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Abstract Two diazotrophic cyanobacteria (Anabaena cylindrica PCC 7122 and Nostoc sp. PCC 7120) were cultivated to produce cyanophycin, a nitrogen reserve compound, under nitrogen fixing conditions. In preliminary continuous experiments, Nostoc sp. was shown to be more efficient, accumulating a higher amount of cyanophycin and showing a greater capability to fix atmospheric nitrogen in the biomass (67 mgN d−1 of fixed nitrogen per liter of culture). The operating conditions were then optimized to maximize the cyanophycin productivity: the effect of incident light intensity, residence time and nitrogen availability were investigated. Nitrogen availability and/or pH played a major role with respect to biomass production, whereas phosphorus limitation was the main variable to maximize cyanophycin accumulation. In this way, it was possible to achieve a stable and continuous production of cyanophycin (CGP) under diazotrophic conditions, obtaining a maximum cyanophycin productivity of 15 mgCGP L−1 d−1. Key points • Diazotrophic cyanobacteria produce stable amount of cyanophycin in continuous PBR. • Nostoc sp. proved to be more efficient in producing cyanophycin than Anabaena sp. • P deprivation is the major variable to increase cyanophycin productivity in continuous.

There is increasing interest in new protein sources for the food and feed industry and for the agricultural sector, and microalgae are considered a good alternative, having a high protein content and a well-balanced amino acid profile. However, protein production from microalgae presents several unsolved issues, as the biomass composition changes markedly as a function of cultivation operating conditions. Continuous systems, however, may be properly set to boost the accumulation of protein in the biomass, ensuring stable production. Here, two microalgae and two cyanobacterial species were cultivated in continuous operating photobioreactors (PBR) under nonlimiting nutrient conditions, to study the effects of light intensity and residence time on both biomass and protein productivity at steady state. Although light strongly affected biomass growth inside the PBR, the overall protein pool did not vary in response to irradiance. On the other hand, shorter residence times resulted in protein accumulation of up to 68 % in cyanobacteria, in contrast with green algae, where a minor influence of residence time on biomass composition was observed. Energy balance showed that light conversion to protein decreased with light intensity. Protein content was also related to energy costs for cell maintenance. In conclusion, it is shown that residence time is the key variable to increase protein content and yield of protein production, but its effect depends on the specific species.

Two diazotrophic cyanobacteria (Anabaena cylindrica PCC 7122 and Nostoc sp. PCC 7120) were cultivated to produce cyanophycin, a nitrogen reserve compound, under nitrogen fixing conditions. In preliminary continuous experiments, Nostoc sp. was shown to be more efficient, accumulating a higher amount of cyanophycin and showing a greater capability to fix atmospheric nitrogen in the biomass (67 mg

This work evaluates the feasibility of renewable jet-fuel production from waste cooking oil (WCO) via catalytic transfer hydrogenation (CTH) using isopropanol as hydrogen donor. Results were compared to a commercial hydroprocessed renewable jet (HRJ) fuel technology, employing process simulation-based techno-economic analysis (TEA) and life-cycle assessment (LCA). The two routes were compared in terms of product yield, energy consumption, economic and environmental metrics, and allocation methods. The total capital expenditure of CTH plant (7.3M$) was significantly lower than that of HRJ ($149.7M$). The annual revenues were comparable (∼150M$/year), due to similar fuel yields. To be profitable, the liquid fuel should be sold at $3.00/gal and $1.67/gal for CTH and HRJ, respectively. The cumulative fossil energy demand (CED) of HRJ was 1.6 times that of CTH and the total 100-year GWP of CTH was 8% less than HRJ’s, with both systems not sequestering CO2 through co-product offsets. Mass-, energy-, and market-value allocations were utilized. Sensitivity analysis indicated that both systems were driven by transportation factors and not process inputs. Trend analysis on CTH’s energy-return-on-investment (EROI) showed that wide improvements could be made in energy efficiency (EROI = 10.30–11.30). From an investment/construction perspective, CTH (95% cheaper) appears to outperform HRJ at similar revenues.

