The aim of this study was to characterize the leachate derived from biochar produced from malt spent rootlets (MSR) and to evaluate the required washing level in order to provide water free from inorganic substances. MSR biochar was placed in a column and subjected to six serial washes with distilled water, and the leachate was analysed for main anions and heavy metals. The 1st wash aliquot contained increased levels of mainly phosphates (980 mg/L) and chlorides (760 mg/L), and lower levels of nitrates, sulfates, fluoride and bromide, which were decreased over washes. Zero concentrations were observed after three washes for most anions. The increased levels of Zn, Be, Cs, Mn, V and Se determined in the 1st wash aliquot were eliminated in the successive washes. The toxic potency of each wash aliquot, determined by the use of the fairy shrimp Thamnocephalus platyurus showed that the 1st and 2nd MSR biochar leachates were toxic with 4.52 and 1.46 toxic units (TU), respectively, followed by a significant elimination of toxicity after further washes.
Keywords: Biochar; Leachate; Malt spent rootlets; Physicochemical characteristics; Thamnocephalus platyurus; Toxicity.