JPH0562000B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for controlling the addition rate of an organic polymer flocculant used in sludge dewatering treatment. [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 with chemicals. It has the advantage of being able to use high-performance dehydrators such as presses and centrifuges. However, since there is an optimal range for the addition rate of organic polymer flocculants, if the addition rate is too low or too high, the dehydration condition will not be good, 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, making chemical addition and automation 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 this current situation, when using an ionic organic polymer flocculant, the amount of colloid charge of the separated liquid after adding and mixing the ionic organic polymer flocculant is measured, and the value is set to zero or the flocculant used. A method has been proposed in which the addition rate of the flocculant is adjusted to a predetermined value having the same sign as . (Unexamined Japanese Patent Publication No. 59-183897, same
(No. 59-183899) These methods provide a method for controlling the flocculant addition rate that can adequately deal with variations in sludge concentration and quality, and automation has made it possible to significantly reduce labor costs. According to this method, the operating conditions of the dehydrator were always maintained in the best condition, and the waste of flocculant due to large excess addition was completely prevented. However, in terms of flocculant addition rate, the addition rate carried out in the method is greater than the minimum addition rate that can be operated with the dehydrator used. Industrially, it is often more economical to reduce the polymer addition rate, even if it worsens dehydration results such as cake moisture content and processing speed. In such cases, this method has drawbacks that are difficult to deal with. The present invention has improved the method for measuring colloidal charge and determined the relationship between the addition rate of a cationic organic polymer flocculant, the colloidal charge of sludge, and the cake water content. We have now provided a method that enables stable dehydration operations. [Means for Solving the Problems] The present invention provides a method for dewatering sludge by adding and mixing a cationic polymer flocculant, and the amount of colloid charge in the liquid after the addition of the flocculant is determined based on a standard positive colloid solution and Add a color change indicator, perform back titration with a titrant, and measure the end point of the titration by detecting the color change reaction of the color change indicator using dual wavelength photometry. This is a method for controlling the addition rate of a polymer flocculant, which is characterized in that the addition of the cationic polymer flocculant is controlled so that the cationic polymer flocculant is added. That is, in the present invention, a colloid titration method is used to measure the amount of colloid charge, and a specific method thereof is a back titration method in which a positive colloid standard solution is added to the collected sludge and then titrated with a titrant. Furthermore, the accuracy and sensitivity of measuring the amount of colloid charge was increased by using a method of measuring the color change reaction of a color change indicator using dual wavelength photometry to detect the end point of titration. As the cationic organic polymer flocculant used in the present invention, any commonly used flocculant can be used, but N,N'-dimethylaminoalkyl acrylate or methacrylate with an alkyl group of 2 or 3 carbon atoms may be used. acid salts (abbreviated as esters), vinylbenzylmonoditrimethylammonium acid salts, cationic modified acrylamide acid salts, vinylpyridine and its substituted derivatives,
These include homopolymers and copolymers of cationic monomers such as acrylamine and substituted derivatives thereof. In addition, copolymers of the above-mentioned cationic monomers with monomers such as acrylamide, acrylonitrile, and acrylic acid alkyl esters, as well as polyvinylimidazoline acid salts, chitosan acid salts,
Cationized starch can also be used. On the other hand, the method for measuring the amount of colloid charge in the liquid used in the present invention is a highly accurate colloid titration method using a standard positive colloid solution and a color change indicator, and dual wavelength photometry is also used to measure the color change state of the indicator. In particular, it is preferable to use a real-time method (Japanese Unexamined Patent Application Publication No. 116447/1999) for determining the titration end point because the apparatus becomes simpler. To explain this real-time method simply, the difference in the amount of transmitted light at two predetermined wavelengths is measured at the point of addition of the indicator before the start of titration, and the difference in the amount of transmitted light at two predetermined wavelengths is The titrant is added while measuring the difference in the amount of transmitted light, and the amount of titrant added when the amount reaches a value multiplied by the predetermined constant is determined as the titration end point. Another preferred real-time method is to irradiate light while adding a titrant to a sample prepared by adding a positive colloid standard solution to collected sludge, and detect the amount of transmitted light in two detection bands during the color change reaction of the color change indicator and the amount of light present between them. One method is to detect any two of the amounts of transmitted light at the absorption point, and set the titration end point when both amounts of transmitted light become equal. In addition, it is necessary to add about 100 to 500μ to the positive colloid solution and titrant solution with an accuracy of 1μ.
It is necessary to use a highly accurate billet or the like. The amount of indicator added is 100 to 200 μ with an accuracy of about 10 μ.
A simple means (such as a dispenser) that can add a certain amount can be used. As a reagent, methyl glycol chitosan (MGCh) or polydiallyldimethylammonium chloride (registered trademark: Catfloc) is suitable as a positive colloid standard solution, polyvinyl potassium sulfate (PVSK) is optimal as a titrant, and toluidine blue (TB) is optimal as an indicator. ) is good. The sample used to measure the amount of colloidal charge in sludge is a liquid containing few suspended solids, such as a dehydrated separated liquid. In addition, in a dehydrator that uses a cleaning liquid, it is necessary to collect a separated liquid that is not contaminated with cleaning liquid. Furthermore, it is preferable for the sample collection location to be close to the chemical addition point, since this reduces control time delays. In the present invention, the specific method for measuring the amount of colloid charge and adding the flocculant may be continuous or discontinuous, and may be automatic or not. Automatic control is preferred. A relatively economical control method is to add the flocculant automatically or artificially, measure the amount of colloid charge constantly or at regular intervals immediately after adding the flocculant, and then add the flocculant. At the same time, adjust the addition amount while comparing with the colloid charge amount to obtain a predetermined colloid charge amount (-0.001 to -
0.1meq/). The flocculant addition, including colloid charge measurement, may be fully automated. In the present invention, since the amount of colloid charge can be measured extremely accurately and quickly, the amount of coagulant added can be accurately controlled depending on the magnitude of the amount of colloid charge. Therefore, there is no need to add too much or too little flocculant, and the amount of flocculant that can maintain high dewatering efficiency can be reduced to the minimum necessary amount. [Operation] The operation of the present invention will be explained with reference to FIGS. 1 and 2. Using the method of the present invention, sewage mixed raw sludge (SS = 18.7
g/) was condensed using a cationic polymer flocculant (Evagrowth C104G, strong cation, manufactured by Ebara Infilco), and the flocculated sludge was dehydrated using a belt press at a processing rate of 120 kg/m·hr. The relationship between the resulting cationic polymer flocculant addition rate, cake moisture content, gravity filtration rate, and amount of colloid charge in the liquid is shown in FIG. The relationship between the amount of colloid charge in the separated liquid and the addition rate of flocculant was a smooth relationship as shown in FIG. 1, unlike the previously reported shape with an inflection point. On the other hand, as is conventional, the dewaterability of flocculated sludge reaches its maximum value near the flocculant addition rate at which the amount of colloidal charge becomes zero. This result shows that if the amount of colloid charge in the separated liquid is near zero and in the negative region, the water content of the dehydrated cake obtained is somewhat high, and although the gravity filtration speed is somewhat low, it is still possible to operate the dehydrator. This shows that the amount of coagulant added can be reduced. These relationships are the same regardless of the type of dewatering machine in the sludge dewatering operation using a cationic polymer flocculant. As an example, using a centrifugal dehydrator, a cationic polymer flocculant (Evagrowth C123, medium cation, manufactured by Ebara Infilco Corporation) is added to mixed raw sewage sludge (SS = 12.7 g/hr) to achieve a processing rate of 12 m ³ /hr. As a result of the dehydration treatment, the changes in cake water content, SS recovery rate, separated liquid SS, separated liquid light transmittance, and colloid charge amount with respect to the flocculant addition rate are shown in graphs in Figure 2. These results show that when the coagulant addition rate increases and the colloid charge amount approaches zero, the separated liquid light transmittance and SS recovery rate increase, and the separated liquid SS and cake moisture content decrease. By the way, the control settings when actually using the present invention vary depending on the type of sludge, polymer flocculant, dehydrator, desired dewatering performance, etc.
Although it cannot be determined definitively, it is approximately −0.001~−
It is in the range of 0.1meq/. Furthermore, the object to be actually controlled may be the sludge flow rate in addition to the flocculant flow rate. [Example] Specific examples of the present invention will be described below, but the present invention is not limited thereto. Example 1 Mixed raw sludge from a sewage treatment plant was dehydrated using a belt press type dehydrator using a cationic polymer flocculant, Evaclose C104G (manufactured by Ebara Infilco, ester-based strong cation). In the present invention, a dual-wavelength photometric colloid titration device using a back titration method is used.
No. 59-183897) used a single wavelength photometric colloid titration device, and in conventional method 2) the injection amount of flocculant was controlled by a solid matter proportional control method. The fluctuation range of sludge concentration is 1.5~2.8%, and the pH is 6.0~
6.5, the ignition loss was 65-80% SS. The results are shown in Table-1.

