1 Basic methods of sewage treatment
Physical processing
The commonly used methods for separating suspended solids, floating solids, and large particles in wastewater through physical action include:
Grille filtration: intercepts large particles such as tree branches and plastic impurities to prevent blockage of subsequent equipment.
Precipitation method: using gravity to settle suspended solids to the bottom, such as removing sand particles from a sedimentation tank.
Air flotation method: Injecting bubbles to make oil or fine particles float to the water surface for easy separation.
Filtration and adsorption: Use porous media such as sand and activated carbon to filter small particles.
Chemical treatment
By adding chemical agents to alter the properties of wastewater, pollutants can be precipitated or transformed:
Coagulation precipitation: Add coagulants such as aluminum salts and iron salts to coagulate and precipitate the colloid.
Redox: Using oxidants such as ozone and chlorine to decompose organic matter or reduce heavy metal ions.
Adsorption method: Activated carbon adsorbs organic matter and heavy metals.
Neutralization method: Adjust the pH value and treat acidic or alkaline wastewater.
Biological processing
Utilizing microbial metabolism to decompose organic matter and nutrients, economically and environmentally friendly:
Activated sludge process: Aeration promotes the growth of microorganisms to form sludge, which decomposes organic matter.
Biofilm method: Microorganisms attach to the surface of fillers to form biofilms, purifying wastewater.
Anaerobic digestion: Under anaerobic conditions, organic matter is decomposed to produce gases such as methane.
2 Standard process for sewage treatment
Preprocessing stage
Goal: Remove large impurities and protect subsequent equipment.
Steps:
Grille: intercepts floating objects (such as plastic, tree branches).
Sedimentation tank: for settling heavy particles such as sand and gravel.
Regulating pool: Balance water quality and quantity to ensure stable treatment.
First level processing (physical processing)
Goal: Remove suspended solids and some colloids.
Core facility: Primary sedimentation tank, which uses gravity to settle sludge, and the supernatant enters the next stage.
Secondary treatment (biological treatment)
Objective: To degrade organic matter and improve water quality.
Common processes:
Activated sludge process: Microorganisms decompose organic matter and separate sludge in a secondary sedimentation tank.
Biofilm method: Sewage flows through biofilms, where microorganisms degrade pollutants.
Third level processing (deep processing)
Objective: To further remove recalcitrant organic matter, nitrogen, phosphorus, and pathogens.
Common techniques:
Coagulation precipitation: Removing residual suspended solids.
Activated carbon adsorption: adsorbs trace pollutants.
Ozone oxidation: decomposes recalcitrant organic matter.
Membrane separation: intercepting bacteria, viruses, etc.
Disinfection and discharge
Objective: To eliminate pathogens and ensure safe effluent.
Common methods: chlorination, ultraviolet disinfection, ozone treatment.
Final destination: meet emission standards or reuse for irrigation, industry, etc.
Sludge treatment and disposal
Goal: To avoid secondary pollution and achieve sludge resource utilization.
Process: Concentration, dehydration, incineration, landfill, or land use (such as fertilizer).
3 Technical characteristics and application
Physical processing: suitable for removing large impurities, with low cost, commonly used for pretreatment.
Chemical treatment: For specific pollutants such as heavy metals and oils, the reaction is rapid but may produce by-products.
Biological treatment: suitable for large-scale processing of organic matter, with low operating costs, but requires control of temperature, pH, and other conditions.