JP2002059197A - Method of treating excess sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To part a method of treating excess sludge which is capable of solubilizing sludge without supplying energy from outside by combining a solubilizing process for the excess sludge and a process for recovering the energy in the sludge. SOLUTION: In the method of treating the excess sludge which consists in introducing the sludge generated in a water treating process step into an anaerobic digester 9 to subject the sludge to digestion treatment and introducing the sludge subjected to the digestion treatment into a solubilizing tank 9 and subjecting the sludge to solubilizing treatment, the digester gas G generated in the anaerobic digester 9 is recovered and burned and the sludge is subjected to the solubilizing treatment by the combustion heat of the digester gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating excess sludge, and more particularly, to a method for dissolving excess sludge generated from an organic wastewater treatment facility without supplying external energy. The present invention relates to a method for treating sludge.

[0002]

2. Description of the Related Art Conventionally, in order to treat sewage flowing into a sewage treatment plant or the like, an activated sludge method in which sewage flows into a reaction tank for activated sludge, and is aerated and stirred to perform biological treatment. I have. Surplus sludge generated in the water treatment process is usually landfilled after dewatering, but since the disposal site is gradually disappearing, solute is added to the excess sludge to solubilize the sludge. However, a method has been attempted in which the amount of generated sludge is reduced to zero or close to zero by biodegradation in the system.

[0003]

However, according to the conventional method for treating excess sludge, even if the amount of generated sludge can be reduced to almost zero by solubilizing the excess sludge, the electric power of the ozone generator can be reduced. A large amount of energy is required for consumption and for heating the biological treatment tank, and there is a problem that the treatment cost for solubilizing sludge increases.

[0004] In view of the above-mentioned problems of the conventional method for treating excess sludge, the present invention provides a process for solubilizing excess sludge,
An object of the present invention is to provide a method for treating excess sludge, which can combine a process for recovering energy in sludge and solubilize sludge without supplying energy from outside.

[0005]

In order to achieve the above object, a method for treating excess sludge according to the present invention comprises introducing sludge generated in a water treatment step into an anaerobic digestion tank to perform digestion, and In a method for treating excess sludge, in which the treated sludge is introduced into a solubilization tank and solubilized, the digestion gas generated in the anaerobic digestion tank is collected and burned, and the sludge is solubilized by the heat of combustion of the digestion gas. Processing.

According to the method for treating excess sludge of the present invention, energy contained in excess sludge is recovered in an anaerobic digestion tank in the form of digestion gas mainly composed of methane, and the digestion gas is burned and used as a heat source. Since the sludge is solubilized, the sludge can be solubilized without supplying external energy.

In this case, the sludge sent to the anaerobic digestion tank or the sludge in the anaerobic digestion tank can be heated by the heat of combustion of the digestion gas.

Thus, the activity of the anaerobic bacteria can be maintained without supplying energy from the outside, and stable anaerobic digestion can be performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for treating excess sludge according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a processing flow according to the method for treating excess sludge of the present invention. The sewage A flowing into a sewage treatment facility such as a sewage treatment plant is subjected to pretreatment 1 such as dust removal and sand removal or sludge removal in a first sedimentation basin, and then overflows to an aeration tank 2 sequentially. Organic matter in the sewage is biodegraded in the tank 2 by activated sludge. And
The sludge mixture flowing into the final sedimentation basin 3 from the aeration tank 2 is separated into treated water B and sludge, and the treated water B is discharged outside the system after disinfection.

On the other hand, most of the sludge settled in the final sedimentation tank 3 is returned to the aeration tank 2 as returned sludge C by the returned sludge pump 11, and a part of the sludge is guided to the sludge concentration tank 4. .

The concentrated sludge D concentrated in the sludge concentration tank 4
Is led to the anaerobic digestion tank 6 through the heat exchanger 5 by the concentrated sludge pump 12,
It is kept for about several weeks. The digestion gas G mainly composed of methane generated during this stay period is temporarily stored in a gas tank 7 connected to an anaerobic digestion tank 6, and then sent to a heating boiler 10 via a booster 14 as a heat source of the boiler. . From the heavy oil tank 8, heavy oil H for pilot
Is supplied to the heating boiler 10 and ignites the digestion gas compressed by the booster 14 and burns while injecting the digestion gas.

