JPS6061013A - Solid/liquid separating apparatus - Google Patents

Abstract

PURPOSE:To obtain concentrated sludge of high density always stably by performing two-stage series separation comprising screen separation and precipitation separation, an recycling precipitated sludge to feed suspension liquid simultaneously. CONSTITUTION:Liquid suspension 1 admixed with high molecular flocculant 2 is conducted to a flocculating tank 3, and flocculated slurry 4 is produced by stirring and mixing the suspension to form coarse floc. The flocculated slurry is let flow down on a sloped wedge wire screen 6 through a distribution tank 5, and the slurry is separated to concentrated sludge 7 and separated liquid 8 passed through the screen 6. The separated liquid 8 passed through the screen 6 is conducted to a setting tank 10 where it is separated to settled sludge 11 of ca. 1- 1.5% solid content and supernatant 12. The supernatant 12 is discharged. The settled sludge 11 separated in the settling tank 10 is recycled and mixed with the feed liquid suspension 1, and subjected to the solid-liquid separation as above- described by the screen 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-liquid separation method for separating suspended solids in a suspension into highly concentrated concentrated sludge.

Conventionally, screens are increasingly used as a method for separating suspended solids in suspended or turbid liquids.This method uses a screen to separate flocs formed by a polymer flocculant. This method uses wedge wire screens, rotating screens, and other screens for separation, and the solid-liquid separation time is extremely short, and the separated sludge concentration is higher than that of conventional coagulation and sedimentation, making it difficult to perform subsequent dewatering or other processes. It has the advantage of making sludge treatment advantageous.

However, it is impossible to completely separate flocs in the liquid using screenin, and there is a problem in that a considerable amount of solid content remains in the separated liquid that passes through the screen. In addition, even if sedimentation treatment is performed to further separate the solid content in the separated liquid separated by the screen, the concentration of the settled sludge does not reach even half of the sludge separated by the screen, and when both sludges are dewatered. Another problem was that the sludge that had been concentrated to a high concentration in the Suclean system was diluted by low-concentration settled sludge, making dewatering and other sludge treatments disadvantageous.

The present invention aims to solve these conventional problems and provide a solid-liquid separation method that can always stably obtain highly concentrated concentrated sludge and that also makes sludge treatment advantageous. .

The present invention involves adding at least a polymer flocculant to a suspension to form flocs, then concentrating and separating the flocs using a screen, and separating the separated liquid that has passed through the screen by sedimentation. The method is characterized in that sludge is mixed into the suspension.

An embodiment of the present invention will be described with reference to the drawings.
At least 2 polymer flocculants are added to the suspension l containing suspended solids.
However, when trying to remove chromaticity, phosphorus, COD, etc. from the liquid at the same time, an inorganic flocculant such as iron salt or aluminum salt is used in combination. This suspension l to which at least the polymer flocculant 2 has been added is led to a flocculation tank 3, stirred and mixed to form coarse flocs to form a flocculation slurry 4, and passed through a distribution tank 5 to a temperature of about 60 degrees. The sludge is allowed to flow down an inclined wedge sewage screen 6 and is separated into a thickened sludge 7 and a separated liquid 8 that passes through the screen 6. The concentrated sludge 7 separated by this Sgeleen 6 is concentrated to a high solids concentration of 4 to 4.5% in the case of surplus activated sludge, for example, and reaches the storage tank 9.

The separated liquid 8 that has passed through the screen 6 contains solids that could not be completely separated by the screen 6, and cannot be discharged as is. Therefore, this separated liquid 8 is led to the precipitation tank 1O to have a solid content of 1 to 1.5%.
It is possible to separate the precipitated sludge 11 into a supernatant liquid 12 and discharge the supernatant liquid 12.

Further, the settled sludge 11 separated in the settling tank 10 is recycled, mixed with the original suspension 1, and solid-liquid separated again in the screen 6 as described above. What should be noted here is that the storage tank 9 contains the concentrated sludge 7 from which the precipitated sludge 11 has been separated by the screen 6.
If the introduction into the storage tank 9 is delayed, the concentrated sludge 7 that has been concentrated to a high concentration by the screen 6
This has the undesirable result that the concentration of sludge is diluted by the low concentration of settled sludge 11.

In this way, only the highly concentrated screen-separated thickened sludge 7 is supplied to, for example, the dewatering step 13, so that the throughput of the sludge dewatering step is improved and the amount of dewatered filtrate produced is reduced.

As described above, the present invention forms coarse flocs in a suspension, separates the flocs as highly concentrated concentrated sludge using a screen, and separates the separated liquid that has passed through the screen by precipitation. Since sludge is recycled into a raw suspension, the following effects can be obtained.

(2) The two-stage series separation method of screen separation and precipitation separation makes it possible to stably obtain a clear treated liquid even if the solid content recovery rate in the screen deteriorates.

■ Since settled sludge is recycled to the raw suspension and the sludge supplied to the dewatering process is only high-concentration screen thickened sludge, the processing capacity of the dewatering process is improved.

■ By recycling the settled sludge into the original suspension, the settled sludge itself becomes effective as a coagulation aid.

Next, examples of the present invention will be shown.

After adding 1500 da/l of pec15 to the biologically treated water obtained by biologically nitrifying and denitrifying human waste without diluting it, Ca(OH
) 2 to pH 4 to 5, then add 10 m9/l of a nonionic polymer flocculant, mix to form a flocculation slurry, and place this on a 60° inclined wedge wire screen (openings 0.5 mm). When the sludge was allowed to flow down, a solid sludge with a solid concentration of 4 to 4.8% was obtained in a separation time of 1 to 3 seconds, but the solid content of the separated water that passed through the screen was 500 to 1000 m9.
There were as many as /l. This separated water was subjected to solid-liquid separation in a sedimentation tank at a sedimentation rate of 20 mm/min to obtain precipitated sludge with a solid concentration of 1 to 1.5%.

This precipitated sludge was recycled into the above-mentioned biologically treated water and subjected to the above-mentioned screen separation again. No deterioration of the screen separation effect was observed, and on the contrary, the amount of nonionic polymer flocculant added was reduced to 7 m9/l. was able to reduce it.

In addition, the highly concentrated concentrated sludge obtained by screen separation was dehydrated using a filter press dehydrator, but the offshore overspeed was 2.
The moisture content of the obtained dehydrated cake was 65-67% with high values of 8-3.0 kll DS/m@hr.

[Brief explanation of drawings]

The drawing is a system explanatory diagram showing one embodiment of the present invention. 1...Suspension, 2...Polymer flocculant,
3...Floc formation tank, 4...Agglomerated slurry, 5...Distribution tank, 6...Incline wedge wire screen, 7... Thickened sludge, sludge...separated liquid, 9...storage tank, 1G...
...Sedimentation tank, 11...Settled sludge, 12...
...Supernatant liquid, 11...Dehydration step. Patent applicant: Patent attorney representing Ebara Infilco Co., Ltd.
Masayuki Takagi, Patent Attorney 1) Minoru, Patent Attorney Takao Maruyama

Claims (1)

[Claims] After adding at least a polymer flocculant to the suspension to form flocs, the flocs are concentrated and separated using a screen, the separated liquid that has passed through the screen is separated by sedimentation, and the resulting precipitated sludge is transferred to the suspension. A solid-liquid separation method characterized by mixing in a turbid liquid.