Unraveling the impacts of Cu+-based treatments on sludge dewaterability: The overlooked role of Cu3+

The high water content of sewage sludge increases the processing costs and hampers its further disposal. Fenton technology has proven to be efficient and been widely used to enhance sludge dewaterability, but it usually needs acidification and subsequent neutralization, thus consuming a lot of chemicals. It’s well documented that hydroxyl radicals produced in various Fenton or Fenton-like reactions play a crucial role in sludge dewatering. Based on the latest study, Cu+ and Cu+/H2O2 pretreatments for the enhanced dewaterability of sludge without extra pH adjustment were proposed. Results showed that Cu+ with and without H2O2 can significantly improve the dewatering performance of sludge, which was ascertained by a capillary suction time (CST) reduction rate of about 80 %. The proteins and polysaccharides in tightly-bound extracellular polymeric substance (TB-EPS) were decreased, while increased in soluble extracellular polymeric substance (S-EPS). In addition, a hydrophobic and porous surface was formed, and zeta potential increased after conditioned. These changes may release bound water and thus improve sludge dewaterability. The results of electron spin resonance and scavenging tests signaled that the Cu3+ was mainly accountable for the dissolution of EPS, rather than the hydroxyl radicals (OH). Our results substantiate and untangle a distinct reinforcement mechanisms for sludge dewatering by high valent copper (Cu3+). This study demonstrates for the first time that Cu3+ plays an important role in sludge dewatering, which has long been credited to hydroxyl radicals. It also urges re-evaluation of the Fenton(-like) system for sludge dewatering, given that Cu3+ could also cause potential oxidative destruction of EPS compared with reactive oxygen species.