Plant-based versus metal-based coagulants in aquaculture wastewater treatment: Effect of mass ratio and settling time

Abstract Azadirachta indica, or Neem, is a natural plant commonly used in medicine and pesticides due to the useful compounds it contains. This study aimed to determine the performance of Neem leaves as a natural coagulant in the removal of turbidity, total suspended solids (TSS) and colour from real aquaculture effluent. The experiment was conducted to determine the effect of mass ratio of the TSS (mg)/mass of coagulant (mg) on the removal of turbidity, TSS and colour, in which the ratio is calculated based on the TSS concentration as an index of aquaculture pollution. The experiment was carried out with a ratio range of 0.1 to 1000 mg TSS per mg coagulant and a total volume of 500 mL. The operational conditions were fixed at 180 rpm and 3 min for rapid mixing, 10 rpm and 20 min for slow mixing and settling time from 30 min to 60 min. The results showed a turbidity removal of 82.7%, TSS removal of 81.37% and colour removal of 65.8% at an optimum ratio of 1000 and coagulant dosage of 0.3 mg/L. For comparison, the performance of alum was also tested and showed higher turbidity, TSS and colour removals of 99.7%, 98.8% and 97.3%, respectively, based on the optimum ratio of 1 with a dosage of 362.7 mg/L. Both coagulants showed a similar optimum settling time of 30 min. From these results, it is clearly seen that Neem has a high potential for use as a coagulant, indicating further exploration to optimize the extraction of active compounds from the leaves.