Optimization Of The Process Of Anaerobic Digestion On Wheat Straw

As a large agricultural country of China, approximately 0.7 billion tons of crop straws are generated annual. Currently, the agricultural residua have no specific technical application and create huge disposal problems. Considerable amount of straw are incinerated in outdoors, leading to seriously air pollution and waste of resources, which is the serious problem faced by the humanity in general. The anaerobic digestion is the most interesting process for treating agricultural residua because it combines production of clean bioenergy with reducing of pollution. Based on the study of key and process technology of dry anaerobic digestion to produce biogas on the agricultural residua in Yellow River Delta, which is a subitem of Technology Support Project in Shandong Province (2008GG2007003), this study investigated the batch and semi-continuous experiments of wheat straw.Firstly, the batch experiment was conducted to evaluate the effect of particle side and substrate concentration on the anaerobic hydrolysis of wheat stalk, and the largest cumulation hydrogen production 49.91mL and degradation of wheat stalk 59.6% were obtained at the best condition parameters of 1mm and 8%TS.Based on the best condition parameters obtained above, new batch experiment was conducted to further investigate the effect of different inocula on the anaerobic hydrolysis of wheat stalk. The results showed that the optimal inoculum for the anaerobic hydrolysis of wheat stalk was the dairy manure slurry. The CrI 36.1% of dairy manure slurry-inoculated system showed that the hemicellulose in the wheat stalk is much more degraded than that of digested sludge-inoculated system. Modified Gormpertz can be well used to fit the cumulation hydrogen production in the anaerobic hydrolysis of wheat stalk with different inocula. The dairy manure slurry-inoculated system has a better hydrolysis characters such as the potential of hydrogen production 38.5mL/gVS, lag time 55.6h, and the degradation of cellulose 75.2%.Secondly, the semi-continuous lab-scale CSTR reactor was adopted to investigate the influence of reflux ratio (26%, 40%) and hydraulic retention time (HRT=20, 40 and 60d) on the anaerobic digestion of wheat straw as a sole substrate to produce biomethane based on the results of batch experiments. During the experiment period, the optimal technological parameters were obtained by the detected anaerobic indexes in the process of the reactor such as biogas production rate, methane yield, volatile fatty acid, pH and ammonia nitrogen etc. The result showed that the optimum reflux ratio was 26% (based on the total volume of the leachate), and the optimum HRTs was 40d, which can promise a higher biogas production rate 106.1mL/gVSd, methane content 55.6%. XRD analysis indicated that anaerobic digestion increased the crystallinity of wheat straw to 45.9%. The degradation of wheat straw reached up to 85.77% in the process of anaerobic digestion of wheat straw as a sole substrate. This should be attribute to the degradation of the amorphous cellulose in the anaerobic digestion of wheat straw, which destroyed the crystalline structure to a certain extent. And the degradation of cellulose is found to be benefit to generate more biogas.