The Truth About Activated Carbon and Suspended Solids in Water

A common question in water treatment is whether activated carbon can reduce suspended solids (SS) in water. The short answer is no, not effectively. Activated carbon is not designed for this primary purpose, and understanding why requires a look at its fundamental mechanism versus the nature of suspended solids.

How Activated Carbon Works: Adsorption, Not Filtration

Activated carbon is an exceptionally porous material with a vast internal surface area. Its power lies in adsorption—a process where dissolved pollutant molecules (like chlorine, volatile organic compounds/VOCs, or some bad tastes and odors) are chemically bound to the carbon's surface. It acts like a microscopic sponge for contaminants you can't see.

The Nature of Suspended Solids

Suspended solids are undissolved, discrete physical particles floating in water. They include silt, clay, organic fragments, rust, algae, or other visible cloudiness (turbidity). These particles are typically too large to be captured by the adsorption sites inside activated carbon's pores.

Why Activated Carbon Falls Short for SS Removal

Pore Size Mismatch: The pores in activated carbon are excellent for trapping small dissolved molecules but are generally too small or not structured to trap larger suspended particles. The particles simply cannot enter the primary adsorption sites.

Surface Blockage: When water with high suspended solids passes through activated carbon, these particles can physically clog the surface of the carbon granules or block the entrance to pores. This dramatically reduces the carbon's efficiency for its actual job—adsorbing dissolved chemicals—by preventing contact. It leads to a short filter life and increased pressure drop.

The Correct Tools for Suspended Solids

To effectively remove suspended solids, mechanical filtration methods are used, which physically strain particles based on size:

Sedimentation/Filtration: Allowing particles to settle or using filter media like sand.

Cartridge Filters: Common spun polypropylene or pleated filters that trap particles as small as 1 or 5 microns.

Membrane Filtration: Such as microfiltration (MF) or ultrafiltration (UF), which can remove particles down to fractions of a micron.

Practical Takeaway in Water Treatment

In a typical water treatment sequence, mechanical filtration (to remove SS) always comes before the activated carbon stage. This protects the activated carbon filter from being fouled by particulates, allowing it to function efficiently and last longer for its intended purpose of removing dissolved chemical contaminants.

Therefore, while a layer of activated carbon might catch some very fine particles incidentally, it is neither an efficient nor an economical method for reducing suspended solids. For clearer water free of cloudiness, a proper mechanical filter is the right choice.