Vermicomposting of cod (Gadus morhua) offal mixed with sphagnum peat

Decker, Stephanie J. (2000) Vermicomposting of cod (Gadus morhua) offal mixed with sphagnum peat. Masters thesis, Memorial University of Newfoundland.

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Abstract

Vermistabilization is the stabilization of organic wastes using earthworms. Most studies have analysed the use of earthworms in the stabilization of sewage sludge and vegetable wastes, however, there have been no in-depth studies which examine vermicomposting with fish offal. -- Sphagnum peat mixed with cod (Gadus morhua) offal was vermicomposted for 8 weeks with earthworms (Eisenia fetida) following a two week pre-composting period. Vermicomposting samples were compared with the same mixtures in the absence of earthworms. Results showed that the maximum proportion of cod offal that can be used during vermicomposting to ensure a 100% survival rate was 13% (dry wt). Cod offal of 15% or more (dry wt.) was toxic to the earthworms resulting in death; this was true even when the pre-composting period was extended by more than two weeks. Peat was selected as the bulking agent because peat adsorbs much of the ammonia (NH₃) gas, which is released during the decomposition of the cod offal, as ammonium ion (NH₄⁺). As a result of the ammonia gas being adsorbed there is a reduction in the amount of nitrogen that is lost during the decomposition process. Results indicated that, when earthworms were initially added to a compost mixture, the level of ammonium ion should not exceed 1.0 mg/kg to allow for an earthworm survival rate of 100%. -- The rate of organic matter stabilization was determined by measuring the reduction in the volatile solids content of the waste. Vermicomposting for 8 weeks produced a material with a significantly higher percentage of ash compared to composting for a similar period (P<0.05). It was concluded that vermicomposting resulted in a more stable material compared to composting. Results also indicated that earthworms increased the proportion of some available nutrients (i.e., phosphorus, potassium, calcium, magnesium) which are needed for good plant growth. Thus, the results showed that vermicomposting is an effective method for stabilizing cod offal.

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