JPS5933000A - Dehydration of digested night soil sludge - Google Patents

Abstract

PURPOSE:To contrive to improve the efficiency of dehydration, while inhibiting the increase of sludge in volume, by prewashing digested night soil sludge with water to reduce the content of alkali components, in advance of pH-adjusting, freeze-thawing and dehydrating said sludge. CONSTITUTION:Digested sludge (a) formed by the aerobic or anaerobic treatment of night soil is washed with washing water (b) pref. in an amount of 2, more pref. 4, or more times the digested sludge at a water-washing site 11. Thereafter, the sludge washed with water is thickened by precipitation-separation at a precipitating site 12 and further thickened to a concentration of about 6-8% in terms of solid matter at a centrifugal thickening site 13. The pH of the conc. sludge is then adjusted using an acid such as sulfuric one or an acidic flocculant such as ferric chloride at a pH-adjusting site 1. Hereon, the increase of sludge in volume caused by the formation of CO2 is eliminated, since alkali components such as bicarbonate are previously removed by the washing with water. Thereafter, the sludge is carried through a freeze-thawing site 2 to a dehydrating site 3 and separated therein into an effluent (c) and dehydrated cake (d).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dehydrating digested human waste sludge, and more specifically, to a method for dehydrating digested sludge produced by aerobic or anaerobic digestion of human waste.

A conventional processing method of this type will be explained with reference to FIG. Aerobic or anaerobic digested sludge from human waste is concentrated using a centrifugal concentrator to reduce the energy required in the freeze-thaw process, and then the pH is adjusted using an acid such as sulfuric acid or an acidic flocculant such as ferric chloride. After being carried out in the pH adjustment section 1, it is frozen and thawed in the freezing and thawing section 2,
Improves dehydration. The sludge with improved dewatering properties was dehydrated in the dewatering section 3, and separated into a dehydrated cake and a desorbed liquid.

However, according to the above conventional method, the alkalinity component mainly consisting of bicarbonate and carbonate in the digested sludge reacts with acid to generate carbon dioxide gas, and this carbon dioxide gas is dispersed in the sludge. do. Therefore, there were disadvantages such as an increase in the apparent sludge volume, a decrease in the actual throughput in the freeze-thaw treatment, and a decrease in the effect of the freeze-thaw treatment.

This invention aims to eliminate the drawbacks of the conventional methods as described above, and it suppresses the generation of carbon dioxide gas by washing the human waste digested sludge with water in advance to reduce the alkalinity component. The object of the present invention is to provide a method for dehydrating human waste digested sludge with improved freezing treatment effect.

An embodiment of the present invention will be described below with reference to FIG. In the figure, a conventional pH adjustment section 1 is preceded by a water washing section 1 for digested sludge, and a settling section 12 for concentrating the washed sludge.
The sludge concentrated by sedimentation is further concentrated by a centrifugal concentration section 13. This will be explained in detail in the case of aerobic digestion sludge.

The aerobically digested sludge is first washed in the washing section 11 with water at least twice the amount of sludge, preferably at least four times the amount of the sludge. The table below shows the water washing dilution factor in this case, the amount of gas generated when the pH was adjusted to 2.5 with sulfuric acid, and the value of the filtration specific resistance after freezing treatment.

As can be seen from this table, the amount of gas generated was reduced by 75% when the dilution factor was 2 times or more, and when the dilution factor was 4 times or more, the amount of gas generated was zero and the filtration specific resistance was also reduced by 85%.

The sludge thus washed with water in the water washing section 11 is then concentrated in the sedimentation section 12 by separating the sediment, and further concentrated in the centrifugal concentration section 13 to a solid content concentration of 4 to 8%. The thickened sludge is then first treated according to conventional procedures.

That is, the pH is adjusted with sulfuric acid or the like in a pH adjustment section 1, and the material is sent to a freeze-thaw section 2 where it is frozen to improve its dehydration properties, and then dehydrated in a dehydration section 3.

In the above embodiment, sulfuric acid was used as the acid in the pH adjusting section 1, but any acid such as hydrochloric acid, ferric chloride, or any other acid that can adjust the pH to a predetermined value may be used.

Furthermore, the precipitation section 12 may be removed and the product may be directly concentrated in the centrifugal concentration section 13.

As described above, according to the present invention, by washing the digested sludge with water before pH adjustment, the alkalinity can be reduced, gas generation can be significantly suppressed, and the freeze-thaw treatment effect can be improved.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of a conventional method, and FIG. 2 is a flowchart of an embodiment of the present invention. 1. pH adjustment section, 2. Freeze-thaw section, 3. Dehydration section,
11..Water washing section, 12..Sedimentation section, 13..Centrifugal concentration section. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) In the dehydration treatment of digested sludge produced by aerobic and anaerobic digestion of human waste, the digested sludge is washed with water, and then the pH is adjusted with an acid such as sulfuric acid or a flocculant such as ferric chloride. A method for dewatering digested human waste sludge, which is characterized in that the dehydration treatment is performed after the dewatering property is improved by freeze-thawing treatment. (2) The method for dehydrating human waste digested sludge according to claim 1, wherein water in an amount twice or more of the amount of digested sludge is used in washing with water. (3) The method for dewatering human waste digested sludge according to claim 1, wherein the pH is adjusted after the water-washed digested sludge is concentrated in a concentration section.