Samples of sewage sludges from nine Scottish works were collected over a 12-month period. On average, 0.24 Globodera cysts/litre sludge were recovered, of which 11 % had viable contents. The incidence was not significantly related to season or to the presence of vegetable-processing plants in the catchment. Exposure of cysts in sludge to mesophilic anaerobic digestion, cold anaerobic digestion, pasteurisation and aerobic thermophilic digestion reduced viability of encysted eggs by almost 100%. Treatment with lime at pH 11.5, aerobic stabilisation in an oxidation ditch, accelerated cold digestion and activated-sludge treatment did not reduce viability acceptably within the normal retention time for the process. None of the treatments appeared to affect the fabric of the cyst itself, rendering these sludges unsuitable for application to land for seed potato production. However, the numbers of cysts applied, even in untreated sludge, would be unlikely to increase significantly levels of cysts in ware potato land already infested.
- G. pallida
- Globodera rostochiensis