Methods for Treating Waste Water of Livestock and Fowl Cultivation
Multi-media filter is a process of using one or several filter media to pass water with higher turbidity through a certain thickness of granular or non-granular material under a certain pressure, thereby effectively removing suspended impurities and clarifying the water. Commonly used Filter materials include quartz sand, anthracite, manganese sand, etc., which are mainly used for water treatment to remove turbidity, soften water, and pre-treatment of pure water. The turbidity of the effluent can reach below 3 degrees.
The feature of livestock breeding wastewater is high suspended matter, high organicThing and high ammonia nitrogen, biodegradability is strong. At present large-scale cultivation wastewater treatment is adopted to conventional anaerobism-well foster group technology or SBR treatment process conventionally.
The meaning of filtration, in the water treatment process, filtration generally refers to the process of intercepting suspended impurities in water with a filter material layer such as quartz sand and anthracite, so that the water is clarified. The porous material used for filtration is called filter material, and quartz sand is the most common filter material. The filter material has many kinds of granular, powder and fiber. Commonly used filter materials include quartz sand, anthracite, activated carbon, magnetite, garnet, ceramics, and plastic balls. Multi-media filter (filter bed) is a media filter that uses more than two media as the filter layer. It is used in industrial circulating water treatment systems to remove impurities and adsorbed oil in sewage, so that the water quality meets the requirements of recycling . The role of filtration is mainly to remove suspended or colloidal impurities in water, especially to effectively remove tiny particles and bacteria that cannot be removed by sedimentation technology. BODs and COD also have a certain degree of removal effect.
The filter body mainly includes the following components: simplified; water distribution component; support component; backwash air pipe; filter material; exhaust valve (external), etc.
Selection basis of filter material:
(1) It must have sufficient mechanical strength to avoid rapid wear and tear during the backwashing process;
(2) Better chemical stability;
(3) It does not contain substances that are harmful to human health or toxic, and does not contain substances that are harmful to production or affect production;
(4) When selecting filter materials, try to use filter materials with adsorption capacity, large dirt interception capacity, high water production, and good effluent quality.
In the filter material, the pebbles mainly play a supporting role. During the filtration process, due to its high strength, the mutual spacing and gaps are stable, and the pores are large, which facilitates the smooth passage of filtered water during the washing process; similarly, backwashing During the process, backwash water and backwash air can pass smoothly. In the conventional configuration, pebbles are divided into four specifications, and the paving method is from bottom to top, first large and then small.
The common multi-media filters used in water treatment are: anthracite-quartz sand-magnetite filter, activated carbon-quartz sand-magnetite filter, activated carbon-quartz sand filter, quartz sand-ceramic filter Wait.
The main considerations for the filter layer design of the multi-media filter:
1. Different filter materials have a large density difference to ensure that no mixed layer phenomenon occurs after backwashing disturbance.
2. Select the filter material according to the purpose of water production.
3. The particle size requires that the particle size of the lower filter material is smaller than that of the upper filter material to ensure the effectiveness and full utilization of the lower filter material.
In fact, taking the three-layer filter bed as an example, the upper filter has the largest particle size and is composed of light filter materials with low density, such as anthracite and activated carbon; the middle filter has a medium particle size and a medium density, which is generally composed of quartz sand; The filter material is composed of heavy filter material with the smallest particle size and the highest density, such as magnetite. Due to the limitation of density difference, the filter material selection of the three-layer media filter is basically fixed. The upper filter material plays the role of coarse filtration, and the lower filter material plays the role of fine filtration, so that the role of the multi-media filter bed is fully exerted, and the effluent quality is significantly better than that of the single-layer filter bed. For drinking water, the use of anthracite, resin and other filter materials is generally prohibited.
