Challenge

A Midwest steel mill had been using well water containing iron and manganese for their plant cooling and drinking water system.  Without removal of the contaminants significant fouling in the cooling and piping systems occurred.  In addition, the water had an objectionable appearance, taste, and odor when used for drinking water.  The well supply had an iron concentration range from 7-10 milligrams/liter (mg/l) and manganese concentration was approximately 2 mg/l.  Both are significantly higher than Secondary Maximum Containment Levels (SMCL) for drinking water standards.  In an effort to reduce plant maintenance and improve the drinking water quality, the mill decided to install a treatment system to remove the iron and manganese.   

Solution

In late 2002, the mill placed into operation a new two million gallon per day (MGD) well water treatment system provided by Siemens.  Siemens proposed a process consisting of aeration, detention, flocculation, sedimentation, and filtration to meet the performance requirements. 

Water from the wells is pumped to an aluminum induced draft aerator which is used to add dissolved oxygen to oxidize dissolved iron.  Using the aerator to oxidize iron minimize operating cost as it reduces required chemical oxidants.  An added benefit of the aerator is the removal of undesirable gasses from the water supply.  Water flows from the aerator to a detention tank, which provides residence time to allow the oxidation reaction to reach completion and floc formation to begin.  Water flows from the detention tank into a two train Aquarius® packaged clarification and filtration system.  The Aquarius system includes two stages of flocculation, sedimentation with tube settlers, and dual media filtration in a single tank package.   

Filtered water is stored in a below grade clearwell and pumped to the plant distribution system.  Backwash waste from the filter and sedimentation compartments is pumped to a holding pond which overflows to an outfall.  Each unit backwashes once per day; yielding a 98.5% net water production for the plant.

Results

The plant now easily meets drinking and process water requirements, with non-detectable iron concentration and manganese concentration at 0.025 mg/l.  In addition to producing drinking water the removal of the iron and manganese has kept the cooling system from fouling, greatly reducing maintenance and energy costs.

The water treatment system at the steel mill is efficiently treating high levels of iron and manganese to near non-detectable levels using a system that requires little operator attention, has low associated operating costs, and minimal downtime.