Effects of disinfectants on wastewater effluent toxicity

Wastewater disinfection is most commonly achieved by halogenation, ozonation or ultraviolet (UV) irradiation. All of these processes are known to be capable of inducing chemical changes among non-microbial aqueous constituents, which can lead to changes in effluent toxicity behavior. Undiluted effluent samples from seven wastewater treatment facilities were exposed to commonly-applied disinfectants (chlorination/dechlorination, ozonation and UV irradiation) and assayed for their toxicity behavior; Ceriodaphnia dubia survival and reproduction were used as measures of chronic toxicity. The results of these assays confirmed the ability of all the disinfectants to alter toxicity response behavior. The toxicity responses demonstrated site-specificity and strong temporal variations. In general, when undisinfected effluent did not display toxicity, no toxicity was observed following any of the disinfection procedures; when toxicity was displayed in the undisinfected effluent, all disinfectants demonstrated the ability to alter toxicity, in most cases resulting in an increase. The changes in toxicological response attributable to disinfectant exposure followed the trend: chlorination/dechlorination> ozonation> UV irradiation, but substantial variations from this trend were evident in individual samples.