The main aim of anaerobic co-digestion of rice straw is to enhance volumetric methane yields and process stability to achieve synergetic effects. However, high carbon to nitrogen ratio of rice straw causes poor process stability for mono-digestion. This study investigated the co-digestion of rice straw and de-oiled rice bran, a nitrogen-rich by-product of the rice milling industry. The spent bio-slurry ( from running de-oiled rice bran which inherently contains various types of microbes was used as an inoculum for process start-up. A series of experiments were conducted to optimise the methane yield in semi-continuous anaerobic digester operating at 30 days of hydraulic retention time at mesophilic temperature conditions. Co-digestion studies of rice straw and de-oiled rice bran with three different mixing ratios were conducted by maintaining a specific total solids concentration of 5.0, 7.5, and 10.0% total solids concentration for the designated digester. The biogas production, methane contents, volatile matter degradation efficiency were determined to evaluate the stability and performance of the system. The digester maintained at 5% and 7.5% TS showed nearly similar results in terms of methane yield and volatile matter conversion efficiency. During the entire experimentation the percentage of methane content in the produced biogas was in the range of 24.8–55.4%. The average methane yield of 0.169 and 0.173 L/g-VS was found for digester maintained at 5.0% and 7.5% TS respectively. However, the volatile solid mass removal efficiency of 40.13% and 37.94% was recorded for the digester maintained at 5% and 7.5% TS respectively. Since no chemical or thermal pre-treatment was adopted during the entire process it is highly economical and adaptable for concerned industries. Ultimately, the results of the present study were compared to the previous studies on anaerobic co-digestion of RS, which shows the promising result with no extra added input cost.

中文翻译：

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稻草和脱油米糠厌氧共消化生产生物甲烷

稻草厌氧共消化的主要目的是提高甲烷体积产量和工艺稳定性，以实现协同效应。然而，稻草碳氮比较高，导致单一消化过程稳定性差。本研究调查了稻草和脱油米糠（碾米工业的富氮副产品）的共同消化。用过的生物浆（来自运行的脱油米糠，本身含有各种类型的微生物）被用作工艺启动的接种物。进行了一系列实验，以优化半连续厌氧消化器在运行温度下的甲烷产量。中温条件下的水力停留时间为30天。通过维持特定总固体浓度5.0%、7.5%和10.0%总固体浓度，对三种不同混合比例的稻草和脱油米糠进行共消化研究。确定沼气产量、甲烷含量、挥发物降解效率，以评估系统的稳定性和性能。维持在 5% 和 7.5% TS 的沼气池在甲烷产量和挥发物转化率方面显示出几乎相似的结果在整个实验期间，产生的沼气中甲烷含量的百分比在24.8-55.4%的范围内。对于维持在 5.0% 和 7.5% TS 的消化池，平均甲烷产量分别为 0.169 和 0.173 L/g-VS。然而，对于维持在 5% 和 7.5% TS 的消化池，挥发性固体物质去除效率分别为 40.13% 和 37.94%。由于整个过程没有采用任何化学或热处理预处理，因此非常经济且适用于相关行业。最终，本研究的结果与之前关于 RS 厌氧共消化的研究进行了比较，结果表明无需额外增加投入成本即可获得有希望的结果。