Application of Taguchi optimization for evaluating the capability of hydrochar, biochar, and activated carbon prepared from different wastes in multi-elements bioadsorption

Abstract

Adsorption processes play important roles in the removal of metals from wastewaters. A laboratory experiment was conducted to find out effective factors in improving biosorption removal of heavy metals (HMs) using three char types (hydrochar (HC), biochar (BC), and activated carbon (AC)) prepared from different wastes (coffee, tomato, & sesame wastes) using Taguchi optimization. Metals adsorption was investigated at initial concentrations of 50,100, & 200 mg L−1 under three different temperatures (15, 25, & 35 °C). Results of ANOVA regarding metal adsorbtion efficiency (qe) showed that the first rank among the tested factors belonged to the initial concentration. According to the results, the level of 200 mg L−1 had the highest qe for the four metals studied, which was in the range of 1746–1992 mg g−1. The second rank for Cd and Pb was related to the char types, but for Zn and Ni was related to the temperature. HC was selected as the optimal bioadsorbent for Cd, Pb, & Zn. The signal to noise ratio (SNR) value for Ni was in the range of 59.21–69.84 while for the other HMs it was in the range of 53.85–65.99. Based on the SNR main effects, the optimal levels in the adsorption of studied HMs were HC, coffee or tomato waste, 200 mg L−1, 25 or 35 C for char type, source, initial concentration, and temperature, respectively. The results related to FTIR showed that the highest number of functional groups was related to HC and the coffee and tomato chars. According to SEM images, the number of pores in the AC and BC obtained from coffee and tomato wastes was more than in the sesame waste. Results of present study revealed high capability of HC prepared from coffee and tomato wastes in bioadsorption removal of HMs.