Biotrickling filters beat scrubbers
4 Jun 2003
Chemical engineers at the University of California, Riverside, have developed an environmentally-friendly method of degrading hydrogen sulphide from sewage emissions.
The technique, known as biotrickling filtration, can be carried out by modifying a standard chemical scrubber, research leader Marc Deshusses says in the Proceedings of the National Academy of Sciences.
Biotrickling filters work by passing the waste stream through a bed of material which is coated with a film of bacteria that degrade chemical contaminants. The bacteria are almost 100 per cent efficient at removing H2S once the biofilms become established, and can also degrade other odour chemicals containing sulphur and nitrogen.
'Hydrogen sulphide odours can be treated in biotricking filters at rates similar to those observed in chemical scrubbers,' Deshusses says. 'Biotreatment is cheaper, safer and more environmentally friendly,' he adds. Chemical scrubbers can be expensive to run, as they consume chemicals which can themselves be hazardous or lead to the formation of halomethane pollutants.
The team converted an existing scrubber at the Orange County Sanitation District (OCSD), packing the scrubber vessel with polyurethane foam cubes inoculated with H2S-degrading bacteria, replacing the unit's liquid pump with a smaller model, disconnecting the chemical supply system and modifying the control systems accordingly.
'Continuous operation of the scrubber for more than eight months showed stable performances and robust behaviour for hydrogen sulphide treatment, with pollutant removal performance comparable to that achieved using a chemical scrubber,' the team's paper says. Contact times of just 1.6 seconds were effective, similar to those found in scrubbers.
The costs of running the converted unit were much lower, the team says - the OCSD scrubber would cost some $30 000 per year less to run than a chemical scrubber.
'If one assumes that 25 to 40 per cent of the chemical scrubbers worldwide could be converted to biotrickling filters, it would represent a total market of $1billion-3billion, and would result in net energy and chemical savings of approximately $0.25 billion - 2 billion per year,' Deshusses says.
