Purification of polluted water during construction(Se)

Well water contamination problem at an excavation site was resolved on site using a newly synthesized material.

Emergence of a problem

A tunnel construction proceeded in an area contaminated with naturally derived heavy metals. In one location, the detected level of selenium in the well water exceeded the standard.
Contaminated soil countermeasures were implemented previously using seepage control near this construction site; therefore, it was possible that the leachate had leaked out through breaks in the construction.
Therefore, it was necessary to implement immediate countermeasures by setting up a selenium disposal facility at the construction site.

Diagnosis

In this case, the tunnel construction contractor did not contact us directly, but a cooperative company reached out to us for help.
We were later informed that the situation was delicate because the treatment material proposed by the cooperative company did not work properly and it would probably be difficult to conform to the standard simply by increasing the additive amount. We began our study soon after the cooperative company asked us if there was a treatment material that was effective for removing selenium.
Further, we identified the following as a result of the diagnosis:

・It would be impossible to the set up on-site high-spec treatment equipment because of space and budget limitations.
・Therefore, a rudimentary and simple process was required.

Validation

We first tested some of the more promising materials using samples of contaminated water taken from the site. We basically assumed that the treatment of selenium would not be difficult and that it would not take long to select the appropriate material.
However, while various materials were tested, their results were all negative.

Planning

From the test results, we felt it would be necessary to deviate from our past approach of dealing with selenium, and we thus synthesized new materials using a completely different type of reaction.
Because no adsorption materials were effective, we felt that a simple adsorption reaction would probably not be effective, and we decided, right from the beginning of the analysis phase, that the selenium must be in a state that made adsorption difficult.
Therefore, we tested a two-step reaction approach involving not only an adsorption reaction but also a reaction that would allow the selenium to be adsorbed more easily.

Solution to the problem

After adding the newly synthesized material TKS105 to the contaminated water, the concentration fell all at once to the non-detection level, in contrast to the past experience in which the concentration scarcely changed.
In addition, we found that a lower additive amount and shorter time period were required before the effect was observed.
This result was immediately reported to the cooperative company, and on-site tests were started right away.
The effect was also achieved on site without any problems, and treatment could be conducted until the non-detection level was reached.
This treatment method was also adopted because the process of adding the specified amount of material to the contaminated water and stirring the mixture for several minutes was extremely simple and could be immediately implemented at the site.

Comments from the person in charge

This case made us keenly aware that dealing with actual pollutants was not easy.
However, AMEC will continue to proactively deal with such difficult treatment requirements because tackling such a difficult problem gives us the chance to create new materials.