TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The solid spent product(s) are: spent cereal solid materials including spent grains from grain distilleries, draff, brewer's grains and maize; or spent agricultural wastes including animal waste, such as animal slurry and plant material including maize grain/silage, sugar beet (such as fresh sugar beet pulp, ensiled sugar beet pulp, and dried sugar beet pulp pellets), vinasses, sugar cane, potato, grasses, wheat feed, grains, vegetables, and fruit waste, such as pomace.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The process further comprises: processing the biogas to obtain methane with purity of greater than 95%; monitoring one or more micronutrient levels and adding the micronutrients to the anaerobic digestion process as required; and an acidogenic phase prior to the anaerobic digestion, where greater than 50 wt.%, preferably 90 wt.% of the solids (on a weight of liquid/dry weight of solids basis) of the slurry are derived from a material comprising spent cereal and yeast in a ratio of 3:1-1:3. The methanogenesis comprises anaerobic digestion by mesophilic acidogenic and methanogenic bacteria at 30-40 degrees C. The anaerobic digestion has average retention time of 35-45 days. 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. The slurry, prior to anaerobic digestion, is subjected to a milling or other suitable grinding or homogenizing process to reduce the particle size, increase surface size area and/or aid solubilization of the solids in the slurry. The acidogenic phase has an average hydraulic retention time of only 24 hours (with no recycling). The liquid digestate is stored for a period of up to 180 days. At least a portion of the liquid digestate is subjected to evaporation to concentrate the liquid digestate such that it is suitable for use as a liquid fertilizer. At least a portion of the liquid digestate is subjected to evaporation to form a solid product suitable for use as a solid fertilizer. A portion of the biogas is used to mix the anaerobic digester. Preferred Components: The slurry further comprises: silage in an amount of up to 20% of the total solids on a dry basis; and spent pot ale, pot ale syrup, water. The slurry initially comprises dry solids content of up to 20 wt.%, up to 15%, up to 12%, or up to 10%. The liquid with a high bicarbonate alkalinity is provided as a liquid digestate obtained from the digestion or treatment of other waste products and/or by recycling a portion of the liquid digestate. The bicarbonate alkalinity of the slurry during the process is at least 3000 mg/l. 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. The pH is 7-7.4. The liquid digestate is recycled to form a slurry with new spent solid cereal product(s) and/or further processed for use in agriculture. EXAMPLE - No suitable example given.