JPH0417118B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides ammonium ion (hereinafter referred to as "NH ₄ ⁺ ")
The present invention relates to a denitrification treatment method and apparatus for wastewater including

(Prior Art and Problems) Since NH ₄ ⁺ in wastewater eutrophicates water and significantly reduces water quality, it is necessary to remove it in advanced treatment of wastewater.

Conventional methods for removing NH ₄ ⁺ include (1) ammonia stripping method (2) ion exchange method (3) biological nitrification and denitrification method (4) chlorination method (5) activated carbon method, etc. Each treatment method had the following drawbacks.

The ammonia stripping method has poor stripping efficiency, requires a large amount of air, requires large-scale equipment, and increases operating costs. Furthermore, in some cases, the stripped ammonia gas may not be completely collected and may cause air pollution.

In the ion exchange method, NH ₄ ⁺ is added to an adsorbent such as zeolite.
However, it is difficult to regenerate the adsorbent. Two adsorption towers are required to perform adsorption and regeneration alternately. Further, the adsorbent is regenerated with a chemical solution containing sodium ions, etc., but since the regenerated liquid contains NH ₄ ⁺ , it is necessary to further treat the regenerated waste liquid.

In the biological nitrification-denitrification method, NH ₄ ⁺ is nitrified to nitrate ions by nitrifying bacteria in an aerobic atmosphere, and then the nitrate ions are reduced to nitrogen gas by denitrifying bacteria in an anaerobic atmosphere, but the reaction rate is slow. As a result, equipment becomes larger.

The chlorination method decomposes NH ₄ ⁺ into nitrogen gas by blowing in chlorine gas, but it requires a large amount of chlorine and is difficult to adjust. is generated, and if the amount added is small, the decomposition reaction of NH ₄ ⁺ will not proceed.

The activated carbon method adsorbs NH ₄ ⁺ on activated carbon, but the adsorption capacity of activated carbon is low, and regeneration of activated carbon requires a complicated and energy-intensive regeneration method of drying, thermal decomposition, and activation.

(Purpose) The present invention was made to solve the above-mentioned problems, and it removes NH ₄ ⁺ in wastewater by adsorbing ions with zeolite, and at the same time, injects the zeolite with microorganisms in the same device. In addition to continuous regeneration through treatment, the treated water is separated by a reverse osmosis membrane, a part of the concentrated liquid is returned to the zeolite adsorption tower, and the remainder of the concentrated liquid and the permeated liquid are further treated with microorganisms to perform denitrification. The present invention provides a method and apparatus for treating wastewater.

(Structure and function of the present invention) The apparatus for carrying out the treatment method of the present invention is NH ₄ ⁺
An adsorption tower filled with nitrifying bacteria to nitrify NH ₄ ⁺ and zeolite to adsorb ions of NH 4 +, and sodium or calcium ions and nitrifying bacteria required to exchange NH ₄ ⁺ with the free radicals of the zeolite after nitrification. a reverse osmosis membrane for separating a concentrated solution containing the concentrated solution, a means for returning a part of the concentrated solution to the adsorption tower, and a means for denitrifying the remaining concentrated solution and the permeate in an anaerobic atmosphere using denitrifying bacteria The present invention is comprised of a two-phase fluidized bed catalytic reduction tower for carrying out this process, and a means for replenishing the two-phase fluidized bed catalytic reduction tower with a carbon compound. When treated water (wastewater), which has been given sufficient dissolved oxygen through aeration, is introduced into a zeolite adsorption tower and allowed to pass through, NH ₄ ⁺ is ion-exchanged with sodium ions or calcium ions by the ion adsorption action of zeolite and is supplemented in the zeolite. At the same time as being captured,
The nitrifying bacteria nitrify NH ₄ ⁺ from nitrite ions to nitrate ions, and as a result, the zeolite is continuously regenerated within the same adsorption tower. A concentrated liquid containing sodium or calcium ions and nitrifying bacteria required for exchange with zeolite free radicals after nitrifying NH ₄ ⁺ is separated from the primary treated water exiting the adsorption tower using a reverse osmosis membrane. A portion of the liquid is returned to the adsorption tower via a return means. The remainder of the concentrate and the permeate are led to a two-phase fluidized bed catalytic reduction column. The two-phase fluidized bed catalytic reduction tower is loaded with a carrier inhabited by denitrifying bacteria that reduce nitrate ions to nitrogen gas, and the denitrifying bacteria reduce nitrate ions to nitrogen gas. The carbon compound is for supplying a carbon source necessary for the propagation of denitrifying bacteria, and is methanol, BOD, etc. Hereinafter, the present invention will be explained in detail together with an explanation of embodiments of the apparatus.

(Structure and operation of the apparatus of the embodiment) The figure is a schematic diagram showing an embodiment of the apparatus of the present invention. Wastewater is supplied to a raw water tank 2 from a raw water supply pipe 1, aerated with air blown from an air source 3, provided with sufficient dissolved oxygen, and introduced by a pump 4 into an adsorption tower 5 filled with zeolite 6. be done. Zeolite 6 is inhabited by nitrifying bacteria (for example, a species of the genus Nitrobacter, Microtechnical Research Institute No. 2545), which nitrates the NH ₄ ⁺ captured by ion adsorption to nitrate ions. The reaction within the adsorption tower 5 proceeds as shown in the following equation.

