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Cationic Lignin Polymers as Flocculant for Municipal Wastewater.

ABSTRACT: 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.

SUBMITTER: Moore C

PROVIDER: S-EPMC8625770 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Poly(lactic acid) choline iodide ester methacrylate, poly(PLA4ChMA), is a cationic degradable polymer that can flocculate particles and dewater oil sands from tailings ponds. This novel material has yet to be characterized in terms of environmental and human health. If ingested, this substance may become bioaccessible. The bioaccessibility (bioaccessible fraction) of an ingested contaminant is a measure of the portion of an ingested dose that solubilizes and may be available for systemic absorption. In the present study, the partially degraded flocculant and its degradation products, modelled using lactic acid and choline chloride, were subjected to a modified physiologically based extraction test (PBET). Bioaccessible fractions were estimated by proton nuclear magnetic resonance (1H-NMR) spectroscopy and by high-performance liquid chromatography (HPLC). The measured bioaccessibility of lactic acid in gastric solution containing choline chloride is ∼100% but slightly dropped to 94% in intestinal solution at a solid-to-liquid ratio of 1:200. The partially degraded poly(PLA4ChMA) did not degrade further during the PBET and is not solubilized (i.e., 0% bioaccessibility) in the gastric phase but is fully solubilized (i.e., 100% bioaccessibility) in the intestinal phase. At the end of PBET intestinal digestion, the molar ratio of lactic acid to choline chloride in the presence of degraded poly(PLA4ChMA) was 2, approximately the same as in the initial solution. Thus, lactic acid and choline chloride are solubilized to the same extents in both gastric and intestinal solutions. Results suggest that HPLC can be used to directly estimate the bioaccessibility of lactic acid, whereas 1H - NMR may be used to indirectly quantify the bioaccessibility of both lactic acid and choline chloride by determining their molar ratio in PBET extracts. In future works, these findings may be applied to the estimation of risks from exposure to poly(PLA4ChMA) as well as to the remediation of contaminants flocculated by poly(PLA4ChMA) in tailings ponds and in other wastewaters.

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Cationic Lignin Polymers as Flocculant for Municipal Wastewater.

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