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Wastewater from livestock farms contains high concentrations of suspended solids, organic contaminants, and nitrogen compounds, such as ammoniacal nitrogen. Discharging livestock effluents into water bodies without appropriate treatment leads to severe environmental pollution. Compared to conventional treatment methods, electrochemical oxidation exhibits higher nitrogen removal efficiencies. In the present work, the electrochemical removal of ammoniacal nitrogen from real livestock wastewater was investigated through a lab-scale reactor. Preliminary experiments were carried out to investigate the effects of different anode materials, including boron-doped diamond and iridium/ruthenium-coated titanium, on the total nitrogen removal efficiency using synthetic wastewater. Boron-doped diamond, a well-known non-active electrode, allowed to obtain 63.7 ± 1.21 % of total nitrogen degradation efficiency. However, the iridium/ruthenium-coated titanium electrode, belonging to the class of active anodes, showed a higher performance, achieving 78.8 ± 0.76 % contaminant degradation. Coupling iridium/ruthenium-coated titanium anode with a stainless-steel cathode improved the performance of the system, achieving even 96.2 ± 2.73 % of total nitrogen removal. The optimized cell configuration was used to treat livestock wastewater, resulting in the degradation of 67.0 ± 2.25 % of total nitrogen and 37.3 ± 0.68 % of total organic carbon when sodium chloride was added. At the end of the process, the ammonium content was completely removed, and only 17.7 ± 0.51 % of the initial nitrogen turned into nitrate. The results show that the proposed system is a promising approach to treating livestock wastewater by coupling high contaminant removal efficiencies with low operational costs. Anyway, further studies on process optimization with an emphasis on power requirements and electrode costs need to be carried out.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a biodegradable polymer with excellent thermal and mechanical properties comparable to fossil-based plastics. Scaling up the production of this polymer could provide a viable solution for reducing the use of fossil-based materials. However, its current production capacities are limited, with only a few facilities implementing the process at pilot or semi-industrial scales. The primary challenge lies in the high production costs, with 40% of the expenses attributed to the feedstock used for fermentation. Additionally, the energy required for sterilization in processes using pure methanotrophic cultures further reduces its economic viability. In this study, the economic aspects of the PHBV production process were assessed at an industrial level (100,000 t/y PHBV), using cheap and renewable substrates such as valeric acid and methane. A mixed methanotrophic consortium was used to reduce the need for sterility. The techno-economic analysis was based on estimating both fixed investment and operating costs. Then, a sensitivity analysis was performed to analyse the effect that the polymer content has on the final selling price: the initial biomass concentration was set to 30 g L-1, and the PHBV content was considered to be 20, 30, 40, 50 and 70% wt on a dry weight basis. The results revealed that increasing the polymer content beyond 40% wt led to a more competitive PHBV selling price, thus opening significant market opportunities.

The increasing need for biodegradable polymers demands efficient and environmentally friendly extraction methods. In this study, a simple and sustainable method for extracting polyhydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-co-HV) from Methylocystis hirsuta and a mixed methanotrophic consortium with different biopolymer contents was presented. The extraction of biopolymers with 1,3-dioxolane was initially investigated by varying the biomass-to-solvent ratio (i.e., 1:2 w v−1, 1:4 w v−1, 1:6 w v−1, 1:8 w v−1 and 1:10 w v−1) and extraction time (6, 8 and 10 h) at the boiling point of the solvent and atmospheric pressure. Based on the results of the preliminary tests, and only for the most efficient biomass-to-solvent ratio, the extraction kinetics were also studied over a time interval ranging from 30 min to 6 h. For Methylocystis hirsuta, the investigation of the extraction time showed that the maximum extraction was reached after 30 min, with recovery yields of 87% and 75% and purities of 98.7% and 94% for PHB and PHB-co-HV, respectively. Similarly, the extraction of PHB and PHB-co-HV from a mixed methanotrophic strain yielded 88% w w−1 and 70% w w−1 recovery, respectively, with 98% w w−1 purity, at a biomass-to-solvent ratio of 6 in 30 min.

