Method and apparatus for treating organic waste water

#The present invention relates to an apparatus for discharging an organic sludge, in particular to a method and an apparatus for treating, by biological digestion, organic wastes containing organic sludge discharged from a sewage treatment process, such as a sewage treatment plant, a night soil treatment plant, and the like, and from a manufacturing process, such as a food factory, a chemical factory, and the like.

#Conventionally, an aerobic biological treatment method, which is referred to as an activated sludge method, has been used to treat organic waste water. This method is carried out as shown in FIG. 8, wherein organic waste water, such as sewage, introduced from organic waste water reservoir 1 into biological treatment tank 3 is decomposed into an inorganic matter, such as carbon dioxide or water, under aerobic conditions in biological treatment tank 3 by biological oxidation, which is oxidative decomposition performed by a microorganism. The waste water which has been treated in the biological treatment tank 3 is solid-liquid separated into treated water C and sludge D in precipitation tank 5. In general, a portion of sludge D is returned as a microorganism source to biological treatment tank 3, and the residual sludge is treated as an excess sludge E.

#In this case, however, precipitated and concentrated sludge containing an organic solid, which has been solid-liquid separated in the precipitation tank 5, is treated through the steps of concentration, digestion, dehydration, composting, and incineration. Such a treatment is not preferred because it requires a large quantity of labor, time, and expense.

#FIG. 1 is a structural diagram schematically showing an apparatus for treating an organic waste water suitable for executing a method of treating an organic waste water according to an embodiment of the present invention;

#FIG. 2 is a structural diagram schematically showing an apparatus for treating an organic waste water suitable for executing a method of treating an organic waste water according to another embodiment of the present invention;

#FIG. 3 is a structural diagram schematically showing an apparatus for treating an organic waste water according to the prior art;

#A first aspect of the present invention is directed to a method of biologically treating an organic waste water which comprises the steps of biologically treating the organic waste water by a biological treatment device, solid-liquid separating the waste water treated by the biological treatment device into treated water and a sludge by a solid-liquid separation device, returning a portion of the sludge separated by the solid-liquid separation device to the biological treatment device, concentrating at least a portion of a residual sludge by a concentration device, and solubilizing the concentrated sludge by thermophilic bacteria in a solubilizing tank. According to this method, at least a portion of the sludge separated by the solid-liquid separation device is concentrated by the concentration device, and then directed to the solubilizing tank. Therefore, it is possible to ensure the nutritive conditions suitable for growth of thermophilic bacteria, and attain a high solubilization ratio by the production of a solubilizing enzyme. Further, since at least a portion of the sludge is concentrated and then sent to the solubilizing tank, the quantity of the treated sludge sent to the solubilizing tank is decreased such that the size of the solubilizing tank can be reduced.

#A second aspect of the present invention is directed to a method of treating an organic waste water according to the first aspect of the present invention, wherein at least a portion of the treated liquid solubilized by the solubilizing tank is returned to the biological treatment device. Consequently, the solubilized treated liquid is biologically digested in the biological treatment device simultaneously with the decrease of the sludge.

#A third aspect of the present invention is directed to a method of biologically treating an organic waste water which comprises the steps of biologically treating the organic waste water by a biological treatment device, solid-liquid separating the waste water treated by the biological treatment device into treated water and a sludge by a solid-liquid separation device, concentrating the sludge separated by the solid-liquid separation device in a concentration device, returning a portion of the sludge to the biological treatment device, and solubilizing at least a portion of a residual sludge by thermophilic bacteria in a solubilizing tank. According to this method, all the sludge separated by the solid-liquid separation device is concentrated, and a portion of the concentrated sludge is directed to the solubilizing tank. Therefore, the following advantages can be obtained in addition to the advantage that a high solubilization ratio can be ensured and the size of the solubilizing tank can be reduced in the same manner as in the first aspect of the present invention. More specifically, a portion of the sludge separated by the solid-liquid separation device is concentrated and then directed to the biological treatment device. Therefore, the quantity of microorganisms in the biological treatment device is increased more than in the first aspect of the present invention. Consequently, the quantity of microorganisms in the biological treatment device can be kept at a high concentration, and an organic matter is fully decomposed by the microorganisms. As a result, the sludge load is reduced such that the quality of treated water can advantageously be improved.