Enhanced Biogas Production from Rice Husks and Okra Stalks by Co-digestion with Ostrich Dung and Cow Manure

In this study, two sides were studied. First one included single and combined pretreatment which were performed to treat milled rice husks compared to increase the production of biogas untreated rice husks. The other side included investigate the effect of two types of mixing: mixing rice husks and okra stalks using three mixing ratios inoculated with ostrich dung compared to rice husks and okra stalks inoculated with ostrich dung separately and mixing ostrich dung and cow manure using three mixing ratios with rice husks compared to using rice husks inoculated with ostrich dung and cow manure separately. The ten reactors, which were carried out in this study, were in batch mode. Single pretreatment included hydrothermal and oxidative pretreatment with 50% (v/v) H2O2, while combined pretreatment consisted of both hydrothermal and H2O2 pretreatment. The cow manure was used as inoculum in this anaerobic co-digestion process. The results clarified that the increase of biogas productions were by 5.42%, 48.05%, and 59.07% for hydrothermal, H2O2, and combined pretreatment of hydrothermal and H2O2, respectively. For first mixing, 25:75 ratio (rice husks: okra stalks) was better than other ratios in the production of biogas (48.77 ml/g VS). In the second case of mixing, 75:25 ratio (ostrich dung: cow manure) was better than other ratios in the production of biogas (21.85 ml/g VS). Kinetic study was applied using modified Gompertz model, and there was well agreement between the predicted and measured values of the all pretreatments with correlation coefficient > 0.95. The pretreatment samples of rice husks and the mixing of materials improve the production of biogas and methane.