Supramolecular aggregation of colloidal natural organic matter masks priority pollutants released in water from peat soil

Role of organic nanoparticles on transport and fate of various dyes in aqueous solution

This work studies the interaction of organic nanoparticles (ON) with various dyes in aqueous solution, to elucidate the role of ON on transport and fate of dyes in the environment, and on dyes removal from wastewater. Studied dyes are Acid Red 66 (AR66), Methylene Blue (MB), Reactive Black 5 (RB5), and Reactive Violet 5 (RV5). ON are extracted from organic matter of anthropogenic origin through resuspension of its colloidal fraction, and successive filtration and dialysis of the obtained suspension. Mechanisms of interaction are investigated initially through three-dimensional excitation emission matrix (3DEEM) analysis. Obtained data indicate that dynamic interactions occur strongly between dye molecules and ON aggregates. 3DEEM spectra of mixed samples containing ON together with one of the tested dyes, present a shape similar to the one of ON alone, but each of them is characterized by specific differences in terms of peaks quenching and shift. The analysis of these singularities suggests that dye molecules are bound to the functional groups of ON through H-bonds, according to the following steps: i) dyes reach the surface of ON aggregates; ii) the molecules pass through the hydrophilic surface of ON aggregates, and reach their hydrophobic core; iii) the dyes are sequestrated into the hydrophobic core of ON aggregates. Nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies analysis confirm the formation of supramolecular aggregates with stable micellar hydrophobic structure, mainly consisting of aliphatic fractions of ON, which explain the disappearance of aromatic groups signals from dyes.

Environmental concentration PFOS as a light shield for lake exopolymers against photodegradation by formation of sandwiched supramolecular nanostructures

EPS (exopolymers) play a central role in global carbon cycling due to huger amount in aquatic environment, and PFOS (Perfluorooctane sulfonate) is also ubiquitous and persistent pollutant. Whether and how can PFOS of environmental concentrations affect behavior and fate of EPS was unclear. In this study, for the first time interaction between lake EPS and PFOS of environmental concentrations was visually probed by AFM-IR technique. It was found that EPS could effectively trap PFOS and the latter of environmental concentrations could trigger nanoscale reassembly of the former. Sandwiched PFOS-EPS nanostructures were formed via supramolecular interaction between EPS and PFOS, confirmed by fluorescence quenching titration and FTIR spectroscopy. The PFOS microlayers sandwiched in EPS was proven to be a light shield that could protect EPS from photodegradation because of its high reflectivity and nearly zero absorbance of UV-Vis light. The light shielding effect of PFOS was confirmed by evidences from photodegradation experiments, including change of concentrations of ions released and molecular weight distribution patterns. These novel findings provided valuable information for deep insight into environmental behavior of PFOS and its effects on biogeochemical carbon cycle of biopolymers in global waters.

Characterization of anthropogenic organic matter and its interaction with direct yellow 27 in wastewater: Experimental results and perspectives of resource recovery

The concept of natural organic matter of anthropogenic origin is introduced and its characteristics and interaction with chemical pollutants are investigated by adopting several distinct analytic methodologies. Scanning electron microscopy indicates that the used sample of anthropogenic organic matter (AOM) has an amphiphilic nature, which allows its supramolecular organization in water. Fourier transform infrared spectroscopy, in turn, gives a clear indication about the presence of polysaccharide markers, lipidic and amidic fractions, and suggests the absence of free organic acid. AOM sample and AOM mixed with dye sample were examined by the three-dimensional excitation-emission matrix fluorescence spectra and the nuclear magnetic resonance mono-dimensional spectra. The results highlighted the interactions occurring between the AOM and the reactive dye, selected as a representative chemical pollutant. Electron Spin Resonance confirms that the used AOM is able to completely include the dye in its structure. Overall, the obtained results indicate that the fate, transport, and toxicity of pollutants in the environment can be drastically influenced by the presence of AOM.

Microaerobic Digestion of Low-Biodegradable Sewage Sludge: Effect of Air Dosing in Batch Reactors

The adoption of prolonged solid retention times during the biological treatment of urban wastewaters is a well-known strategy to reduce sewage sludge production. However, it also results in the production of a biological sludge with low percentages of biodegradable organic matter, also characterized by high humification degrees, which may hamper the anaerobic digestion treatment aimed at sludge stabilization. To accelerate the hydrolytic stage, the application of microaerobic conditions during the anaerobic digestion of low-biodegradable sewage sludge was investigated in this study. In particular, six bio-methanation tests of a real sewage sludge were carried out, introducing air in the bioreactors with doses ranging between 0 and 16.83 L air/kg VSin d, in order to evaluate the air dosage that optimizes the biomethane production and organic matter degradation. Notably, the lower air loading rates investigated in this study, such as 0.68 and 1.37 L air/kg VSin d, led to an increase in methane production of up to 19%, due to a higher degradation of total lipids and proteins. In addition, these microaerobic conditions also resulted in a decrease in the sludge humification degree and in lower volatile fatty acid accumulation.