PLANA - Biological wastewater treatment technologies

Why biological treatment?

Biological methods are distinguished by the ability to treat wastewater to extremely low concentrations of pollutants at acceptable energy costs, while not introducing hazardous process products or hard-to-dispose waste into the environment. The result of the biological process — spent and mineralized sludge — is a natural substance that does not harm nature and humans. More than 98% of wastewater treatment plants in the world use biological treatment methods to treat domestic and some industrial effluents.

According to russian technical recommendations and norms, the main method for wastewater treatment from biodegradable organic pollutants, nitrogen and phosphorus compounds is the biological method. This provides for preliminary mechanical treatment of wastewater, biological nitri-denitrification in aerotanks, as well as biological or biological-reagent removal of phosphorus. Additional treatment of wastewater from the remaining biogenic elements, nitrogen and phosphorus compounds can also be carried out by the biological method, supplemented by clarification and filtration.

Biological treatment consists in the removal of organic and biogenic elements by activated sludge biocenosis. Biochemical processes in biological treatment technology are based on the development of either a suspended floating biocenosis or attached biocenoses on special polymer beds with a high specific surface area. During biological treatment, successive processes of deep mineralization of organic substances occur in the regime from high loads in the first stages to low loads in the last — nitrification, denitrification, dephosphatization of treated wastewater. Active or able to assimilate many other pollutants, adapting to runoff during growth. At the end of the process, the sludge-water mixture goes through the stage of separation into clarified water and spent activated sludge.

MBBR: Thin film biocoenosis on mobile floating media

When using MBBR (Moving Bed Bio Reactor) technology, biocenosis grows on the walls and in the pores of mobile carrier having the following features:

High mobility in the aquatic environment
Developed protected surface (300…3000 m2/m3)
Restriction of biocenosis film thickness (0.5..1.2 mm)
Good supply of oxygen and nutrition
Self-cleaning from fouling while driving

Biocoenosis film on MBBR_carrier A film of biocenosis on an MBBR carrier.

SBR: Suspended Activated Sludge in a Batch Bioreactor Process

For the SBR (Sequencing Batch Reactor) technology, the stages of biological treatment proceed sequentially and cyclically in one tank:

Loading, biosorption
Loading, mixing
Loading, aeration
Aeration
Settling
Decantation (discharge of clarified water)
Excess sludge extraction
Resting state

Cycle duration 6, 8 or 12 hours. With two or more SBR reactors, the start of the cycles is shifted in time in each of them, ensuring the continuity of the purification process in the WWTP.

Benefits of the MBBR process

Compact biological treatment lines.
Wide load range.
Possibility of application at «poor» drains.
Toxic shock resistance.
Reducing the amount of sediment.

Benefits of the SBR process

The ability to «adjust» to changing loads by changing the duration of the phases in the cycle.
No media and downloads.
Ease of maintenance and operation.
High degree of automation.

MBR: Suspended activated sludge + water filtration through membranes

MBR (Membrane Bio Reactor) technology involves the use of polymeric ultra- or microfiltration membrane blocks for effective separation of the silt-water mixture. In the case of domestic wastewater treatment, the MBR section is both an aerobic bioreactor and a settling filter. The final purification of water takes place on the same membranes. The use of lamellar membranes with a self-healing surface ensures a long service life of the membrane unit (several years).

Advantages of MBR technology

Sustainable achievement of high cleaning rates.
Complete retention of all suspended solids and microorganisms.
Low sensitivity to fluctuations in flow and quality of wastewater.
Reducing the area of treatment facilities.
Decreased sediment volume.
Possibility of reconstruction of old WWTPs based on MBR technology.