Upgrading wastewater treatment plants to urban mines: Are metals worth it?

•Recovery of metals from wastewaters was studied to support circular economy.•We studied the fluxes of fifty elements in four different matrices.•A methodology integrating criticality, financial and mining perspectives is presented.•We classified metals according to their interest for circular economy.•We determined the best place to recover each metal in a wastewater system. After usage, extracted metals end up back to the environment but dispersed at much lower concentrations. Wastewater treatment plants (WWTP) are one of the last sites where metals go through before discharge into the environment. This article assesses the relevance of recovering up to forty-nine metals from WWTP from a strategic, financial and mining perspectives. The WWTP matrices are also compared with other deposits to put forward their relevance as a future urban mine. Results show a strong recovery potential for magnesium throughout the plant. The most suitable matrix to recover chromium and copper is sewage sludge. Palladium, platinum or tungsten, found mainly in incinerated sewage sludge ash would require further investigation. In treated wastewaters, a dozen metals (including calcium, potassium, sodium, silicon, nickel and zinc) are either strongly critical or interesting for financial potential. There are potent incentives to transform WWTP into urban mines to shift towards circular economy.