Low Rate Anaerobic Digesters

UEM has installed more than 60 Low Rate Anaerobic Digester systems for various industries such as distilleries, breweries, pharmaceuticals, pulp & paper, citric acid, yeast, chemicals, etc.

These digesters provide a large volume (hydraulic retention time: 15- 45 days), offering better process stability with consistent performance and biogas generation. BOD reductions of 80%- 95% and COD reductions 60% - 80% can be achieved, depending on the nature of the wastewater. These digesters can be constructed in a rectangular or circular above ground or below ground construction. Under an anaerobic environment, organic pollutants (BOD, COD, etc.) get reduced and biogas is generated through a series of biomethanisation reactions. The large quantities of biogas generated have been used to replace fuel in boilers and to generate electricity in generators, offering quick returns to our clients.

Hybrid Anaerobic Digesters

UEM has installed more than 20 Hybrid Anaerobic Digesters for various industries such as petrochemicals, breweries, paper, soaps & cosmetics, food, etc. The Hybrid Digester is a combination of USB (Upflow Sludge Blanket) and UFF (Upflow Filter - an open design plastic media offering high specific surface area and maximum void space). The bottom portion of Hybrid Digester is maintained with acclimatized sludge bed. The effluent is first passed through this sludge bed and is intimately mixed with highly active microorganisms in the sludge bed. As a result, the effluent receives a significant portion of its treatment in the sludge bed zone itself. The other portion of the Hybrid Digester is filled with fixed media (Open Design Plastic Media) so that the effluent, after passing through the sludge blanket bed, passes through this media where the removal of largely soluble organics takes place. It also provides critical retention of the biological solids in the reactor. In short, Hybrid Digesters have been designed to achieve BOD and COD (organic pollutants) reductions of up to 90% and 70% respectively and have the advantage of requiring less volume. Additionally, the biogas generated has been used to replace fuel in boilers, reducing operating costs and adding value for our clients.

Other advantages incude:

The UFF zone acts as a very large clarifier and arrests the bio solids and active bio sludge leaving the digester. The media surfaces also allow growth of additional biomass inventory which increases the treatment efficiency.
Unlike in a UASB, a granular sludge bed is not necessary for a Hybrid Digester System. In a Hybrid Digester, even a flocculant sludge performs satisfactorily.
A Hybrid Digester provides consistent performance due to a higher biomass inventory in the UASB zone as well as biomass growth on the surface of the fill media.
The high biomass inventory also results in a longer SRT (Solids Retention Time). Longer SRTs result in better treatment and lower waste sludge production.
The longer SRT allows the Hybrid Digester System to handle higher levels of shock load and influent solids. This provides a more stable operation.
The digester roof is made of imported geo-membrane which has anti-corrosion properties and a long life. The biogas, if required, can be stored below the floating roof and thus a separate gas holder is not required.

A variation of this technology is a Twin Hybrid Digester System. Under the normal operating conditions of this system, two Hybrid Digesters receive the flow in series. The design also allows for parallel operation for start-up.

This system can also have the provision to reverse the flow once the system matures to further improve its overall performance. The basic explanation for the improved performance with this type of system (once it matures) is that the biological solids levels in the lag (second) digester are always greater than it would be at the existing operating conditions. This elevated level of biosolids permits the lag digester to remove soluble organics to concentrations less than the normal equilibrium levels.