Physical treatment method is through the physical action to separate, recover the sewage insoluble, suspended pollutants (including oil film and oil beads), in the treatment process does not change its chemical properties. Commonly used filtration, precipitation, flotation and so on.
(1) filtration: the use of filtering media to intercept the suspended matter in the sewage. Filter media are sieve, gauze, particles, commonly used filtration equipment are grids, screens, microfilters and so on.
1) grid and screen. In the drainage project, wastewater through the sewers flowing into the water treatment plant, first of all, should be slanted in the channel through a set of metal is longitudinally parallel to the frame (grille), perforated plate or filter (screen), so that floating or suspended matter can not be passed by the grille, fine screen or filter media is blocked on the grille.
This step is a pre-treatment of wastewater, the purpose of which is to recover useful substances; the initial diffuse clear wastewater for later treatment, reduce the load on the sedimentation tank or other treatment equipment; to protect the pumping machinery, in order to avoid clogging of particles failure. Protection of pumps and other treatment equipment. Grid retention effect depends mainly on the quality of sewage water and the size of the grid gap. Slag removal methods are manual and mechanical two. Grid slag should be cleaned and disposed of in a timely manner.
Screen is mainly used to retain particle size in several millimeters to tens of millimeters of fine suspended debris, such as fiber, pulp, algae, etc., usually made of metal wire, chemical fiber weaving, or perforated steel plate, aperture is generally less than 5mm, the smallest can be 0.2mm. Screen filtering device has a rotating drum, rotary, rotary, fixed vibration inclined sieve, etc.. No matter what kind of structure, not only to be able to retain dirt, but also easy to unload and clean up the screen surface.
2) granular media filtration (also known as Tong, filtering, amazing material filtration). Wastewater through the granular filter media (such as quartz sand) bed, in which fine suspended solids and limbs are retained on the surface of the filter media and internal voids. Commonly used filter media are quartz sand, anthracite and garnet. In the filtration process, the filter media at the same time on the suspended matter of physical retention, sedimentation and adsorption and so on. The effect of filtration depends on the size of the pore size of the filter media, the thickness of the filter media layer, the filtration rate and the nature of the sewage and other factors.
When the wastewater flows from top to bottom through the granular filter media layer, the larger suspended particles are first retained in the surface layer of the filter media in the void, so that this layer of the filter media void is getting smaller and smaller, and gradually formed a layer of mainly by the group of particles to be intercepted by the composition of the filter membrane, and by which the main filtration effect. This role belongs to the resistance to retention or sieve filtering.
Wastewater through the filter media layer, many of the filter media surface provides a huge effective area for suspended solids to settle, the formation of countless small "sedimentation pool", suspended solids are very easy to settle down. This effect belongs to gravity sedimentation.
Because of the huge surface area of the filter media, there is an obvious physical adsorption between it and the suspended matter. In addition, sand in the water often with a negative surface charge, can adsorb positively charged iron, aluminum and other limbs, thus forming a positively charged film on the surface of the filter media, and then adsorption of negatively charged colloidal soil and a variety of organic matter, such as colloids, contact flocculation occurs on the sand particles.
(2) Sedimentation method. Sedimentation is the use of sewage in the principle of the relative density of suspended solids and water is different, with the help of gravity settling effect to make the suspended solids from the water to separate out. According to the concentration of suspended particles in water and flocculation characteristics (i.e., the ability of each other post agglomerates) can be divided into four types:
1) Separation of sedimentation (or free sedimentation). In the sedimentation process, the particles do not polymerize with each other and settle separately. The particles are only subject to its own gravity in the water and the role of water resistance, its shape, size, mass are not changed, the rate of descent does not change.
2) coagulation precipitation (or called flocculation settlement). Coagulation refers to the role of coagulant, so that the colloid and fine suspended solids in the wastewater coagulation for the separable floc, and then gravity settling to be separated and removed. Coagulation precipitation is characterized by the precipitation process, the particles contact collision and aggregation of each other to form larger flocs, so the size and mass of the particles will increase with the depth of the increase in the sedimentation rate also increases with the depth.
