Study of the side reaction prevention for the dissolution of organic wastes with sub-critical water

研究目的本课题组一直致力于从城市污水污泥、餐厨垃圾等有机废弃物中开发资源化回收装置，将固体废弃物溶于亚临界水中，用磷酸镁铵沉淀法收集溶解磷，再用甲烷发酵法将溶解的有机物转化为沼气作为能源。但在亚临界水中，除了主要的水解反应溶解废物外，废弃物的热解副反应还会形成气态物质和碳化、焦油物质，成为亚临界水设备堵塞的原因。本研究的目的是：(1)阐明副反应机理，建立预防方法；(2)设计资源回收装置，将该技术商业化，并制定装置操作规程。研究结果(1)利用模型物质的实验结果，概述了有机物的热分解机理。(2)确定了投加氢氧化钠抑制污泥和餐厨垃圾热分解的最佳操作条件和亚临界水温。(3)对资源化回收装置进行了初步设计，制定了操作规程。(4)对装置的能量、磷资源回收效率和经济效益进行了评价。我们将与国内与环境相关的植物制造商合作，致力于以亚临界水处理为核心技术的有机废物资源化回收工厂的利用和推广。

Research objectOur group has been developing the resource recovery plant from the organic wastes such as sewage sludge and kitchen garbage through that the solid wastes were dissolved in sub-critical water, then dissolved phosphorus was precipitated and collected with the MAP (magnesium ammonium phosphate) method, and finally the dissolved organic matter was converted to biogas as an energy source with methane fermentation method.However, in the sub-critical water, in addition to the main hydrolysis reaction to dissolve the wastes, the side reaction of thermal decomposition of the wastes simultaneously proceeds to form the gaseous substance and the carbonized and tar substances which become cause of blockade of the sub-critical water equipment. The purpose of this research is (1) to elucidate the side reaction mechanism and to establish its prevention method, and (2) to design the resource recovery plant to commercialize this technology and to draw up the operating instructions of the plant.Research results(1) The mechanism for the thermal decomposition of organics has been outlined from experimental results using model substances. The sodium hydroxide addition was found to be effective as a method to suppress the thermal decomposition.(2) The optimum operating conditions for sodium hydroxide addition and sub-critical water temperature were determined to suppress the thermal decompositions of sewage sludge and kitchen garbage.(3) The resource recovery plant was basically designed and its operation guideline was drawn up.(4) The resource recovery efficiency of energy and phosphorus and the cost performance of the plant were appraised, and it could verify that the commercialization of this technology is possible.ProspectWe will cooperates with the domestic environmental-related plant manufacturers and aim toward the utilization and the spread of the resource recovery plant from the organic wastes with the sub critical water process as a core technology.