JPH0334398B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for controlling the amount of flocculant added in sludge dewatering treatment using an organic polymer flocculant. In recent years, organic polymer flocculants have been widely used in place of inorganic flocculants for sludge dewatering treatment.
The flocculant has a preferable addition rate range for dehydration treatment, and it is necessary to avoid not only under-dosing but also over-dosing, and from a maintenance management perspective, the chemical addition rate must always be kept within an appropriate range by some method. I felt a sense of annoyance. In view of the current situation, the present invention provides a method for controlling the amount of organic polymer flocculant added that can sufficiently cope with changes in the quality and concentration of sludge, overcomes the above-mentioned drawbacks, saves on chemical costs, and reduces labor costs through automation. The purpose of this is to make it possible to significantly reduce the amount of sludge and reduce the overall cost of sludge treatment. The present invention is based on the ratio (B/
A) is determined in advance, and the value between the value obtained by measuring the flocculant addition rate A that begins to remain in the liquid from time to time and multiplying it by the value of the ratio and the addition rate A measured at any time is determined during dehydrator operation. This is a method for controlling the addition rate of a polymer flocculant, characterized in that the addition rate is set to a certain amount. The present invention was completed as a result of careful study of the relationship between the addition rate of the organic polymer flocculant and the amount remaining in the liquid, as well as the correlation between these and dehydration properties.
The relationship between the addition rate of the organic polymer flocculant and the amount remaining in the liquid is schematically shown as the solid line A in FIG. In other words, in the region where the addition rate of flocculant is low,
All of the added flocculant is adsorbed to the sludge particles and does not remain in the liquid, but when it exceeds a certain addition rate (addition rate A), it begins to remain in the liquid, and from then on most of the added flocculant disappears into the liquid. It will remain inside.
On the other hand, the relationship between the moisture content of the dehydrated cake obtained as a result of dewatering tempered sludge to which a flocculant has been added, the amount that can be treated (processing amount), and the flocculant addition rate is as shown by the solid lines A and C in Figure 1. become. That is, dewatering cannot be performed in a region where the addition rate of flocculant is extremely low, and when the addition rate exceeds a certain addition rate (addition rate B), dehydration becomes possible, and the best condition is reached around the addition rate A, and gradually deteriorates thereafter. Based on this relationship, in order to maintain the best dewatering performance, it is sufficient to operate the dehydrator at around the addition rate A. Specifically, the amount of flocculant remaining in the liquid is measured by an appropriate means and the amount of flocculant remaining in the liquid is measured and adjusted to a specified value. The amount of flocculant added or the flow rate of sludge may be controlled so that the value falls within the value of . However, in some cases, when the flocculant addition rate is less than A, that is, even when no flocculant remains in the liquid, if the flocculant is added, if the addition rate is around A, the dehydration property may not deteriorate significantly. However, it is possible to reduce the flocculant addition rate to B if it is okay to sacrifice dehydration properties a little. In other words, considering the balance between the advantage of being able to save on flocculant and the disadvantage of deterioration of dewatering performance, the most energy can be saved by setting the flocculant addition rate between A and B for dewatering. This is the idea and purpose of the present invention. However, in actual sludge treatment, the sludge concentration and quality fluctuate drastically, and it is troublesome to constantly adjust the dehydrator to the desired flocculant addition rate. Although it may be possible to save the most energy by operating the coagulant addition rate at B or between B and A, it is not easy to maintain this state at all times because it requires manpower to monitor and adjust the flow rate. However, from numerous experimental studies, it has been found that even if the values of A and B in the addition rate vary due to qualitative variations and concentration variations in sludge, the ratio of A and B does not change. This can be done by determining the ratio (B/A) of the dehydration method and condensing agent used in advance.
This means that the minimum addition rate B at which the dehydrator can be operated can be determined by simply measuring the flocculant addition rate A. If the above addition rate B can be automatically determined, the set value of the flocculant addition rate used during operation of the dehydrator can also be set to the above B or any value between B and A. Furthermore, the above addition rate A is determined by a method based on viscosity measurement of a separated liquid (viscosity method),
It can be easily determined using analytical methods such as total organic carbon measurement (TOC method), nitrogen concentration measurement method, and colloid titration method, and automation is also possible. In addition, the measurement of sludge concentration and flow rate, which was necessary in the past, is no longer necessary, which saves manpower. According to the experience of the present inventors, the addition rate ratio (B/A) is 0.7 to 0.8 for a centrifugal separator, 0.5 to 0.8 for a belt press, 0.7 to 0.8 for a screw press, and The value is smaller. Also, the difference between the dewatering performance at addition rate B and that at addition rate A seems to be smaller for models with cloth than for models without it, but this difference also differs depending on the sludge, so in reality It is best to use a sludge and dewatering machine to find the optimal setting value for the addition amount. As described above, according to the present invention, the present invention provides a method for controlling the flocculant addition rate that can sufficiently cope with fluctuations in sludge concentration and quality encountered in actual sludge treatment, and can reduce chemical costs and reduce labor costs. This brings about great practical effects such as cost reduction. Some examples will be described below. Example 1 Mixed raw sludge from a certain sewage treatment plant was dehydrated using a belt press type dehydrator using a cationic organic polymer flocculant. As a method of controlling the flocculant addition rate, the present invention and the sludge concentration and optimum addition rate are investigated before the start of operation.
We compared a conventional method in which the sludge flow rate and flocculant solution flow rate are set and then the flow rate is fixed for operation. Table 1 shows the results.
Shown below. In the method of the present invention, the amount of colloid charge was automatically measured at any time, and the addition rates A and B and the predetermined amount of colloid charge were measured.

