Closing the Nutrient Cycle in Two-Stage Anaerobic Digestion of Industrial Waste Streams

摘要

Industrial waste streams from brewing industries and distilleries provide a valuable but largely unused alternative substrate for biogas production by anaerobic digestion. High sulfur loads in the feed caused by acidic pretreatment to enhance bioavailability are responsible for H2S formation during anaerobic digestion. Microbiological oxidation of H2S provides an elegant technique to remove this toxic gas compound. Moreover, it allows for recovery of sulfuric acid, the final product of aerobic sulfide oxidation, as demonstrated in this study. Two-stage anaerobic digestion of brewer's spent grains, the major byproduct in the brewing industry, allows for the release of up to 78% of total H2S formed in the first pre-acidification stage. Desulfurization of such pre-acidification as in continuous acidic biofiltration with immobilized sulfur-oxidizing bacteria resulted in a maximum H2S elimination,capacity of 473 g m(-3) h(-1) at an empty bed retention time of 91 s. Complete H2S removal was achieved at inlet concentrations of up to 6363 ppm. The process was shown to be very robust, and even after an interruption of H2S feeding for 10 days, excellent removal efficiency was immediately restored. A maximum sulfate production rate of 0.14 g L-1 h(-1) was achieved, and a peak concentration of 4.18 g/L sulfuric acid was reached. Further experiments addressed the reduction of fresh water and chemicals to minimize process expenses. It was proven that up to 50% of mineral medium that is required in large amounts during microbiological desulfurization can be replaced by the liquid fraction of the digestate. The conducted study demonstrates the viability of microbial sulfur recovery with theoretical recovery rates of up to 44%.