Sludge Drying:
Definition & Overview
What is sludge drying?
Sludge drying is a second-stage sludge dewatering process that further removes moisture from sludge cake produced by mechanical dewatering equipment.
In wastewater treatment, sludge drying reduces the weight and volume of the final waste product for easier, safer, and more cost-effective storage, transportation, and disposal.
What is the sludge drying process?
The sludge drying process comes after mechanical sludge dewatering and works as follows:
Sludge cake is transported from the exit of the first-stage mechanical dewatering equipment and fed into the sludge dryer
The sludge dryer spreads the cake evenly on its drying surface to ensure effective drying
The sludge dryer uses either heat to evaporate water or electro-osmosis to dehydrate the sludge cake further to a drier, smaller cake
The dried sludge cake is then either disposed of in landfills or used in applications like fertilizer and biochar
What are some common sludge drying methods and sludge dryer machines?
Common sludge drying methods are broken down into two categories:
Thermal drying: evaporation by heat
Non-thermal drying: dewatering by electro-osmosis
The thermal drying method can be subdivided into two categories:
Convection: heat transfer by direct contact between sludge cake and hot gas
Conduction: heat transfer by contact between sludge cake and hot surfaces
Below is a table that depicts sludge drying methods, sludge dryer machines, and their manufacturers:
| Sludge Drying Method | Drying Subcategory | Sludge Dryer Machine | Manufacturer |
|---|---|---|---|
| Non-thermal | Electro-osmosis | ELODE EODS-3000 3m | Elode USA |
| Thermal | Convection | Belt Dryer BT | Huber Technology |
| Thermal | Conduction | K-S Paddle Dryer | Komline-Sanderson |
Each sludge drying method has its pros & cons.
Learn more about how thermal dryers compare to non-thermal dryers like ELODE.
What is a sludge drying system?
A sludge drying system further dries dewatered sludge cake and consists of a sludge dryer and various additional equipment.
Additional equipment for thermal and non-thermal sludge dryers include:
Conveyors to transport sludge cake
Hoppers to store sludge cake
However, thermal dryers create byproducts like heat, steam, odors, dust, and gases.
As a result, thermal drying systems often require many more custom-fabricated moving parts, connections, and equipment like:
Exhaust stacks
Hot heat exchangers
Cyclone dust separators & respective cleaning/emptying
Odor treatment / scrubbers
Blower motors + assembly
Duct work
Pellet cooler at dryer exit
Steam condensers & respective huge water supply
Boilers and furnaces
Compressors
Dust filters, fins to clean
Fume/dust scrubber
Demister
Extra drain, piping, or electrical work
This additional equipment dramatically increase a thermal drying system’s costs, footprint & space requirements, installation & building costs, energy usage, downtime & maintenance, and time to ROI.
Learn more about how thermal dryers compare to non-thermal dryers like ELODE.
What is the cost of a sludge drying system?
A thermal sludge drying system’s equipment and installation will cost a typical US wastewater treatment plant $5-6 million.
A non-thermal sludge drying system like ELODE will cost $1-2 million.
Dry sludge with electro-osmosis
Our ELODE non-thermal sludge dryer further dewaters sludge cakes produced by mechanical sludge dewatering equipment. Compared to thermal dryers, ELODE is more cost-effective, energy-efficient, and has a small footprint.
Save on operating costs by reducing your sludge cake by 50% or more in just 3 minutes with ELODE.