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

Abstract

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, β-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.