JPH0316700A - Method for dehydrating sludge and chemicals used therefor - Google Patents

Abstract

PURPOSE:To dehydrate digested sludge separated from sewage by using chemicals obtd. by adding at least one of chitosan and chitosan salts to an aq. ferric chloride soln. CONSTITUTION:Digested sludge separated from sewage is dehydrated with chemicals obtd. by adding at least one of chitosan and chitosan salts to an aq. ferric chloride soln. by 0.5-5wt.%. The aq. ferric chloride soln. contains 35-40wt.% ferric chloride. The amt. of the chemicals added is 2-5l per 1m<3> of the sludge. The solid matter in the sludge is effectively dehydrated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for dewatering sludge produced in a treatment process for sewage, etc., and a drug used therein.

[Conventional technology]

Since urban sewage and domestic gray water contain a large amount of organic matter, the activated sludge method, in which aerobic microorganisms are fed with the organic matter, is widely used for treatment.

The sludge produced by the above activated sludge method is usually treated as follows. That is, the supernatant liquid is removed from the settling tank where the sludge settles, and only the sludge is inserted into the digestion tank. In this state, the sludge is in a sticky state. Is the solid content of the sludge settled in this digestion tank? After shrinking, the sludge is further dehydrated using a dehydrator and taken out as a dehydrated cake. The removed dehydrated cake is either dumped or incinerated.

When dewatering the digested sludge, an inorganic flocculant, which is an electrolyte, is usually first introduced into the tank to neutralize the electrical charge of colloidal particles floating in the sludge. This causes the colloidal particles to aggregate and form small flocs. Next, a polymer flocculant is introduced into the tank to crosslink and bond the small flocs, thereby lengthening and coarsening the flocs. In this way, the solid content in the sludge is turned into large flocs to promote dewatering.

[Problem that the invention seeks to solve]

However, as described above, adding the inorganic flocculant and the polymeric flocculant in two stages is very time-consuming and undesirable from a management standpoint. Therefore, it is possible to introduce both into the tank at the same time, but if both are allowed to coexist at the same time, the presence of the polymeric flocculant will prevent the flocculation caused by the inorganic flocculant, and the flocculation caused by the polymeric flocculant will occur. There is a problem in that large flocs cannot be obtained and solid-liquid separation cannot be performed satisfactorily because the precipitate is hindered by the presence of the inorganic flocculant. Therefore, it is common knowledge that both cannot be used at the same time.

The present invention was made in view of the above circumstances, and provides a dewatering method that can effectively process sludge by simultaneously introducing an inorganic flocculant and a polymer flocculant when dewatering sludge. Its purpose is to provide drugs for use. (Means for Solving the Problems) In order to achieve the above object, the present invention provides a chloride solution containing 0.5 to 5% by weight of at least one of chitosan and chitosan salts when dewatering digested sludge of sewage. The first gist is a sludge dewatering method in which a chemical consisting of diiron aqueous solution is added at a ratio of 2 to 5 liters per 1 nf of sludge to dehydrate the solid content in the sludge, and the sewage digested sludge is dehydrated. A drug for treating at least one of chitosan and chitosan salts at 0. The second gist is a drug consisting of an aqueous ferric chloride solution containing 5 to 5% by weight.

[Effect]

In other words, in order to improve the efficiency of the sludge dewatering process, the present inventors wondered if it would be possible to use an inorganic flocculant and a polymer flocculant as a single solution, which had traditionally been introduced in two stages. I conducted a series of studies from my standpoint. As a result, by using ferric chloride as an inorganic flocculant and using at least one of chitosan and chitosan salts as a polymeric flocculant within a predetermined range, it is possible to The present invention was achieved by discovering that an excellent agglomeration effect can be obtained. Next, the present invention will be explained in detail. The sludge flocculation promoting agent used in the present invention is a solution containing at least one of chitosan and chitosan salts in an aqueous ferric chloride solution.

The above ferric chloride aqueous solution contains 35 to 4 ferric chloride.
An aqueous solution containing 0% by weight (hereinafter abbreviated as "%"), particularly 36 to 38%, is suitable. This is because if the ferric chloride content is too high or too low within this range, the flocs tend to become insufficiently long. In addition, the chitosan contained in the ferric chloride aqueous solution is
crab. It is obtained by further deacetylating chitin obtained from the outer shells of crustaceans such as shrimp and Ochia ξ, and can be represented by the general formula below. (Left below) Examples of the above-mentioned chitosan include commercially available products as shown in Table 1 below. (Margin below) Chitosan salts are those in which the ξ group of chitosan is a salt, and is chitosan hydrochloride. Examples include chitosan acetate.

Both chitosan and chitosan salts are cationic and have the property of being soluble in organic acids.

