The use of biotechnology is becoming widely recognised as an abatement strategy which endorses the concept of “best available technology not entailing excessive cost” (BATNEEC), according to Sutcliffe Croftshaw Ltd.

The company has developed biological systems for the treatment of a wider range of gaseous phase VOC emissions, including a proportion of those previously considered suited only to incineration. Sutcliffe Croftshaw says that these systems can offer lower capital and operating costs compared to other technologies with the advantage of a small overall footprint and low maintenance requirement.

Operation of the SC BIOSCRUBBER

The systems use an inert polymer support to deploy a high density specialist biomass effecting rapid VOC removal from industrial and manufacturing process and stack emissions. Most industrial processes which utilise solvents can benefit from the system (including chemicals manufacturing and processing, pharmaceuticals, printing and packaging, textiles etc), says Sutcliffe Croftshaw.

Containment compounds are contacted with selected microbes either as a single organism or as consortia which have a high degradation efficiency with respect to a wide range of VOC and odour forming compounds. These compounds are oxidised to carbon dioxide and water by the action of microbial enzymes (biological catalysts) which allow the microbes to use the contaminants as a source of energy for cell growth.

In SC Biosystems, VOC-laden air from the process exhaust stream is fed to the system where the solvent-laden air is then either humidified or the solvents are scrubbed to the liquid phase before being contacted with a selected, high efficiency biomass which carries out the VOC degradation to carbon dioxide and water.

Low level emissions (of several hundred milligrams per cubic metre) and low solubility solvents, such as toluene and styrene, are treated using the SC BIOREACTORª while variable and higher concentration emissions of more water-soluble solvents (up to several grams per cubic metre) are dealt with by the SC BIOSCRUBBER.

Variable VOC emissions treated

In one example, the SC BIOSCRUBBER was installed on a coating process to handle the solvent emissions from a number of sources within the factory. A total of 30,000m3/hr of exhaust air containing variable amounts of solvents from the coating inks have to be treated. The system operates by first stripping the solvents from the exhaust gas into water using tow fluidised bed wet scrubbers. This process ensures that the exhaust air from the scrubbers meets legislative requirements while the variable VOC emission is converted to a more controlled flow of solvent-contaminated water. The water is transferred via buffer tanks to a Biotrickling Filter where the solvents are oxidised to water and carbon dioxide. Biological degradation of the solvents takes place at ambient temperature, the fuel for the process being the solvent itself.

The process is stated to provide the ideal mechanism for buffering variable solvent loads, allowing controlled destruction of the VOC regardless of the specific production schedule. Operating costs for the system are minimal in comparison with other technologies, as the major part of the running cost for the system is the power required to push the air through the scrubbers, states Sutcliffe Croftshaw. The company adds that it has ensured that this low operating cost is further reduced by providing for the shut-down of one of the two scrubbers when production levels decrease and airflow drops below 15,000m3/hr.

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