Urban sludge reuse in agriculture: Waste treatment and parasitological risk

The development of an extraction-concentration method for the nematode eggs existing in urban treatment-plant sludge made it possible to study the viable nature of these eggs by cultivating them in deionized water at 30°C for 30 days. The criterion selected to show viability was the development of eggs at the larval stage. Sludge samples from various origins (physical, biological and chemical treatments) were analyzed: 93% of the eggs proved to be viable in primary sedimentation sludge. Eggs that can grow have been detected in samples from biological treatments, with, however, a lower frequency for systems calling for lagooning and compositing with, respectively, 26 and 25% of viable eggs. Anaerobic digestion gave intermediate results with 66%, whereas a prolonged aeration led to a limited effect, 93% of eggs being considered as viable. A 15 day chemical treatment with lime did not produce complete elimination of viable eggs: the analysis showed 66% of eggs developing at the larval stage. This study thus confirmed that nematode eggs are strongly resistant to most of the classical waste treatments.