very expensive. The goal was to address the complex waste needs at the lowest possible cost and at the same time minimize operating costs.

Clarifiers next to aeration basins

Sludge storage

SOLUTION

Transport the pretreated industrial waste to the plant and treat it in a separate sequencing batch reactor (SBR) activated sludge plant. The industrial waste was treated more effectively and economically in a separate plant rather than combining it with the city domestic waste. Other portions of the project included an ultraviolet light disinfection system to meet stream standards. Aluminum dome final clarifier covers were placed on the existing plant units to achieve ammonia reduction and improve settling. A two million gallon bolted steel digested sludge holding tank and pumping station were added to provide storage and sludge transfer flexibility for twice per year land application to meet sludge regulations.

A groundwater dewatering system was installed for the final clarifiers and SBR tank installation because of the sand layer connection with the Iowa River and high groundwater conditions. The system has been maintained for tank maintenance and the discharge water has been connected to the plant non-potable water system. Recently, an additional well was placed to provide draw-down of groundwater at the plant administration building.

UV Disinfection

UV Disinfection

OUTCOME

On completion, this unique and innovative project produced a high quality effluent on a continuous basis and enabled the City to meet or exceed all discharge requirements for protection of public health and the environment as originally conceived.

Final effluent

RECOGNITION

ACEC of Iowa Engineering Excellence: The SBR received the Grand Conceptor Award (highest honor in the large projects division) in this competition.