Grain Processing

Abstract

The present invention provides a process for producing biogas and/or methane from solid spent cereal products derived from, for example, the mashing process of malt whisk(e)y and/or beer production. There is also provided a system for producing biogas and/or methane from solid spent cereal products derived from, for example, the mashing process of malt whisk(e)y and/or beer production.

1 . A process for producing biogas and/or methane, the process comprising:
 (a) providing a slurry comprising one or more solid spent cereal product(s; and   (b) subjecting the slurry to an anaerobic digestion comprising methanogenisis at a pH of pH 6.6-7.6, in order to obtain a biogas and a liquid digestate.   
     
     
         2 . The process according to  claim 1  further comprising processing the biogas in order to obtain methane at greater than 95% purity. 
     
     
         3 . The process according to either of  claim 1  or  2  wherein greater than 50%, 60%, 70%, 80% or 90% of the solids (on a wt of liquid/dry wt of solids basis) of the slurry has been derived from a material comprising spent cereal and yeast in a ratio of 3:1-1:3. 
     
     
         4 . The process according to any preceding claim wherein the slurry further comprises silage in an amount of up to 20% of the total solids on a dry basis. 
     
     
         5 . The process according to any preceding claim wherein the slurry initially comprises a dry solids content of up to 20% on a wt/wt basis, up to 15%, up to 12%, or up to 10%. 
     
     
         6 . The process according to any preceding claim wherein the slurry comprises spent pot ale, pot ale syrup, water and/or a liquid which possesses a high buffering capacity for maintaining the anaerobic digester at the desired pH. 
     
     
         7 . The process according to  claim 6  wherein the liquid with a high buffering capacity for maintaining the anaerobic digester at the desired pH possesses a high bicarbonate alkalinity. 
     
     
         8 . The process according to  claim 7  wherein the bicarbonate alkalinity of the slurry during the process is at least 3,000 mg per litre 
     
     
         9 . The process according to any of  claims 6 - 8  wherein the liquid which possesses a high buffering capacity is a liquid digestate obtained from anaerobic digestion of soluble waste products and/or a liquid digestate obtained from the process according to any preceding claim. 
     
     
         10 . The process according to any preceding claim wherein the pH is 7.0-7.4. 
     
     
         11 . The process according to any preceding claim wherein the liquid digestate is recycled to form a slurry with new spent solid cereal product(s) and/or further processed for use in agriculture. 
     
     
         12 . The process according to any preceding claim wherein the methanogenisis comprises anaerobic digestion by mesophilic acidogenic and methanogenic bacteria at between 30° C.-40° C. 
     
     
         13 . The process according to any preceding claim wherein the anaerobic digestion has average retention time of 35-45 days. 
     
     
         14 . The process according to any preceding claim wherein a starter culture of microorganisms for carrying out an anaerobic digestion is obtained from a waste sewage sludge treatment plant, or from a conditioned microbial population obtained from the anaerobic digestion of soluble distillery waste products. 
     
     
         15 . The process according to any preceding claim wherein the slurry, prior to anaerobic digestion is subjected to a milling or other suitable grinding or homogenising process in order to reduce the particle size, increase surface size area, and/or aid solubilisation of the solids in the slurry 
     
     
         16 . The process according to any preceding claim further comprising monitoring one or more micronutrient levels and adding said one or more micronutrients to the anaerobic digestion process as required. 
     
     
         17 . The process according to any preceding claim further comprising an acidogenic phase prior to the anaerobic digestion 
     
     
         18 . The process according to  claim 17  wherein the acidogenic phase has an average hydraulic retention time of only about 24 hours (with no recycling). 
     
     
         19 . The process according to any preceding claim wherein the liquid digestate is stored for a period of up to 180 days. 
     
     
         20 . The process according to any preceding claim wherein at least a portion of the liquid digestate is subjected to evaporation in order to concentrate the liquid digestate such that it is suitable for use as a liquid fertiliser or    
     
     
         21 . The process according to any of  claims 1 - 19  wherein at least a portion of the liquid digestate is subjected to evaporation to form a solid product suitable for use as a solid fertiliser. 
     
     
         22 . The process according to any preceding claim wherein a portion of the biogas is used to aerate the anaerobic digester. 
     
     
         23 . An anaerobic digestion system as substantially described herein with reference to and as illustrated in  FIG. 2 .