Thermal degradation of organic pollutants in sewage sludge

摘要

Sewage sludge from a domestic water treatment plant was heated in an air atmosphere at different temperatures (105-500 ℃) for 1 hour in order to study the degradation of some organic pollutants. The compounds studied were: linear alkylbenzene sulphonates (LAS) with an alkylic chain of 10-13 atoms of carbon, and nonylphenolic compounds, including nonylphenol (NP) and nonylphenol ethoxylates with 1 and 2 ethoxy groups (NP1EO+NP2EO). These compounds were studied because they frequently exceed the limits proposed for sludge application to land in Europe. The lowest temperature did not show variations with respect to the initial sludge, but at 250℃ the concentrations of LAS and NP were reduced by around 30% and NP1EO+NP2EO disappeared. Logically, at 500 ℃ all compounds studied were totally removed. The study was completed with a thennogravimetric analysis of LAS, NP and NP1EO+NP2EO separately carried out at different times of treatment and different temperatures. The results showed that an increase of the treatment time at moderate temperatures (<250 ℃) reduced the concentrations of NP and NP1EO+NP2EO, which can be interesting since probably the beneficial properties of the sludge for the soil are practically not changed.