JP2000167588A - Method and apparatus for purifying seawater such as waste water produced from seedling breeding using diatom minute seaweed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove nutrient salts containing nitrogen and/or phosphorus in seawater, in purifying seawater containing nutrient salts in high concn. such as seedling breeding waste water by a diatom, by providing a water feed pipe, a drain pipe and an aerator and performing aeration stirring at a light period and stopping aeration stirring at a dark period. SOLUTION: At a light period, the transparent or translucent cylindrical container of a water purifying cylinder 7 is filled with breeding waste water of seedlings or the like and minute seaweed 9 are added to the waste water to be well mixed therewith under stirring while the waste water is aerated by an aerator 8. This waste water is allowed to stand for several days in this state to advance the water purification by a diatom. At a point of time when water purification is advanced to a certain degree, only purified seawater is taken out of the purifying cylinder 7. At a dark period, in such a state seawater in the purifying cylinder 7 is purified at a light period, the aerator 8 is stopped to stop stirring. On and after 10 hr from the start of the dark period, the density of the diatom in purified water is reduced and, therefore, drainage is performed from the upper layer of the purifying cylinder 7 by a pump 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for purifying seawater such as seedling rearing wastewater using microalgae, and a method for removing microalgae from purified seawater.

[0002]

2. Description of the Related Art Conventional techniques for purifying seawater such as seedling rearing wastewater and improving water quality include a method using macroalgae and a method using bacteria. In the conventional method of purifying seawater using macroalgae, the range of the nutrient concentration in which macroalgae can grow is narrow, and in the case of high-concentration nutrients such as seedling rearing wastewater, there are cases where the plants die. In addition, seawater purification using macroalgae was poor in versatility because growth was impossible even at extremely low concentrations.

[0003] In a method of purifying seawater using bacteria,
Although some bacteria can cope with a wide range of nutrient concentrations, it was difficult to remove the grown bacteria, so they had to be mixed with seeds and seedlings. Also, there was no measure for secondary utilization of the grown bacteria. In other words, purification by microalgae requires a high-density culture because the amount of nutrient absorption per microalgae is small compared to large seaweeds. On the other hand, releasing microalgae cultured at high density may cause red tide, so removing microalgae after purification is an essential requirement, despite removal of microalgae. Was extremely difficult, so that it had not reached the stage of practical use.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for purifying seawater containing a high concentration of nutrient salts and to manufacture an efficient water purification apparatus.

[0005]

Means for Solving the Problems In order to solve the above problems, the present inventors have made intensive efforts, and as a result, by culturing microalgae in wastewater containing a high concentration of nutrients, nitrogen in seawater has been improved. And efficiently remove nutrients containing phosphorus,
We found that the water quality could be improved. We have also developed a method for removing microalgae from purified seawater.

That is, the present invention relates to (1) a water purification apparatus using a microalgae of seawater containing a high concentration of nutrients such as wastewater for raising seedlings and the like, comprising a water supply pipe, a drainage pipe, and an aeration apparatus. (2) a water purification device using microalgae, wherein aeration and agitation are stopped in the dark period.
(1) The nitrogen and / or phosphorus in seawater is reduced by culturing microalgae in seawater containing high concentrations of nutrients such as seedling rearing wastewater using the water purification apparatus described in (1). (3) The method for removing microalgae according to (3), wherein the settled portion is removed in a dark period.

[0007] The seawater such as seedling rearing wastewater in the present invention includes the rearing wastewater of all organisms reared using seawater and the wastewater used for rearing parents such as parent fish for producing seeds. In the present invention, the nutrients for the purpose of removal are four types of nutrients: ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, and phosphate phosphorus.

In order to carry out the method of the present invention, seawater such as seedling rearing wastewater or the like, to which vitamins have been added as required, may be used as a culture solution of microalgae. Put this seawater in a transparent or translucent container,
A small amount of microalgae is added there. Furthermore, seawater is constantly stirred by aeration. This container is installed indoors or outdoors, and if it is indoors, light is irradiated by a fluorescent lamp or the like. If it is outdoors, install it in a location exposed to sunlight.