In this work, process simulation is used to calculate material and energy balances for several different hydrogen production processes. Process simulation outcomes are then used to estimate three key performance indicators: the energy return of energy invested, the levelized cost of hydrogen and the life cycle assessment. We compared several hydrogen generation processes, each denoted by a unique colour code: (i) green hydrogen, produced by electrolysis of water using electricity from renewable sources, (ii) grid hydrogen, produced by electrolysis using grid electricity, (iii) grey hydrogen, produced from natural gas using steam reforming and (iv) blue hydrogen, like grey one, but coupled with carbon capture and storage. In conclusion, the most sustainable hydrogen production method is the green hydrogen, produced by water electrolysis.

In view of the low-carbon transformation of the power sector, natural gas-fired power generation is the only technology, among fossil resources, that will continue to provide an important source of flexibility for the power system in the coming years. However, the carbon dioxide emissions produced by the operation of such plants call for carbon capture and storage equipment, whose deployment needs to be assessed and compared with the main renewable technologies: wind power and photovoltaics. This work uses process simulation in order to assess two different carbon capture processes: a traditional one, based on monoethanolamine, and an innovative one, based on hot potassium carbonate. Process simulation is also used for the transportation of carbon dioxide to the sequestration site. Mass and energy balances from the simulations are then used for the calculation of the Energy Return on Energy Invested, the Levelized Cost of Energy and as inputs for the Life Cycle Assessments of both alternative designs. The life cycle analyses of the considered power technologies exhibited higher contributions due to fossil-based power plants towards climate-related impact categories, while renewable sources were revealed to be more burdensome for the exploitation of mineral resources. The calculated Energy Return on Energy Invested for gas-fired power plants with carbon capture and storage is between 5.2 and 12.4, comparable with the values of photovoltaics and wind power. On the other hand, their Levelized Cost of Energy is between 10.2 and 20.0 eurocent per kilowatt-hour, much higher than that of renewables. The conclusion is that, at present, the sustainability of gas-fired power stations equipped with carbon capture and storage should be carefully considered and not taken for granted.

Modeling microalgal mixotrophy is challenging, as the regulation of algal metabolism is affected by many environmental factors. A reliable tool to simulate microalgal behavior in complex systems, such as wastewaters, may help in setting the proper values of operative variables, provided that model parameters have been properly evaluated. In this work, a new respirometric protocol is proposed to quickly obtain the half-saturation constant values for several nutrients. The protocol was first verified for autotrophic exploitation of ammonium and phosphorus (Monod kinetics), as well as of light intensity (Haldane model), further elaborated on specific light supply basis. It was then applied to measure the kinetic parameters of heterotrophic growth. The half-saturation constants for nitrogen and phosphorus resulted comparable with autotrophic ones. The dependence on acetate and dissolved oxygen concentration was assessed. Mixotrophy was modeled as the combination of autotrophic/heterotrophic reactions, implemented in AQUASIM, and validated on batch curves with/without bubbling, under nutrient limitation, and different light intensities. It was shown that the reliability of the proposed respirometric protocol is useful to measure kinetic parameters for nutrients, and therefore to perform bioprocess simulation.

Natural gas is a well known energy carrier. It is often used for producing heat and power, but can also be applied as a fuel in the transport sector. The production of synthetic natural gas (SNG) from coal or biomass is an interesting opportunity for both exploiting coal and biomass, and for replacing oil products for transportation and other uses. SNG has many important advantages with respect to other synfuels: it can be transported efficiently and cheaply using existing natural gas pipelines and distributing networks, it is an easily convertible feedstock, both in natural-gas combined-cycle power plants and in petrochemical facilities, it can count on a high social acceptance with respect to coal, and it can be stored underground, enabling efficient operation throughout the year independently of a fluctuating demand. Unfortunately, the commercial deployment of technologies for the production of SNG is currently constrained by technical barriers, so that more research is required before extensive applications on the industrial scale can be achieved. An important issue to be addressed is the strong exothermicity of the methane formation reactions, so that conventional fixed-bed catalytic reactors cannot be safely used (Sudiro et al., 2009). Following the 1970s energy crisis much work has been initiated in the US on coal-to-SNG: SNG process technologies and catalysts were developed and tested extensively. But most have been cancelled in the 1980 because of the changing energy picture. One industrial plant has actually been realized in North Dakota, which began operating in July 1984 and today produces more than 54 billion standard cubic feet of synthetic natural gas annually (1.53 billion Nm3/yr). Coal consumption is about 6 million tons each year. The heart of this plant is a building containing 14 gasifiers (www.dakotagas.com). Nowadays, the rise of natural gas prices have created a strong interest in producing SNG from the cheaper and much more abundant coal. A renewed interest in basing more energy consumption on coal and petcoke has resulted in a revival of several older technologies that have been enhanced to improve efficiency and to lower investment cost. Methanation is used as the final syngas purification step in the production of ammonia, but methanation for SNG production is more complex. The main industrial application of methanation has been the removal of CO from H2-rich feed gases in ammonia plants. With 5

