JPS59183898A - Method for controlling addition ratio of high-molecular flocculant - Google Patents

Abstract

PURPOSE:To reduce the total cost of treatment by reducing the cost of a chemical agent, by measuring the concn. of a nonionic high-molecular flocculant remaining in a liquid after said flocculant is added to sludge while controlling the addition ratio of the flocculant so as to hold the concn. thereof to a predetermined value. CONSTITUTION:The concn. of a nonionic high-molecular flocculant remaining in a liquid after said flocculant is added to sludge is measured and the addition ratio of the flocculant is controlled so as to adjust the measured value to a definite range. The range of the remaining concn. of the flocculant for making a dehydrating state well is slightly varied according to the kind of sludge or the type of a dehydrator but pref. 0-100mg/l in usual. This method is useful as a method for controlling the addition of the nonionic high-molecular flocculant capable of sufficiently corresponding to the variation of the quality or concn. of sludge encountered in practical sludge dehydrating treatment and the optimum automatic control of a dehydrating process is enabled by the automatic addition of a chemical agent.

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 a high-performance dehydrator such as a dehydrator.

However, since there is an optimal range for the loading 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 very frustrating 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 method measures the sludge flow rate and concentration to determine the solids throughput, and then calculates the amount of solids from the optimum addition rate determined in advance by another means to control the chemical injection bond flow rate. With this method, if the sludge concentration meter and flowmeter 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 the optimum chemical injection rate changes due to qualitative changes in the sludge.

In actual sludge treatment, there are many opportunities to encounter fluctuations in the degree and quality of sludge, 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 the concentration and quality of sludge when using a nonionic organic polymer flocculant, thereby reducing chemical costs. The purpose of this project is to reduce the overall cost of sludge treatment by making it possible to significantly reduce labor costs through automation.

The present invention measures the concentration of the flocculant remaining in the liquid after adding and mixing the nonionic organic polymer flocculant, and adjusts the addition rate of the flocculant so that the peak is within a certain range. It is characterized by

The present invention was made possible by determining the relationship between the addition rate of a nonionic organic polymer flocculant and the flocculant remaining in the liquid, and examining the correlation between these and the actual sludge dewatering properties. It is something that The relationship between the addition rate and the residual concentration is qualitatively shown in Figure 1, and the area where sludge dewatering is good is within the addition rate range shown by the diagonal leg in the figure. This relationship is
It was confirmed that this method holds true even if the concentration and type of sludge differ, and even if the molecular weight of the flocculant changes. This fact shows that even if the quality and concentration of sludge changes, the dewatering process can be easily achieved by simply adjusting the amount of flocculant added or adjusting the total flow rate of sludge so that the residual concentration of flocculant can be maintained within a predetermined range. This means that it can be kept in good condition.

In this case, the measurement of sludge concentration and flow rate and the determination of the optimum chemical addition rate, which were necessary in the conventional proportional control method, are no longer necessary.

Normally, the range of the residual concentration of the coagulant that provides good dewatering conditions varies slightly depending on the type of sludge and the model of the dehydrator, but it is generally within the range of 0 to 1007 Mg/7. If so, the smaller the residual amount, the more efficient the use of the chemical will be, and it will be more economical. However, when the residual concentration is omy7t, the flocculant addition rate is reduced within the range that can maintain labor savings.
Although it is possible to reduce chemical costs, depending on the disposal of the dehydrated cake, it is necessary to maintain the dewatering performance and throughput at the highest level. The range of ~10.0 my/L is most preferable and may be determined by taking into consideration the rate of change in sludge concentration, measurement accuracy of residual concentration, measurement time, etc.

As a method for measuring the residual coagulant, any commonly used method may be used, but it is preferable to use a method that requires a short measuring time. For example, it is convenient to apply a method of measuring the viscosity of a separated liquid (viscosity method), a method of measuring total organic carbon (CTOC method), or a method of measuring nitrogen concentration.

It is usually preferable to use a liquid containing few suspended solids, such as a dehydrated separation liquid, as the liquid used for measuring the residual concentration.

In addition, in a dehydrator that uses cleaning fluid, accuracy is better if the sample is collected without being contaminated by cleaning fluid. Furthermore, it is preferable for the sample collection location to be close to the chemical addition point, since this will reduce the time delay in control.

As described above, the present invention is a method for controlling the addition rate of a nonionic organic polymer flocculant that can fully cope with the fluctuations in sludge quality and concentration encountered in actual sludge dewatering treatment, and automates the addition of chemicals. This enables optimal automatic control of the dehydration process, which brings great practical effects such as reductions in chemical costs and labor costs.

Some examples will be described below.

Example 1 Sludge from a certain water treatment plant was dehydrated using a centrifugal dehydrator using a nonionic organic polymer flocculant (Evagrowth N-700 (trade name of Ebara Infilco), nonionic polyacrylamide, molecular weight 12 million). .

Because the concentration of sludge at this water treatment plant fluctuates dramatically, we have people constantly monitoring the dewatering state and adjusting the amount of chemicals injected. In the method of the present invention, the residual flocculant concentration in the separated liquid is automatically measured using a TOC automatic analyzer, and the flow rate of the chemical injection pump is automatically determined using that value.

No supervisor was required in the method of the invention. Table 1 shows the results.
Shown below.

Table 1 However, sludge properties: Concentration 4 to 7% PH' 6.5 to 7.0 Loss on ignition 65 to 70% In addition, as a conventional method, the optimal sludge is Calculate the required amount of flocculant from the addition rate,
Although the chemical injection pump flow rate was set, the operation was unstable due to fluctuations in the concentration and quality of the sludge.

As described above, according to the method of the present invention, the dehydration process is stabilized, the chemical addition rate is reduced, and the cake moisture content is reduced. A/'Effects such as reduction in project costs were recognized.

Example 2 Gravel washing wastewater sludge generated at a certain gravel crushing plant is dehydrated using a continuous granulation and dehydration device using a nonionic organic polymer flocculant. The amount of sludge generated changes depending on the operating conditions of the gravel manufacturing plant, and the concentration also changes, so the amount of flocculant added needs to be constantly adjusted while monitoring the dewatering state, resulting in a situation where labor costs cannot be ignored.

In the method of the present invention, automatic control was adopted in which the viscosity of the dehydrated separated liquid was measured to determine the residual concentration of the flocculant, and the chemical injection pump was linked, and the results shown in Table 2 were obtained.

From Table 2, it can be seen that according to the present invention, the dehydration state is improved, which is useful for reducing chemical costs, labor costs, etc.

Note that the conventional method was carried out in the same manner as in Example 1.

Table 2 Here, Sludge concentration 10-25% pH 6.5-7.5 Loss on ignition 40-50 Coagulant: Evagrowth N-100 (trade name of Ebara Infilco)
(Nonionic polyacrylamide, molecular weight 10 million)

[Brief explanation of drawings]

FIG. 1 shows the relationship between the flocculant addition rate and the residual flocculant degree. Representative Patent Attorney Masahiro Shiozaki

Claims (1)

[Claims] 1. In a method of dewatering sludge by adding and mixing a nonionic organic polymer flocculant to the sludge, the amount of flocculant remaining in the liquid at the flocculant addition rate is measured, and the concentration is adjusted to a predetermined value. 1. A method for controlling the addition rate of a polymer flocculant, the method comprising controlling the flocculant addition rate so as to maintain . 2. The method for controlling the addition rate of a gastric molecule flocculant according to claim 1, characterized in that the flocculant addition rate is controlled so that the flocculant residual concentration is 1 to 100 μ/l.