Researchers Find Plant Extract Effectively Removes Microplastics from Drinking Water
A new study led by São Paulo State University researchers demonstrated that a saline extract derived from the seeds of the Moringa oleifera plant can remove polyvinyl chloride (PVC) microplastics from drinking water when used as a coagulant, with efficiency comparable to that of traditionally used aluminum sulfate (alum), while performing effectively across a broader pH range and eliminating the need for a flocculation step in filtration. The findings were published in the American Chemical Society’s ACS Omega.
Based on their findings, the researchers believe that Moringa oleifera seed extract could serve as a sustainable alternative to conventional alum coagulants for microplastic removal in drinking water treatments.
The Need for a Sustainable, Optimized Microplastic Filtration Process
Microplastic pollution in water, crops, and food animals is an issue of growing concern due to their ubiquity, persistence, and potential adverse effects on human and environmental health.
Conventional drinking water treatment plants employ a coagulation–flocculation–sedimentation process, which can remove a significant fraction of microplastics but has broad efficiency variability (40–70 percent), and incomplete removal is often reported. Additionally, the conventional use of aluminum and iron-based coagulants is subject to increasing regulatory scrutiny due to concerns about nonbiodegradability, residual toxicity, and disease risks.
In this context, the researchers sought to address the need for process optimization and sustainable coagulant alternatives for microplastic removal in water filtration.
Greater Than 98 Percent Microplastic Removal Rate Achieved
The study evaluated the removal of aged PVC microplastics from low-turbidity drinking water using Moringa oleifera seed saline extract (MOS-SE) or alum in both direct filtration systems—which include coagulation, flocculation, and filtration—and in-line filtration systems, which omit the flocculation step.
Under optimized in-line filtration conditions at pH 6.0, researchers achieved turbidity reductions of 99.4 percent with 30 milligrams per liter (mg/L) of MOS-SE. This result was comparable to the 98.6 percent reduction achieved with 9 mg/L alum. Microplastic removal rates of 98.5 percent for MOS-SE and 98.7 percent for alum were confirmed by scanning electron microscopy (SEM).
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SEM analysis also showed complete removal of microplastics larger than 15 micrometers (μm), with only smaller particles remaining after treatment. Researchers said the findings confirmed that turbidity measurements were a reliable indicator of microplastic removal performance.
Potential for Process Simplification and Cost Savings
The study found no statistically significant differences in removal efficiency between direct filtration and in-line filtration for either coagulant, despite flocculation increasing aggregate sizes by approximately 41 percent. Average aggregate diameters increased from 43.5 μm to 61.4 μm for MOS-SE and from 46.2 μm to 65.5 μm for alum following 25 minutes of flocculation. However, the larger flocs did not improve removal performance, leading researchers to conclude that the flocculation step was unnecessary under the tested conditions.
According to the researchers, this finding could support process simplification and cost reductions for facilities treating low-turbidity drinking water.
Effectiveness at a Wider pH Range
MOS-SE also demonstrated effective performance across a wider pH range than alum. More than 99 percent microplastic removal was achieved at pH values ranging from 5.0 to 8.0 when sufficient MOS-SE dosage was applied (greater than or equal to 20 mg/L). Alum delivered satisfactory removal only between pH 5.0 and 7.0 and showed no improvement over untreated controls at pH 8.0, predominated by negatively charged aluminum species, which cannot neutralize negatively charged particles.
Tradeoff: Increase in Dissolved Organic Carbon
Researchers also evaluated the treatment's effects on natural organic matter. While increasing MOS-SE dosage raised dissolved organic carbon levels because of residual organic compounds originating from the seed extract, the treatment reduced specific ultraviolet absorbance (SUVA) by 88 percent at dosages above 30 mg/L. The reduction indicated effective removal of hydrophobic, aromatic natural organic matter, which is associated with the formation of disinfection byproducts such as trihalomethanes during chlorination.
However, the researchers noted that the increase in dissolved organic carbon remains a limitation that may require additional treatment considerations and warrants further research into seed purification methods.
