A biological filter for the abatement of chromium in the water intended for human consumption

The discharge of heavy metals into the environment is a serious issue that truly affects the quality of water. Moreover, the effects of the ingestion of hexavalent chromium (CRVl) on human health are well-known. Sheep wool is a precious material with unique properties, traditionally and mainly used in the clothing industry, in which only high quality wool is felted; the majority of the non-treated wool becomes waste, which implies huge disposal costs.

Some studies have shown that keratin has the ability to absorb heavy metals, particularly chromium. Furthermore, the Ministerial Decree of 14th Novemeber 2016 introduced a limit value of 10ug/L concerning the concentration of CrVl in potable water.

The purpose of this study is to develop a wool-based biological filter for the adsorption of total chromium and hexavalent chromium present in water intended for human consumption.

Laboratory Tests

Raw wool and wool felt underwent a series of physical-chemical treatments aimed at improving their capacity of absorption of CrVl, both through batch tests and through a filtration process. Water samples with two different concentrations of CrVl were used: 2mg/L and 0,2 mg/L. They were put in contact with raw wool and felt.
  • The first treatments performed on wool and felt, based on the employment of physical methods, did not have significant results.

  • As the picture shows, the first results were achieved by performing an hydrolysis treatment.

  • The highest adsorption results were achieved with raw wool, but the methods used did not always comply with legal limits concerning total chromium and not even the ones concerning hexavalent chromium.I

  • As the picture shows, the best results were achieved by optimizing the hydrolysis process in an acid environment

  • The highest adsorption results were achieved with raw wool, with methods that comply with legal limits concerning both total chromium and hexavalent chromium. This might be due to the fact that the applied treatment allows an easier exposure of the contact areas in raw wool rather than in felt;

  • Raw wool can maintain its ability to adsorb even when the number of filtrations increases from 1 to 10.

  • The low-power microwave treatment (252 W) seems to be more effective than the high-power one (700 W)


Despite the tests are still in their initial phase, the obtained results show that raw wool can be a promising product to promote, since it allows to bring the CrVl level below legal limits on the water intended for human consumption (10µg/L). Surely, further analyses are necessary to calculate the maximum absorption capacity and to consider the possibility to recycle filters, through backwashing, in order to verify if such materials have the features needed for an application on the field. This approach is aimed at enhancing some materials, transforming them from waste to resources.