JP7818293B2 - Dairy cow waste treatment system - Google Patents

Description

The present invention relates to a treatment system that combines physical and biological treatment of dairy cow waste.

Currently, the methane fermentation (anaerobic fermentation) treatment method described in Patent Document 1 is being introduced mainly in Hokkaido as one of the livestock waste treatment methods. In this treatment method, methane gas (biogas) is produced from livestock waste (organic waste), and this methane gas is used as a renewable energy source for power generation, boilers, etc. Furthermore, the residue (digestive liquid) after methane fermentation is mostly water, but contains large amounts of fertilizer components such as nitrogen, phosphorus, and potassium, and is used as liquid fertilizer.
In this way, the methane fermentation method makes it possible to realize recycling-based agriculture with less environmental impact (GHG emissions) than the general composting method.

Japanese Patent Application Laid-Open No. 2002-192193

However, the amount of digestive fluid produced by dairy cows is enormous, and there are many constraints to using all of it as liquid fertilizer, such as "requiring a field (such as pasture) large enough to spray it three times a year (twice a year in Hokkaido),""requiring facilities to store four to six months' worth of digestive fluid," and "whether we can gain the understanding of local governments and residents."
Furthermore, the purification and wastewater treatment of excess digestive fluid requires a large initial investment and running costs.
Furthermore, the reuse of sawdust, which is used in the dairy industry as bedding and as a moisture-regulating secondary material for solid compost production, is also an issue.

The present invention was made with an eye on the above-mentioned conventional problems, and aims to provide a new and useful dairy cow waste treatment system that combines technologies that have not been widely used in the livestock farming field until now, such as physical treatment and biological treatment used in industrial wastewater and sewage treatment facilities, to purify excess treated water to below the effluent standards that allow it to be discharged into rivers, thereby minimizing the size of the liquid fertilizer storage tank for the digestive fluid.
Another object of the present invention is to provide a new and useful dairy cow waste treatment system that can reduce the cost of purchasing sawdust by recovering and recycling it when sawdust is used as bedding and is inevitably contained in dairy cow waste.

The present invention was made to solve the above-mentioned problems and provides a dairy cow waste treatment system that includes an anaerobic fermentation tank that produces biogas and sulfides from the centrifuged liquid of dairy cow waste, which has been centrifuged as a physical treatment to remove solids; an aerobic treatment tank that receives treated water from the fermentation tank, removes organic matter, and nitrifies the contained ammonia nitrogen to produce nitrate nitrogen and/or nitrite nitrogen; and a denitrification tank that uses the sulfides to denitrify the nitrate nitrogen and/or nitrite nitrogen contained in the treated water from the aerobic treatment tank. The aerobic treatment tank and the denitrification tank are configured in a circulating manner, and the treated water from the fermentation tank is extracted as liquid fertilizer, and the treated water from the aerobic treatment tank is purified so that it can be discharged into a river.

Preferably, the biogas desulfurization device uses treated water from the aerobic treatment tank as washing water, and the washing wastewater is returned to the denitrification treatment tank for the purpose of utilizing sulfide.
Preferably, the aerobic treatment tank is composed of a DHS treatment tank in the first stage and an AUF treatment tank in the second stage, and phosphorus-containing sludge is recovered in a settling section provided in the DHS treatment tank.
Preferably, the fermentation treatment tank is a UASB treatment tank, and the denitrification tank is a UAF treatment tank.
Preferably, a receiving tank is provided between the UASB treatment tank and the UAF treatment tank, and the liquid fertilizer and ash are recovered from the receiving tank.
Preferably, the physical treatment unit comprises a screen treatment unit and a centrifuge unit, and the sawdust is separated and recovered from raw water containing dairy cow excrement including sawdust in the screen treatment unit at the front stage, and ash is separated and recovered in the centrifuge unit at the rear stage, and the remaining centrifuged liquid is sent to the biological treatment unit.
Preferably, the biogas is used as a heat source for drying the sawdust separated and recovered in the screen treatment section, and the exhaust heat is used to warm the centrifuged liquid introduced into the UASB treatment tank.

