JPS59183897A - Method for controlling addition ratio of high-molecular flocculant - Google Patents

Abstract

PURPOSE:To lower the cost by conserving the expense for a chemical agent, by measuring the colloid charge amount in a liquid after an ionic high-molecular flocculant is added to sludge while controlling the addition ratio of the flocculant to adjust the colloid charge amount to a predetermined value. CONSTITUTION:After anionic high-molecular flocculant is added to and mixed in sludge, the colloid charge amount of the liquid component thereof is measured and the addition ratio of the ionic high-molecular flocculant is adjusted so as to set the measured value to a definite range. The range of the colloid charge amount for making a dehydration state well is slightly varied according to the charge density of the flocculant or the type of a dehydrator but it is pref. 0-+ 0.5meq/l in a cationic org. high-molecular flocculant and 0--0.5meq/l in an anionic org. high-molecular flocculant. The aforementioned method enables the optimum automatic control of a dehydrating process due to the automatic addition of a chemical agent and can develop the effect for reducing labor cost or the like.

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 a dehydrator.

However, since there is an optimal range for the addition rate of organic polymer flocculants, if the addition rate is too low,
If the amount is too much, the dehydration condition will not be good, so there is a problem that the chemical addition rate must always be kept within an appropriate range by some method.

For this purpose, a proportional control method has conventionally been used in which the addition rate of unit solids 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. With this method, if the sludge concentration meter and flow meter are sufficiently reliable, the subsequent proportional control itself is easy to deal with fluctuations in sludge concentration, so it is possible to automate chemical addition, but in reality, Densitometer reliability is not sufficient. Furthermore, this method cannot be applied if there is a change in the quality of the sludge or if the optimum 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 safer side, resulting in an increase in chemical costs.

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 objective is to reduce the cost of sludge treatment as a whole 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 is within a certain range. ,
do.

The present invention has been made clear by 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 sludge dewatering properties. The relationship between the addition rate of the ionic organic polymer flocculant and the amount of colloid charge is shown qualitatively by the straight lines shown in FIGS. 1(a) and 1(b). In addition, the flocs that are generated gradually increase as the flocculant is added, but they rapidly become coarser at or near the inflection point A, and from points where the flocculant addition rate is slightly lower than point A, and after a while, they become smaller again. Become.

The point where coarsening rapidly progresses and the point where it begins to decrease will vary 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.

In dehydrators using polymer flocculants, such as reeds and belt press centrifuges, the dehydration capacity is highest in the region where the aggregates become coarser.

From 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, all the work required for the conventional proportional injection method, such as measuring the sludge concentration and flow rate, as well as determining the optimum chemical addition rate, becomes unnecessary.

Normally, the range of colloid charge that provides good dehydration is:
Although there are slight variations depending on the charge density of the flocculant used and the model of the dehydrator used, it is O~+0.5 meq/l for cationic organic polymer flocculants, and 0 to +0.5 meq/l for anionic organic polymer flocculants. O~-0.5meq/e 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 O, it is possible to reduce the flocculant addition rate within the range that maintains labor savings and reduce chemical costs, but it is possible to reduce the dewatering performance and throughput by disposing of the dehydrated cake. It is necessary to maintain the highest condition, and the specific colloid charge setting value at that time is the rate of change of sludge concentration,
The determination is made taking into consideration the measurement accuracy of the colloid charge amount, the measurement speed, etc., but the absolute value is usually 0.01 me (1
/A' level.

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.

By using a commercially available automatic titration device, microcomputer, etc., 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. It is preferable for the liquid sampling location to be closer to the chemical addition point, as this will reduce control time delays.

In addition, even in the case of a dehydration method in which two types of ionic flocculants are sequentially added, it is necessary to control not only the addition rate of the second flocculant, but also the addition rate of the first flocculant. The present invention 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 sufficiently cope with fluctuations in sludge quality and concentration encountered in actual sludge dewatering treatment, and by automating chemical addition. Optimum automatic control of the dehydration process becomes possible, and important practical effects such as reductions in chemical costs and labor costs are achieved without compromising on practical effects.

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. 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 to obtain a predetermined amount of colloid charge. The amount of chemicals added was adjusted while visually inspecting the mixture every 15 minutes.

The results are shown in Ibara 1.

Table 1 Here, Sludge concentration 1.5-3tttt pH' 6.0-7.0I Loss on ignition 60-75 Coagulant Evagrowth C-123 (trade name of Ebara Infilco) (neutral thione) The relationship between the average chemical addition rate of L, the moisture 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 the addition of perII in the step 11 before aggregation, and there is no instability in the processing state, and compared to the conventional method, chemical costs are reduced, labor costs are reduced, etc. The effect of

Example 2 Sludge from a certain water purification plant was centrifuged using anionic organic polymer flocculation method. Since the sludge thickening tank at this water treatment plant is small, the sludge concentration B fluctuates significantly due to weather, etc., making it difficult to control the chemical injection f6. ).

The results are shown in No. 2.

Table 2 Here, sludge concentration 4-9% tt pH 6.5-7.0 〃 Loss on ignition 65-70% Coagulant Evagrowth A-152 (trade name of Ebara Infilco Ltd.) (medium anion) Average chemical addition in Table 2 The relationship between the rate, 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 had multiple wastewater treatment facilities, and surplus sludge was mixed and dehydrated using a centrifugal dehydrator. The generation ratio of surplus sludge changes as the product type changes, and the optimal addition rate of organic polymer flocculant changes. Therefore, when operating a 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. When the method of the present invention is used, 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 3 Sludge concentration 0.9-1.5% // pH 6.5-7.5 Loss on ignition 65-8° Coagulant used Evagrowth C 123 (Product name of Ebara Infilco Co., Ltd.) (]) AM type, neutral thione) ・

[Brief explanation of the drawing]

Figures 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 the relationship between the average chemical addition rate, dehydrated cake water content, and processing amount in 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. Agent! Buried soil Tadashi Shiozaki Hirodo 12)
-'Hime Wholesale Tsu No. 21 Cation, )su Chest Cable Leakage Y Ai Ding 4 Richi Hat Emperor's Aptitude (悴) Fig. 3

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 after the flocculant is added. 2 When the ionicity of the flocculant is positive, the amount of colloid charge is +0.01 to +0.5 meq/7. If negative, -0,01 to -0,5meq/A!
A method for controlling the addition rate of a polymer flocculant according to claim 1, characterized in that the flocculant addition rate is controlled so that the following is achieved.