From Wastewater Treatment Plants to Biorefineries: Successful Cases in the Recovery of Nutrients from Urban Wastewater

The increasing demands established by legislation and the need to care for the environment are transforming conventional wastewater treatment plants (WWTP) into more sustainable and eco-efficient biorefineries that generate value-added bioproducts that are increasingly present in the society. This study demonstrates the success story of the world's largest 100% solar anaerobic photobiorefinery, based on the use of purple phototrophic bacteria (PPB) to obtain high-quality treated water and biofertilizers from domestic wastewater. The case of success in the recovery of struvite from waste streams rich in nutrients from the WWTP is also demonstrated. The photobioreactors, with a treatment capacity of 350 m3/d (1500 e.p.), consistently meet the discharge parameters with values of TCOD <40 mg/L, BOD5 <23 mg/L, TSS < 15 mg/L and TP < 2mg/L. Furthermore, phototrophic biomass has proven to be a low-cost raw material in the formulation of biofertilizers with a CNP ratio of 100:15:13. And an NPK ratio of 100:98:25. In the case of struvite, the removal efficiency of P2O5 has been greater than 80% and that of NH4 + close to 40%. The treated stream was 80 m3/d, producing approximately 15 tons per year of struvite rich in P2O5 (28%) that can also be used as raw material for the formulation of fertilizers.