Positive feedback on dewaterability of waste-activated sludge by the conditioning process of Fe(II) catalyzing urea hydrogen peroxide.

The treatment and disposal of sludge is a complex environmental problem because of the high moisture content. Herein, We reported the process of Fe(II) activating Urea hydrogen peroxide (UHP) to improve waste activated sludge (WAS) dewaterability for the first time. Fe(II)/UHP was proven to significantly improve WAS dewaterability. Specifically, under the optimal conditions with 60/35-Fe(II)/UHP mg/g TSS, the CST, SRF, and WCSC of WAS reduced from 215.3 ± 7.5s, 9.2 ± 0.32 (× 1012 m/kg), and 92.2 ± 0.7% (control) to 62.3 ± 4.3s, 2.8 ± 0.09 (× 1012m/kg), and 70.4 ± 0.4%, respectively. Further analysis revealed that •OH was generated in the Fe(II)/UHP system and played the dominant role in enhancing WAS dewaterability. •OH was found to attack extracellular polymeric substances (EPSs) and cells, causing EPSs fragmentation and decomposition part of EPSs into micro-molecule organics or even inorganics, and leading to cell destruction, thus liberating the EPSs-bound and cells-bound water. •OH also degraded the protein in centrifugal liquor (CL) into micro-molecule organics such as amino acids, which could reduce the viscosity and electronegativity of CL. The above facts ultimately reduced solid-liquid interface interaction but increased hydrophobicity, flocculation, and flowability of WAS. Meanwhile, the broken WAS flocs were then re-flocculated via adsorption bridging and charge neutralization induced by Fe(II) and Fe(III). Moreover, Fe(II)/UHP treatment achieved the reduction and stabilization of heavy metals of dewatered sludge, which further enabled its land application. Finally, the Fe(II)/UHP process was found to be more attractive than the Fe(II)/persulfate, classical Fenton processes, and cPAM in terms of cost savings and practical implementation.

Enhancing the dewaterability of waste activated sludge by the combined ascorbic acid and zero-valent iron/persulfate system.

In this work, a reducing/chelating agent, ascorbic acid (H2A) was introduced to the traditional zero-valent iron (Fe0)/persulfate (PS) process for waste activated sludge dewatering. The experimental data indicated that H2A-Fe0/PS process significantly enhanced the dewatering performance of sludge and enhanced the oxidation efficiency of Fe0-PS treatment. Under optimal conditions, the capillary suction time ratio before and after treatment (CST0/CST) of H2A-Fe0/PS treated sludge increased by 118% and 31.3% compared with untreated sludge and Fe0-PS treated sludge, respectively. The mechanism investigations revealed that the H2A-Fe0/PS induced excellent enhancement for sludge dewaterability could be credited to the reduction and chelating capacity of ascorbic acid. Free radicals including SO4•-, O2•- and •OH produced in the H2A-Fe0/PS process destroyed proteinaceous components and humic substances in sludge extracellular polymeric substances (EPS), thus reducing the negative charge and water holding capacity of sludge, improving the sludge rheological properties. As a result, the dewatering performance of sludge has been significantly improved.

In-depth research on percarbonate expediting zero-valent iron corrosion for conditioning anaerobically digested sludge.

Anaerobically digested sludge (ADS) is commonly hard to dewater for the presence of extracellular polymeric substances (EPS) and the liberation of glutinous soluble microbic products during anaerobic digestion. Sodium percarbonate (SPC) expediting zero-valent iron (ZVI) corrosion (SPC/ZVI) process firstly conditioned ADS to amend its dewaterability. Results showed that SPC/ZVI conditioning decreased moisture content of dewatered cake from 90.5% (control) to 69.9% with addition of 0.10 g/g TS SPC and 0.20 g/g TS ZVI. Mechanistic research indicated that the enhanced ADS dewaterability mainly resulted from •OH and Fe(III)/iron polymers yielded in SPC/ZVI. •OH disrupted EPS, damaged cytoderm & cytomembrane, and lysed intracellular substances, unbinding the bound water. Meanwhile, the breakage and inactivation of microbe by •OH prompted the production of macro-pores in ADS. •OH adjusted the conformation of extracellular/intracellular proteins by intervening in the H-bonds and S-S bonds, availing the hydrophobicity and slight flocculation of ADS. •OH further facilitated the despiralization of α-helical to ß-sheet structure in ADS pellets, benefiting cell-to-cell aggregation. Additionally, Fe(III)/iron polymers from ZVI corrosion accelerated to gather ADS and maintained its floc structure. Consequently, SPC/ZVI conditioning not only adjusted the natures of ADS and its EPS but also the features of residual pellets, which further induced the advancement of ADS dewaterability. In addition, SPC/ZVI conditioning possibly surmounts some limitations existing in ZVI/Peroxide or ZVI/Persulfate technique.