JPH0143600B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for dewatering and drying organic sludge.

[Conventional technology]

Generally, when organic wastewater such as sewage and human waste is treated by a biological treatment process such as an activated sludge method, an aeration blower 28 for supplying oxygen to the aeration tank 22 is arranged as shown in FIG. Conventionally, the function of this aeration blower 28 was simply that of the aeration tank 22.
It only performs a single function, which is to supply oxygen to the human body, and to this day this has been taken for granted without any question being raised.

On the other hand, organic sludge such as sewage sludge, human waste sludge, and surplus sludge 24 is dehydrated by various dehydrators 25 and becomes a dehydrated cake 26 with a water content of around 80%. Since it is very inconvenient to dispose of it by landfilling or the like, it is necessary to dry it using various drying machines 27. but,
The reality is that the conventional dryer 27 consumes a large amount of fuel, making it an energy-intensive process. Moreover, it is undeniable that the current state of the industry is that intensely foul-smelling exhaust gas 37 is discharged from this drying process, and that the deodorizing process 35 of the foul-smelling exhaust gas 37 requires a large amount of equipment and maintenance costs.

In addition, in Fig. 1, 21 is organic wastewater, 32
is settling tank, 33 is return sludge, 34 is treated water, 36
is oil for the drying machine 27, and 38 is deodorizing gas.

[Purpose of the invention]

The present invention eliminates the above-mentioned problems of the prior art, and provides an extremely rational sludge treatment method that can significantly save energy in the organic sludge drying process and simultaneously perform deodorization of malodorous components in the drying exhaust gas. The purpose is to provide the following.

[Structure of the invention]

The present invention is based on the technical idea that the energy possessed by the air discharged from the aeration blower, which was conventionally used only for supplying oxygen to the aeration tank, can also be used for drying water-containing materials such as sludge dewatering cake in a new embodiment. A vertical drying process is installed in the middle of the piping route that connects the aeration blower discharge side and the aeration part of the wastewater treatment process or organic sludge treatment process, and organic sludge, mainly activated sludge, is dried by the machine. In the dehydration step, dehydration is carried out so that the moisture content is below the liquid limit, the obtained dehydrated cake is made into lumps or granules, and a packed bed of the lumped or granulated dehydrated cake is formed in the drying step, and the drying is performed. Aeration blower compressed air is aerated into the process packed bed to aerate and dry the dehydrated cake, and the air flowing out from the drying process is
This is a method for treating organic sludge, characterized in that the organic sludge is supplied to the aeration section having a diameter that will not be clogged by dust entrained from the packed bed and used for aeration.

Note that the term "organic sludge" in the present invention refers to sludge containing organic matter, and is used to include coagulated sedimentation sludge and coagulated floatation sludge in the tertiary treatment of sewage.

Next, one embodiment of the present invention will be described with reference to FIG. 2. An aeration section 3 is provided below the water surface in an aeration tank 2 for organic wastewater 1, and a mechanical dewatering process 5 for surplus sludge 4 ( A dehydrated cake 6 discharged from a belt press, filter press, screw press, etc., which has been dehydrated to a moisture content below the liquid limit, is separated into particles with a particle size of several cm.
The granulated material is supplied to a drying step 7 equipped with a dehydrated cake filling section 7'.

Therefore, the discharge air 9 of the aeration blower 8 is vented into the drying process 7, and the discharge air 9 is transferred to the dehydrated cake 6.
The exhaust air 10 is brought into direct contact with the air diffuser 3.
and used for aeration in the aeration tank 2.

As is clear from the theory of adiabatic compression of gas, the temperature of the discharged air 9 of the aeration blower 8 rises to 70 to 80°C when the water depth of the aeration section 3 is about 5 m.

Conventionally, the thermal energy of the discharged air 9 has not been utilized effectively at all, but in the present invention, it is effectively utilized for drying the dehydrated cake 6 through ventilation.
As a result, the aeration blower 8 performs the important combined functions of supplying oxygen to the aeration tank 2 and drying the dehydrated cake 6.

