JP4596533B2 - Wastewater treatment method - Google Patents

Description

  The present invention relates to a method for treating wastewater containing ammoniacal nitrogen, and more particularly, to a method for treating wastewater using a granular microbial granule (hereinafter simply referred to as granule).

  2. Description of the Related Art In recent years, in the field of wastewater treatment, biological treatment is frequently used in which treatment is performed by changing the pollutant in wastewater to harmless substances using the physiological activity of microorganisms. The activated sludge method is the mainstream as a general biological treatment method, but it is difficult to increase the concentration of microorganisms in the system with the normal activated sludge method. It is difficult to manage biota, it is difficult to manage the processing performance such as bulking, large-scale sedimentation facilities are required, and a large amount of waste such as excess sludge is generated. I came.

As a technology to solve these problems, use a method of solid-liquid separation of activated sludge using membranes, a method of attaching microorganisms such as sponges and polymer carriers, and so-called granules that self-granulate microorganisms. A method for performing the processing has been developed. Among them, the method using granules has been attracting attention because it can retain a large amount of microorganisms in a reaction tank, and therefore has a high reaction rate per unit volume and easy solid-liquid separation (for example, Patent Document 1).
JP 2002-336885 A

  However, biological treatment of wastewater using granules is an effective method because it can process pollutants at high speed, but slow formation of granules has been regarded as a problem. In particular, when ammoniacal nitrogen is treated with microorganisms under aerobic conditions, it is necessary to form granules containing nitrifying bacteria, mainly ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. Since it is very slow and the amount of extracellular polymer formed is very small, it is very difficult to granulate and it has hardly been put into practical use.

  It is also possible to introduce granules mainly composed of anaerobic bacteria formed in a reactor represented by UASB (Upflow Anaerobic Sludge Blanket) as the core of nitrifying granules. However, since it is mainly composed of anaerobic bacteria and the cells die under aerobic conditions, there is a possibility that the transfer of the biota to the granule mainly composed of nitrifying bacteria does not proceed smoothly.

  Therefore, the object of the present invention is to make it possible to reliably and quickly form granules containing denitrifying bacteria even under aerobic conditions that have been difficult to form so far, and it is possible to put biological treatment using granules with nitrification performance into practical use It is to provide a method for treating waste water.

In order to solve the above-mentioned problems, the wastewater treatment method according to the present invention comprises forming an organic substance as a substrate when performing nitrification treatment by contacting wastewater containing ammonia nitrogen with nitrifying bacteria under aerobic conditions. The granules containing mainly denitrifying bacteria mainly containing facultative anaerobic bacteria, or the crushed material of the granules are introduced as nuclei, so that the nitrifying bacteria can be grown on the surface of the granules containing mainly denitrifying bacteria. And forming a granule having nitrification performance.

  In the wastewater treatment method according to the present invention, water containing nitrifying bacteria can be added together with granules containing denitrifying bacteria. As the water containing nitrifying bacteria, a microbial preparation prepared by culturing nitrifying bacteria in a culture solution or activated sludge can be used.

  That is, in the present invention, granules containing denitrifying bacteria mainly composed of facultative anaerobic bacteria are formed under oxygen-free conditions using organic substances as a substrate, and the nitrifying bacteria are granulated by introducing the granules or crushed materials thereof. It has been found that it is possible to grow granules on the surface of the glass and to form granules having nitrification performance. Since this granule is mainly composed of facultative anaerobic bacteria, it can grow even under aerobic conditions, and therefore it can smoothly transition to a granule mainly composed of nitrifying bacteria.

  Thus, according to the wastewater treatment method according to the present invention, granulation can be performed in a short period of time even in a system that has been difficult to form so far, and efficient target biological treatment can be performed. it can. Therefore, by using the method according to the present invention, it is possible to make the reaction tank compact and improve the dewaterability of sludge, and as a result, practical wastewater treatment can be achieved at low cost.

  Hereinafter, preferred embodiments of the present invention will be described in detail, particularly when ammoniacal nitrogen in waste water is treated.

<Granule formation method>
Granules containing denitrifying bacteria used in the present invention are produced by passing water containing organic matter and nitrate nitrogen or nitrite nitrogen through a biological reaction tank. In general, denitrifying granules are much easier to prepare than nitrifying granules, and water containing appropriate concentrations of organic substances such as alcohols and acetates and nitrate or nitrite nitrogen is added. It is usually formed in about 2 weeks to 1 month by passing water countercurrently. In the present invention, this granule can be produced by other business sites, factories or the like, or by reaction tanks installed on site. In addition, when a granule of denitrifying bacteria is prepared at a site where a granule having nitrification performance is required, it can be prepared by diverting the nitrification reaction tank. In this case, granulated denitrifying bacteria were prepared by passing water containing organic matter and nitrate nitrogen or nitrite nitrogen in an upward flow under anaerobic conditions in advance, and then adding ammonia nitrogen. Supply water and oxygen. In the case where the diameter of the granules containing denitrifying bacteria is large, it is also very effective to add them after crushing.