According to the dairy cow waste treatment system of the present invention, it is possible to purify excess treated water to a level below the effluent standards that allow it to be discharged into rivers, and the size of the liquid fertilizer storage tank can be minimized.
In addition, sawdust can be collected and recycled, reducing the cost of purchasing it.

1 is a configuration diagram of a dairy cow excrement treatment system according to an embodiment of the present invention. FIG. 2 is a conceptual diagram of the structure of the concentration adjusting tank of FIG. 1. FIG. 2 is a conceptual diagram of the structure of the UASB treatment tank of FIG. 1. FIG. 2 is a conceptual diagram of the structure of the UAF treatment tank of FIG. 1. FIG. 2 is a conceptual diagram of the structure of the DHS treatment tank in FIG. 1. FIG. 2 is a conceptual diagram of the structure of the AUF treatment tank in FIG. 1. FIG. 2 is a conceptual diagram of the structure of the desulfurization device of FIG. 1. This is a photo of the recycled sawdust after drying. This is a photograph of the solid matter (solid compost) separated by a centrifuge.

A dairy cow excrement treatment system 1 according to an embodiment of the present invention will be described with reference to FIG.
This dairy cow waste treatment system 1 treats an organic raw material that is a mixture of dairy cow waste (feces, urine) and sawdust used as bedding. A physical treatment section is provided before the biological treatment section to remove as much sawdust that is unsuitable for fermentation, impurities, SS (floating matter, mainly ash), etc. as possible, making the subsequent biological treatment more effective.
The organic raw material is charged into the raw material tank 3, and while being stirred, water is added to dilute it 3 to 4 times. As a result, the moisture content is increased from about 82 to 83% to about 94 to 95%, and the organic raw material becomes a slurry. The AUF treated water from the subsequent stage is used as the dilution water.

The physical treatment section is configured to include a screen section 5 and a centrifugal separation section 7 .
The screen section 5 is constructed of a drum-type wedge wire screen, for example, manufactured by Ando Screen Manufacturing Co., Ltd., and the mesh size of the screen is set to about 1 mm, which is suitable for separating sawdust (and other impurities).
The centrifugal separation section 7 is configured as a screw decanter type centrifuge, for example, manufactured by IHI Rotating Machinery Engineering Co., Ltd., and is set to approximately 1,500 to 2,500 G, which is suitable for separating SS and the like (suspended matter, especially ash).

The diluted organic raw material in a slurry state is sent to the screen section 5, where solid-liquid separation is performed, and sawdust (including other impurities) is separated and recovered as a solid content. After the impurities are removed, the sawdust is dehydrated in a dehydrator (not shown). The sawdust recovery rate is about 80%, and the moisture content after dehydration is about 70%. The dehydrated sawdust is sent to the dryer 9, where it is sterilized, dried, and recycled. The dilution water used for solid-liquid separation is the AUF treated water from the subsequent stage.
Meanwhile, the screen filtrate and the dehydrated effluent from the dehydration are sent to the centrifugal separator 7 via the intermediate receiver 11. Here, gravity separation is performed, and as much of the solid matter as possible, such as suspended solids (SS) (particularly ash), is separated and recovered. This recovered SS, which has a moisture content of 70% or less, is transported to a compost shed, where a small amount of moisture-adjusting auxiliary material is added to make it into a raw material for solid compost.

The centrifuged liquid is sent to the concentration adjusting tank 13. Here, water is added to dilute the liquid while stirring, and the concentration is adjusted.
As shown in Figure 2, a heater 13b is attached to the inside surface of the tank body 13a, and the stirring bar of an agitator 13c is inserted from above. Centrifuged liquid, i.e., raw water, is introduced through one opening on the upper side of the tank body 13a, and dilution water is introduced through the other opening, forming a liquid level below the opening. Adjusted water is discharged from the opening on the lower side and sent to the downstream UASB treatment tank 15.

Dairy cow waste is characterized by its high ash content, and the ash leaches out in the downstream UASB treatment tank 15 due to the decomposition of organic matter. If this ash accumulates in the downstream UASB treatment tank 15, it will hinder treatment within the tank. Therefore, by adding an appropriate amount of downstream AUF-treated water as dilution water based on the analytical properties of the centrifuged liquid, the CODcr volumetric load and CODcr concentration in the downstream UASB treatment tank 15 are optimized.

