Using Shells, Limestone, and Plastics For Removing Heavy Metals, Ammonia and Improving Water Quality in Fish Farms | ||||
| Egyptian Journal of Aquatic Biology and Fisheries | ||||
| Article 192, Volume 29, Issue 4, July and August 2025, Page 2513-2529 PDF (488.81 K) | ||||
| DOI: 10.21608/ejabf.2025.448430 | ||||
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| Author | ||||
| Hamed et al. | ||||
| Abstract | ||||
| Intensified aquaculture and seafood processing generate millions of tonnes of low-value by-products such as seashells, limestone fines, and discarded plastics. These waste streams present both environmental challenges and opportunities for resource utilization. In this 16-week pond trial, we evaluated the combined application of seashell chips, crushed limestone, and polyethylene terephthalate (PET) plastic bottles (2kg m⁻³) as water-conditioning substrates to improve pond water quality and tilapia performance. All three materials significantly increased pH (from 7.5 to 8.2–8.5), elevated alkalinity (115 to 155– 188mg L⁻¹ CaCO₃), and enhanced hardness (149 to 178– 190mg L⁻¹ Ca + Mg). Water transparency improved by 20–35% (from 22 to 26– 30cm). Substantial reductions were observed in unionized ammonia (39–46%, from 0.76 to 0.41– 0.46mg L⁻¹), nitrite (64–77%), and nitrate (36–62%). In addition, the substrates sequestered 38–45% of dissolved heavy metals, lowering total concentrations from 3.70 to 2.01– 2.96mg L⁻¹. These improvements in water chemistry were directly translated into better fish performance. Tilapia in PET-plastic ponds achieved 25% greater weight gain (50g vs. 39g in controls), a 9% improvement in feed conversion ratio (1.82 vs. 2.01), and higher survival rates (97% vs. 91%). Overall, the findings demonstrate that repurposed seashells, limestone, and waste plastics can serve as effective, multifunctional biofilter media, stabilizing water chemistry, reducing toxic compounds, and significantly enhancing tilapia growth. This approach highlights a scalable circular-economy strategy for sustainable aquaculture. | ||||
| Keywords | ||||
| Water quality; Calcium carbonate; Heavy metal removal; Ammonia mitigation | ||||
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