O2Compost has partnered with Northwest Fish By-Products, Inc. to demonstrate the technical and economic viability of composting approximately 1.5 million pounds of waste salmon from Northwest fisheries.

A bench scale pilot project has been completed to evaluate both waste salmon and crab shells to determine initial recipes for each and to evaluate suitable methods for controlling potentially offensive odors. The annular space between the outside of the slip form box and the bin wall (see photograph) was filled with finished compost to serve as:

1) an insulative layer to ensure that all raw materials reached temperatures sufficient to destroy pathogens, parasites and weed seeds; and 2) a biofilter layer to absorb and manage objectionable odors. When filled, the top of the bin was also covered with approximately 12-inches of finished compost (See Photograph).

The salmon waste results from mortalities at fish farms located throughout the Puget Sound Region, numerous hatcheries and several fish processing plants located in the Seattle vicinity. A conservative projection of salmon waste in Washington State is placed at 30 million pounds per year, and growing.

The salmon is brought to the composting site in 1,000 pounds “totes” and is tipped onto a bed of previously blended bulking materials. At this point in the process, the odor is moderate to strong, however the mix is immediately mixed and placed onto the aerated static pile and capped with a biofilter layer of horse manure and bedding. Within 30-minutes, all impacts from odor have been mitigated. This process was observed by a representative from the Health District (with 100% approval) as being an efficient process utilizing best management practices. Objectionable odors during composting have been non-existant.

Within hours, the pile temperatures have consistently exceeded 131 degrees Fahrenheit, the minimum requirement for pathogen destruction, and within 3-days there is no evidence of fish remains. At no time during this demonstration project have there been problems with animals (wild or domestic) digging into the pile to recover fish. There have been no incidence of bird activity nor have there been any flies associated with the compost piles.

The method of composting used to produce all three varieties of compost is referred to as ASP or “Aerated Static Pile” Composting. In this case, airflow is introduced into the pile using high-pressure blowers to replenish oxygen and to optimize the biologic conditions throughout the pile. One of the by-products of the biologic process is heat. The temperature is managed at sufficiently high temperatures to destroy pathogens, parasites, weed seeds and fly larvae in the mix of raw materials. By maintaining oxygen rich conditions, the ASP method of composting mitigates objectionable odors and produces a superior finished compost product. The compost has no “fishy” odor, and will not attract cats, dogs or wildlife. It is nutrient rich and full of beneficial microorganisms. The net results are beautiful and bountiful landscapes and vegetable gardens.