What is biochemical treatment of wastewater?
Biochemical treatment is the use of microorganisms to remove soluble organic matter and some insoluble organic matter from wastewater by the process of their life activities, so that the water can be purified.
In natural rivers, there are a large number of microorganisms that live on organic matter, and they oxidize or reduce the organic matter (such as industrial wastewater, pesticides, fertilizers, feces, and other organic substances) that people discharge into the rivers day and night, and ultimately convert it into inorganic matter.
Biochemical treatment of wastewater is to strengthen this process under artificial conditions. People will countless microorganisms all concentrated in a pool, to create a very suitable environment for microbial reproduction, growth (such as temperature, pH, oxygen, nitrogen, phosphorus and other nutrients), so that the microbial proliferation, in order to improve its decomposition of organic matter speed and efficiency. Then pump the wastewater into the pool, so that the organic substances in the wastewater are oxidized and degraded in the process of microbial life activities, so that the wastewater can be purified and treated. Compared with other treatment methods, the biochemical method is characterized by low energy consumption, no dosage, good treatment effect and low treatment cost.
How do microorganisms decompose and remove organic pollutants from wastewater?
There are carbohydrates, fats, proteins and other organic matter in the wastewater, which is the food for microorganisms, part of which is degraded and synthesized into cellular material (combinatorial metabolites), and the other part is degraded and oxidized into water, carbon dioxide, etc. (catabolic metabolites), and the organic pollutants in the wastewater are degraded by the microorganisms and removed in this process.
How to ensure the maximum activity of microorganisms?
In addition to nutrition, microorganisms need the right environmental factors, such as temperature, pH, dissolved oxygen, osmotic pressure, etc., to survive. If the environmental conditions are not normal, it will affect the life activities of microorganisms and even mutate or die.
What temperature range is most suitable for microbial reproduction?
In wastewater biological treatment, the most suitable temperature range for microorganisms is generally 16-30°C, with the highest temperature at 37-43°C. When the temperature is lower than 10°C, microorganisms will no longer grow.
In the appropriate temperature range, the temperature increases every 10 ℃, the metabolic rate of microorganisms will increase accordingly, COD removal rate will also increase by about 10%; on the contrary, the temperature decreases every 10 ℃, COD removal rate will be reduced by 10%, so in the winter, COD biochemical removal rate will be significantly lower than in other seasons.
What should be the optimal pH conditions for microorganisms?
Microbial life activities, material metabolism and pH are closely related. Most of the microorganisms adapt to the pH range of 4.5-9, and the optimal pH range of 6.5-7.5. When the pH is lower than 6.5, fungi start to compete with bacteria, and when the pH reaches 4.5, the fungi will take the complete advantage in the biochemical tank, and the result is to seriously affect the sludge settling results; when the pH is more than 9, the metabolism of the microorganisms will be impeded.
Different microorganisms require different adaptation ranges for pH. In aerobic biological treatment, the pH can vary between 6.5-8.5; in anaerobic biological treatment, microorganisms have more stringent requirements in terms of pH, which should be between 6.7-7.4.
What is dissolved oxygen?
Oxygen dissolved in the water column is called dissolved oxygen. The oxygen on which the organisms and aerobic microorganisms in the water body depend for their survival is dissolved oxygen. Different microorganisms have different requirements for dissolved oxygen. Aerobic microorganisms need to be supplied with sufficient dissolved oxygen, generally speaking, dissolved oxygen should be maintained at 3mg/L is appropriate, the minimum should not be less than 2mg/L; parthenogenetic microorganisms require dissolved oxygen in the range of 0.2-2.0mg/L; and anaerobic microorganisms require dissolved oxygen in the range of 0.2mg/L or less.
Why are microorganisms particularly affected by high concentrations of saline wastewater?
The unit structure of microorganisms is cell, cell wall is equivalent to semi-permeable membrane, in the concentration of chloride ions less than or equal to 2000mg/L, the cell wall can withstand the osmotic pressure of 0.5-1.0 atmospheric pressure, even if coupled with the cell wall and cytoplasmic membrane has a certain degree of toughness and elasticity, the osmotic pressure that the cell wall can withstand will not be greater than 5-6 atmospheric pressure. But when the concentration of chloride ions in aqueous solution in 5000mg / L or more, the osmotic pressure will increase to about 10-30 atmospheric pressure, in such a large osmotic pressure, microbial water molecules will be a large number of water molecules will be infiltrated into the solution outside the body, resulting in the loss of cellular water and the occurrence of plasma wall separation, and in severe cases, microbial death.
