Traditional wastewater treatment systems are usually designed according to the following treatment processes:
Collection hole - Regulating tank - Anaerobic - Aerotank tank - Sedimentation tank - Disinfection tank
The method using new AAO & MBBR technology is quite preeminent compared to previous technologies. The following table compares the advantages and disadvantages of the AAO & MBBR plan with traditional technology as follows:
1. Process diagram of AAO & MBBR
After primary treatment, wastewater will flow into anaerobic activated sludge tank (Anaerobic Tank), followed by an aerobic microorganism tank (Aerobic), living microorganisms cling to mud particles in the tanks. Here will take place the process of microorganisms oxidize organic chemicals at high speed, after this process, the inorganic and organic substances in the wastewater will decrease gradually, this process is significantly reduced. Total Nitrogen (Total-Nitrogen) and Total Phosphase (Total - Phosphase) content
- The development of the activated sludge method:
The aerobic process of the tank has the effect of handling carbon and nitrogenized organic matter (Nitrification), anaerobic microorganism tank (anaerobic process) Anoxic has denitrification (Denitrification) and phosphate (dephosphorization). ), this technology is suitable for the treatment of many types of waste. The processing is as follows:
NH4 + Oxidation, NO2-, + NO3-
NO2-, NO3- Redution N2 => escape to air
PO43- Microorganism (PO43-) salt => sludge
- Principle of operation
- Preliminary separation of rubbish and mechanical residue:
Using automatic or manual trash rack to separate trash, reduce total suspended sediment (SS) in the treatment process then meet SS≤100-150ppm. For small-scale factories, use manual garbage barriers to reduce investment and management costs. With the size of the barrier: Step 1 (5 cm); Step 2 (1 cm), will remove from solid objects and garbage with a size greater than or equal to 1 cm in wastewater.
- Flow regulator & anaerobic:
Wastewater entering anaerobic conditioning tank combined with anaerobic is "evenly" or "regulated" in terms of both flow and concentration for more stability in properties, degreasing. Air conditioning & anaerobic tanks will be kept in wastewater for 6 hours thanks to our use of enhanced treatment with MBBR media (traditional technology saves 12 hours-24 hours).
The anaerobic process leads to a significant reduction of Hydrocarbons (BOD, COD, about 50 - 55 compared to waste water from upstream wastewater, total phosphorus reduction by 60 ‰ -70 ‰, Sulfide (H2S) insignificant reduction. is about 30 ‰, total nitrogen is almost less reduced and converted to Ammonium (NH4).
A high amount of Nitrogen (Ammonium Nitrogen) will imbalance the nutritional composition (BOD / N / P) and cause poisoning or inhibition of microorganisms. Therefore, the oxidation of NH4 à NO3 and reduction of Nitrogen NO3 à N2 is the indispensable cause to choose the AAO technology mentioned above. In order to reduce the installation area of the equipment and reduce the investment cost, we recommend performing the Anoxic process in the oxic tank.
2. Anoxic-Oxic biological treatment:
Microbial oxidation of hydrocarbon, sulfur and phosphorus compounds (reducing BOD, COD, and H2S metabolism) and carrying out Ammonium Nitrification (NH4). Anoxic-Oxic tank will be kept in wastewater for 4 hours thanks to our use of enhanced treatment with MBBR (traditional technology for 6 hours-12 hours), reducing the construction area by 50 minutes.
Products of this process will be:
Hydrocarbon à CO2 + H2O, significantly reduces COD, BOD
NH4 à NO3 reduces N
H2S à SO4-2
PT à PO4-3 reduces P
Total denitrification through anoxic process (Anoxic), where NO3 is converted to N2 in the absence of oxygen or in the absence of aeration. This is a required process to reduce Nitrogen in wastewater. AO module performs oxidation (Oxic) to reduce BOD, convert NH4 àNO3 and create a recirculation mechanism of liquid NO3 (soluble in wastewater) and a part of activated sludge to Anoxic compartment (lack of gas) to de-Nitrogen . Thus, microbiological technology to treat wastewater to meet the TCVN as mentioned above, requires anaerobic (anaerobic), Oxic (aerobic) process.
After the oxidation process (by aeration) in the Oxic compartment (aerobic) with mobile microbial buffer, activated sludge (ie microorganism growth and activities participating in the process) are kept on ... in the Oxic compartment. These media allow to increase the microbial density up to 8000-14000 g / m3. With this density, the oxidation processes to reduce BOD, COD and NH4 take place much faster. (In the conventional Aeroten activated sludge method, the concentration of microorganisms only reaches 1000-1500 g / m3, in equipment with a fixed microbiological buffer, only 2500-3000 g / m3). Thus, there will be oxygenation space and wastewater treatment capacity with quite wide range of BOD and NH4 parameters (BOD ≤ 400-500 g / m3; NH4 ≤ 40-50 g / m3). Other devices (Aeroten, V69, CN 2000, trickle biofilter) do not achieve the same.
The suspended activated sludge (ie does not adhere to the microbial buffer) will be transferred to the filter compartment. Here a portion of sludge is retained to return to the storage compartment and treat excess sludge; A small part of the sludge is carried by the return pump to the anoxic tank - that is, the tank does not aerate to perform the denitrification process. So from the regulating tank, if we choose a microbiological treatment (biological treatment), the processes will take place as described above. This is the AAO treatment method - a combination of anaerobic - anaerobic - aerobic processes, allowing to minimize, to achieve the most economical of the TCVN and QCVN of pollutants in wastewater.
Pressure filtration, microfiltration: Eliminate suspended impurities, replace bacteria with water disinfectants, reduce building area to 80 and minimize environmental pollution caused by residual disinfectants.
Conclusion of technology selection
AAO treatment principle:
Wastewater will be treated thoroughly if using AAO chain processes.
- Anaerobic: to remove Hydrocarbons, precipitate heavy metals, phosphorus precipitates, active chlorine ...
- Lack of gas: to reduce NO3 to N2 and continue to reduce BOD, COD.
- Aerobic: to convert NH4 to NO3, reduce BOD, COD, Sulfide ...
- Sterilization: by microfiltration or by chemicals - mainly calcium Hypocloride (Ca (OCl) 2) to disinfect pathogenic bacteria ...
Oxic process (aerobic) is performed in the optimal mode (high microbial density and diversity, are attached and participate in the biological treatment process with simulating the suspension of microorganisms through suspended adhesive pads (adhesion media). This allows for a large surface contact between the microorganism and the wastewater, promoting the efficiency of the treatment process.
Air as a source of oxygen for biological processes is fed at a low head (Hs ≤ 2m in water column, compared to other methods, Hs = 4 - 5 m) and therefore requires less energy. . The air is distributed through a fine diffuser or tube, facilitating the efficient dissolution of oxygen into the water.
Advantages of AAO technology:
- Low operating costs.
- The treatment system can be relocated when the plant relocates.
- When expanding, increasing capacity, it is possible to install more modular modules without removing it for replacement.
Currently, this technology is applied in medical stations, hospitals, daily activities ... Cho Ray Hospital inaugurated a centralized wastewater treatment plant with a capacity of 4,000m3 / day and night with construction cost of over 90 billion. Dong, become a pioneer in construction activities Waste water treatment system.
Works used AAO technology Japan, incorporating a variety of microbiological treatment of organic pollutants, ensures a thorough treatment to the highest standards of hospital wastewater, low and stable operating costs, and high degree of automation ...
Cho Ray Hospital is the first hospital to pilot a wastewater treatment system with this technology.