Commonly used inorganic coagulants are aluminum sulfate, ferrous sulfate, ferric chloride and polymerized aluminum; commonly used organic flocculants are polypropylene cool gel, etc., and coagulants such as water glass, lime, etc., can also be used.
3) Regional settlement (also known as congestion settlement, layer settlement). When the wastewater content of suspended solids is high, the distance between the particles is small, the polymerization force between the collection can make it become a whole, and sink together, and the position of the particles between each other does not change, so the clarified water and water mixing there is a clear interface between the interface, and gradually move downward, this kind of settlement is called the regional sedimentation. Add high turbidity water sedimentation tank and secondary sedimentation tank in the settlement (in the sedimentation of the later) are such.
4) compression sedimentation. When the concentration of suspended solids in suspension is very high, the particles are in contact with each other, extrusion, in the upper layer of particles under the action of gravity, the lower layer of particles in the interstices of the water is squeezed out of the particle group is compressed. Compression precipitation occurs in the sludge hopper at the bottom of the sedimentation tank or sludge thickening tank, proceeds very slowly. According to the different nature of the suspended material in the water, there are two kinds of equipment, sand sedimentation tank and sedimentation tank.
Sedimentation tank is used to remove sand, cinder and other relatively dense particles in the water. Sand sedimentation tank is generally located in front of the sewage treatment plant to prevent wear and tear of other mechanical equipment for sewage treatment.
Sedimentation tank is the use of gravity to make suspended impurities and water separation. It can separate particles with a diameter of 20 to 100?,m or more. According to the direction of water flow in the sedimentation tank, it can be divided into three types: advection type, spoke flow type and vertical flow type.
①Applanation type sedimentation tank. Wastewater flows from one end of the pool, according to the horizontal direction of the flow in the pool, the suspended solids in the water gradually sink to the bottom of the pool, the clarified water from the other end of the overflow.
②Spoke flow sedimentation tank. Pools are mostly circular, larger diameter, generally in 20 ~ 30m or more, suitable for large-scale water treatment plants. Raw water enters the center cylinder through the inlet pipe, and then flows radially to the perimeter of the sedimentation tank through the orifice on the cylinder wall and the peripheral perforated baffle, in the radial direction. Due to the increasing cross-section of the water, the flow rate gradually becomes smaller, the particles settle down, and the clarified water overflows from its surroundings into the collection tank for discharge.
3 vertical flow sedimentation tank. The cross-section is mostly circular, but also square and polygonal. Water from the center of the pipe into the pool at the mouth, through the reflection plate blocking the distribution of the whole horizontal section around, slowly upward flow. Sinking speed exceeds the upward flow rate of particles are sunk to the sludge hopper, the clarified water from the surrounding buried mouth overflow pool.
In the method of sewage treatment and utilization, precipitation (or floating) method is often used as a pretreatment before other treatment methods. Such as biological treatment method, sewage treatment, generally need to go through the pre-settlement tank to remove most of the suspended material in order to reduce the load of biochemical treatment, and the biological treatment of the effluent still need to go through the secondary sedimentation tank treatment, mud-water separation to ensure the quality of the effluent water.
(3) Flotation method. The air through the sewage, and in the form of tiny bubbles precipitated from the water to become a carrier, the relative density of sewage close to the water of tiny particles of pollutants (such as emulsified oil, etc.) attached to the bubbles, and with the bubbles rose to the surface, and then skimmed off the mechanical method, so that the pollutants in the sewage can be separated from the sewage. Hydrophobic substances are easy to float, while hydrophilic substances are not easy to float. Therefore, sometimes in order to improve the efficiency of air flotation, need to be added to the sewage flotation agent to change the surface properties of pollutants, so that some of the hydrophilic substances into hydrophobic substances, and then removed by air flotation, this method is called "flotation".
