JPH0325234B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for coagulating dredged mud water. When dredging sediment deposited in rivers, lakes, and ports using pumps, and transporting the resulting muddy water to a landfill using a mud pipe, a flocculant is added midway through the mud pipe to remove silt, clay, etc. in the muddy water. A method is used in which suspended solids, mainly consisting of fine particles, are aggregated during transportation, and then sedimented and separated at the destination landfill. This method utilizes the fluidity of muddy water during transport to provide the necessary agitation for dissolving and coagulating the flocculant, and generally the flocculant is added at the point where the mud pipe reaches the seawall from the dredger. The sludge is then coagulated in the pipe that runs from this point to the landfill. However, as the reclamation process progresses, the sludge pipes are lengthened and the residence time after the addition of flocculant becomes longer, or when the flow conditions inside the pipes change due to branching, etc., the flow conditions inside the pipes change, causing growth due to agglomeration. The flocs are destroyed, and the sedimentation and separation of the flocculated mud becomes incomplete. Generally, in order to form a coagulated floc suitable for sedimentation separation, it is necessary to continue moderate stirring for a certain period of time, and there is a limit to the duration for which the flocs thus formed can maintain a stable state suitable for sedimentation separation under stirring. However, if the stirring time in the tube becomes long or the stirring conditions become violent, the flocs will be destroyed, making it unsuitable for sedimentation separation. The floc formation time and stable state duration are also affected by other flocculation conditions, such as changes in soil quality due to differences in dredging location and changes in suspended solids concentration due to changes in mixing rate. receive,
Even within the same residence time, the flocs are destroyed,
The sedimentation separation effect may deteriorate. When the flocs are destroyed and the sedimentation separation effect deteriorates, suspended solids flow out, which reduces the landfill yield and deteriorates the water quality of the runoff, causing environmental pollution. There is a point. This invention was made to improve the problems in the conventional method as described above, and by adding flocculant at multiple positions in the slurry pipe, the residence time or flocculation conditions in the pipe can be changed. The purpose of the present invention is to provide a dredging mud water coagulation treatment method that can efficiently coagulate dredged mud, improve sedimentation separation properties, improve landfill yield, improve the quality of leftover water, and prevent environmental pollution. It is said that This invention is a method in which dredged mud is transported through a mud pipe, a flocculant is added during the transport to cause flocculation, and the flocculated mud is separated by sedimentation at the destination. After at least 1 minute and 30 seconds, add the organic polymer flocculant again,
This is a dredging mud coagulation treatment method characterized by repairing broken flocs and maintaining a stable floc state. Examples of organic polymer flocculants that can be used in the present invention include polyacrylamide, partial hydrolysates of polyacrylamide, polyacrylates, and other known organic polymer flocculants. In the conventional treatment method, these flocculants are injected at one point in the slurry pipe, but after adding the flocculant, it is injected for 10 to 20 seconds.
Flocs are formed in seconds, and a stable agglomerated state is reached in about 30 seconds. This state lasts from 1 minute and 30 seconds to 2 minutes, but if the stirring state continues after that, the flocs will break down, and after 3 minutes, the flocs will be about 1/2 of the stable flocculation state, and after 5 minutes, it will be about 1/2 of the stable flocculation state. /5 sedimentation rate. For this reason, it is desirable to keep the residence time in the mud pipe after adding the flocculant to around 30 seconds to 2 minutes, but as the landfill position, that is, the position of the outlet from the mud pipe, moves as the landfill progresses. When the flocculant is injected at one point, the residence time cannot be within the above range. In addition, the sludge pipes are complicatedly branched, and sludge is discharged from many points and landfilling proceeds at the same time, so it is practically impossible to move the injection point of the flocculant. To deal with this, multiple flocculant injection points are provided in the middle of the slurry pipe, and the flocculant is added at two or more points at least 1 minute and 30 seconds after the first flocculant is added. By dispensing the flocculant at , a stable floc state can be maintained for a long time. This is because even if the flocs generated by the initial coagulant injection are destroyed, they are repaired by new coagulant. A long residence time is not necessarily required after the second and subsequent additions of the flocculant. The location of the flocculant injection point is based on the normal flow rate in the pipe of 3 to 5 m/sec, and the residence time is between 1 minute and 30 seconds, which is the upper limit of the duration of stable flocs.
Preferably, there is one injection point for every minute. Of course, after the first injection, it may be allowed to stay beyond the above range and then injected again before the outlet. In this way, there may be two or more injection points. If the slurry pipe has branches, two or more injection points can be provided for each branch. The total amount of flocculant to be added is 3 to 13 mg/(based on sludge), which is less than the amount added in the case of normal one-point injection, and this may be dispensed. As for the injection ratio at each point, it is desirable that 60 to 80% of the total amount be injected at the first injection point, and 40 to 20% after the second injection point. Since the injection point, addition amount, dispensing ratio, etc. of the flocculant differ depending on the type of dredged sludge, dredging and landfill conditions, etc., the flocculation conditions can be determined in advance by a jar test or field test. Next, the present invention will be explained in more detail with reference to Examples. The drawing shows a system diagram of the embodiment, where 1 indicates a mud pipe, 2
is a landfill. The mud feeding pipe 1 has an outlet 3 at its end.
is open at one end of the landfill 2. The reclaimed land 2 is configured in the shape of a pond, and is connected to a retarding pond 5 through a partition bank 4, and the retarding pond 5 is provided with a spillway 6. 7
is a coagulant tank, and a chemical injection pipe 9 is connected via a pump 8.
is connected to the mud feeding pipe 1, and a chemical feed pipe 9 to a dispensing pipe 10 are connected downstream of the mud feeding pipe 1 via a flow rate type 11. The connection part of the chemical injection pipe 9 to the mud feeding pipe 1 is the first injection point 12, and the connection part of the dispensing pipe 10 is the second injection point 13.
It is becoming. The dredged mud water in the example has a silt and clay content of 95%.
% or more, the sludge interface velocity during natural sedimentation of mud water is
This muddy water is obtained by pump dredging port sludge with poor settling properties at a rate of 0.065 m/hr. It is sent to a landfill site 2 through a sludge pipe 1, and is treated with a coagulant (polyacrylamide partial hydrolyzate) from a coagulant tank 7 by a pump 8. ) and dispensed from the first injection point 12 and the second injection point 13. The mud feeding rate of the mud feeding pipe 1 is 1200 m ³ /hr, the chemical injection rate of the first injection point 12 is 10 mg/, the chemical injection rate of the second injection point 13 is 3 mg/, and the flow rate is from the first injection point 12 to the second injection point. The residence time of No. 13 was 120 seconds, and the residence time from the second injection point 13 to the outlet 3 was 10 seconds. Table 1 shows the properties of the flocculated sludge near the outlet 3 for the above two-point injection method and the case where the entire amount is injected only from the first or second injection point. Shown in 2.

