Baffles: the Unsung Hero in Additional Plant Capacity and Biogas Production

Presentation Description: In 2017, Dublin San Ramon Services District (DSRSD) initiated an optimization study as part of the design project to investigate the potential of optimizing their existing primary sedimentation tanks (PSTs). The field studies coupled with computational fluid dynamic (CFD) modeling indicated that optimizing existing tanks (four in total) and adding additional PST will meet and/or exceed DSRSD’s goals of enhancing solids capture across the PSTs and providing additional capacity.

Optimization at DSRSD included the following: i) adding guide vanes that feed the PSTs to optimize flow distribution to each PST, ii) modifying the launders from longitudinal to lateral, iii) adding scum removal equipment, iv) adding a canopy over the hopper to alleviate solids re-suspension during peak flow events, and v) addition of perforated baffles across the PSTs to foster a more uniform flow velocity and in turn increase solids capture.

Since finishing the bulk of construction (2021), the PSTs have exceeded the anticipated solids capture across the PSTs: improved from approximately 45 to upwards of 70 percent under normal flow conditions. Stress testing has indicated that the PSTs equipped with the baffle system are capable of achieving solids removal across the PSTs at 46 percent at overflow rates (OFR) as high as 8,000 gpd/sf (for perspective, the industry standard is < 2,500 gpd/sf). Such an OFR is more than triple the flowrate that DSRSD’s PSTs could have historically sustained (before installing the baffle system) while maintaining reasonable performance.

Besides PST performance improvements, the plantwide benefits have been more profound than originally anticipated. Specifically, the additional biosolids/organics capture across the PSTs has translated to an additional biogas production of approximately 20 percent. This increase is attributed to a combination of higher solids/organics capture across the primaries and primary solids having higher BTU content than waste activated sludge. Furthermore, the downstream activated sludge process benefitted as it has increased capacity due to lower loads from the PSTs, as well as lower blower demands. Details on such benefits will be presented as part of the presentation by comparing/contrasting before and after baffle installation.

.1 SWRCB Wastewater Education Units