CN106830622B - A sludge dewatering method based on zero-valent iron-silicate system - Google Patents

Abstract

The invention discloses a sludge dewatering method based on a zero-valent iron-silicate system. Firstly, adding high-concentration silicate solution into sludge, fully aerating and stirring, then adding zero-valent iron powder, oxidizing the zero-valent iron by oxidizing substances or oxygen in the sludge to generate Fe²⁺Forms a complex which can rapidly reduce dissolved oxygen with silicate, thereby generating a large amount of high-activity oxygen-based free radicals. The substances with strong oxidizing property firstly destroy the outer layer of the sludge, consume the released organic matters, then destroy the internal sludge, so that a large amount of protein and polysaccharide are released into free water, and finally, a large amount of extracellular polymer combined water and interstitial water are released by inactivating and breaking the walls of microbial cells in the sludge; at the same time, a large amount of iron ions will hydrate to form a coagulant. The invention has simple medicament, no toxicity, no harm and convenient use, and can quickly reduce the water content of the sludge to below 60 percent when the sludge is deeply dehydrated.

Description

A sludge dewatering method based on zero-valent iron-silicate system

technical field

The invention belongs to the technical field of comprehensive utilization of solid waste, and in particular relates to a sludge dehydration method based on a zero-valent iron-silicate system.

Background technique

Sludge dehydration is the most difficult part of sludge treatment. The bulky sludge brings inconvenience to its external transportation and greatly increases the cost of sludge treatment. After the sludge has been concentrated and digested, it still has a water content of about 95%-97%, and the volume is still large. For comprehensive utilization and final disposal, the sludge needs to be dehydrated. The ideal dehydration should remove the water to the greatest extent, while the solid particles of the sludge should be retained on the dewatered mud cake as much as possible, and the cost of this operation is required to be the lowest.

There are roughly three forms of water in sludge: the water existing in the gaps between sludge particles is free water and interstitial water, accounting for about 70% of the sludge moisture; the water existing in the capillaries between particles is called capillary water , accounting for about 20%, and the internal water existing inside the sludge particles and the attached water adhering to the surface accounted for about 10%. In general, free water and interstitial water can be removed by gravity concentration and dehydration methods such as gravity sedimentation and natural dehydration, while capillary bound water cannot be removed without applying greater centrifugal force and pressure. In addition, the retained water inside the solid has a strong bond with SS, and it is difficult to remove it by general mechanical operations, while the adsorbed water on the solid surface and the interstitial water in the gap part have a strong chemical binding force with the surface of the particle group. Strong and cannot be removed mechanically. Therefore, for attached water and capillary water, effectively changing the chemical and physical properties of sludge is an important method to remove these two parts of water.

Sludge conditioning refers to pretreatment of sludge to improve the concentration and dehydration efficiency of sludge, and to improve the properties of sludge in a planned way for economical subsequent treatment. In order to reduce the compressibility of sludge (mainly for broken extracellular polymer EPS), many physicochemical methods have been proposed and used. Among them, the advanced oxidation method is very effective for the pretreatment of sludge. Many studies have shown that the reactive oxygen species (ROS) produced by the advanced oxidation process can destroy the sludge flocs and consume part of the organic matter. Thereby significantly reducing sludge specific resistance (SRF) and capillary water absorption time (CST), increasing sludge dehydration rate, and reducing dehydration time. However, advanced oxidation, especially the traditional Fenton oxidation process, has two relatively large disadvantages. One is the high price of its raw material hydrogen peroxide, and there is a huge safety risk during transportation and storage, and the other is the pH value. The value has strict requirements (pH<3).

Contents of the invention

In order to overcome the shortcomings of the prior art methods, the present invention proposes a sludge dewatering method based on a zero-valent iron-silicate system.

The sludge conditioner of the present invention includes individually packaged silicate and zero-valent iron. First, fully dissolve the silicate in the sludge, aerate and stir and add zero-valent iron, the zero-valent iron will reduce the organic matter or heavy metal ions in the sludge, or react with water to form ferrous ions, which enter the water Form a complex with silicate, the complex has a stronger reducing ability, oxygen is reduced to superoxide anion radical ( O ₂ ^- ) and further reduced to H ₂ O ₂ , H ₂ O ₂ and complex The ferrous ions in the state form the Fenton effect, generate hydroxyl radicals, and realize the oxidative damage to the sludge flocs.

