Effect of L-tyrosine on aerobic sludge granulation and its stability

Aerobic sludge granulation and its stability remain challenging in applications. Tyrosine, a compound in extracellular polymeric substances (EPSs) extracted from sludge, is reported to be closely associated with sludge granulation and its stability. In order to confirm this, this study investigated the effect of L-tyrosine on granulation and disintegration of granular sludge in two identical sequencing airlift bioreactors (SABRs): one dosed with L-tyrosine (6 mg L-1) and the other without dosing. Changes in the physiochemical and biological properties of the aerobic granular sludge (AGS) and organic and nitrogen removal in both reactors operated under different ratios of chemical oxygen demand (COD) to nitrogen were closely monitored for 120 days. The L-tyrosine dosing shortened full granulation of AGS by 1 month. Disintegration of the granules and deterioration in the COD and nitrogen removal capability were not observed in the L-tyrosine dosed reactor even when the ratio of COD/N in the influent was reduced from 4 to 1 unlike the control reactor. This clearly confirmed the contribution of L-tyrosine in promoting AGS granulation and its stability. Both the enrichment of quorum sensing auto-inducer relating bacteria genera (21%) and the stable production of EPS were suggested as main reasons for the positive effect of L-tyrosine on the granulation and stability of AGS.