WINERY WASTEWATER TREATMENT BY MICROALGAE CO-CULTURE FOR LOW-COST BIOMASS PRODUCTION IN A BIOREFINERY CONCEPT

The growing industrialization, the high level of pollution, and the reduction of resources lead to the necessity to find an alternative way to handle the entire production chain from the raw materials to the finished products. The zero-waste strategy and the circular economy are the best solutions to remediate the dramatic conditions in which our planet pours. Moreover, the reduction of fossil fuels reserves and the continuously increasing demand for energy around the world has led to the necessity to find an eco-sustainable alternative to conventional fuels. In the last few years, biofuel production from different plant sources has been increasingly studied by researchers. The production of third-generation biofuels from raw materials that do not compete with food crops is attracting more and more attention. Third-generation biofuels can be produced from microalgal biomasses or from their intracellular components such as lipids. Moreover, their production, if compared to conventional biomasses, reduces land and water utilization along with the use of pesticides. Microalgae are unicellular microorganisms able to grow under autotrophic, heterotrophic or mixotrophic conditions depending on the carbon source used in their metabolism as well as light conditions. They are composed mainly of lipids, proteins and carbohydrates, whose relative proportions depend in particular on the species and growth conditions. They are generally used for human or animal nutrition, or extraction of added-values components for chemical and pharmaceutical industries, but also for biofuel production. In recent years, lipid, protein, and pigment extraction from microalgae has been widely studied for various applications such as the productions of biodiesel from the lipid fraction and of nutraceuticals and dyes from vitamins, proteins, and pigments. However, it is important to stress that the microalgae biorefinery concept is the only way to make microalgae competitive with products obtained from conventional sources, and that the use of microalgae to produce only biofuels or only nutraceuticals has not yet reached clear-cut economic feasibility. The biggest challenges are the relatively high cost of biomass production and the energy demand for the extraction and separation processes. Therefore, in order to make microalgae products economically viable and increase their marketability, it is necessary to reduce costs, for example by valorizing process residues as co-products. It is generally accepted that the sale of co-products will make the production of biofuels from microalgae economically feasible. Indeed, it was estimated that the residue of microalgal biomass after lipid extraction could be worth between 100 and 225 USD per ton and could yield co-products ranging in value from 0.95 to 2.43 USD per gallon of biodiesel produced. Moreover, the microalgae protein fraction has an economic value that ranges from 0.86 USD/kg as feed to 5.57 USD/kg as food. Moreover, thanks to their capability of also metabolizing organic carbon, microalgae can in fact be grown in wastewaters, thus reducing the use of fresh water, the cost of growth medium, the energy consumption and, at the same time, the wastewater polluting impact. There are several studies in the literature focusing on the use of microalgae to treat wastewaters such as municipal and textile wastewaters, among others. In this contest, agri-food wastewaters are good candidates to be used as microalgae medium because they are rich in nutrients and the resulting biomass obtained after treatment could be used for the extraction of high added value components, such as protein and pigments. Between them, winery wastewaters (WWWs) which are released from different activities of the wine making process, namely tank washing, transfer, bottling and filtration, are suitable to be treated by microalgae. The polluting impact of WWWs is related to their high organic load (polyphenolic compounds, sugars, organic acids and esters), low pH (3\u20135), high content of suspended particles and large volumes (0.5\u201314 L per liter of wine produced). Owing to the release of organic compounds and inorganic ions, their disposal in land without adequate treatment can change the physicochemical properties of groundwater such as color, pH and electrical conductivity, among others. Whit regard to the open issues recalled above, the research project has aimed to develop a biorefinery from microalgae. Winery wastewaters were used as growth medium both for microalgal biomass production and reduction of pollutant impact, the protein fraction was extracted from the biomass as high added-value component, and the residual biomass was submitted to pyrolysis process to produce biofuels. The topic addressed by this thesis is organized and subdivided into chapters as follows. Chapter 1- Literature review on the biorefinery concepts, the application to microalgae production and the microalgae world situation concerning their metabolisms, growth system, industrial application (wastewaters treatment, extraction of high-added-value components and, biofuels production). Chapter 2- The optimization of winery wastewaters concentration in microalgae growth medium to obtain both high microalgae concentration and productivity and good results in terms of reduction of pollutant impact. Three different winery wastewaters collected from different steps of the winemaking process were studied. The co-culture of Chlorella vulgaris and Arthrospira platensis was grown under continuous light and air supply. The optimized parameters obtained in the previous section were studied at different light conditions to identify the prevalent metabolism of the microalgae to consume the pollutant molecules present in the wastewaters. Moreover, the microalgae growth was performed into different photobioreactor configurations: tubular photobioreactor (TP), column photobioreactor (CP) and, open pond (OP) to improve the biomass concentration and the pollutant impact removal efficiency. Chapter 3- To perform a scale-up of the process the co-culture was grown in 20 L column photobioreactor, the growth medium under the condition optimized in the previous chapters was supplied continuously by a pump system. Chapter 4- The extraction of high-added value components from microalgal biomass were investigated taking into account the biorefinery concept. The optimization of the protein extraction process from A. platensis by Ultrasound-Assisted Extraction was performed using Box-Behnken Design in which the effects of extraction time, solvent volume, and mass of A. platensis were investigated. Moreover, the extraction and purification of c-phycocyanin from A. platensis and the subsequent protein extraction on wet c-phycocyanin residue was performed. The protein extraction from the co-culture grown in the different photobioreactor configurations was carried out under the condition optimized in the previous chapter. Moreover, the effect on cell size and cell wall thickness of growing the co-culture in presence of winery wastewaters was investigated. Variation of protein expression as function of photobioreactor configuration was also assessed. Chapter 5- The energetical recovery of the produced co-culture biomass was investigated. The pyrolysis process was carried out on microalgal biomass obtained from wastewater treatment in membrane photobioreactor. The operational condition of the process and, the distribution of reaction products and their composition ware studied. Chapter 6- A final discussion of the process was performed based on the results obtained from the previous chapters

