By Bill Wiegand, PE, and Jeff Ashley, PE

Pre-sedimentation (pre-sed) is an effective water treatment method, often utilized with source waters with high solids, turbidity, and/or organics during certain times of the year, such as spring runoff. The pre-sed process helps reduce these materials from the raw water to more acceptable levels. As a result, other primary treatment processes, such as high-rate settling and filtration, are greatly improved and optimized. Pre-sed systems can be built to site-specific needs to address unique raw water quality in lakes, rivers, and streams.

The pre-sed process can involve fairly simple methods, such as settling ponds where hydraulic retention time is the primary variable used to settle large solids, to more sophisticated processes that can reduce larger amounts of turbidity and organics for volatile source waters. Whatever solution you and your design engineering team decide to use, the end goal is always the same: reduce source water solids, turbidity, and/or organics as economically and sustainably as possible before the water is introduced to the main treatment plant processes.

A well-designed pre-sed process solution typically results in the following three benefits: