An examination of the surface characteristics of activated sludge in relation to bulking during the treatment of paper mill wastewater

Abstract

Abstract The addition of mineral talc, Aquatal ® (Toulouse, France), to activated sludge treating paper mill effluents and its effect on settlement characteristics has been investigated. One laboratory study and a full‐scale investigation on a large waste water treatment plant (WWTP) with a capacity of 500.000 population equivalent (p.e.) have been carried out using this mineral. The sludge in the full‐scale plant was filamentous and had specific sludge volume index (SSVI) values in excess of 250. The talc dosing which was adapted to sludge settleability reduced SSVI values by 38%, improved the total suspended solids' concentrations by 86% and reduced the specific sludge load by 34%. In the laboratory‐scale plant, the sludge had SSVI values of 200–260 before treatment and was hydrophilic. The use of Aquatal ® at a dose of 0.7 g/g mixed liquor suspended solids (MLSS) took 2 weeks to reduce the SSVI to 78. It also increased the hydrophobicity to a balanced 50%. The use of mineral converted the somewhat diffuse flocs into a compact structure.