Trimethoprim (TMP) is among the emerging pollutants that cause harmful effects on the aquatic environment and human health if not accurately controlled. This antibiotic is one of the most regularly administered drugs, thus, its contamination of water bodies has received much concern in recent years. In this case study, a comparison between adsorption and electrochemical oxidation was carefully performed to identify the best treatment for removing TMP from impacted water. Adsorption with commercial activated carbon F400 as an adsorbent showed higher TMP removal efficiencies (70.6%) than natural zeolites (17.6%). The experimental data for TMP adsorption onto F400 were well-fitted by the linear form of the Langmuir isotherm (R2 = 0.986). The values of qmax and KL were 18.40 mg g−1 and 1.40 L mg−1, respectively. The pseudo-second order model provided the best correlation with the experimental data. Electrochemical oxidation over two platinum-coated titanium electrodes led to 70.1% TMP removal after 330 min of treatment. The optimal operative conditions were achieved at a concentration of NaCl of 0.04 M and an applied current density of 120 A m−2. Cost estimates for both technologies indicated that electrochemical oxidation of TMP is comparable to adsorption if operating at low current density. Each process presents several advantages and limitations, and the choice of the right approach needs to consider different factors, including the composition of the wastewater and the cost and availability of resources.

In recent years, the development of renewable energy and the improvement of technologies for its production has aroused particular interest. In this perspective, pressurised anaerobic digestion (PAD), i.e. the anaerobic digestion process occurring at a pressure higher than the atmospheric one, has attracted significant attention. PAD enables the production of pressurised biogas, reducing energy costs required for biogas upgrading and injection into the distribution grid. In addition, PAD presents the advantage that by increasing pressure, the solubilisation of CO2, as compared to CH4, increases, resulting in the production of biogas with a high content of CH4 (v/v% CH4 = 90%). Furthermore, results in the literature reported the potential of the autogenerative PAD, in which biogas accumulates in the headspace of the reactor and leads to a gradual increase in autogenerated pressure. In this research, the effect of autogenerated final pressure on the specific methanogenic yield (SMY) was investigated by simulating an autogenerative PAD process of sodium acetate and using a modified ADM1 (Anaerobic Digestion Model No 1) model in batch mode; moreover, the kinetic parameters of the process were assessed. Simulation results showed a good agreement with experimental results and highlighted that SMY increases by increasing the autogenerated final pressure.

Polyhydroxyalkanoates (PHAs) are biobased and biodegradable polymers that may be considered to replace fossil-based materials. However, their widespread deployment is slowed down because of the high production cost and their low quality. Using methane during the generation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-HV) could reduce the production costs, which are usually owed to the carbon source used, and enhance the performance of the material. In fact, the properties of PHB-co-HV make it more suitable than the most common homopolymer, named poly(3-hydroxybutyrate) (PHB), for many applications since it is more flexible, has a wider thermal processing range, a lower crystallinity and permeability to water. In this work, the production of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was simulated using an innovative process scheme consisting of two bioreactors working in series equipped with a gas recycling unit, which was designed to increase the methane mass transfer from the gas to the liquid. During the first step, a Methylocystis dominated culture was grown on ammonia and methane to reach a high cell concentration; then, the cells were moved to the second bioreactor and subjected to nutrients starvation to favour the metabolic pathway addressed to the accumulation of PHB-co-HV. The effect of the variation of valeric acid concentration (100-400 ppm), which was used as co-substrate, on the fraction of PHB-co-HV stored in the cells and the percentage of 3-hydroxyvalerate (3-HV) was investigated: results showed that the highest the valeric acid concentration, the lower the total polymer content and the higher the HV fraction accumulated.

Thanks to their properties, fossil fuel-based plastics are widely used daily (for industrial, domestic and environmental applications). However, they are not biodegradable, and their end of life is the cause of one of the most dangerous pollution in the world. Plastic, if recovered, can be recycled or used to recover energy, but it is not possible to recover all the tons of waste produced, so some end up in landfills. Therefore all non-recycled and non-collected plastic can take up to a thousand years to degrade. So the scientific idea is to produce biodegradable plastic capable of replacing conventional plastics. One possible solution is the poly(3-Hydroxybutyrate) (PHB) of the polyhydroxyalkanoates (PHA) family. PHB is a biopolymer accumulated in intracellular granules, under unfavourable growth conditions, by many prokaryotes and can be extracted with eco-friendly solvents. In particular, the extraction phase consists of the disruption of the cells and the subsequent separation of the biopolymer from the non-biopolymeric material (non-PHB). Currently, solvent extraction is the most used method for PHB recovery because it guarantees a high recovery yield and keeps the characteristics of the extracted biopolymer almost unaltered. In this study, the extraction of PHB with eco-friendly solvents was investigated. Simulations were carried out using 1,2-propylene carbonate as the solvent and acetone as the anti-solvent. Two process schemes were analyzed, without and with the recirculation of solvents (by distillation) and with two different types of biomass (wet and dry). The present work aims to study the final recovery yield in different operating conditions and the influence of PHB solubility on the process. The simulation results confirm the importance of solubility for optimizing the extraction process and underline the problem related to the lack of data in the literature.