By connecting a plurality of such containers for purifying seawater in series, it is possible to finally purify the seawater containing nutrients substantially equal to that of natural seawater and to improve the water quality. is there. In the present invention, seaweed purification and water quality improvement can be performed more efficiently by selecting microalgae having higher nutrient absorption ability and using the high-concentration nutrient-resistant strain.

Furthermore, by adding high-concentration nutrient-tolerant strains to breeding wastewater at a high density from the initial stage of purification, it is possible to purify breeding wastewater such as seeds and seedlings in a shorter time than when a minute amount of microalgae is added. It turned out that. By imparting a light cycle with light to microalgae in seawater, their movement can be controlled to some extent. That is, by stopping the aeration for stirring in the dark period, the microalgae settles at the bottom of the culture vessel, and only a relatively small amount of the microalgae is present in the seawater in the upper layer of the culture vessel. By utilizing this feature and extracting seawater from the upper layer of the culture vessel in the dark using the principle of a pump or siphon, purified seawater with relatively few microalgae can be obtained.

The use of purified seawater from which nutrient salts have been removed as described above may be used in the case where microalgae is further removed and water is discharged to natural sea areas, or in the case where seawater for breeding seeds and seedlings is used again while leaving a small amount of microalgae. There are times when you do. Furthermore, when removing microalgae, most of the remaining microalgae can be precipitated by transferring purified seawater containing microalgae into an opaque black container and allowing it to stand still. Releases the upper water into the natural seas after the microalgae settle out.

Many species of microalgae are cultivated as feed organisms for breeding marine animals and are readily available as materials for seawater purification. And as a secondary utilization method of the microalga grown by seawater purification, it can be diverted to feed. Therefore, when the purified seawater containing the microalgae is used again as seawater for raising seedlings, it is used as it is as seedwater for seedlings or diluted appropriately.

[0013]

Next, the present invention will be described in more detail by way of examples. The main microalgae used in the present invention is Tetras
elmis tetrathele , but besides, Chaetoceros
Gracilis , Isochrysis Tahiti strain, Nannochloropsis oculata, etc. can also be used. In addition, seawater to which nitrogen and phosphorus were appropriately added was used for the purification experiment.

[0014]

Example 1 Sodium dihydrogen phosphate dihydrate (NaH
_{2 PO 4 · 2H 2 O:} MW = 156) 8.05mg / l and sodium nitrate (NaNO _3: MW
= 85) The microalga Tetraselmis tetrathele was added to a Guillard F liquid medium supplemented with 158 mg / l in a dry weight of 50 μl.
g / l was added at an initial concentration, and the concentrations of phosphate phosphorus and nitrate nitrogen were compared with the control without addition. As shown in FIGS. 1 and 2, Tetraselmis tetrat
The hele addition section rapidly absorbed phosphate phosphorus and nitrate nitrogen. On the other hand, there was almost no change in the non-added group.

[0015]

EXAMPLE 2 As in Example 1, 8.05 mg of sodium dihydrogen phosphate dihydrate (NaH ₂ PO ₄ .2H ₂ O: MW = 156)
/ l and ammonium sulfate ((NH ₄ ) ₂ SO ₄ : MW = 1
32) The microalga Tetraselmis tetrathele was added to a Guillard F liquid medium supplemented with 125.4 mg / l in a dry weight of 50 μl.
g / l of the initial concentration, the changes in the concentration of phosphoric acid phosphorus and the concentration of ammonia nitrogen were compared with those in the group without addition of Tetraselmis tetrathele . As shown in FIGS. Both phosphorus and ammonia nitrogen showed a rapid decrease, but almost no change was observed in the non-added group.

[0016]

Example 3 In order to remove microalgae from purified seawater, a light-dark cycle of light was applied to the incubator, and the amount of microalgae in the upper layer of the incubator was measured. The incubator has a 12 hour light period and 1
After a dark period of 2 hours, the algal cell dry weight and ammonia nitrogen concentration of the microalga at 5 cm below the surface of the incubator were measured every 2 hours. As a result, as shown in FIG. 5, the algal mass became minimal 10 hours after entering the dark period, but the absorption of ammonia nitrogen continued even after entering the dark period. As a result, it was found that in the construction of a water purification system, purified seawater containing relatively little microalgae can be obtained by removing purified water from the upper layer about 10 hours after the dark period.

