Key points
- TMC’s commercial system adds a hydrocyclone step to the dewatering process to filter out abraded nodule fragments below one millimeter, so the return water consists of sediment and water only.
- Separated sediment is released through a return pipe at a depth of 2,000 meters, a depth chosen because most biomass, including zooplankton and commercial fisheries, is concentrated in the top 1,000 meters of the water column.
- More than 95% of entrained sediment settles within 1-2 kilometers of the collector vehicle, and material discharged at 2,000 meters dilutes to background concentrations within several kilometers.
- Up to 98% of sediment disturbed during nodule collection is returned directly to the seafloor.
