JP2871073B2 - Septic tank sludge treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating septic tank sludge.

[Conventional technology]

One aspect of the conventional single treatment septic tank sludge treatment method is
This will be described with reference to the drawings.

After the coagulant 2 is injected into the septic tank 1 in the coagulant mixing tank 13, the coagulant 2 is separated into solid and liquid in the solid-liquid separation tank 14, and a part of the solid, colloidal and soluble substances becomes separated sludge 15 to form a system. The liquid is discharged outside and treated in a sludge treatment step, while the separated liquid is subjected to downstream biological treatment, for example, a diluted activated sludge method. In the dilution activated sludge method, the separated liquid is diluted with dilution water 16 in a dilution adjusting tank 17, aerated by an aerated air 20 in an aeration tank 18, and then settled in a settling tank 21.
As a result, excess sludge 22 is discharged out of the system, and is discharged as treated water 23. In the figure, reference numeral 19 denotes returned sludge.

Generally, a polymer flocculant is used as the flocculant 2 in the above-mentioned processing system, and a solid-liquid separation tank 14 is generally a tank that performs gravity separation, flotation separation, and mechanical separation.

[Problems to be solved by the invention]

In the conventional system shown in FIG. 5, effluent can water in the solid-liquid separation step (BOD _5: 30 ppm or less, SS: 70 ppm or less) does not reach the addition of subsequent biological treatment was required. Biological treatment is a method of applying a normal activated sludge method after dilution adjustment,
All the components such as aeration tank and sedimentation tank were too large, and complicated sludge operation such as MLSS / SRT management was required and operation management was complicated. Therefore, if the latter biological treatment can be omitted, the facility can be greatly reduced in size and operation management can be simplified. However, to eliminate the biological treatment, it is necessary to improve the BOD and SS removal function in the solid-liquid separation process. . However, the solid-liquid separation itself has a function of removing a solid and a part of a colloid, but has little function of removing a soluble substance, and a slight residual of a solid is inevitable. (Fixed materials and some colloids are evaluated by SS as water quality measurement items, and some colloids and soluble substances are evaluated as BOD.) In solid-liquid separation, fine particles are coarsened with a flocculant and then gravity. It is essentially intended to remove solids by the difference in specific gravity in separation, by the difference in buoyancy in flotation, and by the difference in centrifugal force in centrifugation. Colloids and soluble substances are only removed incidentally.

The present invention has been made in view of the above-mentioned technical level, and aims to provide a septic tank sludge treatment method capable of omitting biological treatment.

[Means for solving the problem]

That is, the present invention relates to the septic tank sludge separated liquid quality (BOD, SS)
Water quality without additional biological treatment (BOD: 30pp
m or less, SS: 70 ppm or less). The present invention is a method for solid-liquid separation of septic tank sludge, which can completely remove solids and colloids (SS removal rate: 100%). Using a filtration membrane (there is no example of applying ultrafiltration membrane separation to the pretreatment of septic tank sludge), and using an ultrafiltration membrane that can remove only a part of soluble organic substances, how the BOD is 30 ppm or less Have been reached after various studies have been made to determine whether or not to obtain. There are various factors that affect the function of removing soluble substances in an ultrafiltration membrane. One of them is the molecular weight of the membrane fraction, and it is known that the smaller the molecular weight of the membrane, the better the function. On the other hand, if the molecular weight cut-off is small, the membrane permeation flux is small and the volume of the apparatus is large, and it is necessary to clarify the maximum molecular weight cut-off that maintains a predetermined function. In the present invention, after injecting a flocculant such as a sulfate band, ferric chloride, and a polymer flocculant as a flocculant, the mixture is treated with an ultrafiltration membrane having a cut-off molecular weight of 10,000 or less, so that a high membrane permeation flux is obtained. While maintaining, confirm that BOD can be maintained at 30 ppm or less,
The present invention has been completed.

That is, the present invention relates to (1) after injecting a flocculant into a septic tank sludge,
Septic tank sludge treatment method characterized in that the separation liquid is separated by an ultrafiltration membrane of 000 or less and BOD 30 ppm or less can be discharged without passing through a biological treatment step. (2) Septic tank before injecting flocculant The septic tank treatment method according to the above (1), wherein the sludge is subjected to solid-liquid separation in advance.

The ultrafiltration membrane used in the present invention may be a commercially available ultrafiltration membrane such as polyacrylonitrile and polyolefin, and the membrane module may be any of a tubular type, a hollow fiber type, a spiral type and the like.

