Peng Dai, a graduate student from South Dakota State University in the US, found that waste steel chips are an inexpensive yet efficient means of removing E. coli bacteria from storm water.

A summer rainstorm does wonders for nature, but the runoff it creates may contain contaminants, such as E. coli. The water can carry animal or human waste into rivers and streams. E. coli contamination is one of the major water quality impairments of, for instance, the Big Sioux River, a river in South Dakota.

Testing showed that carbon steel chips can remove anywhere from 85 to 98 per cent of E. coli from simulated storm drain water. The steel tips used are waste materials gathered from a machine shop.

The chips ranged in size from 0.5 to 8 millimetres, and were tested in water with varying concentrations of E. coli. The research showed that small chips, 0.5 to 2mm, worked best, and the longer the contact time, the better. After 20 minutes, the steel chips removed nearly 99 per cent of E. coli. The chips can be reused.

The research is going to be put immediately into practice. A site in Brookings, South Dakota, where storm water from a residential area drains into a retention pond will get a structure through which the water passes, filled with steel chips for E. coli removal.

Photo: Max Pixel