Replacing fossil plastic with green and biobased alternatives is one of the most significant challenges of this century. Polyhydroxyalkanoates, more specifically, poly(3-hydroxybutyrate) (PHB), have been found as a very promising alternative to traditional plastics, but currently, they are about 2% of the bioplastics produced. In this work, the growth of a methanotrophic strain belonging to the Methylocystis species, a natural producer of poly(3-hydroxybutyrate), was modelled in a bubble column bioreactor fed with methane, considering a discontinuous feeding strategy. Three-dimensional simulations were performed by using a CFD approach. The biomass growth strategy based on the variation of the methane bubble diameter, in a range of 0.003–0.005 m, and the aspect ratio, in the range 5–16, was simulated. Their effects were assessed on the process efficiency and performance in terms of methane fed, biomass and PHB yields. When the bubble diameter was varied, the best performance was achieved at a diameter of 0.005 m with methane fed of 34.2 g, biomass yield of 0.534 gbiomass/gCH4 and PHB yield of 0.327 gPHB/gCH4. When the aspect ratio was varied, the best performance was achieved at an aspect ratio of 10 with methane fed of 34.9 g, biomass yield of 0.523 gbiomass/gCH4 and PHB yield of 0.321 gPHB/gCH4. Finally, the estimation of the PHB yield was performed. CFD analysis allowed to verify the absence of death or stagnant zones inside the reactor.

Poly(3-hydroxybutyrate) (PHB) is a thermoplastic polyester that can be synthesised by many bacteria under unfavourable growth conditions. Among all its properties, biodegradability is the most attractive since it makes PHB a potential alternative to non-biodegradable plastics. However, the current market penetration of this polymer is limited by the high production costs, which accounts for approximately 40% of the total price, and the complexity in scaling-up the biological process. In this work, an innovative approach is presented, simulating the production of PHB through a double stage aerobic fermentation in which a Methylocystis strain grows and accumulates PHB granules. The effects of the reactor geometry on PHB yields were investigated in terms of aspect ratio (A), which was varied in the range 5-16 both at constant volume and variable volume: in the first case, the working volume was kept constant at 100 L and the diameter of the reactor was varied in the range 0.2-0.3 m; in the second case, the working volume was varied between 100 and 340L, keeping constant the diameter at 0.3 m. The effect of the geometry on transition parameters was evaluated as well. Results show that a maximum transition superficial gas velocity (Ut) of 0.05 ms-1 was obtained at A=16; while the productivity of PHB ranged between 0.12 and 0.25 kgm-3d-1.

Polyhydroxyalkanoates (PHAs) are a very promising alternative to traditional plastic materials since they are biobased and can degrade in soil, water, and sediments. Among all the existing PHAs, Poly-3-hydroxybutyrate (PHB) is the most well-known homopolymer. However, to the current state, PHAs represent only about 2% of the total bioplastics produced because their diffusion on a large scale is still limited due to their high market price. Techno-economic assessments showed that raw materials, such as sugars and oils account for up to 40% of the total costs. In this work, an innovative PHB production process scheme is presented. The expensive carbon sources are replaced by methane, which is cheap, abundant, and can be found as natural gas and in the biogas derived from the anaerobic digestion, thus allowing an integrated biorefinery. Process simulations were carried out to estimate the Poly-3-hydroxybutyrate production yields. Two aerobic fermentations were simulated into 400L semi-continuous reactors: the first for biomass growth in the presence of micro and macro-nutrients; the second for the PHB accumulation in a nutrient-deprived medium. Since both the biomass growth and PHB accumulation reactions take place in the liquid phase, the mass transfer from a gas to a liquid need to be maximised to increase biopolymer production. In this context, the effects of the superficial gas velocity (Ug) on the mass transfer rates and PHB yields were assessed. Several values of Ug, in the range 0.004 to 0.027 m s-1, that does not limit the viability of the cells, were tested. The PHB production increased with the superficial gas velocity.

