Optimization of a Microwave Assisted Extraction of Organic Sulphur from Domestic Sewage Sludge by UV-Vis Spectrophotometry Determination

Abstract

An alternative method for microwave-assisted extraction of organic sulphur in sewage sludge samples was optimized based on response surface methodology. The extraction process was defined by a 2³ factorial design. In the factorial design, the temperature, the extraction time and the volume of hydrochloric acid in the solvent mixture were evaluated. The samples were extracted with a mixture of nitric acid and hydrochloric acid. The data obtained for study were based on the concentration of sulphur in the sulfate form (S-SO₄^2-) obtained spectrophotometrically in the sludge samples. The initial extraction parameters were adjusted so that spectrophotometric determination was feasible. According to the levels (minimum and maximum) defined for each parameter, the methodology showed that the best extraction conditions were achieved with an extraction temperature of 150 °C, using a longer extraction time (40 min). This study was carried out to evaluate the efficiency of microwave-assisted extraction in spectrophotometric determination of sulphur in sludge samples.