CIRCOX - Aerobic COD Removal

CIRCOX is a fully closed aerobic system with outstanding performance. It is very suitable for aerobic polishing of anaerobic effluent in urban areas because the bioreactors are relatively small and require little space, whilst the technology has a high volumetric conversion.

In addition to COD removal, CIRCOX nitrifies ammonia and fully removes nitrogen with the special extension of an anoxic zone. In combination with a DAF - this is necessary as solids wash through the system - CIRCOX results in high quality water. Biological sludge slowly grows in high concentrations on biofilms on a carrier. The mixing of water, gas and biomass is very good which leads to high conversation rates.

• Removal of organic compounds (COD), ammonia and sulphides
• Compact design as volumetric loading rates are five times higher than conventional systems
• High conversion rates (over 5 kg of COD/m3 per reactor per day)
• Odourless off-gas and effluent
• Good oxygen transfer rates
• Low biological sludge production

CIRCOX® uses biofilm on a carrier material. This granular sludge is kept in suspension by means of airlifts. They have a high density and excellent settling properties. The granules are retained by a tilted plate settler on top of the reactor.

Companies and municipalities have to remove nutrients from their effluents - such as nitrogen and phosphate - before they can reuse the water. There are also strict discharge limits on the nutrients levels that must be met. Paques has a number of technologies that can deal with these requirements.

Paques’ technologies provide a number of solutions for

• Reject water treatment from sludge digestion
• Post-treatment of anaerobic effluent
• Effluent polishing at (municipal) wastewater treatment plants

Reject water treatment from sludge digestion

If nitrogen limits in the final effluent of the wastewater treatment plant exceed regulations, it is an option to remove ammonia from the reject water from the sludge digestion, rather than to increase the nitrogen removal capacity of the main plant. Typically 15-25% of the total nitrogen load of a municipal wastewater treatment plant derives from the reject water. Paques ANAMMOX® technology removes ammonia in a cost-effective and sustainable manner. Because of a shortcut in the nitrogen cycle, ammonia is removed without the use of an external carbon source such as methanol. This requires 60% less energy compared to conventional treatment.

Post-treatment of anaerobic effluent

Effluent from anaerobic reactors still contains low levels of BOD and possibly ammonia and phosphate. Paques offers several technologies for post-treatment of anaerobic effluents.

The CIRCOX® reactor is a very efficient aerobic system for the treatment of anaerobic effluents. It uses biofilm on a carrier material in an airlift reactor. This compact system is a fully closed aerobic system with outstanding purification performance, as the purified effluent can be directly discharged to surface water. BOD removal can be combined with total nitrogen removal (nitrification/denitrification) in one reactor system.

The combination of PHOSPAQ™ and ANAMMOX® recovers and removes phosphate and ammonia cost effectively and energy efficiently. Contrary to conventional nitrification/denitrification, the ANAMMOX® process does not need a carbon source for denitrification. This leaves the full potential of BOD in the wastewater to be used for the production of biogas. Furthermore, ANAMMOX® requires 60% less energy to operate. PHOSPAQ™ recovers phosphate as struvite that can be used as fertilizer.

Effluent polishing

To raise the effluent quality of (municipal) wastewater treatment plants, a treatment stage can be added to reduce concentrations of nitrogen, BOD, phosphate and TSS. The ASTRASAND® continuous sand filtration technology has proven to be very effective for the final removal of ammonia and nitrate. It also removes phosphates, TSS and BOD effectively. The removal of different components can be combined in a single filter. The ASTRASAND® filtration process removes total nitrogen and phosphate to levels below 2 mg/l and 0.15 mg/l respectively.

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).