Pilot plant test of biogas production by rice straw sequencing batch dry anaerobic digestion and its kinetic analysis

Abstract: The organic waste can be converted by anaerobic digestion into a clean energy source of methane under gentle conditions. Dry anaerobic digestion, one kind of anaerobic digestion, was often used to treat municipal waste and had achieved great results for decades in Europe and America. The dry anaerobic digestion of biogas production technology is a better way than wet fermentation to handle rice straw. It has lots of advantages, such as bigger processing capacity, simpler device, lower energy loss and water consumption. However, dry fermentation of straw is very easy to fail due to heterogeneity of substrate, acid inhibition, etc. There were a few researches on the key technology in exploring the AD efficiency of rice straw based agricultural waste. Therefore, this paper studied the biogas production characteristics of pilot-scale dry anaerobic digestion using rice straw as feedstock. The parameters were determined by the laboratory pre-experiment, rice straw was stacked on the field for 3 days with moisture of 67.58% adjusted by 500 kg biogas slurry, rice straw pretreated (269 kg, TS of 89.19%) was mixed with inoculums (300 kg, 28.06%). The pilot-scale dry anaerobic digestion was conducted under the conditions of constant temperature at 30-35℃ for 55 days. The result of the pilot-scale experiment showed that the biogas yield of rice straw was 308.20 m3/t, the methane yield of rice straw was 167.44 m3/t, the maximum methane content reached 57.88% and the maximum biogas production rate reached 12.73 m3/(t·d) after 55 days of dry anaerobic digestion. According to the results of biogas production, the pilot-scale experiment had excellent daily biogas production and higher methane concentration, and the whole process ran stably. The modified Gompertz equation was commonly used to perform kinetic analysis of anaerobic digestion, so the Gompertz model was used to fit the methane production curve of rice straw. The fitted methanogenic potential value was quite close to the actual methanogenic potential value, and R2 value is 0.990 7, which indicated that the Gompertz model was also suitable for fitting the methane production in this study. Although the pilot-scale test ran successfully, the conditions could be optimized for a better result. The study can provide theoretical guidance and basis for batch dry anaerobic digestion on the treatment of rice straw.