Optimized SA/CMC/Diatomite Beads with Dual-Ion Cross-Linking for NH3-N Removal

This study addresses the pressing issue of high-ammonia nitrogen wastewater, such as landfill leachate, by developing immobilized microbial beads that combine high mechanical strength with efficient denitrification performance. The beads were prepared using a composite of sodium alginate (SA), carboxymethyl cellulose (CMC), and diatomite (DE), with a dual-ion (Ca2+-Al3+) stepwise cross-linking technique to encapsulate Alcaligenes faecalis. The material ratios were systematically optimized through single-factor and response surface methodology (RSM), identifying the optimal conditions as: SA 2.0%, CMC 1.5%, DE 1.0%, CaCl2 2.25%, and Al2(SO4)3 2.0%. Under these conditions, the beads achieved a mechanical strength of 3.20 N and exhibited an ammonia nitrogen removal rate of 93.10% after 96 h of treating actual landfill leachate (NH3-N ≈ 1000 mg/L). In conclusion, the SA-CMC-DE dual-ion cross-linked beads demonstrate structural stability and efficient mass transfer, offering an economically viable and novel solution for the treatment of high-ammonia nitrogen wastewater.