Air flotation requires a high degree of dispersion of bubbles, the amount is more conducive to improving the effect of air flotation. The stability of the bubble layer should be appropriate, not only to facilitate the stabilization of slag on the water surface, but also does not affect the transportation of slag and dewatering. There are two ways to generate air bubbles:
1) Mechanical method. Make the air through the microporous tube, microporous plate, perforated turntable, etc. to generate tiny bubbles.
2) Pressure dissolved air method. Air dissolved in water under a certain pressure, and reached saturation, and then suddenly reduce the pressure, the oversaturated air will be in the form of tiny bubbles escaping from the water. At present, the air flotation process in wastewater treatment is mostly used in the pressure dissolved air method.
The main advantages of air flotation are: equipment operating capacity is better than the sedimentation tank, generally only 15 ~ 20min to complete the solid-liquid separation, so it occupies less space, higher efficiency; air flotation method of sludge produced by the dryer, not easy to decay, and the system of surface scraping, the operation of the more convenient; the entire work is the water through the air, increasing the amount of latent dissolved oxygen in the water, to remove the water, organic matter, algal surface Active agent and odor, etc. has a significant effect, the quality of its water for subsequent treatment and use of water to provide favorable conditions.
The main drawbacks of air flotation are: higher power consumption; equipment maintenance and management workload increases, the running part of the possibility of clogging; scum on the water surface, vulnerable to wind, rain and other climatic factors.
In addition to the above two methods of air flotation, the more commonly used methods and electrolytic air flotation.
(4) centrifugal separation method. Sewage containing suspended pollutants in high-speed rotation, the use of suspended particles (such as emulsified oil) and sewage by the centrifugal force is different, so as to achieve the purpose of separation method. Commonly used centrifugal equipment are cyclone separator and centrifugal
2, chemical treatment method
To the sewage chemical reagents, the use of chemical reactions to separate, recycling of pollutants in the sewage, or pollutants into harmless substances. This method can make the pollutants and water separation, recovery of certain useful substances, but also to change the nature of the pollutants, such as reducing the acidity and alkalinity of wastewater, remove metal ions, oxidation of certain toxic and harmful substances, and so on, and therefore can achieve a higher degree of purification than the physical method. Commonly used chemical methods are chemical precipitation, neutralization, redox and coagulation.
The limitations of chemical treatment are as follows:
Because of the chemical treatment of wastewater often use chemicals (or materials), the cost of treatment is generally higher, the operation and management requirements are more stringent.
The chemical method also needs to be used in conjunction with physical methods. Before chemical treatment, often need to use precipitation and filtration and other means as a pre-treatment; in some cases, and need to use precipitation and filtration and other physical means as a post-chemical treatment.
( 1) chemical precipitation.
Chemical precipitation method is to put some chemical agents into the wastewater, so that it and the dissolved pollutants in the wastewater exchange reaction, the formation of difficult to banyan in the water salts (precipitates) from the water to precipitate, so as to reduce or remove the pollutants in the water. Chemical precipitation method is mostly used in water treatment to remove calcium ions, mirror ions and heavy metal ions in wastewater, such as scales, pans, lead, scales and so on. According to the use of different precipitating agents, precipitation method can be divided into lime (also known as hydroxide precipitation), sulfide method and silver salt method.
The sum of Ca2+ and Mg2+ in water is called total hardness, which can be divided into carbonate hardness and non-carbonate hardness. Carbonate hardness can add lime to make the water Ca 2 + and Mg2 + to form CaC03 and Mg (OH) 2 precipitation and reduce, such as the need to remove non-carbonate hardness at the same time, can be used lime - soda softening method, so that the Ca 2 + and Mg2 + to form CaC03 矛llMg ( OH) 2 precipitation removed. Therefore, when the raw water hardness or alkalinity is high, the first chemical precipitation method as a pretreatment of ion exchange softening to save the running costs of ion exchange.
