Agricultural crop residues like stems, straws and leaves are valuable resources for biofuel production, especially methane, due to anaerobic digestion. Biogas from agricultural lignocellulosic wastes is capable of attaining sustainable energy yields without environmental pollution. Farmers in many developing countries burn these wastes throughout their fields, imposing environmental hazard due to emission of greenhouse gases. The main problem in this field is the recalcitrance of the agricultural lignocellulose waste that limits its enzymatic degradation and hydrolysis efficiency and consequently decreases biogas production. Therefore, efficient pre-treatments prior to anaerobic digestion are essential. Various pre-treatment methods are used for increasing the anaerobic digestibility of lignocellulose biomass, such as physical (mechanical, thermal, etc.), chemical, biological and combined pre-treatments. This paper reviews different pre-treatments used in anaerobic digestion for the agricultural lignocellulosic wastes and explains the advantages and disadvantages of each. The most frequently used pre-treatments for main agricultural wastes in process of biogas production are also introduced.
Various conditions of a parboiling process affect the qualitative parameters of paddy milling. In this study, the effects of drying temperature (45 and 60 °C), moisture content (8, 10 and 12% w.b.), steaming time (10, 20 and 30 min) and paddy varieties (Hashemi and Alikazemi) were investigated on head rice yield (HRY). The samples were husked using a rubber roller husker and whitened by a laboratory abrasive whitener. Results showed that the main effects of all parameters were significant on HRY (P <0.01). The utilization of higher temperature (60 °C), in comparison with non-parboiled rice, without reducing the milling quality was found as one of the advantages of parboiling. Among all experiments, the highest HRY (68.647%) was achieved in the combination of Alikazemi/45 °C/10 min/8%. In the majority of cases, the combinations including Alikazemi variety had higher HRY than Hashemi. For Hashemi variety, the highest HRY (67.297%) was achieved in combination 45 °C/10 min/8%. In terms of HRY, parboiling causes an increase of 25.8% and 43.3% respectively for Hashemi and Alikazemi. Therefore, it is highly recommended in processing of Alikazemi variety.