Many older existing wastewater filters in the United States include multi-media beds consistent with current drinking water designs. While multi-media provides acceptable suspended solids reduction they have reduced filter run times when compared to larger mono-media filter designs. Increasing filter run time decreases frequency of backwash resulting in lower power consumption and required operator attendance while increasing effective plant capacity.

This case study examines operating results from wastewater filter locations before and after rehabilitation from multi-media to mono-media. The unique application allows a direct full-scale comparison of pre- and post-rehabilitation operating data. In addition to changing the media design, simultaneous air and water backwash was incorporated to maintain the media operating condition. A comparison of backwash waste produced and Total Suspended Solids (TSS) reduction is made.

Increased filter performance is identified as reduction in backwash waste volume and maintained or increased TSS removal. The decrease in filter backwash waste is attributed to an increase in solids capacity of the larger media. Extending the backwash interval has allowed the plants to reduce power costs by subsequently reducing the operating time and expense of backwash pumps. A decreased frequency of backwash events has also reduced the required operator attendance for filter operation. Equally important is the reduction in backwash recycle to the head of the treatment plant and overall capacity of the plant.

The potential for this modification is wide spread as the owners of older wastewater filters contemplate modifications and upgrades to their current systems. On-site pilot testing can easily be accomplished to select the optimum media for a given plant using the existing filters as a baseline.