Z−Na+NH ₄ ⁺ →Z−NH ₄ +Na ⁺ ...(1) (Z indicates zeolite) NH ₄ ⁺ +1.50 ₂ →NO ₂ ^- +H ₂ O+2H ⁺ ...(2) NO ₂ ^- +0.50 ₂ → NO ₃ ^- (3) Primary treated water containing nitrate ions, sodium ions, hydrogen ions, and nitrifying bacteria is introduced from the adsorption tower 5 into the intermediate tank 8 through the pipe 7. In the intermediate tank 8, the PH of the primary treated water may be adjusted by a PH adjusting mechanism (not shown) as the case may be.

The primary treated water in the intermediate tank is pressurized by a pump 9,
After the NH ₄ ⁺ is nitrified by the reverse osmosis membrane 10, a concentrated solution containing nitrifying bacteria and sodium ions required for exchange with the free radicals of the zeolite is separated. A part of the concentrated liquid is returned to the adsorption tower 5 by a return pump 11 through a return pipe 12. A portion of the concentrate and the permeate are introduced into the intermediate tank 15 through pipes 13 and 14, respectively.

Reference numeral 16 denotes a methanol addition device, into which a predetermined amount of methanol and the like required in the next step is added, and the methanol is introduced into a two-phase fluidized bed catalytic reduction tower 19 through a pipe 18 by a pump 17.

In the two-phase fluidized bed catalytic reduction tower, activated carbon or granulated polyvinyl alcohol (e.g., JP-A-60
-183095) is filled as a carrier.

In the two-phase fluidized bed catalytic reduction tower 19, nitrate ions are reduced to nitrogen gas by denitrifying bacteria in an anaerobic atmosphere. The reaction formulas in the two-phase fluidized bed catalytic reduction tower are (4) to (5)
It seems like.

2NO ₂ ^- +6H ⁺ →N ₂ +2H ₂ O+2OH ^- ...(4) 2NO ₃ ^- +10H ⁺ →N ₂ +4H ₂ O+2OH ^- ...(5) To promote fluidization in the two-phase fluidized bed catalytic reduction tower. Additionally, it is also possible to return a part of the secondary treated water to the two-phase fluidized bed catalytic reduction tower using the pump 20. 21 is a nitrogen gas discharge pipe. Reference numeral 22 denotes a treated water tank, in which the pH is adjusted by a pH adjustment mechanism (not shown) as the case may be, and the water is discharged to the outside as final treated water.

Note that the adsorption tower 5 is backwashed once every 7 to 10 days with the final treated water that does not contain NH ₄ ⁺ through the pump 24. In this case, the backwash wastewater is returned to the raw water tank 2 through the pipe 25.

(Example) In the illustrated apparatus (two-stage series adsorption tower), each adsorption tower has a height of 24 cm and a stage area of 16 cm ² (φ4.5 cm),
Zeolite was filled (filling rate 50%) and the nitrifying bacteria described above were added.

In addition, the two-phase fluidized bed catalytic reduction tower has a stage area of 16 cm ²
(φ4.5 cm) and a volume of 191 cm ³ , and activated carbon (filling rate: 30%) was used as a carrier.

Wastewater containing 15ppm of _NH4 ⁺ is fed into this equipment.
It was fed at a flow rate of 30 c.c./min.

The concentrated liquid obtained from the reverse osmosis membrane device is returned to the adsorption tower at a rate of 15 c.c./min. It was introduced into a fluidized bed catalytic reduction tower.

The fluidized liquid velocity in a two-phase fluidized bed catalytic reduction tower is
When the system was operated continuously at 480 c.c./min with a residence time of 7 minutes, no NH ₄ ⁺ was detected in the final treated water even after more than 3 months had passed.

Note that the amount of N ₂ generated was approximately 19 c.c. per 11 liters of water to be treated.

(Comparative example) When the same wastewater as in the above example was continuously supplied at a rate of 30 c.c./min to a two-stage series adsorption tower (zeolite filling rate 50%) with the same specifications, zeolite breakthrough occurred in about 15 days. It was seen.

(Effects) As described above, according to the present invention, NH ₄ ⁺ can be efficiently removed without secondary pollution or harmful substance emissions, and zeolite adsorption and regeneration can be performed simultaneously in the same device. Therefore, unlike conventional methods, there is no need to temporarily stop the operation of the equipment for zeolite regeneration operations, and wastewater can be treated continuously and quickly, and the equipment can be made more compact. .

[Brief explanation of drawings]

The figure is a schematic configuration diagram of an apparatus according to an embodiment of the present invention. 5... Zeolite adsorption tower, 10... Reverse osmosis membrane,
19...Two-phase fluidized bed catalytic reduction tower.

Claims (1)

[Claims] 1. Wastewater containing ammonium ions is passed through an adsorption tower filled with zeolite to which nitrifying bacteria is attached and a reverse osmosis membrane, and a part of the concentrated water from the reverse osmosis membrane is absorbed into the adsorption column. Wastewater is refluxed to a column and the remaining concentrated water and permeated water are guided to a two-layer fluidized phase catalytic reduction column filled with a carrier supporting denitrifying bacteria for denitrification in an anaerobic atmosphere. Denitrification treatment method. 2. The denitrification treatment method according to claim 1, wherein a carbon source necessary for the growth of denitrifying bacteria is supplied to the treated water introduced into the two-phase fluidized bed catalytic reduction tower. 3. An adsorption tower filled with nitrifying bacteria and zeolite, a reverse osmosis membrane for separating a concentrated liquid containing exchanged sodium or calcium ions and nitrifying bacteria, and a part of the concentrated liquid being transferred to the adsorption tower. A denitrification treatment apparatus for ammonium ion-containing wastewater, comprising a return means, and a two-layer fluidized phase catalytic reduction tower into which the remainder of the concentrated liquid and the permeated liquid are introduced, and in which denitrifying bacteria are supported.