Problem: Inadequate capacity to handle biosolids from an increase in the local population.
Solution: Enhanced dewatering and cake pumping to minimize the amount of solids to be handled.
Facing a swift population increase, the Region of Peel in Ontario in 1999 began planning a $375 million expansion to upgrade its two wastewater treatment plants — the smaller Clarkson Wastewater Treatment Facility and the main G.E. Booth Lakeview Wastewater Treatment Facility (GEB).
Part of the master plan dictated how the expansions would handle solids disposal. The Region of Peel processes its biosolids by dewatering the material and then sending it to fluidized-bed incinerators, according to William Fernandes, the region’s manager of capital works and operations for the wastewater division. After reviewing many process combinations, the region’s planner determined that the most cost-effective processing method was to continue centralizing incineration at GEB and add dewatering at the Clarkson facility.
However, juggling the swiftly growing capacity with construction projects required some interim planning to manage capacity.
“We chose to build a structure to temporarily house an additional pair of dewatering centrifuges and cake pumps to supplement the dewatering operation while the [GEB] plant expansion was under way,” Fernandes said.
The region issued a request for proposals for the centrifuges and cake pumps to move the material to the incinerators. For the temporary structure, they chose a pair of KSP-65VHDL high-pressure cake pumps from Schwing Bioset (Somerset, Wis.). Fernandes called the pumps “low maintenance, reliable, and easy to operate.”
This temporary dewatering facility operated from 2000 to 2006. In 2006 when GEB’s permanent dewatering facility was completed, the pumps and centrifuges were moved into the general processing area, and the temporary dewatering structure was converted for use as a chlorination–dechlorination building. Other portion’s of GEB’s upgrade and expansion continue today.
Better Satellite Dewatering
With the immediate solids needs under control, the region returned its attention to optimizing solids hauling from the Clarkson facility. Before its upgrade, Clarkson sent 35 truckloads per day to GEB to be dewatered and incinerated, Fernandes said. The material Clarkson sent was only 3% solids. The expansion plan called for increasing the solids percentage of the material from 3% to 26%.
To do this, the biosolids handling section of the Clarkson facility underwent an overhaul, including installation of three rotary-drum thickeners, a pair of dewatering centrifuges, a dewatered-solids conveyor system, and another pair of KSP-65VHDL high-pressure cake pumps. A solids storage silo, truck loading facility, polymer makeup systems, odor-control scrubbers, and chemical tanks also were added.
At Clarkson, “dewatered solids are routed to the storage silo,” Fernandes said. “The driver pulls into the bay, positions his truck under the loading chute, exits the vehicle, and walks over to the control room to do the actual loading operation himself.”
Once the truck is loaded, the driver can immediately set off to deliver the solids to GEB for incineration.
With the Clarkson expansion complete, only three trucks per day are needed to carry solids to the incinerators at GEB, Fernandes said. This results in reduced transportation costs, benefits to the environment, and less traffic in the area.
Efficient Solids Receiving
To enable efficient receiving of Clarkson’s solids at GEB, the infrastructure for accepting that material also had to be altered. No longer a liquid, the inbound material could not be unloaded into a channel and routed for dewatering as it had in the past. An unloading station was needed to accept the dewatered cake.
After issuing a request for proposals, the region again turned to Schwing Bioset, which supplied a package consisting of a truck-receiving station, two 90-m3 receiving silos, three 60-m3 dewatering silos — all with a sliding-floor discharge design — and six additional KSP-65VHDL cake pumps to move material from each silo to the incinerator or between silos, Fernandes said.
The sliding-floor feature consists of a hydraulic cylinder, which actuates an elliptical frame across the silo floor, moving material toward a screw-type feeder. Material exits the silo to a cake pump, which moves the cake to the incinerator. The entire receiving-silo process is enclosed to minimize the risk of odors.
The decision to add another fluid-bed incinerator at GEB — bringing the total to four — means that, when fully operational, GEB will have the installed capacity to burn 440 Mg/d of dry wastewater solids. When the GEB facility’s construction is completed, its capacity will be increased by 30%, from 336 to 516 million L/d. That’s enough additional capacity to see the Region of Peel into 2031.
At press time, the Clarkson expansion has been completed, and the GEB expansion and upgrade continues, with completion slated for 2011.
© 2010 Water Environment Federation. All rights reserved.