Too big, unreliable, unable to cope with varying loads, only capable of treating water-soluble VOCs - just a few of the common misconceptions surrounding biological VOC treatment. The truth is, biotechnology has been used to treat odourous off-gases for years. More recently, however, the technology has moved on - and is continuing to do so - to the extent that biotechnology is now recognised as a genuine and reliable treatment for VOC-contaminated off-gases. Richard Ambrose and Dr Bruno Erasin, of Air Services, IBS Viridian, explain.
A project, partly co-funded by the BOC Foundation for the Environment and the Department of Trade and Industry (DTI), under the Biotechnology Means Business (BMB) initiative, was proposed and managed by IBS Viridian Ltd. The project was aimed at solvent-using companies, in order to identify a biotechnological solution to treat VOC-contaminated off-gases. With technical support from the SATRA Technology Centre and engineering backup from Automet Filtration (now Camfil Ltd) IBS Viridian set about demonstrating the benefits of biotechnology for the treatment of VOCs.
Following prototype trials, an 8m3 demonstration system was constructed at the Wellingborough site of R Griggs and Co - manufacturers of Dr Martens boots. The unit was designed to treat a combination of soluble solvents (acetone and methyl ethyl ketone) and insoluble compounds (toluene and hexane) up to maximum concentrations of 0.4 mg Carbon/m3.
The start-up phase of the BIOVOX demonstration unit required a biocommissioning period in which a specially selected blend of naturally occurring bacteria was introduced into the main reactor support media. The stock cultures were used from the initial laboratory trial and grown for a period of time on a mixture of the known solvents to be treated. The enriched, mixed natural bacterial cultures (consortia) were also supplied with nutrients to ensure that the ideal conditions for the micro-organisms, for supporting rapid biodegradation of the solvents, was achieved. The nutrients were dosed into the reactor by an automated dosing system on a daily basis, according to expected carbon loads. The VOC concentrations of the inlet and outlet BIOVOX plant were monitored using FID and GC analysis. Acetone and methyl ethyl ketone were almost entirely removed (>99%) and toluene removal stabilised above 90% after a prolonged commissioning stage. Over a 168 day period the outlet concentrations of VOCs remained well below the target levels of 50mg C/m3. Peak load tests were also undertaken with other commonly used solvents with concentrations up to 2.5g C/m3 at the inlet. Tests found that the process could easily treat variable loads. Ethyl acetate and isopropanol were successfully removed to levels well below 50mg C/m3.
The BIOVOX demonstration unit successfully confirmed that biological treatment processes for the control and abatement of VOCs is technically feasible and is capable of high removal efficiencies. A comparison of capital and operating costs between this innovative biological system and a catalytic incinerator, treating 9,000m3/h at a mean VOC concentration of 0.4g C/m3 found CAPEX and OPEX cost savings of between 30% and 60% respectively. The process demonstrated at the footwear manufacturing plant has shown that biological systems, when controlled and implemented within manufacturing industry, can have both cost and process benefits.
IBS Viridian Ltd have now commissioned two full-scale BIOVOX processes and are currently constructing two others. The system is attracting enormous attention from a number of industrial sectors including printing, painting, furniture coating, laminating and adhesive processes.