Soil Remediation after Sewage Sludge or Sewage Sludge Char Application with Industrial Hemp and Its Potential for Bioenergy Production

Sewage sludge reuse in agriculture is increasing and is highly encouraged; however, it may pose environmental risk. Therefore, an integrated approach combining soil phytoremediation and further plant usage for bioenergy production is needed. In this study, we have examined the potential of industrial hemp (Canabis sativa L.) to remediate sewage sludge (SS) and sewage sludge char (SSCh)-amended soil (25-200 Mg ha(-1)) and improve soil quality. Additionally, hemp's biomass and probable bioenergy yield was calculated for biomass and methane production. Heavy metal soil content increased with SS and SSCh dose, though hemp cultivation significantly reduced their soil concentrations. The heavy metals' removal efficiency could be ranked Zn > Cu > Cr > Ni. There was an enrichment of micro- (Ca, Mg, Mn, S) and macro-nutrients (P) in SS and SSCh-amended soils. P and S removal by hemp was highly efficient, whereas other macronutrients did not show a substantial decrease in the soil. Only marginal removal was detected for Ba, Fe, Na, Ti and Al. The study showed that the optimal fertilization with SS or SSCh could be up to 25 Mg ha(-1), when the highest efficiency of contaminant removal from the soil and the highest plant biomass production and bioenergy production were observed.