Biochar, a new ecological solution to purify wastewater
Biochar is a substance similar to charcoal but is produced from farming waste.
Scientists from The Pennsylvania State University have demonstrated that it was extremely effective at absorbing contaminants found in wastewater, such as the residues from pharmaceutical products. These residues are a problem for wastewater treatment plants that are not equipped to remove them.
To achieve this result, the researchers produced two types of biochar using farming by-products: one from cotton gin waste and the other from guayule bagasse. Guayule is a shrub that grows in the arid regions of the Southwestern United States. Its branches are ground to obtain latex and rubber. The remaining dry and fibrous residue is known as bagasse. The team then tested the efficacy of these materials in absorbing three common pharmaceutical compounds — docusate, erythromycin and sulfapyridine — found in water.
Absorption or adsorption?
Absorption of a contaminant by biochar occurs in two ways. In the first, the substance penetrates into a piece of biochar like water into a sponge. In the second, the molecules stick to the surface of a solid biochar particle, a physical phenomenon known as adsorption.
The biochar from cotton gin waste proved to be much more effective than the biochar from guayule bagasse. It absorbs 70% of sulfapyridine, 74% of erythromycin and 98% of docusate, compared to 5%, 50% and 50% respectively for bagasse.
The study also showed that by increasing the temperature of the oxygen-free pyrolysis process used to turn the agricultural waste into biochar (from around 340 to 700°C), biochar’s capacity to adsorb the pharmaceutical compounds considerably improved.
The prospect of using abundant farming waste that is normally destroyed by burning is highly promising for agriculture in arid regions in the United States, as well as Africa and Asia. The method could make it possible to decontaminate and recycle the wastewater used in irrigation at very low cost.
The next step in the project is testing different combinations of biochar and developing a blend of materials able to absorb a wide range of contaminants found in water.
« Adsorption of pharmaceuticals from aqueous solutions using biochar derived from cotton gin waste and guayule bagasse », Biochar, 16 novembre 2020 - link.springer.com/article/10.1007/s42773-020-00070-2