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In the context of today’s large-scale animal husbandry development, animal manure treatment has become a core issue of environmental protection and efficient use of resources. Chicken manure, pig manure, cow manure and other types of animal manure, rich in large amounts of organic matter and nitrogen, phosphorus, potassium and other key nutrients, if properly handled and utilized, they will be able to change into a very high quality organic fertilizer. However, untreated manure will not only occupy a large amount of valuable land resources, but also very easy to cause a series of serious environmental pollution problems, such as water eutrophication, soil pollution and air pollution. Solid-liquid separation, as a crucial pre-treatment link in the manure treatment process, can significantly reduce the water content of manure, greatly improve the subsequent processing efficiency, and truly realize the recycling of resources and the effective protection of the environment. Next, this article will be in-depth and detailed discussion of solid-liquid separation from chicken manure, pig manure, cow manure and other animal manure in the specific methods, applicable equipment and practical application cases.
The Characteristics of Animal Manure
Chicken manure
Chicken manure is known as a high nutrient content of organic fertilizer, which is rich in nitrogen, phosphorus, potassium and a variety of trace elements. Due to the relatively short digestive system of chickens, the food in the intestinal tract does not stay for a long time, which leads to the presence of more incompletely digested feed particles in chicken manure. Chicken manure has a fine texture, moisture content is usually in the range of 70% – 85%, and viscous, these characteristics make the solid-liquid separation of chicken manure quite challenging.
Pig manure
Swine manure is also rich in nutrients, but its texture and moisture content vary depending on the breed of pig, the type of feed fed, and the farming method. Generally speaking, the moisture content of pig manure is around 80% – 90%, and the texture is relatively soft and uneven, with some large solid particles, such as undigested feed residues and bedding, mixed in.
Cow dung
Cattle manure is characterized by high fiber content and loose texture. As ruminants, cattle chew and digest their food many times, and the organic matter in cow dung is decomposed to a relatively high degree. The moisture content of cow manure is usually between 75% – 85%, in view of its unique fiber structure, in the process of solid-liquid separation of cow manure, we must give full consideration to the handling of fibers to prevent clogging of equipment.
Other animal manure
In addition to the common chicken manure, pig manure and cow manure, sheep manure, rabbit manure and other animal manure also have their own unique properties. Sheep manure is fine texture, relatively low water content, about 60% – 70%, which contains a high proportion of organic matter and nitrogen, phosphorus, potassium and other nutrients. Rabbit manure is smaller in particle size, with water content between 70% – 80%, and rich in protein and minerals.
Solid-liquid Separation Principles and Methods
Gravity settling method
Gravity settling method is mainly with the solid particles and the density difference between the liquid, under the action of gravity, so that the solid particles naturally precipitate to the bottom of the container, so as to achieve the purpose of solid-liquid separation. The method is simple, relatively low cost, but the separation efficiency is also relatively low, more suitable for larger particles, density difference is more obvious solid-liquid mixture. In the treatment of animal manure, gravity settling method is usually used as a preliminary means of pretreatment, able to remove some of the larger solid particles and suspended solids.
Filtration
Filtration is through a specific filter medium, such as filter mesh, filter cloth, etc., the solid particles and liquid successfully separated. According to the different filter pressure, can be subdivided into atmospheric filtration, pressurized filtration and vacuum filtration. Atmospheric pressure filtration equipment is simple in construction and convenient in operation, but the filtration speed is relatively slow, which is more suitable for small-scale solid-liquid separation scenarios. Pressurized filtration and vacuum filtration can effectively improve the filtration speed and separation efficiency, which is more suitable for large-scale industrialized production needs. In the treatment of animal manure, according to the specific characteristics of manure, carefully select the appropriate filter media and filtration equipment, in order to avoid clogging problems, and then improve the filtration effect.
Centrifugal separation method
Centrifugal separation method is the use of strong centrifugal force, so that the solid particles in the solid-liquid mixture and the liquid in the centrifugal force field to produce very different trajectories, so as to achieve solid-liquid separation. Centrifugal separation equipment has significant advantages such as high separation efficiency and speed, and is suitable for treating solid-liquid mixtures of various natures. In the treatment of animal manure, centrifugal separation method can efficiently remove fine solid particles and colloidal substances, however, its equipment investment is larger, and the operating cost is relatively high.
Extrusion method
Extrusion method is through the mechanical force on the solid-liquid mixture extrusion operation, prompting the liquid from the solid particles in the gap between the extrusion, so as to realize the solid-liquid separation. Common extrusion equipment includes screw extruder, hydraulic extruder, etc., such equipment has the advantages of simple structure, easy operation and so on. In the treatment of animal manure, extrusion method can effectively reduce the water content of manure, but need to pay special attention to control the pressure and speed of extrusion to prevent unnecessary damage to the equipment.
The Choice and Application of Solid-liquid Separation Equipment
Spiral extrusion solid-liquid separator is a kind of equipment widely used in the field of manure treatment, its working principle is to use the continuous rotation of the spiral shaft to push the manure forward, in the process, through the filtering effect of the screen mesh and the extrusion effect of the spiral shaft, to achieve effective separation of solid and liquid. This equipment has the outstanding advantages of compact structure, small footprint, large handling capacity and so on. It is suitable for treating all kinds of animal manure. When dealing with chicken manure, the screw extruder solid-liquid separator can effectively remove the water in chicken manure, so that the water content of chicken manure can be successfully reduced to about 40%-50%, which greatly facilitates the subsequent processing and use.
