Biogas

Beside a protein product, the two residual fractions, the press cake and the brown juice contain high nutrient and energy value, which should be exploited. The press cake and the brown juice can be processed through anaerobic digestion (AD) to produce bioenergy in the form of biogas-methane and carbon dioxide. Methane can be directly supplied to the gas grid after upgrading of the biogas and, thereby, substitute the use of fossil natural gas with bio-natural gas. Bio-natural gas will have a major value as a secure back-up energy source, when wind or solar energy are insufficient. If the press cake is valorized for other uses, methane can also be produced from the brown juice. As this fraction is soluble, a UASB reactor system can be used allowing for low operational times for the conversion. The liquid effluent from the AD processes, which contains residual organic matter and nutrients, are valuable as an organic fertilizer. The nutrients from the effluent can be separated out and the remaining water can be purified by membrane processes to allow for admission to the environment.