Removal of heavy metal ions in wastewater, generally used to add carbonate method, the generation of metal ions, carbonate solubility product is very small, easy to recover. Such as the use of carbonate pin treatment of wastewater containing pounds.
ZnS04 + Na 2C03 one by one → ZnC03 ↓ + NazS04
This method has the advantage of economic simplicity, a wide range of sources of medicines, and therefore the most widely used in the treatment of heavy metal wastewater. Problems are poor labor hygiene conditions, pipeline easy to scale and corrosion; precipitation volume is large, dehydration is difficult.
(2) Neutralization method.
Neutralization is a treatment method that uses the chemical principle that acid and alkali interact to produce salt and water, and adjusts the wastewater from acidic or alkaline to the neutral neighborhood. For wastewater with a concentration of acid or alkali greater than 3%, the first thing to do is to recover the acid and alkali. For low concentration of acid and alkali wastewater, can take the neutralization method for treatment.
Acidic wastewater treatment, usually by adding lime, caustic pot, carbonic acid pot or limestone, marble as clean, material to neutralize acidic wastewater. Alkaline sewage treatment, usually by adding nitric acid, hydrochloric acid or the use of carbon dioxide gas neutralization of alkaline sewage. In addition, for acidic and alkaline sewage can also be used to neutralize each other's approach to treatment.
(3) redox method.
Redox method is through the chemical agents and pollutants in the water between the redox reaction, the sewage in the toxic pollutants into non-toxic or slightly toxic substances in the method. This method mainly deals with inorganic pollutants, such as heavy metals and oxide pollution. The use of high health acid Royal, liquid chlorine, ozone and other strong oxidants or electrode anode reaction, the harmful substances in the wastewater oxidation and decomposition of meta-hazardous substances; the use of iron powder and other reductants or electrode cathodic reaction, the harmful substances in the wastewater to harmless substances; ozone oxidation of wastewater decoloration, disinfection and deodorization; air oxidation of sulfurous wastewater treatment; reduction method of treatment with brocade plating wastewater are examples of oxidation reduction method for wastewater treatment. Reduction method of wastewater treatment are examples of oxidation.
Water treatment commonly used oxidizing agents are oxygen, ozone, chlorine, hypochlorite, etc.. Commonly used reducing agents are ferrous sulfate, sulfite, iron filings, casting powder.
(4) coagulation.
Coagulation is not easy to settle fine particles and colloidal particles in the wastewater containing electrolytes to destabilize the limb and make it polymerization and sinking. Commonly used coagulants are aluminum sulfate, ferrous sulfate, ferric chloride, polyethylene sub-stock or polypropylene cool gel. In order to accelerate the coagulation is often accompanied by the addition of coagulant lime, activated silica gel, bone glue and so on.
3, physical and chemical treatment method
Physical and chemical method (referred to as physical and chemical method), is the use of extraction, adsorption, ion exchange, membrane separation technology, gas lift and other physical and chemical principles, treatment or recovery of industrial wastewater treatment methods. It is mainly used to separate the inorganic or organic (difficult to biodegrade) dissolved or colloidal pollutants in wastewater, recover useful components, and purify the wastewater in depth. Therefore, it is suitable for treating wastewater with a high concentration of impurities (as a recycling method) or wastewater with a low concentration (as a deep treatment of wastewater). The use of physicochemical treatment of industrial wastewater, generally after pretreatment to reduce the suspended solids, oils, harmful gases and other impurities in the wastewater, or to adjust the pH value of the wastewater, in order to improve the recovery efficiency and reduce losses. At the same time, the concentrated residue should be post-treatment to avoid secondary pollution. Commonly used methods include extraction, adsorption, ion exchange, membrane analysis (including dialysis, electrodialysis, reverse osmosis, ultrafiltration, etc.).
(1) Extraction method.
