Mining Sludge To Neutralize Sewage Wastewater


Making useful products out of waste has been a goal for humans since before alchemists were trying to make gold from lead. U.S. Geological Survey (USGS) engineers have shown up the ancient alchemist by using sewage sorcery to produce clean water and valuable fertilizer using mining waste sludge.

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"As environmental scientists, we kind of hesitate to use this analogy, but it really is like killing two birds with one stone," said Philip Sibrell, lead author of the study, in a press release. "This new technology could reduce or eliminate the need to dispose of acid mine drainage sludge, instead making that same sludge useful in addressing the urgent need to reduce the amount of phosphorus going into aquatic ecosystems; it's a win-win situation."


The USGS technique may help solve a lose-lose situation involving two types of contaminated water.

Water flowing from metal and coal mines can be highly acidic and toxic to life. To deal with this pollution, called acid mine drainage, the liquid is mixed with a chemically basic material, such as limestone. Disposing of the resulting iron-rich sludge is difficult and expensive, but it looks like there’s a way to turn that poison into gold.

USGS chemists discovered that the sludge can be used to absorb excess phosphorus from agricultural and municipal wastewater. Phosphorus is essential to plant growth, but too much of it in a waterway can cause algae blooms, which make the waters inhospitable to other life. For example, West Point Lake near Atlanta had a serious problem with phosphorus overload until treatment facilities began removing the chemical.

Conventional means of removing phosphorus using iron salts are costly because of the low concentrations yet high volumes of phosphorus in wastewater. By using the iron-rich sludge to filter out phosphorus, the USGS has found a way to save money and use waste to clean up other waste.

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The technique allows users to remove the phosphorus from the sludge and re-use it as a fertilizer. Considering that natural phosphorus deposits, such as the phosphate islands of Nauru and Banaba, are under heavy pressure and running out, producing phosphorus from wastewater is like making gold from lead.

"This wonderful result shows the inventive application of some very sophisticated environmental chemistry to create a new life cycle for what otherwise would have been some problematic waste products," said USGS Director Marcia McNutt in a press release. "It sets the bar high for future studies in environmental remediation."


The tailings pond at the Syncrude mine north of Fort McMurray, Alberta, Canada. Tailings ponds in the tar sands are unlined and leach toxic chemicals into the surrounding environment. In addition, thousands of birds a year are killed when they land on the oil covered waste water lakes. The tar sands are the largest industrial project on the planet, and the world's most environmentally destructive. The synthetic oil produced from them is 3 times more carbon intensive than conventional oil supplies. (Ashley Cooper, Corbis)

Dried acid mine drainage residuals that are formed during treatment of the drainage. (Philip Sibrell, USGS)

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