Biofuel production and phosphorus recovery through an integrated treatment of agro-industrial waste

The present study aimed to develop an integrated treatment of agro-industrial waste for biofuel (biogas and syngas) production and for phosphorus recovery. In the first step, an anaerobic digestion (AD) process was carried out on two different mixtures of raw agro-industrial residues. Specifically, a mixture of asparagus and tomato wastes (mixture-1) and a mixture of potatoes and kiwifruit residues (mixture-2) were investigated. The results proved that the properties of mixtures notably affect the evolution of the digestion process. Indeed, despite the lower organic load, the maximum biogas yield, of about 0.44 L/gCODremoved, was obtained for mixture-1. For mixture-2, the digestion process was hindered by the accumulation of acidity due to the lack of alkalinity in respect to the amount of volatile fatty acids. In the second step, the digestates from AD were utilized for syngas production using supercritical water gasification (SCWG) at 450 °C and 250 bar. Both the digestates were rapidly converted into syngas, which was mainly composed of H2, CO2, CH4, and CO. The maximum values of global gasification efficiency, equal to 56.5 g/kgCOD, and gas yield, equal to 1.8 mol/kgTS, were detected for mixture-2. The last step of the integrated treatment aimed to recover the phosphorus content, in the form of MgKPO4·6H2O, from the residual liquid fraction of SCWG. The experimental results proved that at pH = 10 and Mg/P = 1 it is possible to obtain almost complete phosphorus removal. Moreover, by using the scanning electronic microscopy, it was demonstrated that the produced precipitate was effectively composed of magnesium potassium phosphate crystals. © 2018 by the authors

Green extraction of value-added compounds form microalgae. A short review on natural deep eutectic solvents (NaDES) and related pre-treatments

Sustainability and renewability are demanding the most important challenges that need to be achieved. Therefore, microalgae and Natural deep eutectic solvents (NaDEs) are two classes that deserve particular attention that can allow to meet the sustainability. Microalgae, as raw materials, can produce a variety of value-added compounds, which have numerous applications in pharmaceutical, nutraceutical and cosmetics sector. While, NaDES have peculiar characteristics that allow the recovery of various value-added compounds from microalgae biomass in sustainable manner. Microalgal compounds can be extracted using organic acids, alcohols or sugars by employing the NaDES process. These solvents act as are non-toxic, non-volatile and renewable during NaDES process. Considering the properties shown by microalgae and NaDES separately, a combined microalgae-NaDES extraction is extremely promising for future industrial applications. However, this technology requires proper pre-treatment of microalgal biomass to attain the complete recovery of valuable compounds. In conclusion, this review summarize the potential application of NaDES for extraction of intracellular compounds from microalgal biomass and their related pre-treatments to improve the extraction efficiency

Characterization of Extracts from Haematococcus pluvialis Red Phase by using Accelerated Solvent Extraction

The request for natural products such as antioxidant pigments derived from microalgae, i.e. ß-carotene, lutein and astaxanthin, is growing. In this context, astaxanthin, a powerful antioxidant produced by Haematococcus pluvialis, used as an additive in animal feed and as a food supplement, has been extracted by accelerated solvent extraction using acetone and ethanol as green and safe solvents, and hexane and chloroform:methanol (1:1) performing the best operating conditions. The obtained extracts showed not only the recovery of mainly astaxanthin but also other carotenoids, such as lutein and in lesser part of ß-carotene. In addition, the composition of the extracts was analyzed by highlighting the content of other valuable bio-products such as proteins, carbohydrates, lipids and Total Dietary Fibers. The best extraction performance was found using acetone and ethanol as solvent

Integrated approach for wastewater treatment and biofuel production in microalgae biorefineries

The increasing world population generates huge amounts of wastewater as well as large energy demand. Additionally, fossil fuel’s combustion for energy production causes the emission of greenhouse gases (GHG) and other pollutants. Therefore, there is a strong need to find alternative green approaches for wastewater treatment and energy production. Microalgae biorefineries could represent an effective strategy to mitigate the above problems. Microalgae biorefineries are a sustainable alternative to conventional wastewater treatment processes, as they potentially allow wastewater to be treated at lower costs and with lower energy consumption. Furthermore, they provide an effective means to recover valuable compounds for biofuel production or other applications. This review focuses on the current scenario and future prospects of microalgae biorefineries aimed at combining wastewater treatment with biofuel production. First, the different microalgal cultivation systems are examined, and their main characteristics and limitations are discussed. Then, the technologies available for converting the biomass produced during wastewater treatment into biofuel are critically analyzed. Finally, current challenges and research directions for biofuel production and wastewater treatment through this approach are outlined

Microalgae-based biorefineries for sustainable resource recovery from wastewater

Extensive and improper utilization of water from industrial, municipal, and agricultural activities generate 380 trillion L/y of wastewater worldwide. Wastewaters from different sources contain enormous amounts of nutrients such as carbon, nitrogen, and phosphorus. Thus, the recovery of these nutrients via appropriate sustainable process becomes a necessity. Among various processes microalgae-based technologies has attracted considerable attention and its strategies for sustainable and low-cost treatment of wastewater has allowed removal of over 70% nutrient loads from the wastewater. After the treatment of wastewater, the harvested microalgae biomass contains value-added biomolecules which can used for bioenergy production and nanoparticle synthesis. At present, high operational costs represent a major limitation for the development of microalgae-based biorefineries. Thus, the main aim of the review is to provide the knowledge about the potential of low-cost microalgae-based integrated biorefinery for wastewater treatments and resource recovery. Also, this review provides the insight of microalgae biomass-based bioenergy products, nanoparticles synthesis their application within the concept of circular bioeconomy. Furthermore, this review also provides information on different established industries which used microalgae for wastewater treatment