The temperature is also adjusted to a moderate fermentation temperature of around 35 to 37°C.
Such pretreatment makes it possible to treat the downstream UASB treatment tank 15 with a high CODcr volume load.

The concentration-adjusting solution is sent to the UASB processing tank 15 .
The UASB treatment tank 15 is based on the UASB (Up-flow Anaerobic Sludge Blanket) method. As shown in FIG. 3, the inside of the tank body 15a is filled with a large amount of highly active anaerobic microorganisms (mainly methane-producing bacteria and acid-fermenting bacteria) that have been aggregated to form granular sludge with excellent settling properties. A settler (solid-gas separator) 15b is attached above the granular sludge. Treatment in the tank proceeds in an anaerobic, methane fermentation-preferential environment.

The concentration-adjusted solution, i.e., raw water, is introduced into the bottom of the tank body 15a of the UASB treatment tank 15 and diffuses within the granular sludge. Then, under high-speed, high-load operation, the organic matter is decomposed by the action of acid-fermenting bacteria and methanogens to produce biogas (methane gas and carbon dioxide).
The generated biogas floats in the liquid, is separated by the settler 15, and is discharged outside the tank. Because the biogas contains more than several thousand ppm of hydrogen sulfide, it is passed through the desulfurization device 17, where it is washed and desulfurized using weakly alkaline AUF treated water as washing water.

As shown in Figure 7, the desulfurization device 17 has a long cylindrical body 17a filled with numerous plastic basket-shaped filters 17b. A sprinkler is used to direct AUF-treated water downward from the top of the long cylindrical body. This water comes into contact with the rising biogas injected from the bottom, dissolving the hydrogen sulfide contained in the AUF-treated water. The cleaned biogas is recovered from the upper port. A portion of carbon dioxide is further removed from the biogas, and the remaining biogas is generally temporarily stored in a gas holder and used as fuel. In this dairy cow waste treatment system 1, this biogas is used as fuel for the gas burner installed in the dryer 9. Furthermore, the waste heat generated by the sterilization and drying of sawdust in the dryer 9 is used to heat the concentration adjustment tank 13.
On the other hand, the washing wastewater in which hydrogen sulfide is dissolved is discharged from the lower port and sent to the downstream UAF treatment tank 23, where the recovered and removed hydrogen sulfide is used for denitrification.

Due to the characteristics of the centrifuge section 7, the organic matter contained in the centrifuged liquid sent to the UASB treatment tank 15 contains a high proportion of persistent organic matter, which contains a large amount of ash, and these are eluted by the decomposition of the organic matter, causing an increase in the SS concentration (mainly ash).In addition, the total nitrogen concentration is also high, and some of it is converted to ammonia by the action of organic nitrogen-decomposing bacteria, causing an increase in the concentration of ammonia nitrogen.
Furthermore, organic matter is decomposed by the action of sulfate-reducing bacteria, producing sulfides (mainly hydrogen sulfide and its compounds), which are incorporated into the biogas and dissolved in the liquid.

The UASB treated water flows out from the upper opening of the UASB treatment tank 15 .
The UASB treated water is sent to the receiving tank 19, where the ash is collected at the bottom, and then returned to the intermediate receiving tank 11, where it merges with the route that is treated in the centrifugal separator 7. Therefore, the ash collected at this stage is also recycled as solid compost.
Furthermore, the UASB treated water is a methane fermentation digestate into which almost all of the fertilizer components nitrogen, phosphorus, and potassium contained in the raw materials have been transferred, and can of course be used as liquid fertilizer, but subsequent processing can purify it to the point where it can be released into rivers.Therefore, by starting to store the amount of liquid fertilizer that you want to use in the liquid fertilizer storage tank 21 several weeks before use, you can ensure that you have the necessary and sufficient amount to suit the timing of use, and you can minimize the size of the liquid fertilizer storage tank 21.
The portion not used as liquid fertilizer is sent to the UAF treatment tank 23.

