Molecular insights into the mechanism and the efficiency-structure relationship of phosphorus removal by coagulation.

Types and structures of phosphorus compounds influence the removal of phosphorus by coagulation. Until now, the molecular-level interaction between coagulants and phosphorus (especially organophosphates) and the relationship between removal efficiency and phosphorus structure have not been clear. This work investigated the removal of phosphorus with different structures using conventional coagulants (poly aluminum chloride (PACl) and polymerized ferric sulfate (PFS)) and a novel covalently-bound inorganic-organic hybrid coagulant (CBHyC). CBHyC removed more than 98% of phosphate and most of organophosphates, had more stable performance than PACl and PFS, and was less affected by pH, initial phosphorus concentration, and co-occurring materials. Molecular dynamics simulation demonstrated that CBHyC removed phosphorus mainly through electrostatic attraction and hydrophobic interaction. Furthermore, this work established QSAR (quantitative structure activity relationship) models for removal efficiency and organophosphate structure for the first time. The model showed that atomic charges of phosphorus atoms (QP) and hydrogen atoms (QH+) in the system and the energy gap (ΔEMO) affected electronegativity and hydrophobicity, thus influencing organophosphate removal efficiency. The model had high fitting precision and good predictive ability and has the potential to greatly reduce the cost of optimizing processes and conditions for phosphorus removal.

[Effect of composite flocculants made of polyaluminium chloride and polydimethyldiallyammonium chloride on ultra-filtration membrane characteristics].

The composite flocculants made of polyaluminium chloride and polydimethyldiallyammonium chloride (PAC-JY01) were used to treat the humic acid-kaolin simulation of water simples by enhanced coagulation. The effluent from coagulation continued to be treated by ultrafiltration. The objective of this research is to identify the mechanism of coagulation affecting UF due to different treated water quality and operational status of UF. The research shows that, in the coagulation-ultrafiltration (UF) hybrid process, the optimum coagulant dosage and pH value are 3 mg/L and pH = 6, respectively. At the optimum condition, the removal efficiency of UV254 and turbidity are 79.30%, 99.70%, respectively. In test conditions, the larger flocs are easy to deposit on the membrane surface causing membrane fouling.

[Purification of Al13 species in polyaluminum chloride (PAC) by column chromatography and the character of the fractions].

The polynuclear keggin species, Al12AlO4(OH)24(H2O)12(7+) (Al13), was separated and purified from polyaluminum chloride (PAC) by column chromatography method. The three fractions were characterized by Al-Ferron timed complexation spectrophotometry, TEM and ZATESIZER tester. Jar tests were performed to test the coagulation efficiency of the three fractions in treating synthetic or actual water samples. The results show that the sample purified by the column chromatography method influenced by the size of the species. The bigger molecules were eluted first, then the smaller ones. Al13 would be obtained by taking out the middle fraction. Compared with the other two fractions, the third fraction gives the best results for turbidity, humic acid and color removal, and achieves the highest charge-neutralizing ability. Al13 species is a higher positive-charged species and can be applied in a wide pH range, and it is much more steady in hydrolyzing process and most effective polymeric Al species in water and wastewater treatment.

Characterization and coagulation of a polyaluminum chloride (PAC) coagulant with high Al13 content.

A polyaluminum chloride (PAC) coagulant was prepared from AlCl3 x 6H2O and Na2CO3. The Al13 species in PAC was separated and purified by the SO4(2-)/Ba2+ deposition-replacement method, and characterized by 27Al-NMR and XRD. From 27Al-NMR spectroscopy, it was found that PAC obtained after separation and purification contained more Al13 (PAC-Al13, for short) than original PAC before separation and purification. In XRD spectra, a strong Al13 signal appeared in the range of 2theta from 5 to 25 degrees. Jar tests were performed to test the coagulation efficiency of AlCl3, PAC and PAC-Al13 in treating synthetic or actual water samples. Compared with PAC and AlCl3, PAC-Al13 gives the best results for turbidity, humic acid and color removal, and achieves the highest charge-neutralizing ability. Under the study conditions, PAC-Al13 gave about 90% humic acid removal and almost 100% reactive blue dye removal when its dosages were 4.0 and 15 mg/L as Al, respectively. The Al13 species has a higher positive charge and is the most effective polymeric Al species in water and wastewater treatment.

On-line optical determination of floc size of Fe(III) coagulants.

This study investigated the floc aggregation, average floc size, floc size variance and floc growth velocity when ferric chloride (FeCl3) and polyferric chloride (PFC) were used to treat the simulated water samples. The factors including coagulant dose, ionic strength and solution pH, which affect the floc aggregation, were studied. Experiments were carried out in a bench-scale reactor using photometric dispersion analyzer (PDA). Results showed that there were great differences between the floc aggregation of PFC and FeCl3. The average floc size and floc growth velocity of PFC were much larger than those of FeCl3. Compared with FeCl3, PFC gave a better coagulation performance in wider range of pH, dosage and ionic strength. It was also found that the coagulation efficiency of PFC did not depend on average floc size but on floc growth velocity.

[Electrical charges and coagulation efficiency of Al13 species in polyaluminum chloride (PAC)].

The polynuclear Keggin species, Al12AlO4(OH)24(H2O)12(7+) (Al13), was separated and purified from polyaluminum chloride (PAC) by gel column chromatographic method. The purified Al13 was characterized by Al-Ferron timed complexation spectrophotometry method and ZATESIZER 3000HSA tester compared with PAC and ALCl3. Jar tests were performed to test the coagulation efficiency of the three coagulants in treating synthetic or actual water samples. The results showed that Al13 could be obtained by the column chromatographic method and the content of it could reach about 99%. Compared with PAC and AlCl3, Al13 gives the best results for turbidity, humic acid and color removal, and achieves the highest charge-neutralizing ability. Al13 species is a higher positive-charged and wide pH range application, it is much more steady in hydrolyze process and most effective polymeric Al species in water and wastewater treatment.

[Purification and characterization of nano Al13 species in polyaluminum chloride].

The polynuclear Keggin species, Al12AlO4(OH)24(H2O)12(7+) (Al13), was firstly separated and purified from polyaluminum chloride (PAC) by the ultra-filtration and column chromatography method. The Al13 yield was characterized by Al-Ferron timed complexation spectrophotometry, 27Al-NMR, TEM and ZATESIZER 3000HSA. The results showed that the purified sample by the ultrafiltration method influenced by membrane pore radius and the concentration of PAC solution. High purity Al13 would be obtained by choosing appropriate membrane and concentration of PAC. When using the column chromatography method, the bigger molecules were eluated first, then the smaller ones. Al13 would be obtained by taking out the middle educt. From Al-Ferron timed complexation spectrophotometry, it was found that the obtained sample contained more than 90% and 100% of Al13 by using the two methods mentioned above respectively. The TEM and ZATESIZER 3000HSA results showed that Al13 was mainly aggregated as line type and branch type in B = 2.5 solution, and the size was about several decade and several hundred nm.