Polyhydroxybutyrate (PHB) is a possible sustainable alternative to fossil-based plastic, today the cause of one of the primary forms of pollution in the world, since it is biodegradable, recyclable and compostable. Furthermore, PHB can be accumulated in several bacterial strains as a product of their metabolic activity. Solvent extraction (SE) is the most used technique, thanks to the high recovery yields and purity, to extract PHB from bacteria. In particular, a two-step SE is required: the accumulated PHB in the bacterial biomass is firstly dissolved in a solvent to obtain a mixture rich in PHB; then, an anti-solvent is added to reduce the total solubility allowing the biopolymer to precipitate and to be recovered from the residual biomass. However, despite its wide application, the SE technique is characterised by several limitations, such as the high cost and the use of halogenated solvents (i.e. chloroform). In this work, a non-halogenated based extraction process for PHB recovery from wet bacterial biomass is proposed. Simulations were carried out using butyl acetate (BA) as solvent and hexane (HEX) as anti-solvent. The process scheme also includes a distillation column and a cooling system (when necessary) to recover both the solvent and the anti-solvent. The effects of the PHB solubility during the precipitation step and the solvent recovery on process performance were investigated. The recovery yield was higher than 90% and increased as the solubility decreased. The simulation results highlighted that the proposed strategy is an effective and sustainable alternative to conventional processes for PHB recovery.

In recent years, the discharge of various emerging pollutants, chemicals, and dyes in water and wastewater has represented one of the prominent human problems. Since water pollution is directly related to human health, highly resistant and emerging compounds in aquatic environments will pose many potential risks to the health of all living beings. Therefore, water pollution is a very acute problem that has constantly increased in recent years with the expansion of various industries. Consequently, choosing efficient and innovative wastewater treatment methods to remove contaminants is crucial. Among advanced oxidation processes, electrochemical oxidation (EO) is the most common and effective method for removing persistent pollutants from municipal and industrial wastewater. However, despite the great progress in using EO to treat real wastewater, there are still many gaps. This is due to the lack of comprehensive information on the operating parameters which affect the process and its operating costs. In this paper, among various scientific articles, the impact of operational parameters on the EO performances, a comparison between different electrochemical reactor configurations, and a report on general mechanisms of electrochemical oxidation of organic pollutants have been reported. Moreover, an evaluation of cost analysis and energy consumption requirements have also been discussed. Finally, the combination process between EO and photocatalysis (PC), called photoelectrocatalysis (PEC), has been discussed and reviewed briefly. This article shows that there is a direct relationship between important operating parameters with the amount of costs and the final removal efficiency of emerging pollutants. Optimal operating conditions can be achieved by paying special attention to reactor design, which can lead to higher efficiency and more efficient treatment. The rapid development of EO for removing emerging pollutants from impacted water and its combination with other green methods can result in more efficient approaches to face the pressing water pollution challenge. PEC proved to be a promising pollutants degradation technology, in which renewable energy sources can be adopted as a primer to perform an environmentally friendly water treatment.

In the last few years, many industrial sectors have generated and discharged large volumes of saline wastewater into the environment. In the present work, the electrochemical removal of nitrogen compounds from synthetic saline wastewater was investigated through a lab-scale experimental reactor. Experiments were carried out to examine the impacts of the operational parameters, such as electrolyte composition and concentration, applied current intensity, and initial ammoniacal nitrogen concentration, on the total nitrogen removal efficiency. Using NaCl as an electrolyte, the NTOT removal was higher than Na2SO4 and NaClO4; however, increasing the initial NaCl concentration over 250 mg·L−1 resulted in no benefits for the NTOT removal efficiency. A rise in the current intensity from 0.05 A to 0.15 A resulted in an improvement in NTOT removal. Nevertheless, a further increase to 0.25 A led to basically no enhancement of the efficiency. A lower initial ammoniacal nitrogen concentration resulted in higher removal efficiency. The highest NTOT removal (about 75%) was achieved after 90 min of treatment operating with a NaCl concentration of 250 mg·L−1 at an applied current intensity of 0.15 A and with an initial ammoniacal nitrogen concentration of 13 mg·L−1. The nitrogen degradation mechanism proposed assumes a series–parallel reaction system, with a first step in which NH4+ is in equilibrium with NH3. Moreover, the nitrogen molar balance showed that the main product of nitrogen oxidation was N2, but NO3− was also detected. Collectively, electrochemical treatment is a promising approach for the removal of nitrogen compounds from impacted saline wastewater.

Bubble column reactors basically consist of a vertical cylinder filled by a liquid phase in which a gas phase is distributed in the liquid at the column bottom by an appropriate distributor system and moves along the column in the form of bubbles. The aim of a bubble column is to control the rate of mass transfer and reaction between the phases. The liquid phase is modelled as a continuous phase and can be operated in batch mode, or it may move co-currently or counter-currently to the flow of the gas phase. Two-phase and slurry bubble columns are widely used in the chemical- and biochemical industry for carrying out gas-liquid and gas-liquid-solid (catalytic) reaction; in particular, they are used for microalgae growth, aerobic fermentations processes, aerobic treatment of small quantities of highly polluted effluents, as well as oxidation, hydrogenation, chlorination, chemical gas cleaning and, also various biotechnological applications. In this paper, the mass transfer of CH4 to liquid in a bubble column was investigated by means of Computational Fluid Dynamic simulations in a turbulent regime. The effects of the variation of the most significant fluid dynamic parameters, such as inlet gas velocity, on CH4 concentration in the liquid phase and mass transfer from gas to liquid were studied by using COMSOL Multiphysics® Modeling Software. Results point out that the higher inlet velocities, the higher the mass transfer rate, which trend shows a pick after which it reduces to zero when CH4 concentration in the liquid becomes equal to saturation one.

