Advanced Wastewater Treatment Plant with Cannibal Solids Reduction
Calif., is discharged into Basalt Pond. In order for the city to continue doing this, the North Coast Regional Water Quality Control Board (RWQCB) required that Healdsburg's existing secondary plant be upgraded to perform Advanced Wastewater Treatment (AWT) as required in the city's NPDES permit. City officials selected HDR to provide project scoping, a basis of design report, design, bidding, equipment pre-purchase assistance and construction management and engineering services for the new treatment plant.
The plant was designed to treat 1.4 million gallons per day (mgd) during average dry weather flow (ADWF) and 7.0 mgd (with flow equalization) in peak hours. This plant utilizes a membrane bioreactor (MBR) system that combines a secondary biological treatment process, along with an immersed membrane process, to separate suspended solids from water using a very fine filter. Using MBR technology allows the Healdsburg facility to maximize long-term system value that extends beyond the initial capital cost because of benefits like better use of existing space, simplified operation and consistently higher quality effluent.
Because the MBR process is the heart of the wastewater treatment plant, a sidestream screen located in the piping between the aeration basins and the membrane tanks was provided. This is to ensure that any debris entering the open aeration basins will be removed prior to the sensitive membrane process because the upstream processes are important to maximize the efficiency of the MBR system.
UV technology alternatives that are validated and certified to be used for California Title 22 reuse applications were evaluated. After economic and non-economic evaluations were completed based on Healdsburg's site specific results, the HDR team recommended an open channel UV reactor with a low pressure/high intensity UV disinfection lamp system for this project.
Sludge storage and handling relies on the cannibal process to reduce the quantity of solids handling requirements at the wastewater treatment plant. The solids handling system includes a storage tank (aerobic digester), fine screens and a final sludge dewatering device and its controls, which are housed in a masonry building.