The following is a detailed description of the "coarse screen + fine screen + sedimentation tank + hydrolysis and acidification tank + A2/O + secondary sedimentation tank + advanced treatment + ultraviolet disinfection" combined process designed for treating 300 tons of domestic sewage per day:
1. Coarse Screen
Function: Remove the larger suspended or floating substances in the wastewater, protecting the subsequent treatment equipment.
Principle: The wastewater passes through a set of inclined metal grids. Large debris is retained and can be removed either mechanically or manually.
2. Fine mesh grille
Function: Further remove smaller suspended particles to prevent blockage of subsequent pumps and pipes.
Principle: With a smaller gap, a rotating or stepped grid can be used to intercept fine impurities.
3. Sand settling tank
Function: Remove the relatively dense inorganic particles in the wastewater to prevent equipment wear or pipeline blockage.
Principle: By reducing the flow rate or centrifugal force, the sand particles will settle under the influence of gravity, while the organic matter will be carried along with the water and enter the next unit.
4. Hydrolysis and Acidification Tank
Function: Decompose the refractory macromolecular organic substances into small molecular organic substances, enhance the biodegradability of wastewater, and create conditions for subsequent nitrogen and phosphorus removal.
Principle: Under anaerobic conditions, hydrolytic bacteria and acidifying bacteria break down proteins, fats, polysaccharides, etc. into small molecules such as fatty acids and alcohols, without producing methane.
5. Anaerobic-Anoxic-Oxic process
Function: Simultaneously remove organic matter (COD/BOD), nitrogen and phosphorus.
Anaerobic section: The polyphosphate bacteria release phosphorus, and at the same time, the hydrolysis and acidification products are further degraded.
Anoxic section: Denitrifying bacteria utilize the carbon source in the wastewater to reduce nitrate (NO₃⁻) to nitrogen gas (N₂), thereby achieving nitrogen removal.
Aerobic section (Oxic): Nitrogen-oxidizing bacteria convert ammonia nitrogen (NH₄⁺) into nitrate (NO₃⁻); Polyphosphate-accumulating organisms absorb excessive phosphorus; Heterotrophic bacteria degrade organic matter.
6. Secondary Sedimentation Tank
Function: To separate the activated sludge from the purified wastewater, achieving the separation of sludge and water.
Principle: Utilizing gravitational sedimentation (usually in a radial flow or vertical flow configuration), the sludge settles at the bottom, and the supernatant flows over to the advanced treatment unit.
7. In-depth processing
Filtering (sand filtration, activated carbon filtration): Remove residual SS and colloidal substances.
Coagulation and sedimentation: Adding PAC/PAM to enhance the removal of phosphorus and colloids.
Membrane treatment (MBR/ultrafiltration): Further retains microorganisms and particulate matter.
Principle: Physical interception or chemical flocculation are employed to ensure that the effluent's SS and TP meet the standards.
8. Ultraviolet disinfection
Function: To kill pathogenic microorganisms (such as Escherichia coli, viruses, etc.) and ensure the hygiene and safety of the discharged water.
Principle: Ultraviolet light damages the DNA/RNA structure of microorganisms, without the need to add chemical agents.