To achieve the above object, the present invention takes the following technical solutions:

A method for dewatering sludge based on a zero-valent iron-silicate system, comprising the following steps: first mixing evenly a silicate solution with pH=4-10 with the sludge, and then adjusting the pH value of the system to 5-9, Then add zero-valent iron powder, aerate and stir, and finally mechanically dehydrate to complete; wherein, the concentration of silicate in the system is 2-50mmol/L.

The silicate is Na ₂ SiO ₃ or Na ₂ Si ₂ O ₅ .

The zero valent iron powder is micron zero valent iron or nanometer zero valent iron.

The time for aeration and stirring is 30-180min.

The method of aeration and stirring is as follows: air or oxygen is introduced into the sludge while stirring, and the ventilation rate is 1mL/s-100mL/s.

The mechanical dehydration is centrifugal dehydration or filtration dehydration.

A sludge conditioner comprising individually packaged silicate and zero valent iron powder.

The principle of the present invention is as follows: when the sludge conditioner of the present invention is used, the silicate is first prepared into a high-concentration silicate solution and added to the sludge to adjust the pH of the system to 5-9, and then add zero-valent iron powder, fully aerated and stirred, zero-valent iron is oxidized by oxidizing substances or oxygen in the sludge, and the ferrous ions produced enter the sludge water to form complexes with silicate in it, and the complexes can quickly Reduce the dissolved oxygen in the sludge, thereby generating a large number of highly active oxygen free radicals. These strong oxidizing substances will first destroy the outer area of the sludge and consume the released organic matter, which is conducive to further destruction of the internal sludge, and a large amount of protein and polysaccharides will be released into the free water. Finally, through the effective inactivation and wall breaking of microbial cells in the sludge, a large amount of extracellular polymer bound water and interstitial water are released. At the same time, after the further consumption of zero-valent iron, a large amount of iron ions will undergo hydration, which can be used as a coagulant and play the role of traditional iron salts.

Among them, (1) the silicate added in the system includes sodium metasilicate, sodium disilicate, and other carbon-free silicon-oxygen compounds with similar complexing ability; (2) the sludge after adding silicate The pH value is 5-9. Below this pH range, the dissolved ferrous ions mainly exist in the form of non-coordination, and the reducing ability is weak; Oxygen molecules will not be reduced and hydrogen peroxide will be generated; (3) Aeration and stirring is required during the treatment process, and oxygen is a necessary condition for this treatment process; (4) After the treatment process, the sludge needs to undergo conventional mechanical dehydration process, The dehydration method can be filtration or centrifugation. Filtration methods include vacuum filters, plate and frame filter presses, and belt filters, and centrifugation methods include dehydration using high-speed sedimentation centrifugal dehydrators.

The present invention has the following advantages and beneficial effects:

(1) The sludge conditioner provided by the invention has simple ingredients and low cost.

(2) In the present invention, sludge dehydration can be realized by simply adding silicate and zero-valent iron powder, aeration and stirring, and the operation is simple, the equipment requirements are low, and the time consumption is short.

(3) The present invention can not only oxidize and remove organic matter and microorganisms in sludge, but also reduce heavy metal ions in sludge by zero-valent iron, without causing secondary pollution.

Description of drawings

Fig. 1 present invention uses the operation schematic diagram of this sludge conditioner;

Fig. 2 is the variation situation of the SRF and the CST value of sludge after adopting sludge conditioning agent conditioning 60min in embodiment 1;

Fig. 3 adopts the variation situation of protein concentration (PNConc.) of different regions in the sludge after adopting sludge conditioning agent conditioning 90min for embodiment 2;

Fig. 4 shows the variation of polysaccharide concentration (PS Conc.) in different regions of the sludge after conditioning with the sludge conditioner for 90 minutes in Example 2.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the scope of the present invention.

Example 1

This embodiment provides a sludge dehydration conditioner, the first component is sodium disilicate, and the second component is micron zero-valent iron.

First, prepare sodium disilicate into a solution with a concentration of 200mmol/L, take 25mL of this solution and add it to 1L of concentrated sludge from a sewage treatment plant with a water content of 95%, carry out sufficient aeration and stirring, and add 2g of micron zero-valent Iron, after 60 minutes of aeration and stirring, the sludge was taken out for related parameter determination, and at the same time, part of the original untreated sludge was taken for a blank control experiment. The results showed that the sludge specific resistance (SRF) and capillary water absorption time (CST) both decreased significantly. As shown in Figure 2, the SRF decreased from 1.8*10 ¹³ m/Kg of the original sludge to 0.15*10 ¹³ m/Kg, a drop of 91.6%; at the same time, CST also dropped from 5.5sL/g TSS of the original sludge to 1sL/g TSS, a drop of 81.8%.

