Coli-Tainted Water Purified Using Waste Steel
Contaminants of water bodies such as E. Coli bacteria, negatively impact water quality- this is no shocker. E. coli contamination is indisputably a major water quality impairments of the Big Sioux River according to South Dakota Department of Environment and Natural Resources.
Even testing at several storm water drainage sites at Brookings demonstrated that these bacteria concentrations at drainage sites after a summer storm can be as high as 2,000 colony forming units (cfu) per 100 milliliters (mL).
“Storm water can carry human and animal waste into rivers and streams,” said Peng Dai, a graduate student in the South Dakota State University Department of Civil and Environmental Engineering, who is the lead investigator in a study employing waste steel to remove such contaminants from water bodies.
He explained that a small column testing showed carbon steel chips can get rid of a percentage of Ecoli anywhere between a 85 to 98 percent from simulated storm drain water. The steel chips tested are waste materials gathered from a Sioux Falls machine shop.
Dai later examined steel chips ranging in size from 0.5 to 8 millimeter. He employed them to reduce the amount of bacteria in simulated storm water with E. coli concentrations of low (10 cfu/100 mL) to extremely high (106 cfu/100 mL) levels.
Finally, he evaluated the effect of pH levels 5, 7 and 9, as well as contact times of 5 to 20 minutes. “I controlled the nutrient levels in the simulated storm water so that the E. coli survived but did not multiply,” Dai explained.
He found that the 0.5 to 2 mm chips worked best. In addition, “the longer the contact time, the better. At 20 minutes, the steel chips can remove nearly 99 percent of E. coli,” Dai said.
Although lower pH produced better results, Dai recorded removal rates of at least 90 percent for all pH levels regardless.
Furthermore, in addition to the continuous flow testing, Dai was able to simulate intermittent storm water events in which water circulated for six hours, then the chips were dry for six hours, followed by six hours of flow. “They worked the same—the chips still keep a high efficiency removal rate,” said Dai. His research provided the groundwork for another graduate student who is designing a filter for pilot-scale testing.
“The structure (of the south Brookings site where storm water from a 10-acre residential area drains into a retention pond), which looks like an open-top box, will be positioned at the inlet of the pond, so the storm water drainage passes through the steel media for E. coli removal.” He anticipates having the structure in place this summer.