JPH0417719B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for controlling the addition rate of an organic polymer flocculant used in sludge dewatering treatment. 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 with chemicals, such as belt presses and centrifugal separation. It has the advantage of being able to use high-performance dehydrators such as dehydrators. However, since there is an optimum range for the addition rate of organic polymer flocculants, the dehydration condition will not be good if the addition rate is too low or too high, so there is always some way to control the chemical addition rate. 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. In response to the current situation, the present invention provides a method for controlling the flocculant addition rate that can sufficiently cope with fluctuations in sludge concentration and quality when using an ionic organic polymer flocculant, thereby reducing chemical costs. The aim is to reduce the overall cost of sludge treatment by making it possible to significantly reduce labor costs through automation. The present invention is characterized by measuring the amount of colloidal charge of the liquid after adding and mixing the ionic organic polymer flocculant, and adjusting the addition rate of the flocculant so that the value falls within a certain range. The present invention was clarified as a result of determining the relationship between the addition rate of an ionic organic polymer flocculant and the amount of colloidal charge of the liquid, and examining the correlation between these and the actual dewatering properties of sludge. The relationship between the addition rate of the ionic organic polymer flocculant and the amount of colloid charge is qualitatively shown as the straight lines shown in Figure 1 a and b. In addition, the number of blocks generated gradually increases with the addition of the flocculant, but the number of blocks generated increases at or near the inflection point A, especially at A.
From a point where the coagulant addition rate is slightly lower than that point, coarsening progresses rapidly, and after a while, it becomes smaller again. The point where coarsening rapidly progresses or the point where it begins to decrease varies depending on the type of sludge, the type of flocculant, the method of mixing the two, the mixing device, etc., but the area where the coarsening of aggregates occurs is shown in the figure. The addition rate is within the range indicated by the diagonal line. Furthermore, in a dehydrator using a polymer flocculant, such as a belt press centrifuge, the dehydration capacity is highest in the region where the aggregates become coarse. Based on these facts, in order to keep the dehydrator in good condition, it is sufficient to adjust the amount of flocculant added or adjust the flow rate of sludge so that the amount of colloid charge falls within a predetermined range (the shaded area in the figure). In this case, the measurement of sludge concentration and flow rate, as well as the determination of the optimum chemical addition rate, which were necessary in the conventional proportional injection method, are all unnecessary. Normally, the range of colloid charge that results in a good dehydration state varies slightly depending on the charge density of the flocculant used and the type of dehydrator used, but for cationic organic polymer flocculants, it is 0 to +0.5meq. /,
0 to − for anionic organic polymer flocculants
0.5meq/ is good. Therefore, the optimal chemical addition rate should be set between these values, but it is more economical to have a smaller chemical addition rate, that is, a smaller absolute value of the colloid charge amount. Needless to say. However, when the colloid charge amount is 0, it is possible to reduce the flocculant addition rate within the range that maintains labor savings and reduce chemical costs. It is necessary to maintain the colloid charge amount in the highest condition, and the specific set value of the colloid charge amount at that time is determined by taking into account the rate of change of sludge concentration, the measurement accuracy of the colloid charge amount, the measurement speed, etc., but it is usually an absolute value. 0.01meq/ as value
It will be about. As a method for measuring the amount of colloid charge, a commonly used colloid titration method can be used as is. Usually, a method is used in which toluidine blue is used as an indicator, polyvinyl potassium sulfate is used as a titrant, and the titration end point is detected using a colorimeter. If a commercially available automatic titration device or microcomputer is used, titration work, calculation of colloid charge amount, control of chemical injection pump, etc. can be performed automatically. The liquid used for the measurement is not particularly limited as long as it is not inconvenient for the titration operation, but it is usually preferable to use a liquid containing few floating solids, such as a dehydrated separation liquid. In addition, in a dehydrator that uses a cleaning liquid, it is more accurate to collect a separated liquid that is not contaminated with cleaning liquid. moreover,
It is preferable for the liquid sampling location to be close to the chemical addition point, since this reduces control time delays. In addition, even in the case of a dehydration method in which two types of ionic flocculants are sequentially added, the present invention can be used not only to control the addition rate of the second flocculant but also to control the addition rate of the first flocculant. can be used. As described above, the present invention is a method for controlling the addition rate of an ionic organic polymer flocculant that can fully cope with the fluctuations in sludge quality and concentration encountered in actual sludge dewatering treatment, and it dewaters by automating chemical addition. Optimum automatic control of the process becomes possible, which brings great practical effects such as reductions in chemical costs and labor costs. Some examples will be described below. Example 1 Mixed raw sludge from a certain sewage treatment was dehydrated using a belt press type dehydrator using a cationic bioorganic polymer flocculant. In the method of the present invention, the separated liquid was automatically subjected to colloid titration using a colorimetric method, and the amount of chemical injection was automatically controlled so as to obtain a predetermined amount of colloid charge. In the conventional method, the amount of chemicals added was adjusted while visually observing the material once every 15 minutes.
The results are shown in Table 1.

[Table] Here, sludge concentration 1.5-3% 〃PH 6.0-7.0 〃Ignition loss 60-75 Coagulant Evagrowth C-123 (trade name of Ebara Infilco Ltd.) (medium cation) In addition, the average chemical addition rate in Table 1 The relationship between the water content of the dehydrated cake and the throughput is shown in Figure 2. As described above, according to the present invention, there is no increase in the moisture content of the dehydrated cake due to excessive addition of a coagulant, and there is no instability in the processing state, and the effects of reducing chemical costs and labor costs are recognized compared to conventional methods. . Example 2 Sludge from a certain water purification plant was dehydrated using an anionic organic polymer flocculant using a centrifuge. This water purification plant is
Because the sludge concentration tank is small, the sludge concentration fluctuates significantly depending on the weather, making chemical injection control difficult.
The plant was operated with an excessive amount of flocculant at all times (conventional method).
The results are shown in Table 2.

[Table] Here, sludge concentration 4 to 9% 〃PH 6.5 to 7.0 〃Ignition loss 65 to 70 Flocculant Evagrowth A-152 (trade name of Ebara Infilco) (medium anion) Note that the average chemical addition rate in Table 2 and The relationship between the moisture content of the dehydrated cake and the throughput is illustrated in Figure 3. As described above, according to the method of the present invention, effects such as a reduction in the chemical addition rate, a reduction in the moisture content of the dehydrated cake, and a reduction in labor costs are recognized. Example 3 A certain food factory has multiple wastewater treatment facilities.
Excess sludge 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, 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 to 1.5% 〃PH 6.5 to 7.5 〃Ignition loss 65 to 80 Coagulant used Evagrowth C123 (trade name of Ebara Infilco) (DAN type, medium cation)

[Brief explanation of drawings]

Figure 1 a and b show the relationship between the ionic organic polymer flocculant addition rate and the amount of colloid charge, and Figure 2 shows Table 1.
Figure 3 shows the relationship between the average chemical addition rate in Table 2, the moisture content of the dehydrated cake, and the throughput.

Claims (1)

[Claims] 1. In a method of dewatering sludge by adding and mixing an ionic polymer flocculant, the amount of colloid charge in the liquid after the addition of the flocculant is measured, and the amount of colloid charge is set to a predetermined value. A method for controlling the addition rate of a polymer flocculant, the method comprising controlling the flocculant addition rate so as to achieve the following. 2 If the ionicity of the flocculant is positive,
Claim 1 characterized in that the coagulant addition rate is controlled so that the amount of colloidal charge is 0 to +0.5 meq/, and when it is negative, 0 to -0.5 meq/. Method for controlling addition rate of molecular flocculant.