JPS5857995B2 - How to remove phosphates from liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing phosphates present in tap water, sewage, human waste water, industrial water, factory wastewater, boiler water, and all other liquids.

Generally, in the various liquids mentioned above that are discharged into natural water systems, inorganic phosphates such as orthophosphates, various condensed phosphates, and organic phosphates exist in various states. The presence of phosphates is a factor that induces the occurrence of "oto" and "red tide" in closed or stagnant waters such as lakes, inland seas, and inner bays, and when water is used for various purposes, biological substances may be present in equipment and piping. This results in the generation of chemical slime and the formation of chemical scale, which is a major cause of accidents.

Therefore, in order to remove the phosphates present in these liquids, various phosphorus removal methods are being considered, and representative ones include biological treatment, ion exchange resin method, and chemical coagulation and precipitation. Laws, etc. can be mentioned, but among these,
The chemical coagulation-sedimentation method is currently regarded as a somewhat completed treatment technology, and treatment equipment on an actual treatment scale is already in operation in many places.

The removal of phosphates by this chemical flocculation treatment is a method in which phosphates present in the liquid are removed as insoluble phosphates by adding a specific flocculant, and the flocculant is usually Slaked lime (Ca(OH)2), aluminum sulfate [A12(SO4)2], ferric chloride (FeCls), and the like are used.

However, the biggest drawback of the chemical flocculant-sedimentation method is that it generally requires a large amount of flocculant and the processing cost is high, regardless of the type of flocculant used.

■ A large amount of sludge is generated in proportion to the amount of medicine injected, and the settling and thickening properties of this sludge are extremely poor ※※ (Lime sludge is an exception) ■ Furthermore, this sludge has poor dewatering properties (Lime sludge (Exception), and because it requires a dog sludge treatment facility and processing costs, it has many problems in practical use, even though it is a current technology.

In addition, the inventors of the present invention have proposed a novel treatment method in which a cylindrical or cone-shaped dephosphorization tower is filled with phosphate minerals containing calcium phosphate having a certain particle size, and the pH of the liquid to be treated is lowered to 6. - 11, and then add a calcium agent such as calcium chloride in accordance with the temperature of the soluble phosphates contained in the liquid to be treated, and allow the mixture to pass through and come into contact with it at a constant flow rate. A method of removing soluble phosphates by crystallizing and fixing calcium hydroxyapatite crystals on the surface of filled phosphate minerals has also been proposed.

In this case, typical chemical reactions on the phosphate mineral surface are as follows.

By applying this new dephosphorization method, it is extremely easy to separate and dehydrate phosphate minerals to which calcium hydroxyapatite is fixed, and compared to so-called flocculated sludge using the conventional chemical flocculation sedimentation method, it requires less concentration equipment. It is an excellent dephosphorization technology that not only does not require conventional sludge treatment facilities such as dehydrators and drying equipment, but also can recover phosphorus as a resource.

However, in this new catalytic dephosphorization method, soluble phosphates contained in the liquid are fixed as calcium hydroxyapatite (Ca5(OH)(PO4)s) crystals under appropriate pH conditions. CaCl2, Ca(OH)a, etc. are added as calcium agents, but
When an alkalinity component is contained in the liquid to be treated, calcium carbonate is produced according to the reaction formula shown below.

This calcium carbonate is not produced because the apatite production rate is higher than the calcium carbonate production rate if the pH of the liquid is in the pH range suitable for calcium hydroxyapatite production or is adjusted. However, complete pH control is difficult in actual processing equipment, and if the alkalinity component is concentrated, it is inevitable that the reaction of formula (2) will proceed to some extent the moment the calcium agent is added.

Although the amount of calcium carbonate crystals produced under such conditions is extremely small, over a long period of time, the calcium carbonate crystals gradually grow fixedly on the surface of the phosphate mineral.

As a result, the surface activity of the phosphate mineral deteriorates, the dephosphorization function decreases, and no dephosphorization effect can be expected at first.

As described above, the post-contact phosphorus method has limited applicability to liquids that contain large amounts of alkalinity components and also soluble phosphates, but it is possible to reduce the alkalinity components by some method. If removed, the scope of application of the catalytic dephosphorization method will be expanded.

and a conventional method for removing the M-alkalinity component in the liquid;
In other words, softening methods include biological methods (biological nitrification method or biological nitrification, denitrification method, but only applicable when the liquid contains nitrogen components) and chemical or physicochemical methods. Although biological methods are capable of effectively removing N-alkalinity components, they require treatment facilities such as dogs, and operation management is not always easy.

On the other hand, chemical or physicochemical methods require agents to remove M-alkalinity components, and depending on the method, a large amount of sludge is generated, but M-alkalinity can be easily removed using simple treatment facilities and simple methods. - It is commonly adopted as a water treatment technology because it can remove alkalinity components.

The biggest drawback of biological methods is that they cannot be applied unless the wastewater to be treated contains nitrogen compounds (preferably NH4-N), whereas chemical or physicochemical methods cannot be applied. It has the advantage that it can be applied to any kind of wastewater and the effect of removing M-alkalinity components is reliable.

