JP2513495B2 - Denitrification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for denitrifying nitrate nitrogen or nitrite nitrogen, and more particularly to reducing nitrate nitrogen or nitrite nitrogen contained in wastewater. The present invention relates to a denitrification method for removing nitrogen as gaseous nitrogen.

2. Description of the Related Art A considerable amount of research has been conducted on the nitrogen circulation system in the natural world, and organic nitrogen and ammonium salts were eventually oxidized to nitrite nitrogen and nitrate nitrogen by nitrifying bacteria under aerobic conditions. It is well known that the nitrite nitrogen and the nitrate nitrogen are reduced to gaseous nitrogen by a facultative anaerobic denitrifying bacterium under anaerobic conditions.

In recent years, with the progress of eutrophication in water bodies and the abnormal occurrence of algae and red tides due to this, many attempts have been made to utilize a part of the nitrogen circulation system as a nitrogen removal process in wastewater. That is, first, municipal sewage and industrial wastewater are brought into contact with activated sludge under aerobic conditions to oxidize organic substances and to remove organic nitrogen and ammonium salts.
A method is used in which nitrite nitrogen and nitrate nitrogen are oxidized, and then anaerobic conditions are applied to reduce and denitrify nitrite nitrogen and nitrate nitrogen.

The denitrification action is known in prokaryotes, but not in eukaryotes. Conventionally, facultative anaerobic denitrifying bacteria that act during the above-mentioned denitrification are less likely to form large flocks than aerobic bacteria, and therefore it is difficult to separate the cells after denitrification. There's a problem.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention solves the above-mentioned problems and reduces nitrate nitrogen or nitrite nitrogen-containing substrates, for example, these nitrogen compounds in waste water by using a microorganism to produce a gaseous form. It is an object of the present invention to provide a denitrification method for removing nitrogen as nitrogen.

Means for Solving the Problems In the process of advancing the metabolic research of several filamentous fungi, which are plant pathogenic fungi, the present inventors added nitrates and nitrites to the medium to suppress the aeration and to control the filamentous fungi. When cultured,
It was found that catabolic nitric acid, nitrite respiration and yeast also have similar effects. Such catabolic nitric acid and nitrite respiration have never been known in eukaryotes as described above.

The present invention has been made based on such findings,
The present invention is constituted by bringing a substrate containing nitrate nitrogen or nitrite nitrogen into contact with a filamentous fungus or yeast under anaerobic conditions to denitrify. In the present invention, it is preferable to use a strain selected from microorganisms belonging to the genera Rhizopus, Gibberella, Fusarium and Hansenula.

The filamentous fungus referred to in the present invention refers to a group of organisms consisting of hyphae, the hyphae branching to form mycelia and having no chlorophyll, but on the taxonomy of organisms, fungi among fungi are constituted. Of the four classes of zygosity, ascomycetes, basidiomycetes and incomplete fungi that exclude so-called yeasts that asexually reproduce by budding, a group of microscopic organisms whose body is filamentous Refers to. Among these filamentous fungi, the genus Rhizopus, Gibberella
Genus Fusarium, Neurospora
genus ospora) and the like can be preferably used.

On the other hand, yeast is a fungus in which vegetative cells increase due to budding, and includes spore yeast that sexually reproduces and aspore yeast that does not sexually reproduce. Among these yeasts, the genus Hansenula can be preferably used.

Some of the strains of filamentous fungus or yeast as described above have been deposited at the Institute of Microbial Science and Technology (FERM) with the accession number shown in Table 1, and with the strain numbers shown in the table, ( Those having ordinary knowledge in the technical field can be easily obtained from the Fermentation Research Institute (IFO) and the Institute for Applied Microbiology (IAM) of the University of Tokyo.

In addition, the mycological properties of the deposited microorganism Fusarium oxysporum are described in T. Satoh et al., Agricultural and Biological Chemistry [Agr.
hem., 40, 953-961 (1976)].

