To determine the optimum wastewater treatment parameters a jar test (6-jar apparatus manufactured by Velp Scientifica) was used. The jar test is the most widely used method for evaluating and optimizing the flocculation process. The set-up used was the following: initially the wastewater was rapidly stirred at 200 rpm, the aluminum salt and mucilage were added and the mixture was stirred for another 5 min at the same speed. For the next 15 min, the mixture was stirred at 45 rpm and then it was allowed to settle for a period of 10–30 min. After sedimentation, the supernatant liquid was collected and analyzed. All experiments were performed at room temperature (22 ± 1 °C). No pH control was applied, since the pH did not change during flocculation.
The complete design of a flocculation process includes consideration of both particle destabilization and particle transport [27,33]. As a first step towards designing a flocculation process, the optimum doses of flocculants were determined. In the case of the synthetic wastewater, doses of up to 25 and 50 mg/L of okra and mallow mucilage were examined, respectively. In the case of the effluent, up to 25 mg/L of okra and 250 mg/L of mallow mucilage were used. After preliminary experiments, the optimum coagulant doses were 0.025 mM and 0.5 mM for synthetic wastewater and effluent, respectively. It was decided that these doses will be used throughout the main experimental work described above.