Dear Haziqah Su,

isotherms such as Langmuir describe the equilibrium of sorption at a constant temperature. Basically, you use sorption isotherms to determine the maximum sorption capacity of a material at a given temperature for a specific sorbate. Therefore, you vary initial concentration in the water/gas phase to construct the isotherm, e.g. in sorption experiments. On the x-axis of the plot you have the equilibrium concentration of the sorbate in solution. If it does not change you can not draw the isotherm. I would therefore recommend to use different copper concentrations. Maybe you can add copper to your wastewater in the lab? Or do you just wat to determine the effectiveness of the jar test? Maybe there is a way to do it the other way around and vary the amount of coagulant to determine sorption coefficients.

Best regards

Jonas Bauer

Copper concentration before each batch experiment should be the initial concentration for that experiment. I understand your concern with using the same initial concentration for all the test, since the parameters vary for each test (hope i am correct). Therefore, I don't think the initial concentration should be the same for each batch experiment.

Adsorbent dose data is usually used to fit isotherms.

Raw wastewater surges are not high, so concentration changes may not be necessary.

Competitive adsorption is to be looked for when dealing with real wastewater streams.

You can use different initial concentrations, e.g. by diluting samples, as well as you can change the concentration of the adsorbent. Forget about time here, it has to be long enough to get closer to the equilibrium state