[Table] In this sludge, the addition rate A was 1.0%toDS, and the addition rate B was 0.7%toDS. According to the present invention, an extremely stable operating state was achieved when the addition rate was between 0.7% and 0.9%, and the water content was between 72% and 74%. On the other hand, in the conventional method, the set value of the addition rate cannot be adjusted due to fluctuations in sludge concentration.
When the content was between 0.7 and 1.0%, the operation became extremely unstable, and a state in which dewatering was partially impossible appeared, and the moisture content of the cake also increased. Therefore, we had no choice but to set the addition rate to 1.4%, and although the treatment became stable, the result was
The addition rate was 1.6%, and an increase in water content due to excessive flocculant was observed. Example 2 Gravel washing wastewater sludge generated at a certain gravel crushing plant is
It is dehydrated using a centrifuge using a nonionic organic polymer flocculant. The amount of sludge generated varies depending on the operating conditions of the gravel manufacturing plant, and the concentration also fluctuates, so conventionally it was necessary to adjust the amount of coagulant added while monitoring the dewatering state. As methods for controlling the amount of flocculant added, the method of the present invention and the conventional method 3
compared people. In the method of the present invention, the flocculant addition rate A is determined as the addition amount based on the liquid using an automatic measuring device that estimates the residual concentration from the viscosity of the filtrate, and is multiplied by a predetermined value to determine the amount of added liquid, and the amount of flocculant added is automatically determined. controlled.

【table】

[Table] The addition rate A of this sludge was 0.08%toDS, and the addition rate B was 0.06%toDS. Therefore, the addition rate ratio is 0.06/0.08=0.75. According to the present invention, an extremely stable dehydration state was achieved at an addition rate of 0.06 to 0.08%, and the water content was 53 to 51%. In the conventional method, a stable treatment state was achieved only at a considerably high addition rate, and the moisture content of the cake increased slightly, but the present invention has the advantage of being able to perform dehydration treatment at low cost.

[Brief explanation of the drawing]

FIG. 1 shows the correlation between the addition rate of the organic polymer flocculant and the amount remaining in the liquid.

Claims (1)

[Claims] 1. In a method of dewatering sludge by adding and mixing an organic polymer flocculant to the sludge, the maximum value of the flocculant addition rate ( Addition rate A) and minimum addition rate that allows dehydration (addition rate B)
The ratio (B/A) is determined in advance, and then the addition rate A is measured at any time to determine the addition rate B, and the dehydration operation is performed at a value between the addition rate B and the addition rate A measured at any time. A method for controlling the addition rate of an organic polymer flocculant, characterized by: 2. The organic polymer flocculant according to claim 1, wherein the flocculant has ionic properties, and the flocculant addition rate A is determined by measuring the residual flocculant amount as a colloidal charge amount. Addition rate control method.