Protein-rich spent yeast is a waste by-product of brewing and other fermentation industry. A continuous-flow hydrothermal treatment called ‘flash hydrolysis’ was deployed for protein recovery and yeast disposal. A feed slurry with 1–15 wt% yeast was hydrolyzed at temperatures ranging between 160 and 280 °C for a very short residence time of 10 ± 2 s. Using 10 wt% yeast at 240 °C, 66.5% carbon, 70.4% nitrogen and 61.0% overall yeast biomass was solubilized in liquid hydrolysate. The liquid hydrolysate in which 63.1% of analyzed amino acids in yeast feed were solubilized, was tested as nutrient for cultivation of E. coli in a continuous bioreactor. The steady-state E. coli concentration was 1.18 g L−1 and 0.93 g L−1 using liquid hydrolysate and commercial yeast extract, respectively. Finally, the kinetic parameters for yeast solubilization (reaction order, activation energy and pre-exponential factor) were found to be 0.86, 21.3 kJ mol−1 and 19.36 [L g−1]n−1 s−1, respectively.

Metabolically engineered cyanobacteria are promising photosynthetic cell factories to produce valuable compounds in view of a bio-based industry. However, when the producer population is affected b...

Cyanophycin, an intracellular reserve molecule synthetized by cyanobacteria, is considered as a potential biobased raw material for the industrial sector. It is usually produced through the cultivation of photosynthetic microorganisms in batch systems, which are affected by the high variability of cyanophycin accumulation due to varying growth phases, which lower the overall productivity. In this work, Synechocystis sp. PCC 6803 was cultivated in a continuous photobioreactor to increase cyanophycin productivity and to assess the feasibility of large-scale application. A stable production of the compound was obtained at steady-state. The effect of residence time and inlet phosphorus concentration on the biomass and cyanophycin productivity was evaluated, to identify the optimal conditions for its accumulation. A maximum value of cyanophycin productivity of about 30 mg L−1 d−1 was obtained, doubling the one achieved in the batch system. A quantitative correlation between the phosphorus quota and the cyanophycin produced was eventually proposed, highlighting a threshold of 4 mg of phosphorus per g of biomass for cyanophycin accumulation.

In this study, the feasibility of integrating microalgae cultivation in a biogas production process that treats the organic fraction of municipal solid waste (OFMSW) was investigated. In particular, the biomass growth performances in the liquid fraction of the digestate, characterized by high ammonia concentrations and turbidity, were assessed together with the nutrient removal efficiency. Preliminary laboratory-scale experiments were first carried out in photobioreactors operating in a continuous mode (Continuous-flow Stirred-Tank Reactor, CSTR), to gain preliminary data aimed at aiding the subsequent scaling up to a pilot scale facility. An outdoor experimental campaign, operated from July to October 2019, was then performed in a pilot scale raceway pond (4.5 m2), located in Arzignano (VI), Italy, to assess the performances under real environmental conditions. The results show that microalgae could grow well in this complex substrate, although dilution was necessary to enhance light penetration in the culture. In outdoor conditions, nitrification by autotrophic bacteria appeared to be significant, while the photosynthetic nitrogen removal was around 12% with respect to the inlet. On the other hand, phosphorus was almost completely removed from the medium under all the conditions tested, and a biomass production between 2&ndash, 7 g m&minus, 2 d&minus, 1 was obtained.

