JPH0366040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a new process that can treat organic wastes such as sewage sludge, human waste sludge, and kitchen waste in an extremely energy-saving manner. Below, sewage sludge will be explained as an example of a typical organic waste.

Conventionally, a wide variety of processes have been proposed for treating sewage sludge, but all of them have at least one of the following serious problems.

A large amount of auxiliary fuel is required to dry and incinerate the dehydrated cake.

Since it is self-combusted, it requires large amounts of additives such as pulverized coal and wood flour.

Energy cannot be recovered from sludge simply by disposing of it. In addition, even in the process of recovering energy such as electricity by driving a gas engine using methane gas generated in anaerobic digestion, there is no established rational method for disposing of digestion residue, so the amount of energy exceeds the amount of energy recovered. A major contradiction remains unresolved: energy is consumed in this process.

The sludge that flows into the anaerobic digestion tank has a poor ability to thicken, and when the sludge concentration becomes low, a large amount of heat is inevitably required to heat the digestion tank, and auxiliary fuel such as heavy oil is required, especially in the winter.

The present invention provides a process that can solve all of the above problems.

That is, the present invention performs an anaerobic digestion treatment on organic waste capable of methane fermentation, such as sewage sludge and kitchen waste,
Digestion residue is aerated with an oxygen-containing gas and then mechanically dehydrated, and the dehydrated cake is transferred to an aeration tank of a biological treatment process for organic wastewater and/or an aeration blower that supplies air to the aeration treatment process for the digestion residue. This is a method for treating organic waste, which is characterized by bringing it into direct contact with discharged air and drying it using the retained heat.

Next, one embodiment of the present invention will be described with reference to the drawings.

Sewage sludge 1 (raw sludge, surplus sludge, mixed raw sludge)
is concentrated in the concentration step 2, and the thickened sludge 3 flows into the anaerobic digestion step 4 (methane fermentation step). The digestive gas 5 generated here drives a gas engine 6 to recover motive power (or electric power) 7. Reference numeral 8 denotes an exhaust heat recovery path for recovering exhaust heat from the gas engine 6 and heating the digestion process 4 .

Therefore, the digested residue 9 (meaning digested sludge or a mixed slurry of digested fluid and digested sludge) is aerated in the aeration tank 22, and then the screw press,
It is dehydrated in a mechanical dehydration step 10 using a filter press or the like, and becomes a dehydrated cake 11 with a water content of 60 to 70% and dehydrated separated water 12.

If the digestion residue 9 is sufficiently aerated with air (or oxygen), the amount of dehydration aid injected in the mechanical dehydration step 10 can be reduced by 30 to 40%, and the moisture content of the dehydrated cake will also decrease by several percent, and the cause of this. It was found that this was due to the alkalinity and colloidal content of the digested residue being reduced by the action of microorganisms.
In addition, it has been recognized that if the digested residue 9 is treated with mechanical dehydration step 10 after adding and mixing fiber components 23 such as old newspapers, paper, and residue removed from sewage, a dehydrated cake with an even lower water content can be obtained. It was done. The fiber component is most preferably a residue (for example, one removed by a screen) that is inexpensive to obtain. Note that the fiber component 23 may be added before the aeration treatment.
24 is a blower for aeration.

Thus, in the drying step 17, the dehydrated cake 11 is brought into direct contact (indirectly contacted) with the discharge air 15' of the aeration blower 16 for supplying air 15 to the aeration tank 14 in the biological treatment step of the sewage 13. ), and is dried to a moisture content of 10-15% by its retained heat. Note that, if desired, the retained heat of the air discharged from the blower 24 may be used in combination, or the retained heat alone may be used for drying.

Conventionally, aeration blowers have been used only for aeration in wastewater biological treatment processes, and this has not been questioned as a matter of course.However, in the present invention, the blower 16 is Discharge air 15' is 80~90
Noting that the temperature also rises to .degree. C., this thermal energy is used to dry the dehydrated cake 11, and then the cooled air 15 is used for aeration.

