• Minimize hauling and disposal costs
• Improve system performance and uptime
• Enhance regulatory compliance
• Reduce environmental impact

Equipment Options for Sludge Dewatering

As you know, sludge dewatering separates sludge into solid and liquid forms to minimize waste and help meet regulatory compliance requirements. Some of the most common types of equipment used for dewatering are plate and frame press, belt press, centrifuge and of course pumps for sludge transfer. We will examine some of the advantages and disadvantages for some of the most common technologies. 

Plate and Frame Filter Presses

A plate and frame filter press consists of plates that form chambersand a frame. Sludge is injected into the press with a high-pressure pump (typically an AOD), filling the chambers. The solids are retained in the cavity and water is squeezed out through the cloth and the integrated piping formed by the compressed plates. Once the press cycle is complete the plates are separated, and the dry cake falls into a dumpster or similar collection device.  

A Plate and Frame Filter in Action

Advantages

• Simple to operate
• Application of pressure forms high solids cake
• Produces a dryer cake with as much as 30% dryness
• Works well on sludge that is hard to de-water
• Many cloth media choices

Disadvantages

• Cycle times can be long
• Batch process
• Labor intensive
• Cloth replacement can be difficult
• May require additional chemicals for optimum performance  

Belt Filter Presses

There are many different designs but in general a “Belt Filter” relies on a series of rollers and belts to separate liquid from solids. In most cases the sludge is pumped onto the belt evenly through a manifold.  The addition of a flocculant upstream allows the water to flow by gravity through the belt and is discharged into a pan  Rollers then squeeze the sludge between two belts at the nip point to extract the remaining water. Dewatered solids fall off the belt and are transferred by a conveyor or auger to a collection device and the filtrate is discharged or recycled.   

Advantages

• Automatic process
• Requires moderate polymer dosage rates
• Quiet operation
• Easy to control and see the effects of polymer
• Simple to use and relatively easy to maintain  

Disadvantages

• The press belts require continuous washing (usually by recycled effluent water)
• Lower % cake solids
• Performance is driven by feed stock which can vary
• Does not work well with sludge that has a high FOG content 

Centrifuge

A centrifuge separates solids and liquids by spinning them in a rotating drum. Solid material is pushed outward and separated from the liquid. The water is discharged into a pan and solids are transferred to a truck or container using an auger or conveyor. 

A Centrifuge in Action

Advantages

• Works well with sludge that has a high FOG content
• Can handle large capacities
• Does not require belt washing
• Under the right circumstances can achieve higher cake solids than a belt press with a high polymer dosage rate 

Disadvantages

• Powered by large motors, so it requires more energy
• Requires higher polymer dosage
• Higher noise level
• Expensive to maintain 

Pumps

Pumps are required for sludge transfer. Two of the most common types of pumps used are air operated diaphragm (AOD) and progressive cavity. 

AOD

• Inexpensive
• Has a simple design that operates using compressed air
• Great for moving large quantities quickly
• Easy to control speed 

Progressive Cavity

• Expensive
• Great for transferring very heavy solids
• Harder to repair and maintain 

Chemical Treatment Options for Sludge Dewatering

There are several options to help treat sludge prior to the dewatering process. It is important to use the right type, amount and combination of each of these products to ensure that you get the best results. There is no one size fits all solution. Watertech has experience working with many kinds of sludge dewatering technologies and can help recommend a treatment program that will work best for you. 

Coagulants

Coagulants can enhance drainage, remove unwanted contaminants and eliminate odors when used on a dewatering device. They are typically dosed in combination with flocculants to enhance the sludge dewatering process. Coagulants are available as organic, inorganic or blended compounds. 

Flocculants (Polymers)

In every case, flocculant selection is a critical factor in the performance of the dewatering equipment. Polymer type, make-down, aging time and injection point selection can also dramatically impact performance. 

Diatomaceous Earth (D.E.) – Pre-coating

D.E. is a natural occurring mineral that is often used to pre-coat filter media. For those of you who are interested, D.E. is made from diatoms, ancient fossilized algae. They have a honeycomb-like structure made of silica that helps to improve filtering capacity by providing a porous framework to collect suspended solids and build cake. It is an easy and cost-effective way to enhance the performance of a dewatering device like a plate and frame press.  

Diatomaceous Earth (D.E.) – Body Feeding

D.E. can also be added directly into the sludge. The small diatoms create a very complex, porous matrix that works well to collect small particles, allowing a much shorter filtration cycle.

Get Expert Help for Sludge Management

At Watertech, we take a holistic approach to wastewater treatment — combining equipment, chemicals, and service to deliver reliable results. We understand that each facility is unique, and our experienced engineers work with you on-site to identify the best solutions for your process, compliance, and cost-saving goals.

If your sludge is giving you trouble, let’s talk. Request a site survey to assess your system and explore treatment strategies tailored to your needs.