Sustained oxidation of Tea-Fe(III)/H2O2 simultaneously achieves sludge reduction and carbamazepine removal: The crucial role of EPS regulation.

Establishing an economic and sustained Fenton oxidation system to enhance sludge dewaterability and carbamazepine (CBZ) removal rate is a crucial path to simultaneously achieve sludge reduction and harmless. Leveraging the principles akin to "tea making", we harnessed tea waste to continually release tea polyphenols (TP), thus effectively maintaining high level of oxidation efficiency through the sustained Fenton reaction. The results illustrated that the incorporation of tea waste yielded more favorable outcomes in terms of water content reduction and CBZ removal compared to direct TP addition within the Fe(III)/hydrogen peroxide (H2O2) system. Concomitantly, this process mainly generated hydroxyl radical (•OH) via three oxidation pathways, effectively altering the properties of extracellular polymeric substances (EPS) and promoting the degradation of CBZ from the sludge mixture. The interval addition of Fe(III) and H2O2 heightened extracellular oxidation efficacy, promoting the desorption and removal of CBZ. The degradation of EPS prompted the transformation of bound water to free water, while the formation of larger channels drove the discharge of water. This work achieved the concept of treating waste with waste through using tea waste to treat sludge, meanwhile, can provide ideas for subsequent sludge harmless disposal.

Enhanced sludge dewaterability by ferrate/ferric chloride: The key role of Fe(IV) on the changes of EPS properties.

The complex characteristics of extracellular polymeric substances (EPS) seriously affect the improvement of sludge dewaterability. Ferrate (Fe(VI))/ferric chloride (Fe(III)) was applied through its strong oxidability to effectively enhance sludge dewaterablity by changing the properties of EPS in this study. Results confirmed that water content (WC), specific resistance to filtration (SRF) and capillary suction time (CST) fell from 82.8 %, 9.3 × 1010 s2/g and 35.1 s to 76.1 %, 2.6 × 1010 s2/g and 16.2 s, respectively, when adding 12 mg Fe(VI)/g VSS and 12 mg Fe(III)/g VSS with the dosing interval of 5 min. Investigations of the mechanism strongly suggested that Fe(VI) was successfully catalyzed by Fe(III), promoting the generation of methyl phenyl sulfone (PMSO2) and facilitating the electron transfer, with Fe(IV) having the major role in the oxidation process. Furthermore, sludge water-holding capacity and hydrophilicity waned after oxidation due to the destruction of EPS structure, which promoted the decrement of bound water to enhance the discharge of sludge water, so as to improve the efficiency of dewatering.

Improvement of sludge dewaterability by energy uncoupling combined with chemical re-flocculation: Reconstruction of floc, distribution of extracellular polymeric substances, and structure change of proteins.

This study innovatively combines energy uncoupling and chemical re-flocculation helped to accelerate residual sludge dewatering. Ferric chloride (FeCl3) and 3, 3', 4', 5-tetrachlor-osalicylanilide (TCS) were employed as the flocculant and uncoupler, respectively. The results showed that the specific resistance to filtration (SRF) and the water content of sludge filtered cake fell dramatically from 11 × 1012 m/kg and 80.2% to 1.1 × 1012 m/kg and 77.1% respectively, when the addition of TCS ranged from 0 to 0.12 g/g VSS with flocculation conditioning. The distribution of sludge extracellular polymeric substance (EPS) was altered radically after adding TCS, leading to the collapse and fragmentation of EPS, causing the reduction and formation of fragmentized sludge flocs. Meanwhile, the stretching and deformation vibrations of CO and NH bonds suggested the strong attack between TCS and EPS proteins, while variations of the main secondary structures of protein (i.e. α-helix, ß-sheet and random coil) indicated the loose structure of proteins and enhanced hydrophobicity. Consequently, the cracked and loose structure of residual sludge resulted in the release of bound water. After TCS addition combined with chemical re-flocculation, the channels of sludge water discharge were widened, guaranteeing the discharge of sludge water. Therefore, the sludge dewaterability was elevated under the energy uncoupling combined with chemical re-flocculation. As well, the application of TCS would not destroy sludge cells, in which bioenergy (sludge carbon source) could be retained and effectively utilized in the subsequent disposal process. The findings reported here not only widen our perception of the energy uncoupling technology, but also encourage researchers to explore both effective and economic methods on the basis of energy uncoupling, aiming to achieve high-efficiency of reduction and dewatering in the future.