The focus of water treatment is increasingly shifting to the recovery of raw materials. In the same way as drinking water companies and waterboards, sludge final-processors and waste-to-energy plants are concerning themselves with the recovery and useful reuse of residuals. For the time being, in the wastewater and sludge cycle the investment is being directed mainly at phosphorus recovery.
The preliminary research project, ‘Recovery of heavy metals and rare earth metals from wastewater and sludge final-processing’ (KWR 2016.021), showed that there are opportunities for the recovery of (scarce) heavy metals and rare earth metals, including copper, zinc, gold and palladium. Removing metals improves effluent quality, sludge quality and residual ash, and therefore opens disposal possibilities.
We still have a lot to learn about the load and concentration, in combination with speciation (appearance), of the metal, which would provide the basis for the development of a suitable recovery technology. This project uses sample pre-processing and analysis with validation to study more closely, and test on a small-scale, the potential of the various technologies (new and newly-applied) for the removal and/or recovery of the selected metal(s) from water – i.e., (sources of) drinking water, membrane concentrate, WWTP influent and effluent – wastewater treatment sludge and fly ash.
The effectiveness of the selected technology is tested on a small scale for one or more of the streams with a view to underpinning the economic feasibility. This also involves directing attention to: 1) determining the potential alternative disposal routes for domestic wastewater treatment sludge with a lowered content of heavy metals like copper and zinc; 2) the disposal possibilities of recovered (scarce) heavy metals and rare earth metals; and 3) the sustainability aspects.