Invasion moving boundary problem for a biofilm reactor model

The work presents the analysis of the free boundary value problem related to the invasion model of new species in biofilm reactors. In the framework of continuum approach to mathematical modelling of biofilm growth, the problem consists of a system of nonlinear hyperbolic partial differential equations governing the microbial species growth and a system of semi-linear elliptic partial differential equations describing the substrate trends. The model is completed with a system of elliptic partial differential equations governing the diffusion and reaction of planktonic cells, which are able to switch their mode of growth from planktonic to sessile when specific environmental conditions are found. Two systems of nonlinear differential equations for the substrate and planktonic cells mass balance within the bulk liquid are also considered. The free boundary evolution is governed by a differential equation that accounts for detachment. The qualitative analysis is performed and a uniqueness and existence result is discussed. Furthermore, two special models of biological and engineering interest are discussed numerically. The invasion of Anammox bacteria in a constituted biofilm inhabiting the deammonification units of the wastewater treatment plants is simulated. Numerical simulations are run to evaluate the influence of the colonization process on biofilm structure and activity.Comment: 20 pages, 11 figures, original pape

Anaerobic processes for waste biomass treatment: applications and mathematical modeling

The increasing global energy demand and depletion of fossil fuels are driving international policies to promote the use of alternative energy sources, leading to the mitigation of global warming and greenhouse gas (GHG) emissions. In this context, the sustainable valorisation via biological anaerobic processes of organic waste biomasses represents a promising technology for producing renewable energy and value added chemicals in a biorefinery concept. Anaerobic Digestion (AD) and Dark Fermentation (DF) are the most explored biological routes to produce renewable energy in the form of methane and hydrogen gas, respectively. Due to its high flexibility and applicability to a wide range of organic substrates, AD has been largely adopted in full scale applications, with increasing interest from both academia and industries. Conversely, low biohydrogen yields and incomplete biomass conversion limit DF scaled-up applications as a self-standing biotechnology for energy production. Moreover, the combination of different anaerobic processes, such as DF-AD or DF-Photo-Fermentation (PF), might be adopted to overcome the main drawbacks deriving from the application of DF processes. A significant example is represented by the use of DF by-products, such as organic acids and alcohols, for H2 production via PF. The combined DF-PF process results in the increase of the total hydrogen yield (usually evaluated in terms of mol H2 mol C6H12O6-1) and the production of poly-β-hydroxybutyrate (PHB), which are stored by Purple Non-Sulphur Bacteria, performing the PF step, as a carbon reserve available under nutrient starvation. In this thesis, different anaerobic technologies have been applied to achieve higher biogas yields and/or by-products valorisation in a biorefinery concept. In particular, the enhancement of AD performances, in terms of biogas productivity, has been addressed by optimizing the crucial start-up phase of an anaerobic fluidized bed reactor. The stability of DF and enhancement of biohydrogen yields have been obtained by optimizing the operative conditions of a DF reactor continuously fed with cheese whey in thermophilic regimen, and by adopting a combined DF-PF configuration for the energetic valorisation of the organic fraction of municipal solid wastes, respectively. Contextually, the valorisation of Dark Fermentation effluents (DFE) was achieved by i) producing PHB via PF, ii) extracting value added acids with anionic resins or iii) using DFE as a complex media for the dissolution of recalcitrant materials. Furthermore, a 1-D mathematical model has been presented to analyse and predict the microbial colonization of anaerobic multispecies biofilms

A mechanistic mathematical model for photo fermentative hydrogen and polyhydroxybutyrate production

