water quality index
Physical index
Including temperature (thermal pollution), color, smell and taste, solid matter, etc.
chemical index
Organic matter indicators: COD, BOD, TOC, TOD, oil pollutants, phenolic pollutants, surfactants, organic acids and bases, organic pesticides and benzene compounds
Inorganic indicators: PH, phytonutrients, heavy metals, inorganic non-metal toxic and harmful substances
biological indicators
Total bacteria, coliforms, viruses
Several key indicators
COD
Chemical oxygen demand refers to the chemical measurement of the amount of reducing substances that need to be oxidized in water samples.
BOD
Biochemical oxygen demand is the abbreviation of biochemical oxygen demand, which refers to the amount of dissolved oxygen consumed by microorganisms to decompose certain oxidizable substances, especially organic substances, in a certain volume of water within a certain period of time.
TOD
Total oxygen demand refers to the amount of oxygen required to convert reducing substances in water into stable oxides after burning at high temperatures.
TOC
Total organic carbon is a comprehensive indicator that indirectly expresses the content of organic matter in water.
Function and composition of sewage treatment system
Sewage collection pipe network
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Sewage treatment plant
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drain outlet
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self-purification of water
After pollutants are discharged into the water body with sewage, through physical, chemical and biochemical effects, the concentration of pollution is reduced or the total amount is reduced, and the polluted water body is partially or completely restored to its original state.
physical purification
The concentration of pollutants in water bodies is reduced through dilution, mixing, precipitation and volatilization, but the total amount remains unchanged.
chemical purification
The pollutants in the water body change their existing forms and reduce their concentration through processes such as oxidation and reduction, acid-base reaction, decomposition and synthesis, adsorption and condensation, but the total amount does not decrease.
biochemical purification
Pollutants in water bodies change their existing forms through the life activities of aquatic organisms, especially microorganisms. Organic matter becomes inorganic, harmful and harmless, and the concentration is reduced and the total amount is reduced.
grit tank
Removes inorganic particles and impurities with a large specific gravity such as gravel and a small amount of organic impurities with a large specific gravity in the water. The principle is to use gravity separation or centrifugal separation
Horizontal flow grit tank
Simple structure and good treatment effect, suitable for medium and large sewage treatment plants
Cyclone Grit Tank
Tangential water inflow, centrifugal separation, and energy consumption are generally not used
Aeration grit tank
The amount of organic matter in the sedimentation sand is required to be less than 5%, which can assist pre-aeration and slag removal, etc., but it consumes energy and has a negative impact on the operation of the anaerobic or anoxic section of the biological denitrification treatment system.
Theoretical basis of physical treatment of sewage
A treatment process that changes the quality of urban sewage through physical gravity or mechanical force
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Sedimentation tank
It can remove suspended particles and B O D5 at the same time. In the sewage treatment process, there are usually primary sedimentation tanks and secondary sedimentation tanks.
Classification: advection type, vertical flow type, radial flow type sedimentation tank
Methods to improve the effect of sedimentation tanks: inclined plate, aeration, reflux
Sedimentation types: free sedimentation, flocculation sedimentation, regional sedimentation, compression sedimentation
Chemical treatment of sewage
neutralization method
Neutralization method for acid-base wastewater: Acid-base wastewater. Alkaline wastewater is a common industrial wastewater. It is discharged directly and is easy to corrode pipes, etc., so it needs to be treated properly.
Agent neutralization method: Neutralizing agents for acidic wastewater include lime, caustic soda, carbonate, limestone, and carbide slag.
Neutralizing agents for alkaline wastewater include sulfuric acid, hydrochloric acid, acidic waste gas, etc.
Neutralizer: When the neutralizer is a slurry, the wet addition method can be used; when the neutralizer is a block material, the filtration method can be used
Filtration and neutralization method: Using limestone, marble, dolomite, etc. as filter material, the acidic wastewater is allowed to pass through the filter layer to neutralize the water.
chemical coagulation
Definition: The coagulation method is like putting coagulation agents in wastewater, which destabilizes the colloidal particles and fine suspended solids and aggregates into alum particles of hundreds of microns or even several millimeters, which can then be separated by gravity sedimentation or other solid-liquid separation methods. Removal of wastewater treatment technology.
Principles of coagulation: compression double electron layer effect, adsorption bridging principle, net trapping effect
Processing objects: tiny suspended solids and colloidal impurities
Chemical precipitation method
Definition: A method of adding certain chemicals to wastewater to cause a direct chemical reaction with the removed pollutants in the wastewater to form precipitates that are difficult to tolerate in water and thereby separate and remove pollutants.
