Treatment method:
1, coagulation pretreatment
The turbidity and suspended solids concentration of antibiotic wastewater are high, so coagulation pretreatment is used to remove high suspended solids and turbidity in the water quality pretreatment part, making the water quality history suitable for subsequent biological treatment.
Basic principle of solidification
Coagulation clarification is a common unit operation in water supply and wastewater treatment practice. It refers to a water treatment method in which colloids and fine suspended solids in wastewater are condensed into flocs under the action of coagulants and then separated and removed. The reasons for the stability of colloidal solution or suspension are: the particle size of solid particles is too fine, which forms Brownian motion with charge; In addition, there is a hydrophilic colloid in the solution, which is a soluble macromolecule, such as protein, starch, humic acid, etc. Their molecules all have hydrophilic polar groups, such as -OH, -COOH, -NH3, etc., which have strong affinity for water, and keep a thick water layer around them, which can expand into real solutions. Colloids or suspensions form dispersion system through fine particle size, charged charge and dissolution in water, so coagulants must be added to destroy their stability and make them aggregate into flocs of hundreds of microns or even millimeters before they can be removed. Coagulation refers to the process that colloidal pollutants and fine suspended solids in water are destabilized and aggregated into separable flocs under the dissociation of coagulant and hydrolysate, including coagulation and flocculation, which are collectively called coagulation.
Coagulation mechanism
In coagulation treatment, it mainly works through the mechanism of compressing electric double layer and electric neutralization.
Coagulation:
Coagulation refers to the effect of adding inorganic electrolyte to compress the electric double layer, reducing zeta potential, reducing repulsive energy between particles, alleviating Brownian motion, and making particles closely contact and gather together.
Effect of Coagulation Pretreatment on COD and Sulfate Concentration in Raw Water
In the process of coagulation pretreatment, it is hoped that not only high concentration of ss can be removed, but also high concentration of COD and some biological inhibitors such as sulfate can be removed at the same time. Due to the introduction of sulfate ion in water quality preservation, according to the above contents, sulfate is the main biological inhibitor in antibiotic pharmaceutical wastewater. Therefore, in the pretreatment part, the influence of coagulation pretreatment process on the change of COD and sulfate concentration was studied. With the extension of settling time, the removal rate of COD and sulfate will gradually increase, which is mainly because with the extension of settling time, insoluble COD adheres to floc and sinks continuously, and is finally removed. The removal of sulfate provides convenience for the next anaerobic biological treatment, and reduces the sulfate concentration, thus reducing the toxic effect of hydrogen sulfide produced after sulfate-reducing bacteria cannot be discharged in time on anaerobic microorganisms.
Biochemical treatment of antibiotic wastewater
2. Aerobic biological treatment of wastewater
Principle of aerobic biological treatment of wastewater
Aerobic biological treatment is a stable and harmless treatment method, which mainly consists of aerobic microorganisms and degrades organic matter on the premise of providing free oxygen. All kinds of organic pollutants in wastewater are mainly colloid and dissolved organic matter, which are used as nutrient sources for microorganisms. These high-energy organic substances gradually release energy through a series of biochemical reactions, and finally stabilize into low-energy inorganic substances. After being ingested by microorganisms, through metabolic activities, on the one hand, organic matter decomposes stably, providing energy for microbial life activities; On the other hand, it transforms and synthesizes new protoplasm components, that is, microorganisms grow and reproduce themselves. This part is the growth part of activated sludge or biofilm in wastewater biological treatment, which is usually called residual activated sludge.
Basic process of activated sludge process
Activated sludge process is one of the most widely used aerobic biological treatment technologies for wastewater. It means that air is continuously blown into a large amount of wastewater in which organic pollutants are dissolved. After a period of time, activated sludge is formed in the water, and a large number of aerobic microorganisms live on the activated sludge. This microorganism feeds on dissolved organic matter, gains energy and continues to grow, thus purifying wastewater. It consists of an aeration tank, a secondary sedimentation tank, an aeration system and a sludge reflux system. The wastewater from the primary sedimentation tank and the activated sludge from the bottom of the secondary sedimentation tank enter the aeration tank at the same time. Under the action of aeration tank, the mixed solution gets enough dissolved oxygen to make the activated sludge and wastewater fully contact. Soluble organic pollutants in wastewater are adsorbed by activated sludge and decomposed by microorganisms living on activated sludge, thus purifying wastewater.