【table】

【table】

[Table] Regarding the state of sludge accumulation near the outlet 3, in the case of two-point injection, the agglomeration and granulation of sludge particles were good, and the formation of coarse flocs was clearly observed by visual observation. The sludge was piled up in layers. On the other hand, when the sludge was injected only through the first injection point, the sludge spread rapidly at the outlet 3 and the flocs became relatively small. In addition, in the case of injection only at the second injection point, the distance to the outlet 3 is short, so the flocculating effect is not sufficiently exerted, and the partially flocculated sludge sinks, but
Unagglomerated substances were dispersed as turbidity. Next, in the above test, the turbidity at the entrance of the partition bank 4 was 7 for 10 days in the case of two-point injection.
~9 degrees, SS was 14 to 18 mg/, which was below the spillway discharge standard, but when only the first injection point was injected, the turbidity was 16 degrees, and SS was 32 mg/, when only the second injection point was injected. The turbidity was 32 degrees and the SS was 65 mg/. From the above results, it can be seen that in the case of two-point injection, the flocculation and granulation properties of sludge particles are higher than in the case of one-point injection, the sedimentation compaction property is large, and the clarification effect of separated water is also high. The above embodiment is an example in which the present invention is applied to muddy water obtained by dredging port sludge with a pump, but it can be similarly applied to other dredged muddy water such as rivers, lakes, and marshes. When dredging these freshwater systems, as with conventional methods,
Inorganic flocculants such as PAC, Alba sulfate, and ferric chloride can also be used together, and these can be added prior to the addition of the organic polymer flocculant. In addition, organic polymer flocculants other than the polyacrylamide type mentioned above can be used.
Depending on the properties of the dredging mud, several types may be used in combination; for example, cationic and anionic types may be used in combination. In these cases, one flocculant can be injected at the first injection point and the other flocculant can be injected at the second or subsequent injection points to produce a combined effect. Furthermore, the selection of the injection point and other aggregation conditions can be changed as desired. As described above, according to the present invention, an organic polymer flocculant is added to the dredged mud of the mud pipe, and at least one
After 30 minutes, the organic polymer flocculant is added again to repair the broken flocs and maintain a stable floc state, so a stable flocculation state can be maintained for a long time and the landfill yield can be reduced. In addition to improving water quality, the quality of leftover water can also be improved.

[Brief explanation of the drawing]

The drawing is a system diagram showing one embodiment of the present invention, in which 1 is a mud feeding pipe, 2 is a landfill, 5 is a reservoir, 7 is a flocculant tank, 9 is a chemical injection pipe, and 10 is a dispensing pipe. .

Claims (1)

[Claims] 1. In a method of transporting dredged mud through a mud pipe, adding a coagulant during transport to cause flocculation, and separating the flocculated mud at a destination by sedimentation, A flocculation treatment for dredged mud water characterized by adding an organic polymer flocculant and adding the organic polymer flocculant again after at least 1 minute and 30 seconds to repair broken flocs and maintain a stable floc state. Method. 2 The addition ratio of flocculant is 60 to 80% at the first injection point,
Claim 1 which is 40-20% at the second injection point
Aggregation treatment method for dredged mud water as described in Section 2. 3. The method for coagulating dredged mud water according to claim 1 or 2, wherein the flocculant is polyacrylamide, polyacrylamide partial hydrolyzate, or polyacrylate.