The main chemical or physicochemical methods include a stripping method under liquid acidity and a softening method by adding Ca(OH)2 (a type of coagulation-sedimentation treatment).

The former method of stripping under acidic conditions involves adding acid to the liquid to be treated, setting the pH of the liquid to a range of 3 to 6 depending on the degree of the M-alkalinity component to be removed, and then stripping under acidic conditions. In this method, the resulting liquid is introduced into a stripping device to diffuse the M-alkalinity component into the atmosphere.

The latter softening method by adding Ca(OH)2 is a method in which Ca(OH)2 corresponding to the M-alkalinity component in the liquid is added to the liquid, and the M-alkalinity component is removed as a precipitate of CaCO3. The CacO3 precipitate is concentrated using a thickener and then taken out of the treatment system.

An object of the present invention is to provide a method for efficiently and stably removing phosphates over a long period of time from a liquid containing squid phosphates and an M-alkalinity component while maintaining the above-mentioned advantages. It is.

Another object of the present invention is to eliminate various drawbacks of conventional methods, to economically obtain treated water of extremely high quality with extremely simple operations, and to significantly reduce treatment equipment and treatment costs. The aim is to create an effective method that can be used to measure

The present invention removes M-alkalinity components in the liquid to be treated as much as possible by chemical or physicochemical treatment, and then removes phosphate minerals containing calcium phosphate having a certain particle size, such as from Jordan. From Florida, from Mexico, from Canada, from Kurokura, Kanagawa Prefecture, from Ashio Copper Mine, Tochigi Prefecture, from Yoron Island,
It is characterized by contacting by passing the liquid through a packed tower filled with phosphate rock from Nagatari, Fukuoka Prefecture, Inuku Mine, Hokkaido, etc., and prevents the reduction of the catalytic dephosphorization effect due to the M-alkalinity component in the liquid. It is something to do.

An embodiment of the present invention will be described with reference to the drawings. For example, BOD 100OO~14000 I/LT-N (total nitrogen) 4000~5000 In9/l -po2 800
~120011t971! , M-alkalinity component 800
The target raw water is 0 to 12,000 instant/l, and after removing coarse solids and other impurities through appropriate pretreatment, this raw water is diluted appropriately (about 10 times) as necessary, and then processed using the activated sludge method. Processed by

In the illustrated example, the water treated by the activated sludge method (secondary treated water) is introduced into the M-alkalinity component removal device 2 from the secondary treated water inflow pipe 1.

As mentioned above, this M-alkalinity component removal device 2 may be carried out using either a chemical or physicochemical method, that is, an acid stripping method or a Ca(OH)2 addition method, or a combination of both methods. Good too.

The secondary treated water that has undergone the M-alkalinity component removal process in the M-alkalinity component removal device 2 is made by crushing and sieving phosphate minerals containing calcium phosphate to give a constant particle size. It is led to the catalytic dephosphorization step 3, which is filled with
Here, add an appropriate amount of acid or alkaline agent to adjust the pH condition to the optimum for the catalytic dephosphorization reaction, for example 6.0 to 11.0,
Further, a calcium agent such as calcium chloride is added to contact the phosphate mineral, and the dephosphorized treated water is discharged from the treated water outflow pipe 4.

In the catalytic dephosphorization process in which the secondary treated water is brought into contact with phosphate minerals, a packed tower filled with phosphate minerals containing calcium phosphate having a certain particle size is used as the dephosphorization tower. This method removes various phosphates present in the solution by passing the solution containing phosphates through the solution at a constant flow rate, and the pH of the solution is adjusted to the optimum pH for the chemical reaction for phosphorus removal. It is effective to adjust the range to 6.0 or higher, and further add an appropriate amount of calcium agent depending on the phosphate concentration in the liquid to be treated, so that the calcium agent flows into the packed tower in an ionic state. It is.

In this case, the pH value of the liquid to be treated needs to be set to 6.0 or higher, as the removal rate of phosphates decreases significantly on the acidic side. Contained metal hydroxides or insoluble carbonates may precipitate on the surface of the phosphate mineral in the packed tower and reduce its surface activity. is preferably adjusted within the range of 6.0 to 11.0, more preferably within the range of 8.8 to 9.2.

Furthermore, the calcium agent added is C3720
The calcium agent is added in a molar weight ratio of 1 to 20, and care must be taken at the injection point so that the calcium agent flows into the packed column in an ionic state.

Therefore, as an effective specific means, for example, it is preferable to inject it directly into a packed column or immediately before it.

Further, if necessary, in the catalytic dephosphorization step, a part of the effluent of the treated water can be directly circulated to the packed tower, or it can be returned to the raw water inflow pipe and passed through the packed tower.