The basic conditions for the effective operation of activated sludge treatment system are:
(1) The wastewater contains enough soluble and easily degradable organic substances as necessary nutrients for microbial physiological activities; (2) The mixed solution contains enough dissolved oxygen; (3) The activated sludge is suspended in the tank and can fully contact with the wastewater; (4) The activated sludge continuously flows back, and the remaining sludge is removed in time to keep the mixed solution at a certain concentration; (5) No substances toxic to microorganisms enter.
Purification process of activated sludge process
During the normal development of activated sludge microorganisms, there are biomacromolecules composed of protein, carbohydrates and nucleic acids. These biopolymers are charged dielectrics. Therefore, the bioflocculant formed by this microorganism has physiological, physical and chemical adsorption, coagulation and precipitation functions. After contacting with suspended and colloidal organic pollutants in wastewater, it can make the latter unstable, condense and adsorb on the surface of activated sludge.
Activated sludge has a large surface area and can be widely contacted with mixed liquid. In a short time, a large number of suspended solids and colloidal organic pollutants in wastewater can be removed by adsorption, which greatly reduces the COD value of wastewater.
Under the catalysis of transmembrane enzyme, small molecular organics can be directly absorbed by bacteria through the cell wall, but large molecular organics are first adsorbed on the cell surface, hydrolyzed into small molecules under the action of hydrolase, and then absorbed into the cell. Part of the adsorbed organic matter can be removed by sludge discharge.
3. Anaerobic wastewater treatment
Principle of anaerobic treatment of wastewater
Anaerobic wastewater treatment is a stable and harmless treatment method. In the process of anaerobic biological treatment, complex organic matter is degraded and transformed into simple and stable compounds, and energy is released at the same time. Most of the energy exists in the form of CH4, which can be recycled. At the same time, only a small amount of organic matter is transformed into new cell components.
The first stage can be called hydrolysis and fermentation stage. Hydrolysis and fermentation of complex organic matter under the action of microorganisms. Hydrolysis can be defined as the process of transforming complex insoluble polymers into simple soluble monomers or dimers. Because of its huge relative molecular weight, macromolecular organic compounds can't penetrate the cell membrane, so they can't be directly used by bacteria, and are decomposed into small molecules by tiny extracellular enzymes in the first stage. For example, cellulose is hydrolyzed into cellobiose and glucose by cellulase, and starch is hydrolyzed into maltose and glucose by amylase. Hydrolysates of these small molecules can be dissolved in water and used by bacteria through cell membranes. Then, these substances are transformed into simpler compounds in the cells of fermenting bacteria and secreted outside the cells. Fermentation is a biodegradation process, in which organic compounds are both electron acceptors and electron donors. In this process, dissolved organic compounds are transformed into final products mainly composed of volatile fatty acids. The main products in this stage are volatile fatty acids, acids, lactic acid, CO2, H2, H2S and methylamine. At the same time, acidification bacteria also use some substances to synthesize new cell substances.
Acidification process is completed by a large number of diverse fermentation bacteria. Among them, the important groups are Clostridium and Bacteroides. Most of them are strictly anaerobic, but usually about 1% facultative anaerobic bacteria exist in anaerobic environment, which can protect strictly anaerobic bacteria from oxygen damage and inhibition.
The second stage is called hydrogen-producing and acetic acid-producing stage, which is a kind of specialized bacteria, called hydrogen-producing and acetic acid-producing bacteria, and converts fatty acids such as propionic acid and butyric acid and ethanol into acetic acid, CO2 and HZ.
