Synthesis of high-grade struvite from municipal effluents and application in the remediation of acid mine drainage

Abstract

Access to clean water resource is a fundamental need and right to all citizen in any given country. However, the water needs to comply with different standards, specifications and guidelines thus ensuring that potential ecotoxicological effects are not ensued from the consumption of contaminated water. In recent decades, the contamination of the environment with municipal wastewater (MWW) and acid mine drainage (AMD) has been a matter of primary concern. This has impaired the quality of water and its suitability to nurture natural life and make its inherent values. In this study, we explored the synthesis of struvite from municipal wastewater and appraise its application for the treatment of acid mine drainage. Batch experiments were used to accomplish the goals of this study, specifically the one-factor-at-a-time (AFAAT) initiative as process parameters. Evaluated parameters include contact time (mixing time) and feed dosage whereas temperature and pH were ambient. Characterisations of feed and product solid samples were done using HR-SEM-EDS, FTIR, XRD and XRF. Aqueous samples were characterised using inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), Gallery-plus and multi-parameter probes. Synthesis of struvite was done at 1 g: 100 mL of activated magnesite and municipal wastewater, respectively. The mixtures were mixed at 60 minutes at 300 rpm. The product sludge was used for AMD treatment. The obtained results revealed 30 minutes of equilibration and 15 g of dosage in 1000 mL at 300 rpm of mixing speed. Interaction of struvite with AMD led to > 99% removal efficacy for Al, Fe, Mn and other metals except for sulfate, which demonstrated close to 30% removal efficacy. XRD confirmed the synthesis of struvite with 60% purity. This was further confirmed by elevated concentration of phosphate in XRF results. After the interaction of struvite and Raw Acid Mine Drainage (RAMD), the product mineral confirmed the presence of Fe-based minerals and gypsum hence denoting that Fe and sulfates are removed from AMD. The pH was observed to be ≥ 9.5 and this was suitable for attenuation of all the chemicals. Thus, this technology could valorise struvite synthesized from municipal wastewater effluents and open new horizons for the effective and sustainable management of wastewater effluents and AMD. This will minimize the footprints of acid mine drainage and municipal wastewater on different spheres of the environment. Although an economic feasibility and life cycle analysis need to be done to conclusively proof the feasibility of this technology.