Mesophilic Composting of Arctic Char Manure

Compost Science & Utilization, (2005), Vol. 13, No. 1, 34-42

Paul R. Adler* (1) and Lawrence J. Sikora (2)
1. National Center for Cool and Cold Water Aquaculture,
United States Department of Agriculture-Agricultural Research Service, Kearneysville, West Virginia

2. Animal Manure and By-products Laboratory, United States Department of Agriculture-Agricultural
Research Service, Beltsville Agricultural Research Center, Beltsville, Maryland

Manure in coldwater aquaculture production systems is typically settled in quiescent zones created within raceways to concentrate it prior to being pumped to storage in off-line settling basins. As the water passes through the off-line settling basins, the solids settle out and the excess water is discharged to surface water. Since the basins are not frequently emptied, the organic solids mineralize and nutrients flow out of the basins with the surface water discharge. A system was tested to remove solids from settling basins frequently and treat by mesophilic composting. Two carbon (C) sources (wheat straw or oak sawdust) were evaluated. Manure was applied to beds of carbon sources at a rate of about 1cm of arctic char manure (8% solids) every 10 days using a vacuum tank spreader modified for side discharge over the plots. The open and porous structure of wheat straw resulted in several advantages over the oak sawdust; there was not runoff during application even during freezing winter temperatures when the oak sawdust compost was frozen solid, aerobic conditions were maintained with lower amounts of C, and decomposition rates were higher resulting in less time needed to reach stability (about 90d vs. 140d). Inorganic nitrogen (N) increased as the organic matter decomposed with either C source. Mineralization and nitrification rates were higher with wheat straw. Water-extractable P decreased as the organic matter from both C sources decomposed. Land requirements are about 0.001 ha to compost the manure for each 1 Mg Arctic char produced annually, but could be significantly higher for the wheat straw since experimental loading rates were limited by the reduced capacity of the oak sawdust compost. A layered mesophilic compost system may be a viable manure management system to store and treat manure and replace long-term storage in off-line settling basins for fish farmers. In this system, solids would continue to be settled in the off-line settling basins but pumped onto straw nearby for storage and stabilization on land thereby minimizing discharge of nutrients to surface water.

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