Ammonium removal from wastewater: advances, challenges and future prospects with microelectronic sludge as a prospective adsorbent precursor

Abstract Ammonium (NH 4 ⁺) contamination in wastewater drives eutrophication and oxygen depletion, yet conventional biological treatment delivers inconsistent removal under variable and high-strength influent conditions. Adsorption has emerged as a flexible complementary strategy. However, its performance in real wastewater is constrained by competitive cation interference, regeneration instability, and a persistent gap between laboratory and operational outcomes. This review aims to critically evaluate adsorption-based NH 4 ⁺ removal and to establish mechanistic and performance benchmarks for next-generation adsorbent design. The analysis integrates evaluation of adsorbent materials, removal mechanisms, operational factors, and regeneration behaviour, supported by a bibliometric assessment of Scopus and Web of Science databases (2010–2025, n = 810). The results confirm rapid research growth while revealing no published studies investigating microelectronic sludge (MES) as a prospective adsorbent precursor. Mechanistic evaluation indicates that chemisorption at finite active sites governs NH 4 ⁺ uptake, making adsorption performance sensitive to multi-ion competition. Materials with multiple concurrent interaction pathways generally outperform single-mechanism systems, nevertheless, adsorption capacity declines progressively during regeneration, and long-term performance under real conditions remains insufficiently validated. These findings highlight a fundamental limitation in current adsorbent design to sustain selectivity and stability under realistic wastewater conditions. MES is proposed as a compositionally integrated precursor candidate. Its SiO 2 –Al 2 O 3 –Fe oxide matrix enables ion exchange, electrostatic interaction, and surface complexation without external modification. Addressing this performance gap requires systematic investigation of MES adsorption behaviour, regeneration stability, and co-contaminant leaching under realistic wastewater effluent conditions.