Performance of Azolla-Based Floating Wetland for Domestic Wastewater Remediation

Nature-based wastewater treatment systems offer sustainable alternatives to conventional infrastructure due to lower operational costs and high environmental adaptability. This study investigates the efficiency of a laboratory-scale floating wetland (FW) utilizing plants of the genus Azolla to treat domestic wastewater under varying operating conditions. The experimental setup consisted of two 9-L reactors with different initial Azolla biomass loads of 20 g and 40 g, operated in batch mode. System performance was evaluated by the systematic characterization of chemical oxygen demand (COD), ammonia nitrogen, phosphorus, pH, dissolved oxygen, and alkalinity. The experimental period was divided into three phases: an initial acclimation period comparing reactors exposed to constant artificial light and natural light, an active monitoring phase, and a nutrient removal kinetic phase to assess daily pollutant removal rates, both conducted under natural light conditions.

The comparative analysis, during the first phase, demonstrated that light regime significantly affected FW performance, with natural light yielding higher removal efficiencies for both organic matter and ammonia nitrogen. COD removal was 90 and 96% in artificial and natural light, respectively, while the corresponding ammonia nitrogen removal was 18 and 40%. Furthermore, in the second phase, a higher initial biomass concentration (40 g) led to an 8% increase in phosphorus removal. During the nutrient removal kinetic phase, in the 4^th week of operation, the first-order removal constants were 0.1 and 0.26 d^-1 for COD, 0.2 and 0.36 d^-1 for ammonia nitrogen, and 0.43 and 0.4 d^-1 for phosphorus, for the 20 and 40 g FW, respectively. However, biomass yield was higher in the 20-g culture, compared to the 40-g during the entire operation period. These findings indicate that although Azolla-based FW are inherently robust, optimizing initial biomass concentration and light exposure is essential for achieving specific effluent quality targets.