Performance Evaluation of Moringa oleifera Seeds Aqueous Extract for Removing Microcystis aeruginosa and Microcystins from Municipal Treated-Water

Introduction: Toxic microcystins (MCs) produced by cyanoprokaryotes-particularly
by the cosmopolitan cyanobacterium Microcystis aeruginosa- pose adverse effects
on aquatic organisms and their ecosystem and may also cause serious impacts on
human health. These harmful monocyclic heptapeptides are the most prevalent
cyanotoxins reportedinfreshwaters andmustbeeliminatedforavoidingMCsrelease
in receiving water bodies. Hence, this work aimed to test the efficacy of Moringa
oleifera seeds water-based extract (MO) as a natural coagulant for removing
cyanobacteria (especially M. aeruginosa), microalgae, and its associated MCs from
pre-treated municipal wastewaters.
Methodology: Four different MO coagulant doses (25, 50, 75 and 100 mgL−1)were
investigated for cyanobacteria and microalgae removal by conventional coagulation
assays and morphology-based taxonomy studies. Additionally, water turbidity and
chlorophyll a (Chl a) content were also determined. Further, the presence and
concentration of MCs soluble in water, remaining in the particulate fraction, and
f
locculated within the residual sludge were assessed using high-performance liquid
chromatography coupled with diode array detection (HPLC-DAD).
Results: The treatment with MO at 100 mg L−1 substantially reduced the number of
cyanobacterial and microalgal species in the treated samples (average removal rate of
93.8% and 86.9%, respectively). These results agreed with a ~44% concomitant
reduction in Chl a and ~97% reduction in water turbidity (a surrogate marker for
suspended solids content). Notably, MCs concentrations in the treated water were
significantly lowered to 0.6 ± 0.1 µg L−1 after addition of 100 mg L−1 MO. This value is
belowtheWHOrecommendedlimitsforMCspresenceindrinkingwater(<1.0 µgL−1).