An Experimental Study On Dry Anaerobic Digestion Of Rice Straw

Anaerobic digestion is one of the feasibility technologies to utilize the rice straw, which can convert it into biogas. But there is little research has been conducted on anaerobic digestion of rice straw to biogas. Dry fermentation experiment is designed to improve the biodegradation efficiency and biogas production and to simplify the treatment process of the digested straw. In addition, it was showed that dry fermentation technology has both functional and economical advantages, and has great potential of application in China in the future for agriculture solid waste treatment and disposal.Dry anaerobic digestion technology with leachate circulated for untreated straw conversion to biogas was investigated in bioreactors at 35℃. Biogas production, pH, COD and methane content were tested. After 180 days of anaerobic digestion, it was observed that the Reactor 2 with TS 20% (R2) had the largest biogas production (2048L in total) while the biogas production were 1199.9L, 905.9L and 51.7L, respectively, in Reactor1, Reactor3 and Reactor4. The hemicelluloses of the digested straw in R2 decreased from 28.2% to 18.3%, and the pH value in zymotic fluid was stable at 7.0-7.5. The reactor R3 with TS 30% (R3) went on a long period of acidification before its biogas production turned higher, while its methane content was higher than that from R2. Leachate recirculation reduced the waste stabilization and was effective in enhancing methane gas production and improving leachate. The result indicated that sluge could be the inoculum source for anaerobic mesophilic digestion of the treatment of rice straw at dry condition. This study provided useful parameters for the design of large-scale dry anaerobic digester for straw conversion to biogas.On the other hand, it is found that co-disposal of refuse with coal ash and pre-treatment of alkali has many advantageous over conventional anaerobic digestion in terms of biogas production and volume reduction, due to the better adsorption and filtration roles with coal ash and pre-treatment of alkali. This result showed that coal ash and pre-treatment of alkali had some effectiveness on anaerobic digestion.Therefore, according to the results collected in this experiment, the best reactor is TS20%, with pre-treatment of alkali and addition of coal ash, which gas production increased 47.6%. This study could provide useful parameters for the design of field-scale dry fermentation for rice straw and coal ash disposal.