JPH0568993A - Treatment of sludge of purifying tank - Google Patents

Abstract

PURPOSE:To miniaturize an apparatus by a method wherein solid matter is separated and removed from the sludge of a purifying tank and, after a flocculant is injected in a separated liquid, this separated liquid is separated into membrane transmitted water and a membrane conc. liquid by an ultrafiltration membrane separation means and membrane separated water is treated with a biological treatment means to obtain high nitrogen removing function. CONSTITUTION:Purifying tank sludge 1 and a flocculant 2 are mixed in a chemical mixing tank 3 to flocculate and grow particles and the mixture is introduced into a mechanical separation tank 4 to be separated into excessive sludge 5 and a separated liquid 6. Next, the separated liquid 6 and a flocculant 7 are mixed in a chemical mixing tank 8 to perform flocculation reaction and introduced into an ultrafiltration membrane separation tank 9 to block all part of SS a greater part of and soluble matter, and this blocked mixture is fixed as solid matter by a flocculant to be removed as flocculated sludge 11. Membrane transmitted water 10 is introduced into a biological treatment process 12 and nitrogen slightly remaining in the membrane transmitted water is almost perfectly removed by biological digesting and denirifying action and the biological excessive sludge 13 generated in this process 12 is circulated to the mechanical separation tank 4 along with flocculated sludge 11 to be discharged as excessive sludge 5.

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 septic tank sludge.

[0002]

2. Description of the Related Art A conventional single treatment septic tank (without mixing of domestic wastewater) sludge treatment system will be described with reference to FIG.

In FIG. 3, after the coagulant 2 is injected into the purification tank (not shown) sludge 1 in the coagulant mixing tank 23, the solid-liquid separation tank 2
According to 4, the basic constitution is adopted in which a solid matter (separated sludge) and a part 25 of the colloidal and soluble substances are removed and the separated liquid is subjected to a biological treatment (diluted activated sludge method) means of a downstream. A polymer flocculant is generally used as the flocculant 2, and a gravity separation tank, a floating separation tank, a solid-liquid separation tank 24,
A mechanical separation tank or the like is used. The solid matter 25 removed in the solid-liquid separation tank 24 is treated in a sludge treatment step (not shown).

In FIG. 3, reference numeral 26 is dilution water, and 27 is
Is a dilution adjustment tank, 28 is an aeration tank, 29 is returned sludge, 30 is aerated air, 31 is a sedimentation tank, 32 is excess sludge, and 33 is treated water.

[0005]

In the conventional method shown in FIG. 3, the biological treatment facility, which is the center of the conventional method, has the following basic problems.

(1) It has only a function of removing organic substances and solids, and almost no function of removing nitrogen. That is, BO
Although it has the function of removing D, part of COD, and SS (suspended matter), organic nitrogen and ammonia nitrogen are assimilated by the purification microorganisms as nitrogen sources for their growth (10 to 15% of inflowing nitrogen).
There is only about (%) removal function.

(2) The device volume is too large. That is,
The total average residence time based on the stock solution flow rate excluding the amount of returned sludge is 3
It is a day, and it must be doubled or more to add a nitrogen removal function.

The present invention has been made for the purpose of overcoming these basic problems of the conventional method, and providing a biological treatment method having a high rate of nitrogen removal function and yet having a small apparatus volume.

[0009]

According to the present invention, a coagulant is injected into a liquid obtained by separating and removing solid matter from a septic tank sludge by a mechanical separating means, and then it is subjected to an ultrafiltration membrane separating means to obtain a membrane permeated water and a membrane concentrate. Separated, the membrane separation water is guided to the biological treatment means for treatment, and the membrane concentrated liquid and biological surplus sludge generated in the biological treatment means are circulated to the mechanical separation means and collectively discharged as excess sludge out of the system. A method for treating septic tank sludge, which is characterized in that

In order to simultaneously achieve the function of removing nitrogen at a high rate and reducing the volume of the bioreactor, it is necessary to reduce the pollutant load (particularly nitrogen load) involved in the biotreatment together with the devising of the biotreatment process. It is necessary to strengthen the processing function and improve the solid-liquid separation process.

Therefore, in the present invention (1) as a solid-liquid separation method, an ultrafiltration membrane capable of completely removing solids and colloids and also capable of removing a part of soluble substances is applied to BOD and CO.
Not only D and SS but also organic nitrogen is blocked at a high rate.
Concentration, (2) If the blocked pollutant components are not fixed as solids, they are merely concentrated and flow out to the dehydrated filtrate in the sludge treatment process, which eventually becomes a load of biological treatment. Injecting coagulant before immobilization, (3) introducing coagulated sludge generated by membrane separation and biological excess sludge generated by biological treatment into the mechanical separation process, and taking out collectively as excess sludge, It aims to unify the excess sludge generation system.

That is, a feature of the present invention is that ultrafiltration membrane separation is applied as a pretreatment for biological treatment in septic tank sludge treatment, and that a coagulant is injected before this ultrafiltration membrane separation, The three points are to introduce the coagulated sludge generated by the ultrafiltration membrane separation and the biological excess sludge generated by the biological treatment into the mechanical separation step before the ultrafiltration membrane separation.

[0013]

[Operation] By applying ultrafiltration membrane separation, BOD, C
OD, SS, and organic nitrogen can be removed, which can reduce the load on the subsequent biological treatment.

By injecting the coagulant, contaminants such as BOD, COD, and organic nitrogen, which are blocked by the membrane separation, can be fixed as a solid matter, and the membrane permeation flux is increased / stabilized by the aggregation / coarsening of fine particles. .. (Agglomeration and coarsening of solids and colloids reduces membrane permeation resistance to maintain a high permeation flux and increase permeation flux stability.

