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hubie [soylentnews.org] writes:

Heavy metals contaminate ground and surface waters from a variety of sources such as industrial effluent [soylentnews.org] or fertilizers or pesticide applications [soylentnews.org]. Cadmium and lead are the most common and toxic metals found in aqueous environments. They are persistent, they migrate, they accumulate in biological tissues, and they are carcinogenic. Removing these metals effectively and cheaply has been a big environmental challenge. There are a number of approaches to remove them including reverse osmosis, ion-exchange, chemical precipitation, coagulation, electrochemical treatment [soylentnews.org], and physical adsorption [soylentnews.org]. Of these, adsorption is seen as very promising due to it being cost-effective, widely available, and easy to implement. There are a wide variety of adsorbent materials from the mundane (activated carbon, diatomaceous earth, polymers, etc.) to the exotic (carbon nanotubes and graphene oxide), but biochar [colostate.edu] has shown to be very efficient and cost-effective.

Biochar is generated from incomplete combustion of organic material at low temperatures under oxygen-starved conditions. It can be made using any organic material, such as forest and crop residues, algae, etc., and it results in a material with unique physiochemical properties such as producing a very porous material with abundant functional groups [msu.edu] that bind to the metals. A group of researchers investigated the effectiveness of biochar made from banana waste [nature.com], particularly the stem and leaves. They chose bananas because it is the fourth-most grown crop in the world. After a harvest, the stems and leaves are discarded in the field. Since the bananas only make up about 12% of the plant mass, this means a significant amount of biowaste is generated. They found that they could recycle the banana waste residues effectively for preparing adsorbents for treatment of heavy metals in contaminated water, and they hope that this would promote agricultural waste recycling as well as providing material for treating contaminated water.

Reference:
Liu, X., Li, G., Chen, C. et al. Banana stem and leaf biochar as an effective adsorbent for cadmium and lead in aqueous solution. [Open] Sci Rep 12, 1584 (2022).
DOI: 10.1038/s41598-022-05652-7 [doi.org]

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