In daily life, people use salt (sodium chloride) pickled vegetables and fish, sterilization and preservation of food, is the use of this reason. Engineering experience data show that: when the concentration of chlorine ions in wastewater is greater than 2000mg / L, the activity of microorganisms will be suppressed, COD removal rate will be significantly reduced; when the concentration of chlorine ions in wastewater is greater than 8000mg / L, it will result in the expansion of sludge volume, the surface of the water flooded with a large number of bubbles, and microorganisms will be killed one after another.
However, after a long period of domestication, microorganisms will gradually adapt to grow and reproduce in the high concentration of salt water. At present, someone has already domesticated microorganisms that can adapt to more than 10,000mg/L chloride ion or sulfate concentration. However, the principle of osmotic pressure tells us that the microorganisms that have been adapted to grow and reproduce in high concentration of brine, the salt concentration of the cytosol is very high, and once when the concentration of salt in the wastewater is low or very low, the water molecules in the wastewater will penetrate into the microorganisms in large quantities, so that the microorganisms cells are swollen, and in serious cases, rupture and die. Therefore, after a long period of domestication and can gradually adapt to the growth and reproduction of microorganisms in high concentration of salt water, the salt concentration of biochemical feed water is always required to be maintained at a fairly high level, can not be high or low, or the microorganisms will be a large number of deaths.
What is aerobic biochemical treatment and partially aerobic biochemical treatment? What is the difference between the two?
Biochemical treatment according to the growth of microorganisms on the different requirements of the oxygen environment, can be divided into aerobic biochemical treatment and anoxic biochemical treatment of two categories, anoxic biochemical treatment can be divided into parthenogenetic biochemical treatment and anaerobic biochemical treatment.
In aerobic biochemical treatment process, aerobic microorganisms must grow and reproduce in the presence of a large amount of oxygen, and reduce the organic matter in the wastewater; and parthenogenetic biochemical treatment process, parthenogenetic microorganisms only need a small amount of oxygen to grow and reproduce and degrade the organic matter in the wastewater, if the water is too much oxygen, parthenogenetic microorganisms instead of growing poorly, thus affecting the efficiency of the treatment of organic matter.
Parthenogenetic microorganisms can be adapted to wastewater with high COD concentration, the influent COD concentration can be increased to more than 2000mg/L, and the COD removal rate is generally in the range of 50-80%; whereas aerobic microorganisms can only be adapted to wastewater with low COD concentration, and the influent COD concentration is generally controlled to be less than 1,000-1,500mg/L, and the COD removal rate is generally in the range of 50-80%, and the time required for both the parthenogenetic and aerobic biological treatment is very short. The time of aerobic biochemical treatment is not too long, generally in 12-24 hours.
People use the difference between aerobic biochemical treatment and aerobic biochemical treatment and the same length, the combination of aerobic biochemical treatment and aerobic biochemical treatment, so that the COD concentration of higher wastewater first aerobic biochemical treatment, and then let the treatment of aerobic tank effluent as the feed water of the aerobic tank, such a combination of treatment can reduce the volume of biochemical tanks, both to save the investment in environmental protection and to reduce the daily operating costs.
Anaerobic biochemical treatment and aerobic biochemical treatment of the same principle and role. The difference between anaerobic biochemical treatment and parthenogenetic biochemical treatment is that anaerobic microorganisms do not need any oxygen in the process of reproduction and growth and degradation of organic substances, and anaerobic microorganisms can be adapted to wastewater with a higher COD concentration (4000-10000mg/L). The disadvantage of anaerobic biochemical treatment is that the biochemical treatment time is very long, and the residence time of wastewater in the anaerobic biochemical tank generally requires more than 40 hours.
What are the applications of biological treatment in wastewater treatment engineering?
Biological treatment is the most widely used and practical technology in wastewater treatment engineering, there are two major categories: one is called activated sludge method, the other is called biofilm method.
Activated sludge is a form of aerobic wastewater treatment based on the biochemical metabolism of suspended biological communities. Microorganisms in the growth and reproduction process can form a large surface area of the bacterial colloid, it can be a large number of flocculation and adsorption of suspended colloidal or dissolved pollutants in wastewater, and these substances are absorbed into the body of the cell, in the participation of the oxygen, these substances are completely oxidized to emit energy, CO2 and H2O. activated sludge sludge concentration is generally in the 4g/L. In the biofilm method, microorganisms can form a large surface area of the bacterial colloid and adsorbed into the cell.