Extraction method is added to the sewage and water insoluble and less dense than water organic solvents, fully mixed contact with the pollutants redistributed from the water phase to the solvent phase, the use of solvents and the difference in density of water, the solvent will be separated from the sewage purification methods. And then use the solute and solvent boiling point difference of solute vapor recovery, regeneration of the solvent can be recycled. The solvent used is called extractant, and the substance proposed is called extractant. Extraction is a liquid-liquid phase mass transfer process, is the use of pollutants (solutes) in water and organic solvents in the two phases of the solubility of the separation.
In the choice of extractant, should pay attention to the extractant to be extracted (pollutants) selectivity, that is, the size of the solvency, usually the greater the solvency, the better the effect of the extraction; extractant and the greater the difference between the density of water, the easier the extraction and separation of water. Commonly used extractants are oxygenated extractants, phosphorus extractants, nitrogen extractants. Commonly used extraction equipment are pulse sieve plate tower, centrifugal extractor.
(2) Adsorption.
Adsorption of wastewater treatment is the use of - a kind of porous solid material (adsorbent) surface to adsorb one or more dissolved pollutants, organic pollutants, etc. (known as fused or adsorbent), in order to recycle or remove them, so that the wastewater can be purified. For example, the use of activated carbon can be adsorbed in the waste white water, such as盼, 隶, wrong, oxygen and other highly toxic substances, and has a decolorization, deodorization and other effects. Adsorption method is currently used for the depth of sewage treatment, can be divided into static adsorption and dynamic adsorption of two methods, that is, in the sewage were in the static and flow dynamics of adsorption treatment. Commonly used adsorption equipment has a fixed bed, moving beds and mobile beds.
In the wastewater treatment of commonly used adsorbents are activated carbon, sulfonated coal, charcoal, coke, diatomaceous earth, wood shavings and adsorption resin. Activated carbon and adsorption resin are more commonly used. General adsorbents are loose porous structure, has a huge specific surface area. The adsorption force can be divided into molecular gravity (van der Waals force), chemical bonding force and electrostatic force. Most of the adsorption in water treatment is the result of the above three adsorption force **** the same action.
Adsorbent adsorption saturation must be regenerated, the adsorbent from the adsorbent pore removal, to restore its adsorption capacity. Regeneration methods include heat regeneration, steam blowing off, chemical oxidation regeneration (wet oxidation, electrolytic oxidation and ozone oxidation, etc.), solvent regeneration and biological regeneration.
Because the adsorbent is more expensive, and the adsorption method of water pre-treatment requirements are high, so it is mostly used in water treatment.
(3) Ion exchange method.
Ion exchange method is the use of ion exchange agent ion exchange effect of replacement of sewage in the ionic state of pollutants. With the production of ion exchange resin and the development of ion exchange technology, due to the effect of good, easy to operate, in recent years in the recovery and treatment of industrial sewage in the toxic substances, get some application. Such as the use of cation exchange agent to remove (recovery) of copper, nickel, cadmium, zinc, mercury, gold, silver, platinum and other heavy metals in sewage.
Ion exchange method is mostly used in industrial water treatment softening and desalination, the main removal of metal ions in wastewater. Ion exchange softening method using Na + exchange resin.
(4) Membrane analysis method.
1) electrodialysis. Electrodialysis is under the action of DC electric field, the use of anion and cation exchange membrane on the solution of anion and cation selective permeability (i.e., the cation membrane only allows cations to pass, the negative membrane only allows anion to pass), so that a part of the solution in the ions migrate to the other part of the solution, so that the electrolytes in the solution and the separation of water, so as to achieve the concentration, purification, separation of a kind of water treatment method. Electrodialysis is a new method developed on the basis of ion exchange technology, in addition to sewage treatment, can also be used for sea water desalination, preparation of deionized water (pure water) and so on.
2) reverse osmosis.
