JPH0334400B2 - - Google Patents

Description

[Detailed description of the invention]

1. Technical Field of the Invention The present invention relates to a method for controlling the amount of an organic polymer flocculant used in sludge dewatering treatment. 2 Description of the prior art In recent years, organic polymer flocculants, which have been widely used as sludge dewatering aids, require less addition than inorganic flocculants, produce less dehydrated cake, and are easier to handle as chemicals. It has the advantage of being able to use high-performance dehydrators such as belt presses and centrifuges. However, since there is an optimal range for the addition rate of organic polymer flocculants, the dehydration condition will not be good if the addition amount is too low or too high, so there is always some way to control the amount of chemicals added. It was a hassle to keep it within an appropriate range. For this purpose, a proportional control method has conventionally been used in which the addition rate per unit solid is kept constant. That is, this is a method of measuring the sludge flow rate and concentration to determine the amount of solids treated, and calculating the addition amount from the optimum addition rate determined in advance by another means to control the chemical injection pump flow rate. This method deals with fluctuations in sludge concentration.
If the reliability of the sludge concentration meter and flow meter is sufficient, the subsequent proportional control itself will be easy, and automation of chemical addition will be possible, but in reality, the reliability of the concentration meter is not sufficient. Furthermore, this method cannot be applied if there are qualitative changes in the sludge and the optimal chemical injection rate changes. In actual sludge treatment, there are many opportunities to encounter fluctuations in sludge concentration and chamber conditions, and it is often difficult to optimize control of dewatering operations by automating chemical addition. Therefore, it is necessary to manually adjust the amount added while constantly monitoring the dewatering state, and labor costs account for an extremely large proportion of the total sludge treatment cost.
Further, even if the actual chemical addition rate is within the appropriate range, it is inevitable that the chemical addition rate will be on the safe side, which is a high addition rate, resulting in an increase in chemical costs. 3. Purpose of the Invention In order to address the current situation, the present invention aims to provide a flocculation method that can sufficiently cope with fluctuations in sludge concentration and quality when sludge is flocculated using an organic polymer flocculant and dewatered using a belt press type dehydrator. The purpose is to provide a method for controlling the amount of additive added, reduce chemical costs, and enable a significant reduction in labor costs through automation, thereby reducing the overall cost of sludge treatment. 4 Structure of the Invention The present invention was completed as a result of investigating the relationship between the amount of organic polymer flocculant added and the thickness of the dehydrated cake, and examining the relationship between them and the moisture content of the dehydrated cake (hereinafter referred to as cake moisture content). In the relationship between the amount of flocculant added and the thickness of the dehydrated cake, the amount of flocculant added at which the dehydrated cake thickness becomes the maximum value (this amount of addition is called the amount A) is determined, and then the amount of added amount A is It is characterized by agglomeration and dehydration treatment using a value multiplied by a constant between 0.7 and 1.5. The thickness of the dehydrated cake can be determined by literally measuring the thickness of the dehydrated cake, but specifically, since the thickness of the dehydrated cake is almost uniform except for both ends in the width direction, the thickness of the uniform part is measured. Just measure it. The relationship between the amount of organic polymer flocculant added and the thickness of the dehydrated cake is qualitatively shown in Figure 1. Regarding the relationship between the amount of coagulant added and the thickness of the dehydrated cake, as the amount of coagulant added increased, the thickness of the dehydrated cake increased, and conversely decreased beyond a certain amount. That is, there is an amount of coagulant added, that is, an amount A at which the thickness of the dehydrated cake becomes a maximum value. On the other hand, the relationship between the amount of flocculant added and the cake moisture content is
It will look like Figure 2. That is, in the region where the amount added is small, the particle size and strength of the aggregates are small, and the operation of the dehydrator becomes impossible due to seepage from the filter cloth, protrusion, poor peeling, overflow of the gravity filtration section, etc. As the amount added increases, it becomes possible to operate the dehydrator, and the moisture content of the cake decreases in a certain section. However, if the amount added is too large, the aggregates tend to disperse, resulting in poor dehydration properties. As a result of comparing the relationship between FIG. 1 and FIG. 2, it became clear that the vicinity of the addition amount A is the region where the dehydrator operates well and the cake moisture content is low and economical. According to numerous experimental results, the absolute value of the dewatered cake thickness and the absolute value of the addition amount A shown in Figure 1 vary depending on the quality of the sludge, the type of flocculant, the operating conditions, etc. It has been confirmed that the area near A remains a region with good dehydration. Furthermore, the width of the "neighborhood" ranged from 0.7A to 1.5A, regardless of the properties of the sludge, the type of flocculant, the dewatering conditions, etc. Based on these facts, if the addition amount is adjusted to the addition amount A or around it, the condition of the dehydrator can be maintained in good condition. At that time, the measurement of sludge concentration and flow rate, which was necessary in the past, becomes unnecessary. By the way, as a method for determining the relationship between the amount of coagulant added and the thickness of the dehydrated cake, it is possible to sample the sludge and then measure it in batches using the laboratory test method suitable for the dehydrator used, but it is also possible to A monitor line may be provided to continuously sample the sludge, and the amount of flocculant added may be changed at predetermined intervals so that the thickness of the dewatered cake can be measured. Of course, actual measurements can also be made using an actual dehydrator and changing the amount of flocculant added at appropriate intervals. Further, it is not necessary to perform these measurements manually, and the addition amount A can be determined by automation as appropriate using a data processing device. Furthermore, since the added amount A is the point where the differential value of the dehydrated cake thickness with respect to the added amount is zero, the added amount A can also be automatically determined using this differential value. In any case, it is sufficient to clarify only the relationship between the amount added and the thickness of the dehydrated cake in the vicinity of the amount A. The addition amount A can be determined by applying existing automatic control methods. Thus, if the addition amount A is found, it is 0.7A to 1.5A.
The amount to be added to the sludge to be actually supplied to the dehydrator can be set between Setting values can be selected by taking into consideration the rate of change in sludge properties, response speed of the dehydrator, cake moisture content, etc. In general, the best and most economical operating condition will be obtained if the additive amount A is set as it is (1.0 A), but if you want to save the flocculant extremely, set it to around 0.7 A, and the sludge properties will change. If the current is so severe that problems such as control time delay remain even after automating the control method according to the present invention, it is sufficient to set it close to 1.5A. Of course, as described in the explanation of the method for determining the addition amount A, the selection of the set value and the actual flow rate control of the chemical injection pump can all be automatically controlled. In the present invention, as the flocculant, commonly available flocculants can be used as they are. Here, the amount of flocculant added refers to the amount of flocculant added to form flocs. For example, when there is only one type of flocculant (in this case, the flocculant is an organic polymer flocculant), the amount added. means. If more than one, it refers to the amount of flocculant responsible for floc formation. For example, when used in combination with an inorganic flocculant, it refers to the amount of the organic polymer flocculant, and when multiple organic polymer flocculants are used, it refers to the amount of the flocculant responsible for floc formation. 5 Description of Examples Example 1 Mixed raw sludge from a certain sewage treatment plant (concentration 2.5%, PH6.5,
Ignition loss: 68%) was dehydrated using a belt press type dehydrator using a cationic organic polymer flocculant (Evagrowth C-123, Ebara Inferco Co., Ltd. trade name, medium cation). Table 1 and Figure 3 show the results of the average addition rate per unit solid matter, cake moisture content, dehydrated cake thickness, addition amount A, etc.

