Historical development of Al30 highlighting the unique characteristics and application in water treatment: A review

Unraveling the characteristics of dissolved organic matter removed by aluminum species based on FT-ICR MS analysis

Given the complexity of dissolved organic matter (DOM) and its interactions with coagulant chemicals, the mechanisms of DOM removal by aluminum (Al) coagulants remains a significant unknown. In this study, six test waters containing DOM with molecular weight (MW, <1 kDa, 1-10 kDa and >10 kDa) and hydrophobicity (hydrophilic, transphilic and hydrophobic) were prepared and coagulated with Al0, Al13 and Al30. The molecular-level characteristics of DOM molecules that were removed or resistant to removal by Al species were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that at the molecular level, saturated and reduced tannins and lignin-like compounds containing abundant carboxyl groups exhibited higher coagulation efficiency. Unsaturated and oxidized lipids, protein-like, and carbohydrates compounds were relatively resistant to Al coagulation due to their higher polarity and lower content of carboxyl groups. Al13 removed molecules across a wider range of molecular weights than Al0 and Al30, thus the DOC removal efficiency of Al13 was the highest. This study furthers the understanding of interactions between Al species and DOM, and provides scientific insights on the operation of water treatment plants to improve control of DOM.

Compositional and structural identification of organic matter contributing to high residual soluble aluminum after coagulation

Understanding the complexation of aluminum (Al) with dissolved organic matter (DOM) is of great significance for the control of residual Al in drinking water after treatment. Here, we used high-resolution and accurate mass measurements to identify the composition and structure of DOM contributing to the formation of soluble organically-bound Al during coagulation at near neutral pH (pH 7.50). The results showed that the organic compounds contributing to soluble organically-bound Al were primarily phenolic compounds and aliphatic compounds. Among them, phenolic compounds with a sulfonic acid group could greatly enhance the hydrolysis of polymeric Al and the formation of high concentrations of monomeric/oligomeric Al-DOM complexes. These organic molecules had a mass-to-charge ratio concentrated below 350. Based on the assumption that oxygen-containing functional groups providing unsaturation in the molecular structure were carboxyl groups, it was inferred that the maximum number of carboxyl groups in phenolic compounds and aliphatic compounds was concentrated between 1-2 and 2-4, respectively. The presence of these molecules was responsible for soluble organically-bound Al accounting for over 80 % of the total soluble Al in the supernatant after coagulation in this study. These findings deepen the understanding of the complexation of Al with DOM. In drinking water treatment plants, the combination of coagulation with processes that can remove such characteristic organics is beneficial for controlling residual Al.

Effects of electrostatic neutralization of Keggin Fe13 on the removal of micro and nano plastic

The successful preparation and identification of Keggin-structure Fe₁₃ clusters in recent years further enriched the potential application scenarios of ferric coagulants. Comparing the coagulation efficiencies and mechanisms of Fe₁₃ in the removal of nano/microplastics with conventional polymeric Al₁₃ and monomeric Al/Fe, this work aimed to elucidate the coagulation behaviour of Fe₁₃ compared with the traditional mono ferric coagulant, which has the coagulation applied bottleneck of quick and violet hydrolysis. The results showed that Fe₁₃ has a similar electrostatic neutralization potential to Al₁₃, which could keep a positively charged species, especially in acid conditions. The Fe₁₃ species has a selective removal potential toward the microplastics with a polar functional group like ester. Moreover, Fe₁₃ could hydrolyze to form active sol-gel hydroxides in neutral and alkalinity conditions, which is like the behaviour of traditional monomeric Fe coagulants but seldom restabilization. The electrostatic neutralization of Fe₁₃ could enhance the removal of nano plastic from - 25-75% compared with monomeric Fe at pH 4. The higher floc density as a monomeric Fe coagulant and better electrostatic neutralization potential of Keggin Fe₁₃ posed a good prospect for Fe₁₃ to replace the monomeric Fe coagulants in conventional coagulation.