Reverse osmosis has been used in the treatment of heavy metal-containing wastewater, sewage treatment and desalination. In the world's fresh water supply crisis today, reverse osmosis combined with the steam museum method of desalination technology has a bright future. It is another important use is associated with ion exchange system, as a pretreatment method of ion exchange to prepare deionized ultrapure water. In wastewater treatment, reverse osmosis is mainly used for the removal and recovery of heavy metal ions, the removal of salt, organic matter, color and radioactive elements.
Currently widely used in the field of water treatment semi-permeable membrane cellulose acetate membrane and polycool rubber membrane sulfonated polyphenylene acetate and other polymers. Commonly used reverse osmosis devices are tubular, spiral, hollow fiber type and plate and frame type. Osmosis water can be reused.
4, biological treatment method
Biological treatment method is the use of natural environment of microorganisms in the biochemical role, oxidation and decomposition of organic pollutants dissolved in sewage or limb state and some inorganic toxicants (such as fluoride, sulfide), and will be converted into stable and harmless inorganic substances, so that wastewater can be purified method. This method has the advantages of low investment, good results, low operating costs, etc., in the treatment of municipal wastewater and industrial wastewater has been the most widely used.
Modern biological treatment method according to the microorganisms in the biochemical reaction whether oxygen, divided into aerobic biological treatment and anaerobic biological treatment of two categories.
(1) Aerobic biological treatment.
In the presence of oxygen, relying on aerobic bacteria and parthenogenetic bacteria to complete the biochemical wastewater treatment process is called aerobic biological treatment. This method requires a supply of oxygen. According to the state of aerobic microorganisms in the treatment system, can be divided into activated sludge and biofilm method.
1) The activated sludge method is one of the most widely used biological treatment methods. The method is to the aeration tank rich in organic pollutants and bacteria in the wastewater constantly through the air (aeration), after a certain period of time will appear suspended flocculent mud particles, which is actually by the aerobic bacteria (and parthenogenetic aerobic bacteria) adsorbed organic matter and aerobic bacterial metabolic activity of the products of the aggregates composed of a very strong decomposition of organic matter ability, called " active sludge ". Activated sludge". The mixture of sewage and activated sludge from the aeration tank is separated by sedimentation in the settling tank, the clarified water is discharged, and the sludge is returned to the aeration tank as seed sludge to continue operation. This activated sludge-based biological treatment method is called activated sludge method". The wastewater stays in the aeration tank for 4 to 6 h, and about 90% of the organic matter (BOD6) in the wastewater can be removed. Activated sludge method has a variety of tank type and operation mode, usually ordinary activated sludge method, completely mixed surface aeration method, adsorption regeneration method.
2) Biofilm method is to make the sewage flow continuously through the solid filler (gravel, cinder or plastic filler), microorganisms in the filler on the large number of reproduction, the formation of sludge-like film called biofilm, the use of biofilm treatment of sewage, known as biofilm method. Biofilm mainly consists of a large number of bacteria, fungi, algae and protozoa. The microorganisms on the biofilm play the same purifying function as activated sludge, adsorb and degrade the organic pollutants in the water, and the senescent biofilm detached from the packing material will flow into the sedimentation tank along with the treated sewage, and then the sewage can be purified after settling and separating in the sedimentation tank. Commonly used biofilm method of biofilter, biological contact oxidation tank, biological turntable and so on.
(2) anaerobic biological treatment.
In the anaerobic conditions, the use of anaerobic microorganisms in the decomposition of organic matter in sewage, so that the method of sewage purification is called anaerobic biological treatment. In recent years, the world's energy constraints, so that the sewage treatment to energy saving and energy direction, thus promoting the development of anaerobic microbial treatment methods. A large number of new high-efficiency anaerobic bioreactors have appeared one after another, including anaerobic biofilter, upflow anaerobic sludge bed, anaerobic sulfide bed and so on. They are characterized by high concentration of biological groups in the reactor, long sludge age, so the treatment capacity is greatly improved, thus making the anaerobic biological treatment method has the advantages of small energy consumption, energy recovery, small amount of residual sludge, stable and easy to deal with the sludge generated, and high treatment efficiency for high concentration of organic wastewater. Anaerobic biological treatment method after years of development, has become one of the main methods of sewage treatment.
