JPS6316100A - Biological nitraification and denitrification for drainage containing ammonia - Google Patents

Abstract

PURPOSE:To reduce the operating cost of the title method by comparting a nitrifying stage so that a plug flow is caused, and introducing both raw water and returned sludge into an inflow end of the nitrifying stage which is held at a specified pH. CONSTITUTION:Raw water 1 contg. ammonia is introduced into an inflow end 4 of a nitrifying stage 3 together with returned sludge 2. The nitrifying stage 3 is comparted and only the inflow end 4 is maintained at pH not less than 8.5. One part of ammonia contained in the raw water 1 is nitrified in the inflow end 4, and thereafter the residual ammonia is mixed with circulated denitrifying liquid 9 in the following nitration tanks 5-8 and successively nitrified. NO2<-> formed in the nitrifying stage is introduced into a denitrifying stage 11 and denitrified by adding alcohol 13 or the like as a hydrogen donor. Thereby the stable nitration can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an energy-saving and resource-saving biological nitrification-denitrification method in which nitrogen is biologically nitrified to No, - and then denitrified.

[Technical Background and Prior Art of the Invention] Biological denitrification methods utilize the action of nitrifying bacteria (nitrite bacteria, nitrate bacteria) to convert nitrogen compounds into NOx (1101, NOI) under aerobic conditions.
After nitrification (oxidation), H is removed using the action of denitrifying bacteria.
This method reduces and removes ox to nitrogen and gas under anaerobic conditions. The reaction process until the completion of denitrification is expressed stoichiometrically as shown in the following equation.

Nitrification reaction (aerobic conditions) HTh” + 1.50 → 110!-+2B”+E,
O nitrite bacteria-1(1) MO,-+α50. → MO, - Nitrate bacteria - 1 (2) Denitrification reaction (anaerobic conditions) 110, ``+4 → N O, - 140 Denitrification bacteria ---- (3) No, ''+ 1.5 horses → α5N , ↑＋
OH-Juma0 Denitrification bacteria---(4) The conditions for the above nitrification reaction, like other aerobic microbial reactions, are that dissolved oxygen, water temperature, and pH are maintained appropriately. Unlike the case of oxidizing carbonaceous compounds, the nitrification reaction is an insect acid reaction that generates 2 equivalents of ■+ for 1 equivalent of ammonia, as shown in the 7% ('') formula, so as the nitrification progresses, , p″H decreases. However, the optimum pH range for nitrifying bacteria is 7.8 to a8, and when pTi drops to about 5, nitrification almost stops. Therefore, in order for the nitrification reaction to proceed smoothly, the pi of the wastewater must be maintained near neutrality.

As shown in equations (1) to (4) above, it is necessary to supply oxygen for nitrification and a hydrogen donor for denitrification, but when treating a large amount of nitrogen contained in wastewater, , oxygen supply power cost, methanol used as hydrogen donor,
Large amounts of valuable industrial chemicals such as alkaline agents for pT1 control are consumed, which poses a major problem in terms of operating costs for denitrification treatment equipment.

In the nitrification process of denitrification equipment, ammonia is normally converted into NO
However, as can be seen from equations (1) to (4) above, it is better to stop nitrification and denitrify at No. It requires less quantity and is advantageous in terms of operating costs. That is, No.
, the amount of oxygen for type nitrification is No, I/4 for type nitrification (1,5 ot
/20z), and the amount of hydrogen donor consumed for NOx reduction is also no.

5/15 (t5H, /2.s-) is sufficient. As described above, most of the actual denitrification treatments are carried out by NOs type nitrification, even though the denitrification treatment using No type nitrification has obvious advantages. This is because it is extremely difficult to maintain this in the NO1 type nitrate gold denitrification treatment equipment. However, there is a report that the higher the pH and ammonia concentration, the easier it is for NO1 type nitrification to occur (Journal of the Sewage Sports Association 701, 7, JI & 74. 1970/7, Yasunori Toya "Study on biological denitrification method (1) J)". From the following chemical equilibrium equation, free NH,
It can be easily inferred that this is to inhibit the activity of nitrate bacteria that nitrifies o to no.

NH4++0Tl-→NH, +4O--(5)NH,:
Free ammonia From this equation (5), the higher the ammonia concentration and pH, the higher the free HE concentration, which falls within the condition range of No. type nitrification. However, performing nitrification under these conditions increases the nitrogen removal rate,
This is difficult due to the cost of supplying alkaline agents, and has not yet been implemented.

[Purpose of the invention]

An object of the present invention is to provide a method for controlling the nitrification type of ammonia contained in wastewater to the No. 1 nitrification type, which is advantageous in terms of energy saving and resource saving.

[Structure of the invention]

The present invention provides a method for biologically nitrifying and denitrifying ammonia, in which the nitrification process is sectioned so that a plug flow occurs;
Raw water and returned sludge are allowed to flow into the inflow end of the nitrification process where the pH is maintained at a5 to 1 (L5) to nitrify some of the ammonia, and then the remaining ammonia is nitrified in the nitrification process that follows the inflow end. The method is characterized in that nitrite ions are accumulated in the nitrification process, and then the nitrite ions are denitrified under anaerobic conditions, and then the denitrification solution is circulated to the nitrification tank following the raw water inflow end. This is a biological nitrification and denitrification method for wastewater containing ammonia.