In conventional continuous bioreactor operations, it is a common practice to decouple the hydraulic retention time (HRT) from the solid retention time (SRT). When dealing with photosynthetic microorganisms, light intensity plays a major role in the growth kinetics; thus, the effect of HRT and SRT on biomass productivity may differ from that in chemotrophic bioreactors. In this study, we assessed the role of uncoupled SRT and HRT on biomass productivity in continuous photobioreactors (PBRs) based on simple mass balances, light transfer, and kinetic models to highlight the specific features of PBRs. Under a non-limiting nutrient supply, SRT is the fundamental variable used to maximize productivity and control the biomass concentration and light penetration in a PBR. Operating at SRT > HRT does not enhance the productivity. If the goal is biomass production, it is instead convenient to operate at SRT

Microalgal biomass has been considered as a possible alternative source of carbohydrates and lipids in fermentative/reactional processes, called third generation of biofuels. Carbohydrates from microalgae are mostly composed by glucose and some pentose-derived polymers that must be hydrolyzed to be efficiently used. When enzymatic hydrolysis is applied a pretreatment is required. Sonication/ultrasonication is one of the most promising methods, and in this paper the influence of pretreatment time, sonication intensity and biomass concentration was validated, and the energy consumed in the process compared as well. Sonication intensity had the major role on the enzymatic accessibility. Pretreatment time can be used to decrease hydrolysis time. More than 90% of hydrolysis efficiency was reached when higher amplitude (sonication intensity) and pretreatment time were used. The applied energy influenced indirectly the hydrolysis process. The best saccharification/energy relation was reached when 50% of amplitude for 25 min was applied, obtaining 91% of hydrolysis yield and spending 2.4 MJ/kg of dry biomass. Keywords: Microalgae, Ethanol, Fermentation, Amylase, Cellulase, Sonication

Microalgal-bacteria consortia application on wastewater treatment has been widely studied, but a deeper comprehension of consortium interactions is still lacking. In particular, mixotrophic exploitation of organic compounds by microalgae affects gas (CO2 and O2) exchange between microalgae and bacteria, but it is not clear how environmental conditions may regulate algal metabolism. Using a respirometric-based protocol, we evaluated the combined effect of organic carbon and light intensity on oxygen production and consumption by C. protothecoides, and found that the chemical oxygen demand (COD) was not consumed when incident light increased. Batch experiments under different incident lights, with C. protothecoides alone and in consortium with activated sludge bacteria, confirmed the results obtained by respirometry. Continuous system experiments testing the combined effects of light intensity and residence time confirmed that, under limiting light, mixotrophy is preferred by C. protothecoides, and the nutrient (COD, N, P) removal capability of the consortium is enhanced.

The supply of nutrients is a great issue to a sustainable scale-up of microalgal biofuels production, as these photosynthetic microorganisms require large amounts of N, P and other micronutrients to grow, which turns into high fertilizers demand. Additionally, recovery and reuse of nutrients (particularly N & P) are a must to reduce the non-point pollution emanating from their release into water or air during the downstream processing steps to biofuels or bioproducts. In the recent years, strong research efforts have been paid for developing nutrient recovery and recycling techniques, in order to reduce the net amount of fertilizers required. One possibility is exploiting nutrients from waste streams, such as wastewaters, while others focus on the recovery of N and P from the non-fuel fraction of the produced microalgal biomass, which is then recycled to the cultivation system, in a closed-loop perspective. In both cases, the presence of possible contaminants as well as nutrients bioavailability can impact the biomass productivity compared to standard synthetic media. Although the nutrients recovery and reuse has been in the forefront for a few years, there are no review publications available yet. In this paper, state-of-the art studies on nutrients recovery and recycling methods in microalgae processing from the last decade are reviewed. The study focuses on the different N and P recovery methods and yields, as well as on their subsequent use in algal cultivation and impact on algae productivity. Possible bioproducts exploitation is considered, and perspectives of closed-loop material balances on a large-scale are eventually provided.

Nannochloropsis is commonly recognized as a valuable biomass source for the production of both biofuels and high value nutraceuticals compounds. Phosphorus is one of the main nutrients affecting microalgal growth and composition. In this work, the effect of using higher P concentrations in cultivation of Nannochloropsis salina was studied showing an increase of the phosphate uptake rate related with the higher P availability in the medium. This enhanced uptake was preferentially stored in the cells rather than being used for growth, indicating the activation of a luxury uptake phenomenon. The intracellular P storage in N. salina was measured and the presence of polyphosphate granules was detected. The kinetic of accumulation and consumption of internal phosphorus was quantified in batch cultures, as a function of P concentration and light intensity. Finally, the effect of P, also in combination with different light supply rates was analyzed in continuous steady-state experiments, showing that operating in this mode strongly influences not only the biomass productivity, but also the nutrient uptake.

