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Summary and Application of Solid liquid Separation Technology

May. 25, 2019

Bioseparation technology is one of the key technologies to develop the national economy at the end of the last century and the beginning of this century. The development of biological separation technology has provided a variety of biological products for human beings.


Solid-liquid separation technology is an important part of biological separation technology. This paper mainly summarizes the related knowledge of solid-liquid separation technology and its application in the industrial field. According to the characteristics of industrial development, the future development trend of solid-liquid separation technology is briefly deduced.


Solid-liquid separation technology is also widely used in farms and industrial sites, such as dewatering of farm manure, sludge treatment and so on.

ZHEHAN has successfully developed a solid liquid separator suitable for farm excrement treatment through three years of technological research and development.

Its core component is the high-quality Johnson screen, through the auger transmission and extrusion, the water is discharged from the Johnson screen.


1. Preface


Solid-liquid separation is an important unit operation. Screening or precipitation are usually used to remove solids from the liquid phase. Microfiltration, clarification and deep bed filtration are used in water treatment.

The existing traditional solid-liquid separation technology mainly concentrates on pressure filtration, filtration, gravity sedimentation and so on. It is widely used in medical and health, paper making, environmental protection, food, fermentation, and other industries.


In many production processes, the solid-liquid separator is one of the key equipment. Its technical level and quality directly affect the possibility of industrialized large-scale production in many processes, the advancement, and reliability of the process, product quality and energy consumption, environmental protection and other economic and social benefits.


Taking the solid-liquid separator of the farm as an example, in a cattle farm, the treatment of cow dung is a very troublesome thing. We can dehydrate cow dung by cow dung drying machine, and then it will be very convenient to deal with it.

In the process of material wet processing, solid-liquid separation technology has been paid more and more attention. Because imperfect technology will affect the quality of products, cause material loss, and cause more serious pollution to the environment, especially the particle suspension, because of its small particle size, slow settling rate, small pore size of filter cake, poor permeability, resulting in the reduction of the separation efficiency of particle suspension.


As an expert in the metal filtration industry, ZHEHAN recommends the use of Johnson screen for filtration. Its advantages are V-shaped wire structure, not easy to plug, easy to clean and reuse.

With the rapid shortage of global water resources and the deterioration of living environment, people have put forward higher requirements for solid-liquid separation technology, and many researchers around the world have done a lot of in-depth research in this area.


For example, the Johnson intake screen for urban water intake and the Johnson screen for desalination.


1. Historical development


The earliest separation technology can be traced back to the distillation technology in China's summer and Shang Dynasty liquor-making industry; the ancients mastered the evaporation concentration and crystallization technology in sugar and salt production, and the distillation method was used to extract oil from coal tar. In the eighteenth century, the British Industrial Revolution brought about the birth and development of the giant chemical industry, along with the birth and development of the separation project.


In 1901, British scholar Davis first defined the concept of separation operation in his book Chemical Engineering Manual. In 1923, American scholar Lewis and McAdams co-authored and published Principles of Chemical Engineering, which established the theory of separation engineering.


2. Overview of Solid-liquid Separation Technology


Solid-liquid separation refers to the separation and removal of suspended solids in fermentation broth (or culture broth), such as precipitates of cells, bacteria, cell fragments, and proteins, or their flocculants. In principle, the solid-liquid separation process can be divided into two categories: sedimentation separation and filtration separation.



Therefore, solid-liquid separators can also be divided into two categories accordingly. On this basis, according to the driving force and operating characteristics, it is further subdivided into several solid-liquid separators.


3.1 Solid-liquid Separation Equipment


(1) Filtration equipment: plate and frame filter press, vacuum drum filter.


(2) Centrifugal equipment: filter centrifuge, sedimentation centrifuge.


3.2 Filtration Mode


(1) Conventional filtration: The direction of material-liquid flow is perpendicular to the filter medium (a certain interface which can separate solid-liquid mixture from the liquid).


(2) The flow direction of cross-flow filter media is parallel to that of filter media. The filter medium is usually a microporous membrane or ultrafiltration membrane.


3.3 General Flow of Solid-liquid Separation Technology


(1) Before making clear the separation process requirements, we must first clarify the separation problems to be solved and clarify the separation process requirements. Some factors that have a great influence on equipment selection should be considered. Such as health requirements, toxicity, foaming, etc.


(2) To determine the settling characteristics of materials, the settling characteristics of materials can be determined by the settling test of measuring barrel. The method is to put the material sample into the measuring barrel and shake it evenly, then let it settle down. After half an hour, the height of the clear liquid layer is measured, the settling speed is determined, and the volume ratio of sediment is measured after 24 hours.