In the biofilm method, microorganisms attach to the surface of the packing material and form a gelatinous connected biofilm. The biofilm is generally a fluffy flocculent structure with more micropores and a large surface area, which has a strong adsorption effect and is conducive to the microorganisms to further decompose and utilize these adsorbed organic matter. In the treatment process, the flow of water and air agitation so that the biofilm surface and water contact, organic pollutants in wastewater and dissolved oxygen for the biofilm adsorption, biofilm microorganisms continue to decompose these organic substances in the oxidation and decomposition of organic substances at the same time, the biofilm itself is also constantly metabolism, senescence of biofilm fall off by the treatment of the effluent water from the biological treatment facilities out of the water and in the sedimentation tank and water Separation. The sludge concentration of the biofilm method is generally 6-8g/L. In order to increase the concentration of sludge, it is necessary to increase the sludge concentration of the biofilm method.
In order to increase the sludge concentration and thus improve the treatment efficiency, the activated sludge method can be combined with the biofilm method, i.e., by adding fillers to the activated sludge tank, this kind of bioreactor with both film-attached microorganisms and suspended microorganisms is called a composite bioreactor, which has a high sludge concentration of about 14g/L. The biofilm method and the activated sludge method can be used to increase the sludge concentration of the activated sludge tank and the biofilm method.
What are the similarities and differences between biofilm and activated sludge?
Biofilm method and activated sludge method are different reactor forms for biochemical treatment, the main difference from the appearance is that the microorganisms of the former do not need filler carriers and the biological sludge is suspended, while the microorganisms of the latter are fixed on the filler, however, they treat wastewater and purify the water quality of the mechanism is the same. In addition, the biological sludge of both is aerobic activated sludge, and the composition of the sludge has some similarity. In addition, the microorganisms in the biofilm method can form a more stable ecosystem because they are fixed on the packing material, and their living energy and consuming energy are not as large as those in the activated sludge method, so the residual sludge of the biofilm method is less than that of the activated sludge method.
What is meant by activated sludge?
From the microbial point of view, the sludge in the biochemical tank is a biological group composed of a variety of biologically active microorganisms. If you put the sludge particles under a microscope, you can see that there are many kinds of microorganisms in it – bacteria, molds, protozoa and post-zoa (e.g., rotifers, insect larvae and worms, etc.), which form a food chain. Bacteria and molds can decompose complex organic compounds, obtain the energy necessary for their own activities, and construct themselves. Protozoa feed on bacteria and molds, which are in turn consumed by the later animals, which can also live directly on bacteria. This kind of flocculent mud particles full of microorganisms with the ability to degrade organic matter is called activated sludge.
Activated sludge is composed of microorganisms, but also contains some inorganic substances and adsorbed on the activated sludge can no longer be biodegradable organic matter (i.e., microbial metabolic residues). The water content of activated sludge is generally 98-99%. Activated sludge, like alumina, has a large surface area, so it has strong adsorption and oxidative decomposition of organic matter.
How to evaluate activated sludge in activated sludge and biofilm process?
The growth of activated sludge in the activated sludge method and the biofilm method are not the same.
In the biofilm method, activated sludge growth is evaluated by direct observation of the biological phase using a microscope. In the activated sludge method, the evaluation of activated sludge growth evaluation in addition to direct observation of the biological phase with a microscope, commonly used evaluation indexes are: mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), sludge settlement ratio (SV), sludge settlement index (SVI) and so on.
When looking at the biological phase with a microscope, which group of microorganisms directly indicates good biochemical treatment?
The presence of microfauna (e.g. rotifers, nematodes, etc.) indicates that the microbial community is growing well and the ecosystem of activated sludge is stable, which is the best time for biochemical treatment.
What is meant by Mixed Liquid Suspended Solids (MLSS)?
Mixed Liquid Suspended Solids (MLSS) is also known as sludge concentration, which refers to the weight of dry sludge contained in a unit volume of biochemical tank mixture in milligrams/liter, and is used to characterize the concentration of activated sludge. It includes both organic and inorganic components. Generally speaking, it is appropriate to control the MLSS value in the SBR biochemical tank at around 2000-4000mg/L.
What is meant by Mixed Liquid Volatile Suspended Solids (MLVSS)?
Mixed Liquid Volatile Suspended Solids (MLVSS) refers to the weight of volatile substances in the dry sludge contained in the mixed liquor of the biochemical tank per unit volume, and the unit is also milligrams/liter, which does not include the inorganic matter in the activated sludge, and therefore can more accurately represent the number of microorganisms in the activated sludge.
