Phytotoxicity of Sewage Sludge Biochars Prepared at Different Pyrolysis Conditions

Abstract

The aim of this study was to evaluate the phytotoxicity of several biochars prepared from sewage sludge pyrolysis. Pyrolysis was carried out at three different lab-scale reactors and conditions: an Auger reactor for low temperature (300ºC), a stirred batch reactor and a fluidized bed reactor (530ºC). The starting material is anaerobically digested and thermally dried sewage sludge from a wastewater treatment plant located in Spain. Some phytotoxicity experiments were performed for biochars: for germination tests, corn seeds were used with (a) aqueous solutions prepared from biochars and (b) nutritive solutions prepared with equal nutrient content as the latter. Additional germination test for gaseous phytotoxic emissions from biochars were performed with cress (Lepidium sativum L.) and corn. Finally, seedling growth tests (shoot weight) with corn were carried out.