This work presents a risk analysis of a plant that uses supercritical fluid extraction technology with carbon dioxide as a solvent to obtain bioproducts from microalgae. Given the high pressure at which it operates, the extraction plant called "Luwar" could be affected by dangerous events, such as the gas release in concentrations that are harmful to human health. In order to limit the damage, the risk analysis is of primary importance. The gas release could occur following the breakage of a pipe, which was the scenario being considered. It was analyzed using the commercial software "Phast & Safeti", an alternative tool to the methods traditionally used in the literature in hazard events of this type, such as the Threshold Limit Value-Time Weighted Average (TLV-TWA) and the Threshold Limit Value-Short Term Exposure Limit (TLV-STEL), that are defined on the basis of the characteristics of the substance dispersed in the air. Since the pressure of the extraction vessel is the highest in the system, the risk analysis was carried out on the breakage of a pipe coming out of the extractor. The results obtained made it possible to identify the risk parameters on the basis of which to make the best choices in terms of safety to cope with the type of hazard analyzed.

In this work, a risk analysis of a supercritical fluid extraction plant is presented. The plant aims to extract valuable compounds from microalgae and uses carbon dioxide as a solvent at high temperature and pressure. Hazard events that could occur are related to the high pressure at which equipment operate and they, in addition to causing damage to the plant structure, could cause the release of CO2, which in high concentrations endangers the health of workers involved in the activities, therefore, an assessment of this type is crucial. The hazard scenario considered in this work is the equipment rupture. Generally, the rupture is analysed through methods based on indices determination such as the Fire and Explosion Index, the Probit analysis and the Safety Weighted Hazard Index. In this case, the commercial software “Phast & Safeti” of DNV GL Company was used, based on the modelling of the plant together with the process conditions definition. Among the equipment present in the plant, the extraction vessel was chosen since the extraction pressure of bioproducts is the highest in the plant and is equal to 500 bar. Risk parameters obtained after the analysis allow to select the most appropriate safety system able to limit the damage to structures and people.

Microalgae are among the most interesting eukaryotic photosynthethic microorganisms able to use solar energy, nutrients and carbon dioxide to convert them into proteins, carbohydrates, lipids and other valuable organic compounds including carotenoids. Astaxanthin is one of the most interesting antioxidant molecules which has attracted crescent interest due to its positive effects on health and the numerous applications in different sectors, from nutraceutical to cosmetic and aquaculture. Even though the astaxanthin properties are well-known, its price still remains high if associated to the algal form, exceeding ~6000 Eur/Kg. This can be explained by considering the process expenses related to the extraction and purification steps of microalga intracellular metabolites. In fact, the downstream stage of this biotechnological process often accounts for more than 60–70% of total production costs. Optimized extraction and purification operations might contribute to microalgae market with the advantage to commercialize a natural existing astaxanthin form. The aim of this paper is the evaluation of the use of commercial activated carbon Darco™ G-60 for the purification of astaxanthin from an extraction broth. Astaxanthin was firstly extracted from Haematococcus pluvialis red phase supplied by Micoperi Blue Growth, an Italian Company that is working for a long time and it is specialized in the microalgae growth. Extraction was performed by Accelerated Solvent Extractor (ASE®200 DIONEX) at 100 bar and 67°C by using ethanol as green solvent with the main advantage to separate all the unipolar fractions as well as insoluble fractions from astaxanthin extracts (fibers, carbohydrate, ashes). In the second step, astaxanthin was purified with a column filled with activated carbon. Experimental tests by changing the mass of activated carbon were carried out (50mg, 100mg and 200mg)and with a flow rate in the range 0.9-1.0ml/min. All the experimental tests were carried out at room temperature (20°C). Results showed that by using activated carbon, it is possible to obtain an adsorption capacity of DARCO G60 in the range 21,9-23,9 mg/g.

