Effects of shock loads of salt on protozoan communities of activated sludge

The effects of wastewater salinity variations on communities of microorgani sms taken from activated sludge were studied. Batch cultures were grown for 96 h at final salt concentrations of 3, 5, 10, 20 and 40 NaCl g/l. Protozo a and small metazoa was counted and ciliated protozoan species in these cul tures were identified. An increase in salt concentration from 3 to 10 g/l g radually affected the microbial community and few protozoa and metazoa surv ived at 96 h. Ciliate abundance was species dependent: Vorticella spp. and Opercularia articulata resisted the high dosages of NaCl better than other ciliates. Total ciliate abundance and diversity fell drastically at 20 g/l, which would compromise reliability in activated sludge processes. At 40 g/ l neither protozoa nor metazoa survived after 24 h. This study evaluates th e effects of a short-term NaCl shock on the dynamics of activated sludge mi croorganisms and their community composition. The study also contributes to the understanding of the wastewater treatment process.