A novel immobilization technique for the development of sustainable anammox gel beads for low nitrogen loadings

Abstract

This study aimed to develop a sustainable anammox gel beads using sodium alginate (SA) mixed with three different support materials including sodium silicate (SS), polyvinyl alcohol (PVA), and colloidal silica (CS). A detailed characterization and comparison of anammox gel beads were conducted using four lab-scale semi-continuous stirred tank reactors (Semi-CSTRs) and SA–SS beads showed superior durability with better reactor performance. SA–SS (B2) beads showed the minimum reduction effective diameter of 24% in comparison to SA (B1) beads, SA–PVA​ (B3) beads, and SA–CS(B4) beads of 98%, 57%, and 96%, respectively indicating higher integrity of B2 beads. Moreover, R2 reactor containing B2 beads showed the maximum biomass retention after 30 days of operation, relative to the initial mass of 72% compared to R1, R3, and 3%, 44%, and 5%, in R1, R3, and R4, respectively. Total nitrogen removal efficiencies of 8%, 80%, 64%, and 10% were achieved by R1, R2, R3, and R4 reactors, respectively. The diffusion coefficients (De) of ammonium in anammox gel beads was maximum for B2 beads (26.2μm2/s) compared to B1 (18.8μm2/s), B3 (22.4μm2/s), and B4 (13.9μm2/s) beads indicating the enhanced internal mass transfer.