On the other hand, the digested sludge E generated in the anaerobic digestion tank 6 is supplied from the anaerobic digestion tank 6 by a sludge supply pump 13 to a sludge solubilization tank 9 disposed close to the heating boiler 10.
The sludge is solubilized little by little and heated in the sludge solubilization tank 9 to 200 ° C. or higher by the combustion gas of the heating boiler 10. At the time of heating, a batch operation is performed to perform treatment in the sealed sludge solubilization tank 9 or, if the inside of the sludge solubilization tank 9 is pressurized by the sludge supply pump 13, the digested sludge E is treated at a high temperature. More effective. The sludge F solubilized by the high-temperature treatment as described above is returned to the aeration tank 2 in the water treatment step, and is decomposed by activated sludge as a biodegradable organic substance.

The hot water I heated in the heating boiler 10 circulates between the heating boiler 10 and the heat exchanger 5 by a circulating water pump 15 and is guided to the heat exchanger 5. Heat exchange is performed between the concentrated sludge D and the warmed water, and the temperature of the sludge is increased. Then, the hot water I whose temperature has been lowered by heat exchange with the concentrated sludge D is again
0 and circulates with the heat exchanger 5. The exhaust gas J discharged from the heating boiler 10 is normally released to the atmosphere as it is. However, when the amount of exhaust heat is large, a waste heat boiler or the like can be further provided at a later stage to recover energy. is there.

Next, the operation of the method for treating excess sludge of the present invention will be described. In the processing flow shown in FIG. 1, the sludge extracted as excess sludge from the water treatment step is concentrated by gravity in the sludge concentration tank 4 to about 1 to 2%. The concentrated sludge D settled at the bottom of the sludge thickening tank 4 is continuously or intermittently withdrawn by the concentrated sludge pump 12 and heated to a predetermined temperature of about 35 ° C. or about 55 ° C. in the heat exchanger 5. After being heated, it is led to the anaerobic digestion tank 6. Thereby, the temperature in the anaerobic digestion tank, the temperature that is the optimal region of the mesophilic bacteria, around 35 ℃, or the temperature that is the optimal region of the thermophilic bacteria,
Since the temperature can be maintained at around 55 ° C., the activity of anaerobic bacteria can be maintained, and stable anaerobic digestion can be performed.

In the anaerobic digestion tank 6, the temperature is 30 to 60 ° C.
The sludge is kept for about one to several weeks while maintaining the predetermined temperature. In the anaerobic digestion tank 6, the concentrated sludge D is stirred in an oxygen-free state. At this time, the sludge organic matter is decomposed by the action of acid fermentation bacteria and methane bacteria growing in the tank, and the organic acid and methane gas are removed. And so on. The digestion gas G mainly composed of methane volatilized in the upper space from the sludge is led to the gas tank 7 and is temporarily stored.

Next, in the sludge digested in the anaerobic digestion tank 6, organic substances mainly composed of anaerobic bacteria remain. Conventionally, this was concentrated and dewatered and carried out as a dewatered cake outside the system. However, here, the digested sludge E is subjected to a solubilization treatment. As a solubilization method, a method of chemically solubilizing with ozone or an oxidizing agent, a method of using thermophilic bacteria, a method of irradiating ultrasonic waves, and the like have been studied. G is used as a heat source. That is, the digested sludge E is retained in the sludge solubilization tank 9 adjacent to the heating boiler 10 for a predetermined time, the anaerobic bacteria are sterilized by the combustion heat of the digestion gas G, and the proteins of the microorganisms are denatured. Disrupt and elute intracellular cytoplasm into the mixture. For solubilization, it is necessary to determine the structures of the heating boiler 10 and the solubilization tank 9 so that the sludge becomes 200 ° C. or higher, and the treatment time is set in consideration of the temperature.

