Moore Courtney, Gao Weijue, Fatehi Pedram
Green Processes Research Centre and Biorefining Research Institute, Lakehead University, Thunder Bay, ON P7B5E1, Canada.
Polymers (Basel). 2021 Nov 9;13(22):3871. doi: 10.3390/polym13223871.
The radical polymerization of acid-washed and unwashed softwood kraft lignin with [2-(methacryloyloxy) ethyl] trimethylammonium chloride (METAC) was attempted to investigate the production of lignin-based flocculants for simulated wastewater. The incorporation of METAC onto lignin resulted in a cationic charge density (2.3-3.3 meq/g), increased water solubility (89-96% in neutral pH), and increased molecular weight (70,000-210,000 g/mol) of lignin. The lignin-METAC polymers generated from acid-washed lignin had higher molecular weights than those generated from unwashed lignin. The lignin-METAC polymers showed lower resistance to thermal decomposition than unmodified lignin due to the inclusion of PolyMETAC. The unmodified acid-washed lignin samples did not significantly affect the COD of the wastewater, while the unmodified unwashed lignin samples contributed to the COD, implying that unmodified lignin was not suitable for wastewater treatment. The flocculation of wastewater with lignin-METAC led to the chemical oxygen demand (COD) reduction of 17-23% and total organic carbon (TOC) drop of 51-60%. The lignin-METAC polymer with the highest molecular weight (produced from acid-washed lignin) reached the highest COD removal, while lignin-METAC polymer with the highest charge density (produced from unwashed lignin) reached the highest TOC removal. Focused beam reflectance measurement (FBRM) studies revealed that the lignin-METAC polymer produced from acid-washed lignin with a high molecular weight generated larger and more flocs in wastewater than the lignin-METAC polymer produced from unwashed lignin. The comparison of theoretical and experimental dosages required for neutralizing the charges of wastewater demonstrated that charge neutralization was the main flocculation mechanism, although a bridging mechanism was also involved for component removals from wastewater. The use of 1 mg/L of alum along with 65 mg/L lignin-METAC in a dual coagulation-flocculation system led to higher average phosphorous (42%) and COD (44%) removals than the singular flocculation system only using 65 mg/L of lignin-METAC (with phosphorous removals of 3.4% and COD removals of 18.7%). However, lignin-METAC flocculant slightly increased the ammonia-nitrogen content in both singular flocculation and dual coagulation-flocculation systems due to the residual ammonia content of lignin-METAC. The coagulation-flocculation system determined that the use of lignin-METAC (65 mg/L) could reduce the alum dosage significantly while maintaining a similar organic content reduction of 44% for wastewater.
尝试用[2-(甲基丙烯酰氧基)乙基]三甲基氯化铵（METAC）对酸洗和未酸洗的软木硫酸盐木质素进行自由基聚合，以研究用于模拟废水的木质素基絮凝剂的生产。METAC与木质素结合后，木质素的阳离子电荷密度为（2.3 - 3.3 meq/g），水溶性增加（在中性pH下为89 - 96%），分子量增加（70,000 - 210,000 g/mol）。由酸洗木质素生成的木质素-METAC聚合物的分子量高于由未酸洗木质素生成的聚合物。由于包含聚METAC，木质素-METAC聚合物对热分解的抗性低于未改性的木质素。未改性的酸洗木质素样品对废水的化学需氧量（COD）影响不显著，而未改性的未酸洗木质素样品会导致COD增加，这意味着未改性的木质素不适用于废水处理。用木质素-METAC对废水进行絮凝可使化学需氧量（COD）降低17 - 23%，总有机碳（TOC）降低51 - 60%。分子量最高的木质素-METAC聚合物（由酸洗木质素制成）实现了最高的COD去除率，而电荷密度最高的木质素-METAC聚合物（由未酸洗木质素制成）实现了最高的TOC去除率。聚焦光束反射测量（FBRM）研究表明，由酸洗木质素制成的高分子量木质素-METAC聚合物在废水中产生的絮体比由未酸洗木质素制成的木质素-METAC聚合物更大、更多。中和废水电荷所需的理论剂量与实验剂量的比较表明，电荷中和是主要的絮凝机制，不过桥连机制也参与了从废水中去除成分的过程。在双凝聚-絮凝系统中，使用1 mg/L的明矾与65 mg/L的木质素-METAC，其平均磷去除率（42%）和COD去除率（44%）高于仅使用65 mg/L木质素-METAC的单一絮凝系统（磷去除率为3.4%，COD去除率为18.7%）。然而，由于木质素-METAC中的残余氨含量，木质素-METAC絮凝剂在单一絮凝和双凝聚-絮凝系统中都会使氨氮含量略有增加。凝聚-絮凝系统确定，使用木质素-METAC（65 mg/L）可以显著减少明矾用量，同时保持对废水有机含量的类似降低效果，降低率为44%。
