Toxicity effects of gamma-irradiated wastewater effluents

Conventional wastewater disinfection is typically accomplished via chlorina tion, ozonation or ultraviolet (UV) irradiation. For each of these disinfec tants, changes in the composition of the disinfected waters are known to oc cur and have been linked to changes in the toxicity responses of the disinf ected effluent. The toxicity responses of wastewater effluent samples expos ed to an alternative disinfectant, gamma (gamma) radiation, have been studi ed and compared with the responses to chlorinated (with dechlorination) and undisinfected municipal wastewater effluent samples. Predisinfection sampl es were taken from six wastewater treatment plants. Multiple samples from e ach facility were split and subsamples were exposed to gamma-irradiation, a s well as chlorination/dechlorination in batch reactors. The disinfected an d undisinfected subsamples were than assayed for toxicity using the Cerloda phnia dubia chronic toxicity test. Wastewater disinfectant doses were suffi cient to meet coliform limitations for effluent quality in all cases; furth ermore, the batch disinfectant exposure protocols accomplished extents of c oliform inactivation that were comparable to those observed in the disinfec tion unit operations at the full-scale facilities from which the samples we re collected. Analysis of data from these assays showed that gamma-irradiat ion induced significantly less toxicity in terms of C. dubia survival and r eproduction than chlorination/dechlorination. Toxicity in the gamma-irradia ted effluent either decreased or was unchanged as compared to an undisinfec ted sample; effluent samples subjected to chlorination/dechlorination often showed a statistically significant increase in toxicity as compared to the undisinfected samples and the gamma-irradiated samples. (C) 1999 Elsevier Science Ltd. All rights reserved.