Behind the remarkably enhanced dewaterability of sludge by co-conditioning strategy: The key role of rheological characteristics and protein secondary structure evolution

The combined use of tannic acid and polymeric quaternary ammonium salt was newly reported for enhancing sludge dewaterability in our previous work. However, the conclusion regarding protein precipitation effect was lack of in-depth investigation. Herein, in this work, sludge flocs property and protein secondary structure variation was further characterized. Results showed that the compressibility reduced from 1.06 to 0.61, while the elastic modulus (G′), the viscous modulus (G″) increased from 26.93 to 70.21 Pa and 2.56 to 5.96 Pa, respectively. The above changes indicated that the sludge flocs became denser, exhibiting improved deformation resistance and structural strength. From the perspective of protein secondary structure identification, α-helix increased from 18.59 % to 24.03 %, β-turn decreased from 32.41 % to 25.38 %, giving rise to an enhancement of the protein hydrophobicity and implying a possible disruption of orderly hydrogen-bonding networks. Overall, this work provided an in-depth insight of the dewaterability improvement behind the co-conditioning strategy.