Sludge treatment and dewatering

In mechanical and biological wastewater treatment, organic pollutants are removed either through solid-liquid separation or by microorganisms within activated sludge. This process generates excess sludge that must be removed on a regular basis.

Since biological excess sludge consists of approximately 99% water, it is dewatered prior to disposal. This significantly reduces both its volume and weight. Depending on its composition, the separated water can be returned to the wastewater treatment plant.

Flocculants are often added to the sludge to improve dewatering efficiency. Depending on the specific process, intermediate storage in a sludge tank may be required.

Common methods for sludge dewatering include:

 

Belt filter press:

In this process, the sludge is passed between two filter belts through a series of rollers, where it is continuously dewatered.

Advantages:

• Continuous operation without the strict necessity for a sludge buffer tank,
• Suitable for large volumes of sludge,
• Achieves a high dry-solids content in the filter cake.

 

Screw press:

A screw press dewaters sludge using a rotating screw. Through gradual compaction, water is pressed out of the sludge.

Advantages:

• Compact design and small footprint
• Continuous operation
• High dry-solids content achievable in the filter cake
• Sufficient for many industrial applications

 

Chamber Filter Press:

In a chamber filter press, sludge is pumped under high pressure into enclosed filter chambers located between a series of filter plates. Water passes through the filter cloths, while the dewatered sludge remains as a filter cake.

Advantages:

• High dewatering efficiency
• Relatively low requirement for flocculants, depending on sludge characteristics
• Very high dry-solids content achievable in the filter cake, depending on the type of sludge and operating conditions

Note: The chamber filter press operates discontinuously (in batches). Therefore, appropriate intermediate sludge storage and a suitable design for the feed system are required.

 

Wastewater Recycling and Water Reuse

In light of climate change and increasing water scarcity, the reuse of treated wastewater is becoming increasingly important. In the industrial sector, in particular, wastewater recycling offers significant potential for reducing fresh-water consumption, lowering costs, and conserving natural resources.