Effects of thermally dried sewage granules on earthworms and vegetation during pot and field trials

Trials with thermally dried sewage granules investigated their effects on a variety of earthworm species in laboratory and field situations. Initial laboratory results from small pots suggested that deleterious effects to earthworms might result from field application of granules. A field trial showed that this was not the case. After 9 months, earthworm population size and structure in permanent grassland was not affected by sewage granule applications, at rates up to twice guideline level (8 tonnes per hectare). Earthworm numbers in control plots and those with sewage applied were not significantly different (p > 0.05). A significant increase in biomass production of vegetation (p < 0.001) was recorded where granules were applied. Deep burrowing species of earthworm appeared to benefit from an increased availability of plant material.