Quartz sand filter:
The quartz sand filter is a filter that uses quartz sand as the filter material. It can effectively remove suspended solids in water, and has obvious removal effect on colloids, iron, organic matter, pesticides, manganese, bacteria, viruses and other pollutants in water. It has the advantages of low filtration resistance, large specific surface area, strong acid and alkali resistance, oxidation resistance, PH application range of 2-13, and good pollution resistance. The unique advantage of the quartz sand filter lies in the optimization of the filter material and filter. The design of the filter realizes the adaptive operation of the filter. The filter material has a strong adaptability to the raw water concentration, operating conditions, pre-treatment process, etc., that is, the filter bed automatically forms a state of sparse top and bottom density during filtration, which is beneficial to the The effluent quality is guaranteed under various operating conditions, the filter material is fully dispersed during backwashing, and the cleaning effect is good. The sand filter has the advantages of fast filtering speed, high filtering precision, and large dirt interception capacity. It is widely used in the pretreatment of various process water, domestic water, circulating water and wastewater, such as electricity, electronics, beverages, tap water, petroleum, chemical industry, metallurgy, textile, papermaking, food, swimming pool, municipal engineering, etc. Quartz sand filter equipment has the characteristics of simple structure, automatic control of operation, large processing flow, few backflushing times, high filtration efficiency, low resistance, and convenient operation and maintenance.
Activated carbon filter:
The filter material is activated carbon, which is used to remove color, smell, residual chlorine and organic matter. Its main mode of action is adsorption. Activated carbon is an artificially made adsorbent.
Activated carbon filters are widely used for pretreatment of domestic water and water in the food industry, chemical industry, power and other industries. Because activated carbon has a well-developed pore structure and a huge specific surface area, it has a strong adsorption capacity for dissolved organic matter in water, such as benzene and phenolic compounds, and it is difficult to remove organic matter by biological and chemical methods. Pollutants, such as chroma, odor, surfactants, synthetic detergents and dyes, have good removal effects. Granular activated carbon has a plasma removal rate of over 85% for Ag^+, Cd^2+ and CrO4^2- in water. After passing through the activated carbon filter bed, the suspended solids in the water are less than 0.1mg/L, the COD removal rate is generally 40% to 50%, and the free chlorine is less than 0.1mg/L.
The backwashing of the filter mainly refers to that after the filter is used for a certain period of time, the filter material layer traps and absorbs a certain amount of debris and stains, which makes the water quality of the filter drop. The main characterization: the filter is normally filtered. The water quality deteriorates, the pressure difference between the inlet and outlet pipes increases, and at the same time, the flow rate of a single filter decreases. The principle of backwashing: the water flow reversely passes through the filter layer to expand and suspend the filter layer, and the filter layer is cleaned by the shear force of the water stream and the collision friction force of the particles so that the dirt in the filter layer is separated and discharged with the backwash water.
The necessity of backwash
(1) During the filtration process, suspended solids in the raw water are trapped and adsorbed by the filter material layer and continuously accumulated in the filter material layer, so the pores of the filter layer are gradually blocked by dirt, forming a filter cake on the surface of the filter layer, and filtering the water head The loss keeps increasing. When a certain limit is reached, the filter material needs to be cleaned to restore the working performance of the filter layer and continue working.
(2) Due to the increase in water head loss during filtration, the shear force of the water flow on the dirt adsorbed on the surface of the filter material becomes larger, and some of the particles move to the lower filter material under the impact of the water flow, which will eventually cause suspended solids in the water. The content continues to rise, and the water quality deteriorates. When impurities penetrate the filter layer, the filter loses its filtering effect. Therefore, to a certain extent, the filter material needs to be cleaned in order to restore the dirt holding capacity of the filter material layer.
(3) The suspended matter in the sewage contains a large amount of organic matter. Long-term retention in the filter layer will cause the enrichment and reproduction of bacteria and microorganisms in the filter layer, and anaerobic corruption will occur. The filter material needs to be cleaned regularly.