Solubility: It is the amount of solute contained in each unit of saturated solution at a specified temperature and pressure, which is the maximum extent to which a substance can be dissolved or the concentration of a saturated solution
Solubility product: Solubility product means that although the electrolyte is difficult to tolerate, some anions and cations still enter the solution, and at the same time the anions and cations entering the solution will be deposited on the solid surface. When the rates of the two processes are equal, the solution is difficult to dissolve. The dissolution of the capacitive electrolyte reaches an equilibrium state, and the amount of solid is no longer decreasing. This equilibrium state is called dissolution equilibrium, and its equilibrium constant is called solubility product constant, referred to as solubility product.
redox method
Oxidation method: advanced oxidation technology of ozone and chlorine oxidation wastewater, including Fenton reagent, hydrogen peroxide combined with ultraviolet light, Fenton reagent, ultraviolet light combined with semiconductor, ozone as the main body, electrochemical oxidation, photochemical oxidation, and ultrasonic oxidation
Chemical reduction method: mainly used to treat wastewater containing chromium or mercury and dechlorination of water
Commonly used methods: chemicals, electrolysis, catalytic reduction and combined methods
adsorption method
Understand Henry's isotherm and Langmuir's thermoform of adsorption
Adsorbent: activated clay, fuller's earth, diatomite and other natural minerals; activated carbon, silica gel, activated alumina; adsorption resin
Adsorption process and equipment: Mixed contact is adsorption device, fixed bed adsorption, moving bed adsorption, fluidized bed adsorption
Application: mercury removal, advanced treatment of printing and dyeing wastewater, some organic wastewater
Ion exchange method
Application: softening, desalination
Ion exchanger: mainly includes sulfonated coal and ion exchange resin
Ion exchange process and equipment: exchange, backwash, regeneration, cleaning
Selection of ion exchangers: consider pH, exchange capacity, degree of cross-linking and exchange potential
Extraction method
Used in water treatment processes, it mainly extracts and recovers useful resources from wastewater containing high concentrations of heavy metal ions and certain high-concentration organic industrial wastewater, so as to achieve the purpose of comprehensive management.
Membrane analysis
A method of using natural or artificial synthetic molds to separate, classify, purify and enrich certain substances in aqueous solutions using external energy or chemical potential differences as driving force.
Aerobic biological treatment
principle
Aerobic biological treatment is a treatment method that uses good microorganisms to degrade organic matter in the presence of molecular oxygen in sewage, making it stable and harmless.
process
Microorganisms use the organic pollutants present in the sewage to form low-energy substances for aerobic metabolism. These high-energy organic substances gradually release energy through a series of biochemical reactions, and are finally stabilized as low-energy inorganic substances to meet the requirements of harmlessness. for return to the natural environment or further disposal
Classification
activated sludge process
Definition: Activated sludge is a kind of biological floc with oxygen-consuming microorganisms as the main body. It is formed by the mutual flocculation of organic particles of bacteria, protozoa and some inorganic matter. It feeds on the biodegradable organic matter in the sewage. The content of organic pollutants in sewage is generally measured by BOD, which represents the amount of dissolved oxygen consumed during the biochemical reactions of microorganisms decomposing biodegradable organic matter present in the water.
composition
Active microorganisms, microbial self-oxidation residues, organic matter adsorbed on activated sludge that has not been degraded by microorganisms, and inorganic suspended solids
Evaluation indicators of activated sludge
Sludge age: the average residence time of activated sludge in the aeration tank
Mixed liquor suspended solids concentration
Also called sludge concentration mixed liquid suspension, the content of organic matter in the solid is closer to the concentration of active microorganisms than MLSS.
Sludge settling ratio S V
Can the proportion of sludge after standing for 30 minutes reflect the sludge settling performance?
Sludge Index SVI
Refers to the volume of wet sludge formed per unit mass of dry mud after the mixed liquid in the aeration tank settles for 30 minutes. Reactive sludge settling and concentration performance
sludge bulking
There are two types of sludge bulking. One is the expansion of sludge filamentous bacteria caused by the reproduction of a large number of filaments in activated sludge. The second is non-filamentous expansion caused by the accumulation of large amounts of highly viscous substances in the bacteria in the jelly mass.
Basic process of activated sludge process
Including aeration tank sedimentation tank, sludge return, and remaining sludge removal system
The process of activated sludge degrading organic matter
Adsorption stage, oxidation stage, floc formation and coagulation sedimentation stage
Factors affecting activated sludge growth
Dissolved oxygen, nutrients, pH and temperature
Basic form of aeration tank
Push flow aeration tank, complete mixing aeration tank, closed loop reaction tank, sequencing batch reaction tank
Types of activated sludge process
Ordinary activated sludge process
Also known as traditional activated sludge method. The main shortcomings are that A cannot adapt to the impact load; the oxygen demand delay pool of B is larger in the front and smaller in the back, and the air supply is uniform, which results in insufficient oxygen in the front section and excess oxygen in the back section.
Adsorption biodegradation process
sequential batch activated sludge process
Circulating activated sludge process
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Aerobic biological treatment
principle
Aerobic biological treatment is a treatment method that uses good microorganisms to degrade organic matter in the presence of molecular oxygen in sewage, making it stable and harmless.
process
Microorganisms use the organic pollutants present in the sewage to bring back some organic matter with these functions. After a series of biochemical reactions, they release energy and finally stabilize as low-energy inorganic matter to achieve harmless requirements for return. Natural environment fire further disposal
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