[0017]

Embodiment 4 An example shown in FIG. 6 is a sectional view of a water purification column in a light period. Fill a transparent or translucent cylindrical container with breeding wastewater such as seeds and seeds, and add microalgae. Further, the mixture is aerated and stirred so that the wastewater and the microalgae are well mixed.
In this state, it is left for several days to purify the water with microalgae. When the water purification by the microalgae progresses, only the purified seawater is taken out of the purification column. FIG. 7 is a sectional view of the water purification column in the dark period. When the seawater in the purification cylinder is purified in the state of FIG. 6, the ventilation device is stopped in the dark period to stop stirring. Since the density of microalgae in the purified water decreases 10 hours after the start of the dark period, the drainage is gently drained from the upper layer of the purification column by the principle of a pump or siphon.

[0018]

Embodiment 5 FIG. 8 is a sectional view of the whole water purification apparatus.
In FIG. 7, purified seawater drained from the water purification column is collected in the next purification column for further purification, and purification is performed in the same procedure as described above. Such an operation using the purifier is repeated a plurality of times to finally reduce the nutrient concentration to the same level as natural seawater. The purified seawater is further released to the natural sea area after removing microalgae, or used as breeding water with initial feed for the next seed and seedling while leaving some microalgae.

[0019]

According to the present invention, harmful inorganic nutrients such as nitrogen and / or phosphorus are efficiently removed from breeding wastewater such as seeds and seedlings by using microalgae, and the grown microalgae is purified by a light-dark cycle. It can be more removed and released without affecting natural waters. Further, the removed microalgae can be reused as feed for seeds and seedlings.

[Brief description of the drawings]

Fig. 1: Microalga Tetraselmis tetr in the presence of nitrate nitrogen
The figure which shows the comparison of the absorption of phosphoric acid phosphorus in the athele addition section and the non-addition section.

Fig. 2: Microalgae Tetraselmis tetr in the presence of nitrate nitrogen
The figure which shows the comparison of the absorption of nitrate nitrogen in the athele addition section and the non-addition section.

Fig. 3 Microalgae Tetraselmi in the presence of ammonia nitrogen
The figure which shows the comparison of the absorption of phosphoric acid phosphorus in the s tetrathele addition section and the non-addition section.

Fig. 4 Microalga Tetraselmi in the presence of ammonia nitrogen
The figure which shows the comparison of the absorption of ammonia nitrogen in the s tetrathele addition section and the non-addition section.

FIG. 5 is a graph showing changes in algal body weight and ammonia nitrogen concentration according to the light cycle of light.

FIG. 6 is a sectional view of the water purification column in the light period.

FIG. 7 is a cross-sectional view of a water purification column in a dark period.

FIG. 8 is a cross-sectional view of the entire water purification device.

[Explanation of Signs ] 1. Microalga Tetraselmis tetrathe in the presence of nitrate nitrogen
5 shows a change in nutrient concentration in the le- added group. 2 Microalgae Tetraselmis tetrathe in the presence of nitrate nitrogen
5 shows a change in the concentration of nutrients in the le-free group . 3 Microalgae Tetraselmis te in the presence of ammonia nitrogen
The change of nutrient concentration in the trathele- added group is shown. 4 Microalgae Tetraselmis te in the presence of ammonia nitrogen
The change of nutrient concentration in the trathele-free group is shown. 5 shows the change in algal cell dry weight of microalgae due to the light and dark cycle of light. 6 shows changes in the concentration of ammonia nitrogen due to the light cycle of light.

Claims (3)

[Claims] 1. A water purification device using a microalgae of seawater containing a high concentration of nutrients, such as seedling rearing wastewater, comprising a water supply pipe, a drainage pipe, and an aeration device. Is a water purification device using microalgae, which stops aeration and stirring. 2. Using the water purification device according to claim 1,
A water purification method characterized by reducing nitrogen and / or phosphorus in seawater by culturing microalgae in seawater containing a high concentration of nutrients such as seedling rearing wastewater. 3. The water purification device according to claim 1,
A method for removing microalgae, comprising removing a sediment portion in a dark period.