JPH0811233B2 - Method for purifying eutrophied raw water - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating eutrophied raw water, and more particularly to a method suitable for treating raw water such as tap water or cleaning lakes, which can effectively remove phosphorus.

[0002]

2. Description of the Related Art In the treatment of tap water from eutrophic lakes and rivers, algae are abnormally generated, and the honeycomb method is adopted as a biofilm treatment for the removal of algae. It is used together with sand and anthracite filtration.

[0003] These algae have a fine particle size of 2 to 5 microns, and are usually in the form of communities with large flocs, as typified by blue-green algae (microcystis of the blue-green algae). It returns to particles and is difficult to filter with sand and anthracite. However, the porosity of the biofilm treatment using a honeycomb is too large, and it is difficult to efficiently recover the water-bloom even if the circulation treatment is performed. As a result, algae must be killed by increasing the amount of chlorine, resulting in the formation of highly carcinogenic trihalomethanes. In eutrophic lakes and rivers, BOD, COD,
The removal of SS and the like can be achieved to a certain extent by coagulation sedimentation and combined use of activated carbon and sand filtration, but it is difficult to treat a large amount of water at high speed at high performance and at low cost.

In such a case, according to the biofilm treatment with foamed plastic developed by the same applicant (see, for example, Japanese Patent Publication No. 63-85), sand filtration and standard activated sludge method are compared. As a result, it is possible to perform a processing process that is far superior in terms of processing speed and processing performance. However, with this method alone, it is difficult to achieve complete removal of fine particles and recovery of phosphorus at the same time as with water-bloom.

Therefore, the carrier particles in the floating layer of the foamed plastic have a diameter of 0.5 to 10 mm and have an irregular shape, and the porosity of the filter layer is 70 to 80%. At the same time, microfiltration is performed in an upward flow, and at the same time, a small amount (usually 1 to 5) is required for algae aggregation and phosphorus immobilization in water.
(mg / l) treatment by injecting inorganic coagulant such as aluminum chloride or iron coagulant not only effectively removes algae but also removes nitrogen and phosphorus absorbed in the body by algae. It is possible to recover and simultaneously recover orthophosphoric acid dissolved in water by immobilizing it as iron phosphate.

[0006] As a result, in the treatment of raw water in the tap water, algae can be completely recovered, pre-chlorine and medium-chlorine treatment steps can be eliminated, and the chlorine injection amount for final sterilization can be drastically reduced. As a result, the production of trihalomethane can be minimized.

In the case of lake purification, about 60% of nitrogen, about 75% of phosphorus and about 30% of TOC (organic carbon) can be removed by the complete removal of algae even after the one-pass treatment, and the removal should be repeated. As a result, 90% or more of phosphorus, which causes abnormal generation of algae, is removed, and once treated, the abnormal generation of algae can be prevented for about 3 years due to lack of phosphorus in the lake water.

The treatment speed at that time is as high as 20 m / H, and a large amount of water can be stably treated at low cost by adding a trace amount of a coagulant. Since the equipment is also capable of high-speed processing, it is not only compact and the rationalization of initial and running costs is greatly improved, but it is also possible to adsorb and remove trace toxic chemical substances (for example, trihalomethane, dioxins, organic phosphorus, etc.) by biofilm filtration. As the carrier used at this time, foamed plastic is suitable, but its properties and materials must be appropriately determined.

In the case of eutrophication raw water treatment, BO of raw water
The D, COD, and SS concentrations are also relatively low, and there is an assumption that a large amount of water must be treated at high speed. To this end, the carrier particles have a diameter of 0.5 to 15 mm, and the particle shape is indefinite from the viewpoint of maintaining the filtration performance and preventing clogging,
The porosity is also preferably maintained at 60 to 80%, and the upward flow treatment is more desirable for improving the filtration efficiency.

Furthermore, in order to immobilize oritriic acid eluted in water and promote aggregation of microalgae, it is preferable to inject 0.5 to 5 mg / l of an inorganic flocculant mainly composed of iron. Become. By satisfying these conditions, the eutrophication raw water can be efficiently and suitably treated. Iron-based flocculants and substitutes include ferric sulfate, ferrous chloride, ferric chloride, calcium carbonate, magnesium salt, polysulfuric acid,
Examples include ferric hydroxide (polyiron), aluminum sulfate, and polyaluminum chloride.

In these eutrophic raw waters, carbonic acid assimilation by algae is prominent, PH is 8 to 9 and dissolved oxygen is 10 to 10.
As high as 15, there is no need to aerate even with biofilm treatment. Therefore, it is necessary to appropriately determine the filter medium in order to improve the biofilm filtration performance. However, in the upstream river water where algae are rarely generated, dissolved oxygen is also low, so that aeration is required.

From such a viewpoint, the present inventor considers that the limitation of phosphorus is the most important point in the eutrophication prevention measures, and the standards should be adjusted to the complete recovery of algae and the immobilization of phosphorus. I got the knowledge.

[0013]

In view of the problems of the prior art and the knowledge of the inventor, the main object of the present invention is to:
An object of the present invention is to provide an efficient and effective purification treatment method for treating tap water containing algae and the like.

