Coupling of conformational and ionization equilibria in linear poly(ethylenimine): a study based on the site binding/rotational isomeric state (SBRIS) model.

The conformational and ionization properties of linear poly(ethylenimine) are studied by combining the site binding model (SB) with the rotational isomeric state (RIS) model, developed by Flory to calculate the conformational properties of neutral linear molecules. The resulting approach (the SBRIS model) is used to rationalise the experimental poly(ethylenimine) titration curves. By fitting the experimental macroconstants, conformational and binding parameters are obtained. The obtained values are consistent with previous binding and structural information. The emergence of triplet interaction between protonated sites is explained as a natural consequence of the coupling between binding and conformational equilibria. When only nearest neighbour interactions are considered, transfer matrix techniques are used in the calculations. In order to account for excluded volume and long-range electrostatic interactions, Monte Carlo simulations are performed. The results indicate that at high ionic strengths, long-range interactions have a very limited impact on the titration curves. However, for long chains, they have a significant influence on the radius of gyration.

Ammonia recovery from acidogenic fermentation effluents using a gas-permeable membrane contactor.

A gas-permeable membrane (GPM) contactor was used to recover ammoniacal nitrogen from a synthetic and a biowaste fermentation broth under different pH (from 6 to 11) and temperatures (35 and 55 °C). Ammonia mass transfer constant (Km) increased as pH and temperature increased. For synthetic broth, pH 10 provided the best results, when considering the Km (9.2·10-7 m·s-1) and the reagents consumption (1.0 mol NaOH·mol-1 TAN and 0.6 mol H2SO4·mol-1 TAN). Biowaste fermentation generated a broth with a high concentration of ammoniacal nitrogen (4.9 g N·L-1) and volatile fatty acids (VFA) (41.1 g COD·L-1). Experiments using the biowaste broth showed a lower Km (5.0·10-7 m·s-1 at pH 10) than the synthetic broth, related to the solution matrix and other species interference. VFAs were not detected in the trapping solution. Overall, these results show that GPM is a suitable technology to efficiently separate ammoniacal nitrogen and VFA from fermentation broths.