JPH0675708B2 - Method for removing phosphorus from liquid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for removing phosphorus contained in domestic wastewater such as sewage and human waste, factory wastewater, and the like.

[Conventional technology]

In removing phosphorus in the liquid, a liquid containing phosphorus is added in the presence of calcium ions, and the granular material has a phosphorus removing ability.
For example, a method of contacting with phosphate rock, bone charcoal, MgO, slag, etc. is a known method established as a catalytic dephosphorization method. In this catalytic dephosphorization method, in order to accelerate the phosphorus removal reaction, it is known to remove a carbonate substance that inhibits the phosphorus removal reaction or to add F ion as a promoter.

[Problems to be Solved by the Invention]

However, sewage secondary treated water (usually 1-2 m as phosphorus)
When the catalytic dephosphorization method is applied to (containing g / l),
Even if decarbonation (removal of carbonic acid substances in the liquid) is carried out, the phosphorus concentration of the treated water is only 0.2 to 0.4 mg / l constantly, and if this treated water is reused as scenic water, algae will grow in the waterway. Breed.

In addition, even if F ions are added, the phosphorus concentration of the treated water is limited to 0.2 to 0.4 mg / l at most, and if a large amount is added, CaF ₂ precipitates and the amount of sludge generated increases. was there.

An object of the present invention is to solve the above-mentioned conventional problems in the catalytic dephosphorization method and to provide a method capable of achieving high phosphorus removal performance by an extremely simple operation.

[Means for Solving the Problems]

The present invention, in the catalytic dephosphorization method of removing phosphorus by contacting a liquid containing phosphorus in the presence of calcium ions, with a granular material having a phosphorus-removing ability, a salt solution is added to the liquid containing phosphorus. The method for removing phosphorus in a liquid is characterized in that the electrical conductivity of is adjusted to 2,000 μ / cm or more and then catalytic dephosphorization is performed.

[Action]

The operation of the present invention will be described with reference to the drawings showing the embodiment. In FIG. 1, for example, treated water (sewage secondary treated water) 1 obtained by treating sewage with activated sludge is introduced into a pretreatment step 2. In the pretreatment step 2, mineral acid is added to the sewage secondary treated water and air is blown in to remove (decarbonate) the carbonate substances in the liquid, and then nitric lime and Ca salt are added to perform the dephosphorization reaction. The Ca concentration and pH required for this are adjusted. Further, in this pretreatment step 2, a salt solution 7 is added, followed by a dephosphorization step 4
Adjust the electric conductivity of the liquid flowing in to 2,000 μ / cm or more. For example, normal sewage has an electric conductivity of 500 to 1,500 μ / cm, but it is adjusted to 2,000 μ / cm or more by adding the salt solution 7 in proportion to the flow rate, or in the pretreatment step 2 or It is also preferable to provide an electric conductivity meter in the flow path to the dephosphorization step 4 and operate in conjunction with a salt solution injection pump to maintain the value at 2,000 μ / cm or more.

NaCl, MgCl ₂ , Ba is used as a salt solution to enhance electrical conductivity.
A solution such as Cl ₂ or CaCl ₂ or seawater can be used,
Seawater is more preferred.

Next, the liquid whose electric conductivity is adjusted to 2,000 μ / cm or more is transferred to the dephosphorization process 4 in which the particulate matter having the phosphorus removal ability is filled after removing the suspended matter in the liquid in the sand filtration process 3. . In the dephosphorization step 4, calcium phosphate is crystallized on the granular material having a phosphorus removing ability to remove phosphorus in the liquid, and dephosphorized water can be obtained. Dephosphorization process 4
May be either an upward flow type or a downward flow type, and may be a fixed bed type or a fluidized bed type. As the granular material having a phosphorus removing ability, phosphorus ore, bone charcoal, light burned magnesia, converter slag, etc. can be used.

The salt solution 7 may be added not only in the pretreatment step 2 but also in any place before the dephosphorization step 4, but when seawater is used as the salt solution, the salt filtration step 3 is performed as in the illustrated example. If added before, turbidity and phosphorus in seawater can be removed together, which leads to purification of seawater.

FIG. 2 is an example of using the sand filtration / dephosphorization step 6 in which the sand filtration step 3 and the dephosphorization step 4 of FIG. 1 are integrated. The sand layer is at the bottom and the granular material having the phosphorus removing ability is at the top. The effluent from the pretreatment step 2 is allowed to pass through after being formed.

〔Example〕

Sulfuric acid was added to the secondary treated water containing sewage containing 2 mg / l of phosphorus, and p
Prepare the ones adjusted to H4.5 and the electrical conductivity adjusted to various predetermined values by adding seawater, and add CaCl ₂ solution (20,000 mg / l as Ca) to each to add Ca. Adjust to 60-70 mg / l and add more NaOH solution
The pH was set to 9.0.

On the other hand, in pure water containing 2 mg / l of phosphorus, CaCl ₂ solution was added to adjust Ca to 60 to 70 mg / l, and seawater was added to adjust the electrical conductivity to various predetermined values. Each Na
An OH solution was added to bring the pH to 9.0.

Put each of these liquids 1 in a beaker and add phosphorus ore to 1,000m.
After adding g / l and reacting for 1 hour, the phosphorus concentration of the supernatant water was measured to see the effect of electrical conductivity. These experimental results are the third
As shown in the figure, when the electric conductivity was 2,000 μ / cm or more, the phosphorus concentration of the supernatant water was significantly reduced.

The results of using a NaCl solution in place of seawater to adjust the electric conductivity are also shown in FIG. 3, and seawater was better than the NaCl solution in phosphorus removal performance.

〔The invention's effect〕

As described above, the present invention, in the catalytic dephosphorization method,
The phosphorus removal performance can be remarkably improved by the extremely simple operation of adjusting the electric conductivity of the liquid to be treated to 2,000 μ / cm or more by adding a salt solution.

[Brief description of drawings]

FIG. 1 and FIG. 2 are system explanatory diagrams each showing an embodiment of the present invention, and FIG. 3 is a diagram showing the relationship between the phosphorus concentration in supernatant water and the electrical conductivity in the experimental results. 1 ... sewage secondary treated water, 2 ... pretreatment process, 3 ... sand filtration process, 4 ... dephosphorization process, 5 ... dephosphorized water, 6 ...
... sand filtration / dephosphorization process, 7 ... salt solution.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Izumi Hirasawa 1-6-27 Konan, Minato-ku, Tokyo Ebara In Filco Co., Ltd. (72) Hiroshi Nakamura 1-6-27 Konan, Minato-ku, Tokyo Ebara Within Infilco Corporation

Claims (1)

[Claims] 1. In a catalytic dephosphorization method of removing phosphorus by contacting a liquid containing phosphorus with a granular material having a phosphorus removing ability in the presence of calcium ions, a salt solution is added to the liquid containing phosphorus. A method for removing phosphorus from a liquid, which comprises performing catalytic dephosphorization after adjusting the electrical conductivity of the liquid to 2,000 μ / cm or more.