(3) Determining the filtration characteristics of materials is generally expressed by the growth rate of filter cake, which can be determined by Brinell funnel test. The method is to determine the time needed to filter a certain amount of samples, or to test with the top feed leaf filter device, directly determine the thickness of the filter cake, and then calculate the growth rate of the filter cake.


(4) The primary solid-liquid separation equipment is selected according to the determined separation requirements and material separation characteristics.


3.4 Main Solid-liquid Separation Technologies


(1) Flocculation is the principle of using charge neutralization and macromolecule bridging to form larger particles. It is characterized by enlargement of solid particles, easy settling, filtration, and centrifugation to improve the separation speed of factor and clarity of the liquid. However, it has some shortcomings, such as strict conditions, difficult enlargement, and the introduction of flocculants may interfere with the separation and purification after purification.


(2) Under the action of gravity produced by centrifugation, the settling speed of particles is accelerated and precipitated. There are many kinds of centrifugal equipment, but each has its own advantages and disadvantages. When we use centrifugal equipment, we can depend on the specific situation.


(1) High-speed refrigeration centrifuge: It is suitable for material recovery with small particle size and thermal instability, and for laboratory application. However, due to its small capacity and difficulty in continuous operation, the large-scale industrial application is poor.


Disc centrifuge: suitable for large-scale industrial applications, can be the continuous or batch operation, operation stability is good, easy to scale up, promotion. The disadvantage is that the cleaning of slag is troublesome in semi-continuous or batch operation, the water of solid is high in continuous operation, and the total separation rate is low.


(3) Tube centrifuge: batch operation, high speed, good solid separation effect, low water content, easy to expand, but limited capacity, small capacity, frequent disassembly and assembly, noise.


(4) Tilting bridge centrifuge: continuous operation, easy amplification, easy industrial application, stable operation. However, it is difficult to recover very small solid particles, and the equipment investment is high.


Basket centrifuge: It is a kind of filtration under the action of centrifugal force. It is suitable for the recovery of large solid particles, easy to enlarge, simple and stable operation, and suitable for industrial application. The disadvantages are a batch operation or semi-continuous operation, low speed, poor separation effect, heavy operation, high investment in centrifugal equipment and high operation cost.




Filtration is the separation of the pore size of the filter medium. The equipment includes plate and frame filter, plate (vacuum) filter, vacuum rotary filter and so on. It is characterized by simple equipment and easy operation. It is suitable for large-scale industrial applications, but its separation speed is low. The separation effect is affected by the change of material properties, and the labor intensity is high.


3. Membrane filtration


In traditional concepts, filtration is only a means of filtration and separation, but with the development of membrane technology, filtration has expanded into a selective method to filter out the certain size of substances. The target product can be filtered out or preserved in solution according to design. In the process of separation, membranes do not involve phase change, no secondary pollution, and have the function of concentration and enrichment of biofilm. At the same time, they are a highly efficient separation method. To a certain extent, they can replace traditional separation technologies such as filtration, adsorption, recrystallization, distillation, and extraction. Therefore, as a new and effective biochemical separation method, membrane separation technology has been international. It is generally acknowledged that it is a promising major production technology from the end of the 20th century to the middle of the 21st century.


Membrane separation is the separation and purification of substances using filter media with certain selective permeability. The essence of the process is that substances can be separated by different transmission speeds through the membrane. The process is similar to screening, and the size of particles intercepted by the membrane with different pore sizes is different. In the process of separation, the role of the membrane is mainly embodied in three aspects [6]: completing the identification and transmission of substances, acting as interface and reaction field. Recognition and permeation of substances are necessary conditions and internal factors for the separation of various components in the mixture; in separation, the membrane acts as an interface, dividing the permeating liquid and the remaining liquid (material-liquid) into two incompatible phases; and as a reaction field, because the surface of the membrane and the inner surface of the pore contain functional groups that can interact with specific solutes, it can be physically acted and physically transformed. Chemical or biochemical reactions improve the selectivity and speed of membrane separation. The driving forces of membrane separation are different, such as concentration difference, potential difference, and pressure difference. The common membrane filtration methods are osmosis, dialysis, electrodialysis, reverse osmosis, nanofiltration, ultrafiltration, and microfiltration.


In the next blog, I will mainly explain the concept and application of solid-liquid separation technology.


If you are interested in the solid-liquid separator and Johnson screen, you can see the content of our product page.


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