Backwash parameter control and determination
(1) Expansion height: When backwashing, in order to ensure that the filter material particles have enough gaps so that the dirt can quickly drain out of the filter layer with water, the filter layer expansion rate should be larger. However, when the expansion rate is too large, the number of particles in the filter material per unit volume decreases, and the chance of particle collision is also reduced, so it is not good for cleaning. Double-layer filter material, the expansion rate is 40%----50%.
Note: During production operation, randomly check the filling height and expansion height of the filter material, because during the normal backwashing process, part of the filter material will be lost or worn and needs to be supplemented. The relatively stable filter layer has the following advantages: to ensure the stability of the filtered water quality and ensure the effect of backwashing.
(2) Backwash water volume and pressure: General design requirements, the strength of backwash water is 40 m3/(m2•h), and the pressure of backwash water is =0.15 MPa. (3) Backwash air volume and pressure: the strength of backwash air is 15 m/(m•h), and the pressure of backwash air is =0.15 MPa.
Note: During the backwashing process, the incoming backwash air is collected at the top of the filter, and most of it should be discharged through the double-hole exhaust valve. In daily production. It is necessary to check the patency of the exhaust valve frequently, which is mainly characterized in the degree of freedom of the valve ball lifting.
Air-water combined backwash
(1) Flush with air first, then backwash with water: First, lower the water level of the filter to 100 mm above the surface of the filter layer, let in air for a few minutes, and then backwash with water. Suitable for filters with heavy surface pollution and light internal pollution.
Note: The corresponding valve must be closed in place; otherwise, when the water level drops below the surface of the filter layer, the upper part of the filter layer will not be infiltrated by water. During the up and down disturbance of the particles, the dirt cannot be effectively discharged, but will go deep into the filter layer. mobile.
(2) Air and water combined backwash: air and backwash water are simultaneously fed from the lower part of the static filter layer. The air merges into the sand layer to form large bubbles during the ascent process, and turns into small bubbles when it encounters the filter material. It has a scrubbing effect on the surface of the filter material; the backwashing water loosens the filter layer, so that the filter material is in a suspended state, which is beneficial to the air scrubbing of the filter material. The expansion effects of backwash water and backwash air are superimposed on each other, and the effect is stronger than when they are performed alone.
Note: The backwash pressure and intensity of water are different from those of air. Pay attention to the sequence to avoid backwash water from entering the air duct.
(3) After the air-water combined backwash is completed, stop entering the air, keep the backwash water at the same flow rate, and continue washing for 3 to 5 minutes to remove the air bubbles left in the filter bed.
Note: Pay attention to the state of the double-hole exhaust valve on the top.
Analysis of Causes of Filter Material Hardening
(1) If the dirt trapped on the surface of the filter layer cannot be effectively removed within a certain period of time, in the subsequent backwashing process, if the backwashing air is unevenly distributed, it will cause uneven expansion height. When the air is rubbed and the amount of rubbing is small, impurities such as oil stains on the surface of the filter material cannot be effectively removed. After the next normal filtration cycle, the local load increases, the impurities will sink into the interior from the surface and the pellets will gradually increase , And extend to the filling depth of the filter at the same time, until the entire filter fails.
Remarks: In actual operation, the phenomenon of uneven backwash air often occurs, mainly due to the perforation of the bottom air distribution pipe, the blockage or damage of the partial filter cap, or the deformation of the grid tube spacing.
(2) The surface filter material of the filter layer has small particles, there is less chance of collision with each other during backwashing, and the momentum is small, so it is not easy to clean. The attached sand particles are easy to form small mud balls. When the filter layer is re-graded after backwashing, the mud ball enters the lower filter material and moves to the depth as the mud ball grows up.
(3) The oil contained in the raw water is trapped in the filter. After backwashing and the remaining part, it accumulates over time, which is the main factor leading to the hardening of the filter material. When to perform backwashing can be determined according to the water quality characteristics of the raw water and the effluent water quality requirements, using standards such as limited head loss, effluent water quality or filtration time.