JPS62110798A - Method for purifying waste water - Google Patents

Abstract

PURPOSE:To treat waste water having a comparatively high content of ammonia by using a purifying tank of a simple structure when the ammonia-contg. waste water generated from methane fermentation is passed through the purifying tank provided with an aquatic plant culture bed and purified. CONSTITUTION:When ammonia-contg. waste water generated from methane fermentation is passed through the purifying tank 1 provided with an aquatic plant culture bed, the purifying tank 1 is separated into a raw water receiving zone A, a treating zone B, and an overflowing zone C by two sheetings 2 and 3 through which water can be circulated partially and freely. The lower bed 4 of the treating zone B is formed with gravel and the upper air-permeable bed 5 is formed with soil which is used as the culture soil for growing the aquatic plant 6 such as Eichhornia crassipes. The height of an overflow port 7 provided at the terminal end of the overflowing zone C is made controllable, and the overflow port 7 is lowered as the root of the aquatic plant grows. Consequently, the depth of the air-permeable part of the treating zone B can be regulated. The waste water having a comparatively high content of ammonia is treated with simple operation by using the purifying tank of the simple structure.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is a method for denitrifying an ammonia-containing aqueous solution produced after methane fermentation treatment of industrial wastewater, domestic wastewater, etc. to reduce the ammonia concentration below the regulatory value. It is related to.

2. Description of the Related Art A method of anaerobically decomposing and purifying industrial wastewater containing organic matter and domestic wastewater discharged from households using soil bacteria is known as the so-called methane fermentation method.

According to this methane fermentation method, ammonia and sulfur compounds are produced along with flammable gases such as methane and hydrogen.
Contains about 3000 ppm of ammonia.

Until now, such ammonia-containing wastewater has been discharged into rivers and the like by diluting the solid content by filtration, for example, and then diluting it with 100 to 300 times the amount of water to bring the ammonia concentration below a permissible range.

However, such a dilution method requires a large amount of dilution water and also has a huge volume after treatment, which inevitably increases the size of the equipment.

A method of removing ammonia by chemical treatment has also been proposed, but this method requires a special treatment agent, resulting in high costs and is not practical.

On the other hand, it is known that certain aquatic plants such as water hyacinth have the ability to absorb and remove ammonia nitrogen from water, and this can be used to remove ammonia from methane fermentation wastewater. is also being considered.

However, this water hyacinth has an ammonia concentration of 1
001] Growth inhibition started to occur near +1 In, and 20
0. If it exceeds ρ1°, it will wither and die, so it has the same drawback as the conventional dilution method in that it must be diluted considerably in order to be applied to methane fermentation wastewater, and cannot be put to practical use as is.

Problems to be Solved by the Invention An object of the present invention is to reduce the volume of an ammonia-containing aqueous solution produced by methane fermentation to as small a volume as possible without diluting it with a large amount of water when treating it with aquatic plants to remove ammonia. The purpose is to provide a method that can be applied as is.

Means for Solving the Problems The present inventors aimed to develop a method for smoothly removing ammonia without inhibiting the growth of aquatic plants even in the presence of relatively high concentrations of ammonia. As a result of intensive research, we found that aquatic plants are more than 100.010-1
- results in growth inhibition in the presence of ammonia, 200 pp.
The reason why the root threads die after 300 m is due to a lack of dissolved oxygen in the water when the root threads absorb ammonium ions and convert them into nitrate. Therefore, the root threads are not sufficiently supplied with oxygen. For example, it has been found that even in the presence of ammonia at a fairly high concentration of 800 to 000 ppI11, no illumination damage occurs, and based on this finding, the present invention has been accomplished.

That is, the present invention divides ammonia-containing wastewater generated from methane fermentation treatment into an area with an aquatic plant cultivation bed, a treatment area, and an overflow area, and transforms the treatment area into a culture soil with a gravel layer in the lower layer and an aerated soil layer in the upper layer. In addition to having a structure in which aquatic plants are planted, the height of the overflow port provided at the end of the overflow area can be adjusted vertically, and the height of the overflow port can be adjusted in sequence according to the growth of the roots of the aquatic plants. The present invention provides a method for purifying wastewater characterized by adjusting the depth of the vent by lowering the depth of the vent.

Next, one example of an embodiment of the present invention will be described according to the accompanying drawings.

FIG. 1 is a longitudinal cross-sectional view for explaining an example of the structure of a septic tank used in the method of the present invention.
It is divided into a raw water receiving area A, a treatment area B, and an overflow area C by two weir plates 2 and 3. A gap is provided below the two weir plates 2, and a gap is provided above the weir plate 3, allowing free circulation in each area. The treatment area B has a structure in which aquatic plants such as water hyacinth 6,6, etc. are planted in a culture soil having a gravel layer 4 as a lower layer and an aerated soil layer 5 as an upper layer. This gravel layer 4 is composed of inorganic solids such as gravel, slag, etc. with a particle size of 20 to 30 mm, and the aerated soil layer 5
The soil layer is composed of porous granules having a grain size of one shoulder or less, such as river sand, soil, etc., and it is preferable to use a material with good air permeability, water permeability, and water retention as the aerated soil layer.

The thickness of the gravel layer 4 should be such that it can sufficiently support the aerated soil layer 5 and that the supplied wastewater can be smoothly distributed.
Although there is no particular restriction, the thickness of the aerated soil layer 5 needs to be at least greater than the depth reached by the root threads of aquatic plants, and is usually selected in the range of 15 to 30 cz.

