Where there's muck...

Biggs, managing director of waste research and sourcing company Akristos, says it's nothing to be uneasy about. "It's just like sand," he says disarmingly of the sewage ash – a sterile, odourless, red-coloured powder – that he is testing as a raw material in a range of ecobricks that will appear this spring.

While some will shudder at the thought of bricks made of sewage, lots of us already drink what was once somebody else's urine without too many qualms. The water that comes out of a London tap has on average already been through seven other people before it passes the lips of the eighth.

Ash in the pan
Like recycled tapwater, sewage ash is safe. Incineration kills off the pathogens and locks away any heavy metals from industrial effluent within the beads of glass produced by the intense heat. Few people will ever touch the material in its powder form. The first manual handling at most automated brick factories occurs only after a brick has been fired, and 1000 degrees C should overcome most squeamishness. Andrew Gunn of research consultancy MWH says it poses no health risk as long as the precautions that apply to the handling of all aggregates are followed.

Nor is making bricks from human sewage a particularly novel idea. It was first attempted over a century ago, and brickmakers in Japan are currently producing bricks made entirely from incinerated sewage. Japan, though, faces more urgent sewage disposal problems than Britain.

What's more it works. A recent study by CIRIA, called The Use of Sewage Sludge in Construction, reported that bricks containing up to 10% by volume of sewage ash passed British brick standards for compressive strength, water absorption and durability. And Andy Smith of ceramic research and testing body Ceram says British brickmakers have successfully substituted 30% of the aggregate in bricks with ash.

Using more than this, as in Japan, bumps up the costs. Too much ash in the mix can lead to discolouration, or concentrations of soluble salts that rise to the surface of the brick to form a scum. Counteracting the problem means adding expensive chemicals to the brick mix. "There's a solution for every problem, but it costs money," says Smith.

Looks good on paper
Biggs recognises the problem. "I don't want ecobricks to be like organic veg," he says. "A premium is not realistic." So while up to half of the raw materials that go into ecobricks will be waste products, Biggs will also incorporate water treatment residues (see factfile below) and waste from the ceramic industry as well as sewage ash.

He also sees the production advantages rather than the disadvantages. "We don't envisage any problems with using sewage ash," he says. "They make clays less plastic, which helps getting them out of the moulds. The trials have been successful so we may use ash in the launch ecobricks this spring."

The final decision on the exact constituents of ecobricks will depend on the results of those trials, but Biggs expects to incorporate sewage ash at some stage. After all, he already has a market. United Utilities, the water and electricity company in northwest England that provides him with the ash for free, has a seven-year building programme and is keen to buy back its waste product in the form of paving and engineering bricks.

Construction is a market well worth cultivating for water companies hedged in by restrictions on how they dispose of waste. Since 1998 there has been a ban on dumping sewage sludge at sea, higher standards of water purity have resulted in the production of more residues, and there is a £2 per tonne tax on landfill, which is the usual disposal route in the UK.

The bottom line
Not all water companies regard construction as a viable disposal mechanism, though. Severn Trent, for example, tried ash in brickmaking a few years ago but gave up because it couldn't control the colour of the bricks.

Even a free supply of ash may prove a costly proposition for brickmakers, who tend to locate their factories where the clay is rather than the conurbations that play host to the UK's eight sewage incinerators. Currently it's uneconomic to haul sewage ash any further than 30 miles from an incinerator. It's not a problem for Biggs: the Brick Business is making ecobricks for him at a factory close to United Utilities' incinerator.

Ultimately, transport costs may be trivial compared with the image problem. There's a stigma attached to human sewage that all the sustainability Brownie points in the world may not overcome. John Renshaw, quality manager at the Brick Business, recalls making a brick out of sewage ash 15 years ago. "It was heated to 750 degrees C – nothing will survive that," he says. "I still wore gloves to handle it, though."