JP2001137900A - Dehydration method for sludge mainly composed of inorganic particle and refining agent for dehydration thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dehydration method for sludge which forms flocculated floc having good filtration dehydratability by using a refining agent for dehydration prepared by using titanium oxysulfate and polymerized silicic acid in combination in place of aluminum salts and iron salts for the sludge mainly composed of inorganic particles, and to obtain a refining agent for dehydration thereof. SOLUTION: This dehydration method for the sludge mainly composed of the inorganic particles consists in adding and mixing the titanium oxysulfate to the sludge mainly composed of the inorganic particles in a range of 5 to 20% in terms of TiO2 per solid of the sludge, then regulating its pH to 8 to 11 by using an alkaline agent, adding the polymerized silicate to the sludge in the range of a molar ratio of 1 to 10, more preferably 3 to 5 to the titanium in the titanium oxysulfate and subjecting the sludge to mixing and agitating to perform floc formation, then subjecting the sludge to a mechanical dehydration treatment with a filter press, or the like. The refining agent is used for this sludge. The highly efficient dehydration treatment and the reduction of the weight of dehydrated cake are made possible. The formed dehydrated cake and separated water are free from the worry about the influence of the free chlorine on the natural environment and the formation of trihalomethanes, or the like, and are environmentally safe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dewatering sludge mainly composed of inorganic particles and a conditioning agent for the dewatering.

[0002]

2. Description of the Related Art Conventionally, sludge mainly composed of inorganic particles such as wastewater generated in water purification treatment of water and sludge and wastewater generated in civil engineering works is subjected to gravity sedimentation without using a conditioning agent. After dewatering with a filter press or centrifugal separator, or conventionally, as an aggregating agent for inorganic particles, aluminum salts such as aluminum sulfate and polyaluminum chloride, or iron salts such as iron sulfate and iron chloride and slaked lime are used. A method of improving the filtration dewatering property of sludge by using it and then mechanically dewatering with a vacuum dehydrator or the like is mainly used.

[0003]

However, the above-mentioned conventional method of dewatering sludge as it is is very low in filtration dewatering property due to fine particles which are largely mixed in the sludge, and the dewatering equipment becomes large. There is a problem that a very long operation of the dehydration process is required. In addition, the method using ferric chloride and slaked lime improves the filtration dewatering property of sludge, but has the drawback that the amount of cake generated in the dewatering treatment increases, and that disposal and disposal requires enormous cost and labor. is there. The flocculation produced by using these metal salts alone has a small floc, and the rate of improvement in the filtration dewaterability of the sludge is small. The present invention, in view of the problems of these conventional methods, high filtration dewatering efficiency,
Moreover, it is an object of the present invention to provide a harmless sludge dewatering method that does not contain a harmful substance that causes secondary pollution in the generated cake and the separated water, and a conditioning agent therefor.

[0004]

The gist of the present invention is to use a titanium oxysulfate and a polymerized silicic acid together and treat the sludge to be treated with a ratio of silicon to titanium in the titanium oxysulfate of 1 or more and 10 or less. A sludge dewatering method mainly composed of inorganic particles, which is subjected to mechanical dehydration treatment by a filter press or the like after addition and mixing to aggregate the inorganic particles, and a conditioning agent used for the sludge.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus according to the present invention is configured as described above, and titanium oxysulfate is added to wastewater or sludge mainly composed of inorganic particles generated in water purification treatment and civil engineering work. After mixing, the pH is adjusted to 8 to 11 using an alkaline agent such as sodium hydroxide or sodium carbonate to generate hydrous titanium oxide to cause the aggregation of the inorganic particles. Next, the polymerized silicic acid is added in a range where the molar ratio to titanium in the titanium oxysulfate to which the previously added silica is added is 1 or more and 10 or less, and the mixture is sufficiently mixed and stirred to form flocs. And dehydration with a centrifuge

[0006]

DETAILED DESCRIPTION OF THE INVENTION The sludge dewatering method comprising inorganic particles as a main component of the present invention and a conditioning agent for the same are prepared by using titanium oxysulfate and polymerized silicic acid in combination, and the molar ratio of silicon to titanium in titanium oxysulfate. Is added and mixed at a ratio of not less than 1 and not more than 10 to generate aggregated flocs of inorganic particles, and then subjecting the sludge to dehydration treatment. In order to cause the inorganic particles to aggregate using these metal salts, it is necessary to generate a metal hydroxide. Simply adding titanium oxysulfate to sludge as it is and mixing does not produce hydroxide due to dissociation of titanium oxysulfate and hardly causes agglomeration, but adjust the pH in the range of 8 to 11 using an alkali agent. As a result, hydrated titanium oxide is generated and causes an agglomeration action. But,
The flocculation floc due to the metal salt is small and the improvement in filtration dehydration property is small, and the flocculation floc produced by adjusting titanium oxysulfate with alkali is also the same.

When polymerized silicic acid is added to and mixed with the primary agglomerated hydrous titanium oxide, a small floc grows due to the action of the polymerized silicic acid having a large molecular weight to form a large flocculated floc having high dewaterability. Addition ratio of titanium oxysulfate in the range of solids per 5-20% of the sludge as TiO ₂ is proper. When the addition ratio of titanium oxysulfate is 5% or less, there is almost no improvement in the dehydration by filtration, and even when added in an amount of 20% or more, the improvement ratio becomes very small. The molar ratio between titanium and silicon can be increased by increasing the molar ratio when the solid concentration is low, and decreasing the molar ratio when the solid concentration is high. As the molar ratio increases, the amount of the polymerized silicic acid increases and the sludge viscosity increases. Therefore, it is usually appropriate to set the molar ratio in the range of 3 to 5.

