Removing Microbes From Water

By Canter, Neil

Water is a very precious resource that we use every day in industrial and personal applications. As the supply of water declines, there is more need for ensuring that the water quality ensures it is safe to use. One lubricant application that uses water extensively is metalworking fluids. In fact, water is the largest component in most metalworking fluids. The water utilized is taken usually from a municipal source or well.

We take for granted that water coming out of the tap in an industrial facility is relatively pure. But in fact this is not the case. Water can contain a number of different metal cations and anions that can adversely affect the performance of a metalworking fluid.

One other factor is that water can contain microbes such as bacteria, fungi and viruses. The first two in particular are well known for their ability to grow in metalworking fluid systems, causing the fluid to fall apart. They can adversely affect not only fluid performance but also worker health and safety.

Microbes are present not only in water used for industrial applications but in drinking water and wastewater. Yan Jin, professor of environmental soil physics at the University of Delaware in Newark, Del., says, “In general, there is a greater concern for microbial contamination in surface water (from a lake, river or stream) than in ground water (located beneath the ground in the soil).”

The greatest source of microbial contamination is in wastewater, according to Jin. This problem can lead to closures of beaches along lakes or oceans that occur occasionally during the summer due to sewer overflows following wet-weather events, for example.

The dominant technology used to disinfect water in the United States is chlorine. While chlorine is effective against bacteria. It does not work as well on other organisms such as viruses and protozoa. In addition, chlorine can generate toxic byproducts including trihalomethanes and halogenated acetic acids during the disinfection process. An alternative that can be more effective against all organisms and yet not produce hazardous byproducts would be welcome.

Zerovalent iron

Jin, in collaboration with Pei Chiu, associate professor of civil and environmental engineering at the University of Delaware, has determined that zerovalent iron can be an effective technology to remove microbes from water. Chiu says, “Zerovalent iron is elemental iron, which has been used in the past to treat other contaminants in water such as heavy metals, halogenated solvents and pesticides.”

The mechanism that iron uses to treat contaminants in water is a red-ox (reduction, oxidation) process. Iron is oxidized to slowly generate corrosion products. The electrons released reduce the chemical contaminants.

For the first time, the two researchers found that zerovalent iron is also effective at removing viruses and the bacterium, E. coli 0157:H7 from water. Jin says, “We have determined that zerovalent iron is very effective at removing viruses in particular but can also deal with bacteria. Our focus has been on viruses because they are more difficult to treat.”

Influent solutions containing the microbes were pumped through a column containing a mixture of sand and zerovalent iron. This column acts in a similar fashion to a filter.

The researchers determined not just whether the microbes were removed but also the rate of removal. Figure 3 shows two of the columns used on a platform above a pump.

Zerovalent iron has potential as an antimicrobial pesticide in a metalworking fluid system. One concern is the possibility that iron corrosion products such as ferric and ferrous oxides might end up going into the metalworking fluid system, which could lead to a problem.

Metalworking fluids operate under alkaline conditions at a pH of approximately 9. Chiu comments, “In water that exhibits an alkaline pH, the chances of iron corrosion products entering a metalworking fluid system are minimal. Typically, zerovalent iron will be converted to iron (II), which, when formed, adsorbs onto the iron surface and does not leach into the filtrate leaving the filter.”

There is a good deal of flexibility in how the zerovalent iron can be used in a particular application. Chiu says, “There are different types of zerovalent iron which are available. They differ in their particle size and composition and can be incorporated into different types of filter media with different porosities.”

Wastewater treatment

The researchers also have evaluated the potential for zerovalent iron to treat wastewater. Work has been focused on determining the impact of water chemistry parameters such as pH, dissolved oxygen and organic matter content on the effectiveness of zerovalent iron.

Jin says, “Our initial work on pH shows that zerovalent iron is effective on water with values ranging from 5 to 9. We have also determined that zerovalent iron is effective in the presence of anions such as nitrate, chloride and sulfate.”

Further work is ongoing to determine the impact of other components present in wastewater. One other aspect of this work is to determine the actual mechanism that zerovalent iron used to remove microbials. Jin adds, “We do not know yet all the processes/ mechanisms that make zerovalent iron so effective. A better understanding of the mechanisms will enable us to figure out the long-term stability of zerovalent iron and whether there are any adverse byproducts that could affect water quality.”

Further details on the experiments run to show the effectiveness of zerovalent iron are found in a paper published in 2005.1 The researchers are exploring a number of commercial opportunities for this technology.

Further information can be obtained by contacting Bruce Morrissey, director of technology for the University of Delaware at brucem@udel.edu.

The two researchers found that zerovalent iron is also effective at removing viruses and the bacterium, E. coli 0157:H7 from water.

Zerovalent iron can be an effective technology to remove microbes from water.

Reference

1. You, Y., Han, J., Chiu, P. and Jin, Y. (2005), “Removal and Inactivation of Waterborne Viruses Using Zerovalent Iron,” Environmental Science & Technology, 39 (23), pp. 9263-9269.

Neil Canter heads his own consulting company, Chemical Solutions in Willow Grove, Pa. Ideas for Tech Beat items can be sent to him at neilcanter@comcast.net.

Copyright Society of Tribologists and Lubrication Engineers Apr 2008

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