JPH02164493A - Dephosphorization of waste water - Google Patents

Abstract

PURPOSE:To dephosphorize waste water with high efficiency by adjusting pH to a specific numerical value over two stages in order to insolubilize phosphorus to convert phosphorus to crystals having good separability. CONSTITUTION:Raw waste water is mixed with the phosphorus insolubilized matter- containing slurry returned through a line 8 in a dissolving tank and the waste water enhanced in the concn. of soluble phosphorus is mixed with the aqueous slaked lime solution supplied from a lime 6 in a slurry crystallizing reaction tank 2 to form the phosphorus insolubilized matter-containing slurry. At this time, the pH of said slurry is adjusted to 6.5-7.0 in the first stage adjusting chamber 2A of the slurry crystallizing reaction tank 2 to form crystals so that about 90% of the total production amount thereof is good in compactness and the pH of the slurry is adjusted to 8.0-8.5 in the second stage adjusting chamber 2B of said reaction tank 2 to perfectly crystallize the remaining phosphorus. Next, the phosphorus insolubilized matter-containing slurry is sent to a membrane separation apparatus 4 through a recirculation tank 3 and water is filtered and separated to enhance the concn. of the slurry while the greater part of the concn. slurry is returned to the recirculation tank 3 from a line 8 and a part of said slurry is returned to the dissolving tank 1. Treated water is sent to a pH adjusting tower 9 through a line 10 to be neutralized by carbon dioxide in waste water.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a method for removing phosphorus from wastewater.

[Prior art]

As a method for removing phosphorus from wastewater, aluminum salts, iron salts, calcium salts, etc. are added to insolubilize the phosphorus component and separate it into a solid-liquid state. The resulting insolubilized products include aluminum phosphate, iron phosphate, hydroxyapatite, aluminum hydroxide, iron hydroxide, and calcium hydroxide, all of which have low crystal compaction properties and poor solid-liquid separation and dehydration properties. The problem was that it was bad.

Regarding wastewater containing low concentration of phosphorus, a crystallization filtration type dephosphorization method filled with phosphate rock etc. as a seed crystal is known, but this method is used to treat wastewater with a low concentration of several -P/Q. It is effective for P/Q concentration of several tens or hundreds of
In systems where calcium is present, insolubilization occurs rapidly;
This results in a gel-like precipitate with poor dehydration properties, and since the amount of precipitate is large, crystallization filtration has a high load and cannot be put to practical use.

In order to reduce the load on crystallization filtration, a precipitation tank is provided as a pretreatment for crystallization filtration (after insolubilization by adding calcium salts), which reduces the differential pressure during crystallization filtration and lengthens the filtration duration. It is effective because it can be done. The hydroxyapatite obtained in the sedimentation tank is a gel-like precipitate with low compaction and poor separability, and a flocculant for sedimentation is required for solid-liquid separation.

〔the purpose〕

An object of the present invention is to dephosphorize wastewater with high efficiency by converting phosphorus in wastewater into crystals with good separability.

〔composition〕

The present invention was developed as a result of studying the properties of the precipitate generated by the reaction between phosphate ions and calcium ions.
．． We focused on the phenomenon that when the temperature is 8.0 to 8.5, the phosphorus removal rate improves, but the compactability of the precipitate is poor. It was done by

That is, the present invention provides a method of adding a calcium compound to phosphorus-containing wastewater to insolubilize the phosphorus, and then performing solid-liquid separation to remove phosphorus from the wastewater.6. First stage adjustment to adjust to 5 to 7.0,
This is then characterized by performing the two-stage GM (2) consisting of a second-stage adjustment in which the field is adjusted to 8.5 to 8.5.

Usually, about 90% (by volume) of the total amount of crystals is produced in the first stage adjustment, and the remainder is completely crystallized in the second stage adjustment. In this way, the precipitate as a whole not only has excellent compaction properties, but also has a satisfactory phosphorus removal rate. In the first stage adjustment, 6.
If it is less than 0, the phosphorus removal rate will be as low as 70%, and as a result, the proportion of poorly compacted crystals produced in the second stage adjustment will increase, resulting in crystals with poor separability as a whole.

Examples of the calcium compound include calcium hydroxide, calcium oxide, calcium chloride, and the like.

It can also be used as an alkalizing agent for tone plates.

Examples include sodium hydroxide and calcium hydroxide. Preferably, the preparation of the rice field is carried out in the presence of seed crystals, thereby promoting the progress of precipitation. The seed crystals are crystals and bone char produced in the system after the second adjustment tank.

Phosphate rock etc. can be given.

The solid-liquid separation means may be a normal solid-liquid separation method such as a coagulation sedimentation method or a filter press, or UF,
A membrane filtration method using a membrane module such as MF or RO may be used, and there are no particular limitations.

The present invention can be applied to any wastewater containing phosphorus. It can be applied to human waste treatment liquid, textile dyeing wastewater, etc., but it is especially applicable to phosphorus fertilizer manufacturing factory wastewater, highly concentrated organic wastewater,
The present invention is extremely effective for treated wastewater from a wet oxidation treatment method (Zimmerman method), which is a treatment method for organic sludge.

