JPS5837040B2 - Sludge dewatering method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a sludge dewatering method in which sludge is dehydrated by pre-treatment. More specifically, a sludge dewatering method involves adding hydrochloric acid and ferric chloride to sludge to form sludge flocs during sludge dewatering. 6
Regarding this.

Conventionally, there is a method of using iron salts and calcium salts in combination with sludge as separation and dewatering aids, but the amount of calories added to calcium salts (e.g. slaked lime) is determined by the sludge solid content (formerly known as monocarbon).
This calcium salt is contained in the dehydrated cake as it is, which increases the weight of the dehydrated cake. This is a problem because the amount of cake to be processed increases, and calcium salts have low solubility at room temperature and easily clog the filter, and since calcium salts are in the form of solid powder, it is not easy to adjust the amount of injection. It has its drawbacks.

In addition, there are products that use both acid and polymer flocculants, but the size and strength of the sludge flocs change due to slight differences in the stirring intensity and stirring time after addition, so it is necessary to carefully manage the adjustment. Alternatively, operating conditions settings such as the filtration rate of the filtration process and the moisture content of the dehydrated cake may differ depending on the stirring method.
This method has drawbacks such as complicating operational management.

The present invention solves these drawbacks, and includes a method for dewatering sludge in wastewater treatment such as human waste, sewage, and organic industrial wastewater, in which sludge is dehydrated by adding hydrochloric acid and ferric chloride. The object of the present invention is to provide a sludge dewatering method in which sludge is coagulated to form flocs, and the size and strength of the flocs are stabilized, thereby achieving excellent dewatering efficiency. do.

In the sludge dewatering method ζ of the present invention, first, hydrochloric acid is added as a strong acid to the sludge, and the pH of the sludge is adjusted to a range where the alkalinity of the sludge can be neutralized, that is, pH 4.3 to 5.
5 to cause isotropic metamorphosis of the hydrophilic sol in the sludge, and at the same time adjust the solubility of iron hydroxide to a level that does not increase, and then add ferric chloride as an iron salt. (F
e Cl3) is added to generate iron hydroxide flocs in the sludge, thereby promoting the formation of sludge flocs and coagulating the solid content of the sludge.

The drawing is an explanatory diagram of the sludge dewatering method of the present invention, in which sludge 1
After adding HCI 2 and then adding 3 FeCl3 to 1 to form sludge flocs, forced dehydration is performed using a dehydrator 6 as dewatering (4) to form a dehydrated cake and a separated liquid 6.
Separate.

As a method for solid-liquid separation after addition of the flocculant, sludge solids and supernatant water may be separated by natural sedimentation in addition to forced dehydration.

As an example of the sludge dewatering method of the present invention, the properties of raw sludge are as follows: solid content concentration: 38%, SS: 35,200 ppm, 1 pH: 7.
50. Add 35% hydrochloric acid to sludge with ignition loss of 50.9%, stir slowly at 50 rpm for 10 minutes, add ferric chloride solution and stir rapidly at 120 rpm. It lasted 5 minutes.

The amounts of hydrochloric acid and ferric chloride added are at an addition rate of 3.
0 to 13.0% and 7%.

Actual filtration rate of sludge for each addition amount of 6 kg (kg d
s/m''-}4r) and cake moisture content [%] are as shown in the table below and the figure on the right, and show the best values around 6.5% HCl and 37% FeCl.

The points where the curves of water content and filtration rate intersect are approximately at pH 3.4 and 5.5, and dehydration can be carried out within that range, but if the pH is too low, sludge may form. Since equipment immersed in sludge is corroded by acid, a pH of 4.3 or higher is desirable.

Furthermore, sludge flocs with stable size and strength were produced after adding the flocculant.

The dehydration method of the present invention uses hydrochloric acid as a coagulant in the range of 3.0 to 13
Since we added 0% to adjust the pH to 4.3 to 5.5 and dehydrated by adding 7% ferric chloride per ds, there is no need to use a large amount as with conventional calcium salt addition. However, when adding calcium salt, the calcium salt is contained in the dehydrated cake as it is, and the weight of the dehydrated cake increases by the amount added, but when adding hydrochloric acid, there is no increase in the weight of the dehydrated cake due to the flocculant, which is different from the conventional method. The addition of calcium salt reduces the dewatering load for the same amount of sludge (6 ml), and since the actual filtration rate is excellent, the dehydration processing capacity can be improved, and the addition rate of hydrochloric acid is low < pH higher than necessary Since the acid does not become too low, there is less corrosion of equipment caused by acid 6, which reduces chemical running costs during operation.Since 6, 6, hydrochloric acid is in liquid form, it is easy to adjust the chemical dosing, and furthermore, it is less expensive than conventional acids. When using a molecular flocculant in combination, it is necessary to select a polymer flocculant depending on the properties of the sludge, and selection is difficult. After adjusting the pH with hydrochloric acid and adding iron salt, it is possible to obtain flocs with stable size and strength, and therefore with stable dehydration performance and stable water content under the desired dehydration conditions. It has the effect of being able to obtain a cake of a certain amount.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing one embodiment of the present invention, Figure 2 is a pH
FIG. 4 is a diagram showing the relationship between cake moisture content and actual filtration rate. 1...Sludge, 2...}-] C d addition, 3... FeCl3 addition, 4... Dehydration.

Claims (1)

[Claims] 1 In a method for dewatering sludge generated in the treatment of wastewater such as human waste, sewage, and organic industrial wastewater, hydrochloric acid is added to the sludge to adjust the pH to 4.3 to 5.5, and the pH is adjusted to 7.0 O per solid content of the sludge. A sludge dewatering method characterized by dewatering by adding ferric chloride in an amount of % by weight.