JPH0334399B2 - - 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 have 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 quality, and it is often difficult to optimize control of dewatering operations by automating the addition of chemicals. Therefore, it is necessary to constantly monitor the dewatering state and manually adjust the amount added, 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 provides a method for controlling the amount of flocculant added that can sufficiently cope with fluctuations in the concentration and quality of sludge when using an organic polymer flocculant.
In addition to cutting down on chemical costs, the aim is to make it possible to significantly reduce labor costs through automation, thereby lowering the overall cost of sludge treatment. 4 Structure of the Invention The present invention was developed as a result of investigating the relationship between the amount of organic polymer flocculant added and the capillary suction time of flocculated sludge, and examining the relationship between them and the moisture content of the dehydrated cake (hereinafter referred to as cake moisture content). The relationship between the amount of flocculant added and the capillary suction time is such that the amount of flocculant added is determined to be the second bending point, and the organic concentration is calculated by multiplying this amount by a constant of 0.7 or more and 1.5 or more. It is characterized by adding a molecular flocculant to perform flocculation and dehydration treatment. The capillary suction time was developed overseas for the purpose of predicting the dehydration properties of sludge, and an overview of the method for measuring the capillary suction time will now be explained with reference to FIG. 1. When a hollow metallic cylindrical sample holder 2 is placed on absorbent paper 1 and a certain amount of sample is put into the cylinder, the sample (or its mother liquor in the case of a suspension) is absorbed onto the absorbent paper 1 from the bottom of the cylinder. and reaches point A while drawing concentric circles. At this time, the capillary suction time measuring section 3 is electrically activated to start timekeeping, and when point B is reached, timekeeping stops. The capillary suction time is the time, expressed in seconds, required for the area AB to be wetted by the sample. The relationship between the amount of organic polymer flocculant added and the capillary suction time is qualitatively shown in FIG. 2. In other words, when examining the relationship between the amount of flocculant added and the capillary suction time, the capillary suction time sharply decreases as the amount of flocculant added increases, then bends (this point of inflection is called the first bending point). It has become clear that after keeping a constant value for a certain period, it begins to increase as the amount of coagulant added increases (this inflection point is referred to as the second inflection point). The amount of coagulant added that corresponds to this second bending point will be referred to as the addition amount A hereinafter. On the other hand, the relationship between the amount of flocculant added and the cake moisture content is
It will look like Figure 3. In other words, in the region where the amount added is small, the particle size and strength of the aggregates are small, causing problems such as seepage from the filter cloth, protrusion, poor peeling, overflow of the gravity filtration section, outflow from the slits, etc., making it difficult to operate the dehydrator. becomes impossible. As the amount added increases, the dehydrator can be operated, 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 relationships in FIG. 2 and FIG. 3, 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 capillary suction time and the absolute value of the addition amount A shown in Figure 2 change depending on the quality of the sludge, the type of flocculant, the type of dehydrator, operating conditions, etc. However, it has been confirmed that the area around the addition amount A remains a region with good dehydration. Moreover, the width of the above-mentioned "nearby" ranged from 0.7A to 1.5A, regardless of the properties of the sludge, the type of flocculant, the dewatering conditions, etc. From 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 capillary suction time, it is also possible to collect sludge and then measure it in batches using a commercially available device using a laboratory test method suitable for the dehydrator used. However, a monitor line may be provided separately from the actual machine to continuously collect sludge, and the amount of flocculant added may be changed at predetermined intervals so that the capillary suction time can be measured semi-continuously. Further, these measurements do not need to be performed manually, and the addition amount A can be determined by automation as appropriate using a data processing device. Since the addition amount A is the point at which the differential value of the capillary suction time with respect to the addition amount changes greatly, the addition amount A can also be automatically determined using this differential value. In any case, it is sufficient to clarify only the relationship between the addition amount and the capillary suction time in the vicinity of the addition amount A. The addition amount A can be determined by applying existing automatic control methods. Thus, once the addition amount A is determined, the amount to be added to the sludge to be actually supplied to the dehydrator can be set between 0.7A and 1.5A. 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 (1.0A), but if you want to save the flocculant extremely, set it to around 0.7A to improve the properties of the sludge. If the fluctuation is severe and problems such as control time delay remain even if the control method according to the present invention is automated, it may be set 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, commercially available flocculants can be used as they are as the flocculant. 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. Note that the present invention can be applied to either a batch type or a continuous type dehydrator, and to either a dehydrator with or without a gravity filtration section. 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 Infilco Co., Ltd. trade name, medium cation). Table 1 and FIG. 4 show the results of the average addition rate per unit solid matter, cake moisture content, capillary suction time, 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 good dehydration is achieved in the range of 0.7A to 1.5A, and the best is 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). and dehydrated using a centrifuge.
At this water treatment plant, the sludge concentration fluctuates significantly depending on weather and other factors, making it difficult to control chemical injection, and the plant was always operated with an excessive amount of coagulant (conventional method). Table 2 and FIG. 5 show the results of the average addition rate per unit solid, cake moisture content, capillary suction time, addition amount A, etc.

[Table] The amount A added per unit of solid matter in the method of the present invention is 0.09%, and it can be seen that the dehydration treatment 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 contamination was mixed and dehydrated using a centrifugal 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, the sludge concentration,
In addition to checking the flow rate, it was also necessary to check the optimum drug injection rate, which required considerable labor costs. By using the method of the present invention, all of the above-mentioned 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) cation) 6 Functions and Effects of the Invention As described above, the present invention is a method for controlling the amount of organic polymer flocculant added that can sufficiently cope with the fluctuations in sludge quality and concentration encountered in actual sludge dewatering treatment. Automation of addition enables optimal automatic control of the dehydration process, which brings great practical effects such as reductions in chemical costs and labor costs.

[Brief explanation of drawings]

Figure 1 is a schematic explanatory diagram of the capillary suction time measurement device, Figure 2 is a graph qualitatively showing the relationship between the amount of flocculant added and capillary suction time, and Figure 3 is the relationship between the amount of flocculant added and cake moisture content. Figures 4 and 5 are graphs showing the results of different examples of the present invention, and both show the relationship between the average addition rate of organic polymer flocculant, cake moisture content, and capillary suction time. It shows the relationship. 1...Water absorbent paper, 2...Hollow cylindrical sample holder, 3...
...Capillary suction time measuring section.

Claims (1)

[Scope of Claims] 1. When an organic polymer flocculant is added to sludge for flocculation and dewatering treatment, the relationship between the amount of organic polymer flocculant added and the capillary suction time of flocculated sludge becomes a second inflection point. Determine the amount of addition A, and add 0.7 to 1.5 to the amount of addition A.
A method for controlling the amount of an organic polymer flocculant added, the method comprising: setting the amount of the organic polymer flocculant to be a value obtained by multiplying by the following constants. 2. The method according to claim 1, wherein the amount of the organic polymer flocculant added is the amount A.