JPS59228993A - High-degree treatment of biological treating water - Google Patents

Abstract

PURPOSE:To treat the biological treating water with a high degree without increasing the output of sludge by adding slaked lime to the biological treating water to insolubilize phosphoric acid ions in the water, then adding an inorganic flocculant, and separating the formed flocs from liquid. CONSTITUTION:Slaked lime is added to the biological treating water to insolubilize phosphoric acid ions. Since most of the phosphor compds. are converted into orthophosphoric acid by biological treatment, the addition of slaked lime to the original water after biological treatment is highly effective to insolubilization. At that time, the decrease in pH due to nitration can be prevented by adding the slaked lime into an aeration tank. Then an inorganic flocculant such as aluminum sulfate is added, and the formed flocks are separated from liquid by precipitation floating, centrifugation, etc. On that occasion, the separation effect can be improved by adding a flocculant such as polyacrylamide or its partially hydrolyzed substance, and polyacrylic acid sodium to make the flocs coarser.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for more advanced treatment of biologically treated water such as human waste, sewage or industrial wastewater.

Traditionally, biologically treated water has been subjected to flocculation treatment by adding coagulants such as aluminum salts and iron salts to remove phosphorus and reduce COD.
, the chromaticity is reduced. Alternatively, after this coagulation treatment, adsorption treatment using activated carbon is performed to further reduce COD. Since this adsorption treatment is expensive to operate, there is a need for improvements in the pre-treatment flocculation treatment in order to reduce the load placed on the adsorption treatment. If an attempt was made to increase the coagulation effect by increasing the amount of coagulant added, there were problems such as an increase in the cost of the agent and an increase in the amount of sludge generated.

An object of the present invention is to provide an excellent flocculation treatment method for highly treating biologically treated water without increasing the cost of chemicals or the amount of sludge generated.

That is, the present invention provides an advanced method for biologically treated water characterized by adding slaked lime to the biologically treated water to insolubilize phosphate ions in the water, and then adding an inorganic coagulant to separate the generated flocs into solid and liquid. It is a processing method.

In the present invention, the biologically treated water may be a mixed liquid in an aeration tank in activated sludge treatment, or it may be the above-mentioned water obtained by separating sludge from the mixed liquid. Further, treated water obtained by a method of biologically treating wastewater, such as a spray hearth method or a rotating disk method, is also a target of the present invention.

In the present invention, slaked lime is first added to biologically treated water to insolubilize phosphate ions. Most of the phosphorus compounds are converted into orthophosphoric acid through biological treatment, so adding slaked lime to raw water after biological treatment has a large insolubilization effect. In addition, when added to the aeration tank, it is possible to prevent the pH of the mixed solution from decreasing due to nitrification, and to insolubilize the generated phosphate ions. The amount of slaked lime to be added depends on the concentration of phosphate ions and the pH buffering properties of the biologically treated water, but as a guide, slaked lime should be added in an amount of 1 to 3 times the amount of phosphorus in terms of calcium.

The pH is preferably 7 or more, preferably about 9. After insolubilizing the phosphate ions, an inorganic coagulant is then added, either with or without solid-liquid separation.

Inorganic coagulants include aluminum sulfate, aluminum chloride,
Polyaluminum chloride, ferrous sulfate, ferric sulfate, ferric chloride, polyferric sulfate, etc. can be used. Among these inorganic coagulants, iron salts are preferred because they are inexpensive and highly effective.

When an inorganic coagulant is added to biologically treated water after phosphate ions are insolubilized, the COD removal effect is better than when phosphate ions are not insolubilized. The reason is unknown, but inorganic coagulants.

In order to give priority to the removal of phosphate ions over the removal of COD and chromaticity, by insolubilizing phosphate ions in advance, when the Fe''/P ratio increases, an inorganic coagulant that contributes to the removal of COD and chromaticity It is expected that the proportion of

When adding a coagulant, adjust the pH of the biologically treated water with insolubilized phosphate ions to a pH suitable for the coagulating action of the coagulant.
Adjust to. If the pH is acidic, the insolubilized calcium phosphate may be redissolved, so in such a case, it is necessary to remove the insolubilized material before adding the coagulant.

The flocs generated by adding a coagulant can be separated by precipitation, flotation, centrifugation, filtration, etc.

Separate by known solid-liquid separation means. In this case, polyacrylamide or its partially hydrolyzed product.

It is preferable to add a known flocculant such as sodium polyacrylate to coarsen the flocs, as separation efficiency is improved.

According to the present invention, in the condensation treatment of biologically treated water, a part of the liquid mixture in the aeration tank of a human waste treatment plant, which is operated without dilution, is extracted, and 2000 q/i of slaked lime is added to it.
After adding and stirring for 10 minutes, centrifugation was performed, and ferric chloride was added to the supernatant to perform flocculation treatment to remove CODMfl. The results are shown in Table 2. For comparison, a case where slaked lime was not added to the mixed solution and ferric chloride was added to the supernatant obtained by centrifugation is also shown. In addition, after adding ferric chloride, the pH was adjusted to 4.5.

Table 2 It can also be seen from Table 2 that if the phosphate ions in the raw water are insolubilized and removed, the CODM11 removal effect is better than in the case where they are not insolubilized, and the amount of Fe01g added can be reduced. Note that the CODMn removal limit value was considered to be about 320 to 330.

Applicant: Kurita Industries Co., Ltd.

Claims (1)

[Claims] An advanced treatment method for biologically treated water, which is characterized by adding slaked lime to the biologically treated water to insolubilize phosphate ions in the water, and then adding an inorganic coagulant to separate the generated flocs from the same liquid.