As a result, energy for drying the dehydrated cake 6 is substantially unnecessary, and the energy saving effect is significant. In addition, conventional dryers require a deodorizing process for foul-smelling exhaust gas, but the dry exhaust gas, that is, the exhaust air 10, is automatically supplied to the aeration tank 2, and the vast amount of microorganisms present in the aeration tank 2 Another important advantage is that no special deodorizing process is required since the odor is biologically deodorized.

Furthermore, in conventional dryers, a process of removing dust from dry exhaust gas is essential, but in the present invention, the exhaust air 10 containing dust is supplied to the aeration tank 2, so the aeration tank 2 is a kind of collection point. Since it functions as a dust machine, no special dust removal process is required. For this reason, the diameter of the discharge air hole of the air diffuser 3 is made as large as possible, several mm or more, to prevent clogging with dust.

It should be noted that although one filling section 7' may be provided, if a plurality of filling sections 7' are provided in parallel as shown in Fig. 3 and the dried material 11 is taken out after the dehydrated cake 6 is dried, the discharge air 9 to another filling part 7'
Operational management becomes extremely easy if the valve is operated to switch to the .

Therefore, in the drying step, it is essential to keep the moisture content of the dehydrated cake below the liquid limit, rather than regulating the absolute value of moisture. In other words, the dehydrated cake that is below the liquid limit easily becomes lumps or granules (it is not sticky), and even when stacked to form a packed bed, the sludge does not stick to each other, and the sludge at the bottom of the packed bed is Because of its strong supporting force, it is not compacted and can maintain sufficient porosity. Therefore, even if the packed bed thickness is 1 m to 2 m, sufficient voids between the sludge can be maintained, making uniform ventilation easy, reducing ventilation resistance, preventing uneven drying, and making it easy to take out the dried material. In addition, since the packed bed thickness can be set high, sufficient contact time between the aeration blower discharge air 9 and the dehydrated cake can be obtained, which is much lower than the supplied hot air temperature of several hundred degrees Celsius in conventional hot air dryers. ~75℃
The blower discharge air is warm air at a low temperature of about 9.
It is possible to make maximum use of the retained heat of the dried material, and the moisture content of the dried material can be effectively reduced.

The liquid limit water content of the dehydrated cake is:
This was determined by the four-cone method shown in FIG. In other words, the weight is 60° with a tip angle of 60°C.
After setting the cone 101 of No. g so that the tip of the cone is in contact with the surface of the sample 102, the cone 101 is allowed to fall under its own weight, and the penetration depth of the cone 101 is measured. The water content when the penetration depth of the cone 101 is 10 mm is defined as the water content at the liquid limit. In other words,
If a dehydrated cake is sampled and the cone penetration depth is less than 10 mm, it means that the moisture content of this dehydrated cake is below the liquid limit. Note that 103 in Figure 4
1 is a knob, 104 is a scale plate, and 105 is a sample container.

Therefore, the aeration layer 2 is used not only for the biological treatment process of the organic wastewater 1, but also for the aeration tank for aerobic digestion of surplus activated sludge, the re-aeration tank for return sludge, or the aeration tank for oxidation of reducing ions such as Fe ²⁺ ions. Of course, a tank is also fine.

When organic wastewater 1 contains ammonia nitrogen, if the aeration tank 2 not only removes BOD but also nitrates the ammonia nitrogen, it takes about 4.5 liters to oxidize 1 kg of ammonia nitrogen to No. ₃ .
Kg of oxygen is required, so the amount is larger than when only BOD removal to be supplied to the aeration tank 2 is performed.
As a result, the extremely important effect that the amount of water evaporating from the dehydrated cake 6 in the filling section 7' can be significantly increased is achieved.

