Comparative evaluation of suspended sludge performance at two reactor height-to-width ratios for high-ammonia anaerobically digested sludge supernatant treatment

This study presents a comparative evaluation of two sequencing batch reactors (SBRs) with distinct height-to-width (H/W) ratios treating high-ammonia anaerobically digested sludge supernatant via the nitritation-denitritation process. The reactors were designed with constant volumes but differing H/W ratios, 4.8 for R1 and 2.8 for R2, while maintaining identical superficial gas velocity (SGV), to isolate the effects of reactor configuration. Both systems consistently achieved ∼99 % ammonium nitrogen (NH₄⁺-N) removal throughout operation, with total inorganic nitrogen removal efficiencies of 95 % in R1 and 97 % in R2. Kinetic analysis revealed that R2 achieved higher microbial activity, with maximum AOB and denitritation activities of 0.57 and 6.32 g N/g VSS/d, respectively, compared to 0.49 and 5.12 g N/g VSS/d in R1. Conversely, R1 demonstrated better sludge settleability, with final SVI₃₀ values of 90 mL/g compared to 120 mL/g in R2. Microbial community profiling revealed comparable population structures in both reactors, with both systems dominated by the same key functional microorganisms: Nitrosomonas as the predominant ammonia-oxidizing bacteria (AOB) and Thauera as the primary denitrifying bacteria. These findings indicate that while a lower H/W ratio enhances microbial activity and nitrogen removal, a higher H/W ratio improves sludge compaction and settling.