Usability of Brachiaria mutica (para grass) and Cyperus rotundus (nut grass) as bioadsorbents for the removal of methylene blue from aqueous solution: isotherms, kinetics, and thermodynamics studies

Recent decades have witnessed an enormous increase in concentrations of dye effluent and its harmful effect on aquatic environment. The treatment of dye effluent before discharging in aquatic ecosystem is extremely important from the environmental viewpoint because of its toxic, carcinogenic, and mutagenic nature. The objective of the current study was to evaluate the feasibility of dead biomass of aquatic weeds namely, Brachiaria mutica and Cyperus rotundus as adsorbents for the removal of methylene blue dye from aqueous solution. The batch study was performed to study the effect of various parameters such as pH (1–8), adsorbent dose (0.2–1.6 g/100 ml), initial dye concentration (10–80 ppm), contact time (15–120 min), agitation speed (50–250 rpm), and temperature (10–60 °C). The Fourier Transform Infrared Spectroscopy (FTIR) clearly indicated slightly shifting in peak after treatment with methylene blue. Removal efficiencies of methylene blue were 90% for B. mutica and 94% for C. rotundus, achieved at pH of 6 (for B. mutica) and 8 (for C. rotundus), adsorbent dose of 0.8 g (for B. mutica) and 1 g (for C. rotundus), concentration of 50 ppm, contact time of 60 min, shaking rate of 150 rpm, and temperature of 40℃. Maximum adsorption capacities were 21.49 mg/g for B. mutica and 21.94 mg/g for C. rotundus. Freundlich isotherm (R² = 0.818 for B. mutica and 0.945 for C. rotundus) fitted well to experimental data in comparison to Langmuir isotherm. Whereas in case of adsorption kinetics, pseudo-second order was better fitted as compared to first order for both the adsorbents. Thermodynamics parameters show that the adsorption process is endothermic and non-spontaneous at low temperature for both the adsorbents. Thus, present study suggested that both the adsorbents can be effectively utilized for treatment of dye effluent.