assessment of probable toxicity of 3 kinds of metal plating industry wastewater on bacteria of sequencing batch reactor units of industrial wastewater treatment plants

background: the entrance of toxic compounds into wastewater treatment plants (wwtps) can induce disorder in their biological units. therefore, it is necessary to determine the sources of toxic wastewaters. in this study, the toxicity of the wastewater of 3 metal plating industries was assessed using sequencing batch reactor (sbr) bacteria. methods: to obtain the 1-1000 ml/l concentrations, the 3 metal plating wastewater solutions were diluted using distilled water. to determine the growth inhibition in each concentration, the 0.5 cc cultured sbr bacteria on nutrient broth media was used and cultured on nutrient agar media. data were analyzed using the probit analysis in spss software and the 50% effective concentration (ec50) was calculated. findings: according to the probit analysis, there was no effect on the tested bacteria at the concentrations of 1 ml/l, less than 50 ml/l, and less than 100 ml/l of metal plating wastewater in samples 1, 2, and 3, respectively. however, all studied bacterial species were eliminated in the concentration of 1000 ml/l of each metal plating wastewater. maximum and minimum ec50 were recorded for the metal plating wastewater sample number 3 (960 ml/l) and number 1 (6.5 ml/l), respectively. conclusion: results of this study showed that some metal plating wastewaters, even in very low concentrations, can induce adverse effects on the bacterial community structures of biological units of wwtps. thus, it is recommended that effluent standards and in situ treatment rules be applied according to the performed process type in such industries.