CN104370431B - Blue algae dehydrating method - Google Patents

Abstract

The invention discloses a blue algae dehydrating method. The method comprises the steps of performing ultrasonic processing, adding a flocculant and filter-pressing to dehydrate, wherein the specific steps are as follows: ultrasonically processing the blue algae for 2-6min; adding the flocculant in the blue algae after the ultrasonic processing, and uniformly stirring; filter-pressing the blue algae after adding the flocculant to dehydrate. Through the adoption of the method disclosed by the invention, the volume of the blue algae is greatly reduced, the heat value is not changed, and the dehydrating degree is high; the processing speed is high, the operation is simple, the large-scale production is facilitated, and the method has wide application prospect.

Description

Spirulina dehydration method

technical field

The invention relates to the technical field of cyanobacteria pollution, in particular to a method for dehydrating cyanobacteria, in particular to an ultrasonic-assisted dehydration method for cyanobacteria.

Background technique

Algae blooms in eutrophic water bodies are a global problem. In the past two decades, with the rapid development of industry and agriculture, the rapid increase of population, and the acceleration of urbanization, a large amount of untreated domestic sewage and industrial and agricultural production wastewater have been discharged into rivers, lakes and seas, seriously polluting the water environment. Nutritization is intensified. The eutrophication of the water body has led to the flooding of many freshwater lakes and the frequent occurrence of red tides in the bay. The toxic substances (algae toxins) released by a large number of cyanobacteria, the odorous substances and organic substances released after the death of cyanobacteria have seriously deteriorated the local water and air quality, seriously endangering Fishing and drinking water safety undermines the water quality of landscape water bodies. At present, salvage is mainly used to control the growth of cyanobacteria, improve the water quality of the water body, and enhance the water quality and ecological environment.

The moisture content of the rich algae obtained from salvaging blue-green algae is generally 95% to 99%. During the period of blue-green algae outbreaks, thousands of tons of blue-green algae are salvaged or filtered every day in Taihu Lake alone. Due to the high water content of the salvaged cyanobacteria, it brings great costs to transportation and storage, and also brings great difficulties to the final disposal; moreover, the cyanobacteria are extremely perishable, and after rotten, they produce stench, which brings many adverse effects to the surrounding environment. Therefore, the cyanobacteria must be dealt with quickly. If the blue-green algae is directly landfilled, it will take up increasingly scarce land resources; due to the high water content of the blue-green algae, it is not suitable for incineration. Moreover, cyanobacteria contain a large amount of cyanotoxins. Cyanotoxins are intracellular toxins that are released by cell rupture and exhibit toxicity. They are mainly produced by Microcystis aeruginosa, Anabaena, Oscillating algae, and Microcystis viridans, which have caused great harm to the environment. influences.

Dehydrating the salvaged cyanobacteria to reduce the volume of cyanobacteria is a prerequisite for safe disposal and resource utilization of cyanobacteria. At present, there have been some studies on cyanobacteria dehydration technology at home and abroad. The dehydration method of cyanobacteria is mainly mechanical dehydration, but conditioning is required before mechanical dehydration to destroy the colloidal structure of cyanobacteria, the affinity between algae and water, and improve the dehydration performance. At present, the conditioning method commonly used in the dehydration of cyanobacteria is chemical conditioning, that is, adding an appropriate amount of coagulant, coagulant and other chemical agents to the cyanobacteria to neutralize the charge of the cyanobacteria particles, reduce the affinity between the cyanobacteria particles and water molecules, and promote the dehydration of the cyanobacteria particles. Flocculation, thereby improving the dehydration performance of cyanobacteria. Traditional conditioning agents include ferric chloride, mingji, lime, fly ash, clay, etc. These flocculants can be used not only alone but also in combination. As far as the current treatment effect is concerned, the water content of the cyanobacteria mud cake obtained by mechanical dehydration of the cyanobacteria conditioned by the flocculant is still as high as 75% to 90%. The mud cake can not meet the requirements of landfill or incineration, while the flocculant remaining in the cyanobacterial residue will cause long-term ecological risks to the surrounding environment. Using skeleton constructs such as lime and fly ash to condition cyanobacteria, the moisture content of cyanobacteria dregs can be reduced to 57% to 87%. However, the dosage of skeleton constructs is large, which not only greatly increases the volume of cyanobacteria dregs to be treated It is also not conducive to subsequent incineration, landfill and other disposal. At the same time, the bioleaching method (patent application number: 201210437145.9) is also used to promote the deep dehydration of cyanobacteria. This method takes a long time, it takes 48-72 hours, and the degree of dehydration is not high. The moisture content of cyanobacteria after dehydration is 70%.

