Sewage sludge biochars management-Ecotoxicity, mobility of heavy metals, and soil microbial biomass

Production of biochar from sewage sludge may be a promising solution for sewage sludge management and improvement of soil properties, including carbon dioxide sequestration. The aim of the present study was to compare the effects of biochars derived from different sewage sludges on soil physicochemical and biological properties, ecotoxicity, and plant yield. Three biochars (produced at a temperature of 300 °C) were applied into sandy acid soil in doses of 0.5, 1, and 2% (w/w). Depending on the type and dose, the application of sewage sludge biochars into the soil caused diverse effects on the parameters of soil biological activity (microbial biomass [Cmic], soil respiration, and value of metabolic quotient). No correlation between the applied dose of biochars and inhibition of Vibrio fischeri luminescence was observed. The factor with a stronger impact on the activity of V. fischeri was the type of biochar. The use of the OSTRACODTOXKIT F test (MicroBioTests) showed that the addition of sewage sludge biochar (regardless of its dose) reduced the soil toxicity to Heterocypris incongruens compared with the control soil. A significant increase of Poa pratensis L. biomass was obtained in soils with 1 and 2% additions of each of the biochars. The addition of biochars in doses of 1 and 2% to the soil had greater effect on the content of mobile forms of Cu, Pb, and Cd than the 0.5% dose compared with the control. Environ Toxicol Chem 2018;37:1197-1207. © 2017 SETAC.