  In granulated nitrifying bacteria, the diffusion distance of oxygen from the granule surface is directly related to the amount of effective microorganisms, so a relatively small diameter can result in a higher load per reaction tank. However, since the sedimentation rate decreases as the diameter decreases, a diameter of about 0.1 to 1.0 mm is particularly effective. In addition, in the case where granules of denitrifying bacteria are used as nuclei, it is effective to similarly introduce nitrifying bacteria sources. Effective sources of nitrifying bacteria include generally marketed microbial preparations prepared by culturing nitrifying bacteria and activated sludge.

  In the case of nitrification unlike denitrification, since dissolved oxygen is required for the growth of nitrifying bacteria, air or oxygen is supplied from the lower part of the granule reaction tank. There is no particular designation for the shape of the device, and a general one such as a cylindrical or square tank can be used, but in order to secure shearing force for forming granules, the aspect ratio of the tank for forming granules is It is desirable to ensure 1: 1 or more.

  At the initial stage of startup, the granules are not sufficiently formed and the sludge has a low specific gravity, so the sludge flows out of the system. Such sludge is preferably concentrated in a sedimentation tank or the like and returned to the reaction tank. In addition, when a sufficiently large solid-gas-liquid separator (GSS) is installed at the upper part of the reaction tank, the precipitation tank can be omitted.

  In this way, by introducing granules containing denitrifying bacteria as a nucleus and growing nitrifying bacteria on the surface, the biota gradually changes from those mainly composed of denitrifying bacteria to those mainly composed of denitrifying bacteria. Granules with high nitrification performance are formed.

<Device configuration>
In order to stabilize the load into the reactor, the waste water containing ammonia nitrogen is usually once retained in the adjustment tank and then sent to the nitrification reaction tank at a constant flow rate. If there is an organic substance or inhibitor other than ammonia nitrogen in the wastewater, it is desirable to treat it to the extent that there is no problem in advance. Moreover, since it is desirable to process by neutrality-weak alkalinity, pH of waste water is adjusted as needed.

  The nitrification reaction tank is filled with granules containing denitrifying bacteria as the nucleus of the nitrifying bacteria granule, and the nitrification reaction proceeds under aerobic conditions, so aeration with air or oxygen is performed from the lower part of the reaction tank. In addition, since alkalinity is consumed with the nitrification of ammoniacal nitrogen and the pH is lowered, it is desirable to provide equipment for adding an alkali such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate. It is desirable to install a solid-gas-liquid separator (GSS) in the upper part of the reaction tank in order to prevent granule outflow.

  Thus, ammonia nitrogen can be nitrified to nitric acid or nitrous acid by bringing the nitrifying granules into contact with the waste water containing ammonia nitrogen. Nitric acid or nitrous acid can be discharged to the outside of the system by changing to nitrogen gas by using a general denitrification apparatus as required.

  Examples carried out using the method according to the present invention are shown below. Note that this example does not limit the scope of the present invention.

Example 1
A reaction tank having an inner diameter of 50 mm, a height of 3000 mm, and a solid-gas-liquid separator (GSS) installed in the upper part was prepared, and activated sludge from a sewage treatment plant was introduced therein so as to be 2000 mg / L each. Further, stirring blades were installed inside for stirring, and stirring was performed at 5 rpm. Industrial water containing nitrate nitrogen (200 mg / L), methanol (800 mg / L) and phosphorus (30 mg / L) was passed through the reactor in an upward flow. Granules containing about 1 mm of denitrifying bacteria were formed by passing water for about 1 month.

  Activated sludge collected from the wastewater treatment facility of the food factory is put into this reaction tank, drainage containing 500 mg / L of ammonia nitrogen and calcium each is passed, and granules are produced while aeration is performed at 0.5 L / min. did.

Comparative Example 1
Create a similar reaction tank, feed activated sludge and drain water containing 500 mg / L of ammonia nitrogen and calcium, respectively, under conditions where there are no granules containing denitrifying bacteria, and aerate at 0.5 L / min. went. Since the activated sludge flowed out significantly, an operation was performed to return the sludge that flowed out appropriately to the reaction tank.

〔result〕
The nitrification activity per reaction tank after 1 month and 2 months later is shown in Table 1. In Example 1, the activated sludge almost disappears after one month, the granules are well formed in the tank, and the nitrification activity is increased, so that the bacterial flora of the granules changes from denitrifying bacteria to nitrifying bacteria. It was estimated that the On the other hand, in Comparative Example 1, although an increase in sludge and a slight increase in nitrification activity were observed, formation of granules was not confirmed.

Claims (4)

When nitrification treatment is performed by contacting wastewater containing ammonia nitrogen with nitrifying bacteria under aerobic conditions, granulated mainly containing denitrifying bacteria mainly composed of facultative anaerobic bacteria formed using organic substances as a substrate. Or a crushed product of the granule as a nucleus, the nitrifying bacteria are propagated on the surface of the granule mainly containing denitrifying bacteria to form granules having nitrifying performance. Processing method. The method for treating waste water according to claim 1 , wherein water containing nitrifying bacteria is added together with the granules mainly containing denitrifying bacteria. The method for treating waste water according to claim 2 , wherein the water containing nitrifying bacteria is a microbial preparation prepared by culturing nitrifying bacteria in a culture solution. The water treatment method according to claim 2 , wherein the water containing nitrifying bacteria is activated sludge.