Sludge Settling Ratio (SV) ?
Sludge Settling Ratio (SV) is the volume ratio (%) of settled sludge to the mixture in an aeration tank after 30 minutes of stationary settling in a 100 ml cylinder, so it is sometimes expressed as SV30. Generally speaking the SV in a biochemical tank is between 20-40%. The determination of sludge sedimentation ratio is relatively simple, and it is one of the important indexes for evaluating activated sludge, which is often used to control the discharge of residual sludge and the abnormal phenomena such as sludge swelling in timely counter time. Obviously, SV is also related to sludge concentration.
Sludge Index (SVI)
Sludge index (SVI) full name sludge volume index, 1 gram of dry sludge in the wet state of the volume occupied by the number of milliliters, the formula is as follows as:
SVI = SV*10/MLSS
SVI removes the influence of sludge concentration factors, more reflective of active sludge cohesion and sedimentation, generally considered:
When 60＜SVI＜100, the sludge settling performance is good.
When 100 <SVI <200, the sludge settling performance is general
When 200＜SVI＜300, the sludge has the tendency of expansion.
When SVI＞300, the sludge has swelled.
What does Dissolved Oxygen (DO) mean?
Dissolved oxygen (DO) represents the amount of oxygen dissolved in water, and the unit is expressed in mg/L. Different biochemical treatment methods have different effects on the amount of oxygen dissolved in water. Different biochemical treatment methods have different requirements for dissolved oxygen, in the parthenogenetic biochemical process, the dissolved oxygen in the water is generally between 0.2-2.0 mg/L, while in the SBR aerobic biochemical process, the dissolved oxygen in the water is generally between 2.0-8.0 mg/L.
Therefore, the partially oxygenated pool operation should be small aeration volume, aeration time should be short; while in the SBR aerobic pool operation, the aeration volume and aeration time should be much larger and much longer, and we use contact oxidation, dissolved oxygen control in 2.0-4.0mg/L.
What factors are related to the content of dissolved oxygen in wastewater?
The concentration of dissolved oxygen in water can be expressed by Henry’s law: when reaching dissolution equilibrium:C=KH*P [where: C is the solubility of oxygen in water at dissolution equilibrium; P is the partial pressure of oxygen in the gas phase; KH is Henry’s coefficient, which is related to temperature].
Increase the aeration effort to make oxygen dissolution close to equilibrium, and at the same time the activated sludge will also consume the oxygen in the water. Therefore the actual amount of dissolved oxygen in wastewater is related to water temperature, effective water depth (affecting pressure), aeration, sludge concentration, salinity and other factors.
Who provides the oxygen required by the microorganisms in the biochemical process?
Roots Fans
Why do you need to replenish nutrients in the wastewater frequently during the biochemical process?
The method of removing pollutants by biochemical process mainly utilizes the metabolic process of microorganisms, and the life process of microorganisms, such as cell synthesis, requires a sufficient amount and type of nutrients (including trace elements). For chemical wastewater, due to the production of a single product, so the composition of the wastewater quality of the composition of a single component, the lack of microorganisms necessary nutrients, so in order to meet the needs of microbial metabolism, must be added to the wastewater in the nutrient. This is like people eating rice, flour, but also intake of adequate amounts of vitamins.
What is the ratio between each nutrient required by microorganisms in wastewater?
Aerobic biochemistry: C:N:P = 100:5:1 (weight ratio). Carbon (C), Nitrogen (N), and Phosphorus (P)].
Why is there residual sludge produced?
During biochemical treatment, the microorganisms in the activated sludge continuously consume the organic matter in the wastewater. Among the consumed organic substances, some of them are oxidized to provide energy for microbial life activities, and some of them are utilized by microorganisms to synthesize new cytoplasm so that microorganisms can reproduce and multiply. While microorganisms are metabolizing, some of the old microorganisms will die, and therefore residual sludge will be generated.
How to estimate the amount of residual sludge?
In the process of microbial metabolism, part of the organic matter (BOD) is utilized by microorganisms to synthesize new cytoplasm to replace the dead microorganisms. Therefore, there is a correlation between the amount of residual sludge generated and the amount of BOD decomposed. In engineering design, it is generally considered that for every kilogram of BOD5 treated, 0.6-0.8 kilograms of residual sludge (100%) is generated, which translates into 3-4 kilograms of dry sludge with 80% moisture content.
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