Investigation on the capability of Rwandan Macrophytes: Cyperus papyrus and Leersia Hexandra to treat polluted water and wastewater

Abstract

The paint industry's wastewater effluents contain persistent metals that pose significant environmental risks. Conventional treatment methods for the contaminated area, including soil and rivers, are often inadequate. Searching for new alternative solutions is of high interest. This study explores the potential of indigenous Rwandan macrophytes, C. papyrus (CP) and L. hexandra (LH), as sustainable adsorbents. This study assesses CP and LH powder, non-activated biochar, activated biochar, and cellulosic materials derived from these macrophytes as latent options in order to eliminate heavy metals such as cadmium (Cd) and Lead (Pb) from wastewater. Prepared adsorbents were chemically characterized using FTIR spectroscopy, while the effectiveness of eliminating heavy metals was assessed through Atomic Absorption Spectrophotometry. The parameters for adsorption were refined, and the kinetic information was adjusted to align using models of the second and pseudo-first order. The efficiency of the adsorption process was evaluated using both batch and packed bed experiments. Furthermore, the Freundlich and Langmuir isotherms were analyzed, and the thermodynamic parameters were examined. Cellulosic materials were extracted with yields of 40.2% and 35% for CP and LH, respectively. The ideal conditions for adsorption included a pH level of 6, an adsorbent quantity of 1.5 grams, a contact duration of two hours, and an initial concentration of metal at 10 ppm. The removal efficiencies of CP and LH powder were evaluated at percentages 57.6% and 60.1% for Pb and 56.1% and 56.6% for Cd. CP and LH non-biochar were 67.5% and 55.2% for Pb while 61.1% and 50.5% for Cd. on activated biochar were CP 92.2% Pb, 89.9% Cd; LH 89.9% Pb, 86.3% Cd. The removal efficiency of extracted cellulosic material from CP was 78.8% for Pb and 76.7% for Cd while extracted cellulosic material from LH was 73.2% for Pb and 71.2% for Cd, respectively. Nonetheless, Kinetic studies confirmed pseudo-second-order (PSO) behavior (R² > 0.98), indicating chemisorption, while Freundlich isotherms suggested heterogeneous, multilayer adsorption. Thermodynamic analysis revealed the non-spontaneous, endothermic adsorption process. Overall, findings support the use of CP and LH-derived materials serving as efficient and economical adsorbents for cleaning industrial wastewater tainted with heavy metals.