In wastewater treatment there are typically two types of contaminants that require removal – Dissolved Solids and Suspended Solids – and both can cause issues in water treatment systems.
Everyone has experienced dissolved solids in the kitchen when adding salt or sugar to cooking. Similarly in wastewater, dissolved solids are dissociated into the water, existing in a homogeneous molecular state alongside the water molecules.
While you cannot see dissolved solid particles, they often cause the water to be tinted an off-colour when held to light.
Dissolved solids (jar on the right) cause the wastewater to be an off-colour. Image: Wikimedia Commons
Treating dissolved solids can be quite challenging because these particles are in the same liquid phase as the water. Some common treatment methods for dissolved solids include using chemical reactions, molecular sieves (eg. reverse osmosis), or evaporation techniques.
Many materials are also highly insoluble in water, and these remain as larger particles called suspended solids. Typical suspended solids in wastewater are dirt or sand particles, biology, chemical precipitations or industrial solids entrapped in the water.
A clarifier removes suspended solids from wastewater on a very large scale. Image: Wikimedia Commons
Suspended solids can cause a range of issues in wastewater treatment systems if left