Under standard conditions, ethanol, butyric acid and propionic acid will not be degraded because no energy is generated in these reactions. The decrease of hydrogen concentration can lead these reactions to the direction of products. In a well-run reactor, the hydrogen partial pressure is generally not higher than lOPa, and the average value is about 0. 1 pa. When the partial pressure of hydrogen as one of the reaction products is so low, the degradation of ethanol, butyric acid and propionic acid can generate energy, that is, the actual free energy of the reaction becomes negative.
When hydrogen and carbon dioxide form methane, the hydrogen in the system can only be maintained at a very low partial pressure if the hydrogen produced by acetic acid is effectively utilized by methanogens. According to the average hydrogen partial pressure, it can be calculated that a hydrogen molecule in the reactor is at 0. Average 5s, which means that hydrogen molecules can only move by 0. After production 1 mm. It also shows that this biochemical reaction requires close relationship between strains. This phenomenon is called "interspecific hydrogen transfer". There is not only hydrogen transfer, but also evidence that "interspecific formic acid transfer" is quite important.
The third stage is called methane production stage. Methane is produced by methanogens using acetic acid, H2 and CO2.
In an anaerobic reactor, about 70% of methane is produced by acetic acid disproportionating bacteria. In the reaction, carboxyl groups in acetic acid are separated from acetic acid molecules, and methyl groups are finally converted into methane, and carboxyl groups are converted into carbon dioxide. In neutral solution, carbon dioxide exists in the form of bicarbonate.
Methanogenic bacteria using acetic acid are called methanotrophs soxhlet and methanotrophs pasteur. The growth rates of the two are quite different. When the concentration of acetic acid is low, Methionibacterium soxhlet is better than Methionibacterium Pasteurella. Due to the high affinity of Thiobacillus for substrates, it is possible to achieve a high removal rate of organic matter in wastewater treatment, and the growth of Thiobacillus is conducive to the formation of granular sludge with good quality. Therefore, this dominant growth is very beneficial to the system operation.
Anaerobic digestion microorganism
1, fermentation bacteria (acidogenic bacteria)
It mainly includes Clostridium, Bacteroides, Vibrio butyricum, fungi and Bifidobacterium.
The main function of this kind of bacteria is to hydrolyze insoluble organic matter into soluble organic matter through the action of extracellular enzymes, and then convert soluble macromolecular organic matter into fatty acids, alcohols and so on. The results show that the hydrolysis process of organic matter by this kind of bacteria is quite slow, and factors such as pH and average residence time of cells have great influence on the hydrolysis rate. Different organic substances have different hydrolysis rates, such as lipids, which are difficult to hydrolyze. Therefore, when the treated wastewater contains a lot of lipids, hydrolysis will become the rate-limiting step in the anaerobic digestion process. However, the reaction rate of acid production is faster than that of methane production.
Fermentation bacteria are mostly obligate anaerobic bacteria. According to its metabolic function, fermentation bacteria can be divided into cellulolytic bacteria, hemicellulolytic bacteria, amylolytic bacteria, egg autoproteolytic bacteria and lipolytic bacteria.
2. Hydrogen-producing and acetic acid-producing bacteria
Hydrogen-producing and acetic acid-producing bacteria include Zymomonas, Zymomonas, Clostridium and Cryptococcus. These bacteria can degrade various volatile fatty acids into acetic acid and H2.
3. Methanogenic bacteria
Methanogenic bacteria can be divided into two types: one mainly uses acetic acid to produce methane, and the other is small in number, which uses the synthesis of hydrogen and carbon dioxide to produce methane.
Sulfate reduction in anaerobic reaction
In the anaerobic reactor for treating sulfate or sulfite wastewater, these sulfur-containing compounds will be reduced by bacteria. Sulfate reducing bacteria will use sulfate and sulfite as electron acceptors in the process of oxidizing organic pollutants. SRB will reduce sulfate and sulfite to hydrogen sulfide, which will reduce methane production.