Therefore, it is of great significance to study new efficient and rapid dehydration of cyanobacteria and further reduce the water content of cyanobacteria after dehydration.

Contents of the invention

The technical problem to be solved by the present invention is that the high moisture content of the algae-rich water after salvage of cyanobacteria is not conducive to subsequent transportation and final disposal, and the moisture content of the existing cyanobacteria dehydration method is still high after dehydration using flocculants. Technical problems such as increased volume of cyanobacteria to be treated after dehydration of coal ash, lime, etc., provide a cyanobacteria with low energy consumption, fast processing speed, simple operation, greatly reduced volume of cyanobacteria after treatment, no change in calorific value and high degree of dehydration method of dehydration.

In order to solve the problems of the technologies described above, the invention provides a method for dehydrating cyanobacteria, comprising the following steps:

(1) Ultrasonic: Ultrasonic treatment of cyanobacteria;

(2) Add flocculant: add flocculant to the blue-green algae after ultrasonic to obtain flocculant-added blue-green algae;

(3) Filtration dehydration: The cyanobacteria added with flocculants are dehydrated by filtration to complete the cyanobacteria dehydration step.

In the above method, preferably, the frequency of the ultrasonic treatment is 30-110 kHz, the sound intensity is 0.4-0.8 W/cm ² , and the sound energy density is 0.3 W/ml-1.0 W/ml.

In the above method, preferably, the ultrasonic treatment time is 2-6 minutes.

In the above-mentioned method, preferably, the flocculant is an inorganic flocculant and/or an organic flocculant, and the addition amount of the inorganic flocculant is 1wt% to 5wt% of the dry weight of the cyanobacteria; the addition amount of the organic flocculant is 0.05 wt%～0.3wt%.

In the above method, preferably, the flocculant is an inorganic flocculant and an organic flocculant, and the addition amount of the flocculant is 0.8wt% to 3wt% of the dry weight of blue-green algae, and the mass ratio of the inorganic flocculant and the organic flocculant in the flocculant is 10～15:1.

In the above method, preferably, the inorganic flocculant is one or more of polyaluminum chloride, polyaluminum sulfate, polyferric chloride, and polyferric sulfate.

In the above method, preferably, the organic flocculant is polyacrylamide and/or dimethyl diallyl ammonium chloride.

In the above method, preferably, in step (3), the cyanobacteria are dehydrated by pressure filtration using a filter press, and the filter press uses a filter cloth with a pore size of 8-25 μm.

In the above method, preferably, the filter press is a chamber filter press, a plate and frame filter press or a membrane filter press.

The innovation of the present invention is:

The present invention uses ultrasonic waves combined with flocculants to treat cyanobacteria. On the one hand, due to the high energy of ultrasonic waves, it can discharge rapidly in water and produce extreme conditions such as high pressure and high temperature. structure, the affinity between algae and water, release bound water, and improve the dehydration of cyanobacteria; Water and adsorbed water become easily removed gravity water.

Compared with the prior art, the present invention has the advantages of:

(1) The present invention uses ultrasonic waves to treat blue-green algae, so that the degree of dehydration of blue-green algae is high, and the moisture content of the blue-green algae residue after dehydration is only 65-73%. The weight and volume of cyanobacteria are greatly reduced, which greatly reduces the subsequent treatment cost and is beneficial to the subsequent disposal of cyanobacteria. The effect of high-intensity, short-time ultrasonic treatment is better, and the dehydration performance of blue-green algae after treatment is greatly improved, and the precipitation is good. Ultrasonic treatment with too high intensity and too long time will weaken the dehydration of cyanobacteria.

