Occurrence State and Molecular Structure Analysis of Extracellular Proteins with Implications on the Dewaterability of Waste-Activated Sludge

Abstract

The occurrence state and molecular structure of extracellular proteins were analyzed to reveal the influencing factors on the water-holding capacities of protein-like substances in waste-activated sludge (WAS). The gelation process of extracellular proteins verified that advanced oxidation processes (AOPs) for WAS dewaterability improvement eliminated the water affinity of extracellular proteins and prevented these macromolecules from forming stable colloidal aggregates. Isobaric tags for relative and absolute quantitation proteomics identified that most of the extracellular proteins were originally derived from the intracellular part and the proteins originally located in the extracellular part were mainly membrane-associated. The main mechanism of extracellular protein transformation during AOPs could be represented by the damage of the membrane or related external encapsulating structure and the release of intracellular substances. For the selected representative extracellular proteins, the strong correlation (R > 0.97, p < 0.03) between the surface hydrophilicity index and α-helix percentages in the secondary structure indicated that the water affinity relied more on the spatial distribution of hydrophilic functional groups rather than the content. Destructing the secondary structure represented by the α-helix and stretching the polypeptide aggregation in the water phase through disulfide bond removal might be the key to eliminating the inhibitory effects of extracellular proteins on the interstitial water removal from WAS.

Persulfate and zero valent iron combined conditioning as a sustainable technique for enhancing dewaterability of aerobically digested sludge

“…extracellular proteins was considered more important in holding bound water, as they comprise the major hydrophilic groups in the sludge (Wu et al, 2017).…”

Improving waste activated sludge dewaterability with sodium periodate pre‐oxidation on extracellular polymeric substances

“…EPS consists of high hydrophilic substances, and those substances mainly include proteins and polysaccharides. Moreover, protein played more important role in sludge dewaterability than polysaccharides (Wu, Zhang, et al, 2017;Wu, Ni, et al, 2017). The influence of NaIO 4 concentration and initial pH on the properties of different EPS fractions is shown in Figure 1.…”

“…Some advanced sludge treatment processes, such as heat hydrolysis and acid/alkaline treatment, have been developed to improve sludge dewatering efficiency (Guan et al, 2012). In addition, chemical oxidation (Wu et al, 2015), such as the Fenton reaction and potassium permanganate (Wu, Zhang, et al, 2017;Wu, Ni, et al, 2017), has been reported as an effective approach to solubilize EPS. Fenton's oxidation process utilizes Fe (II) to activate H 2 O 2 , generating hydroxyl radicals, which can oxidize proteins and polysaccharides and destroy the connections between EPS and water.…”

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“…bound water) and stabilized microbial aggregation colloid. [6][7][8] That cannot full the disposal requirements of sludge landll and incineration (i.e. DS more than 40% and 50% respectively, in China standard GB/T 23485-2009 and GB/T 24602-2009).…”