en عمومى General مقاله اصیل Original Article <div style="text-align: justify;">Background: Chlorination of wastewater effluent with high levels of residual organic matter has been suspected to the production of toxic and hazardous disinfection by-products (DBPs) including trihalomethane (THM) compounds.<br> Methods: In this study, two rapid techniques including dissolved oxygen depletion (DOD) and optical density (OD) bioassays were used to evaluate the chloroform toxicity of aqueous solution. The activated sludge was collected from aeration tank of a full-scale municipal wastewater treatment plant and used as a biological inoculum. In order to achieve an active and stabilized mixed culture of bacteria, the test cultures were transferred to a fresh nutrient broth culture media every day. The influence of chloroform on DOD and OD bioassays was examined at chloroform initial concentrations of 10-1000 &mu;g/L.<br> Results: It was revealed that the application of chloroform at concentrations of 100 and 1000 &mu;g/L showed moderate and extreme toxicity, respectively, and reduced bacterial activity. The estimated chemical concentration with 50% inhibition of bacterial activity for DOD and OD bioassays was 457 and 961 &mu;g/L, respectively.<br> Conclusion: According to the results, the wastewater effluent should use bioassays in order to evaluate the effects of DBPs where the wastewater effluent is disinfected by chlorine compounds.</div> Trihalomethanes, Chloroform, Disinfection, Wastewater, Biological assay, Oxygen, Inhibition 271 276 http://ehemj.com/browse.php?a_code=A-10-1-190&slc_lang=en&sid=1 Mohammad Mehdi Amin mohammadmehdia@gmail.com 10031947532846007329 10031947532846007329 No 1Environment Research Center, Research Institute for Primordial Prevention of Non-communicable Diseases, Isfahan University of Medical Sciences, Isfahan, Iran, 2Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran Ali Fatehizadeh fatehizadeh@gmail.com 10031947532846007330 10031947532846007330 No 1Environment Research Center, Research Institute for Primordial Prevention of Non-communicable Diseases, Isfahan University of Medical Sciences, Isfahan, Iran, 2Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran Nasrin Bagheri n_bagheri70@yahoo.com 10031947532846007331 10031947532846007331 Yes Corresponding author: Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran, and Student Research Center, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran