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This study aimed at modelling the performance of a novel MBBR configuration, named A/O-MBBR, comprised of a pre-anoxic reactor, with an HRT of 4.5 h, coupled with an intermittent anoxic/aerobic MBBR (HRT = 6.8 h). The lab-scale system was fed with municipal wastewater with an average influent Total Ammonia Nitrogen (TAN) and total COD (TCOD) concentrations of 46 mg of TAN-N L−1 and 310 mg TCOD L−1. During the whole experimental period, TAN removal efficiency was always higher than 96%; denitrification was also very effective, achieving nitrate and nitrite concentrations in the effluent both lower than 5 mg NO x -N L−1 on average. Moreover, TCOD average removal efficiency was equal to 85%. Modelling was performed to investigate the nitrification efficacy enhancement; to this aim, a biofilm model was developed, adopting the equations for mixed-culture biofilms and the Activated Model Sludge n°1 (ASM1) for the biological processes rates. The model allowed to determine the maximum uptake rate for autotrophic growth (μ A was 2.5 d−1) and the semisaturation constant (K OA was 0.2 mg O 2 L−1), suggesting that the nitrification process was 3-fold faster than average and very effective at low oxygen concentrations. The model estimated that about 85% of TAN was removed by the biofilm and only the remaining part by suspended biomass in the bulk liquid. Finally, it was assessed that the A/O-MBBR configuration allowed for a 45–60% savings of the energy requirement compared to a Benchmark WWTP layout. • A coupled anoxic reactor with an intermittent anoxic/aerobic MBBR was studied. • Nitrogenous compounds removal was extremely effective even at short HRTs. • Calibrated nitrification kinetics were 3-fold higher than average. • Model simulations estimated that 85% of TAN removal occurred within the biofilm. • A/O-MBBR allowed for an energy reduction of 45–60% compared to conventional treatments. [ABSTRACT FROM AUTHOR]

An original mechanistic model able to describe the fate of trace elements (TE) in anaerobic digestion systems has been synthetized from mass balance equations. The model takes into account the main biochemical and physico-chemical processes affecting TE bioavailability and it is aimed at evaluating the effect that the combination of such processes exerts on the system performance. Five main modules have been introduced: biochemistry, physico-chemistry, sorption, complexation and precipitation. The model is based on mass conservation principles and is formulated as a set of ordinary differential equations for the soluble and particulate components constituting the system. Model applications of two illustrative cases are provided. The first case is based on experimental results and examines the effect of TE depletion in an AD process of food waste (FW). The second case shows the effects of different metal supplements on methane production and biogas composition. The simulation results confirm that the model can fairly be used to predict the effect of TE dynamics and bioavailability, by considering biological, chemical and physicochemical processes in AD environments. • A model for trace elements fate description in anaerobic digestion has been proposed. • Biochemistry, physico-chemistry, sorption, complexation, precipitation are considered. • The model is based on mass conservation principles. • Model applications of two illustrative cases are provided. [ABSTRACT FROM AUTHOR]

Abstract: The transition of proteins from their soluble functional state to amyloid fibrils and aggregates is associated with the onset of several human diseases. Protein aggregation often requires some structural reshaping and the subsequent formation of intermolecular contacts. Therefore, the study of the conformation of excited protein states and their ability to form oligomers is of primary importance for understanding the molecular basis of amyloid fibril formation. Here, we investigated the oligomerization processes that occur along the folding of the amyloidogenic human protein β2-microglobulin. The combination of real-time two-dimensional NMR data with real-time small-angle X-ray scattering measurements allowed us to derive thermodynamic and kinetic information on protein oligomerization of different conformational states populated along the folding pathways. In particular, we could demonstrate that a long-lived folding intermediate (I-state) has a higher propensity to oligomerize compared to the native state. Our data agree well with a simple five-state kinetic model that involves only monomeric and dimeric species. The dimers have an elongated shape with the dimerization interface located at the apical side of β2-microglobulin close to Pro32, the residue that has a trans conformation in the I-state and a cis conformation in the native (N) state. Our experimental data suggest that partial unfolding in the apical half of the protein close to Pro32 leads to an excited state conformation with enhanced propensity for oligomerization. This excited state becomes more populated in the transient I-state due to the destabilization of the native conformation by the trans-Pro32 configuration. [Copyright &y& Elsevier]

β2-Microglobulin (β2m) is the non-covalently bound light chain of the human class I major histocompatibility complex (MHC-I). The natural turnover of MHC-I gives rise to the release of β2m into plasmatic fluids and to its catabolism in the kidney. β2m dissociation from the heavy chain of the complex is a severe complication in patients receiving prolonged hemodialysis. As a consequence of renal failure, the increasing β2m concentrations can lead to deposition of the protein as amyloid fibrils. Here we characterize the His31→Tyr human β2m mutant, a non-natural form of β2m that is more stable than the wild-type protein, displaying a ten-fold acceleration of the slow phase of folding. We report the 2.9 A˚ resolution crystal structure and the NMR characterization of the mutant β2m, focussing on selected structural features and on the molecular packing observed in the crystals. Juxtaposition of the four mutant β2m molecules contained in the crystal asymmetric unit, and specific hydrogen bonds, stabilize a compact protein assembly. Conformational heterogeneity of the four independent molecules, some of their mutual interactions and partial unpairing of the N-terminal β-strand in one protomer are in keeping with the amyloidogenic properties displayed by the mutant β2m. [Copyright &y& Elsevier]