In this paper, the acidic pretreatment of microalgal biomass is investigated, and the solubilized biomass and hydrolyzed sugars were evaluated. The process is analyzed through the severity factor approach (acidic combined severity factor (ACSF)). A suitable kinetic model is developed and applied, and it is shown that the severity factor theory works. A discussion and comparison are presented with respect to the literature methods, which are mainly related to lignocellulosic biomass. In the case of microalgae, reaction orders for biomass and acid are shown to be the main parameters, and no other assumptions are needed. Two regions of the acidic treatment process have to be evaluated: low and high reactivity regions. Furthermore, a suitable experimental design is required in order to provide an appropriate reaction spectrum to obtain a good estimation of the kinetic parameters. A logarithmic severity factor range (ln ACSF) between 5 and 6 is able to solubilize around 80% of biomass and to hydrolyze more than 90% of sugars present in the biomass.

This study investigated the behaviour of dynamic membrane (DM) filtration for the treatment of stabilised landfill leachate in a bench-scale pre-anoxic and aerobic submerged dynamic membrane bioreactor (DMBR). Four meshes with different openings (10, 52, 85 and 200 μm) were tested to support the development of DM. Differences were observed among the meshes in supporting the development of the cake layer constituting the DM. The treatment of landfill leachate had an impact on sludge characteristics resulting in deteriorated filtration performance of the DM. Effluent turbidity was often higher than 100 NTU for larger mesh pore size (85 and 200 μm). Low effluent turbidity was achieved with meshes with 10 and 52 μm (13 ± 2 and 26 ± 4 NTU, respectively) although at membrane fluxes lower than 10 L m− 2 h−1. The bioreactor exhibited a moderate organics removal of 50–60% and an ammonia oxidation between 80 and 90%. Incomplete nitrification was observed due to increased concentrations of free ammonia and free nitrous acid, with nitrite effluent concentrations up to 1062 mgNO2 --N L−1. Due to the large presence of refractory organic matter in landfill leachate, denitrification was limited resulting in a total nitrogen removal of approximately 20%. © 2018 Elsevier Ltd

In this study, acidic and enzymatic hydrolysis were carried out with Chlorella vulgaris and Scenedesmus obliquus, and a systematic evaluation of the yeast inoculum optimization (Saccharomyces cerevisiae and Pichia stipitis) during the hydrolysates fermentation was made. Acidic hydrolysis with 3% of sulphuric acid at 121 °C and 30 min of reaction time (50–100 g/L of biomass) was found as best condition, and more than 90% of sugars recovery in the liquid phase was achieved even though S. obliquus be more sensible to thermal degradation than C. vulgaris. On the other hand, during the enzymatic hydrolysis, ultrasonication showed to be an effective method of biomass pretreatment to provide higher enzyme accessibility what together with a combination between amylases, cellulase/hemicellulase mix and pectinases achieved more than 90% of sugars recovery in 8 h of hydrolysis time. Thus, both treatments could recover efficiently the sugars present in microalgae. After inoculum optimization (concentration and consortium between S. cerevisiae and P. stipitis) and saline influence on yeast performance were evaluated, the fermentation of microalgal hydrolysate exhibited very different profiles in comparison with the control conditions and ethanol biochemical yield changed between 45% and 61%, emphasizing the importance to optimize this last but not less important step of ethanol production.

Nutrient recycling is of paramount importance for microalgal cultivation aimed at biofuels production. Though different techniques have been assessed at lab-scale level, less information is available on the actual nutrient recovery yields and on the energy balance of a large-scale closed-loop process. In this work two technologies, namely anaerobic digestion (AD) and flash hydrolysis (FH), were investigated by process simulation analysis and compared in terms of both nutrients recovery and energy profitability (EROEI index). FH performs better in terms of nutrients recycling, with up to 70% and 60% of phosphorus and nitrogen recovered in bio-available forms, while incomplete biodegradability limits the nutrients recovery extent in AD. On the other hand, AD requires much lower energy inputs, achieving EROEI values always favorable (2.3–5), while the high thermal requirements of FH, even with heat integration, highlight the need of improving the operating conditions to reduce the energetic burden of this technology (EROEI = 0.8–2.4).

