Chemical Engineering

Managing Water Pollution

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Courtesy of Chemical Engineering

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Equipment and ideas abound for cleaning up plant wastewater and polluted groundwater

Groundwater, surface water, wastewater, drinking water: it’s all essentially the same stuff. Whichever stage of the water cycle you care to look at, chemical engineers are to be found — either trying to stop water from becoming polluted in the first place, or cleaning up afterwards.

Cleaning up outdoors

Many water purification processes rely on naturally occurring microorganisms to oxidize contaminants. One of the most basic techniques is to allow wastewater to flow through natural or artificial wetlands, where aquatic plants and the bacteria that live among their roots remove organic compounds and heavy metals. Reed beds have been used successfully for small-scale sewage treatment and for industrial wastewater, especially as a polishing step after conventional biological treatment plants. Now a five-year study at Purdue University (West Lafayette, Ind.) has shown that artificial wetlands are also valuable for cleaning up surface water runoff — in this case from residential areas, though the principle could apply equally well to hard surfaces in industrial plants.

Purdue soil microbiologist Ron Turco and colleagues started their research in 1998 on three artificial ponds on a newly renovated golf course on the university campus (top photo). Runoff water from nearby roads and parking lots flowed onto the golf course, through the constructed wetland, and into a recovering natural wetland. Contaminants in the entering water included the herbicide atrazine, plus compounds involving chlorides, nitrates, ammonia, nitrogen, organic carbon, phosphorus, aluminum, iron, potassium and manganese.

Of 17 chemicals present in measurable amounts, 11 were significantly reduced as the water passed through the wetland system. Another outdoor water treatment option, this time chemical in nature, is RegenOx, an oxidizing reagent launched last year by Regenesis (San Clemente, Calif.) The company describes it as a breakthrough technology for in-situ remediation of recalcitrant soil and groundwater pollutants, such as chlorinated solvents, explosives and pesticides.

Standard in-situ oxidants such as potassium permanganate and Fenton’s reagent (a combination of hydrogen peroxide and an iron-based catalyst) are typically either too short-lived or too hazardous for general use, says the company, and may require specialized training, equipment and techniques. RegenOx, in contrast, is a safe, nontoxic formulation that can be injected directly into soil using widely-available equipment. It uses several synergistic chemical processes to destroy a broad range of contaminants, says the company, and remains active for up to one month. Unlike other chemical oxidation technologies, RegenOx has no detrimental effect on groundwater.

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