An original mathematical model describing the photo fermentation process is proposed. The model represents the first attempt to describe the photo fermentative hydrogen production and polyhydroxybutyrate accumulation, simultaneously. The mathematical model is derived from mass balance principles and consists of a system of ordinary differential equations describing the biomass growth, the nitrogen and the substrate degradation, the hydrogen and other catabolites production, and the polyhydroxybutyrate accumulation in photo fermentation systems. Moreover, the model takes into account important inhibiting phenomena, such as the self-shading and the substrate inhibition, which can occur during the evolution of the process. The calibration was performed using a real experimental data set and it was supported by the results of a sensitivity analysis study. The results showed that the most sensitive parameters for both hydrogen and PHB production were the hydrogen yield on substrate, the catabolites yield on substrate, and the biomass yield. Successively, a different experimental data set was used to validate the model. Performance indicators showed that the model could efficiently be used to simulate the photo fermentative hydrogen and polyhydroxybutyrate production by Rhodopseudomonas palustris. For instance, the index of agreement of 0.95 was observed for the validated hydrogen production trend. Moreover, the model well predicted the maximum PHB accumulation in bacterial cells. Indeed, the predicted and observed accumulated PHB were 4.5 and 4.8%, respectively. Further numerical simulations demonstrated the model consistency in describing process inhibiting phenomena. Numerical simulations showed that the acetate and nitrogen inhibition phenomena take place when concentrations are higher than 12.44 g L-1 and lower than 4.76 mg L-1, respectively. Finally, the potential long term hydrogen production from accumulated polyhydroxybutyrate in bacterial cells was studied via a fast-slow analysis technique

Photofermentative production of hydrogen and poly-β-hydroxybutyrate from dark fermentation products

The aim of this work is to investigate the hydrogen and poly-β-hydroxybutyrate (PHB) production during the photofermentative treatment of the effluent from a dark fermentation reactor fed with the organic fraction of municipal solid waste. Two different inocula, an adapted culture of Rhodobacter sphaeroides AV1b and a mixed consortium of purple non sulphur bacteria have been investigated under the same operational conditions. Different hydrogen productivities of 364 and 559NmL H2 L(-1) were observed for the Rhodobacter sphaeroides and the mixed culture consortium tests, respectively: the consortium of PNSB resulted 1.5-fold more productive than the pure culture. On the other hand, Rhodobacter sphaeroides culture showed a higher PHB productivity (155mg PHB g COD(-1)) than the mixed culture (55mg PHB g COD(-1)). In all the tests, the concomitant H2 and PHB production was associated to a dissolved COD removal higher than 80%

A Prototype System for Time-Lapse Electrical Resistivity Tomographies

A prototype system for time-lapse acquisition of 2D electrical resistivity tomography (ERT) and time domain reflectometry (TDR) measurements was installed in a test site affected by a landslide in Basilicata region (southern Italy). The aim of the system is to monitor in real-time the rainwater infiltration into the soil and obtain information about the variation of the water content in the first layers of the subsoil and the possible influence of this variation on landslide activity. A rain gauge placed in the test site gives information on the rainfall intensity and frequency and suggests the acquisition time interval. The installed system and the preliminary results are presented in this paper

A preliminary study on a novel bioaugmentation technique enhancing lactic acid production by mixed cultures fermentation

The paper is a preliminary study on the selection of lactic acid producing microorganisms from a mixed microbial population via bioaugmentation. The bioaugmentation technique is based on pH sudden variations occurring in sequential batch steps of a dark fermentation process applied to simple substrates. Different conditions are tested and compared. The structure of microbial communities and concentrations of metabolic intermediates are analyzed to study the possible substrate conversion routes. Obtained results indicate that the initial mixed culture produced a lactic acid percentage of 5% in terms of CODLA/CODPRODUCTS. In the most favourable conditions, the selected culture produced a lactic acid percentage of 59%. The analysis of the composition of microbial communities before and after the bioaugmentation processes, indicates that lactic acid production mainly results from the population change to bacteria belonging to the genus Bacillus. Indeed, the relative abundance of Bacilli increased from 0.67%, to 8.40% during the bioaugmentation cycle

Soil washing optimization, recycling of the solution, and ecotoxicity assessment for the remediation of Pb-contaminated sites using EDDS