Therefore, when the above-mentioned chitosan is blended into the above-mentioned ferric chloride aqueous solution and stirred, a slightly viscous, brown, transparent solution is obtained. The blending ratio of the chitosans needs to be set to 0.5 to 5% with respect to the ferric chloride aqueous solution. If the amount of chitosan is less than the above range, the effect of increasing flocs will be poor, and if the amount of chitosan is more than the above range, floc control by ferric chloride will be inhibited and flocculation will not occur.

When a chemical agent consisting of an aqueous ferric chloride solution containing the chitosans is introduced into a sludge treatment tank at a ratio of 2 to 5 liters per 1M of sludge, the solid content in the sludge becomes large flocs and settles. Therefore, when this is applied to a dehydrator, a dehydrated cake with a low moisture content is obtained. It should be noted that if the amount of the above-mentioned drug added is too small than the above-mentioned range, no coagulation-sedimentation effect will be obtained, and conversely, if the amount of the above-mentioned drug added is too much than the above-mentioned range, the effect will not be so great and it will not be economical.

Furthermore, when adding the above-mentioned drug, other coagulation-precipitating agents or auxiliary agents may be used in combination as necessary in order to enhance the coagulation effect.

Next, examples will be described together with comparative examples.

[Example 1]

In actual sewage treatment plants, digested sludge (organic content: 7
2%, solid content concentration 3%) was fed at a rate of 5 bottles/hour, and the solid content was coagulated and precipitated. At this time, a flocculant having the following composition was used and the treatment was carried out under the following conditions.

<Flocculant> Ferric chloride 3B. 0 parts by weight water
6 2. O Chitosan
1. O〃 Supply rate 151/hour The sludge solid content thus obtained was dehydrated using a dehydrator (belt filter: belt width 1.2 m), and the moisture content of the resulting dehydrated cake was measured and found to be 73%. Met.

[Comparative Example 1] Sludge was coagulated and sedimented in the same manner as in the above example. However, the following 82 kinds of flocculants A were sequentially supplied as flocculants.

Flocculant A> Ferric chloride 38.0 parts by weight water
6 2. 0 〃Flocculant B〉 Anionic polymer flocculant 0.1 parts by weight Feed rate of flocculant B 1501/hour The sludge solid content thus obtained was dehydrated in the same manner as in the above example, The moisture content of the obtained dehydrated cake was measured and found to be 76%.

As described above, according to the above embodiment, a water content that is 3% lower than that obtained by the conventional two-stage chemical solution supply can be achieved by only one-stage flocculant supply. This difference is very large and advantageous when dealing with large amounts of sludge in the thousands or tens of thousands of tons at actual sewage treatment plants. [Example 2.3, Comparative Example 2.3] The blending ratio of chitosan was changed as shown in Table 2 below. Other than that, the sludge was dehydrated in the same manner as in the above example, and the water content of the obtained dehydrated cake was measured. The results are also shown in Table 2 below.

[Examples 4 to 8] In order to investigate the influence of the content of ferric chloride on the flocculation effect, the amount of ferric chloride was varied as shown in Table 3 below. Otherwise, the sludge was dehydrated in the same manner as in Example 1 above, and the water content of the resulting dehydrated cake was measured. The results are also shown in Table 3 below.

From the above results, it can be seen that in the comparative example product in which the amount of chitosan was outside the appropriate range, the water content of the dehydrated cake was high and the dehydration effect was poor.

From the above results, the content of ferric chloride is 35-40%
It can be seen that there is an excellent agglomeration effect within the range of . [Effects of the Invention] As described above, according to the present invention, there is no need to supply an inorganic flocculant and a polymeric flocculant separately to produce and grow flocs in stages to coagulate and precipitate them. , you can effectively weave large flocks in one step. Therefore, the chemical injection in the dehydration process only needs to be done once, and its management becomes very easy. Furthermore, since coagulation and precipitation are more effective than in the past, the water content of the dehydrated cake after dehydration is also lowered.

Claims (3)

[Claims] (1) When dewatering digested sewage sludge, a chemical consisting of a ferric chloride aqueous solution containing 0.5 to 5% by weight of at least one of chitosan and chitosan salts is added to 1 m^3 of the sludge.
1. A method for dewatering sludge, characterized in that the solid content in the sludge is dehydrated by adding 2 to 5 liters of water to the sludge. (2) A drug for dehydrating digested sludge from sewage,
At least one of chitosan and chitosan salts at 0.5
A drug comprising an aqueous solution of ferric chloride containing ~5% by weight. (3) The drug according to claim (2), wherein the ferric chloride aqueous solution contains 35 to 40% by weight of ferric chloride.