(2) The present invention uses a filter press to filter and dehydrate cyanobacteria. The filter press is equipped with a filter cloth with a very small pore size; And the solid recovery rate is as high as 95%.

(3) After the dehydration treatment of cyanobacteria in the present invention, the calorific value drops by less than 2%, which is very suitable for composting, drying, incineration, and production of biomass fuel.

(4) The method of the present invention has simple process, convenient operation, less equipment investment, low operating cost, short dehydration time, fast processing speed, and is convenient for large-scale industrial production.

Description of drawings

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

Fig. 1 is a graph showing the influence of different sound intensities on capillary water absorption time of treated cyanobacteria and water content of dehydrated cyanobacteria in Example 3 of the present invention.

2 is a graph showing the influence of different acoustic energy densities on capillary water absorption time of treated cyanobacteria and water content of dehydrated cyanobacteria in Example 4 of the present invention.

Fig. 3 is a graph showing the influence of different ultrasonic treatment times on the capillary water absorption time of treated cyanobacteria and the water content of dehydrated cyanobacteria in Example 5 of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

Example

All materials and instruments used in the following examples are commercially available.

Example 1

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasonic: The salvaged blue-green algae (the initial water content of the salvaged blue-green algae is 98%) are treated with ultrasonic waves with an ultrasonic frequency of 50kHz, a sound intensity of 0.7W/cm ² , and a sound energy density of 0.8W/ml for 3 minutes.

(2) Adding a flocculant: adding polyferric sulfate to the sonicated cyanobacteria at a ratio of 2% of the dry weight of the cyanobacteria, and stirring evenly to obtain cyanobacteria added with a flocculant.

(3) Dehydration by filtration: the cyanobacteria added with flocculant in step (2) are dehydrated by filtration through a membrane filter press, the pore diameter of the filter cloth of the membrane filter press is 20 μm, and the dehydration of cyanobacteria is completed.

The capillary water absorption time of the untreated cyanobacteria in this embodiment was 89s, and the dry basis calorific value was 19.89 MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (2) of Example 1 was 32 s, the water content of the dehydrated cyanobacteria was 70%, the solid recovery rate was 97.2%, and the calorific value on a dry basis was 19.62 MJ/kg.

Example 2

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasound: The salvaged cyanobacteria (the initial moisture content of the salvaged cyanobacteria is 95%) is subjected to ultrasonic treatment with a frequency of 80kHz, a sound intensity of 0.6W/cm ² , and a sound energy density of 0.5W/ml for 4 minutes.

(2) Adding flocculant: adding polyaluminum chloride to the sonicated cyanobacteria at a ratio of 4% of the dry weight of cyanobacteria, and stirring evenly to obtain cyanobacteria with flocculant added.

(3) Filtration dehydration: the cyanobacteria added with flocculant in step (2) are dehydrated through a plate and frame filter press, the pore diameter of the filter cloth of the plate and frame filter press is about 10 μm, and the cyanobacteria dehydration is completed.

The capillary water absorption time of the untreated cyanobacteria in this embodiment is 365s, and the calorific value on a dry basis is 20.48 MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (2) of Example 2 was 68 s, the water content of the dehydrated cyanobacteria was 68%, the solid recovery rate was 98.4%, and the calorific value on a dry basis was 20.03 MJ/kg.

Example 3

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasonic: The salvaged cyanobacteria (the initial moisture content of the salvaged cyanobacteria is 99%) is subjected to ultrasonic treatment with a frequency of 110kHz, a sound intensity of 0-1.2W/cm ² , and a sound energy density of 0.7W/ml for 5 minutes. .

(2) Adding a flocculant: adding polyferric chloride to the sonicated cyanobacteria at a ratio of 1% of the dry weight of the cyanobacteria, and stirring evenly to obtain cyanobacteria with flocculant added.