Examples of the flocculant used in the present invention include a sulfate band, ferric chloride, and a polymer flocculant.

(Operation)

The injection of the coagulant reduces the permeation resistance due to the coagulation and coarsening of the solid substance and the colloid, keeps the permeation flux high, and improves the blocking performance of the BOD by the membrane.

By using an ultrafiltration membrane, the function of completely removing SS and removing BOD is improved, and in particular, the use of an ultrafiltration membrane having a cut-off molecular weight of 10,000 or less can reduce the BOD to 30 ppm or less.

When using an ultrafiltration membrane with a molecular weight cut off of more than 10,000, the BOD is not less than 30 ppm even if an aggregating agent is injected, and even if an ultrafiltration membrane with a molecular weight cut off of 10,000 or less is used without injecting the aggregating agent. Similarly, the BOD cannot be reduced below 30 ppm.

 One embodiment of the present invention will be described with reference to FIG.

After the coagulant 2 is injected into the septic tank 11 in the coagulant mixing tank 3 to carry out the coagulant reaction, it is introduced into the ultrafiltration membrane module 4 and separated into the separated sludge 5 and the separated liquid 6. In the ultrafiltration membrane module 4, 100% of the SS is blocked (removed) and moves to the sludge 5, and most of the BOD is also removed, so that the BOD concentration in the separated solution 6 is 30 ppm or less. The molecular weight cut-off of the ultrafiltration membrane must be 10,000 or less, regardless of the membrane material and membrane module type. The membrane material may be a commercially available ultrafiltration membrane such as polyacrylonitrile and polyolefin, and the membrane module is a tubular type, a holofiber type,
Any type such as a flat membrane type and a spiral type may be used. Each of the separated sludges 5 is treated in a sludge treatment step. Examples of the flocculant include a sulfate band, ferric chloride, and a polymer flocculant.

Another embodiment of the present invention will be described with reference to FIG. In the embodiment shown in FIG. 2, a solid-liquid separation tank 7 is provided upstream of the embodiment shown in FIG.
The processing is performed by the ultrafiltration membrane module 4.

〔Example〕

FIG. 3 shows a schematic diagram of an experimental apparatus for examining the effect of the present invention.

A predetermined amount of coagulant is injected with a septic tank sludge jar tester collected from a certain complex washing tank, and rapid stirring is performed with a stirring blade rotation speed of 200 r.
pm, stirring time 50 min, then slow stirring 50 rpm
m, stirrer time 10 min. The sludge was subjected to membrane separation using the membrane separation test apparatus shown in FIG. The basic specifications of the membrane separation test device are as follows.

Membrane type: Membrane material: polyacrylinolyl flat membrane (effective membrane area: 28 cm ² ), molecular weight cut off: 10,000, 20,000, 40,000, membrane separation conditions: Permeation pressure: 4 kg / cm ² G, temperature: 22 ~twenty three
℃, flocculant: sulfate band (Al ₂ O ₃ ), ferric chloride (F
eCl ₃ ), injection rate is 600,800ppm for both conditions.

FIG. 4 shows an experimental result on the relationship between the BOD concentration of the septic tank sludge treatment liquid and the molecular weight of the membrane fraction. As the present invention shows,
BOD is 30 ppm or less when the molecular weight cut off is 10,000 or less.

〔The invention's effect〕

According to the present invention, BOD can be discharged to 30 ppm or less without subjecting the septic tank sludge to biological treatment.

[Brief description of the drawings]

FIG. 1 is an explanatory view of one embodiment of the present invention, FIG. 2 is an explanatory view of another embodiment of the present invention, FIG. 3 is an explanatory view of an experimental apparatus for demonstrating the effects of the present invention, FIG. a) and (b) are charts showing experimental results obtained by the above-mentioned experimental apparatus of the present invention, and FIG. 5 is an explanatory view of a conventional septic tank sludge treatment apparatus.

Claims (2)

(57) [Claims] (1) After injecting a flocculant into a septic tank sludge, the mixture is subjected to separation treatment with an ultrafiltration membrane having a cut-off molecular weight of 10,000 or less to obtain a separated solution having a BOD of 30 ppm or less which can be discharged without a biological treatment step. Septic tank sludge treatment method. 2. A method for treating a septic tank according to claim 1, wherein the sludge of the septic tank is solid-liquid separated before the coagulant is injected.