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Municipal waste water treatment is mainly achieved by biological processes. These processes produce huge volumes of waste sludge (up 1.5 million m3/year in the Netherlands). Further processing of the waste sludge involves transportation, thickening and incineration. A decrease in the amount of waste sludge would be both environmentally and economically attractive. Aquatic worms can be used to reduce the amount of waste sludge. After predation by the worms, the amount of final sludge is lower. Additionally it has a distinctive granular structure with improved dewaterability characteristics. If a useful application can be found for the worms that are produced in the predation process, then a valuable product would be obtained from a waste material. Aquatic worms can be used for improved processing of waste sludge and recovery of resources. The waste sludge is produced in biological waste water treatment. In the Netherlands, this sludge is mostly thickened, dried and incinerated. These are costly operations in which only some energy is recovered. Recently, an aquatic worm (Lumbriculus variegatus) was found, which consumes the sludge, grows on it and compacts the non-digested sludge into worm faeces. In a new reactor concept the worms are placed in a mesh, thereby retaining them in the reactor and allowing for separate collection of the compact worm faeces. The latter results in much more efficient processing of the remaining solids, i.e. the worm faeces. Additionally, worm biomass is produced that contains a high protein fraction, offering opportunities for re-use. The thesis describes the scale up of such a worm reactor and the impact it will have on sludge processing |