(3) Filtration dehydration: The cyanobacteria added with the flocculant in step (2) are dehydrated by pressure filtration through a chamber filter press, the pore diameter of the filter cloth of the chamber filter press is 15 μm, and the cyanobacteria dehydration is completed.

The capillary water absorption time of the untreated cyanobacteria in the present embodiment was 76s. Refer to Figure 1 for the capillary water absorption time of cyanobacteria treated in step (2) of Example 3 and the water content of cyanobacteria after dehydration.

It can be seen from Figure 1 that the dehydration rate of cyanobacteria is higher when ultrasonic treatment with a sound intensity of 0.4-0.8W/ ^cm2 is used.

Example 4

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasound: The salvaged cyanobacteria (the initial moisture content of the salvaged cyanobacteria is 98%) is subjected to ultrasonic treatment with a frequency of 30kHz, a sound intensity of 0.8W/cm ² , and a sound energy density of 0-1.5W/ml for 6 minutes.

(2) Adding flocculant: adding polyaluminum sulfate to the sonicated cyanobacteria at a ratio of 5% of the dry weight of cyanobacteria, and stirring evenly to obtain cyanobacteria with flocculant added.

(3) Dehydration by filter press: the cyanobacteria added with flocculant in step (2) are dehydrated by filter press with plate and frame filter press. The pore diameter of the filter cloth of the plate and frame filter press is about 25 μm, and the dehydration of blue-green algae is completed.

The capillary water absorption time of the untreated cyanobacteria in this example is 107 s, and the capillary water absorption time of the cyanobacteria treated in step (2) of Example 4 and the water content of the cyanobacteria after dehydration are shown in FIG. 2 .

It can be seen from Fig. 2 that the dehydration rate of cyanobacteria is relatively high by ultrasonic treatment with a sound energy density of 0.3W/ml-1.0W/ml.

Example 5

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasonic: The salvaged cyanobacteria (the initial water content of the salvaged cyanobacteria is 97%) is subjected to ultrasonic treatment with a frequency of 90kHz, a sound intensity of 0.5W/cm ² , and a sound energy density of 0.7W/ml for 0-10min.

(2) Adding a flocculant: adding dimethyldiallyl ammonium chloride to the sonicated cyanobacteria at a ratio of 0.3% of the dry weight of the cyanobacteria, and stirring evenly to obtain cyanobacteria with flocculant added.

(3) Dehydration by filtration: the cyanobacteria added with flocculant in step (2) are dehydrated by filtration through a membrane filter press, the pore diameter of the filter cloth of the membrane filter press is about 18 μm, and the dehydration of cyanobacteria is completed.

The capillary water absorption time of the untreated cyanobacteria in this example is 187 s, and the capillary water absorption time of the cyanobacteria treated in step (2) of Example 5 and the moisture content of the cyanobacteria after dehydration are shown in FIG. 3 .

It can be seen from Figure 3 that the dehydration rate of cyanobacteria is higher when the ultrasonic treatment time is 2-6 minutes.

Example 6

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasonic: The salvaged cyanobacteria (the initial water content of the salvaged cyanobacteria is 96%) is subjected to ultrasonic treatment with a frequency of 40kHz, a sound intensity of 0.7W/cm ² , and a sound energy density of 0.6W/ml for 5 minutes.

(2) Adding flocculant: adding polyacrylamide to the sonicated cyanobacteria at a ratio of 0.05% of the dry weight of cyanobacteria, and stirring evenly to obtain cyanobacteria with flocculant added.

(3) Filtration dehydration: The cyanobacteria added with flocculant in step (2) are dehydrated by filtration through a chamber filter press. The pore diameter of the filter cloth of the chamber filter press is about 8 μm, and the cyanobacteria dehydration is completed.

The capillary water absorption time of the untreated cyanobacteria in this embodiment is 251s, and the calorific value on a dry basis is 20.15 MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (2) of Example 6 was 64s, the water content of the dehydrated cyanobacteria was 70%, the solid recovery rate was 98.4%, and the calorific value on a dry basis was 19.89MJ/kg.

