Photo: Hans Roggen
Photo: Hans Roggen

The BIOPAQ® Anaerobic Flotation Reactor (AFR) is specifically designed for the treatment of wastewater containing high concentrations of fats, oil and grease (FOG) and other biodegradable compounds such as proteins and starches. The BIOPAQ® AFR will reliably and efficiently convert these organic compounds, typically present in the range from 5-70 g/l of COD present in e.g. the food manufacturing industry. The COD is converted into valuable biogas, while producing a high quality treated effluent.

Biomass retention using the biogas flotation unit prevents biomass loss and permits the decoupling of hydraulic retention time (HRT) from solids retention time (SRT). This allows an SRT >50 days with HRT 's from 1-8 days. At loading rates from 2-8 kg COD/m3/day and a high concentration of well mixed flocculent biomass, the BIOPAQ®AFR combines the high efficiency and compact footprint of a high-rate reactor with the stability and biogas production of an anaerobic CSTR.

Advantages of BIOPAQ®AFR

  • Proven technology, > 10 years operational experience
  • Maximum biogas production from COD, FOG and proteins
  • High flocculent biomass concentration
  • Efficient biomass retention
  • Low HRT, High SRT
  • Loading rates 2-8 kg COD/m3/d
  • Compact footprint
  • No pre-treatment required
  • Low sludge production.
  • Outstanding effluent quality
  • Tailor made solutions
  • Worldwide availability
  • A complete range of standardised concepts
Typical influent characteristics
Characteristic Influent specification
Type of industry Food industry (dairy, vegetable oils, slaughter houses)
COD level 5 - 70 g/l
% of fats maximum 50% of total COD
BOD/COD 0.3 - 0.6
TSS load up to 70 g/l (solids must be largely biodegradable)

Working principle

Industrial wastewater is pumped to the BIOPAQ AFR tank through the Influent Distribution System where it is thoroughly mixed with the reactor's anaerobic biomass to achieve optimal contact between biomass and organic compounds to be degraded.

The AFR reactor is hydraulically mixed by continuously pumping  the reactor contents to the influent distribution system and to the nozzles in the upper layer of the reactor. This exceptionally efficient mixing system ensures maximum conversion of the organic compounds, including fats and proteins, into valuable methane or biogas, which is collected in the head-space of the reactor to be used as green energy in boilers, gas engines or upgraded to pipeline quality Renewable Natural Gas (RNG).

Following anaerobic digestion in the reactor tank, the biomass solids are separated from the treated water through the Dissolved Biogas Flotation (DBF) process. In the DBF process, a portion of the biomass-rich reactor contents is continuously pumped into a high pressure tank where biogas is used to achieve pressurization to 3-5 bar, causing the biogas to go into solution.

This stream is, before being depressurizeed, released in the centre of the Flotation Tank.The small biogas bubbles that are formed after the pressure drop attach to the biomass flocs. As the flow travels towards the tank’s periphery, the flocs float to the surface where they compress into a thick layer that is collected in a trough and pumped back to the AFR reactor. The treated solids-free water below the flotation layer leaves the flotation tank by means of a pump or valve and can be discharged or post treated.