Elucidating the effects of starvation and reactivation on anaerobic sulfidogenic granular sludge: Reactor performance and granular sludge transformation.

In biological wastewater treatment, the bacteria starvation always challenges the stability of system operation. Yet, the effects of starvation and possibility of reactivation are less understood for anaerobic sulfidogenic system. Sulfidogenic systems use sulfate as electron acceptor for organic chemical oxygen demand (COD) degradation, so it will encounter two kind of starvations: (i) complete stoppage of wastewater flow (named complete food starvation) and (ii) remaining organic COD but with very low level sulfate in the influent (named sulfate starvation). In this study, the relative long-term starvation (over 30-day) and subsequent reactivation were studied in two lab-scale continuous gas recirculation sulfate-reducing upflow sludge bed (CGR-SRUSB) reactors. It was observed that the complete food starvation and sulfate starvation decreased the COD removal rate (in the similar range of 60-65%) and the specific sulfidogenic activity (about 45% and 61% respectively), as well as increasing the sludge flotation potential (SFP) from <15% to 58% and 35% respectively. Moreover, the following restoration experiments proved that the perturbed systems could be reactivated within 10-15 days for both cases. The results of investigating the mechanisms showed the performance deterioration were highly attributed to the starvation-induced granular sludge transitions, with respect to the changing of sludge physico-chemical properties (permeability, porosity, hydrophobicity and viscocity) and microbial stuctures (sulfate-reducting bacteria and extracellular polymeric substances). The outcomes of this study can provide useful information for dealing with the prolonged starvation problems in sulfidogenesis-based systems in industrial and municipal wastewater treatment.