Pretreatment for biogas production by anaerobic fermentation of rice straw

The anaerobic digestion was an efficient utilization ways of straw, and the pretreatment processing method have obvious influence to the degradation. The straw pretreatment process was studied in this paper expecting to explore rational pretreatment method. Rice straw was chosen as raw material in this research. At first, the effects of Ca(OH)2 with different concentrations processing was studied, the dissolved quantity of COD was increased to 75.9% at 9 g/L Ca(OH)2 concentration 5 days later, proved that Ca(OH)2 pretreatment contributed to straw hydrolysis. But Ca(OH)2 pretreatment also was easy to cause anaerobic acidification, so the biogas yield was 17.4% less than the control while had not adjusted the pH values. Then the experiments were carried out on effects of the straw smashing size, the ratio of carbon to nitrogen, the pile of bubbles time and were designed on the basis of quadratic orthogonal regressive rotational combination principle with three factors and five levels. A quadratic equation for biogas yield was built. The optimal processing parameters which obtained according to the analysis of the data are as follows: the smashing size of rice straw is 4-6 mm, C/N is 40, the pile of bubbles time is 8d, which approved that it required no over smashing of rice straw and the C/N range for anaerobic digestion was increased by pretreatment processing. These offers experiment evidences for the possibility of high C/N material used for anaerobic digestion.