The global cosmetic market is promptly growing, showing a strong boost with the growth of economic well-being. In this context, the demand of innovative, more and more specific cosmetic ingredients has been the key for searching alternative, preferably naturally-based, active components. Microalgae represent one of the most attracting microorganisms and natural deposit for bioactive compounds for their peculiar compositions and properties. In the cosmetic sector, their efficient application has recently been highlighted by the placing on the market of different cosmetic preparations. A powerful antioxidant, 550 times more effective than vitamin E, with enormous potential for cosmetic and pharmaceutical applications, is astaxanthin. Although high-quality astaxanthin can be obtained from microalgae, particularly from H. pluvialis specie, actually the major part of the market is occupied by the synthetic form (99%), conferring substantial differences between their price. In fact, algal-based astaxanthin costs ?6000 €/Kg, while the synthetic form 600 €/kg. Thus, along with novel natural product launch, the development of cost-effective technologies able to match the existing ones, represents the major challenge for the microalgae application. This study aims to determine the feasibility of microalgal-based astaxanthin production, by exploring both procedural issues and costs evaluation.

The main purpose of this study is to investigate the effects of operative parameters and bioprocess strategies on the photo-autotrophic cultivation of the microalgae Scenedesmus almeriensis for lutein production. S. almeriensis was cultivated in a vertical bubble column photobioreactor (VBC-PBR) in batch mode and the bioactive compounds were extracted by accelerated solvent extraction with ethanol at 67°C and 10 MPa. The cultivation with a volume fraction of CO2 in the range 0–3.0%v/v showed that the highest biomass and lutein concentrations – 3.7 g/L and 5.71 mg/g, respectively – were measured at the highest CO2 concentration and using fresh growth medium. Recycling the cultivation medium from harvested microalgae resulted in decreased biomass and lutein content. The nutrient chemical composition analysis showed the highest consumption rates for nitrogen and phosphorus, with values higher than 80%, while sulfate and chloride were less consumed.

Anaerobic digestion is a technology used to biologically convert organic substrates into biogas in the absence of oxygen. The resulting biogas is a renewable energy source mainly consisting of a mixture of methane (60÷70% v/v) and carbon dioxide (30÷40% v/v), with traces of some minor compounds, such as H2S and NH3. Anaerobic digestion takes place through a sequence of four biological phases - hydrolysis, acidogenesis, acetogenesis, and methanogenesis - performed by the action of particular species of bacteria. Operating parameters such as temperature, pH, pressure and organic substrates govern the process and affect the starting biomass transformation and the content of methane into the biogas. The biogas from anaerobic digestion can be upgraded to biomethane by removing CO2 and the minor compounds. The techniques commonly used for this purpose, like pressure swing adsorption and membrane separation, are energy-intensive as they require the compression of biogas. In this paper, an innovative energy-saving approach for biogas production and its upgrading to biomethane is proposed. The concept is based on anaerobic digestion carried out at a pressure higher than the atmospheric one, called pressured anaerobic digestion (PAD), in order to directly produce high pressure biogas that can be upgraded to high pure biomethane (CH4 = 95% v/v) avoiding the compression phase during the upgrading. The variation of the main operating parameters has been simulated in order to investigate their effect on biomethane production and composition and to define the best operating conditions. The simulation of the process has been carried out by using Aspen Plus®.

Immobilization of living cells is a useful technique that allows to enhance the biotechnological properties of many organisms. Currently, cell-immobilization is obtained via carrier adsorption, self-aggregation and entrapment. We are currently investigating the possibility to immobilize microalgae cells using magnetic nanoparticles on a magnetic surface. The principle is based on the introduction, inside the cell-body of microalgae, superparamagnetic nanoparticles through electroporation. Once microalgae have absorbed enough magnetic nanoparticles they will be responding to an external magnetic field. By using a flat magnetic surface, it will be possible to trap them in a specific position by means of magnetic force. Importantly, immobilized cells will be covered with a thin layer of water and during cell division only one of the daughter cells will keep the magnetic nanoparticles since they will face permanently the magnetic surface. The first step towards this goal is the introduction of magnetic nanoparticles in the microalgae cells. This work will present preliminary results of magnetic cells preparation. Magnetic nanoparticles covered with lipid, to make them biocompatible, and electroporation method to inset nanoparticles in the cells have been used. The protocol to obtain magnetic cells and viability assay that proved the feasibility of the method will be described.

Hexavalent chromium (Cr(VI)) in water systems is a major hazard for living organisms, including humans. The most popular technology currently used to remove Cr(VI) from polluted water is sorption for its effectiveness, ease of use, low cost and environmental friendliness. The electrostatic interactions between chromium species and the sorbent matrix are the main determinants of Cr(VI) sorption. The pH plays a central role in the process by affecting chromium speciation and the net charge on sorbent surface. In most cases, Cr(VI) sorption is an endothermic process whose kinetics is satisfactorily described by the pseudo second-order model. A critical survey of the recent literature, however, reveals that the thermodynamic and kinetic parameters reported for Cr(VI) sorption are often incorrect and/or erroneously interpreted.