By introducing coagulated sludge and biological excess sludge into the mechanical separation means, the excess sludge generation system is unified,
The process is simplified.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. After the septic tank sludge 1 and the coagulant 2 are mixed in the chemical mixing tank 3 to perform particle aggregation / coarsening, the particles are introduced into the mechanical separation tank 4 and separated into the excess sludge 5 and the separation liquid 6. Mechanical separation tank 4
In this case, coarse solid matter (SS) is mainly removed, but this also removes some soluble substances. If coarse solids are removed in advance, the permeation flux of the latter-stage ultrafiltration membrane can be increased and stabilized. After the separation liquid 6 and the coagulant 7 are mixed in a chemical mixing tank 8 to carry out a coagulation reaction, the mixture is introduced into an ultrafiltration membrane separation tank 9 and SS100%
And most of the soluble substances are blocked, fixed as a solid matter with a flocculant and removed as flocculated sludge 11. This coagulated sludge 11
Circulate before the mechanical separation tank 4.

The membrane permeated water 10 is introduced into the biological treatment step 12, and a small amount of nitrogen (most of which is ammonia nitrogen) remaining in the membrane permeated water is biologically digested and denitrified, and this is almost 10
Remove 0%. The biological excess sludge 13 generated from the biological treatment process 12 is circulated to the mechanical separation tank 4 similarly to the coagulated sludge 11. The coagulated sludge 11 and the biological excess sludge 13 are collectively discharged from the mechanical separation tank 4 as an excess sludge 5.

In this, the molecular weight cut-off of the ultrafiltration membrane,
The module type and film material do not matter. The membrane material may be any commercially available ultrafiltration membrane such as polyacrylonitrile or polyolefin, and the module may be any of tubular type, hollow fiber type, flat membrane type, spiral type and the like. The surplus sludge 5 is treated in a sludge treatment process (dehydration, drying, incineration, etc.). Examples of the coagulant include a sulfuric acid band, ferric chloride, and a polymer coagulant.

In order to confirm the effect of the present invention, an experiment was conducted using an experimental apparatus having the same flow as in FIG. Purified sludge 1 collected from a certain sewage treatment plant is introduced into a chemical mixing tank 3, a predetermined amount of coagulant 2 is added, and a mechanical separation tank (centrifugation in this case) 4 separates it into excess sludge 5 and separated liquid 6. Then, the separated liquid 6 is introduced into a chemical mixing tank 8, a predetermined amount of a coagulant 7 is added, and rapid stirring (rotation speed of stirring blade: 120 to 150 rpm) 1
20 minutes, slow stirring (rotating speed of stirring blade: 50 rpm) 3
After performing 0 minutes and performing a coagulation reaction, the ultrafiltration membrane separation tank 9
It was introduced into the column and the membrane separation was performed in a batch system.

The basic specifications of the membrane separation module of the ultrafiltration membrane separation tank 9 are as follows. Membrane type: Membrane material polyacrylonitrile (effective area 0.42 m ² ), molecular weight cutoff 100,000. Membrane module: Tube type Membrane separation conditions: Average permeation pressure 1.5 kg / cm ² G,
Temperature 22-23 ° C. Flocculant: sulfuric acid band, ferric chloride, injection rate: 300,500 ppm for all

FIG. 2 is a schematic view of the test apparatus for the biological treatment step of the membrane-filtered water 10 of FIG. 1, which was separated from the pretreatment (the step before the ultrafiltration membrane separation tank 9). The test apparatus for the biological treatment process in FIG. 2 is a stock solution (membrane permeated water 10) storage tank 15, stock solution pump 16, nitrification tank 17, denitrification tank 18, re-aeration tank 19,
Settling tank 20, treated water 21 discharge line, return sludge 22 return line, and excess sludge 13 return line (this excess sludge 13
Is returned before the mechanical separation tank of FIG. 1).

The total average residence time based on the flow rate of the stock solution (membrane separation water 10) is 3 days. In the nitrification tank 17, BOD removal is performed by nitrification (NH ₄ -N oxidation), and in the denitrification tank 18, the nitrification tank 1 is used.
The oxidized nitrogen produced in 7 is reduced, and alcohol is injected as a carbon source as needed. The re-aeration tank 19 is for removing this residual alcohol.

Table 1 shows the results obtained by the experimental apparatus shown in FIGS.

[Table 1]

The total average residence time of the biological treatment was 3 days, and the TN of the treated water was maintained at 20 ppm or less. (In the conventional method, 150 to 200 ppm at the outlet of the biological treatment step) The method of the present invention was compared with the conventional method. It can be seen that a high nitrogen removal function is provided without increasing the biological treatment volume. The reason for this is the improvement of the pretreatment function due to the addition of the membrane treatment.

[0025]

According to the present invention, a high rate of nitrogen removal can be achieved without increasing the volume of the biological treatment apparatus.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a biological treatment process according to an embodiment of the present invention.

FIG. 3 is an explanatory view of one mode of a conventional method for treating septic tank sludge.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C02F 3/34 101 A 7158-4D 9/00 A 6647-4D

Claims (1)

[Claims] 1. A septic tank sludge is injected with a coagulant into a liquid from which solids have been separated and removed by a mechanical separation means, and then subjected to an ultrafiltration membrane separation means to separate it into a membrane permeated water and a membrane concentrated liquid. A septic tank sludge characterized in that it is introduced to a biological treatment means for treatment, and the membrane concentrate and biological excess sludge generated in the biological treatment means are circulated to the mechanical separation means and collectively discharged as excess sludge out of the system. Processing method.