Tertiary treatment of domestic sewage by constructed wetlands on a pilot scale: development and application of substrate for phosphorus removal and recovery

Abstract

Artificial eutrophication of aquatic ecosystems is one of the main environmental problems of the present time, being characterized by an increase in photosynthetic biomass, as a result of excess nutrients and bringing several undesirable consequences. Phosphorus (P) is the key element to control eutrophication, being one of its main sources, the discharge of sewage into water bodies. In contrast, P is essential for agricultural production and its natural sources are running out. Thus, low-cost ecotechnologies Such As Constructed Wetlands (SACs) that promote P removal and recovery are crucial in controlling eutrophication and food security. However, the large-scale use of SACs is still limited by the large area required, which can be solved by optimizing the Hydraulic Detention Time (HDT), using a substrate that maximizes P adsorption and proper plant management. Thus, the present study intends to develop an adsorbent substrate for P from tailings, evaluate its application in SACs and the reuse of P in agricultural planting. Different proportions of tailings (water treatment sludge, red mud and dregs) rich in elements that have high affinity with PO43- anions (Al, Ca and Fe) will be tested in the production of the substrate. The substrate with the highest P adsorption will be used in the SAC on a pilot scale in a Sewage Treatment Plant. The SAC will be monitored every 15 days for 10 months, with various physical-chemical parameters being evaluated. Regular management of the plants will be carried out and the feasibility of agricultural reuse of P will be evaluated through leaching tests and the use of substrates in lettuce cultivation in a greenhouse. The study aims to improve the SACs for the tertiary treatment of effluents, valuing tailings and stimulating the circular economy. (AU)