Humic acids (HA) are a potential hazard to aquatic ecosystems and human health. Because biological treatment of contaminated water does not satisfactorily remove these pollutants, novel approaches are under evaluation. This work explores electrochemical oxidation of HA in aqueous solution in a lab-scale apparatus using platinum-coated titanium electrodes. We evaluated the effects of HA concentration, current density, chloride concentration and ionic strength on the rate of HA oxidation. The initial reaction rate method was used for determining the rate law of HA degradation. The results showed that the reaction rate was first-order relative to HA concentration, chloride concentration and current density. An appreciable effect of ionic strength was also observed, most likely due to the polyanionic character of HA. We propose a kinetic model that satisfactorily fits the experimental data.

The molecular structure of a commercial sample of humic acids (HA) was investigated by membrane dialysis experiments (MD) and low-pressure size-exclusion chromatography (LP-SEC). MD showed that HA molecules were retained by dialysis membrane with a cut-off of 6–8 kDa, independently from HA concentration (15 or 150 mg L−1), NaHCO3 concentration (0.005–2.0 mol L−1), and from propan 2-ol (0–5 v/v %). SEC experiments at low pressure gave chromatograms with a broad peak, with an elution volume between those of the globular proteins bovine serum albumin (molecular weight = 66.5 kDa) and lysozyme from egg (molecular weight = 14.4 kDa). The pattern of the chromatogram did not vary with HA concentration, and second-run chromatograms of single eluted fractions showed relatively sharp peaks. From these data, we reveal that the commercial HA sample analysed has a macromolecular structure rather than being a supramolecular aggregate of relatively small molecules, as recently proposed for some samples of HA obtained from different sources.

Humic acids (HA) are promising green materials for water and wastewater treatment. They show a strong ability to sorb cationic and hydrophobic organic pollutants. Cationic compounds interact mainly by electrostatic interaction with the deprotonated carboxylic groups of HA. Other functional groups of HA such as quinones, may form covalent bonds with aromatic ammines or similar organic compounds. Computational and experimental works show that the interaction of HA with hydrophobic organics is mainly due to π−π interactions, hydrophobic effect and hydrogen bonding. Several works report that sorbing efficiency is related to the hydrophobicity of the sorbate. Papers about the interaction between organic pollutants and humic acids dissolved in solution, in the solid state and adsorbed onto solid particles, like aluminosilicates and magnetic materials, are reviewed and discussed. A short discussion of the thermodynamics and kinetics of the sorption process, with indication of the main mistakes reported in literature, is also given.

This work aims at contributing to the development of a revolutionary technology based on shape memory alloy (SMA) coatings deposited on-site to large-scale metallic structural elements, which operate in extreme environmental conditions, such as steel bridges and buildings. The proposed technology will contribute to improve the integrity of metallic civil structures, to alter and control their mechanical properties by external stimuli, to contribute to the stiffness and rigidity of an elastic metallic structure, to safely withstand the expected loading conditions, and to provide corrosion protection. To prove the feasibility of the concept, investigations were carried out by depositing commercial NiTinol Ni50.8Ti (at.%) powder, onto stainless steel substrates by using high-velocity oxygen-fuel thermal spray technology. While the NiTinol has been known since decades, this intermetallic alloy, as well as no other alloy, was ever used as the SMA-coating material. Due to the influence of dynamics of spraying and the impact energy of the powder particles on the properties of thermally sprayed coatings, the effects of the main spray parameters, namely, spray distance, fuel-to-oxygen feed rate ratio, and coating thickness, on the quality and properties of the coating, in terms of hardness, adhesion, roughness, and microstructure, were investigated.

In this study, Scenedesmus almeriensis as green microalga was cultivated on bench-scale for carbon dioxide (CO2) capture and lutein production. The autotrophic cultivation of S. almeriensis was carried out by using a vertical bubble column photo-bioreactor (VBC-PBR) with a continuous flow of a gaseous mixture of oxygen (O2), nitrogen (N2), and CO2, the latter in content of 0.0–3.0 %v/v. The liquid phase was batch. S. almeriensis growth was optimized. In addition, lutein extraction was carried out by using accelerated solvent extraction with ethanol as Generally Recognized as Safe (GRAS) solvent at 67 °C and 10 MPa. Upon optimization of CO2 concentration, the maximum biomass productivity, equal to 129.24 mg·L−1·d−1, was achieved during the cultivation by using a content of CO2 equal to 3.0 %v/v and it allowed to obtain a lutein content of 8.54 mg·g−1, which was 5.6-fold higher in comparison to the analogous process carried out without CO2 addition. The ion chemical analysis in the growth medium showed that by gradually increasing CO2 content, the nutrient consumption during the growth phase also increased. This study may be of potential interest for lutein extraction at industrial scale, since it is focused on pigment production from a natural source with a concomitantly CO2 capture.