As described above, the present invention efficiently and economically removes N-alkalinity components contained in a liquid by a chemical or physicochemical method, and furthermore, the present invention can stably and efficiently remove the N-alkalinity component contained in a liquid over a long period of time. In addition to being able to remove phosphates in the liquid, when contacting with phosphate minerals to remove phosphates in the liquid, it maintains appropriate pH conditions and removes calcium agents and concentrated soluble phosphates. The shortcomings of the conventional chemical coagulation-precipitation treatment method are overcome by an extremely simple operation in which the calcium agent is flowed into the catalytic dephosphorization tower in its ionic state without direct contact with the calcium agent, and phosphates in the liquid can be efficiently removed. It is easy to remove, operate, and perform stable processing, is suitable for large-scale processing, requires less site and equipment installation space, and can appropriately reduce processing equipment and processing costs.

Next, an example of the method of the present invention will be described.

The human waste from which the coarse solids have been separated is diluted in a range of 8 to 10 times, and this is treated using the conventional activated sludge method (sludge load O14 to 0.5 kg BOD/kg MLss + day, nitrification does not occur). Loading conditions) Then, add an appropriate amount of hydrochloric acid to this secondary treated water to adjust the pH of the liquid to a range of 4 to 5, and then aerate to release the M-alkalinity component in the liquid into the atmosphere in the form of free carbonate. It was dissipated into.

As a result of this treatment (de-M alkalinity component), the M-alkalinity component contained in the secondary treated water was reduced from 983 m9/l to 150-250 m9/l (CaC
(as O2).

Next, the pH of this was adjusted to 8.8 to 9.2 with an alkaline agent, and phosphate rock from Jordan was crushed and sieved to obtain a particle size of 0.42.
L in a catalytic dephosphorization reaction tank filled with ~0.54 mm
Water was passed at a rate of V207 rL/h.

Under these conditions, the phosphate rock is in a fluid state, and the secondary treated water that has passed through it comes into close contact with the phosphate rock, and calcium chloride is added to this fluid portion in proportion to the concentration of soluble phosphates. /PO4 was added so that the molar weight ratio was 1.0 to 1.5.

This experiment continued for about 4 months, and in order to check the deterioration of the activity of phosphate rock when water was passed for a long period of time, precise analysis was performed on the final treated water one week and three months after the start of operation.

The results are shown in Table 1, and according to the present invention, no reduction in the dephosphorization effect was observed either one week or three months after the start of water flow.

On the other hand, as a comparative example, the results were obtained by continuously passing water through the catalytic dephosphorization reaction tank for three months under the same water flow conditions without removing any M-alkalinity components from the activated sludge treated water (secondary treated water) of diluted human waste. As shown in Table 2, if the M-alkalinity component is not removed to an appropriate low concentration in advance, even if the dephosphorizing effect is noticeable at the beginning of water flow, calcium carbonate will appear on the surface of the phosphate rock after three months. was crystallized, or calcium carbonate was formed independently (as confirmed by microscopy and X-ray diffraction), and the dephosphorization effect was significantly deteriorated.

[Brief explanation of the drawing]

The drawing is a system explanatory diagram showing one embodiment of the present invention. 1... Treated water inflow pipe, 2... M-alkalinity component removal device, 3... Catalytic dephosphorization process,
4... Treated water outflow pipe.

Claims (1)

[Claims] 1. After the liquid to be treated is at least chemically or physicochemically treated to remove M-alkalinity components in the liquid as much as possible, the liquid is brought into contact with a phosphate mineral containing calcium phosphate. A method for removing phosphates from a liquid, the method comprising: 2. In the chemical treatment step, an acid is added to the liquid to be treated to adjust the pH of the liquid to a range of 3 to 6, and the acidified liquid is introduced into a stripping device to diffuse the M-alkalinity component into the atmosphere. A method for removing phosphates from a liquid according to claim 1. 3. Claim 2, wherein the physicochemical treatment step includes adding slaked lime corresponding to the M-alkalinity component in the liquid to be treated, and removing the M-alkalinity component as a precipitate of CaCO3. Method for removing phosphates from the liquid described in Section 1. 4. Claims 2 or 3, wherein the liquid to be treated is a liquid containing at least a nitrogen compound, and is diluted after coarse solids and other impurities have been removed in advance. Method for removing phosphates from the liquid described. 5 In the catalytic dephosphorization process in which the phosphate mineral is brought into contact, an acid or alkaline agent is added in advance to maintain an appropriate pH.
A method for removing phosphates from a liquid according to claim 2, 3, or 4, wherein the treatment is performed while maintaining the conditions. 6 A patent in which the pH of the liquid to be treated is adjusted to 6.0 to 11.0 when brought into contact with the phosphate mineral, a calcium agent is added, and the calcium agent is brought into contact with the phosphate mineral in an ionic state for treatment. A method for removing phosphates from a liquid according to claim 5. 7 The catalytic dephosphorization step is a process in which a calcium agent is added, and the calcium agent is added in a C87104 molar weight ratio of 1 to 20, and is brought into direct contact with concentrated soluble phosphates. 7. A method for removing phosphates from a liquid according to claim 5 or 6, wherein the method is performed by injecting the phosphates in the liquid.