The optimal design and operation at large scale of a continuous fermentation process including a biological reactor/photobioreactor and a gravity settler with partial recycle and purge of the biomass are addressed. The proposed method is developed with reference to microalgae (Scenedesmus obliquus) cultivation, but it can be applied to any fermentation process as well as to activated sludge wastewater treatment. A procedure is developed to predict the effect of process variables, mainly the recycle ratio (R), the solid retention time (θ c ), the reactor residence time (θ), and the ratio between feed and purge flow rates (F I /F W ). It includes a simple steady-state model of the two units coupled in the process and the experimental measurement of basic kinetic data, in both the bioreactor and the settler, for the tuning of model parameters. The bioreactor is assumed as perfectly mixed, and a rigorous gravity-flux approach is used for the settler. The process model is solved in terms of dimensionless variables, and plots are given to allow sensitivity analyses and optimization of operating conditions. A discussion about washout is presented, and a simple method is outlined for the calculation of the minimum values of residence time (θ min ) and recycle ratio (R min ) and of the maximum allowed recycle ratio (R max,operating ) and biomass purge rate (F Wmax ). In particular, it is shown that the system is sensitive to the concentration of biomass lost from the top of the settler (C X S ). The proposed method can be useful for the design and analysis of large-scale processes of this type.

In this work, the effect of nitrogen limitation on Tetradesmus (Scenedesmus) obliquus cultivation was evaluated in a continuous system operated at steady-state to assess the carbohydrate productivity in a single step. Under continuous irradiance (150 and 650 μmol photons m−2 s−1), with an optimized nitrogen limitation in the reactor inlet stream, a carbohydrate fraction of 45% was achieved, with a remarkable productivity of 0.80 g L−1 day−1. Under simulated day-night irradiation, a cyclic steady state was obtained, as a result of alternating light and dark conditions, with an average carbohydrate production of 0.71 and 0.30 g L−1 day−1 (summer and winter, respectively), with a biomass productivity reduced due to the photoperiod. The uptake of nutrient by the cell appeared to be regulated by the light regime, which determines the carbohydrate accumulation as well. Accordingly, it was possible to obtain a stable carbohydrate production in one-step continuous system with day-night and seasonal irradiation by properly managing the nitrogen inlet.

A treatment process for the biological removal of phenol from wastewater generated from the wet scrubbing of syngas is discussed with the objective of reducing Hydraulic Retention Time (HRT) for the process. In phenol biodegradation, a major challenge is posed by the inhibitory effect of high inlet phenol concentrations on the functioning of degrading microorganisms, leading to excessively high HRT values. This study provides a theoretical insight on the effect of reactor configuration and operation mode on the residence time for high strength phenolic wastewaters. Two pre-treated wastewater streams mainly contaminated with phenol, with different flow rates and phenol concentrations, have been considered for evaluation in this work. Various configurations to remove phenol have been studied and compared. The kinetics in the reactors have been estimated using the Haldane-Andrews equation for a variety of microorganisms. The configurations which require minimum residence time for a given extent of phenol biodegradation are those employing two reactors in series with a certain reflux stream. Gulosibacter sp. YZ4 is found to be the most effective microorganism in removing phenol within the minimum retention period. This article is protected by copyright. All rights reserved

In this work, process simulation and cost analysis of an osmotic-driven process for simultaneous clean water and power generation from seawater using the concept of solute-gradient method are developed, with the aim of determining its potential application at the industrial scale. The simulations were carried out by Aspen Plus® software, considering a plant size corresponding to 1 MW power generation, using ethanol–water as the draw solution. Different draw solution regeneration techniques are investigated with the aim of minimizing the thermal requirements while respecting the threshold purity of the extracted water. It is shown that, by optimizing the inlet draw solution flow rate and concentration, power densities of about 5 W/m2 can be obtained using hollow fine fiber membrane, with a projected cost of electricity around 152 €/MWh. Economic analysis, based on Saudi Arabia water cost, shows that the process profitability is strongly affected by the water selling price, which needs to be at least 1.7 €/m3 in order to have the cumulative cash position equal to zero at the end of the plant lifetime (25 years). Nevertheless, it is suggested that both water and power could be industrially produced in a profitable way (DPBP less than 5 years) with a drinking water selling price equal to 2 €/m3, which is about 30% higher than the current value yet a realistic one in the near future.