In this article, microalgae Nannochloropsis sp. was used for fatty acid (FA) extraction, using a supercritical fluid-carbon dioxide (SF-CO2) extraction method. This study investigated the influence of different pre-treatment conditions by varying the grinding speed (200−600 rpm), pre-treatment time (2.5−10 min), and mixing ratio of diatomaceous earth (DE) and Nannochloropsis sp. biomass (0.5−2.0 DE/biomass) on FAs extraction. In addition, the effect of different operating conditions, such as pressure (100−550 bar), temperature (50−75 °C), and CO2 flow rate (7.24 and 14.48 g/min) on eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) recovery, was analyzed. Experimental data evidenced that, keeping constant the extraction conditions, the pre-treatment step enhanced the FAs extraction yield up to 3.4 fold, thereby the maximum extracted amount of FAs (61.19 mg/g) was attained with the pre-treatment with a ratio of DE/biomass of 1 at 600 rpm for 5 min. Moreover, by increasing both SF-CO2 pressure and temperature, the selectivity towards EPA was enhanced, while intermediate pressure and lower pressure promoted DHA recovery. The highest amount of extracted EPA, i.e., 5.69 mg/g, corresponding to 15.59%, was obtained at 75 °C and 550 bar with a CO2 flow rate of 14.48 g/min, while the maximum amount of extracted DHA, i.e., ~0.12 mg/g, equal to 79.63%, was registered at 50 °C and 400 bar with a CO2 flow rate of 14.48 g/min. Moreover, the increased CO2 flow rate from 7.24 to 14.48 g/min enhanced both EPA and DHA recovery.

Astaxanthin and lutein, antioxidants used in nutraceutics and cosmetics, can be extracted from several microalgal species. In this work, investigations on astaxanthin and lutein extraction from Haematococcus pluvialis (H. pluvialis) in the red phase were carried out by means of the supercritical fluid extraction (SFE) technique, in which CO2 supercritical fluid was used as the extracting solvent with ethanol as the co-solvent. The experimental activity was performed using a bench-scale reactor in semi-batch configuration with varying extraction times (20, 40, 60, and 80 min), temperatures (50, 65, and 80 °C) and pressures (100, 400, and 550 bar). Moreover, the performance of CO2 SFE with ethanol was compared to that without ethanol. The results show that the highest astaxanthin and lutein recoveries were found at 65 °C and 550 bar, with ~18.5 mg/g dry weight (~92%) astaxanthin and ~7.15 mg/g dry weight (~93%) lutein. The highest astaxanthin purity and the highest lutein purity were found at 80 °C and 400 bar, and at 65 °C and 550 bar, respectively.

Haematococcus pluvialis microalgae in the red phase can produce significant amounts of astaxanthin, lutein, and fatty acids (FAs), which are valuable antioxidants in nutraceutics and cosmetics. Extraction of astaxanthin, lutein, and FAs from disrupted biomass of the H. pluvialis red phase using carbon dioxide (CO2) in supercritical fluid extraction (SFE) conditions was investigated using a bench-scale reactor in a semi-batch configuration. In particular, the effect of extraction time (20, 40, 60, 80, and 120 min), CO2 flow rate (3.62 and 14.48 g/min) temperature (50, 65, and 80 °C), and pressure (100, 400, and 550 bar.) was explored. The results show the maximum recovery of astaxanthin and lutein achieved were 98.6% and 52.3%, respectively, at 50 °C and 550 bars, while the maximum recovery of FAs attained was 93.2% at 65 °C and 550 bars.

The production of biofuels from renewable sources is a major challenge in research. Methanol, ethanol, dimethyl ether (DME), synthetic natural gas (SNG), and hydrogen can be produced from syngas which is the result of the gasification of biomasses. Syngas composition varies according to the gasification technology used (such as fixed bed reactors, fluidized bed reactors, entrained flow reactors), the feedstock characteristics, and the operating parameters. This paper presents a review of the predominant biomass gasification technologies and biofuels obtained from syngas by biomass gasification.