Why is it necessary to remove heavy solids before biological treatment?

Removing heavy solids before biological treatment is essential because these solids can significantly disrupt the biological activity necessary for effective wastewater treatment. In biological treatment processes, microorganisms break down organic matter to purify the water. If heavy solids are present, they can settle out and create a layer at the bottom of treatment tanks, which can inhibit water flow and restrict the movement and efficiency of the microorganisms that are essential for breaking down pollutants.

Moreover, heavy solids can physically interfere with the microbial population by blocking their access to food sources or by creating an environment that is unsuitable for their survival and activity. This not only affects the efficiency of the treatment process but can also lead to longer retention times and the potential for incomplete treatment, resulting in pollutants not being adequately removed.

This is why pretreatment processes often include sedimentation or screening stages to ensure heavy solids are removed before the wastewater enters the biological treatment phase.