Optimization of the direct synthesis of hydroxyapatite from aquaculture wastewater using Response Surface Methodology

Abstract

ABSTRACT The utilization of phosphorus-rich aquaculture wastewater (AQW) offers a promising avenue for the recovery of valuable compounds, particularly hydroxyapatite (HAp) materials. The aim of this study was to use Response Surface Methodology (RSM) to explore the potential of recycling AQW directly to produce HAp compounds due to its considerable commercial value. Using the Central Composite Design (CCD) within the RSM, about three parameters, such as pH (between 9 and 11), contact time (between 36 and 60 h), and stirring rate (between 120 and 240 rpm) were optimized. The response of the CCD, crystallinity, was evaluated by X-ray diffraction analysis. The optimized conditions, pH of 10, contact time of 48 h, and stirring rate of 180 rpm resulted in HAp crystals characterized according to the Joint Committee on Powder Diffraction Standard, JCPDS (9,003,549), with a crystallite size of 23.6 nm. Remarkably, about 89.97% of the phosphate was removed from the AQW under these conditions, emphasizing the potential of this approach to reduce waste while producing a commercially viable product. The study highlights the viability of developing a zero-waste industry, and the utilization of calcium apatite-based products derived from AQW and offers a promising socio-economic strategy for the future.