Belt filter press
Belt filter press is a kind of solid-liquid separation equipment that can realize continuous operation, and its working principle is to evenly spread the manure on the filter belt, and then realize solid-liquid separation through the synergistic extrusion and filtration of the upper and lower two filter belts. The belt filter press has many advantages such as large processing capacity, high automation degree, good separation effect, etc. It is very suitable for large-scale farms and manure treatment plants. When dealing with pig manure, the belt filter press can reduce the water content of pig manure to about 60% – 70%, and the separated solid pig manure can be directly used as high-quality raw materials for organic fertilizers, while the liquid part can be further processed and comprehensively utilized.
Centrifugal solid-liquid separator
Centrifugal solid-liquid separator is an advanced equipment to realize solid-liquid separation with the help of centrifugal force, and its working principle is to transport manure to the inside of high-speed rotating drum, and under the action of strong centrifugal force, the solid particles are thrown to the wall of the drum rapidly, and the liquid is discharged smoothly from the center of the drum. Centrifugal solid-liquid separator has the advantages of high separation efficiency, fast speed, small footprint, etc. It is suitable for treating all kinds of animal manure, especially manure containing fine particles and colloidal substances. When dealing with cow manure, centrifugal solid-liquid separator can effectively remove the water and fiber impurities in cow manure, so that the water content of cow manure is reduced to about 50% – 60%, laying a good foundation for subsequent composting.
Plate and frame filter press
Plate and frame filter press is a kind of solid-liquid separation equipment with intermittent operation, and its working principle is that the manure is transported to the filter chamber composed of filter plate and filter frame by the pressure pump, and under the action of strong pressure, the liquid is discharged smoothly through the filter cloth, and the solid is accurately retained in the filter chamber. Plate and frame filter press has the significant advantages of high filtration pressure, good separation effect, low water content of the filter cake, etc. It is suitable for special occasions with very high requirements for solid-liquid separation. In dealing with high concentrations of animal manure, plate and frame filter press can reduce the water content of manure to 40% or less, after the separation of the solid can be directly put into use as a high-quality organic fertilizer, the liquid part of the depth of treatment can be carried out.
The Optimization and Combination of Solid-liquid Separation Process
pretreatment steps
In the formal solid-liquid separation before the necessary pretreatment of animal manure can significantly improve the separation effect and the overall operating efficiency of the equipment. The pretreatment step usually covers screening, crushing, mixing and other key links. Screening can accurately remove large debris in the manure, such as tree branches, stones, etc.; crushing can be larger solid particles cleverly broken into smaller particles, to create favorable conditions for the subsequent solid-liquid separation; stirring can make the solid-liquid components in the manure more uniformly mixed to further enhance the separation effect.
multi-process combination
In practice, a single solid-liquid separation method is often difficult to fully meet the complex requirements of animal manure treatment. Therefore, a variety of solid-liquid separation processes are often used in combination with each other. For example, the first gravity settling method for preliminary solid-liquid separation, effectively removing some of the larger solid particles and suspended solids; followed by filtration or extrusion method for further in-depth separation; and finally centrifugal separation of the liquid part of the fine processing, in order to achieve a higher separation accuracy and effect.
Optimization of equipment parameters
In the selection and use of solid-liquid separation equipment, need to be closely combined with the characteristics of animal manure and specific processing requirements, the parameters of the equipment for scientific optimization. For example, for the spiral extrusion type solid-liquid separator, reasonable adjustment of the rotational speed of the spiral shaft and the aperture of the screen, in order to better adapt to the different texture and moisture content of the manure; for the belt-type filter press, it is necessary to accurately adjust the tension of the filter belt and the extrusion pressure, so as to improve the separation effect and the stability of the operation of the equipment.
Solid-liquid Separation of Products After Treatment and Utilization
solid part
The solid product after solid-liquid separation is rich in organic matter and various types of nutrients, which has high utilisation value and can be professionally processed and widely used as organic fertiliser. Common processing methods include composting, drying and granulation. Composting is the mixing of solid manure with appropriate amount of auxiliary materials (e.g. straw, wood chips, etc.) and fermentation under the active action of microorganisms, so that it is gradually converted into stable organic fertiliser. Drying can effectively reduce the moisture content of solid manure and facilitate subsequent storage and transport. Pelleting can make solid manure into granular fertiliser, which greatly improves the commerciality and convenience of the fertiliser.
Liquid part
The liquid product after solid-liquid separation contains a certain amount of organic matter and nutrients such as nitrogen, phosphorus, potassium, etc., which can be processed into high-quality liquid organic fertiliser through our liquid organic fertiliser production equipment, which can further improve the economic value of the manure. Of course you can also carry out further in-depth treatment of the liquid fraction to meet the strict emission standards or to achieve effective recycling of resources. Common treatment methods include biological treatment, chemical treatment and physical treatment. Biological treatment utilises the unique metabolic action of microorganisms to break down organic matter in the liquid into harmless substances, such as aerobic and anaerobic treatment. Chemical treatment is through the addition of specific chemical substances to the liquid treatment, such as coagulation and precipitation, disinfection, etc.. Physical treatment is the use of physical methods to accurately separate and purify the liquid, such as filtration, adsorption and so on.
Solid-liquid separation from chicken manure, pig manure, cow manure and other animal manures is undoubtedly a key core step in realizing manure resource utilization and environmental protection. Different animal manure has unique characteristics, in the selection of solid-liquid separation methods and equipment, we must take into account the characteristics of the manure, the scale of treatment and specific treatment requirements and other factors. Through scientific optimization of solid-liquid separation process and equipment parameters, reasonable use of multi-process combination of innovative ways to significantly improve the solid-liquid separation effect and equipment operating efficiency. Solid-liquid separation of solid and liquid products need to be further refined treatment and efficient use, in order to maximize the recovery of resources and minimize the pollution of the environment. With the continuous progress and innovation of science and technology, it is believed that the solid-liquid separation technology of animal manure will play a more critical and important role in the process of sustainable development of animal husbandry.
