Sustainable phosphate removal using Mg/Ca-modified biochar hybrids: Current trends and future outlooks

Eutrophication, a major environmental and economic issue, stems from the increased nutrient levels in water bodies, notably phosphorus, and demands focused attention. On the other hand, investigating phosphate recovery options receive immediate attention, as phosphate sources are limited. Many studies have been dedicated to the development of tailored biochars as effective agents for phosphate adsorption and recovery from aqueous environments. This review explores the multifaceted advantages of Ca/Mg-rich biochars, with a primary focus on their exceptional phosphate uptake capabilities. Beyond their remarkable phosphate sequestration potential, these biochars offer diverse benefits, including non-renewable phosphate recovery, soil enhancement, resource utilization, waste management, and conversion. Nevertheless, the complex preparation methods, reliance on expensive metallic reagents, and energy-intensive equipment pose significant limitations to the mass production of these composites. In response to these challenges, this review critically evaluates the latest Mg/Ca-biochar synthesis strategies, highlighting the need for sustainable materials and fabrication methods to enhance economic and environmental viability. Furthermore, the potential of spent Ca/Mg-biochar hybrids, enriched with substantial phosphate loadings, is examined, offering insights into their utilization as safe slow-release phosphate fertilizers or their recycling through practical methods. The review also delves into the development of easy, cost-effective, and environmentally friendly regeneration and reuse strategies, which can be implemented for Ca/Mg biochars. Finally, the article summarizes the real-time applications, and limitations, identifies crucial knowledge gaps, and outlines future directions, to advance the use of Ca/Mg-modified biochars in various sustainable environmental applications. [Display omitted] •Emerging Ca/Mg hybrid synthesis approaches are evaluated.•The morphological and physico-chemical features of Ca/Mg biochars are discussed.•Ca/Mg biochars can be effectively used to treat real wastewater systems.•Phosphate-laden Ca/Mg biochars can be recycled as safe phosphate fertilizers.•Future directions of sustainable applications of Ca/Mg biochars are outlined.