A Simple Solution to Big Snail Problems - A Case Study at VSFCD’s Ryder Street Wastewater Treatment Plant

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A treatment facility operating on the northern edge of the San Francisco Bay, in Vallejo, California, was experiencing excessive growth of trickling filter snails in the plant’s two biotowers. Downstream of the biotowers, the snail shells would settle in the plant’s aeration basins and secondary clarifiers and cause major maintenance problems. Periodically the entire aeration basin and clarifier structures were removed from service and manually cleaned to remove the snail shells. As part of a larger plant improvements project, the owner teamed with Carollo Engineers to develop and evaluate solutions to the snail shell problem. Several alternatives were developed, and the most promising alternatives were tested for effective removal or prevention of the snail shell issue.

Pilot testing of an alternative, which included baffles in the aeration basins and the use of grit pumps and classifier systems, proved very effective at snail shell removal. A similar system was designed for permanent installation at the plant, and for a relatively low cost, compared to the excessive manual labor requirements, the snail shell removal system was installed and is currently operating. Initial testing of the system and periodic monitoring of the downstream basins has shown that the custom-engineered snail removal system is very effective at long-term shell removal and disposal.

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