The Zimmermann method and its improved method (for example,
No. 42391, Special Publication No. 59-49073, etc.), air (oxygen) is blown into waste water under high temperature and pressure to reduce COD.
Although the components and NH, -N (ammonium nitrogen) are efficiently oxidized and decomposed, phosphorus is oxidized and remains in the form of phosphate ions. Therefore, wastewater treated by the Zimmerman method and the like contains phosphorus and requires a phosphorus removal process.

The present invention will be explained with reference to the drawings.

FIG. 1 shows one embodiment of the present invention. Reference numeral 1 denotes a dissolution tank provided as necessary, to which raw wastewater is supplied from line 7.

On the other hand, Linnaeus solubilized slurry is supplied through line 8, mixed with raw wastewater and dissolved in dissolution tank 1. In the dissolution tank, the Linnaeus solubilized slurry is usually dissolved by the acidity of the raw water, but in the case of wastewater with low acidity, a mineral acid may be added to the raw water and/or the Linnaeus solubilized slurry for dissolution. The amount of slurry to be added to the dissolution tank varies depending on the acidity of the raw water, but in the case of a wet catalytic oxidation solution for human waste, approximately 1f(, S, p40.01moQ/rrr) may be added to the raw human waste solution. , its phosphorus dissolving power is 1000-2000
Since the amount is about mg-5s/Q, it is desirable to add 2000 s/Q or more, and even if it is added in excess, the unreacted crystals promote the action of seed crystals, so there is no negative effect on membrane permeability.

The phosphorus concentration upon exiting the dissolution tank is preferably 130 mg.
-P/ρ or more, more preferably 300-270 or more. The waste water whose soluble phosphorus concentration has been changed in this way is mixed with the slaked lime aqueous solution supplied from the line 6 in the slurry crystallization reaction tank 2. C through dissolution tank 1
In the production of hydroxyapatite by the reaction between a calcium compound such as a(OH)2 and phosphate ions, a first stage adjustment chamber 2A that adjusts the output of the reaction tank 2 to 6.5 to 7.0;
It consists of a second stage adjustment chamber 2B that adjusts the temperature to 8.0 to 8.5.

The slurry leaving the circulation tank 3 is sent to the membrane separator 4 by a pump. The membrane separator passes the slurry through a number of tubular filters, the water is drained through the tube wall made of filter material, the slurry is concentrated, and most of the slurry is passed through line 8 into the circulation tank. 3 and a portion is returned to the dissolution tank 1. The treated water is sent to the field adjustment tower 9 via a line 10 in order to be neutralized with carbon dioxide gas in the exhaust gas.Normally, the exhaust gas generated from a wet catalytic oxidation tower for human waste contains carbon dioxide produced by oxidizing organic matter in the wastewater. Since it contains a large amount of carbon dioxide, it is advantageous to use it as a southern neutralizing agent.

Note that the Linnaeus solubilized slurry supplied to the dissolution tank 1 may be returned from the membrane separation device 4 or may be returned from the circulation tank 3.

〔Example〕

(1) Wet catalytic oxidation treatment liquid for human urine jT-P 320mg
/Q.

5S100■/Q field 1.5, TOC9■/Q, T-N
6mg/Q), the following method of adding Ca(OH)■
~ ■ Ca(OH) at a concentration of 100 g/fl under the conditions of T
About 1.5 times the equivalent of -P was added, and the mixture was stirred for 5 minutes at 1100 rpm with a stirrer while maintaining a predetermined field.

Next, the reaction solution was transferred to a meter module made of a porous polypropylene tube (pore size 0.2 μm) with an inner diameter of 5.5 mm at an average pressure of 0, 8 kg/as'' and a membrane surface flow rate of 1.5 m/s.
The amount of permeated water and T-P in the permeated water were measured.

In addition, the compactability of the precipitate in the solution after addition of Ca(Of()) was evaluated by measuring the sludge volume after standing for 30 minutes.

(2) Ca(OH)z addition method (3) Results (Comparing Control Example 4 and the present invention, the effects of the present invention are obvious.) [Effects] The present invention has the advantage that the precipitate does not interact with water. Because of its excellent separability, the amount of sludge generated is small, and when membrane separation is used as a solid-liquid separation method, the amount of water permeated through the membrane is large and stable. Even when a filter press method or the like is used as a solid-liquid separation method, the cake has excellent dehydration properties.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. Patent applicant: Osaka Gas Co., Ltd., 1 other agent: Patent attorney, Sa 1) Moriyu External bitemperature 1) Capacity of precipitate after standing for 30 minutes

Claims (1)

[Claims] 1. Adding calcium compounds to wastewater containing phosphorus,
In the method of removing phosphorus from wastewater by solid-liquid separation after insolubilizing phosphorus, the pH is set to 6 to insolubilize the phosphorus.
．． In wastewater, the pH is adjusted in two stages, consisting of a first stage adjustment to adjust the pH to 5 to 7.0, and a second stage adjustment to adjust the pH to 8.0 to 8.5. How to remove phosphorus.