Improvement of constructed wetlands using Lithothamnium calcareum-based fertilizer for sewage treatment

Abstract

The universalization of water supply and sanitary sewage treatment services requires low-cost, high-efficiency solutions. Constructed wetlands (CW) stand out as a promising technology, but their effectiveness in removing nutrients, especially phosphorus, remains limited. The use of fertilizers based on the seaweed Lithothamnium calcareum emerges as a potential strategy to enhance this system. However, no studies have combined this seaweed with macrophytes in CW. Thus, the objective of this study was to evaluate the efficiency of CW tanks by combining different doses of L. calcareum fertilizer (0, 5, 15, and 35 g/L) with the cultivation of the macrophyte Cyperus alternifolius in wastewater treatment, through physicalchemical analyses and assessments of the plants’ photosynthetic metabolism. The experiment was conducted in Araruama, RJ, over 58 days. The results showed that the highest dosage (35 g/L) yielded the best removal efficiencies: 96.7% for phosphorus, 58.5% for chemical oxygen demand (COD), and 34.5% for ammoniacal nitrogen. Additionally, stomatal conductance and photosynthetic performance indices (PI_abs and PI_total) were significantly higher in treatments with added algae, indicating improved nutritional status and photochemical activity in C. alternifolius. It is concluded that integrating L. calcareum-based fertilizer with CW planted with C. alternifolius accelerates pollutant removal and enhances the physiological performance of macrophytes, offering an innovative, low-cost alternative for decentralized sanitary sewage treatment.