In this way, according to the above embodiment, not only is there no need for any special equipment or maintenance costs for removing dust and malodorous components in the dry exhaust gas, but also the air discharged from the aeration blower is directly directed into the drying material filling section. This design eliminates the need for a heat exchanger, and the heat capacity coefficient of the drying material filling section is 2000~2000.
Since it is extremely large at 4000Kcal/ ^m3・hr・℃, the volume of the filling part can be small. As a result, the equipment cost for drying is significantly reduced.

The structure of the filling section 7' is most preferably that shown in FIG. Any type of material may be used as long as the discharged air 9 can come into direct contact with it.

Note that the direct ventilation method may be a fluidized bed or a fixed bed. Moreover, the aeration blower as used in the present invention means an air compressor that supplies oxygen-containing gas to the aeration process.

In Figure 2, 12 is a settling tank, 13 is return sludge, 1
4 is treated water.

〔Effect of the invention〕

The industrially important effects of the present invention are as follows.

It is possible to dry water-containing materials such as sludge dewatering cake in an energy-saving manner without using any heating materials such as heavy oil.

The dehydrated cake, which has been previously dehydrated to below the liquid limit, is agglomerated or granulated, thereby forming a packed bed in the drying process and then being vented and dried, making the drying process extremely simple and efficient.

Since the moisture content of dry matter can be easily reduced to 40% or less, it not only allows natural incineration, but also has the surprising effect of allowing energy recovery by using a boiler incinerator.

Since the exhaust air flowing out from the drying process has a foul odor, conventional deodorization processes such as chemical cleaning, adsorption, and direct combustion deodorization have been indispensable, but the equipment and maintenance costs for deodorization are quite high. There was a problem with that.

However, in the present invention, the discharge air of the aeration blower is used to dry the dehydrated cake, so the foul-smelling air flowing out from the drying process is automatically supplied to the aeration tank and biologically deodorized. Ru. Therefore, there is no need for a special deodorization process, and construction and maintenance costs can be significantly reduced.Furthermore, a blower that supplies dry exhaust air to the aeration tank is not required separately from the aeration blower. There is no need for blower power, which results in significant energy savings. Also, by using the same principle, equipment for removing dust from the dry exhaust air is not required.

Moreover, since the aperture of the air supply port of the air diffuser is set to a value that will not block it with dust, clogging of the air diffuser can be prevented, and
Since the air discharge resistance is small, a sufficient aeration effect (amount of aeration air) can be obtained.

Aeration blower To recover the heat of compressed air,
Since no heat exchanger is required, equipment costs can be significantly reduced. That is, since the aeration blower compressed air is directly vented into the drying process, direct heat exchange and heat transfer with the dehydrated cake progresses, and the heat retained in the aeration blower compressed air is recovered by the heat exchanger. This is because there is no need.

This fact truly demonstrates the superiority of the effect of the present invention when compared with the conventional process in which a large amount of auxiliary fuel is consumed and drying is incinerated.

〔Example〕

Example 1 In a certain human waste processing factory with a human waste processing capacity of 100Kl/day,
Human waste is treated using a biological nitrification-denitrification process (referred to in the field as the low-dilution two-stage activated sludge process). In this process, the aeration water depth of the aeration tank for nitrification is 5 m, and the discharge amount is
Air at 100Nm ³ /min is supplied to the aeration tank.

On the other hand, flocculated sludge generated from the process of coagulating and sedimentating excess activated sludge from the above process and process-treated water using sulfuric acid (the total amount of sludge generated from both processes is 8.5Kg・DS/Kl・human waste) was dehydrated using a fully automatic filter press with a squeezing mechanism (overpressure: 5 kg).
f/cm ² , compression pressure 15Kgf/cm ² ) Result, moisture content 68%
A dehydrated cake of (below the liquid limit rate) was obtained.

