Chlorination in a wastewater treatment plant: acute toxicity effects of the effluent and of the recipient water body

Abstract

This study investigates the impact of wastewater treatment plant (WWTP) effluent on the toxicity of the recipient water body and the effectiveness of the disinfection treatment applied (sodium hypochloride) to assure the compliance of both microbiological and toxicological emission limits. No toxicity was found in the majority of samples collected from the recipient river, upstream and downstream of the WWTP, using three different toxicity tests (Vibrio fischeri, Daphnia magna, and Pseudokirchneriella subcapitata). Only three samples presented toxic unit (TU) values with V. fischeri, and one presented TU with P. subcapitata. The influent toxicity ranged from slightly toxic to toxic (TU = 0.68-4.47) with V. fischeri, while only three samples presented TU values with the other tests. No toxicity was found in the absence of chlorination, while the mean toxicity was 3.42 ± 4.12 TU with chlorination in the effluent. Although no toxicity or very slight toxicity was found in the receiving water, its residual toxicity was higher than the US EPA Quality Standard in two samples. Escherichia coli concentration had a lower mean value in the chlorinated effluent: 13,993 ± 12,037 CFU/100 mL vs. 62,857 ± 80,526 CFU/100 mL for the not chlorinated effluent. This difference was shown to be significant (p < 0.05). E. coli in ten chlorinated samples was higher than the limit established by European and Italian Legislation. The mean highest trihalomethanes (THMs) value was found in the influent samples (2.79 ± 1.40 μg/L), while the mean highest disinfection by-products (DBPs) was found in the effluent samples (1.85 ± 2.25 μg/L). Significant correlations were found between toxicity, sodium hypochlorite, THMs, DBPs, E. coli, and residual chlorine. In conclusion, this study highlighted that the disinfection of wastewater effluents with sodium hypochlorite determines the increase of the toxicity, and sometimes is not enough to control the E. coli contamination.

Toxicity on aquatic organisms exposed to secondary effluent disinfected with chlorine, peracetic acid, ozone and UV radiation

“…This study demonstrated that the disinfection of wastewater effluent with 2.5 mg Cl 2 L -1 resulted in toxicity to cladocerans and fishes. Similarly, Cao et al (2009) and Pignata et al (2012) found increased mortality of D. magna neonates after the treatment of wastewater effluent with sodium hypochlorite (3.0-5 mg Cl 2 L -1 ). The toxicity of chlorinated wastes in aquatic systems depends not only on the amount of chlorine added but on the concentration of residual chlorine remaining in solution.…”

“…Chlorination is a common practice for disinfecting the effluents from wastewater treatment plants before being discharged into receiving water bodies (Hutchinson et al 1998;Pignata et al 2012). However, low levels of residual chlorine can be harmful to aquatic life if chlorinated wastewaters are discharged into the environment (Manning et al 1996).…”

Chlorination by-product concentration levels in seawater and fish of an industrialised bay (Gulf of Fos, France) exposed to multiple chlorinated effluents

“…The discharge of the chlorinated effluents is of main environmental concern, even if concentrations remain low, as the volumes released are generally very important. Along with residual free chlorine or bromine, the CBPs can constitute a threat to marine ecosystems (Taylor, 2006;Deng et al, 2010;Pignata et al, 2012;Khalanski and Jenner, 2012) and possibly to human health through atmospheric volatilisation and subsequent photolysis of brominated compounds into reactive oxidants (Quack and Wallace, 2003;Deng et al, 2010;Parinet et al, 2012).…”

Comparison between Chlorination and UV Disinfection of Untreated Wastewater after Disasters

“…High residual chlorine and disinfection byproducts may damage aquatic organisms including marine products (Cao et al, 2009;Pignata et al, 2012;Watson et al, 2012), while insufficient disinfection may cause viral pollution in oysters (Flannery et al, 2012). These considerations illustrate the need for a simple, effective and feasible method of wastewater disinfection without negative impacts on aquatic organisms.…”