The value of these waste-to-resource products can be substantial. The nutrients nitrogen and phosphorus are worth approximately $31/ton, metals are $480/ton (with gold and silver alone accounting for $103/ton), and energy is $50/ton.⁸ Li et al. estimated that a municipal wastewater treatment facility could transform pollutants into profits with an annual return of millions of dollars from the electricity, fertilizer and clean water resources generated.⁹ Moreover, the economic potential of metals recovery from the biosolids alone was estimated at $13 million per year for a community of 1 million people.

Several metals, such as iridium, silver, platinum and gold, may be present at higher abundance in wastewater biosolids relative to average soil in the earth’s upper continental crust.¹⁰ Importantly, some of these elements present in wastewater are also energy critical (gallium, palladium, silver, and iridium).⁸ Such elements are critical to new energy-related technologies, such that shortages could significantly inhibit largescale deployment or effective production, transmittance, storage or conservation of energy.¹¹     

Other wastewater constituents, such as phosphorus, are agriculturally critical. Largescale food production relies on fertilizer, which is produced using phosphorus mined from non-renewable reserves, with estimates for depletion ranging widely from decades to centuries. Moreover, reserves are geographically concentrated, with most phosphorus being supplied by just six countries around the world.¹² As an industrially and economically important, non-energy raw material for which there is a supply risk, phosphorus is on the European Commission’s list of critical raw materials.

Compared to municipal systems, the economic boon could be even greater for resource recovery from industrial wastewater considering the higher loads of, e.g., organics in petrochemical or food wastewater, nutrients in livestock wastewater and metals in manufacturing wastewater.^{9 (责任编辑：Alice Lee)}