Method and apparatus for the conversion of aquatic plants into biogases and electricity

Abstract

A method for producing a biogas is provided. The method includes the steps of providing a polyculture of aquatic plants to a growth system; continuously providing water, carbon dioxide, air and nutrients to the polyculture contained within the growth system; growing the polyculture for a time sufficient to produce an aquatic plant-based biomass; withdrawing a portion of the aquatic plant-based biomass contained within the growth system; and treating the withdrawn aquatic plant-based biomass to produce a biogas.

1 . A method for producing a biogas, the method comprising the steps of:
 providing a polyculture of aquatic plants to a growth system;   continuously providing water, carbon dioxide, air and nutrients to the polyculture contained within the growth system;   growing the polyculture for a time sufficient to produce an aquatic plant-based biomass;   withdrawing a portion of the aquatic plant-based biomass contained within the growth system; and   treating the withdrawn aquatic plant-based biomass to produce a biogas.   
     
     
         2 . The method of  claim 1 , wherein the polyculture comprises a species of duckweed, a cyanobacteria and an aquatic fern. 
     
     
         3 . The method of  claim 2 , wherein the polyculture comprises multiple species of duckweed. 
     
     
         4 . The method of  claim 3 , wherein the polyculture comprises duckweed of the  Lemna minor, Spirodela, Wolffiella , and  Wolffia  species. 
     
     
         5 . The method of  claim 2 , wherein the aquatic fern is of the  Azolla  species. 
     
     
         6 . The method of  claim 2 , wherein the cyanobacteria is of the  Spirulina  species. 
     
     
         7 . The method of  claim 1 , wherein the polyculture is provided to a plurality of growing trays contained within the growth system. 
     
     
         8 . The method of  claim 7 , wherein the plurality of growing trays are arranged in a vertically-stacked and spaced-apart orientation. 
     
     
         9 . The method of  claim 1 , wherein the nutrients are in the form of a compost tea solution. 
     
     
         10 . The method of  claim 1 , wherein the treatment step comprises subjecting the aquatic plant-based biomass to a pyrolysis process and to a combustion process. 
     
     
         11 . The method of  claim 10 , wherein the pyrolysis process is carried out at a temperature in the range of 1200° F. to 1800° F. 
     
     
         12 . The method of  claim 11 , wherein the pyrolysis process is carried out at a temperature in the range of 1350° F. to 1600° F. 
     
     
         13 . The method of  claim 10 , wherein the pyrolysis process is carried out for a duration of from twelve to twenty minutes. 
     
     
         14 . The method of  claim 1 , further comprising adjusting the pH of the water prior to providing the water to the growth system to a value suitable for growth of the polyculture. 
     
     
         15 - 17 . (canceled) 
     
     
         18 . A method for producing electricity, the method comprising the steps of:
 providing a polyculture of aquatic plants to a growth system;   continuously providing water, carbon dioxide, air and nutrients to the polyculture contained within the growth system;   growing the polyculture for a time sufficient to produce an aquatic plant-based biomass;   withdrawing a portion of the aquatic plant-based biomass contained within the growth system;   treating the withdrawn aquatic plant-based biomass to produce a biogas; and   combusting the biogas in an internal combustion engine.   
     
     
         19 . The method of  claim 18 , wherein exhaust gas from the internal combustion engine comprises carbon dioxide, water vapor, carbon monoxide and nitrogen oxide, and wherein at least a portion of the exhaust gas is recirculated to the growth system. 
     
     
         20 . The method of  claim 18 , wherein the polyculture comprises a species of duckweed, a cyanobacteria and an aquatic fern.