Synechocystis sp. has remarkable mixotrophic capabilities, as well as an efficient exploitation of nitrogen and phosphorus, that may be applied in wastewater treatment based on cyanobacteria. To better investigate the exploitation of algal mixotrophy in bioremediation, this species was used in axenic respirometric tests to ascertain the effect of high light and non limiting CO

Photosynthetic microorganisms have received enormous attention due to their fast growth rate, higher photosynthetic efficiency (PE) and productivity, and high carbohydrates content (up to 50% DW). Microalgae and cyanobacteria are the organisms investigated, but some differences should be discussed between them, regarding carbohydrates composition, light utilization, growth rates, and biomass productivity. The common batch method to evaluate growth capabilities is strongly limited by a number of factors, such as the acclimation of preinoculum and a changing biomass concentration over time, which makes it more difficult to explain the results. Conversely, in a continuous system operated at a steady state, biomass production is constant and is well acclimated to the reactor adapting to environmental conditions. In this chapter, a brief comparison between cyanobacteria and microalgae based on composition, productivity, and PE is completed and the effectiveness of the continuous system as a method to exploit these organisms for carbohydrate production.

Biogas production and its upgrading to obtain biomethane for use as a transportation fuel has been receiving increasing attention, particularly in Italy. In this work, three commercially developed technologies (Pressure Water Scrubbing, Hot Potassium Carbonate and Pressure Swing Adsorption) are critically compared. Accurate process simulations were carried out to evaluate and optimize the performances in terms of biomethane (and CO2) purity and recovery, as well as specific energy consumption and operating costs, considering a biogas throughput of 500 Nm3 h−1. Results from process simulation were used to develop a detailed Discounted Cash Flow analysis of the different technologies, taking into account the recent subsidies issued on March 19th, 2018 by the Italian legislation to promote biomethane development. All the three processes here considered are able to recover more than 90% of biomethane, with a purity higher than 98%. The economic analysis revealed that, according to the new incentive mechanism set by the Italian so-called Biomethane Government Decree (Government Decree 19/3/2018) the investment payback time would range between 3 and 6 years and the Net Present Value would be positive, whereas in the absence of any incentive the investment would not be profitable for any of these technologies.

2-propanol (99.9 wt%) was used as an H-donor to produce jet/diesel-fuel range from waste cooking oil (WCO) over a fixed bed of granular activated carbon in a continuous flow reactor. The reactions were carried out at 2 bar and at a temperature range of 300–400 °C with weight hourly space velocity (WHSV) of 6.7 h−1. An optimum yield of 72% liquid hydrocarbon (LHC) at 380 °C was observed. The LHC contained 32% alkanes, 16% aromatics and 37% alkenes at the optimum temperature. Using 2-propanol as an in situ hydrogen source will potentially reduce the volume ratio of hydrogen source to oil (0.4 L 2-propanol/L WCO) compared to what is reported in the literature for conventional use of hydrogen gas at high pressures. Evaluation of reaction kinetics revealed that the rate of catalytic transfer hydrogenation of WCO is second order with an activation energy of 53 kJ/mol. With 10 hours of continuous catalytic transfer hydrogenation (CTH) of WCO, the catalyst maintained its catalytic activity despite the inherent coke formation. Catalytic Transfer Hydrogenation of waste cooking oil (70% C18:2 & C18:1) using 2-propanol at 2 bars and 380 °C over activated carbon

The development of new technologies to increase the production of biofuels without directly competing with food production is a must. Microalgal biomass has recently been highlighted in this regard. In this chapter, the role of this biomass for bioethanol production is discussed within a biorefinery approach, in the view to promote industrial sustainability. Cultivation aimed at accumulating around 50%–60% of carbohydrates in the biomass (dry weight) and the importance of water and nutrient recycling are reviewed. Saccharification of biomass using enzymes or acids is addressed together with alternative operations (such as hydrothermal liquefaction and flash hydrolysis) that aim at recovering additional products (i.e., biocrude). Because the main monosaccharide in microalgal biomass is glucose, high rates of hydrolysis and fermentation are possible, achieving more than 80% of the efficiency as a sum of these two operations. Anaerobic digestion to treat vinasse after distillation and the recycling of CO2 from the ethanolic fermentation and from biogas combustion could increase the process sustainability. Finally, the advantage of using microalgae rather than other sources of biomass in bioethanol production is estimated with reference to the production rate, even though the cultivation costs remain still high.