Aquatic Worms for Sludge Reduction

Hendrickx, T.L.G., Temmink, H., Elissen, H.J.H., Buisman, C.J.N., Wetsus – Centre of Excellence for Sustainable Water Technology, Wageningen University, The Netherlands



Several techniques are available for reducing the amount of waste sludge produced at waste water
treatment plants. Physical, chemical and mechanical techniques involve a large input of energy and /
or chemicals, and may therefore be costly and not sustainable. A biological approach involves the
aquatic worm Lumbriculus variegatus. The initial experiments with these worms showed promising
results. In addition to a reduction in the amount of solids, we also obtained an end product (worm
faeces) with better settling properties and a potentially valuable product in the form of protein-rich
worm biomass. In the proposed reactor concept, the worms are immobilised in a mesh, which also
acts as a separation between waste sludge and worm faeces. To test the applicability of the reactor
concept, experiments were performed in which the worms were fed with different types of sludge. Two
sludges were obtained from municipal waste water treatment plants, two others were from a lab scale
MBR and a lab scale activated sludge reactor. The reduction in total suspended solids ranged from 12
to 40 %. This shows that the nutritious value of waste sludge for the worms varies with the source of
the sludge; an important factor for the applicability of our process. From the current experiments we
estimated the required size of a worm reactor to be 150 – 860 m3 per tonne of dry solids per day.

Waste sludge, Aquatic worms, Sludge reduction, Sludge type

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