Yoshiaki Harada* and Kenichi Yamasaki*

* Reseach & Development CenterOsaka Gas Co., Ltd.

+ Correspondence should be addressed to Yoshiaki Harada:
(6-19-9 Torishima, Konohana, Osaka 554 Japan)

Abstract

This paper describes study results of applicabilites of the catalytic wet-oxidation process (CWOP), which is an advance treatment technique of sewage sludge. Here is an outline of research results: (1) The CWOP can handle concentrated sludge in liquid phase without adding any dewatering or drying steps which have been needed in the still widely used incineration disposal and other methods. (2) The CWOP can treat almost all organic substances and nitrogen compounds in sludge under the reaction conditions of 280*C[Celsius degeree], 9.12MPa and 1.5hr. (3) The sludge is made soluble first and then low-molecular. It turns carboxylic acids and aldehydes, and finally becomes carbon dioxide and water. (4) The treatment efficiency of organic substances and nitrogen compounds is little affected by fluctuations of the initial reaction pH and air feed ratio. (5) There is no large difference in the treatment efficiency of components between different types of sludge. (6) A trial calculation of heat balance in the CWOP shows that about 70% of the heat of the reaction (thermal energy) through decomposition of organic substances and nitrogen compounds in the sludge is expected to be recovered.(7) The CWOP still has some problems to be solved. One is to find optimum intervals of chemical cleaning to eliminate from the reaction system metallic oxide deposits which are caused through a long-term continuous run. The other is to evaluate the durability of catalyst in the course of treatment run.

Key words: Sewage sludge, catalytic wet-oxidation process, COD, ammonia, heat balance