Generally speaking, stool is not directly discharged, but collected.
The components of pollutants in wastewater are extremely complex and diverse, and it is difficult to achieve the goal of complete purification by any treatment method. It is often necessary to form a treatment system by multiple methods to meet the treatment requirements.
According to the different treatment degree, wastewater treatment system can be divided into primary treatment, secondary treatment and advanced treatment.
Primary treatment only removes suspended solids from wastewater, mainly using physical methods, and the treated wastewater generally fails to meet the discharge standards.
For the secondary treatment system, the primary treatment is pretreatment. Biological treatment is the most commonly used method in secondary treatment, which can greatly remove colloid and dissolved organic matter from wastewater and make wastewater meet the discharge standard. However, after secondary treatment, there are still a certain amount of suspended solids, dissolved organic matter, dissolved inorganic matter, nitrogen and phosphorus and other algae value-added nutrients in the water, and there are also viruses and bacteria. Therefore, higher emission standards cannot be achieved. If it is discharged into a river with small flow and poor dilution ability after treatment, it may cause pollution and cannot be directly used as a supply source of tap water, industrial water and groundwater. Tertiary treatment is to further remove pollutants that cannot be removed by secondary treatment, such as phosphorus, nitrogen, biodegradable organic pollutants, inorganic pollutants and pathogens. The tertiary treatment of wastewater is a "advanced treatment" method which further adopts chemical methods (chemical oxidation, chemical precipitation, etc.) on the basis of secondary treatment. ) and physical and chemical methods (adsorption, ion exchange, membrane separation technology, etc. ) remove some specific pollutants. Obviously, the cost of tertiary treatment of wastewater is high, but water resources can be fully utilized.
Sewage and industrial wastewater discharged into sewage treatment plants can be treated harmlessly through various separation and conversion technologies.
fundamental principle
General technology
physical law
Removal of insoluble suspended solids and oil products from wastewater by physical or mechanical action.
Filtration, precipitation, centrifugal separation, flotation, etc.
Chemical method
Chemical substances are added to change the chemical or physical properties of pollutants in wastewater through chemical reaction, so that the chemical or physical state changes, and then the pollutants are removed from the water;
Neutralization, oxidation, reduction, decomposition, flocculation, chemical precipitation and so on.
Physical and chemical methods
The wastewater is purified under the combined action of physics and chemistry.
Stripping, purging, adsorption, extraction, ion exchange, electrolysis, electrodialysis, reverse dialysis, etc.
biological method
Using the metabolism of microorganisms, organic pollutants in wastewater are oxidized and degraded into harmless substances, also known as biochemical treatment, which is the most important method to treat organic wastewater.
Activated sludge, biological filter, life turntable, oxidation pond, anaerobic digestion, etc.
Among them, the biological treatment of wastewater is based on the method that microorganisms transform complex organic substances into simple materials and toxic substances into non-toxic substances through the action of enzymes. Biological treatment can be divided into aerobic biological treatment and anaerobic biological treatment according to the different needs of microorganisms in the treatment process for oxygen. Aerobic biological treatment is carried out by aerobic bacteria in the presence of oxygen. Through their own life activities-oxidation, reduction, synthesis and other processes, bacteria oxidize some absorbed organic matter into simple inorganic matter (CO2, H2O, NO3-,PO43-,etc. ) get the energy needed for growth and activities, and at the same time convert another part of organic matter into nutrients needed by organisms, so as to make themselves grow and reproduce. Anaerobic biological treatment is carried out by anaerobic microorganisms under anaerobic conditions. Anaerobic bacteria need to get oxygen from CO2, NO3-and PO43-while degrading organic matter, so their degradation products are CH4, H2S and NH3. To treat wastewater by biological method, we must first analyze the biodegradability of pollutants in wastewater. There are mainly three aspects: biodegradability, conditions of biological treatment, and the limit allowable concentration of pollutants that inhibit microbial activity in wastewater. Biodegradability refers to the extent to which the chemical structure of pollutants can be changed through biological life activities, thus changing the chemical and physical properties of pollutants. Aerobic biological treatment refers to the possibility of pollutants being converted into CO2, H2O and biomass by microorganisms through intermediate metabolites under aerobic conditions and the conversion rate of such pollutants. Only under certain conditions (nutritional conditions, environmental conditions, etc. ) Whether microorganisms can effectively decompose organic pollutants. Proper selection of nutrition and environmental conditions can make biodegradation go smoothly. Through the study of biological treatment, the range of these conditions can be determined, such as pH value, temperature and the ratio of carbon, nitrogen and phosphorus.
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In recent years, in the research of water resources recycling, people pay great attention to the removal of various nano-and micro-particle pollutants. Nano-micron particle pollutants in water refer to fine particles smaller than lum, and their components are extremely complex, such as various fine clay minerals, synthetic organic matter, humus, oil and algae. As a carrier with strong adsorption, fine clay minerals often adsorb toxic heavy metal ions, organic pollutants, pathogenic bacteria and other pollutants on their surfaces, while humus and algae in natural water bodies. In the chlorine disinfection process of water treatment, it can form chlorinated hydrocarbon carcinogens with chlorine. The existence of these nano-micron particle pollutants not only has direct or potential harm to human health, but also seriously worsens the water quality conditions and increases the difficulty of water treatment. For example, in the conventional treatment of municipal sewage, flocs in the sedimentation tank float, and the filter is easy to penetrate, which leads to the decline of effluent quality and the increase of operating cost. At present, the traditional conventional treatment process can not effectively remove these nano-micron pollutants in water, and some advanced treatment technologies, such as ultrafiltration membrane and reverse osmosis, are difficult to be widely used because of high investment and cost, so it is urgent to study and develop new, efficient and economical water treatment technologies.