Impact of thermal treatment of mixtures of sewage sludge and plant material on selected chemical properties and Vibrio fischeri response

The aim of the research was to evaluate the effect of temperature during the treatment process as well as the effect of adding plant materials to sewage sludge on selected chemical properties and Vibrio fischeri response. The mixtures were placed in a chamber furnace, under airless conditions. Two temperature procedures were applied: 300 and 600ºC; the exposure time in both cases was 15 minutes. Thermal treatment of sewage sludge without a plant component is not well-founded and may cause an increase in concentration of trace elements. Using the temperature of 300ºC caused significantly lower changes in the contents of total forms of trace elements than using the temperature of 600ºC. The metals extracted from the studied mixtures were not toxic for the Vibrio fischeri. In the case of the fractional composition of humic compounds, thermal treatment of mixtures of sewage sludge and plant materials is not beneficial in terms of labile fractions, but it had a beneficial effect on stabilizing the durable bonds between C compounds in those mixtures.