The UAF treatment tank 23 is based on the UAF (Up-flow Anaerobic Filter) method, and as shown in Figure 4, the inside of the tank body 23a is divided into upper and lower sections by a separator (mesh) 23b. The lower section is filled with a large number of polyurethane sponge carriers 23c (sold by Sekisui Plastics Co., Ltd., for example) on which a biofilm has formed, and the upper section contains the above-mentioned sponge carriers 23c housed inside a plastic basket-shaped filter 17b used as a basket 23d, and a biofilm has also formed on this basket 23d.
The treatment takes place in an anaerobic atmosphere inside the tank.

UASB treated water flows in from the bottom, and AUF treated water from the subsequent stage flows in as circulating water from just above separator 23b at a reflux ratio of 2 to 4.
In the lower part, residual organic matter contained in the inflowing UASB treated water is decomposed by the action of sulfate-reducing bacteria to produce sulfides, which then rise upward together with the sulfides contained in the UASB treated water and the washing wastewater discharged from the desulfurization unit 17.
In the upper part, sulfur-oxidizing bacteria oxidize sulfides to produce sulfur.
This sulfur is utilized in the upper part, where the nitrate nitrogen and nitrite nitrogen contained in the returned AUF-treated water are reduced by the action of sulfur-oxidizing denitrifying bacteria, resulting in denitrification and the production of nitrogen gas.

As described above, the sulfides produced by processing within the dairy cow waste treatment system 1 reduce the oxygen molecules of nitrite and nitrate, resulting in denitrification, which eliminates the need to add organic matter (e.g., ethanol) from outside the system to make up for any shortage, making the system economical.
At the same time, denitrifying bacteria (heterotrophic bacteria) live symbiotically with the remaining organic matter, using it as a nutrient source, and through their action, denitrification occurs, producing nitrogen gas.
The nitrogen gas produced is released outside the system.

The UAF treated water is sent to a receiving tank 25 and then sent to a DHS treatment tank 27 .
The DHS treatment tank 27 is based on the DHS (Down-flow Hanging Sponge) method, and as shown in Figure 5, the inside of the tank body 27a is divided into upper and lower sections by a separator (mesh) 27b. The tank is also filled with a large number of sponge carriers 27c on which a biofilm has formed, housed in baskets 27d.
The carrier (27c+27d) has a multi-stage structure with gaps between each stage, and the separator 27b is disposed between some of the gaps.
The separator 27b separates the carriers (27c+27d) above and below it so that they do not mix with each other.
Furthermore, when the weight of the carriers (27c+27d) is applied, the lower carrier (27c+27d) tends to collapse, but the gaps provided as described above distribute the weight and make it less likely to collapse.Furthermore, the gaps are also used for ventilation.
The inside of the tank is open to the outside and ventilated, resulting in an aerobic atmosphere with oxygen outside the sponge and an anaerobic atmosphere with inorganic oxygen inside the sponge.

UAF treated water flows in dropwise from the top, passes through each stage, and is discharged from the bottom.
As a result of treatment in the UASB treatment tank 15, 60 to 70% of the nitrogen exists as ammonia nitrogen, and the remainder exists as organic nitrogen, and these are introduced into the DHS treatment tank 27 via the UAF treatment tank 23.
In the DHS treatment tank 27, sludge bacteria (heterotrophic bacteria) that decompose and remove organic matter and nitrifying bacteria (autotrophic bacteria) that are involved in nitrification form a biofilm on the surface of the sponge carrier, and the organic matter is removed by the action of the sludge bacteria, and ammonia nitrogen is oxidized by the action of the nitrifying bacteria, converting it into nitrate nitrogen and nitrite nitrogen.

Furthermore, the sludge bacteria store in their biofilm the phosphorus that has been carried to the biological treatment unit in the organic raw materials, so the sludge bacteria, with the phosphorus concentrated, settle in the settling unit 29 located at the bottom and is ultimately recovered as excess sludge. This excess sludge is returned to the intermediate receiving tank 11 and merges with the route that is treated in the centrifugal separation unit 7. Therefore, the phosphorus-containing sludge recovered at this stage can also be used as a raw material for solid compost.
In addition, a small amount of denitrification also occurs inside the sponge due to the action of denitrifying bacteria.

