Use of Moringa oleifera seed as a natural coagulant in domestic wastewater tertiary treatment: Physicochemical, cytotoxicity and bacterial load evaluation

Abstract

This study aimed to evaluate the use of Moringa oleifera (MO) seed aqueous extract for tertiary treatment of a domestic wastewater by coagulation, flocculation, sedimentation, and rapid granular filtration. Jar tests with sand filter coupled were performed in secondary effluent samples with MO and alum dosages to evaluate the capacity to remove apparent color, turbidity, BOD, COD, TOC, nutrients, generated sludge, pH, and alkalinity consumption. Effects on the bacterial load (total coliforms and Escherichia coli), antibacterial activity in vitro (Escherichia coli Strain ATCC 25922), and cytotoxicity (Vero cells) were also evaluated. MO at the optimal dosage of 600 mg/L showed results statistically equal to the use of alum (200 mg/L), achieving bacterial load, turbidity, and apparent color removal higher than 99 %, 92 %, and 66 %, respectively. Differently from alum, the MO dosage increase did not consume alkalinity or change pH value. MO produced a more organic sludge, with total solids 1.8 times lower, and 3 times less bulky sludge than alum. Treatment with MO did not remove nutrients and increased organic matter (BOD, COD, and TOC). However, treatment with MO resulted in an effluent with less cytotoxicity, when compared with alum. MO did not show significant antibacterial activity, which may be related to the applied dosages. These results emphasized that MO seed aqueous extract has the potential to be used as a coagulant for domestic wastewater tertiary treatment, but a purification process of extracting cationic proteins from MO seeds is recommended when the effluent organic load is a concern.