Aquatic weed Eichhornia crassipes as sustainable feedstocks for biochar production: A potential of ammonium adsorption and kinetic models

Abstract

The rapid emergence of unique types of pollutants is of worldwide concern owing to their deleterious effects on living beings. Mitigating pollution in the way of sustainability is the need of the hour to protect the existing environment from degradation. In this regard, eco-friendly biochar was prepared from the intact plant of Eichhornia crassipes (water hyacinth) without neglecting the roots, stems, leaves, and flowers and assessed for its ammonium removal efficiency in the study. Twelve biochars of two categories, viz., treated and normal, were produced under two different pyrolysis temperatures of 300 °C and 500 °C and three residence times of 30, 45, and 60 min. The adsorption experiments were conducted as batch studies in triplicate to examine the impacts of multiple adsorption-inducing factors in biochar. The maximum ammonium removal efficiency of about 83% was shown by the alkali-activated biochar produced at a higher temperature of 500 °C with a longer residence time of 60 min. The biochar showing higher ammonium adsorption was characterized by Scanning Electron Microscopy and Fourier Transform Infra-Red spectroscopy, which revealed the increased number of pores and the presence of C–O, OH, and CO groups that altogether aided the adsorption process. The kinetic study conducted with contact times of 30, 60, and 90 min showed that the linear regression values were >0.999 for the pseudo-second-order kinetic model, which revealed that the ammonia sorption of Eichhornia biochars followed a second-order mechanism of chemisorption. Synthesized biochar has shown significant efficacy in ammonia adsorption, making it worthwhile in applications where ammonia removal is necessary, particularly in wastewater treatment besides agriculture and air purification.