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The feasibility of using Fe 0 /S 2 O 8 2− conditioning (zero valence iron (ZVI)/persulfate (ps)) integrated with horizontal electro-dewatering (HED) to improve the dewaterability of activated sludge (AS) was evaluated. The removal and migration of free and bound water in the ZVI/ps–HED process were determined, along with the organic matter migration between the solid and liquid phases of AS biosolids. Results showed that the optimum conditioning dosages were determined as 0.35 g ZVI/g dry solids (DS) and 0.15 g ps/g DS on the basis of capillary suction time variation. The lowest final water content (WC) of 83.67% in AS occurred after the HED treatment at 40 V and 120 min as determined using the response surface methodology. Despite the disruption of AS flocs and microbial cells through SO 4 − · oxidation during the ZVI/ps conditioning, the particle size and mass fractal dimension of the AS flocs remained relatively stable as the zeta potential increased from −8.5 mV to −4.6 mV. The coagulation of Fe 3+ from the oxidation of Fe 2+ by ps contributed to the relatively stable condition, which favored the subsequent momentum of the electroosmotic flow. Moreover, the ZVI/ps conditioning decreased the bound water content (BWC, from 1.83 g/g DS to 1.38 g/g DS) and increased the free water content (FWC, from 60.27 g/g DS to 60.91 g/g DS), indicating a transformation from free water to bound water. After the ZVI/ps–HED process, the FWC and BWC were removed significantly with ratios of 96.32% and 79.78%, respectively. Along with water removal through the ZVI/ps–HED process, the organic matter in the supernatant/filtrate initially increased and further rose at the HED stage. The analysis of the extracellular polymeric substance (EPS) content showed that the proteins (PNs) and polysaccharides (PSs) at the liquid and solid phases decreased due to oxidative degradation. Furthermore, the ZVI/ps stage significantly reduced the PNs content of slime to 57.22%, the PSs content of EPS to 68.50%, and the PN-like substances in the slime and tightly bound EPS to 74.90% and 52.47%, respectively. In addition, the WC of AS correlated with the contents of PN and microbial by-product-like material in slime, as well as tryptophan in TB-EPS, and the low EPS content in AS indicated good dewaterability. Thus, ZVI/ps should be selected as a pretreatment prior to HED. [ABSTRACT FROM AUTHOR]

Magnetic micro-particles (MMPs) and magnetic field (MF) were utilized as a coupling conditioning unit before dewatering activated sludge (AS) under a horizontal electric field. The removal and migration of free and bound water in AS during coupling magnetic conditioning–horizontal electro-dewatering (CM–HED) were determined. The organic matter migration between the solid and liquid phases of AS biosolids was also analyzed. Results show that MMPs dosage and MF intensity were determined as 0.15 g/g dry solids and 0.065 T for the best dewaterability, respectively. The optimum dewatering conditions for CM–HED with the final water content of 89.98% were 40 V and 120 min as determined using the response surface methodology. MMPs conditioning could induce a slight coagulation among AS flocs, increase the particle size from 85.9 μm to 92.3 μm and decrease mass fractal dimension from 2.18 to 2.07. The MMPs-conditioned AS also showed a network-like structure, banded cells with shrunk surfaces. CM–HED process effectively reduced the free water content (FWC) and bound water content (BWC) but increased the portion of BWC in AS. The corresponding removal ratios of bound water and free water were 52.89% and 95.86% at the anode side and 46.28% and 92.75% at the cathode side, respectively. The coupling magnetic conditioning led to the largest BWC reduction of 23.14% in CM–HED process, and most of this reduction approaching 92.83% occurred during magnetic micro-particle conditioning stage. Gravity field caused the largest sludge reduction of 87.45%. During HED stage, the removal ratio of free water in AS was 63.73% at the anode side and 36.54% at the cathode side, while it was 21.9% and 10.96% for bound water, respectively. Along with water removed by CM–HED process, the organic matter in supernatant/filtrate increased, and a sharp rise occurred during HED stage. Meanwhile, the extracellular polymeric substance (EPS) contents initially decreased at MMPs–MF conditioning stage and then increased at the HED stage. Lower EPS contents in AS indicated better dewaterability. The largest reduction in the EPS content of AS at MMPs–MF conditioning stage corresponded to the largest decline in BWC. Furthermore, the protein-like substances in the supernatant/filtrate increased from 30% to 50%, whereas the fulvic acid-like and humic acid-like substances decreased from 54% to 27% at the HED stage. MMPs significantly reduced the polysaccharide and protein contents in the slime–EPS by 90.26% and 99.25%, respectively. Approximately 92.35% of humic acid-like materials in tightly bound EPS were reduced by MMPs. Thus, coupling magnetic conditioning should be selected as pretreatment prior to HED. [ABSTRACT FROM AUTHOR]

A moderate Mn(Ⅶ) oxidation- in situ Fe(Ⅲ) coagulation (Mn(Ⅶ)-Fe(Ⅱ)) conditioning strategy was proposed to improve sludge filterability and release the water bound in extracellular polymeric substances (EPS). During Mn(Ⅶ)-Fe(Ⅱ) conditioning, flocs disintegration and cell disruption, macro and micro physicochemical properties of activated sludge, especially of EPS, were investigated. Relationships between protein molecular structures in EPS fractions of three layers and sludge dewaterability were also determined. Besides, factor analysis was used to explain the variances of "functional" protein secondary structures, which may have an important effect on sludge dewaterability. Results showed that sludge filterability (CST 0 /CST) increased by 2.40 times and partial bound water was released at 2 min oxidation of 120 mg/g KMnO 4 with subsequent FeCl 2 termination at equivalent molar ratio of 1:3. During this strategy, EPS wrapping on cells surface was disintegrated, and a limited influence occurred on cells. It was also found that CST and bound water content were strongly correlated with aggregated strands, random coil and β -turn percentages in slime (R 2 >−0.82, p < 0.05). Moreover, the dewaterability also presented strong negative correlations with aggregated strands, β -sheet and β -turn in TB-EPS (R 2 >−0.78, p < 0.05). This suggested that unfolding and despiralization of slime protein and moderate weakening rigidity of tightly bound EPS (TB-EPS) protein were beneficial for improvement of sludge dewaterability. In addition, the strong correlation between percentages of "functional" protein secondary structures and factor 1 score (R 2 > 0.85, p < 0.05) demonstrated that EPS migration, rather than only EPS disintegration, may have a key impact on the formation of some protein secondary structures in slime and TB-EPS. The observed protein secondary structures, which may affect sludge dewaterability, were probably derived from inner EPS. Graphical abstract Image 1 Highlights • CST 0 /CST reached 2.40 at a 2min Mn(Ⅶ) oxidation- in situ Fe(Ⅲ) coagulation. • Aggregated strands, random coil, β -turn in slime correlated with dewaterability. • Aggregated strands, β -sheet and β -turn in TB-EPS correlated with dewaterability. • Moderate weakening TB-EPS rigidity was beneficial for dewaterability improvement. • Aggregated strands, β -turn in slime and TB-EPS correlated with EPS migration. [ABSTRACT FROM AUTHOR]