Anaerobic digestion of amine-oxide-based surfactants: biodegradation kinetics and inhibitory effects

Complete biodegradability assessment of polyoxyethylene glycerol ester non-ionic surfactant: Aerobic, anaerobic, combined biodegradation and inhibitory effects

Aerobic and anaerobic biodegradability have become one of the most relevant characteristics for all contaminants. This is especially important in case of surfactants, which are discharged in wastewater treatment plants or directly into the aquatic bodies. The aim of this study is the integral assessment of the biodegradability of the non-ionic surfactant polyoxyethylene glycerol ester PGE-OE17. The aerobic and anaerobic biodegradation of PGE-OE17 was evaluated at different initial surfactant concentrations, and the evolution of the toxicity of the surfactant and its by-products was followed during the aerobic and anaerobic processes using bacteria Vibrio fischeri. PGE-OE17 was not completely biodegradable neither aerobically nor anaerobically, and the increase in the initial surfactant concentration had a negative effect in the biodegradation. Toxicity of the surfactant solutions and degradation by-products had a first increase followed by a gradual decrease during both tests, revealing that toxic substances released can harm the microorganisms and therefore hinder the biodegradation. Additionally, combined aerobic-anaerobic biodegradation tests were performed, consisting in a first aerobic treatment of different duration and initial concentration, followed by a complete anaerobic treatment. Results showed that a balance between aerobic and anaerobic biodegradation duration can maximize the biodegradation rates in comparison with only aerobic or anaerobic tests.

Enhancing methane production from anaerobic digestion of waste activated sludge with addition of sodium lauroyl sarcosinate

In this study, sodium lauroyl sarcosinate (SLS) was used to promote anaerobic digestion of waste activated sludge for producing methane. It was found maximum cumulative methane production increased from 98.1 ± 3.1 to 166.0 ± 4.3 mL/g Volatile Suspended Solids (VSS) with dosage increasing from 0 (control) to 40 mg SLS/g TSS. But the addition of SLS (>10 mg SLS/g Total Suspended Solids (TSS)) resulted in prolonged lag phase time. Microbiological analysis showed that Syntrophobacter and Syntrophomonas both got enriched in reactors fed with SLS. Furthermore, hydrogenotrophic methanogens genus got more enrichment in contrast to acetoclastic methanogens. Mechanism analysis indicated that addition SLS could decrease surface tension, and promote release of organic matters as well as improve activities of hydrolytic enzymes. Besides, SLS could be nearly degraded completely within 3 days, and its degradation intermediates could be further transformed into methane gradually, thus enhancing methane production eventually.

Synthesis and pH-stimuli responsive research of gemini amine-oxide surfactants containing amides

The series of gemini amine-oxide surfactants with the formula C n H2n+1CONH(CH2)2N+O-(CH3)-(CH2)3-(CH3)N+O-(CH2)2NHCOC n H2n+1 (n = 11, 13, 15, and 17) has been synthesized successfully. Their isoelectric point and acid dissociation constant were measured to determine the ionization form of the surfactant molecules in aqueous solution within different pH values. The studies showed that the length of the hydrophobic alkyl chains had a great influence on the pH-stimuli responsive behavior of these surfactants. When n ≤ 13 (n-3-n-OA), the regularity of the pH-stimuli responsive behavior of the surfactant solutions was relatively consistent, while the surfactants with longer hydrophobic alkyl chain lengths lost this regularity (n ≥ 15). In addition, vesicles were observed in most of these surfactant aqueous solutions, with the exception of 11-3-11-OA. Moreover, the obvious flocculation phenomenon was observed within the range of pH 4-5, and they flocculated rapidly when they approached their isoelectric points. This process was reversible, which brought more possibilities for their application in drug delivery and release.

Synthesis and Properties of Amphoteric Amide Surfactants with Reactive Group

Three reactive amphoteric surfactants (M10, M12 and M14) with different alkyl chain lengths have been synthesized using N,N'-dimethyl-1,3-propyldiamine, maleic anhydride and alkyl bromide as raw materials. The compounds had been characterized by mass spectrometry and 1H-NMR. The critical micelle concentration (CMC) and the corresponding surface tension (γCMC) of M10, M12 and M14 were measured at temperatures from 298 K to 313 K. The results showed that the CMC of M10, M12 and M14 are 5,89 × 10−4 mol L−1, 2,63 × 10−4 mol L−1 and 1,35 × 10−4 mol L−1. The γCMC of M10, M12 and M14 are 31.26 mN m−1, 28.79 mN m−1, and 26.87 mN m−1 at 298 K respectively. As the temperature rises, the CMC and the minimum molecule area (Amin) increased gradually, but the γCMC and the maximum surface adsorption capacity (Γmax) decreased moderately. The micelle aggregation number (Nm) was determined and changed slightly in the temperature range of 298 K–313 K, which showed that the micelle aggregation number was insensitive to the temperature change.

Branched alkyldimethylamine oxide surfactants: An effective strategy for the design of high concentration/low viscosity surfactant formulations

HYPOTHESIS

The rational design of branched-tail surfactants is a suitable strategy to obtain low-viscosity surfactant-rich isotropic aqueous mixtures with negligible effects on biodegradability. This opens a way to the design of concentrated ("water-free") surfactant formulations, highly attractive for their ecological and economic benefits.

EXPERIMENTS

The aggregation behaviour of N,N-dimethyl-2-propylheptan-1-amine oxide (C₁₀DAO-branched) in aqueous mixtures is investigated across the entire composition range by polarized optical microscopy, small angle X-ray and neutron scattering, electron paramagnetic resonance, and pulse-gradient stimulated echo nuclear magnetic resonance. The humidity scanning quartz crystal microbalance with dissipation monitoring technique is validated as a tool for the fast screening of surfactants phase behaviour. Furthermore, the shear viscosities and viscoelastic moduli of the systems are determined by rheological measurements.

FINDINGS

With respect to the linear isomer, C₁₀DAO-branched presents a much lower tendency to form lyotropic liquid crystalline phases. Except for a narrow composition and temperature range in which a lamellar structure is observed, C₁₀DAO-branched aqueous mixtures are isotropic liquids whose microstructure changes, with increasing concentration, from micellar solutions to unstructured dispersions of hydrated surfactant molecules. Low-viscosity was found for all these mixtures, including the most concentrated ones. Thus, the introduction of a single short side-chain in the tail is demonstrated to be an effective approach to increase the active concentration in surfactant formulations.

Silica micro- and nanoparticles reduce the toxicity of surfactant solutions

In this work, the toxicity of hydrophilic fumed silica micro- and nanoparticles of various sizes (7 nm, 12 nm, and 50 μm) was evaluated using the luminescent bacteria Vibrio fischeri. In addition, the toxicity of an anionic surfactant solution (ether carboxylic acid), a nonionic surfactant solution (alkyl polyglucoside), and a binary (1:1) mixture of these solutions all containing these silica particles was evaluated. Furthermore, this work discusses the adsorption of surfactants onto particle surfaces and evaluates the effects of silica particles on the surface tension and critical micellar concentration (CMC) of these anionic and nonionic surfactants. It was determined that silica particles can be considered as non-toxic and that silica particles reduce the toxicity of surfactant solutions. Nevertheless, the toxicity reduction depends on the ionic character of the surfactants. Differences can be explained by the different adsorption behavior of surfactants onto the particle surface, which is weaker for nonionic surfactants than for anionic surfactants. Regarding the effects on surface tension, it was found that silica particles increased the surface activity of anionic surfactants and considerably reduced their CMC, whereas in the case of nonionic surfactants, the effects were reversed.