This dehydrated cake was crushed into particles with a particle size of about 1 to 2 cm using a crusher such as a meat chopper, and then filled into the filling section of the flow of the present invention (Fig. 2) (filling section capacity: 8 m ³ ), and the aeration blower discharged air (temperature 65~80℃)
was aerated at an empty loading speed of 0.8 to 1.0 m/sec, and the air discharged from the filling section was supplied to the aeration tank for nitrification. The air discharged from the filling section contained dust and exhibited an odor with an odor concentration of 1000 to 1500, but the air discharged from the water surface of the aeration tank contained very little odor and dust. After aeration for one day, the dehydrated cake was removed from the filling section and its moisture content was measured. As a result, the moisture content was extremely low at 15-20%, and the calorific value was high at 3000kcal/Kg・DS, so it was extremely easy to use in a boiler incinerator. Not only did it self-combust, but steam was also recovered, and even if this was used for heating and bathing in the administration building, there was still surplus steam left.

Example 2 At the human waste treatment plant described in Example 1, the surplus activated sludge and coagulated sludge generated from the treatment process were dehydrated using a centrifugal dehydrator instead of a filter press, and the water content of the dehydrated cake was 81%
(Liquidity limit rate or less) (Cationic polymer addition rate 1.5% to Dry solid). This dehydrated cake was granulated to a size of 1 cm x 2 cm and filled into the filling section of the flow of the present invention (Figure 2). The filling capacity of dehydrated cake is ^10m3
And so. This is combined with aeration blower discharge air (temperature 75
°C) at an empty speed of 0.8 m/sec, and the discharged air was supplied to the nitrification aeration tank. The moisture content of the dried product after one day of aeration was 68%, and it was possible to self-combust in a multi-stage furnace.

Next, when the centrifugal force of the centrifugal dehydrator was lowered to intentionally obtain a dehydrated cake with a water content of 86% (greater than the liquid limit rate), and an attempt was made to dry this using the method of the present invention, the dehydrated cake was High adhesiveness and low water content
Since it was extremely large (6.14KgH ₂ O/Kg・DS), granulation was impossible, and the dehydrated cakes adhered to each other in the packed bed, forming large lumps, making uniform aeration impossible. I was forced to ventilate in this situation, but 1
The moisture content of the dehydrated cake after day aeration is highly uneven; 78
~83%, making self-combustion impossible.

[Brief explanation of drawings]

Fig. 1 is a flow sheet showing a conventional organic wastewater treatment process, Fig. 2 is a flow sheet showing an embodiment of the present invention, Fig. 3 is a flow sheet for the drying process of a dehydrated cake, and Fig. 4 is a flow sheet showing a process for drying a dehydrated cake. It is an explanatory view showing an all-cone method liquid limit measuring device. 1...Organic wastewater, 2...Aeration tank, 3...Aeration section, 4
...excess sludge, 5...mechanical dewatering process, 6...dehydrated cake, 7...drying process, 7'...filling section, 8...aeration blower, 9...discharge air, 10...discharge air, 11...
Dry matter, 12...Sedimentation tank, 13...Return sludge, 14...
treated water.

Claims (1)

[Claims] 1. A vertical drying process is provided in the middle of a piping route connecting the aeration blower discharge side and the aeration part of the wastewater treatment process or the organic sludge treatment process, and organic sludge mainly composed of activated sludge is produced. is dehydrated in a mechanical dehydration step to a water content below the liquid limit, the obtained dehydrated cake is made into lumps or granules, and a packed bed of the lumped or granulated dehydrated cake is formed in the drying step, The aeration blower compressed air is aerated through the drying process packed bed to dry the dehydrated cake, and the air diffuser has a diameter that does not block the air flowing out from the drying process with dust entrained from the packed bed. A method for treating organic sludge characterized by supplying it to a department and using it for aeration. 2. The method according to claim 1, wherein the wastewater treatment step treats ammoniacal nitrogen-containing wastewater, and biologically nitrifies ammonia in the wastewater by the aeration. 3. A plurality of the drying processes are arranged in parallel, the packed bed is formed in each drying process, and the drying process is performed by switching the ventilation of the aeration blower compressed air to each drying process packed bed by operating a valve. The method described in item 1 or 2 of the range box.