Next, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, ammonia-containing raw water 1 flows into an inflow end 4 (first nitrification tank) of a nitrification process 3 together with return sludge 2. In the nitrification step 3, in order to prevent the liquids in the nitrification tanks 4 to 8 from mixing, compartments are formed, and only the inlet end 4 has a pFl of a5.
It is maintained above. After a part of the ammonia in the raw water 1 is nitrified at the inflow end 4, the remaining ammonia is mixed with the circulating denitrification liquid 9 in the subsequent nitrification tanks 5 to 8, and is successively nitrified.

The pH of the subsequent nitrification tanks 5 to 8 does not particularly need to be maintained on the alkaline side, but if the nitrification activity decreases due to excessive pH decrease, the pH may be controlled to about 7.0±15. The reason why the denitrification liquid 9 is circulated is to use the alkali content generated during denitrification for neutralizing the subsequent nitrification tanks 5 to 8.

By performing nitrification under these conditions, NO! produced in the nitrification process S! Most of -(No, " + NO, -) becomes NO□-. Even if the pTl of the inflow end 4 is set to pH 7.0 ± 15, which is the same level as the subsequent nitrification tanks 5 to 8, nitrification It is carried out perfectly, but No!"" hardly accumulates. To accumulate a large amount of NOx-, the pT of the inlet end 4
It is necessary to maintain l at a high level.

On the other hand, even if the pE[ of the entire nitrification process S is controlled to a5~1 (L5), 110!- can be accumulated, but in this case, the consumption of 10A of alkaline agent for pH adjustment becomes excessive compared to the present invention, and it is economical. The effect will be lost.

In the nitrification step 3, a multistage tank may be used as shown in FIG. 1, but a long and narrow tank in which a plug flow is formed as shown in FIG. 2 may also be used. In addition, to induce NO2 type nitrification,
In particular, in the nitrification process S, only the inlet end 4 has pFi set to a5~1(
Since it is important to control the temperature to L5, the succeeding tanks 5 to 8 may be of a one-tank complete mixing type. However, it is more reliable and stable to nitrify ammonia sequentially in the flow direction from the inflow end 4 using a multistage tank or a tank in which a plug flow is formed.
Type 01 nitrification can be performed.

No.'' generated in the nitrification process flows into the denitrification process 11,
Alcohol 13 or the like is added as a hydrogen donor for denitrification. Most of the denitrification liquid is circulated to the subsequent nitrification tanks 5 to 6, and the remainder is discharged via the reaeration tank 14 and the settling tank 15. If No1- in NOx- in the nitrification process does not increase even if the pH at the inflow end is set to a5, temporarily set pll to 9.
．． After the pH increases to about 0 to 115 and No. 1- is accumulated, the pH may be set to a5. However, if the pH is kept at 1 for a long time,
If it is over 1.0, the activity of nitrifying bacteria will be significantly impaired, so care must be taken in this regard.

Next, one embodiment of the present invention will be described.

For implementation, nitrification was carried out using an apparatus with the flow shown in Figure 1.
Denitrification treatment was performed. The conditions for implementation are as follows.

Nitrification tank 50j (Inflow end 1011, subsequent nitrification tank is equally divided into 4 tanks, 2nd to 5th tanks, 101% each) Denitrification tank Sat Raw water 1111,0419%, Borihep) y5%
The concentrated solution was appropriately diluted and used as raw water.

Alkaline agent for PLL adjustment MhOT1 solution Return sludge volume Set to the same volume as the raw water inflow volume Circulating denitrification liquid volume Set to 5 times the raw water inflow volume Set p1! Inlet end a5 Subsequent nitrification tank 3rd tank 7.0 The implementation results are shown in Table 1.

From Table 1, most of the 110x- of nitrified water is MO,'', and the amount of methanol added is also the required denitrification amount of NO,'' (0
11,01! /110. ”-N to 2.50#/to#)
It has been proven that less waste is required. Although not shown, even if the pH at the inflow end is set to 9.0 to 10.5, Table 1
Similar results were seen. Furthermore, when the pH was set to 11.0, the nitrification activity decreased significantly.

〔Effect of the invention〕

As described above, according to the present invention, the nitrification-denitrification method can be improved into an economical method as follows.

■ Oxygen consumption for nitrification is small, so oxygen supply power costs can be reduced.

■ Less alcohol is needed for denitrification.

[Brief explanation of the drawing]

FIG. 1 shows a 70-
FIG. 2 is a 70-schematic diagram for explaining another embodiment. 1-Raw water, 2-Return sludge, 3-Nitrification process, 4-R, big end (first) nitrification tank, 9-Circulating denitrification liquid, 10-Alkaline agent

Claims (1)

[Claims] 1. In the method of biologically nitrifying and denitrifying ammonia, the nitrification process is divided into sections to generate plug flow, and the raw water and returned sludge are kept at a pH of 8.5 to 10.5. After a part of the ammonia is nitrified by flowing into the inlet end, the remaining ammonia is nitrified in the nitrification step subsequent to the inflow end, thereby accumulating nitrite ions in the nitrification step, and then the nitrite ions are accumulated in the nitrification step. A biological nitrification and denitrification method for ammonia-containing wastewater, which comprises denitrifying ions under anaerobic conditions and then circulating the denitrification solution to a nitrification tank following the raw water inflow end.