Purification of astaxanthin from microalgae by using commercial activated carbon

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

Microorganisms. A potential source of bioactive molecules for antioxidant applications

Oxidative stress originates from an elevated intracellular level of free oxygen radicals that cause lipid peroxidation, protein denaturation, DNA hydroxylation, and apoptosis, ultimately impairing cell viability. Antioxidants scavenge free radicals and reduce oxidative stress, which further helps to prevent cellular damage. Medicinal plants, fruits, and spices are the primary sources of antioxidants from time immemorial. In contrast to plants, microorganisms can be used as a source of antioxidants with the advantage of fast growth under controlled conditions. Further, microbe-based antioxidants are nontoxic, noncarcinogenic, and biodegradable as compared to synthetic antioxidants. The present review aims to summarize the current state of the research on the antioxidant activity of microorganisms including actinomycetes, bacteria, fungi, protozoa, microalgae, and yeast, which produce a variety of antioxidant compounds, i.e., carotenoids, polyphenols, vitamins, and sterol, etc. Special emphasis is given to the mechanisms and signaling pathways followed by antioxidants to scavenge Reactive Oxygen Species (ROS), especially for those antioxidant compounds that have been scarcely investigated so far

Microalgae characterization for consolidated and new application in human food, animal feed and nutraceuticals

The exploration of new food sources and natural products is the result of the increase in world population as well as the need for a healthier diet; in this context, microalgae are undoubtedly an interesting solution. With the intent to enhance their value in new commercial applications, this paper aims to characterize microalgae that have already been recognized as safe or authorized as additives for humans and animals (Chlorella vulgaris, Arthrospira platensis, Haematococcus pluvialis, Dunaliella salina) as well as those that have not yet been marketed (Scenedesmus almeriensis and Nannocholoropsis sp.). In this scope, the content of proteins, carbohydrates, lipids, total dietary fiber, humidity, ash, and carotenoids has been measured via standard methods. In addition, individual carotenoids (beta-carotene, astaxanthin, and lutein) as well as individual saturated, monounsaturated, and polyunsaturated fatty acids have been identified and quantified chromatographically. The results confirm the prerogative of some species to produce certain products such as carotenoids, polyunsaturated fatty acids, and proteins, but also show how their cellular content is rich and diverse. H. pluvialis green and red phases, and Nannochloropsis sp., in addition to producing astaxanthin and omega-3, contain about 25–33% w/w proteins on a dry basis. D. salina is rich in beta-carotene (3.45% w/w on a dry basis), S. Almeriensis is a source of lutein (0.30% w/w on a dry basis), and the C. vulgaris species is a protein-based microalgae (45% w/w on a dry basis). All, however, can also produce important fatty acids such as palmitic acid, γ-linolenic acid, and oleic acid. Considering their varied composition, these microalgae can find applications in multiple sectors. This is true for microalgae already on the market as well as for promising new sources of bioproducts such as S. almeriensis and Nannochloropsis sp. © 2018, MDPI AG. All rights reserved

Effect of mechanical pretreatment on Nannochloropsis gaditana on the extraction of omega-3 by using accelerated solvent extraction technology

The omega-3 group includes substances as eicosapentaenoic acid and docosapentaenoic acid that can be partially synthesized by human body and substances as alpha-linolenic acid that have to be necessarily introduced into the body from dietary intake. Omega-3 are important nutrients thanks to their anti-inflammatory properties and healthy properties in the reduction of cardiovascular diseases. The growth forecasts of omega-3 market will lead to an increase in the demand for EPA and DHA and therefore finding new potential sources, such as microalgae which are the first EPA and DHA producers in the marine environment, is very important. The aim of this work is to evaluate the feasibility of mechanical pretreatment on Nannochloropsis gaditana as source of EPA and at the same time evaluating the effect on the extraction yield of two solvents: a mixture of chloroform/methanol/water (Bligh & Dyer methods) and hexane that is GRAS (generally recognized as safe solvent) by using accelerated solvent extraction technology

Extraction of astaxanthin from microalga Haematococcus pluvialis in red phase by using generally recognized as safe solvents and accelerated extraction

Solvent Extraction was tested to extract astaxanthin from Haematococcus pluvialis in red phase (HPR), by investigating effects of solvents, extraction pressure and temperature. Astaxanthin isomers were identified and quantified in the extract. The performances of acetone and ethanol, Generally Recognized As Safe (GRAS) solvents, were explored. Negligible effect of pressure was found, while with increasing extraction temperature astaxanthin recovery increased till a maximum value, beyond which thermal degradation seemed to be greater than the positive effect of temperature on extraction. Furthermore, to maximize the extraction yield of astaxanthin, mechanical pre-treatment of HPR biomass was carried out and several extraction runs were consecutively performed. Experimental results showed that after the mechanical pre-treatment the astaxanthin recovery strongly increased while a single extraction run of 20 min was sufficient to extract more than 99% of total astaxanthin extracted. After pre-treatment, maximum recovery of about 87% was found for acetone (pressure = 100 bar; temperature = 40 °C; total time = 60 min). © 201