[Table] According to the present invention, the amount A added per unit solid is
1.0%, and it can be seen that dehydration is good in the range of 0.7A to 1.5A, and best at 1.0A. Example 2 A certain water treatment plant sludge (average concentration 5%, pH 6.9, ignition loss 65%) was treated using an anionic organic polymer flocculant (Evagrowth A152, Ebara Infilco Co., Ltd. trade name, medium anion). It was dehydrated using a belt press type dehydrator. At this water treatment plant, the sludge concentration fluctuates significantly depending on the weather and other factors, making chemical control difficult, and the plant was constantly operating with an excess of flocculant (conventional method). Second
The table and FIG. 4 show the results of the average addition rate calculated per unit solid, cake moisture content, dehydrated cake thickness, addition amount A, etc.

[Table] The amount A added per unit solid in the method of the present invention is
It becomes 0.075%, and it can be seen that the dehydration process is extremely stable in the range of 0.7A to 1.5A, and is best at 1.0A. Further, in the conventional method, it was necessary to have one worker permanently stationed to manage the operation of the dehydrator, but this is not necessary in the present invention. In this way, according to the present invention, the chemical addition rate can be reduced;
Effects such as reduction in cake moisture content and reduction in labor costs are recognized. Example 3 A certain food factory has multiple wastewater treatment facilities.
Excess sludge was mixed and dewatered using a belt press type dehydrator. As the production type changes, the generation ratio of surplus sludge changes, and the optimal addition rate of organic polymer flocculant changes. Therefore, when operating the dehydrator, in addition to checking the sludge concentration and flow rate, it is also necessary to check the optimum chemical injection rate, which requires considerable labor costs. By using the method of the present invention, all of the above checks are no longer necessary, and the number of manual operations in the dehydration process can be significantly reduced. The results are shown in Table 3.

[Table] Here, Sludge concentration...0.9~1.5% Sludge PH...6.5~7.5 Sludge ignition loss...65~80 Coagulant used...Evagrowth C123 (Ebara Infilco Co., Ltd. trade name, DAM series, medium) As described above, the present invention is a method for controlling the amount of an organic polymer flocculant added that can fully cope with the fluctuations in sludge quality and concentration encountered in actual sludge dewatering treatment, and it is possible to control the amount of organic polymer flocculant added by automating the addition of chemicals. This makes it possible to optimally automatically control the amount of alcohol, which brings about significant practical effects such as reductions in drug costs and personnel costs.

[Brief explanation of the drawing]

Figure 1 is a graph qualitatively showing the relationship between the amount of flocculant added and the thickness of the dehydrated cake. Figure 2 is a graph qualitatively showing the relationship between the amount of flocculant added and cake moisture content.
4 and 4 are graphs showing the results of different examples of the present invention, and both show the relationship between the average addition rate, cake moisture content, and dehydrated cake thickness.

Claims (1)

[Scope of Claims] 1. When adding an organic polymer flocculant to sludge to flocculate it and dewatering it using a belt press type dehydrator, the relationship between the amount of the organic polymer flocculant added and the thickness of the dehydrated cake is determined. An organic polymer flocculant, characterized in that the added amount A at which the dehydrated cake thickness becomes the maximum value is determined, and the value obtained by multiplying the added amount A by a constant between 0.7 and 1.5 is used as the added amount of the organic polymer flocculant. Method for controlling the amount of polymer flocculant added. 2. The method according to claim 1, wherein the amount of the organic polymer flocculant added is the amount A.