Thermocatalytic Pyrolysis of Exhausted Arthrospira platensis Biomass after Protein or Lipid Recovery

Microalgae and cyanobacteria are unicellular microorganism that contain high-added-value compounds. To make their extraction economically feasible, the biorefinery concept is the only solution. In this study, the residues resulting from lipid or protein extraction from Arthrospira platensis biomass were valorized by catalytic pyrolysis using ZSM5 zeolite or amorphous silica–alumina as catalyst. The reaction was performed in a quartz reactor, and the catalysts were placed in a fixed bed, to force the reaction gases to pass through it. The reaction products were analyzed by FTIR and GC–MS analyses. The reaction gases and liquids obtained from the extraction residues had higher hydrocarbon contents compared with the untreated biomass. Moreover, the pyrolysis of biomass after protein extraction led to fractions with lower nitrogenated component contents, while that after lipid extraction to fractions with lower oxygenated component contents. This study showed that the pyrolysis process could be used to valorize the microalgae extraction residues, aiming to make biofuels production and extraction of high-added-value products more economically feasible

Winery Wastewater Treatment by Microalgae to Produce Low-Cost Biomass for Energy Production Purposes

Even though biofuel production from microalgae has become more and more attractive in recent years, it is limited especially by the high cost of microalgae cultivation. However, microalgae can be grown in wastewater in order to reduce their production cost and, at the same time, the polluting impact of wastewaters. Winery wastewaters, which are abundantly released from the wine making process, have a large pollution impact related to their high loads of total solids, chemical oxygen demand (COD) and polyphenol concentration. In this research work a co-culture of Chlorella vulgaris and Arthrospira platensis was used to treat three different winery wastewaters from different steps of the wine production process, in order to produce low-cost biomass intended for biofuel production. Growth of the co-culture and reduction of wastewater pollutant impact were followed by daily determinations of biomass concentration, COD and polyphenol content. The highest productivities of biomass (0.66 gDry Weight/L·day) and lipids (7.10 ± 0.22 gLipid/100 L·day) were obtained using 20% of second washing winery wastewater after 4 days of treatment. Moreover, COD and polyphenol content of the three different wastewaters were reduced by the co-culture by more than 92% and 50%, respectively. These results suggest that winery wastewaters can be used successfully for the growth of A. platensis and C. vulgaris co-culture in order to obtain inexpensive biomass for energy production purposes

