Options to regulate the pH in acified biogasdigesters and effects on the biogas production. [German]Original Title Moglichkeit zur pH-Wertregulation versauerter Biogasfermenter und die Auswirkungen auf die Biogasausbeute.

摘要

Biogasdigesters are increasingly experiencing difficulties with the process stability where acidification of the digester reduces efficiency, resulting in economic losses. This study evaluated the effectiveness of a treatment to reverse or prevent acidification in the biogasdigester. Continuous laboratory tests according to VDI-4630 with 3 digesters were performed, one as control, the other two acidified with propionic acid. Lasting 133 days, the experiment was divided into a degassing, stabilization, acidification and buffering, and final recovery phase. In the degassing and stabilization phase identical operating conditions were created in the digesters in terms of the digestion medium, gas quality and gas yield. In the acidification and buffer phase, 99.5% propionic acid was added gradually by pumps until the test conditions of a pH <6.5 and decreasing biogas quality and yield were reached. At this stage sodium bicarbonate was added. The results showed that sodium bicarbonate stabilized the pH in the digesters. Within 3 days of application of the buffering substance, the pH in the test digesters was similar to that in the control. Furthermore, all critical process parameters in the recovery phase reached those in the control digester. Also, for the single stage mesophile anaerobic test digesters unusually high methane concentrations of 80 Vol.% were recorded. Therefore, the buffering substance sodium bicarbonate could be recommended as a simple and cost-effective treatment to prevent the economic costs of loss of efficiency caused by acidification.