Reducing Sludge Production in Biological Effluent Treatment by Applying the LSP Process, 2000 Environmental Conference Proceedings

- T. Welander, T. Alexandersson, T. Ericsson, L. Gunnarsson, A. Storlie -- The Low Sludge Production (LSP) process is an aerobic biological treatment process based on a new principle. The effluent is treated in two consecutive stages. The first stage, the bacterial stage, is designed and operated to favor the growth of dispersed bacteria, which consume much of the soluble organic matter in the effluent. The second stage, the predator stage, is designed and optimized for the growth of filter-feeding micro-animals, which consume the bacteria from the previous stage. The result is a low net yield of biosludge. The LSP process was developed on a laboratory scale, showing very low sludge yields for a number of different pulp and paper industry effluents. The results were later confirmed in pilot trials. The first full-scale LSP plant was taken into operation in Norway in early 1998. An existing conventional activated sludge plant was reconstructed to an LSP process. The modification resulted in a dramatic decrease in biosludge yield, from approximately 0.20 kg TSS/kg COD removed (=0.35 kg TSS/kg BOD removed) to 0.02 kg TSS/kg COD removed (=0.035 kg TSS/kg BOD removed). Due to the decreased fraction of biosludge in the mixed primary/secondary sludge, the dewaterability of the excess sludge from the treatment plant was greatly improved. The COD-removal over the plant remained on the same level as before the modification, 70-80%, and the discharge limits for COD and TSS have been met with great safety margin during the two years of LSP operation.