[0008] The results of the sludge dewatering method of the present invention and the filtration dewatering test of the conventional method were carried out using a filter press, and the results are as follows. First, as a sludge mainly composed of inorganic particles, gravity sedimentation concentrated sludge is collected from a water purification plant in operation, and this sludge is subjected to a sludge injection pressure of 0.5 MPa, a pressing pressure of 1.5 MPa, and a miscellaneous time of 10 minutes. The filtration speed was calculated, dewatering operation was performed using a small filter press, and the water content and the filtration speed were compared.

The sludge and the chemical used in the filtration and dehydration test of the dehydration method of the present invention are as follows: the sludge used in the test has a solid concentration of 40 g / L, titanium oxysulfate (a commercially available reagent),
Composition TiOSO ₄ nH ₂ O, TiO ₂ content 33.1%,
TiO ₂ addition rate 10% (per sludge solids)
Water glass (reagent first grade product) composition SiO ₂ / Na ₂ O (mole ratio = 2 to 2.3), was carried out tempering operation of the sludge by setting the 52-57% purity. First, titanium oxysulfate is converted to TiO ₂ to a predetermined amount of sludge, weighed and mixed so as to be 10% based on the sludge solid matter, and sodium carbonate or caustic soda is added with rapid stirring to adjust the pH of the sludge. Adjustment was made so as to be about 8 to 11. Next, after sufficiently mixing and stirring the added alkaline agent,
While slowly diluting the diluted solution added with 5 to 10% of water glass, the mixture is added and mixed so that the molar ratio of Si to Ti is 1, or 3, or 5, and the mixture is slowly stirred for about 10 minutes. The coagulated sludge thus obtained was subjected to a dehydration operation using the above-mentioned filter press. The results are shown in Table 1.

[0010]

[Table 1]

According to the present invention, the addition of the three kinds of the above-mentioned heat-treating agents allows the press-in time of the dewatering operation to be 5 minutes and the pressing time to be 13 to 14 hours.
And the sludge having a water content of 55.9 to 56.4% of the dehydrated cake is obtained, and the filtration rate is 2.56 to 3.56 kg / m.
₂ h. Note that the molar ratio of Si to Ti is 3,
Alternatively, it was found that the sludge using the conditioner of No. 5 had a filtration speed of 1.00 to 1.18 kg / m ² h faster than the conditioner of the molar ratio of 1.

Using the same sludge used in the examples, a conventional chemical-free dehydration method (a method of dehydrating the sludge without adding anything to the sludge and using a dehydrator as it is), Iron and slaked lime method (First add 10% ferric chloride to sludge solids and mix, then add 30% slaked lime to solids and mix thoroughly, then press into dehydrator to dehydrate. Method), polyaluminum chloride method (polyaluminum chloride is 10% per sludge solids)
After addition and mixing, the pH was adjusted to 8 to 1 using sodium carbonate.
(A method of dehydrating with a dehydrator after preparing in the range of 0), a dehydration test was carried out for each of the three methods. The results were as follows.

[0013]

[Table 2]

Each of the three conventional methods has a press-in time of 5 minutes and a press time of 17 to 19 minutes in the dewatering operation, and a sludge having a water content of 64.3 to 66.7% of the dewatered cake is obtained. The speed was between 1.78 and 2.10 kg / m ² h. Therefore, comparing the present invention with the conventional method, the sludge dewatering method of the present invention reduces the pressing time of the pressing operation by 3 to 6 minutes and lowers the water content of the dewatered cake by 7.9 to 10.8%,
A result of 0.46 to 1.78 kg / m < ² > h faster filtration speed was obtained also in the filtration speed.

[0015]

As described above, the method for dewatering sludge mainly composed of inorganic matter according to the present invention is a method for dehydration using titanium oxysulfate and polymerized silicic acid in combination with the conventionally used aluminum salts and iron salts. The use of a precipitant produces a flocculent floc having good filtration and dehydration properties, enables a more efficient dehydration treatment than the conventional method, and furthermore, generates a smaller amount of dewatered cake, The separated water is also safe for the environment, without fear of affecting the natural environment or producing trihalomethane due to free chlorine.

Claims (3)

[Claims] 1. A method in which titanium oxysulfate and polymerized silicic acid are used in combination and added to a sludge to be treated at a ratio of silicon to titanium in the titanium oxysulfate of 1 to 10 to coagulate inorganic particles. A method for dewatering sludge mainly composed of inorganic particles, wherein a mechanical dewatering treatment is performed by a filter press or the like. To 2. A sludge consisting mainly of the inorganic particles, was added and mixed titanium oxysulfate with solids per 5-20% range as TiO ₂ of the sludge, the adjustment pH8~11 with an alkaline agent Then, the polymerized silicic acid was added to the sludge in a molar ratio of 1 to 10 or less, preferably a molar ratio in the range of 3 to 5, to titanium in titanium oxysulfate, and mixed and stirred to form flocs. 2. The method for dewatering sludge comprising mainly inorganic particles according to claim 1, wherein a mechanical dewatering treatment is carried out by a filter press or the like. 3. The heat treatment for dehydration according to claim 1, wherein titanium oxysulfate and polymerized silicic acid are used in combination, and the molar ratio of silicon to titanium in the titanium oxysulfate is 1 or more and 10 or less. Agent.