However, some studies show that zero valent zinc (ZVZ) could be up to ten times more effective at eradicating the contaminants than ZVI.
The use of polysulfides is a type of abiotic reduction and works best in anaerobic conditions where iron (III) is available.
The benefit of using polysulfides is that they do not produce any biological waste products; however, the reaction rates are slow and they require more time to create the DVI (dual valent iron) minerals that are needed for the reduction to occur.
In the process, ditionite is consumed and the final product of all the reactions is 2 sulfur dioxide anions.
In ISCR, bimetallic materials are small pieces of metals that are coated lightly with a catalyst such as palladium, silver, or platinum.
The catalyst drives a faster reaction and the small size of the particles allows them to effectively move into and remain in the target zone.
The growing bacteria consume oxygen, which easily accepts electrons, present in the subsurface which increases reducing potential.
EHC is injected as a "slurry" (a mixture that is 15 to 40% solids and weight with the rest being liquid) into the substratum.
Pathway A represents direct electron transfer (ET) for Fe0 to the adsorbed halocarbon (RX) at the metal/water point of contact, resulting in dechlorination and production of Fe2+.
Using this processes, scientists combined sodium dithionite with iron to treat Chrominum VI and TCE effectively.
Both of these materials have iron within some biological matrix (iron is suspended in vegetable oil in EZVI and in organic carbon in EHC) and use microbial organisms to enhance the reduction zone and to create a more anaerobic environment for the reactions to take place in.
The most common type of implementation of ISCR is the installation of permeable reactive barriers (PRBs), but there are instances when the reductant can be directly injected into the subsurface to treat source areas.
The most common way they are made is by filling a trench with ZVI, nanoscale iron, or palladium.
Nanoscale iron particles can also be injected directly into the subsurface to treat plumes, and they have large surface areas and, therefore, high reactivities and can be distributed more evenly in the contamination site.
Because the particles are so small, they have a comparatively large reactive surface, providing a more effective reaction.