Overview

Exeter Township (Exeter) wanted to minimize the costs and environmental impacts associated with their sludge disposal and provide a long-term sludge management plan for themselves and surrounding municipalities.

We began with a feasibility study to determine the viability of Exeter establishing a regional sludge dewatering and drying facility at its wastewater treatment plant (WWTP). The study concluded that the use of a sludge dryer would achieve a Class-A biosolids, which can be used as alternative fuel or fertilizer, product through heat dehydration. This would afford Exeter several more disposal options than what were currently available. Additional capacity, in the system, would also allow Exeter to offer the surrounding municipalities the ability to dispose of their sludge at Exeter, creating a revenue stream for Exeter.

After the study, we provided full design and of the recommended WWTP improvements and installation of the biosolids dryer, turning Exeter into a regional sludge dewatering and drying facility.

Solution Details

Together with Exeter, we pilot tested several sludge dryers prior to the design to determine the most appropriate manufacturer that would be capable of meeting the operational requirements; specifically, blending a wide variety of sludges to accommodate the regional facility approach. Once the sludge dryer manufacturer was determined, full design commenced and included the two new centrifuge units to replace the existing belt filter presses, new sludge transfer pumps, complete drying system, and associated conveyors for discharging the dried biosolids.

The heart of the solids handling process is the biosolids dryer itself. The dryer is capable of drying approximately 72 wet tons of sludge per day. The drying chamber is seven feet in diameter and 20 feet long. The unit, when operating, weighs nearly 80 tons. The basic process of the dryer uses hot thermal oil circulated around the outside of the drying chamber, which heats the moisture in the sludge until it evaporates, thereby removing the liquid from the solids. The evaporated liquid is captured through a condenser and returned to the wastewater treatment process through the plant drain system. Once the desired dryness of the solids is achieved, the drying process is complete. This takes approximately three hours once the dryer is loaded. The final product is greater than 92% solids and meets the requirements of a Class-A biosolids product, in accordance with federal and state regulations.

In addition to the dryer, the existing belt filter press units were replaced with two new centrifuge units. Previously, the WWTP would dispose of sludge cake from the belt filter presses at approximately 17 solids%. The new centrifuge units produce dewatered cake at approximately 24% solids. After sludge cake drying, the WWTP disposes dried biosolids at approximately 95% solids. The significant improvement translates into a recognizable reduction in both landfill mass and disposal expense, and provides a by-product that can be recycled as a fertilizer or an alternative fuel.

The success of this project has invited the interest of other municipalities in the surrounding area. Exeter has positioned itself as the regional dewatering/dryer facility, benefitting other treatment plants by offering a cost-effective method for sludge disposal.