Effect of the Cationic Block Structure on the Characteristics of Sludge Flocs Formed by Charge Neutralization and Patching

In this study, a template copolymer (TPAA) of (3-Acrylamidopropyl) trimethylammonium chloride (AATPAC) and acrylamide (AM) was successfully synthesized though ultrasonic-initiated template copolymerization (UTP), using sodium polyacrylate (PAAS) as a template. TPAA was characterized by an evident cationic microblock structure which was observed through the analyses of the reactivity ratio, Fourier transform infrared spectroscopy (FTIR), 1H (13C) nuclear magnetic resonance spectroscopy (1H (13C) NMR), and thermogravimetry/differential scanning calorimetry (TG/DSC). The introduction of the template could improve the monomer (AATPAC) reactivity ratio and increase the length and amount of AATPAC segments. This novel cationic microblock structure extremely enhanced the ability of charge neutralization, patching, and bridging, thus improving the activated sludge flocculation performance. The experiments of floc formation, breakage, and regrowth revealed that the cationic microblock structure in the copolymer resulted in large and compact flocs, and these flocs had a rapid regrowth when broken. Finally, the larger and more compact flocs contributed to the formation of more channels and voids, and therefore the specific resistance to filtration (SRF) reached a minimum.


Total number of pages (including the cover page): 4 pages This file contains 5 Tables, 4 Texts and 3 Figures.
Contents: Text S1. The details of the preparation of TPAA and CPAA.
Text S2. The details of the FTIR, 1 H ( 13 C) NMR and TG/DSC.

Text S3. Kelen-Tüdӧs method.
Text S4. Analytical method for SRF. Table S1. The calculating data relating to the monomer reactivity ratios in CPAA with the Kelen-Tüdӧs method under nPAAS:nAATPAC=0:1. Table S2. The calculating data relating to the monomer reactivity ratios in TPAA with the Kelen-Tüdӧs method under nPAAS:nAATPAC=1:1. Table S3. The average segment length of AM and AATPAC in CPAA and TPAA, respectively.     Text S1. The details of the preparation of TPAA and CPAA.
The preparation for TPTA and CPAA were as follows. First, a given amount of AM (60.00 mmol), AATPAC (40.00 mmol), urea (0.23 mmol), NaPAA (40.00 mmol; nNaPAA : nTM = 1:1), and deionized water (1.15 mol) was added into a 100 mL quartz jar. Second, the pH of the reaction solution was adjusted to about 4.5 by 0.5 mol L -1 HCl and NaOH, and then exposed under the ultrasonic wave radiation for 30 min to form a homogeneous solution at 20 °C. The ultrasonic wave was generated by an ultrasonicator (KQ 2200E, Kunshan ultrasonic instrument Co., LTD, China) and the frequency of that was 45 KHz. Third, the solution was deoxygenated through nitrogen bubbling for 30 min at ambient temperature. Finally, the quartz jar was sealed immediately after the addition of a given dose of initiator VA-044 to the mixture, and then continuously sonicated at 35-45 °C for 60-90 min. When the reaction was over, the copolymer was aged for 4 h at room temperature to increase the polymerization degree. Afterward, the copolymer was purified by acetone and dried until a constant weight was obtained. The preparation of CPAA was similar to that of TPAA except that no template and ultrasonication were used. The dried products were made into powder for the analyses of FTIR, 1 H ( 13 C) NMR, and TG/DSC. Text S2. The details of the FTIR, 1 H ( 13 C) NMR and TG/DSC.
The FT-IR of the products were recorded on a 550 Series Ⅱ infrared spectrometer (Mettler Toledo Instruments Co., Ltd., Switzerland) using KBr pellets. The 1 H ( 13 C) NMR of the products were conducted on an Avance 500 nuclear magnetic resonance spectrometer (Bruker Company, Ettlingen, Germany) with deuterium oxide (D2O) as the solvent. The thermal stabilities of the copolymers were investigated by TGA/DSC analysis which were carried out at a heating rate of 10 °C·min -1 under a nitrogen flow of 20 mL·min -1 from 20 to 600 °C on a DTG-60H synchronal thermal analyzer (Shimadzu, Kyoto, Japan).

Text S3. Kelen-Tüdӧs method
In the above formula, R is the molar ratio of the AM and AATPAC monomers in the raw material before the copolymerization reaction, and ƒ is the molar ratio of monomers in the polymers at a low conversion less than 15%. When the ƞ and ξ of each point were obtained, the linear fitting curve relating to ƞ and ξ could be plotted, and the rAM and rAATPAC could be obtained through the slope and intercept of the straight line. The calculating data relating to the monomer reactivity ratios with the Kelen-Tüdӧs method are displayed in Table S1 and Table S2.    Table S3.
The microblock structure could be evaluated by the average segment length of the monomers, and the calculation equations were expressed as follows: Here NAM and NAATPAC were the average segment length of the monomer AM and   The total monomer conversion of polymerization was determined by the gravimetric method [2].