This paper presents the results of an experimental study aimed at investigating the applicability of ethylenediamine-N,N′-disuccinic acid (EDDS) as a washing solution for the remediation of Pb-contaminated soil. All aspects of the treatment are analyzed and optimized, including the reuse and the final disposal of the EDDS spent solution. Different molar concentrations of the washing solutions and the efficiencies of varying solid/liquid ratio are tested at different pH values. More than 90% of the mobile Pb fraction is removed in about 24 h at pH 6. Accordingly, soil toxicity strongly decreases as a consequence of the treatment. The regenerated solution exhibits a reduced, but not negligible, extractive capacity. The total extraction of Pb is approximately 50% of the initial value after one regeneration cycle, and almost 20% after a second regeneration cycle. Respirometric tests, conducted using an activated sludge sampled in a municipal wastewater treatment plant, indicate that the spent solutions are not biodegradable, but they do not exert any toxic effect on the biomass. On the contrary, tests on regenerated solutions displayed the same biodegradability as the fresh one

Altered gut microbiota and endocannabinoid system tone in vitamin D deficiency-mediated chronic pain

Abstract Recent evidence points to the gut microbiota as a regulator of brain and behavior, although it remains to be determined if gut bacteria play a role in chronic pain. The endocannabinoid system is implicated in inflammation and chronic pain processing at both the gut and central nervous system (CNS) levels. In the present study, we used low Vitamin D dietary intake in mice and evaluated possible changes in gut microbiota, pain processing and endocannabinoid system signaling. Vitamin D deficiency induced a lower microbial diversity characterized by an increase in Firmicutes and a decrease in Verrucomicrobia and Bacteroidetes. Concurrently, vitamin D deficient mice showed tactile allodynia associated with neuronal hyperexcitability and alterations of endocannabinoid system members (endogenous mediators and their receptors) at the spinal cord level. Changes in endocannabinoid (anandamide and 2-arachidonoylglycerol) levels were also observed in the duodenum and colon. Remarkably, the anti-inflammatory anandamide congener, palmitoylethanolamide, counteracted both the pain behaviour and spinal biochemical changes in vitamin D deficient mice, whilst increasing the levels of Akkermansia, Eubacterium and Enterobacteriaceae, as compared with vehicle-treated mice. Finally, induction of spared nerve injury in normal or vitamin D deficient mice was not accompanied by changes in gut microbiota composition. Our data suggest the existence of a link between Vitamin D deficiency – with related changes in gut bacterial composition – and altered nociception, possibly via molecular mechanisms involving the endocannabinoid and related mediator signaling systems

2-Pentadecyl-2-oxazoline ameliorates memory impairment and depression-like behaviour in neuropathic mice: possible role of adrenergic alpha2- and H3 histamine autoreceptors

Neuropathic pain (NP) remains an untreatable disease due to the complex pathophysiology that involves the whole pain neuraxis including the forebrain. Sensory dysfunctions such as allodynia and hyperalgesia are only part of the symptoms associated with neuropathic pain that extend to memory and affectivity deficits. The development of multi-target molecules might be a promising therapeutic strategy against the symptoms associated with NP. 2-pentadecyl-2-oxazoline (PEA-OXA) is a plant-derived agent, which has shown effectiveness against chronic pain and associated neuropsychiatric disorders. The molecular mechanisms by which PEA-OXA exerts its effects are, however, only partially known. In the current study, we show that PEA-OXA, besides being an alpha2 adrenergic receptor antagonist, also acts as a modulator at histamine H3 receptors, and report data on its effects on sensory, affective and cognitive symptoms associated with the spared nerve injury (SNI) model of neuropathic pain in mice. Treatment for 14 days with PEA-OXA after the onset of the symptoms associated with neuropathic pain resulted in the following effects: (i) allodynia was decreased; (ii) affective/cognitive impairment associated with SNI (depression, spatial, and working memories) was counteracted; (iii) long-term potentiation in vivo in the lateral entorhinal cortex-dentate gyrus (perforant pathway, LPP) was ameliorated, (iv) hippocampal glutamate, GABA, histamine, norepinephrine and dopamine level alterations after peripheral nerve injury were reversed, (v) expression level of the TH positive neurons in the Locus Coeruleus were normalized. Thus, a 16-day treatment with PEA-OXA alleviates the sensory, emotional, cognitive, electrophysiological and neurochemical alterations associated with SNI-induced neuropathic pain