- 18 October 2006 -

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Sludge drying: The small footprint alternative

A growing population in Florida , USA is producing increased wastewater flow, making it harder for authorities to dry the digested sludge effectively. Sludge drying beds were not a viable option - but centrifuges proved to be a suitable replacement.

The Florida panhandle in the US is expanding - especially Walton County - which is now the sixth fastest growing county in Florida . Located half way between Pensacola and Panama City , the county borders the Gulf of Mexico, includes large areas of public land and claims much of Choctawhatchee Bay.

Its setting has attracted many new residential and recreational developments and their associated commercial businesses. The state is also faced with population (baby boomers) growth. The permanent population is about 25,000. During the summer, the population can double or even triple.

Due to the growing population, wastewater flow rates have increased by 15% each year in recent years, causing the utility to struggle to keep up with the drying and disposing of its digested sludge.

This provides extra challenges for Regional Utilities of Walton County, operated by Florida Community Services Corp, which constructs, operates, and maintains a water and wastewater utility system and sells services to customers located within the service territory (which encompasses parts of Florida 's Sandestin Resort). This territory runs north to south from the Choctawhatchee Bay to the Gulf of Mexico , and Regional Utilities currently operates three wastewater treatment plants and multiple well sites, including a sub-aqueous water line. Employees operate the water and wastewater facilities, as well as construct and install water and wastewater lines. The utility currently serves approximately 13,000 customers.

In Walton County , Regional Utilities runs the water supply system, sanitary sewer collection system and the three activated sludge wastewater treatment plants that serve the county's southern region - Sandestin, Point Washington, and Seacrest.

Walton County 's continual growth not only places a large burden on Regional Utilities' treatment plants, but especially affects its sludge drying beds. A couple of days of rain on the beds can lead to severe delays. The company, therefore, required a new way to dry its sludge and allow flow rates to continue; and hence allow the county to successfully treat its wastewater.

More drying beds?
It was not possible to add more drying beds, although this option was considered. Regional Utilities looked into this solution but decided against it for a number of reasons; amongst them was the fact that cleaning sand beds can be labour intensive, as they are mostly cleaned by hand. Moreover, rain is a continual problem, especially in the summer - as the company had already experienced.

The most important problem, however, was lack of available land. The amount of land required for more drying beds was simply not cost-effective, in a place where an acre of land can cost US$6 million.

Regional Utilities also considered land-applying the increased amount of sludge generated. However, it discovered that this would involve paying to haul 98% water - which was, again, not a particularly cost-effective solution.

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