Potential of Biochar from phytoremediation biomasses for the removal of ionic contaminants from wastewater

Abstract

There is a challenge regarding the disposal and handling of post-harvested phytoremediation biomass, but one alternative process is to convert phytoremediation biomass into biochar and bioenergy by pyrolysis. This study aims at utilizing biochar derived from phytoremediation biomasses to remove ionic contaminants from wastewater. Phytoremediation and non-phytoremediation biomasses were pyrolyzed at 550°C in a nitrogen-flowing environment for 30 minutes and the properties were analyzed and compared. The resultant biochar was valorized using 0.1 M Zinc chloride (ZnCl2) and adsorption experiments were performed. Phytoremediation biomasses had higher heavy metal (HMs) content compared to phytoremediation biomasses and the carry-over effect was observed in subsequent biochars. Generally, biochars from phytoremediation biomasses displayed higher ash content, and volatile matter content but had low fixed carbon (FC), pH, and electrical conductivity (EC). The biplot indicated an increase in identified functional groups from non-phytoremediation biochars to phytoremediation biochars except for Cymbopogon citratus (C. citratus). Biochars from Chrysopogon zizanioides ( C. zizanioides) phytoremediation biochars showed low intensities of anatase and dolomite peaks. Biochars from phytoremediation biomasses have fewer porous structures as compared to biochars from non-phytoremediation biomasses. ZnCl2-activation did not alter the ordinary surface functional group profiles but increased the ordinary biochar's surface porosity. The activation of ordinary biochars with ZnCl2 reduced the magnitude of the potential positive charges that can develop and adsorb anions. Generally, phytoremediation biochars indicated negative adsorption capacities suggesting that heavy metals in biochars leached into the AMD solution. The activated phytoremediation biochar from Chrysopogon zizanioides (C. zizanioides) indicated the highest adsorption capacity of 14.12 mg g-1 for PO43-ion at a biochar dosage of 0.04g while Cymbopogon nardus retained 20.72 mg g-1 of NO3-ion. Based on the effect of pH on adsorption, activated non-phytoremediation biochar from Cymbopogon nardus (C. nardus) showed the maximum adsorption capacities of 38.93 mg g-1and 31.52 mg g-1 for PO43-and NO3-ions, respectively at pH 8. Based on the effect of initial concentration on adsorption, ordinary non-phytoremediation biochar from Cymbopogon nardus effectively retained 69.06 mg g-1 of PO43-ion at the initial concentration of 300 mg l-1. The maximum adsorption capacities for PO43-that can be reached by Chrysopogon zizanioides non phytoremediation biochar (BCV1), Chrysopogon zizanioides phytoremediation biochar (BCV2), activated BCV1, activated BCV2 and activated Cymbopogon nardus phytoremediation biochar (BCC2) are 62.99, 72.99, 113.64, 115.70 and 61.38 mg g-1, respectively. In conclusion, the biochar from phytoremediation biomasses showed high potential as an adsorbent for the anionic contaminants in wastewater.