Engineer: Williams Engineering Associates
Owner: Gallo Farms
Project: Cottonwood Dairy Anaerobic Digester
Size: 250 x 1200 ft
Material: 60 mil HDPE
Installer: Environmental Fabrics, Inc.
Cottonwood Dairy. Wastewater Treatment Improvements Atwater, CA, Spring 2004
Cottonwood Dairy is a dairy with an adjacent cheese processing plant. They share the same open lagoon wastewater treatment facility for the processing of waste. Cottonwood dairy currently milks approximately 5500 cows. The cheese plant processes 1,000,000 pounds of milk daily. This operation created unpleasant odors and emitted green house gases.
To solve this problem, Gallo Farms chose to construct an anaerobic digester followed by a storage cell. This system allowed them to reduce odors, reduce wastewater treatment costs, keep out dirt and debris and capture methane, thereby reducing the emission of greenhouse gases. The gas is used to generate both steam and electricity. They were able to obtain a grant from Western United Resource Development and a Self-Generation Rebate from Pacific Gas and Electric. (PG&E)
Environmental Fabrics, Inc. of Gaston, SC was chosen for the fabrication and installation of the anaerobic digester cover. The technology consisted of a 60 mil HDPE impermeable membrane cover, ballast weights, rainwater removal pumps, and a biogas collection system.
After the cover was placed in operation, the system has functioned per design with minimal maintenance. The manager estimates benefits of about $2,000 per day, with a 4 year payback. The higher-than-projected methane production allowed a second generator for the plant. This project was featured on the 2007 AgStar conference on biodigesters.