Sludge specific resistance (Specific Resistance to Filtration, referred to as SRF) is a comprehensive index that expresses the characteristics of sludge filtration. Its physical meaning is: the resistance of a unit mass of sludge on a unit filtration area when it is filtered under a certain pressure. The purpose of finding this value is to compare the filtration performance of different sludges (or the same sludge with different amounts of mixture added). The greater the sludge specific resistance, the worse the filtration performance. Here, a large decrease in SRF value indicates a great improvement in sludge filtration performance after using sludge conditioner. Capillary Suction Time (CST) is also an indicator of sludge dewatering performance. The larger the CST, the worse the dewatering performance of the sludge, and vice versa the better the dewatering performance. The substantial drop of the CST value here also proves the effectiveness of the sludge conditioner provided by the present invention.

Example 2

This embodiment provides a sludge dehydration conditioner, the first component is sodium disilicate, and the second component is nanometer zero-valent iron.

In this example, the sludge to be treated has a moisture content of 97%, which is relatively high. Directly add 10 mmol of sodium disilicate powder into 1 L of concentrated activated sludge from a sewage treatment plant, and fully aerate and stir to dissolve it completely. Then add 2.5g of nanometer zero-valent iron, continue to aerate and stir, and after 90 minutes of treatment, measure the relevant parameters of the sludge, and at the same time, take part of the original untreated sludge for blank control. The results showed that after the sludge treatment, the protein and polysaccharide content in the filtrate and loosely bound extracellular polymer increased significantly, while the protein and polysaccharide content in the tightly bound extracellular polymer decreased. As shown in Figure 3, where Filtrate represents the filtrate, LB-EPS (Loosely Bound Extracellular Polymeric Substance) represents loosely bound extracellular polymers, TB-EPS (Tightly Bound Extracellular Polymeric Substance) represents tightly bound extracellular polymers, and PN Conc. represents protein concentration. Usually we use a bilayer model of extracellular polymers to study the effect of opsonization on extracellular polymers. In this model, extracellular polymers are divided into two layers, the first layer is tightly bound extracellular polymers, which are tightly and stably bound to the cell surface; the second layer is loosely bound extracellular polymers, which It is a loose layer with no obvious boundaries. The concentration of protein in TB-EPS decreased, while that in filtrate and LB-EPS increased, which indicated that the compact structure of TB-EPS was destroyed and the internal protein escaped. Similarly, Fig. 4 shows the concentration of polysaccharide (PS) in the filtrate, LB-EPS and TB-EPS, and similar rules appear. On the whole, after the conditioning of this sludge conditioner, the TB-EPS in the sludge is destroyed and the internal substances overflow.

Example 3

This embodiment provides a sludge conditioner, the first component is layered crystalline sodium disilicate, and the second component is nanometer zero-valent iron.

The operation is shown in Figure 1. Add the prepared sodium disilicate solution to the concentrated sludge, then add zero-valent iron, aerate and stir throughout the process, and after 90 minutes, mechanically dehydrate the treated sludge, and record the dehydration rate . Take the same amount of untreated sludge for dehydration, and compare the dehydration rates of the two. It can be found that the dehydration rate of the sludge treated with the conditioner is greatly improved, and the dehydration time is shorter, showing excellent dehydration performance.

Claims (6)

1. A sludge dewatering method based on zero-valent iron-silicate system, is characterized in that, comprises the following steps: first the silicate solution of pH=4-10 is mixed homogeneously with sludge, then adjusts the pH of system If the value is 5-9, then add zero-valent iron powder, aerate and stir, and finally mechanically dehydrate to complete; wherein, the concentration of silicate in the system is 2-50mmol/L. 2. The sludge dewatering method based on zero-valent iron-silicate system according to claim 1, characterized in that: the silicate is Na ₂ SiO ₃ or Na ₂ Si ₂ O ₅ . 3. The sludge dewatering method based on zero-valent iron-silicate system according to claim 1, characterized in that: said zero-valent iron powder is micron zero-valent iron or nano-zero-valent iron. 4. The sludge dehydration method based on zero-valent iron-silicate system according to claim 1, characterized in that: the time of aeration and stirring is 30-180min. 5. The sludge dehydration method based on zero-valent iron-silicate system according to claim 1, characterized in that: the aeration and stirring method is: while stirring, feed air or oxygen into the sludge, and the ventilation rate It is 1mL/s-100mL/s. 6. The sludge dehydration method based on zero-valent iron-silicate system according to claim 1, characterized in that: said mechanical dehydration is centrifugal dehydration or filtration dehydration.