As an aquatic plant to be planted in the soil having such a structure, water hyacinth is suitable, but other aquatic plants that have the ability to absorb and nitrify ammonia, such as Phytophthora japonica, can also be used.

” The water hyacinth in the second book is Pontederiaceae
It is a type of perennial plant belonging to the genus tederiaceae, and its scientific name is Eichhornia crassipes.
bornia Crassipes), and is widely distributed in ponds, lakes, marshes, and low-lying areas.

This water hyacinth is 1M in the normal treatment area B! 2 per 4~
Planted at a rate of 10 plants.

Next, an overflow lower is provided at the end of the overflow area C to discharge the treated wastewater, and the height of this can be adjusted up and down. As the root threads grow, the height is gradually lowered and
lower the water level and adjust the vent depth. Adjustment of the height of the overflow lower can be done manually whenever necessary, or it can be done automatically by detecting the tip position of the root filament with an appropriate sensor.

This septic tank is usually designed in a rectangular shape as shown in Figure 1, but there is no particular restriction on this shape. It can be set as an overflow area, or conversely, it can be set as a raw water receiving area, a treatment area, and an overflow area sequentially from the outside.

To treat ammonia-containing wastewater using this septic tank, first, the raw water receiving area A has an ammonia concentration of 11,000 pp.
Introduce methane fermentation treated wastewater adjusted as follows. The feed rate of this wastewater is 0.0 ammonia per aquatic plant.
The ratio is selected to be 5 to O.ly/day.

The introduced wastewater passes through the gap at the bottom of the first weir plate 2, enters the gravel layer 4 of the treatment area B, gradually rises up to reach the aerated soil layer 5, and reaches the roots of aquatic plants. The ammonia is absorbed and removed here. The wastewater from which ammonia has been removed then enters the overflow area C through the gap at the bottom of the second weir plate 3, and is discharged to the outside through the overflow lower provided at the end.

In this way, ammonia can be removed at a high removal rate of 80% on average and 92% at maximum.

The septic tank in the method of the present invention can be provided with an air inlet pipe at an appropriate location as necessary to further promote the nitrification effect of ammonia. For example, a sand layer may be provided to facilitate the flow of wastewater.

Effects of the Invention According to the present invention, wastewater containing a relatively high concentration of ammonia can be treated using a septic tank with a very simple structure and with simple operation, and ammonia can be removed with a high removal rate. Therefore, it is suitable as a method for treating wastewater after methane fermentation treatment.

Example Next, the present invention will be explained in more detail with reference to Examples.

Example 5.511. As shown in Figure 1, a concrete septic tank with a width of 2.7 shoulders and a height of 0.7 mm is constructed by two weir plates with water holes at the bottom, each with a length of 0 in the vertical direction.
, 5 Jl, 4.5 shoulder, and 0.5 Jl to form a raw water receiving area, a treatment area, and an overflow area.

Next, gravel with a particle size of 20 to 40 va is spread over the treatment area to a thickness of 30 cm, and on top of that, Kanuma soil is spread to a thickness of 30 cI.
It was layered with I and used as a potting soil. This cultivation soil has 30ca of front and back and left and right
112 plants were planted at intervals of +.

A septic tank with this structure has a BOD of 2500 g/N,
C0D21000+1? #', ammonia content 300p
The wastewater from the methane fermentation process containing pm was passed for 120 days under the conditions of an ammonia area load of 0.5 g/lI2/day, and the ammonia nitrogen removal rate during that period was measured. During this period, the height of the overflow opening was lowered according to the growth of the roots of the water hyacinth, and the water level in the treated area was adjusted so that it was almost at the tip of the roots.

The results thus obtained are shown in FIG. 2 as a solid line graph.

For comparison, the results obtained when the same treatment was performed without adjusting the water level in the treatment area are also shown as a broken line graph.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an example of the structure of a septic tank used in the method of the present invention, and FIG. 2 is a graph showing changes over time in the ammonia nitrogen removal rate of wastewater treated according to the present invention. In the figure, numeral 1 is a septic tank, 4 is a gravel layer, 5 is an aerated soil layer, and 6 is a water hyacinth. Procedural Amendment May 1988 228 1. Indication of the case Patent Application No. 248044 of 1985 2. Name of the invention Wastewater purification method 3. Person making the amendment Relationship to the case Patent applicant Address Address Inashiki District, Ibaraki Prefecture 536-92 Ushiku, Ushiku Town Name: Takaaki Kawa (and 1 other person) 4. Agent 5. Date of amendment order Voluntary 8. Contents of amendment (1) Figure 2 of the drawings will be corrected as shown in the attached sheet. .

Claims (1)

[Claims] 1. When purifying ammonia-containing wastewater generated from methane fermentation treatment through a septic tank equipped with an aquatic plant cultivation bed, the septic tank is connected to the raw water receiving area, treatment area, and overflow area using two dam plates that allow partial circulation. The treatment area is divided into sections and has a structure in which aquatic plants are planted in culture soil with a gravel layer in the lower layer and an aerated soil layer in the upper layer, and the height of the overflow opening provided at the end of the overflow area is adjusted vertically. By making it adjustable and gradually lowering the height of the overflow port according to the growth of aquatic plant roots,
A method for purifying wastewater, comprising adjusting the depth of the aeration section in the treatment area.