Thermocatalytic Pyrolysis of Exhausted Arthrospira platensis Biomass after Protein or Lipid Recovery

Microalgae and cyanobacteria are unicellular microorganisms that contain high-added value compounds. To make their extraction economically feasible the biorefinery concept is the only solution. In this study, the residue resulting from lipid or protein extraction from Arthrospira platensis biomass was valorized by catalytic pyrolysis using ZSM5 zeolite or amorphous silica-alumina as catalyst. The reaction was performed in a quartz reactor, and the catalyst was placed in a fixed bed to force the reaction gases to pass through it. The reaction products were analyzed by FTIR and GC-MS analyses. The reaction gases and liquids obtained from the extraction residues had higher hydrocarbon contents compared to untreated biomass. Moreover, pyrolysis of biomass after protein or lipid extraction led to fractions with lower contents of nitrogenated or oxygenated components, respectively. This study showed that the pyrolysis process could be used to valorize the microalgae extraction residues aiming to make biofuels production and extraction of high added-value products more economically feasible

Mechanistic and Compositional Aspects of Industrial Catalysts for Selective CO₂ Hydrogenation Processes

The characteristics of industrial catalysts for conventional water-gas shifts, methanol syntheses, methanation, and Fischer-Tropsch syntheses starting from syngases are reviewed and discussed. The information about catalysts under industrial development for the hydrogenation of captured CO2 is also reported and considered. In particular, the development of catalysts for reverse water-gas shifts, CO2 to methanol, CO2-methanation, and CO2-Fischer-Tropsch is analyzed. The difference between conventional catalysts and those needed for pure CO2 conversion is discussed. The surface chemistry of metals, oxides, and carbides involved in this field, in relation to the adsorption of hydrogen, CO, and CO2, is also briefly reviewed and critically discussed. The mechanistic aspects of the involved reactions and details on catalysts’ composition and structure are critically considered and analyzed

Graphene-based materials for wastes, biomass and CO2 valorization in catalysis: A technological perspective via molten salt synthesis

The exfoliation of graphite to graphene is one of the main methods of graphene production. In this paper, we provide an overview of the main molten salt methods for the exfoliation of graphite to graphene, including thermal and electrochemical exfoliation of graphite in molten salt. The fundamental mechanism of these methods is discussed in detail, along with the characterization techniques and instruments used to analyze the produced graphene. Additionally, the principles of eutectic salt mixtures, which play a crucial role in the exfoliation process, are discussed. The utilization of graphene-based materials in catalysis, particularly in the CO 2 and biomass valorization to produce sustainable fuels and chemicals, has been reviewed. The molten salt method is a simple and efficient way to produce graphene-based materials by using a molten salt medium to exfoliate the graphite. The purpose of this study is to provide a comprehensive overview of the current state of knowledge regarding the use of molten salt for the exfoliation of graphite to graphene, including their benefits and limitations

Investigating the Effect of Operational Variables on the Yield, Characterization, and Properties of End-of-Life Olive Stone Biomass Pyrolysis Products

In recent years, biomass has emerged as a promising raw material to produce various products, including hydrocarbons, platform chemicals, and fuels. However, a more comprehensive evaluation of the potential production of desirable value-added products and chemical intermediates is required. For these reasons, this study aimed to investigate the impact of various operating parameters on the pyrolysis of end-of-life olive stone, an agriculture and food industry waste, using a tubular quartz reactor operated at 773 K. The results revealed that the product compositions were comparable under batch or semi-batch nitrogen feeding conditions and with reaction times of 1 or 3 h. The product distribution and composition were significantly influenced by changes in the heating rate from 5 to 50 K min−1, while the effect of changing the biomass particle size from 0.3 to 5 mm was negligible in the semi-batch test. This work provides a comprehensive understanding of the relationship between pyrolysis operational parameters and obtained product distribution and composition. Moreover, the results confirmed the possible exploitation of end-of-life olive stone waste to produce high-added value compounds in the zero-waste strategy and biorefinery concept