[0014]

According to the present invention, in the method for purifying raw water from eutrophic lakes and rivers, the particle size of the carrier is 0.5. ~
It is 15mm, and to keep the porosity at about 60-80%,
By using a filter medium made of amorphous plastic
The raw water is treated in an upward flow, and at the same time, an inorganic coagulant is added to 0.5 in order to achieve the coagulation effect of SS and the immobilization and removal of dissolved phosphorus.
It is achieved by providing a method characterized by purifying eutrophied raw water with an infusion of ~ 5 mg / l.

[0015]

EFFECTS OF THE INVENTION According to the present invention, algae can be completely recovered in the treatment of raw water from the tap water, the pre-chlorine and medium-chlorine treatment steps can be eliminated, and the chlorine injection amount for the final sterilization can be drastically reduced. As a result, the production of trihalomethane can be minimized.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below.

FIG. 1 shows an example of an apparatus for carrying out the method for purifying tap water according to the present invention. Raw tap water to be treated is provided in the lower part of the container toward the inside of the container 1. Introduced from the inlet 2, as a carrier, in the filter layer 3 having a particle size of 0.5 to 15 mm and using a filter material made of an amorphous plastic foam so as to keep the porosity at about 60 to 80%. Is circulated upward, and at the same time, an appropriate amount of inorganic coagulant such as calcium or iron coagulant is injected, for example, 0.5 to 5 mg / l, in order to achieve the coagulation effect of SS concentration and immobilization of eluted phosphorus. If necessary, in order to promote the reaction, the raw water that has been appropriately aerated by using the aeration nozzle 4 and purified is sent out from the outlet 5 provided at the upper part of the container.

Reference numerals 6 and 7 are an air vent and a sludge vent, respectively.

Example 1 Blue-green alga recovery process in eutrophic lake Using the apparatus shown in FIG. 1 and using an inorganic flocculant (polyaluminum chloride) 1 mg / l, a microfiltration process was performed at a flow rate of 20 m / H. It was The backwash was performed once a day. Microfiltration device: PVC, 300φ x 3 mH, filter layer 1.5 m Support particles: expanded polypropylene, particle size 3-10 mm,
Irregular bulk density 0.2g / cc Processing result

[Table 1] SS COD BOD T-N T-P Clarity Raw water mg / l 10 8 6 2 0.1 30 cm Treated water mg / l 1 1.4 0.5 0.5 0.5 0.01 1m or more Purification of water quality Phosphorus dropped to 1/10.

Example 2 Raw water treatment of tap water in eutrophic lake Using the apparatus shown in FIG. 1 and using 1 mg / l of inorganic flocculant (polyaluminum chloride), a biofilm treatment was also performed at a flow rate of 10 m / H. Then, microfiltration was performed. The backwash was performed once a day. Microfiltration device: PVC, 400φ x 3 mH, filter layer 1.5 m Support particles: expanded polypropylene, particle size 3 to 7 mm, amorphous bulk specific gravity 0.2 g / cc Treatment result

[Table 2] Precipitated chlorophyll a COD TO degree THM generation ability mg / l μg / l mg / l μg / l Raw water 18-20 80-100 18-25 30-50 60-90 Treated water 1> 1> 3-5 5-10 5-10 We were able to reduce the amount of chlorine for purification and sterilization of water quality, and consequently the THM generation ability.

Example 3 Purification treatment in a certain river Using the apparatus shown in FIG. 1, a biofilm treatment was carried out, and 1 mg / l of an inorganic coagulant was injected at the drain outlet. The flow velocity is 10 m / H. Biofilm treatment device: PVC, 400φ x 3 mH, filter layer 1.5
m Carrier particles: expanded polypropylene, particle diameter 3 to 7 mm, irregular shape, bulk specific gravity 0.2 g / cc Treatment result

[Table 3] SS COD BOD T-N T-P Clarity Raw water mg / l 309 6.5 2.8 0.15 30 cm Treated water mg / l 2 3 2 1.5 0.01 1 m or more Clean treated water Not only was it retained, but the phosphorus was removed significantly.

[0022]

EFFECTS OF THE INVENTION According to the present invention, in the treatment of tap water, algae can be completely recovered, pre-chlorine and medium-chlorine treatment steps can be eliminated, and the chlorine injection amount for final sterilization can be drastically reduced. It is possible to minimize the production of trihalomethane as a result.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus for carrying out a method for treating and treating tap water according to the present invention.

[Explanation of symbols]

 1 Container 2 Inlet 3 Filtration Layer 4 Aeration and Backwashing Nozzle 5 Outlet 6 Air Vent 7 Sludge Vent

Claims (1)

[Claims] 1. A method for purifying raw water from eutrophic lakes and rivers, wherein the carrier has a particle size of 0.5 to 15 mm and a porosity of about 60 to 80%. In order to keep it, the raw water is treated in an upward flow by using a filter medium made of foamed plastic of an indeterminate shape, and at the same time, an inorganic coagulant is added in an amount of 0.5 in order to achieve the coagulation effect of SS and the fixed removal of dissolved phosphorus. A method characterized by purifying eutrophication raw water by injecting ~ 5 mg / l.