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

研究对象本课题组开发了以污泥、餐厨垃圾等有机废弃物为原料，通过亚临界水溶解固体废弃物，再用MAP沉淀、收集溶解态磷的资源化装置（磷酸铵镁）法，最后用甲烷发酵法将溶解的有机物转化为沼气作为能源。然而，在亚临界水中，除了溶解废物的主要水解反应外，废物的热分解的副反应同时进行，形成气态物质和焦油和焦油物质，这些物质成为亚临界水设备堵塞的原因。本研究的目的是（1）阐明副反应的机理，并建立其预防方法，（2）设计资源回收工厂，使该技术商业化，并制定工厂的操作说明。研究结果（1）根据模型物质的实验结果，概述了有机物热分解的机理。氢氧化钠的加入被认为是有效的抑制热分解的方法。(2)确定了抑制污泥和餐厨垃圾热分解的最佳操作条件：氢氧化钠投加量和亚临界水温。(3)对资源回收厂进行了初步设计，并制定了操作规程。(4)通过对能量和磷的资源回收效率以及装置的性价比进行评价，验证了该技术商业化的可能性。今后将与国内环保相关装置厂商合作，以亚临界水处理为核心技术，以有机废弃物资源回收装置的利用和推广为目标。

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.