Example 7

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasound: The salvaged cyanobacteria (the initial moisture content of the salvaged cyanobacteria is 95%) is subjected to ultrasonic treatment with a frequency of 60kHz, a sound intensity of 0.4W/cm ² , and a sound energy density of 0.9W/ml for 5 minutes.

(2) Adding flocculant: add polyacrylamide to the cyanobacteria after ultrasonication at a ratio of 0.2% of the dry weight of cyanobacteria, and stir evenly.

(3) Filtration dehydration: The cyanobacteria added with flocculant in step (2) are dehydrated by filtration through a box filter press, the pore size of the filter cloth of the box filter press is 10 μm, and the cyanobacteria dehydration is completed.

The capillary water absorption time of the untreated cyanobacteria in this embodiment is 347s, and the calorific value on a dry basis is 19.85MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (2) of Example 7 was 85 s, the water content of the dehydrated cyanobacteria was 71%, the solid recovery rate was 97.9%, and the calorific value on a dry basis was 19.62 MJ/kg.

Example 8

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasound: The salvaged cyanobacteria (the initial moisture content of the salvaged cyanobacteria is 95%) is subjected to ultrasonic treatment with a frequency of 60kHz, a sound intensity of 0.4W/cm ² , and a sound energy density of 0.9W/ml for 5 minutes.

(2) Adding flocculant: add an inorganic-organic flocculant to the cyanobacteria after ultrasonication at a ratio of 0.8% of the dry weight of the cyanobacteria. The inorganic-organic flocculant is composed of polyferric sulfate and polyacrylamide, and its mass ratio is 10: 1, and stir well.

(3) Filtration dehydration: The cyanobacteria added with flocculant in step (2) are dehydrated by filtration through a box filter press, the pore size of the filter cloth of the box filter press is 10 μm, and the cyanobacteria dehydration is completed.

The capillary water absorption time of the untreated cyanobacteria in this embodiment is 347s, and the calorific value on a dry basis is 19.85MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (2) of Example 8 was 76s, the water content of the dehydrated cyanobacteria was 76%, the solid recovery rate was 98.3%, and the calorific value on a dry basis was 19.71MJ/kg.

Example 9

A method for cyanobacteria dehydration, comprising the following steps:

(1) Ultrasound: The salvaged cyanobacteria (the initial moisture content of the salvaged cyanobacteria is 95%) is subjected to ultrasonic treatment with a frequency of 60kHz, a sound intensity of 0.4W/cm ² , and a sound energy density of 0.9W/ml for 5 minutes.

(2) Adding flocculant: add an inorganic organic flocculant to the cyanobacteria after ultrasonication at a ratio of 3% of the dry weight of the cyanobacteria. The inorganic organic flocculant is composed of polyaluminum chloride and dimethyl diallyl ammonium chloride Composition, its mass ratio is 15:1, and stir well.

(3) Filtration dehydration: The cyanobacteria added with flocculant in step (2) are dehydrated by filtration through a box filter press, the pore size of the filter cloth of the box filter press is 10 μm, and the cyanobacteria dehydration is completed.

The capillary water absorption time of the untreated cyanobacteria in this embodiment is 347s, and the calorific value on a dry basis is 19.85MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (2) of Example 9 was 79 s, the water content of the dehydrated cyanobacteria was 77%, the solid recovery rate was 98.4%, and the calorific value on a dry basis was 19.64 MJ/kg.

In Examples 1 to 9, the addition amount of the inorganic flocculant is 1wt% to 5wt% of the dry weight of the cyanobacteria; the organic flocculant is 0.05wt% to 0.3wt% of the dried cyanobacteria; the addition amount of the inorganic flocculant is 0.8wt% to 3wt% of the dry weight can be implemented, and the same or similar technical effects can be achieved.

