How can the addition of extracellular polymeric substances (EPS)-based bioflocculant affect aerobic granular sludge (AGS)?

The ability of extracellular polymeric substances (EPS) recovered from aerobic granular sludge (AGS) to act as bioflocculant was tested in a pilot-scale sequencing batch reactor (SBR), fed with low-strength municipal wastewater. EPS were compared with the addition of Na-alginate as a standardized biopolymer. The optimal dosage of both biopolymers was determined through jar-test assays (400 mg L-1 of Na-alginate in a 250 mg Ca L-1 and 50 mg L-1 of EPS in pH of 2 & PLUSMN; 0.2). The addition of Na-alginate (Operational Period I- OP-I) and EPS (Operational Period II -OP-II) led to increased adhesion of particles with 2.9 & PLUSMN; 0.45 and 1.3 & PLUSMN; 0.3 g TSS L-1 during OP-I and OP-II, respectively, and fast settling biomass (SVI30 between 68 and 78 mL g(-1)). Granule pre-dominance occurred at early stages of OP-I (day 37) and OP-II (day 44), presenting diameters mainly within the 212-600 mu m range. The reactor showed removal efficiencies of 85% for biochemical oxygen demand (BOD) and above 50% for N-NH4 during the study periods. Furthermore, the addition of EPS as a bioflocculant promoted a substantial increase in polysaccharides (PS = 153.01 & PLUSMN; 121 mg g(VSS)(-1)) and proteins (PN = 121.96 & PLUSMN; 69 mg g(VSS)(-1)), while the addition of Na-alginate affected mostly the PS content (87 & PLUSMN; 24 mg g(VSS)(-1)). The microbial community shifted mainly from Betaproteobacteria (45%) during OP-I to Alphaproteobacteria (64%) in OP-II. Therefore, EPS affected both physical-chemical and microbial features of the AGS biomass without any change in treatment efficiencies. EPS is a promising resource to be recovered from aerobic granular sludge and to be used as an alternative and sustainable bioflocculant.

Automated summary

The ability of extracellular polymeric substances (EPS) recovered from aerobic granular sludge (AGS) to act as bioflocculant was tested in a pilot-scale sequencing batch reactor (SBR), fed with low-strength municipal wastewater. EPS were compared with the addition of Na-alginate as a standardized biopolymer. The addition of both EPS and Na-alginate led to increased adhesion of particles and improved settling biomass in the reactor.