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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: 0) by Anonymous Coward on Wednesday February 02 2022, @12:12AM (3 children)

    by Anonymous Coward on Wednesday February 02 2022, @12:12AM (#1217867)

    Experiments in the US which already has well-managed soil as well as a temperate climate have not shown a benefit.
    Maybe there is some benefit in specific climates where the soil is not being well managed. In the US, it is an old, common practice to apply "green manure" which is a crop of clover which is grown and then tilled back into the soil. This a accomplishes a few things: it adds nitrogen to the soil, adds carbon, and adds structure to keep the soil from compacting. Maybe the biochar is doing something similar in a tropical climate, but where the nitrogen would come from is only a guess.

    Biochar is not GENERALLY useful to increase crop yield. The experiments were done by ag depts in midwestern universities.

    As for carbon sequestration, that is just a joke; there isn't much biochar mass you can add to a plot of soil. Growing trees capture far more carbon per acre.

  • (Score: 0) by Anonymous Coward on Wednesday February 02 2022, @07:11AM (2 children)

    by Anonymous Coward on Wednesday February 02 2022, @07:11AM (#1217936)

    >As for carbon sequestration, that is just a joke; there isn't much biochar mass you can add to a plot of soil. Growing trees capture far more carbon per acre.

    First you grow the trees then you turn then into charcoal and plant new trees. There's your sequestration.

    • (Score: 0) by Anonymous Coward on Wednesday February 02 2022, @12:46PM

      by Anonymous Coward on Wednesday February 02 2022, @12:46PM (#1217971)

      An acre can store much more carbon in tree form because the trees are vertical. Scattered into chips and placed just under the soil as biochar is a far less dense packaging. Plus carbon stays locked in trees for many, many decades. In the soil, it can erode away. Plus you'd have to plow an entire field to bury the biochar, whereas with trees you need only dig a small hole per tree, if that.

    • (Score: 0) by Anonymous Coward on Friday February 04 2022, @07:42PM

      by Anonymous Coward on Friday February 04 2022, @07:42PM (#1218801)
      First you grow the trees then you convert them into actual papers on sequestration. And there's your sequestration.