In the present invention, utilizing the above filamentous fungus and yeast,
Nitrate nitrogen or nitrite nitrogen is assimilated, but these nitrogens are used exclusively in the form of ions or salts. The concentration of this nitrate nitrogen or nitrite nitrogen cannot be determined unconditionally depending on the type and concentration of the filamentous fungus or yeast to be used.
It is preferably 0 to 5000 ppm. Also, in the substrate,
In addition to these nitrogen, a carbon source and an inorganic salt are appropriately added. The concentration of filamentous fungus or yeast relative to the substrate depends on the morphology of the medium,
It is selected as appropriate in consideration of the assimilation method. Incidentally, the medium may be solid or liquid, and in particular, for the treatment of wastewater, when the present invention is applied, if a substrate necessary for the growth of filamentous fungi or yeast, which is not contained in the wastewater, is added. good.

Since assimilation by filamentous fungi or yeast is more aerobic than denitrification by bacteria, it is not necessary to set the atmosphere to a highly anaerobic condition and air can be used. Also, this assimilation is carried out at a temperature of pH 5-9, 0-50 ° C,
Usually, it is carried out under normal pressure, but it may be carried out under pressure.

The assimilation system may be a batch system, a continuous system, or a semi-batch system, but particularly when it is applied to wastewater treatment, the filamentous fungus and yeast are fixed, and it is efficient to perform the so-called bioreactor system. preferable.

Incidentally, when applying the present invention to the treatment of municipal sewage or industrial wastewater, first, contact these wastewater with activated sludge under aerobic conditions, along with the oxidation of organic matter, organic nitrogen and ammonium salts, A method of oxidizing the nitrite nitrogen and nitrate nitrogen, and then reducing and denitrifying the treated water with a filamentous fungus or yeast may be adopted.

The present invention and its effects will be specifically described below with reference to examples.

Example 1 A three-necked 300 ml Erlenmeyer flask was charged with 180 ml of a liquid medium in which the composition shown in Table 2 was added with sodium nitrite or sodium nitrate at a concentration of 0.5%, and this was described in Table 1 above. Each of the filamentous fungi or yeast was inoculated to a concentration of about 1 g-wet cells / l, the inside was replaced with carbon dioxide, and then a rubber stopper was placed. At a temperature of 26.5 ° C., shaking culture was performed using a rotary shaker, 0.5 ml of the upper gas was sampled for each predetermined time, and the concentration of nitrogen gas was measured by gas chromatography.

The results are shown in Table 3.

 The oxygen content at the start of culture was 1.5% by volume.

Example 2 Sodium nitrite or sodium nitrate containing a stable isotope nitrogen having an atomic weight of 15 in the same composition as in Table 2 of Example 1 was used.
The liquid medium added at a concentration of 0.5% was inoculated with the strains of Fusarium oxysporum, Rhizopus oryzae, and Rhizopus jayvanicas used in Example 1 and the same culture was performed. After 7 days of culturing, nitrogen in the upper gas was trapped in a molecular sieve cooled with liquid nitrogen, introduced into a discharge tube, and the amount of isotope having an atomic weight of 15 in nitrogen was measured by emission spectroscopy. The amount of isotopes with an atomic weight of 15 is 65% for Fusarium oxysporum and 10% for other nitrogen, based on total nitrogen.
It was. From this, it is understood that the filamentous fungi and yeast respire catabolic nitric acid and nitrite.

As is clear from the above results, filamentous fungi or yeasts that are eukaryotes perform catabolic nitric acid respiration, and by using this, a substrate containing nitrate nitrogen or nitrite nitrogen, for example, It is clear that denitrification in municipal sewage and industrial wastewater can be performed.

EFFECTS OF THE INVENTION The present invention utilizes a substrate containing nitrate nitrogen or nitrite nitrogen with a filamentous fungus or yeast to denitrify, so that the cells can be easily separated, and the wastewater in municipal wastewater or factory wastewater can be easily separated. It has an effect that denitrification can be performed efficiently.

Claims (2)

(57) [Claims] 1. A substrate containing nitrate nitrogen or nitrite nitrogen is assimilated by a filamentous fungus or yeast capable of assimilating these nitrogens under aeration-suppressed conditions or anaerobic conditions,
A denitrification method characterized by denitrifying. 2. The denitrification method according to claim 1, wherein a microorganism belonging to any one of Rhizopus, Gibberella, Fusarium, Neurosbora, and Hannula is used as the filamentous fungus or yeast.