Development of a Hybrid System for Simultaneous Removal of Nutrients and Heavy Metals from Wastewater

Abstract

The simultaneous presence of nutrients (nitrogen and phosphorus) and heavy metals in wastewater poses significant environmental challenges, including eutrophication and toxicity. Conventional treatment systems often fail to address these pollutants concurrently due to their differing chemical properties. This study presents a hybrid system integrating constructed wetlands (CWs), microbial fuel cells (MFCs), and biochar-based bio-sorption to achieve e?icient removal of nutrients and heavy metals from industrial and municipal wastewater. A pilot-scale system was tested, achieving removal e?iciencies of 87% for chemical oxygen demand (COD), 82% for total nitrogen (TN), 90% for total phosphorus (TP), and over 92% for heavy metals (Cu, Zn, Pb, Cd). Metagenomic analysis revealed mi- microbial synergistic interactions, while the MFC component generated bioelectricity, enhancing sustainability. The system’s low cost and robustness make it a promising solution for wastewater treatment in resource-constrained settings.

Introduction

1. Background

Industrial and municipal wastewater often contains high levels of:

• Nutrients (e.g., nitrogen and phosphorus) – causes eutrophication,

• Heavy metals (e.g., copper, zinc, lead, cadmium) – harmful to ecosystems and human health.

Conventional treatment methods (like activated sludge or chemical precipitation) are often ineffective at removing both pollutant types simultaneously due to differing chemical properties.

2. Research Objective

Develop a sustainable hybrid system integrating:

1. Constructed wetlands (CW)

2. Microbial fuel cells (MFCs)

3. Biochar bio-sorption

Goals:

• Remove both nutrients and heavy metals,

• Evaluate performance at a pilot scale,

• Study microbial roles using metagenomics and analyze cost-effectiveness.

3. Methodology

A. Sample Collection

• Wastewater sourced from a textile factory and treatment plant in Nagpur, India.

• High initial concentrations:

  • TN: 50–70 mg/L

  • TP: 8–12 mg/L

  • Heavy metals: 15–25 mg/L each

  • COD: 300–500 mg/L

B. Microbial Consortium Development

• Isolated electroactive and metal-tolerant microbes from contaminated sites.

• Dominant species: Sphingomonas, Azospira, Pseudomonas.

• Used 16S rRNA sequencing and metagenomics to identify and co-culture strains for optimized performance.

C. Pilot-Scale Hybrid System Setup

• Constructed Wetland: 3m × 1m × 0.6m with Phragmites australis.

• MFC: Carbon felt electrodes, 450 mL capacity.

• Biochar Filter: 2 kg rice husk biochar (BET surface area: 125 m²/g).

• Capacity: 1000 L/day with Hydraulic Retention Time (HRT):

  • CW: 48 hours

  • Biochar: 6 hours

D. Metagenomics and Functional Analysis

• Used KEGG pathway mapping to confirm gene expression for:

  • Nitrogen and phosphate metabolism,

  • Metal-binding proteins.

• MFC produced max power density of 24.35 mW/m².

4. Results

? Pollutant Removal Efficiencies

• COD: 87%

• TN: 82%

• TP: 90%

• Cu: 95%

• Zn: 93%

• Pb: 96%

• Cd: 92%

?? System Performance

• Constructed Wetland: Nutrient uptake via plants and microbes.

• MFC: Enhanced nitrogen removal and generated bioelectricity.

• Biochar Unit: Effective heavy metal removal through adsorption and ion exchange.

5. Cost Analysis (Indian Context)

• Setup Cost: ?66,400
  (vs ?1,66,000 for conventional membrane bioreactor systems – ~60% cheaper)

• Operational Cost: ?5,400/month

  • Electricity: ?1,245

  • Maintenance: ?4,150

? Advantages

• Economical, efficient, and suitable for rural and peri-urban decentralized wastewater treatment in India.

Conclusion

The study presents a cost-effective, high-performance hybrid system for treating wastewater contaminated with both nutrients and heavy metals. By combining constructed wetlands, MFCs, and biochar filtration, and leveraging microbial consortia, the system demonstrates strong potential for sustainable, decentralized wastewater management, particularly in resource-constrained regions.

References

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Copyright

Copyright © 2025 Nakul Shenode, Dilip Budhlani, Akshata Katturwar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.