Therefore, dry matter 18 has a calorific value of 2500 Kcal/
Kg・DS, moisture content 10-15%,
It has properties that allow it to be supplied to the boiler (or pyrolysis furnace) 19 as fuel, and no auxiliary fuel is required. Steam and oil generated from the boiler 19,
Energy 20 such as gas and char is used for digestion process 4, concentration process 2, mechanical dehydration process 10, and drying process 1.
7 as a heating heat source. 21 is a combustion residue.

In addition, since a large amount of surplus heat energy is always generated from the boiler 19 according to the present invention, the dehydration effect is significantly improved by the combined use of steam in the mechanical dehydration step 10 suitable for effectively utilizing this heat. A screw press is most preferable. Furthermore, since the driving energy 7' of the blower 16 can be provided by the energy recovered from the gas engine 6, in the present invention, the drying of the sludge itself is accomplished using the energy contained in the sludge itself. become.

The process of the present invention described above has the great effect of solving the above-mentioned problems of the conventional process, and also provides the following effects.

Since the dry exhaust gas discharged from the drying process of dehydrated cake has a bad odor, a special deodorizing process was required in the past, but in the present invention, it is biologically deodorized by the microorganisms present in large quantities in the aeration tank of sewage etc. No special deodorizing process is required. Therefore, deodorizing costs and equipment costs can be reduced.

Since auxiliary fuel is not required when drying and incinerating the digested sludge, the costs associated with such disposal are significantly reduced, while energy is recovered from the digested gas, so the cost is essentially spent on sludge treatment. On the contrary, profits can be generated by treating sludge.

Conventionally, there is a method of drying dehydrated cake using the combustion generated heat generated by incineration of the dehydrated cake, but in this method, the combustion generated heat is consumed only in the drying process, so an anaerobic digestion tank is used. cannot be used for heating.

In contrast, in the present invention, since the dehydrated cake is dried using the retained heat of the air discharged from the aeration blower, the amount of surplus combustion generated heat increases, and there is enough heat to heat the anaerobic digestion tank.

Since the anaerobic digestion residue is aerated, in addition to improving the dehydration properties as mentioned above, the
Contaminant components such as BOD and ammonia odor components are removed biologically. Moreover, even when dehydrating by adding residue removed from raw sewage,
Organic matter such as filth attached to the scum can be removed biologically.

Therefore, the dehydrated separated water in the present invention is extremely clear, and the dehydrated cake also does not have a bad odor. As a result, the occurrence of bad odor in the dehydrator room is naturally reduced.

Since methane gas has already been recovered from the anaerobic digestion residue, the organic components are reduced and the calorific value is lowered, but the calorific value increases by adding fiber content.

[Brief explanation of drawings]

The drawing is a flow sheet of one embodiment of the present invention. 1... Sewage sludge, 2... Concentration process, 3... Thickened sludge, 4... Digestion process, 5... Digestion gas, 6...
Gas engine, 7...Power, 7'...Driving energy, 8...Exhaust heat recovery path, 9...Digestion residue, 1
0... Mechanical dehydration process, 11... Dehydrated cake, 12
... Dehydrated separated water, 13 ... Sewage, 14 ... Aeration tank, 15 ... Air, 15' ... Discharge air, 16 ... Blower, 17 ... Drying process, 1
8... Dry matter, 19... Boiler, 20... Energy, 21... Incineration residue, 22... Aeration tank, 2
3...Fiber content, 24...Blower.

Claims (1)

[Claims] 1 Organic waste capable of methane fermentation, such as sewage sludge and kitchen waste, is subjected to anaerobic digestion treatment, the digestion residue is aerated with oxygen-containing gas, and then mechanically dehydrated, and the dehydrated cake is direct contact with the discharge air of an aeration blower that supplies air to the aeration tank of the biological treatment process of industrial wastewater and/or the aeration treatment process of the digestion residue,
A method for treating organic waste, characterized by drying it using the heat it retains. 2. Claim 1, wherein the mechanical dewatering step is carried out by supplying the digested residue to which fibers such as paper are added to a screw press.
Treatment method described in section. 3. The processing method according to claim 2, wherein the addition of fiber to the digested residue is performed after the aeration treatment. 4. The treatment method according to claim 2 or 3, wherein the fiber component is residue removed from sewage.