We have a compost in our back garden. It's a lovely, big, steaming thing with a life of its own. Every time the pail fills up with another pile of potato and onion skins, we take it out and dump it on the heap. In the spring, we end up with some fine quality dirt to spread over the vegetable patch. Why am I sharing our garden secrets with you, the readers of BusinessGreen? Because in an ideal world, when the MacBook on which I'm writing this article reaches the end of its useful life, I'd like to dump it out along with the carrot trimmings, and watch it slowly rot. That wouldn't be the type of functional decomposition that computer scientists were used to.

On the surface, it doesn't seem as far fetched as it might sound. We may not see the fully compostible computer – the internal electrics involved put paid to that – but computer manufacturers have been trying to develop biodegradable casings for years now. The task is even harder than it sounds but if it paid off, it could save huge amounts of carbon.

"We've painted ourselves into a corner," admits Robert Tang-Wai, chief technical officer at Reboot Canada, a non-profit organisation that gives donated PCs to needy recipients across the country. The problem, he says, is that it takes lots of carbon emissions to recycle electrical equipment because of the energy-intensive processes involved.

Recycling PCs is a nasty, messy business, but in many ways computers are among some of the easier products to reclaim. They have to be made largely from metal, so they can be grounded, explains Tang-Wai, which explains why the plastics you'll see on a PC are generally cosmetic, clinging to the front or the sides.

The metals in the devices have to be smelted, which is a relatively easy if energy-intensive way to get them out. Different metals have different weights, and once melted they end up floating on top of each other in layers, making the m relatively easy to skim off and reclaim.

I say 'relatively easy' because compared to printers, recycling PCs is a cake walk. "We gained a lot more ground on recycling CRTs than printers in the past couple of years," says Tang-Wai's boss and Reboot Canada executive director Terry Murphy. CRTs are far from easy to recycle, full as they are made of challenging and often hazardous materials such as cadmium, and lead-impregnated glass. "Our guys don't do a lot of printer processing, because it's such a pain to get at the plastics," he continues.

You will not see many metal computer printers around because they'd be too heavy, says Tang-Wai, and the problem is that today's printers use different types of plastic. The internal frame has to be strong and rigid, because if it bends at all it could jam the paper. The exterior case has to be softer, to cope with the everyday knocks and bumps associated with office life.

Plastic not-fantastic
Unfortunately, plastics don't separate like metals when you melt them down. They fuse into a homogeonous, unusable goop, which means that they have to be disassembled more rigourously prior to recycling. This process is made even more labour intensive by manufacturers' tendencies to jam components together as much as possible to reduce costs and printer size, says Tang-Wai.

Biodegradable plastics would be much easier to handle, and companies have invested heavily in developing a new generation of plastics that break down naturally. One of the main avenues of development is in plastics based on corn starch, which because of its organic nature can be made to fall apart and rot more easily. In 2002, Fujitsu developed plant-based plastics in its labs, and made a whole prototype biodegradable plastic PC casing in 2003, explains Scott Ikeda, general manager of the firm's New York office. Search online and you'll see a spate of reports from last summer suggesting that its PC chassis can rot away entirely, but Ikeda sets the record straight. "In 2005, we announced a commercial version, but it was not biodegradable. It was 50 per cent plant-based and 50 per cent conventional oil-based," he says.

Commercial cost was one factor that nixed the idea of a fully compostible version of the casing, which in any case shipped only in Japan, but there were also other, technical concerns. "You have to think about heat resistance, the strength of the casing, and also the manufacturability and ease of moulding the material," Ikeda says.

But even the half-plastic casing didn't find its way into laser printers. One problem with using biodegradable plastics in laser printers is that they generate substantial heat to melt the toner onto the page, which can affect the casing. Who wants a melting printer? And another problem with using 100 per cent biodegradable plastics is that they must still incorporate a fire retardant material to meet regulations, raising the problem that when the plastic breaks down chemical nasties could be left to collect ion the environment.

"HP has been working for years now on a chemical that you can spray on a plastic to meet the rules, but which is inert enough not to harm the environment," says Tang-Wai, who used to work at HP and has had contact with the engineers there. One possible way around this would be to develop a fire retardant chemical that broke down in the presence of another substance, like methanol, leaving the rest of the plant-based plastic to biodegrade. But researchers still seem some way away from cracking this problem. HP (which declined an interview on this subject) presented a prototype biodegradable printer in 2004, but no such model is yet on the market.

Sony making changes
In the meantime, some headway is being made. Sony reportedly sells a Walkman with a corn starch-based casing in Japan, while Fujitsu has developed a flexible plastic based on castor bean oil for use in cables and connectors, but it is not yet a commercial product. Because the commercial casings that Fujitsu has developed are not 100 per cent biodegradable, the company is focusing instead on selling the ethical sourcing benefits of such a product, presenting customers with PC casings containing less plastic derived from fossil fuels.

It's going to be a while before we see compostible laser printers hitting the market, although if the fire retardant problem could be solved, corn starch-based cases for inkjet devices (which produce less heat) might be viable. But the chemical problem, and the extra costs associated with engineering these materials, remain significant obstacles.

In the meantime, we'll have to look to the other end of the supply chain, where the use of recycled materials in the production of consumer devices is being touted as a means of mitigating their environmental effect. Nokia's recently announced 3110 Evolve, for example, will be made of 50 per cent recyclable materials.

Such measures won't mitigate the environmental impact of our various gadgets, but it's a start, at least.