VanderHaak Dairy Anaerobic Manure Digester Facility

The dairy industry is an important part of Whatcom County's agricultural industry. To ensure continuing value, new techniques have been investigated and implemented to sustain it's economic viability. One interesting solution is anaerobic digestion--a closed system of composting that uses anaerobic bacteria and enzymes to break down organic molecules, which release carbon dioxide and methane gas. The resulting fiber, a byproduct of this process, gives the farm an additional revenue source.

The VanderHaak dairy installed a concrete 10,000 sq. ft. concrete tank to house its digester operation. "Biogas" is collected from the first two stages of the digester tank then utilized as fuel to power a generator. The generator is a CAT G-398, commercially available, natural gas-fueled reciprocating diesel engine modified to burn biogas. Electricity produced by this generator is sold and transferred directly to Puget Sound Energy's grid.

The waste heat, in the form of hot water, is collected from both the engine jacket liquid cooling system and from the engine exhausts (air) system. Approximately 30 to 60% of this waste heat is utilized in the AD system in the highly insulated concrete tank. The remaining waste heat can be used by the farm as a replacement for hot water production (reducing the need for natural gas or propane purchases) and for in-floor heating of the farm and holding areas, as required.

The digester effluent is pumped directly from the AD vessel to a manure solids separator. The mechanical manure separator separates the influent digested waste stream into solid and liquid fractions. The solids are dewatered to approximately a 35% solid material. The separated solids, have the same odor and pathogen reduction characteristics as the liquid stream and is used by the farm for bedding replacement (an expense reduction). Use of the separated solids for bedding typically comprises about 40 to 60% of the generated separated solids from a typical farm. This bedding - i.e. for cows - is more sterile than kiln dried sawdust for cows with 99% pathogens removed. The residual 40 to 60% of non-utilized separated solids may be sold (system-generated income) to other farms for bedding purposes or to after-markets, such as nurseries and composters, for soil amendment material.

The liquid from the manure separator, now with the majority of the large solids removed, gravity flows into the farm's storage lagoon. A large advantage of the effluent from the AD treatment process is that the viscosity of the effluent is such, as opposed to the raw manure influent, that the liquid effluent can be pumped through an irrigation nozzle for field spreading. This gives a greenhouse gas emission reduction and has other potential benefits such as reduced odor reduction and weed seed destruction in the effluent.

Biogas field trip

Steve VanderHaak explains the anaerobic composting process while students stand on the top of the digester

Fiber

Bryan Vanloo, a representative from Andgar, the company who manufactued the digester discusses feedstocks