The DHS-treated water is sent to a receiving tank 31 and then to an AUF treatment tank 33 .
The AUF treatment tank 33 is based on the AUF (Aerobic Up-flow Filter) method and serves as a supplement to the DHS treatment tank 27. As shown in Figure 6, the tank body 33a is divided into upper and lower sections by a separator (mesh) 33b, and the lower section is filled with a large number of plastic baskets 33c on which a biofilm has formed.
The tank is open at the top and aerated at the bottom, making it an aeration tank.

The DHS-treated water is supplied from the bottom of the AUF treatment tank 33 and overflows from the top, where it undergoes the removal of remaining organic matter and the nitrification of remaining ammonia nitrogen. The AUF treatment tank 33 is provided to complement the treatment in the DHS treatment tank 27. By passing the water through this AUF treatment tank 33, it is further biologically purified, ensuring that it can be released into rivers or used as drinking water for dairy cows.
The pH of the AUF-treated water is weakly alkaline (pH = 8.2 to 8.5). As described above, this AUF-treated water is circulated between the AUF-treated water and the UAF treatment tank 23. At the same time, as described above, the AUF-treated water is supplied to the desulfurization device 17 and used to desulfurize hydrogen sulfide in the biogas.

In the biological treatment of dairy cow waste, the challenges are the recovery and removal of ash and the removal of ammonia nitrogen. Ash that can be separated by physical treatment is removed at that stage, and ammonia nitrogen is ultimately converted into nitrogen gas.
The properties of the AUF-treated water are well below the uniform discharge standards set by the Ministry of the Environment, particularly the standard values for nitrate nitrogen (health items) and nitrogen content (environmental items) that are problematic in livestock wastewater, so it can be discharged into rivers. Therefore, it is possible to extract the required amount of water from the system as liquid fertilizer at the required time.
Furthermore, there are regions across the country that have established standards for discharge into lakes, ponds, closed bodies of water, etc., and additional discharge standards that are stricter than the uniform discharge standards may be required. However, this dairy cow waste treatment system 1 can fully comply with these discharge standards by optimizing the load on each biological treatment tank (specifically, CODcr volume load, BOD volume load, NO ₃ -N volume load, etc.).

The sulfides produced in the dairy cow waste treatment system 1 are used for denitrification. Furthermore, the treated water produced in the dairy cow waste treatment system 1 is also used for cleaning the biogas and for other dilution purposes.
The following table shows the analysis results of the final treated water (AUF treated water) treated by this dairy cow waste treatment system 1.

In this way, the dairy cow waste treatment system 1 does not use any chemicals (such as flocculants or desulfurization agents), and all treatment is carried out using only the substances contained in the raw material, the dairy cow waste, making it a process with extremely low environmental impact.
Figure 8 shows the sawdust after drying, and Figure 9 shows the solid compost.

AUF-treated water can also be used within facilities as drinking water for dairy cows. Dairy cows drink large amounts of water, about 100 liters per cow per day, so by using it as drinking water, discharge into rivers can be reduced to zero.

When the final treated water is to be discharged into a river or used within a facility, color may become an issue, although it is not a control item for wastewater standards. In such cases, color removal can be performed in the color removal filtration tank 39.
Activated carbon and ozone water are generally used, but due to economic reasons, their use in the livestock farming sector is difficult. However, in this dairy cow waste treatment system 1, as an example, a color removal treatment is carried out using a special ceramic (for example, New Color Cutter Light, a product of Nippon Genryo Co., Ltd.) that generates hydroxyl radicals using free chlorine as a catalyst.

Although the embodiments of the present invention have been described in detail above, the specific configuration is not limited to these embodiments, and the invention also includes design changes within the scope of the present invention without departing from the gist of the present invention.
For example, the configuration of the equipment and treatment tanks used in physical treatment and biological treatment can be changed as long as the effects envisaged by the present invention can be expected.

