Extracting rare elements and minerals from wastewater for renewable energy

Study describes ways in which environmental biotechnologies will help society achieves sustainability goals.

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Society must switch to renewable energy sources and chemical alternatives for fossil fuels to slow and eventually stop global climate change. Not meeting the challenge will mean that humans will endure the increasingly catastrophic effects of global climate change. The most important step will be replacing fossil sources of fuel and organic chemicals in ways that ensure energy and economic security.

Large expenditures in carbon-neutral or -negative photovoltaic, wind, battery, and catalytic technologies will be necessary to replace fossil fuels. These technologies will demand significant amounts of Crucial Minerals and Materials (CMM), presently scarce. Platinum Group Metals (PGM), rare earth elements (REE), gold, silver, lithium, copper, and nickel are some examples. The problem that follows is to create new, renewable sources for CMM.

An important new source of renewable fuels, chemicals, and CMM can be wastewaters that contain pollutants that can become tomorrow’s renewable resources, suggests a new study. According to a study published in the journal PLOS Water, environmental biotechnology presents an opportunity for recovering renewable fuels, chemicals, and CMM from wastewater.

The study- led by Bruce E. Rittmann from Biodesign Swette Center for Environmental Biotechnology, Arizona State University- defines environmental biotechnology as forming partnerships with microbial communities to provide human society with sustainability services.

Wastewater streams that contain CMM in chemical forms are water pollutants. Mostly, the CMM in the wastewater streams is oxyanions, meaning they are bonded to oxygen (O) and present as water-soluble anions. Performing bioreductions, certain bacteria can convert the CMMs to chemical forms that are insoluble, recoverable, and valuable.

The (Pt, Pd, Rh, Ru, Ir, and Os), along with gold (Au) and silver, are a significant illustration of this type of bioreduction (Ag). Certain bacteria produce elemental nanoparticles that are kept in the extracellular polymer substances (EPS) that surround the bacteria by using these oxyanions as respiratory electron acceptors.

The second important example pertains to REE (e.g., Y, La, Dy, and Nd), lithium (Li), copper (Cu), and nickel (Ni), which precipitate with carbonate (CO32-), hydroxide (OH-), or sulfide (S2-) produced by sulfate-reducing bacteria (SRB). For sulfides, the metal-sulfides become nanoparticles that are retained in the EPS. They also are recovered with periodic biofilm harvesting.

There are two characteristics of practical environmental biotechnology for bioreduction. It does this by supplying an electron donor that the bacteria can utilize to respire the MMC or sulphate. Hydrogen gas is the best option since it can be created in a sustainable manner using the methods mentioned above, and it functions as an electron donor for sulphate, all PGM, as well as gold and silver.

Second, the technology must provide excellent biomass retention because the capable bacteria are autotrophs (fix CO2 as their carbon source and grow slowly). The Hydrogen-based Membrane Biofilm Reactor (MBfR) is ideal in this setting since it delivers Hydrogen directly to a biofilm living on the gas-transfer membranes that deliver the Hydrogen.

Journal Reference:

  1. Bruce E. Rittmann. Environmental biotechnologies can make water pollutants part of the path to mitigating climate change. PLOS Water. DOI: 10.1371/journal.pwat.0000105
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