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Pressure to increase factory output, the high cost of trade effluent treatment, water supply availability, power price increases, tighter consent conditions and environmental requirements – these and other factors have stretched companies’ wastewater treatment plants beyond their original design parameters.
New builds or the addition of extra treatment capacity can be expensive solutions. So over the last 30 years BOC (a member of The Linde Group) has become adept at helping industry to extend the life and improve the performance of these overloaded assets. Its success often rests on upgrading them with retrofitted pure oxygen systems such as the Vitox process to enhance aeration.
However, for all pure oxygen-activated sludge plants, one issue remains: optimum performance has always been limited by the rate of sludge settlement and the knock-on costs of building additional tanks.
The BOC solution
BOC technologists have helped create a system that improves biomass separation and oxygenation of the liquor.
Based on BOC’s innovative oxy/air sidestream process Vairox patent (a development of Vitox), the company has developed Axenis. Axenis incorporates UF membrane separation into the Vairox sidestream making best use of the residual energy in the retentate flowing back to the bioreactor.
The process replaces and improves upon the settlement stage as well as increasing the organic load handling capacity, thus converting an overloaded conventional settlement plant into an Oxy/air MBR with increased flow and COD load handling capacity.
Axenis provides a means of oxygen transfer, pH control by air stripping CO2, UF membrane separation of biomass, together with additional mixing energy as the biomass retentate is delivered back into the bioreactor.
This Oxy-Air MBR process can operate at elevated dissolved oxygen levels (3-5mg/l), at slightly elevated temperatures because of better heat retention and optimal, accurately-controlled pH levels. This ensures a robust biological and membrane performance with lower surplus sludge production compared to similar plants operating at lower temperatures.
The business benefits
BOC has a containerised pilot plant which has been used at a number of customer sites to trial Axenis in ‘field’ conditions. This includes a small laboratory to analyse the biological and membrane performance. This full turnkey service can be tailored to the business’s requirements.
A major business benefit is that an existing plant’s performance can be increased and improved without major extensions or new plant build and with little or no extra space requirement.
Most of the existing aeration plant can usually be used, including the bioreactor, some aeration equipment and initial settlement or solids removal systems. The overloaded final settlement tanks become redundant and the process becomes an Oxy/air MBR capable of operating at between 15 to 25 kg/m3 biomass concentration. Typical increase in performance can be up to 100% in both flow and load. The full system is delivered with minimum disruption, and operates on a footprint less than the space occupied by conventional systems.
Crucially, Axenis provides increased wastewater treatment capacity to a higher standard. The treated water quality is suitable for reuse, as well as river and coastal discharges, helping to meet Environment Agency requirements.
This compact, reliable and robust technology reduces the cost of wastewater treatment, delivering savings in trade effluent charges relating to volume, COD and SS, and potential water supply costs based on less use.
“The Axenis system addresses the needs of industry in demonstrating high environmental credentials, particularly regarding carbon and water footprint. The savings it can make are significant in the current climate of austerity and difficult investment conditions.”
- Produces high quality reusable water
- Reduces cost of wastewater treatment
- Avoids the need for additional treatment capacity
- Makes the most of existing assets
- Sustainable process reduces environmental impact