Flocculation performance enhancement of organic polymer flocculants via adjusting cationic block length: molecular structure and characteristics

Graft copolymerization synthesis of chitosan-polyferric sulfate composite coagulant to improve biogas slurry treatment toward effective irrigation

Biogas slurry from anaerobic digestion of organic wastes can be a potential biofertilizer for agricultural irrigation, which however, is challenged by suspended solids and contaminants. Thus, this study synthesized a composite coagulant and optimized its performance to advance biogas slurry treatment. A natural-synthetic polymer, chitosan (CTS), was modified by 2-methacryloxyethyltrimethyl ammonium chloride (DMC) via graft copolymerization and then combined with polyferric sulfate (PFS) to formulate the composite CTS-g(DMC)-PFS coagulant. Results show that CTS-g(DMC)-PFS exhibited stronger electrical neutralization and adsorption bridging to destabilize and aggregate colloidal particles, thus, exhibiting higher removal of suspended solids, heavy metals, and antibiotics over individual and pristine coagulants. Graft copolymerization of CTS with DMC at the mass ratio of 1:9 maximized its water solubility. Further blending this mixture with PFS at the mass ratio of 1:2 effectively improved the coagulation of biogas slurry, particularly for the removal of antibiotics and heavy metals (e.g. enrofloxacin and Cu). Moreover, CTS-g(DMC)-PFS produced dense and compact flocs for effective sedimentation. Detailed characterization attributed such improvement to the hydrolysis of cationic quaternary ammonium groups on grafted monomers and further coordinative effects between CTS-g(DMC) and Fe to enhance molecular chains and positive charges in CTS-g(DMC)-PFS to facilitate particle aggregation, contaminant adsorption, and then floc sedimentation.

Octopus-inspired flocculant for oily wastewater decontamination: Hydrophilic-hydrophobic convertibility and auto-separation characters

Unilateral hydrophobic flocculant and unsatisfactory floc separation constrained the efficacious purification of oil-containing wastewater. Illumined by the hunting behavior of mimic octopus, a biomimetic flocculant (CNSDA) with temperature-sensitive chains (color pouch) and hollow silica cores (mantle) was manufactured to derive hydrophilic-hydrophobic convertibility and auto-separation capabilities. Physical-chemical information of CNSDA was elucidated through characterization analysis. The flocculation behaviors of temperature-sensitive chains and hollow silica cores were evaluated by flocculation experiments. Results indicated that the configuration of CNSDA molecular chains varied from extension to constriction and revealed hydrophobicity as the temperature crossed 29.6 ℃. Compared with 20 ℃, the flocculation efficiencies rocketed at 40 ℃ by CNSDA, and excess flocculants were adsorbed by as-formed flocs through nonpolar interactions (the residual was low to 2.27 % at 160 mg/L). Concomitantly, the contracted molecular chains were contributed to generating dense flocs with low moisture content that flocked into large ones and expedited the solid-liquid separation process (60 % shorter than cationic polyacrylamide) with the auxiliary of low-density cores. The hydrophobic adsorption mechanism actuated by temperature-sensitive character was the decisive factor for high-efficiency flocculation. This study can provide meaningful references for the conception and exploitation of oily wastewater disposal agents.

Synthesizing cationic polymers and tuning their properties for microalgae harvesting

This study reports a facile technique to synthesize and tune the cationic polymer, poly(3-acrylamidopropyl)trimethylammonium chloride (PAPTAC), in terms of molecular weight and surface change for harvesting three microalgae species (Scenedesmus sp., P.purpureum, and C. vulgaris). The PAPTAC polymer was synthesised by UV-induced free-radical polymerisation. Polymer tuning was demonstrated by regulating the monomer concentration (60 to 360 mg/mL) and UV power (36 and 60 W) for polymerisation. The obtained PAPTAC polymer was evaluated for harvesting three different microalgae species and compared to a commercially available polymer. The highest flocculation efficiency for Scenedesmus sp. and P. purpureum was observed at a dosage of 25 mg-polymer/g of dry biomass by using PAPTAC-90, resulting in higher flocculation efficiency than the commercial polymer. Results in this study show evidence of effective neutralisation of the negative charge surface of microalgae cells by the produced cationic PAPTAC polymer and polymer bridging for effective flocculation. The obtained PAPTAC polymer was less effective for harvesting C. vulgaris, possibly due to other factors such as cell morphology and composition of extracellular polymeric substances of at the cell membrane that may also influence harvesting performance.

Coagulation performance and mechanism analysis of humic acid by using covalently bonded coagulants: effect of pH and matching mechanism of humic acid functional groups

Conventional inorganic coagulants (Al, Fe) and Al/Fe-based covalently bonded flocculants (CAFMs) had different hydrolysis species at different pHs, which subsequently led to differences in their binding sites and complexation ability with humic acid (HA). Studying the binding sites and interactions between CAFMs, AlCl3 (Al), and FeCl3 (Fe) hydrolysates and HA molecules is critical to understanding the coagulation mechanism. The results found that CAFM 0.6, Al, and AlCl3 combined FeCl3 (Al/Fe) removed more than 90% of HA at pH 6, and CAFMs showed higher HA removal rate than that of Al, Fe, and Al/Fe under the same reaction conditions. The flocs of CAFMs contained abundant -NH2/OH as well as the large particle size, compact structure, and excellent settling performance. The hydrolyzed species of Al and Fe were predominantly Alb and Feb at pH 6, but the hydrolyzed species of CAFMs were primarily (Al + Fe)c. Moreover, the hydrolyzed species of Al and Al/Fe were found to complex with HA functional groups such as -COOH, C = O, C-H/C-C, C = C, and C-OH to form ligand bonds, while the hydrolyzed species (Al + Fe)c of CAFMs could deeply interact with HA functional groups including C-O, -COOH, C = O, C-H/C-C, C = C, and C-OH by the adsorption and sweeping.

Intrinsic mechanism for the removal of antibiotic pollution by a dual coagulation process from the perspective of the interaction between NOM and antibiotic

Antibiotics bring potential risks to human health and ecosystem, and their coexistence with natural organic matters (NOMs) could have harmful impacts on the environment. Herein, a polyaluminium chloride (PAC)-polydimethyl diallyl ammonium chloride (PDMDAAC) dual coagulation process was designed to remove the co-pollutants of chlortetracycline (CTC) and humic acid (HA), representing antibiotics and NOMs, respectively. The main research strength was given to understand molecular interactions and their mechanisms associated with the coagulation and flocculation. We found that the co-existing HA and CTC increased the hydrophily and stability of contaminants, and generated HA@CTC complexes with large particles size. The interaction mechanism between CTC and HA was mainly hydrogen bonding, hydrophobic association action, n-π* electron donor-acceptor interaction, and π-π* conjugation. Lewis acid-base interaction was the main force between HA and CTC. The bonding energies of OH…N, OH…O, and hydrophobic association were -12.2 kcal/mol, -13.1 kcal/mol, and -11.4 kcal/mol, respectively, indicating that hydrogen bonding was stronger than hydrophobic association. The interactions between HA and CTC could improve their removal efficiency in the coagulation process. This is due to that the functional groups (COOH and OH) in the HA@CTC could be adsorbed by Al based hydrolysates. Polar interaction dominated the CTC and HA removal, and PAC was more efficient than PDMDAAC to remove HA@CTC complexes due to its higher complexing capacity. Thanks to the low concentration of residual contaminants and the formation of large and loose flocs, the interaction of HA and CTC could alleviate membrane fouling during ultrafiltration process. This study will provide new insight into the efficient removal of combined pollution and membrane fouling control.