Comparative example 1

A method for cyanobacteria dehydration, comprising the following steps:

(1) Add flocculant: Add polyferric sulfate to the salvaged blue-green algae (initial moisture content of the salvaged blue-green algae is 98%) at a ratio of 2% of the dry weight of the blue-green algae, and stir evenly to obtain flocculant-added Spirulina.

(2) Dehydration by filtration: the cyanobacteria added with flocculant in step (1) are dehydrated by filtration through a membrane filter press, the pore diameter of the filter cloth of the membrane filter press is 20 μm, and the dehydration of cyanobacteria is completed.

The capillary water absorption time of the untreated cyanobacteria in Comparative Example 1 was 89s, and the calorific value on a dry basis was 19.89 MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (1) of Comparative Example 1 was 48 s, the water content of the dehydrated cyanobacteria was 87%, the solid recovery rate was 96.3%, and the calorific value on a dry basis was 19.74 MJ/kg.

Comparative example 2

A method for cyanobacteria dehydration, comprising the following steps:

(1) Adding flocculant: Add polyacrylamide to the salvaged blue-green algae (the initial water content of the salvaged blue-green algae is 96%) at a ratio of 0.05% of the dry weight of blue-green algae, and stir evenly to obtain flocculant-added Spirulina.

(2) Filtration dehydration: The cyanobacteria added with flocculant in step (2) are dehydrated by filtration through a box filter press, the pore size of the filter cloth of the box filter press is about 8 μm, and the cyanobacteria dehydration is completed.

The capillary water absorption time of the untreated cyanobacteria in comparative example 2 was 251s, and the calorific value on a dry basis was 20.15 MJ/kg. The capillary water absorption time of the cyanobacteria treated in step (1) of Comparative Example 2 was 108 s, the moisture content of the dehydrated cyanobacteria was 85%, the solid recovery rate was 96.7%, and the calorific value on a dry basis was 19.95MJ/kg.

The above descriptions are only preferred embodiments of the present invention, and do not limit the present invention in any form. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with the art, without departing from the spirit and technical solutions of the present invention, can use the methods and technical content disclosed above to make many possible changes and modifications to the technical solutions of the present invention, or modify them to be equivalent Variations of equivalent embodiments. Therefore, any simple modifications, equivalent replacements, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention that do not deviate from the technical solutions of the present invention still fall within the protection scope of the technical solutions of the present invention.

Claims (4)

1. a kind of blue algae dewatering method is it is characterised in that comprise the following steps：

（1）Ultrasonic：The cyanophyceae salvaging is carried out ultrasonic Treatment；

（2）Plus flocculant：Flocculant is added to obtain the cyanophyceae added with flocculant in the cyanophyceae after ultrasonic；

（3）Filter-press dehydration：Cyanophyceae added with flocculant is carried out filter-press dehydration, completes blue algae dewatering step；At described ultrasound wave The frequency of reason is 30～110kHz, and the sound intensity is 0.4～0.8W/cm², acoustic density is 0.3W/ml～1.0W/ml；Described ultrasonic The time that ripple is processed is 2～6min；Described flocculant is inorganic flocculating agent and organic flocculant, and the addition of described flocculant is 0.8wt%～the 3wt% of cyanophyceae dry weight, in described flocculant, the mass ratio of inorganic flocculating agent and organic flocculant is 10～15: 1； Described inorganic flocculating agent is one or more of aluminium polychlorid, polyaluminium sulfate, poly-ferric chloride, bodied ferric sulfate；Institute Stating organic flocculant is polyacrylamide and/or dimethyl diallyl ammonium chloride.

2. blue algae dewatering method according to claim 1 is it is characterised in that step（3）Middle using pressure filter, cyanophyceae is entered Row filter-press dehydration.

3. blue algae dewatering method according to claim 2 it is characterised in that described pressure filter adopt hole aperture be 8～ 25 μm of filter cloth.

4. the blue algae dewatering method according to Claims 2 or 3 is it is characterised in that described pressure filter is chamber-type press filter, plate Frame pressure filter or diaphragm filter press.