Enhancing sustainability by utilizing engineered sewage sludge biochar for aqueous phosphate sorption

Phosphate contamination in water bodies is a global environmental issue that can result in eutrophication, affecting sectors like agriculture and fishing and thereby jeopardizing the long-term viability of water resources. Phosphate, a non-renewable resource, is a crucial mineral for crop production and a key component of NPK (Nitrogen, Phosphorus, and Potassium) fertilizer. Only 16% of the applied phosphate as fertilizer is utilized by crops; the rest is lost through soil erosion and aquatic runoff, increasing the risk of eutrophication. Therefore, environmental concerns and phosphate depletion have increased the need for phosphate recovery and recycling. This study explored the potential of engineered sewage sludge biochar for the sorption of aqueous phosphate. Biochar was obtained after pyrolyzing sewage sludge at 500°C, which was modified using coprecipitation of FeCl₃.6H₂O and ZnCl₂. At pH 6, the engineered biochar exhibited around 92% phosphate sorption compared to 20% by pristine sewage sludge biochar. The highest sorption capacity (using Langmuir isotherm) was 129 mg/g at 15°C. Phosphate-laden biochar can further be utilized in agricultural fields, where it will act as a slow-release fertilizer to improve soil fertility or restore contaminated soil, thereby providing a sustainable solution for waste management and enhancing soil fertility. This will help achieve SDG 2 (Zero hunger) and SDG 6 (Clean water and sanitation).

Keywords: Eutrophication, Sorption, Engineered biochar, Sewage sludge, Sustainable Development Goals