[Table] 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 flocculant, and there is no instability in the treatment state, and the effects of reducing chemical costs and the like are recognized compared to the conventional method. Example 2 The present invention and the conventional method ( 1) and (2) were applied. In this example, flocculated sludge was mixed and dehydrated using a centrifugal dehydrator. In the conventional method, when the dehydrator is operated, 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 and chemical costs. On the other hand, when the method of the present invention is used, all of the above checks become unnecessary, and it is possible to reduce the number of artificial steps in the dehydration process and to significantly reduce the amount of flocculant. The results are shown in Table-2.

〔Effect of the invention〕

As described above, the present invention is a method for controlling the addition rate of a cationic organic polymer flocculant that can sufficiently cope with fluctuations in sludge quality and concentration in actual sludge dewatering treatment, and it is possible to control the addition rate of a cationic organic polymer flocculant by automating the addition of chemicals. This makes it possible to optimally automatically control the amount of alcohol, which brings great practical effects such as reductions in drug costs and labor costs.

[Brief explanation of drawings]

Figures 1 and 2 are graphs for explaining the effects of the present invention, and Figure 1 shows the relationship between the flocculant addition rate and cake moisture content, gravity filtration rate, and colloid charge amount with respect to SS weight. , Figure 2 shows the relationship between the flocculant addition rate and the cake moisture content, SS recovery rate, separated liquid SS, separated liquid light transmittance, and separated liquid colloid charge amount with respect to the SS weight.

Claims (1)

[Claims] 1 In a method of dewatering sludge by adding and mixing a cationic polymer flocculant, the amount of colloid charge in the liquid after adding the flocculant is measured by adding a standard positive colloid solution and a color change indicator, and back titrating with a titrant. The titration end point was measured by detecting the color change reaction of the color change indicator using dual wavelength photometry, and the cationic polymer flocculant was adjusted so that the colloid charge amount was -0.001 to -0.1 meq/. A method for controlling the addition rate of a polymer flocculant, the method comprising controlling the addition.