DESCRIPTION OF SYMBOLS 1... Dairy cow waste treatment system 5... Screen section 7... Centrifugal separation section 9... Dryer 11... Intermediate receiving tank 13... Concentration adjustment tank 15... UASB treatment tank 17... Desulfurization device 21... Liquid fertilizer storage tank 23... UAF treatment tank 27... DHS treatment tank 29... Sedimentation section
33...AUF processing tank

Claims (7)

The system is equipped with a biological treatment unit that includes an anaerobic fermentation tank that produces biogas and sulfides from the centrifuged liquid of dairy cow waste, which has been centrifuged as a physical treatment to remove solids , an aerobic treatment tank that removes organic matter and nitrifies ammonia nitrogen to produce nitrate nitrogen and/or nitrite nitrogen, and a denitrification tank that denitrifies the nitrate nitrogen and/or nitrite nitrogen .
the denitrification tank receives treated water from the anaerobic fermentation tank;
the aerobic treatment tank receives treated water from the denitrification treatment tank;
The denitrification treatment tank also receives treated water from the aerobic treatment tank, so that the treated water from the denitrification treatment tank and the treated water from the aerobic treatment tank circulate between the denitrification treatment tank and the aerobic treatment tank,
The denitrification treatment tank denitrifies nitrate nitrogen and/or nitrite nitrogen contained in the treated water from the aerobic treatment tank by utilizing the sulfide contained in the treated water from the anaerobic fermentation treatment tank,
the aerobic treatment tank removes organic matter contained in the treated water from the denitrification treatment tank and nitrifies ammonia nitrogen to generate nitrate nitrogen and/or nitrite nitrogen, thereby purifying the treated water from the aerobic treatment tank so that it can be discharged into a river;
A dairy cow waste treatment system characterized in that treated water from the anaerobic fermentation treatment tank is extracted as liquid fertilizer in the required amount at the required time, the amount not used as liquid fertilizer is sent to the denitrification treatment tank, and excess treated water from the aerobic treatment tank is discharged into a river. 2. The dairy cow waste treatment system according to claim 1,
A dairy cow waste treatment system characterized in that a biogas desulfurization device uses treated water from the aerobic treatment tank as washing water, and the washing wastewater is returned to the denitrification treatment tank for the purpose of utilizing sulfides. 3. The dairy cow waste treatment system according to claim 1,
The aerobic treatment tank is composed of a DHS (Down-flow Hanging Sponge) treatment tank in the front stage and an AUF (Aerobic Up-flow Filter) treatment tank in the rear stage, and this dairy cow waste treatment system is characterized in that phosphorus-containing sludge is recovered in a settling section provided in the DHS treatment tank. 4. The dairy cow waste treatment system according to claim 3,
A dairy cow waste treatment system characterized in that the anaerobic fermentation treatment tank is composed of a UASB (Up-flow Anaerobic Sludge Blanket) treatment tank, and the denitrification treatment tank is composed of a UAF (Up-flow Anaerobic Filter) treatment tank. 5. The dairy cow waste treatment system according to claim 4 ,
A dairy cow waste treatment system characterized in that a receiving tank is provided between the UASB treatment tank and the UAF treatment tank , treated water from the UASB treatment tank is sent to the receiving tank, and only the required amount is extracted from the receiving tank at the required time as liquid fertilizer, and ash collected at the bottom of the receiving tank is recovered . 6. The dairy cow waste treatment system according to claim 5,
A physical treatment unit composed of a screen treatment unit and a centrifuge unit is further provided in the upstream of the biological treatment unit , and sawdust is separated and recovered in the screen treatment unit from raw water containing dairy cow excrement containing sawdust. Then, the centrifugal separation unit separates and recovers the solids , and the remaining centrifugal separation liquid is sent to the biological treatment unit .
A dairy cow waste treatment system characterized in that the ash recovered from the lower part of the receiving tank also merges with the route treated in the centrifugal separation section . 7. The dairy cow waste treatment system according to claim 6,
This dairy cow waste treatment system uses biogas as a heat source for drying the sawdust separated and recovered in the screen treatment unit, and utilizes the exhaust heat to warm the centrifuged liquid introduced into the UASB treatment tank.