determining the salt tolerance threshold for biological treatment of salty wastewater

Background: wastewaters with high salt content disturb the metabolic function of microorganisms causing plasmolysis or activity loss in microorganisms, so the efficiency of biological treatment of saline wastewater by conventional microorganisms will decrease. objectives: this study aimed to find the outbreak of disorder in the biological wastewater treatment process and how much salt leads to low efficiency in the wastewater treatment plant. methods: a study unit consisting of two aeration and sedimentation parts was used in this pilot research. initially, 2 to 10 gr of nacl was added to wastewater (ww) then aerated and settled for six and two hours, respectively. during a 10-weeks period, 10 samples were obtained and, the parameters of biological oxygen demand in 5 (bod5), chemical oxygen demand (cod), total suspended solids (tss), ph, turbidity, total dissolved solids (tds) and mixed liquor suspended solids (mlss), were measured. all experiments were done according to standard methods. results: removal efficiency of qualitative parameter including bod, cod, tss and turbidity showed a reduction of about 79.7, 73.9, 67.6 and 66%, respectively by addition of 8 gr/l of nacl to wastewater. by increasing tds by more than 4000 mg/l, biological treatment was done at a low efficiency and was disturbed with tds of about 8000 mg/l, with efficiency of the treatment system strongly decreasing. conclusions: for wastewater with high tds content, modification such as dilution, collection system sanitation, application of halophytic organisms, the use of non-biological methods and so on is recommended.