Abstract

The dewatering of cyanobacteria-laden sludge remains a challenge. Extracellular polymeric substances (EPS) mainly consist of polysaccharides and proteins, which form a stable gel network with water through hydrogen bonding and other interactions. To address this bottleneck, a low-voltage (5 V) electrochlorination system was constructed, employing a Ti/IrO2/RuO2 electrode as the anode, iron as the cathode, and calcium chloride dihydrate (CaCl2·2H2O) as the electrolyte. The results showed that the active chlorine generated during electrolysis degraded the highly water-retentive loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), converting them into low-viscosity, easily removable soluble EPS (S-EPS). Moreover, the total contents of polysaccharides and proteins in EPS decreased. Three-dimensional excitation-emission matrix fluorescence spectroscopy revealed that in the EPS of the algal sludge, the relative proportion of humic-like substances increased, while that of protein-like products decreased. At a CaCl2·2H2O dosage of 1 g/L, the dewatering performance of the algal sludge was significantly improved: the capillary suction time (CST) of the algal suspension decreased from 10.30 ± 0.1 s to 4.1 ± 0.05 s, the proportion of bound water decreased from 43.5% to 9.8%, and the cake solids content increased to 9.48%. The residual water quality of this process was also favorable, with total phosphorus (TP) and total nitrogen (TN) concentrations stabilized at 0.166 ± 0.040 mg/L and 9.0 ± 1.1 mg/L, respectively. Therefore, this study provides an efficient, low-energy electrochemical pretreatment strategy to overcome the dewatering bottleneck in cyanobacteria-laden sludge, thereby reducing the treatment load and cost of downstream mechanical dewatering.

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