Granulometric analysis to estimate influence of anionic surfactant on activated sludge structure

The work concerns the evaluation of the possibility of using laser diffraction analyzer to determine changes in the distribution of sludge floc size in the presence of anionic surfactant. As a model of surfactant linear alkylbenzene sulphonate (LAS) was used. Different concentrations: 10, 100 and 200 mg/dm of LAS was applied. The granulometric analysis showed that the pure activated sludge was composed of particles with a size of 1 m to 2 mm. The largest and fastest changes in the distribution of sludge floc size after the addition of a surfactant at a concentration of 100 mg/dm were observed. The flocs with a diameter above 0.8 mm disappear and the average diameter over volume of particles decrease from 0.29 to 0.19 mm. Doubling the dose of surfactant causes the flocs aggregation. The sludge flocs capability for break-up and aggregation is not proportional to the concentration of LAS. Addition of LAS to the sludge results in decrease of the sludge volume index. This study showed that granulometric measurement may help to estimate an impact of chemical substances contained in wastewater on activated sludge.