by Liz White, editor
Although recent publicity about the work of Dr Geoff Robson at Manchester University produced headlines about composting sofas, his work was not based on flexible foam, but on a generic polyester-polyol-based PU material.
Nevertheless, assessing the feasibility of large-scale composting of bulky flexible foam PU components is one of his eventual aims, the microbiology lecturer admitted, in a 19 Jan telephone interview.
Robson has recently looked at what happens if polyester polyurethanes are placed in an environment containing fungi and nutrients, following an initial study on what happens when you bury PU in earth – designed to mimic the fate of such parts in landfill, said Robson.
“We were interested in finding out what were the major groups of organisms involved in their degradation and colonisation,” he said.
“The initial results we got ... were that the species involved were predominantly, fungi, rather than bacterial,” said Robson. This is not too surprising because “they [fungi] are fairly dominant in the soil,” he noted.
“We wanted to see if we could enhance the rate of degradation,” and his team assessed two ways of stimulating polymer breakdown: adding nutrients to the soil to try to increase fungal growth and, “to take some of the organisms we had previously isolated as being degraders and add them in to the soil to see if that would enhance the rate of degradation,” Robson said.
“Both of those strategies worked, compared to where we left the soil unamended ... We were able to enhance degradation in this way.” In this work, the team used Impranil, a PU dispersion from Bayer MaterialScience, as a nutrient.
Composting — an aerobic route
The next step for Robson is “to move to composting,” and see “what organisms and what rate of degradation you get in aerobic [open to the air] as opposed to anaerobic [without air] composting.” That work is also going to be done with polyester-based PU, but Robson is carrying out a parallel study with polyether-based PU. “We are a long way from publishing anything but what is quite interesting is that the polyether PU also appears to be being degraded,” he said, noting that this is at a much slower rate in composting.
Finally, the work may compost flexible foam to see what happens.
Robson said, “we know that ultimately PU breaks down to CO2 and water.” And PU products take up a large volume in landfill and “don’t degrade quickly in landfill, which is anaerobic,” he said. UK Councils are now focussing on composting green waste streams aerobically at large-scale facilities, said Robson.
His aim, ultimately, is to see if PU can be broken down in this way: “Could you add it to one of these compost streams? What effect would it have on the end product which is used as compost?” Such questions remain to be answered, Robson indicated.
Robson hopes to develop the approach into a viable technology, which local councils could take up. Waste separation can be tricky, he agreed but said, with, “things like foam you could imagine you could more easily pull those out of the stream.” Also, foam may also degrade more rapidly because of its high surface area. “Aerobic digestion needs air and foam is largely air,” he said, pointing out that, of course, that highlights part of the problem – “foams take up an inordinate amount of space versus compact solid plastics.” So maybe dumping your old sofa at the bottom of the garden will be just the job at some future stage: simply add fungi and see the cushions degrade before your eyes!