5, phosphorus removal, nitrogen removal
( 1) phosphorus removal. The main source of phosphorus in municipal wastewater is feces, detergents and some industrial wastewater, in the form of orthophosphate, polyphosphate and organic phosphorus dissolved in water. Commonly used methods of phosphorus removal are chemical and biological methods.
1) chemical method of phosphorus removal. The use of phosphate and iron salts, lime, aluminum salts, etc. to generate iron phosphate, calcium phosphate, aluminum phosphate precipitation, phosphorus from the wastewater exclusion. Chemical method is characterized by the removal of phosphorus is more efficient, stable results, sludge in the treatment and disposal process will not re-release of phosphorus caused by secondary pollution, but the production of sludge is relatively large.
2) biological phosphorus removal. Biological phosphate removal is the use of microorganisms in aerobic conditions, the excess absorption of dissolved phosphate in wastewater, precipitation and separation of phosphorus removal. The whole process is divided into anaerobic phosphorus and aerobic phosphorus absorption two stages.
Wastewater containing excessive phosphorus and phosphorus-containing activated sludge into the anaerobic state, the activated sludge in the polyphosphorus business in the anaerobic state, the body of the accumulated polyphosphorus decomposition of inorganic phosphorus released back into the wastewater. This is "anaerobic phosphorus release". Polyphosphorus bacteria in the decomposition of polyphosphorus produced in addition to part of the energy for their own survival, the rest for the polyphosphorus bacteria to absorb organic matter in the wastewater, and in the anaerobic fermentation of acid-producing bacteria under the action of the conversion into acetic acid back, and then further converted to PHB (poly self - short base butyric acid) stored in the body.
After entering the aerobic state, the polyphosphorus bacteria will be stored in the body of PHB aerobic decomposition, and release a large amount of energy, part of which is for their own proliferation, and another part of which is for their absorption of phosphate in the wastewater, in the form of polyphosphorus accumulation in the body. This is "aerobic phosphorus absorption". In this stage, the activated sludge proliferates continuously. In addition to a part of the phosphorus-containing activated sludge back to the anaerobic tank, the rest as a residual sludge discharged from the system to achieve the purpose of phosphorus removal.
(2) Nitrogen removal.
Life wastewater in various forms of nitrogen accounted for a relatively constant proportion: 50% to 60% of organic nitrogen, ammonia nitrogen 40% to 50%, nitrite and nitrate nitrogen accounted for 0 to 5%. They all come from the protein in people's food. The methods of nitrogen removal are chemical and biological methods.
1) Chemical method of nitrogen removal. Including ammonia absorption and chlorination.
①Ammonia absorption method. First adjust the pH of the wastewater to more than 10, and then desorb the ammonia in the desorption tower
② Chlorination. Chlorination in the wastewater containing ammonia nitrogen. By properly controlling the amount of chlorine added, the ammonia nitrogen in the water can be completely removed. In order to reduce the amount of chlorine, this method is often used in conjunction with biological nitrification, nitrification and then remove the trace residual ammonia nitrogen.
2) Biological nitrogen removal. Biological denitrification is under the action of microorganisms, organic nitrogen and ammonia nitrogen into nitrogen, including nitrification and denitrification of two reaction processes.
Nitrification reaction is in aerobic conditions, wastewater ammonia nitrogen is nitrifying bacteria (nitrite and nitrate bacteria) into nitrite and nitrate. Denitrification reaction is in anaerobic conditions, denitrifying bacteria will nitrate nitrogen (N03-) and nitrite nitrogen (NH2-) reduced to nitrogen. Therefore, the whole denitrification process needs to go through aerobic and anoxic two stages.