Besides the recycled lime, the city also uses fluoride and chlorine as part of the treatment process. Rapid sand filtration is the last step before it is sent to pumps and homes.
The water department has recycled lime softening residuals from the water treatment process since 1957. Before then, residuals were stored in lagoons.
The city invested more than $9 million to expand its lime reclamation facility last year. The city received a $250,000 grant from Ohio EPA’s Recycling and Litter Prevention program that was used to purchase high-volume pumps needed for the expansion. Dayton’s investment (primarily capital improvement funds) is intended to be offset by increased lime sales to external customers and the payback period for the expansion project is expected to be around six-and-a-half years.
Dayton has two water treatment plants that rely on ground water as their source. Lime softens the water and removes minerals that can build up in consumers’ pipes. The lime reclamation facility regenerates the spent lime from the water treatment process in the form of pebbles which are then re-used for water softening at the plant, keeping the spent lime out of landfills. Excess regenerated lime is sold to other water systems. The facility’s carbon dioxide exhaust is used to adjust the pH at the water treatment plants.
Recently, the city began looking for lime residuals from outside sources to supplement the additional capacity of its system. Importing spent lime from other treatment plants will benefit the city while reducing waste. The expansion will also help improve cost efficiency — as the kiln operates closer to capacity, the relative costs for gas used for heating the kiln, labor and maintenance will be lower.
As a part of the expansion, Dayton is constructing several ancillary facilities to receive the lime residuals from off-site sources, process the residuals to feed into the lime kiln, and store the additional finished product.
After the expansion is completed, the city expects to produce about 120 tons per day of lime for re-sale.