Truly, where there’s muck there’s money

IONCE visited Bombay where I was fascinated to see old men dredging for valuables in the sewerage outlet of posh hotels. I later learned that many Indians and Pakistanis make their living from scouring stinking city sewers all over the subcontinent.

In Pakistan’s overcrowded and polluted capital Dhaka, there are about 350 gold bazaars, employing about 20,000 workers. Every morning the workshops are swept out and tiny flecks of gold find their way into the sewage drains. Scores of hopefuls pan the sewers for gold and sell it back to the jewellers.

With gold selling at more than US$1000 an ounce, the Pakistani panners make as much as NZ$20 a day.

These people use the same methods as did the old goldminers in Central Otago, swirling dirty water for flecks of gold in a metal pan. This is the job of the untouchable Dalit caste of people, whose present generation learned its skills from their fathers and grandfathers.

In the Rajasthan city of Bikaner, up to 50 sari-clad women pan for gold in the gutters draining the gold shops. Valuable sites are jealously guarded and passed from generation to generation of gold panners. On a good morning the women can make NZ$10, four times more than an average local labourer.

Inspired by the Indian example, scientists have been looking into the possibility or retrieving gold from modern sewerage systems.

A sewage plant in central Japan recently discovered that sludge in its treatment plant yielded more gold than one of Japan’s best mines. The Tokyo plant collected 2kg of gold from every tonne of sludge ash and they calculated that it could earn the firm 15 million yen (NZ$184,000) a year.

In the United States, most gold finds its way into sewers from mines, electroplating, electronics and jewellery manufacturing, industrial and car exhaust catalysts, but some everyday products like shampoos and detergents may also contain small amounts of precious metals.

America’s ‘‘National Sewage Sludge Repository’’ is stored frozen in 30,000 glass jars at Arizona State University. Scientists searching for chemical pollutants in the repository unexpectedly came across significant quantities of gold, silver, platinum and other metals in sewage collected across the US.

In a recent issue of the journal Environmental Science and Technology, the Arizonans report that during the course of a year, US$13m (NZ$20m) worth of metals, including US$2.6m in gold, could be retrieved from the average US city of 1 million inhabitants.

These figures have been confirmed by the US Geological Survey, which suggests sewage sludge not be classed as a liability but as an asset. They say that apart from the likes of lead, copper, zinc and precious metals, the sewage can be converted to fertiliser, biofuel and biogas.

Daily, Beijing’ huge industrial plants convert 6800 tonnes of sewage into fertilisers and bio-gas. With 1.2 million people, Britain’s Manchester sewage treatment plants produce enough electricity to light 25,000 houses.

The Bill and Melinda Gates Foundation has put millions of dollars into experimental electricity-generating sewage incinerators in Virginia, Ghana, Thailand and India.