US 4,975,106 AGranted

Anaerobic digestion of fish wastes

AssigneeBiotherm International, Inc.

InventorJames R. Ferguson

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Abstract

A method and apparatus for anaerobic digestion of fish wastes and production of useful by-products including fertilizer and biogas. The method includes grinding up the fish wastes and adding liquid to create a suspension of up to 25% solids; optionally adding lipase to break down the fish oil; and anaerobically digesting the fish suspension over a period of approximately 20 days at a temperature in the range of 35.degree.-55.degree. C. with mixing provided by recirculation or other means. After digestion, the suspension is pumped to a secondary chamber for storage, further breakdown by mechanical means such as agitation or recirculation, centrifugation to remove suspended solids, production of an enhanced fertilizer by the addition of seaweed, urea, nitrogen, potash and chelated micronutrients, deodorization, by the addition of potassium permanganate, treatment to reduce the B.O.D. or evaporation to reduce liquid.

Claims19

Dependent claims

A method for digestion of fish wastes comprising the steps of

preparing a culture of anaerobic microorganisms from material selected from the group comprising anaerobically digested cattle manure, manure from other animals, sewage, sludge and mud from the bottom of a pond, said preparation including the feeding of a gradually increasing amount of organic compounds to said material,
feeding the culture into a digestion tank,
grinding the fish wastes into small pieces and adding water thereto to make a suspension of up to 25% solids,
feeding said suspension into the tank at a gradual rate of inflow, increasing said rate to a steady rate and withdrawing material from the tank to maintain a predetermined level of contents therein, the tank being cleared of air and maintained at a temperature between about 15.5 and 55.degree. C., while mixing the suspension in the tank sufficiently to prevent the buildup of a crust on the surface, said steady rate of inflow being such that it would require a predetermined digestion time to fill the tank, if initially empty, to said predetermined level, said digestion time being that required to cause approximately 95% of the connective tissue in the fish wastes to be anaerobically digested.

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Dependencies are inferred from the claim text.