According to the different substrates used, SRB can be divided into three categories:
Hydrogen sulfate reducing bacteria;
Sulfate reducing bacteria (asrb) oxidizing acetic acid;
Sulfate reducing bacteria that oxidize higher fatty acids.
The existence of a small amount of sulfate in the process of organic matter degradation will not affect the treatment process, but compared with methane, the solubility of hydrogen sulfide in water is much greater, and each gram of sulfur in the form of hydrogen sulfide is equivalent to 2 grams of COD, so in the treatment of sulfur-containing wastewater, although the oxidation of organic matter is quite good, the removal rate of COD is not satisfactory.
4. Activated carbon adsorption of antibiotic wastewater
Characteristics of activated carbon water treatment
Activated carbon adsorption technology has been used in medicine, chemical industry and food industry for many years at home and abroad. The characteristics of activated carbon water treatment are as follows:
1. Activated carbon has excellent adsorption characteristics for organic matter in water.
Because of its developed fine pore structure and huge specific surface area, activated carbon has a strong adsorption capacity for organic pollutants dissolved in water, such as benzene compounds, phenol compounds, petroleum and petroleum products, and can well remove organic pollutants that are difficult to remove by biological methods and other chemical methods, such as chroma, odor, methylene blue surfactant, herbicide, insecticide, pesticide, synthetic detergent, synthetic dye, amine compounds and many synthetic organic compounds.
2. Activated carbon has a strong adaptability to the changes of water quality, water temperature and water quantity, and has a good removal effect on sewage with high or low concentration of the same organic pollutant.
3. Activated carbon also has strong adsorption capacity for some heavy metal compounds, such as mercury, lead, iron, nickel, chromium, zinc and diamonds. Therefore, activated carbon is also effective in treating electroplating wastewater and smelting wastewater.
4. The activated carbon water treatment device has the advantages of small floor space, easy automatic control and simple operation and management.
5. Saturated carbon can be reused after regeneration without secondary pollution.
6. Useful substances can be recycled, such as treating high-concentration phenol-containing wastewater, and sodium phenolate can be recycled after being regenerated with alkali.
Basic theory of activated carbon adsorption
Due to the unbalanced molecular attraction or chemical bond force on the solid surface, the contacted gas or solute is attracted and kept on the solid surface. This surface phenomenon is called adsorption. Solids have certain adsorbability, but the adsorbent with practical value is a porous solid with large specific surface area. Activated carbon can be used as adsorbent because of its large specific surface area and high adsorption capacity.
The adsorption between adsorbent and adsorbed substance is caused by intermolecular attraction (i.e. van der Waals force), which is called physical adsorption. Chemical adsorption ion exchange adsorption is called chemical adsorption because of the chemical interaction between adsorbent and adsorbed substance. Refers to the adsorption of adsorbate ions on charged points on the surface of adsorbents due to electrostatic attraction.
Activated carbon adsorption rate
Adsorption speed refers to the mass of substances adsorbed by adsorbent per unit weight in unit time. In wastewater, the adsorption speed determines the contact time between wastewater and adsorbent. The faster the adsorption speed, the shorter the contact time and the smaller the volume of adsorption equipment.
The adsorption speed depends on the adsorption process of adsorbate by adsorbent. The adsorption process of porous adsorbent to adsorbate in solution can be basically divided into three continuous stages: the first stage is called the external diffusion stage of particles, and adsorbate diffuses from solution to the surface of adsorbent; The second stage is called particle pore expansion-dispersion stage, and the adsorbate continues to diffuse to the adsorption points in the pores of the adsorbent; The third stage is called the adsorption reaction stage, and the adsorbate is adsorbed on the surface in the pores of the adsorbent. Generally speaking, the adsorption rate is mainly controlled by membrane diffusion rate or pore diffusion rate.
