How is the sludge filter press used?

Water Content in Municipal Sludge and the Role of Filter Press in Dehydration

The water content in municipal sludge is categorized into free water, capillary water, surface adhesion water, and internal water. Free water, which is unaffected by particles, accounts for about 70% of the total water content and is the primary target for mechanical dehydration in sludge. Capillary water, which exists in the capillaries between sludge particles, accounts for about 20% and is another crucial dehydration target for filter press machinery.

Surface adhesion water is water adhering to the surface of particles or cells, while internal water is present inside the sludge particles (including water inside cells). Traditional dehydration equipment can typically reduce the water content of sludge to around 80%. At this stage, the sludge remains in a fluid-plastic state, with very poor mechanical properties and a compressive strength of less than 20kPa.

When the moisture content of sludge is between 60% and 65%, it is in a viscous state, and the water molecules are enveloped by a colloid layer. This area is called the "viscosity phase area" of sludge, which is the most challenging stage for sludge dehydration. Sludge with a moisture content below 60% is solid, does not produce leachate, and can be directly sent to landfill. Overcoming the "viscosity phase area" helps make the sludge more dispersible, enabling better handling for harmless disposal and resource utilization. Su Dong advocates using filter press to achieve this goal.

Furthermore, when the sludge moisture content drops to 60%, if composting is halted, the fermentation cycle can be reduced by half, increasing economic benefits. The dry mud cake can also be used to create solid fuel, which can be burned after distribution to recover energy, or used as an auxiliary material in brick and cement manufacturing. This reduces sludge production by over 50%, improves sludge reduction, and decreases transportation difficulty, thereby saving transportation costs.