Brewers' spent grains (BSG) are a by-product of beer production which are traditionally used as animal feed. Since this option is declining, the energetic usage becomes an interesting alternative. Although a lot of research projects have been carried out during the last 30 years there is still no mature strategy available. One possibility could be the mechanical pretreatment of BSG to reach an optimized energetic usage. Due to the transfer of digestible components into the press water, the press cake largely consists of combustible components. The press water can be digested to biogas, the press cake can be co-incinerated with wood chips. Although BSG cannot cover the complete energy supply of breweries, it can be an incentive to realize 100 % renewable energy concepts at breweries.

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In order to exploit the theoretical potential of small manure anaerobic digestion (AD) plants for flexible power generation, the technical retrofitting and the prospective additional revenue generated by direct marketing is assessed for two different manure AD plants by means of a profitability analysis. Due to the variation in the economic profitability by the individual direct marketing models, the economy of three plants was simulated in four different scenarios: basic feed-in tariff, direct marketing, electricity balancing market, and flexible operation. Economical operations were calculated and the additional revenue for small manure AD plants taking part in the direct marketing system was calculated.

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