Promising bacteria

Microorganisms in the bioreact RECYCLERS turn old cans and bottles into new ones and old newspapers into today's daily. Now it is the turn of waste tyres in the country? Robert Romine, working at Rouse Rubber Industries, Mississippi, us, has introduced an eco-friendly technique for processing old tyres by using microorganisms (Environmental Health Perspectives, Vol 104, No 11).

Tyres make ideal breeding places for disease carriers like rats and mosquitoes and if burnt, release hazardous materials including soot, benzene, sulphur, heavy metals and petroleum residues. As such number of nations have already implemented landfill bans on scrap tyres.

Romine, initially studied five different bacteria for their effect on ground tyre rubber (gtr).He conducted a seven-day experiment, during which the bacteria were fed on gtr and the biodesulphurisation -- biological removal of sulphur (by microorganisms in this case) -- of the gtr was monitored. By analysing the concentration of sulphate in gtr, it was seen that the Sulfolobus bacteria were the most effective in breaking down the gtr, 13.4 per cent of the sulphur within seven days besides Thiobacillus ferooxidans and T thiooxidans. Romine focussed on Sulfolobus because of its choice of food -- sulphur. He observed that when Sulfolobus bacteria were mixed with finely ground tyre rubber, the bacteria progressively oxidised it, thereby leaching sulphur off the surface from the rubber molecules. Roughly 48 hours after the reaction begins, what is left, according to Romine, is a biodesulphurised substance that can be mixed with virgin rubber in a ratio of about 15 per cent of the former to 85 per cent of the latter, and turned back into usable material for tyres with no loss in desirable performance characteristics. The only byproduct is a mixture of water and dormant microorganisms which die when their cell walls collapse during the wastewater treatment process. It produces nothing that is environmentally harmful. It is much safer and economical than traditional methods, which use toxic chemicals and produce a whole series of harmful byproducts that have to be handled carefully.

Romine says that tyre grinding plants are the ideal places for setting up a bioreactor for tyre processing because these generate a lot of energy in the form of heat which could be used to run the bioreactor, thus further reducing the cost of processing. Romnie has set up a bioreactor pilot project to demonstrate his biodesulphurisation process at Rouse Rubber.

What is so exciting about this environment-friendly concept, according to Romine, is that it involves taking a closer look at the microorganisms around us, how they live and what can they do. "It's like finding cures for cancer in rainforest plants; we have no idea what's out there until we begin to take a close and serious look," he says.