Since the organic matter of the solubilized sludge can be easily biodegraded, it is returned to the aeration tank 2 and decomposed by activated sludge. As described above, since the excess sludge generated in the water treatment step is solubilized and decomposed, the sludge discharged to the outside of the system can be reduced to zero.

While the sludge stays in the anaerobic digestion tank 6 for one to several weeks, phosphorus (eg, polyphosphorus) which has been taken into the microorganisms of the sludge is released outside the body as water-soluble phosphoric acid or the like. The phosphorus contained in the sludge is also eluted by the solubilization and returned to the water treatment step. Therefore, when it is desired to reduce the phosphorus concentration in the treated water B discharged to the outside, it is effective to add a coagulant to the solubilized sludge F, convert it to a phosphate compound or the like, insolubilize it, and separate by precipitation. It is.

Further, in order to enhance the dephosphorization effect in the water treatment step, the aeration tank 2 is made up of two stages of a complete anaerobic tank and an aerobic reaction tank, and a method of biologically dephosphorizing by an anaerobic aerobic method is combined. In addition, the concentration of phosphorus guided to the anaerobic digestion tank 6 as excess sludge can be increased, and the amount of phosphorus removed as a phosphate compound or the like can be increased by coagulation and precipitation.

As described above, in the method for treating excess sludge of the present embodiment, after the excess sludge generated in the water treatment step is concentrated,
The concentrated sludge D is guided to the anaerobic digestion tank 6 to perform digestion at a predetermined temperature, and the generated digestion gas G is burned in the heating boiler 10, and the digestion sludge E is heated at a high temperature using the combustion gas. By doing so, the sludge can be solubilized without supplying energy from the outside. Further, by using the hot water generated in the heating boiler 10 to heat the concentrated sludge D to be sent to the anaerobic digestion tank 6 or the sludge D in the anaerobic digestion tank 6, without supplying energy from outside. Anaerobic digestion can be stably performed while maintaining the activity of anaerobic bacteria. Furthermore, since the solubilized sludge is returned to the water treatment step for biodegradation, sludge carried out of the system can be reduced to zero. Also, when combined with coagulation sedimentation to collect and remove phosphorus, the amount of generated sludge can be reduced to about 1/10 of the conventional activated sludge method, and it becomes inorganic sludge. There is little land required for disposal, and there is no problem such as anaerobic rot and odor.

[0022]

According to the method for treating excess sludge of the present invention,
While recovering the energy contained in the excess sludge in the form of digestive gas centering on methane in an anaerobic digester,
Since the digestion gas is burned and the sludge is solubilized using the heat as a heat source, the sludge can be solubilized without supplying external energy.

Further, by heating the sludge sent to the anaerobic digestion tank or the sludge in the anaerobic digestion tank by the heat of combustion of the digestion gas, the activity of the anaerobic bacteria can be maintained without supplying external energy, Stable anaerobic digestion can be performed.

[Brief description of the drawings]

FIG. 1 is a process flowchart showing an example of a sewage treatment facility according to a method for treating excess sludge of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pretreatment process 2 Aeration tank 3 Final sedimentation tank 4 Sludge concentration tank 5 Heat exchanger 6 Anaerobic digestion tank 7 Gas tank 8 Heavy oil tank 9 Sludge solubilization tank 10 Heating boiler 11 Return sludge pump 12 Concentrated sludge pump 13 Sludge supply pump 14 Booster 15 Circulating water pump A Sewage B Treated water C Return sludge D Condensed sludge E Digested sludge F Solubilized sludge G Digested gas H Heavy oil I Hot water J Exhaust gas

Claims (2)

[Claims] 1. A method for treating excess sludge, wherein sludge generated in a water treatment step is introduced into an anaerobic digestion tank to perform digestion treatment, and the digested sludge is introduced into a solubilization tank and solubilized. A method for treating excess sludge, wherein the digestion gas generated in the anaerobic digestion tank is collected and burned, and the sludge is solubilized by the heat of combustion of the digestion gas. 2. The method for treating excess sludge according to claim 1, wherein the sludge sent to the anaerobic digestion tank or the sludge in the anaerobic digestion tank is heated by the heat of combustion of the digestion gas.