Effect of compression–decompression on helminth eggs present in sludge of a settling tank

The effects on the structure and viability of the helminth ova caused by the compression–decompression produced in raw wastewater, during the effluent use for hydroelectric generation, was evaluated. A device was constructed to simulate the process, using compression times between 7 and 29 min at a pressure of 50 kg/cm2, and decompression times between 0.1 and 32 s. Viability was evaluated using conventional 21 days in vitro incubation and compared with a vital staining technique. The process of compression/decompression appeared to contribute from 82 to 100% immediate egg disintegration; the remaining, apparently intact eggs, were affected enough to disintegrate with time.