- Model UBOX - Anaerobic and Aerobic COD Removal



The BIOPAQ UBOX, which was designed by Paques, combines high efficient biological sewage treatment with biogas purification. This leads to low operational costs, a small footprint and zero odour emission. The system provides a four step sewage treatment: anaerobic treatment, supplementary aerobic treatment, secondary clarification and biogas purification.

The BIOPAQ UBOX modular design is suitable for capacities of 5, 10, 15, 20, 30 and 40 thousand population equivalent (PE). By combining these different modules it is possible to treat larger PE’s. Since implementation in progressive steps is an option, idle capacity is avoided. The BIOPAQ® UBOX is equipped with an exclusive anti-clogging pressurized feeding system. This ensures uniform distribution and an efficient anaerobic treatment of the wastewater, avoiding sludge thickening.

  • Small footprint, compact construction
  • No moving parts
  • Low energy consumption for aeration of the residual biodegradable matter
  • Possibility of energy reuse from biogas production
  • Low sludge production
  • No odour emissions
  • Low maintenance requirements

The BIOPAQ®UBOX bioreactor has two sections: an anaerobic lower section and an aerobic upper section. The wastewater is pre-treated anaerobically, using anaerobic sludge in the bottom part. Biogas is produced and separated in the three phase proprietary separators. The separator modules also effectively keep the anaerobic sludge in the lower part of the reactor.

In the upper part of the reactor air is introduced to enhance aerobic degradation of the residual COD. An efficient separator in the upper part of the tank allows for the discharge of settled effluent while keeping the activated sludge within the reactor, at the same time avoiding air bubbles to interfere with the settling process.

In anaerobic treatment, bacteria convert organic compounds (COD) to biogas in an environment without oxygen. Not only do the bacteria remove contaminating compounds from the effluent, thereby reducing discharge costs, they produce green energy at the same time.

Organic components (COD) are converted to CH4 + CO2 + BIOMASS

The generation of biogas from agricultural waste, municipal slurries and wastewater has been gaining interest from scientists, industry and municipalities interest is rapidly growing now, since renewable energy sources are favoured to limit global warming. Biogas consists mainly of methane and some carbon dioxide. It can be utilized as a fuel for power generation, steam production and drying processes.

New technologies

Paques started the design and supply of installations for COD conversion into biogas in the early nineteen eighties with the application of the BIOPAQ®UASB (Upflow Anaerobic Sludge Blanket) reactor. This was an invention of Professor Gatze Lettinga from Wageningen Agricultural University in the Netherlands. The reactor was scaled up from pilot to full scale and deployed for many types of wastewater.

Paques quickly became global market leader in this field of anaerobic treatment. Its position was further strengthened by the development of a new type of anaerobic reactor called the BIOPAQ®IC (Internal Circulation) reactor. Both the BIOPAQ®UASB reactor and the BIOPAQ®IC reactor are used for wastewater treatment with a wide range of carbohydrate concentrations, i.e. from 1,000 to 20,000 mg COD/l.

Within this range the bacteria form compact granules with very good settling characteristics. Above this range the bacteria tend to grow in a more flocky structure and for this Paques developed the BIOPAQ®UASB+ reactor. For more concentrated wastewaters containing fine organic particles and/or fat and proteins, Paques designed the BIOPAQ®AFR (Anaerobic Flotation Reactor).

For decentralised sewage treatment in warmer climates, Paques has developed the very compact BIOPAQ®UBOX, which combines a first stage anaerobic treatment with a second stage aerobic treatment.

Paques’ reactors are found in all kind of industries and applications, such as Food, Pulp and Paper, Beer and Beverages, Distilleries and Chemical and Pharmaceutical.

In an aerobic treatment system, air is injected which is used by aerobic bacteria to convert BOD to carbon dioxide and water.

Organic components + O2 are converted to H2O + CO2 + BIOMASS

Primary treatment for solids removal and anaerobic treatment are usually followed by aerobic treatment.

Paques offers different solutions the aerobic post treatment, such as

  • Activated sludge for surface water discharge quality
  • Flash aeration for oxidation of odorous compounds
  • CIRCOX® airlift technology for situations with a very limited space available
  • BIOPAQ®UBOX for the compact combination of anaerobic and aerobic treatment

Activated sludge system

The activated sludge system consists of an aeration stage - and an anoxic/oxic compartment if nitrogen has to be removed - and secondary sedimentation with sludge return. Options are first quality surface aeration, fine bubble aeration and jet aeration.

After secondary clarification, further treatment can consist of filtration, de-nitrification (for achieving very low nitrogen concentrations) or effluent softening. For nitrogen removal at higher concentrations and filtration, see ANAMMOX® and ASTRASAND®.

Flash aeration

When treated water will be reused or if water will pass through a sewer, flash aeration is often required. The main reason is odour control, but it will also remove some additional COD, especially when the aeration tank is followed by solids removal such as DAF (Dissolved Air Flotation).

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