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Evaluation of Calpurnia aurea seed extract as natural coagulant for reducing turbidity, color and COD from water and wastewater

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Abstract

Turbidity, color, and chemical oxygen demand (COD) indicate water quality. Natural coagulants offer eco-friendly alternatives for treatment. This study investigates the potential of Calpurnia aurea seed extract as a natural coagulant for water and wastewater treatment. The extract was prepared through a multi-step process involving drying, grinding the seeds,  sieving the seed powder, cold macerating using n-hexane solvent to defatting, and dissolution in distilled water (5 g/L). Protein content was quantified using the Kjeldahl method. Treatment conditions were optimized using the jar test and one-variable-at-a-time (OVAT) approach, yielding optimal parameters of 100 mg/L dosage, pH 3, rapid mixing at 300 rpm for 9 min, slow mixing at 45 rpm for 35 min, and a settling time of 70 min. Under these conditions, turbidity removal efficiencies reached 91.93% (synthetic wastewater), 87.89% (municipal wastewater), 69.93% (textile effluent), and 45.79% (Akaki river water). In this context, the efficiency for the Calpurnia aurea seed extract approaches the turbidity removal efficiencies of up to 99.77% reported for alum in previous studies. Color removal was most effective in textile effluent (63.73%), followed by municipal wastewater (49.77%) and Akaki river water (24.12%). COD reductions were highest in Akaki river water (78.49%), with moderate effects in municipal wastewater (46.28%) and textile effluent (30.75%). The extract’s coagulation mechanism is attributed to charge neutralization and colloidal particle binding. These findings highlight Calpurnia aurea seeds as a promising natural coagulant for improving water quality across diverse wastewater sources.

Data availability

All relevant data are included in the manuscript.

Abbreviations

ANOVA:

Analysis of variance

CASP:

Crude Calpurnia aurea seed powder

CASP-OE:

Oil extracted Calpurnia aurea seed powder

COD:

Chemical oxygen demand

FTIR:

Fourier transform infrared analysis

NTU:

Nephelometric turbidity unit

OVAT:

One variable at a time

PSU:

Practical salinity unit

RMS:

Rapid mixing speed

RMT:

Rapid mixing time

RSM:

Response surface methodology

SMS:

Slow mixing speed

SMT:

Slow mixing time

SPSS:

Statistical package for the social sciences

ST:

Settling time

XRD:

X-ray powder diffraction

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Funding

Jimma University provided funding for this study. The funder had no involvement in the study’s conceptualization, design, data collection and analysis, publication decision, or manuscript preparation.

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Authors and Affiliations

  1. Department of Environmental Health Science and Technology, Faculty of Public Health, Health Institute, Jimma University, Jimma, Ethiopia

    Belay Negassa, Dessalegn Dadi & Samuel Fekadu

  2. Department of Environmental Health, College of Health Sciences and Medicine, Dilla University, Dilla, Ethiopia

    Belay Negassa

  3. Department of Water Resource and Irrigation Engineering, College of Engineering and Technology, Dilla University, Dilla, Ethiopia

    Biritu Derecha

Authors

  1. Belay Negassa
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  2. Biritu Derecha
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  3. Dessalegn Dadi
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  4. Samuel Fekadu
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Contributions

BN: Conceptualization, methodology, investigation, formal analysis, resources, data curation, writing original draft, visualization; BD: Writing review and editing, data curation, visualization; DD: Supervision, conceptualization, methodology, funding acquisition, validation, writing review and editing, visualization; SF: Supervision, conceptualization, methodology, funding acquisition, validation, writing review and editing, visualization.

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Correspondence to
Belay Negassa.

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The authors declare no competing interests.

Ethical approval

This study was conducted in accordance with ethical standards and received formal approval from the Institutional Review Board (IRB) of the Institute of Health, Jimma University, under reference number JUIH/IRB/418/24. The research protocol adheres to all applicable institutional policies, national regulations, and internationally recognized ethical guidelines governing research on wild plant species. The collection and use of Calpurnia aurea seeds adhered to the IUCN Policy Statement on Research Involving Species at Risk of Extinction and the Convention on the Trade in Endangered Species of Wild Fauna and Flora (CITES). The species is not listed as endangered or protected under these frameworks.

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Negassa, B., Derecha, B., Dadi, D. et al. Evaluation of Calpurnia aurea seed extract as natural coagulant for reducing turbidity, color and COD from water and wastewater.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-46299-y

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Keywords


  • Calpurnia aurea
  • Coagulant performance optimization
  • COD
  • Color
  • Natural coagulant
  • Turbidity

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