According to the experiment, the diffusion speed of the membrane outside the particle is directly proportional to the solution concentration. For a certain weight of adsorbent, the membrane diffusion rate is also proportional to the surface area of adsorbent. Because the surface area is inversely proportional to the particle size, the smaller the particle size, the greater the diffusion and dispersion speed of the membrane. In addition, increasing the relative motion speed of solution and particles will make the liquid film thinner and improve the diffusion speed of the film.
Pore diffusion rate is related to the size and structure of adsorbent pores, the size and structure of adsorbate particles and other factors. Generally speaking, the smaller the adsorbent particles, the faster the pore diffusion rate, that is, the diffusion rate is inversely proportional to the higher power of particle diameter. Therefore, it is more advantageous to use powder adsorbent than particle adsorbent. Secondly, the inner pore size of the adsorbent can accelerate the pore diffusion speed, but it will reduce the adsorption capacity.
Factors affecting adsorption of activated carbon
1, physical and chemical properties of adsorbent
Different types of adsorbents have different adsorption effects. Generally, polar molecular (or ionic) adsorbents are easy to adsorb polar (or ionic) adsorbents, while nonpolar molecular adsorbents are easy to adsorb nonpolar molecular adsorbents. Because adsorption occurs on the inner and outer surfaces of the adsorbent, the larger the specific surface area of the adsorbent, the stronger the adsorption capacity. In addition, the particle size, pore structure and distribution, and surface chemical characteristics of the adsorbent also have great influence on the adsorption.
2. Physical and chemical properties of adsorbate
The solubility of adsorbate in wastewater has great influence on adsorption. Generally speaking, the lower the solubility of adsorbate, the easier it is to adsorb. When the concentration of adsorbate increases, the adsorption capacity also increases; However, when the concentration increases to a certain extent, the adsorption capacity increases slowly. If the adsorbate is organic, the smaller its molecular size, the faster the adsorption reaction will proceed.
3. pH value of wastewater
The PH value has an influence on the existing forms (molecules, ions, complexes, etc.). ) and the solubility of adsorbent in wastewater, so its adsorption effect also has corresponding influence. The influence of pH value of wastewater on adsorption is also related to the properties of adsorbent. For example, the adsorption rate of activated carbon in acidic solution is generally higher than that in alkaline solution.
4. Temperature
The adsorption reaction is usually exothermic, so the lower the temperature, the better the adsorption. In wastewater treatment, the temperature generally does not change much, so the temperature has little effect on the adsorption process. In fact, the adsorption operation is usually carried out at room temperature.
5. The influence of * * * objects
* * * The influence of stored substances on main adsorbents is very complicated. Some can induce mutual adsorption, some can adsorb independently, and some can interfere with each other. However, many data show that one solute competes with other solutes for adsorption in some way. Therefore, when a variety of adsorbents exist, the adsorption capacity of adsorbents to a certain adsorbate is lower than that when only this adsorbate is contained. Suspended matter will block the pores of the adsorbent, and oil substances will concentrate on the surface of the adsorbent to form an oil film, which has a great influence on the contact time of adsorption. Therefore, they must be removed before the adsorption operation.
6. Contact time
The contact time between adsorbate and adsorbent should be enough to reach adsorption equilibrium. The time required for adsorption equilibrium depends on the adsorption speed, and the faster the adsorption speed, the shorter the time required for reaching equilibrium.
Four. Research results (conclusion of wastewater treatment test)
1. For this kind of wastewater, the best conditions of coagulation treatment are: the variety of coagulant is ferric trichloride, the mass percentage concentration is 10%, 0.2ml of this coagulant should be added to each L of wastewater, and its optimal pH value is 7.
2. The biochemical treatment of wastewater shows that wastewater contains a lot of inert substances and refractory substances.
3. Under the condition of T=33, 1℃, the anaerobic hydrolysis constant was determined.
4. Because the wastewater contains a variety of organic substances, the adsorption test with activated carbon shows a certain competitive effect, and the total adsorption capacity of activated carbon is not high.
5. The removal of sulfate in anaerobic treatment has a certain relationship with COD in wastewater. For details, please go to Baidu Library.