Rice straw is an abundant agricultural waste in Asia. Anaerobic digestion (AD) as an environmentally friendly process for bioenergy recovery is expected to solve the environmental issues brought about by open burning of rice straw. In order to test the feasibility and scalability of hydrothermal treatment (HTT) on rice straw for subsequent methane production from pretreated straw, this study attempted two peak HTT temperatures (150 and 210 °C, i.e. HTT150 and HTT210, respectively) for holding 0–30 min to pretreat rice straw which was then used for mesophilic methane fermentation. Thereafter energy balance and energy recovery were analyzed on HTT and subsequent AD of rice straw. Results show that HTT150 exhibited a positive effect on subsequent methane production, achieving the highest methane yield of 134 mL (STP) for per gram of added volatile solid (VS_added) of rice straw after being hydrothermally pretreated at 150 °C for 20 min. The maximum specific methane production rate (μ), around 17–40% higher than the control (without pretreatment), was achieved from HTT150 pretreated rice straw. HTT210 was found to have a negative effect on subsequent AD. Considering disposal of rice straw by HTT coupling with subsequent methane production, the highest net energy gain (ΔE = E_out – E_in), energy ratio (E_out/E_in), and energy recovery (in comparison to direct combustion) were obtained at HTT150 for 20 min, about 2741 MJ/t, 2.7, and 30.7%, respectively. Results from this work imply that HTT temperature is critically important when subsequent AD for enhanced methane production and energy balance of the whole disposal system are targeted.

中文翻译：

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通过水热预处理和后续生物甲烷生产从稻草中回收能量

稻草是亚洲丰富的农业废料。厌氧消化（AD）作为一种环境友好的生物能源回收方法，有望解决稻草露天焚烧带来的环境问题。为了测试在稻草上进行水热处理（HTT）以从预处理的稻草中后续生产甲烷的可行性和可扩展性，本研究尝试使用两个峰值HTT温度（分别为150和210°C，即HTT150和HTT210）来保持0– 30分钟预处理稻草，然后将其用于中温甲烷发酵。此后，在HTT和随后的稻草AD上分析了能量平衡和能量回收。结果表明，HTT150对随后的甲烷产生具有积极作用，在150°C下进行20分钟的水热处理后，再_添加）稻草。使用HTT150预处理的稻草可实现最大比甲烷生产率（μ），比对照（未经预处理）高出约17–40％。发现HTT210对随后的AD具有负面影响。考虑到通过HTT处理稻草以及随后的甲烷生产，则净能量收益最高（ΔE = E _out - E _in），能量比最高（E _out / E _in），并在HTT150下进行20分钟的能量回收（与直接燃烧相比），分别约为2741 MJ / t，2.7和30.7％。这项工作的结果表明，当针对提高甲烷产量和整个处置系统能量平衡的后续AD制定目标时，HTT温度至关重要。