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posted by martyb on Tuesday February 01 2022, @12:08PM   Printer-friendly
from the Six-foot-seven-foot-eight-foot-bunch! dept.

Heavy metals contaminate ground and surface waters from a variety of sources such as industrial effluent or fertilizers or pesticide applications. 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, and physical adsorption. 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 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 that bind to the metals. A group of researchers investigated the effectiveness of biochar made from banana waste, 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.

Absorption at Wikipedia.

Journal Reference:
Xiyang Liu, Gaoxiang Li, Chengyu Chen, et al. Banana stem and leaf biochar as an effective adsorbent for cadmium and lead in aqueous solution [open], Scientific Reports (DOI: 10.1038/s41598-022-05652-7)

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  • (Score: 3, Informative) by DeathMonkey on Tuesday February 01 2022, @05:22PM (1 child)

    by DeathMonkey (1380) on Tuesday February 01 2022, @05:22PM (#1217732) Journal

    They don't quantify costs but they believe it will be cheaper since it's sourced from a waste stream. I think they wanted to find out if it actually works first.


    Various types of conventional (e.g., activated carbon, amorphous silica, clay minerals, diatomite, biochar, zeolites, and polymers) and novel nanosized (e.g., carbon nanotubes, graphene oxide, and reduced graphene oxide) adsorbents have been developed for metal treatment4,7. Compared with biochar, activated carbon and nanomaterials are relatively more expensive, while other conventional adsorbents such as natural zeolite/clay minerals generally have low adsorption efficiency; meanwhile, nanomaterials are difficult to be retrieved after adsorption of heavy metals4. Development of green adsorbents such as biochar from waste recycling that possess local availability, low cost, and high adsorption efficiency would be an environmental-friendly approach for heavy metal remediation.

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  • (Score: 3, Informative) by hubie on Tuesday February 01 2022, @05:49PM

    by hubie (1068) Subscriber Badge on Tuesday February 01 2022, @05:49PM (#1217743) Journal

    That is the part that I found interesting about this paper. They're starting from an existing waste stream and also state that banana stems and leaves contain high lignin and low cellulose, which makes them more preferred candidates over other biomaterials for making biochar material that is highly porous with high fixed carbon content.