Upflow Sludge Blanket Filtration (USBF)

The principal of separation by filtration of suspended solids of biological sludge applied in USBF technology is much more efficient, compared with sedimentation.
This efficiency manifests itself in two major ways, by high separation efficiency which results in higher treated water quality and by higher separation velocity, enabling the reduction of the size of the USBF separator.
The advanced USBF system for wastewater treatment plants employs the technology of low loaded biological activation process with nitrification /denitrification and dephosphorization using unified suspended activated sludge.

The activated sludge separation from mixed liquor is accomplished by up-flow sludge blanket filtration (USBF). All biological treatment and sludge separation processes are provided within the compact integrated biological reactor (IBR). The IBR contains three consecutive biological zones:
A. denitrification zone or anoxic zone
B. nitrification zoneor aeration zone
C. anaerobic zone, or separation zone

Anaerobic and denitrification zones are mixed by mechanical mixers, in the nitrification zone is a fine-bubble aeration system with very high oxygen transfer efficiency providing the oxygen delivery and mixing. The pressure air for aeration is provided by blowers.
The USBF separator is build-in in nitrification zone and provides the outflow of treated water. The separated sludge from USBF separator together with nitrates from nitrification zone is recirculated into the denitrification zone, and the mixed liquor from the end of denitrification zone is recirculated to the anaerobic zone. The wastewater inflows into anaerobic zone where it meets with activated sludge recirculated from the denitrification zone. The phosphorus accumulating organisms in activated sludge take in anaerobic conditions some substances from wastewater and release some accumulated phosphorus.


The mixed liquor from anaerobic zone then flows into denitrification zone, where facultative aerobic organisms in activated sludge are taking the oxygen from recirculated nitrates for oxidation and consumption of some substances from wastewater. By this process, nitrates are converted to gaseous nitrogen, which is released to air, and it thus reduces the concentration of total nitrogen in water. The mixed liquor from denitrification zone then flows to nitrification zone, where proceeds the oxidation and consumption of remaining organic substances from wastewater and ammonium is oxidized by nitrification bacteria to nitrates, which are then recirculated to denitrification as described above. The phosphorus accumulating organisms there due to proceeding phosphorus release take in presence of oxygen surplus of phosphorus and convert it to deposited polyphosphates, which results in biological dephosphorization.

USBF technology principles


First stage: In this stage, the influent was entered the system for primary sedimentation. For this stage, a minimum of 60% decrease in TSS concentration is expected.

Second stage: In this stage, raw influent (after aeration) was entered the special elimination system for organic carbon. Nitrification process could also be accomplished in this stage. The hydraulic retention time can about 2 to 8 h.

Third stage: In this stage, the wastewater was entered the denitrification stage after aeration and nitrification. Nitrate may be converted to nitro-gen gas in this stage.

Fourth stage: In this stage, the wastewater was passed from the separators and was filtered from a sludge blanket.

Fifth stage: In this stage, the pre-settled waste water was passed from the channels which were placed on the separators and then was discharged from the system.

Designing parameters:
• DO-dissolved oxygen
• SRT – sludge retention time
• Alkalinity and acidity
• Hydraulic loading


BOD and COD removal ratio:

• high treatment efficiency, including Biological Nutrient Removal (BNR)
• modular, expandable, compact
• no odor, no noise
• minimal amount of moving parts, gravity flow
• low cost of installation, operation
• fluidized bed filtration
• self-regulating hydraulic flexibility
• Handles highly fluctuating flows.