Cristina González-Fernández

• Madrid Institute for Advanced Studies

Industrial anaerobic digestion (AD) represents a relevant energy source beyond today’s fossil fuels, wherein organic matter is recycled to methane gas via an intricate and complex microbial food web. Despite its potential, anaerobic reactors often undergo process instability over time, which is frequently caused by substrate composition perturbatio...

Anaerobic fermentation (AF) processes are sensitive to temperature fluctuations, which can influence the microbial activity and overall metabolic performances. Anaerobic reactors can face unforeseen temperature control failures, leading to instabilities in the process. The present study investigated the effect of two short-term temperature perturba...

Environmental concerns are rising the need to find cost-effective alternatives to fossil oils. In this sense, short-chain fatty acids (SCFAs) are proposed as carbon source for microbial oils production that can be converted into oleochemicals. This investigation took advantage of the outstanding traits of recombinant Yarrowia lipolytica strains to...

This research investigated the acidogenic fermentation (AF) of sugar cane molasses in an up-flow anaerobic sludge blanket (UASB) reactor for the production of carboxylates. The first step was to assess the optimum process temperature (25, 35 or 55 ºC) using two different granular inocula, one from a brewery company (BGS) and other from a paper plan...

Purpose Microalgae are considered a promising source of bioenergy and high value-added products that could help face the rising demand for energy and raw materials. However, microalgae systems entail consumption of materials and energy, with potential environmental, economic, and social costs. While environmental and economic impacts have been anal...

Converting waste into high-value products promotes sustainability by reducing waste and creating new revenue streams. This study investigates the potential of diverse yeasts for microbial oil production by utilizing short-chain fatty acids (SCFAs) that can be produced from organic waste and focuses on identifying strains with the best SCFA utilisat...

Background Short-chain fatty acids (SCFAs) are cost-effective carbon sources for an affordable production of lipids. Hexanoic acid, the acid with the longest carbon chain in the SCFAs pool, is produced in anaerobic fermentation of organic residues and its use is very challenging, even inhibiting oleaginous yeasts growth. Results In this investigat...

Cutaneotrichosporon curvatum and Yarrowia lipolytica can accumulate microbial oils using short-chain fatty acids (SCFA) as carbon sources. SCFAs-rich media often contain significant amounts of nitrogen that prevent high carbon:nitrogen (C:N) ratios necessary to boost lipid production. This work assessed the intrinsic ability of C. curvatum and Y. l...

The carboxylate platform is a sustainable and cost-effective way to valorize wastes into biochemicals that replace those of fossil origin. Short-chain fatty acids (SCFAs) are intermediates generated during anaerobic fermentation (AF) and are considered high-value-added biochemicals among carboxylates. This investigation aimed to produce SCFAs throu...

Global reliance on fossil oil should shift to cleaner alternatives to get a decarbonized society. One option to achieve this ambitious goal is the use of biochemicals produced from lignocellulosic biomass (LCB). The inherent low biodegradability of LCB and the inhibitory compounds that might be released during pretreatment are two main challenges f...

Carboxylic acids have become interesting platform molecules in the last years due to their versatility to act as carbon sources for different microorganisms or as precursors for the chemical industry. Among carboxylic acids, short-chain fatty acids (SCFAs) such as acetic, propionic, butyric, valeric, and caproic acids can be biotechnologically prod...

Added-value chemicals production via food waste (FWs) valorization using open-mixed cultures is an emerging approach to replace petrochemical-based compounds. Nevertheless, the effects of operational parameters on the product spectrum remain uncertain given the wide number of co-occurring species and metabolisms. In this study, the identification o...

Microbial lipids for chemical synthesis are commonly obtained from sugar‐based substrates which in most cases is not economically viable. As a low‐cost carbon source, short‐chain fatty acids (SCFAs) that can be obtained from food wastes offer an interesting alternative for achieving an affordable lipid production process. In this study, SCFAs were...

With the ever-increasing size of anaerobic digesters (AD), the management and disposal of digestate have become a challenging task for AD operators. Anaerobic digestate is rich in nutrients and contaminants; thus, a suitable treatment is required to meet environmental legislation and protect the receiving environment. There has been a thrust among...

This study assessed a strategy for food waste (FW) valorization into multiple products by applying a cascade combination of only two anaerobic processes using open mixed cultures. FWs were firstly subjected to an anaerobic fermentation (AF) to generate an effluent rich in valuable bioproducts. The remaining solid fraction of AF effluent was further...

Background Microbial lipids are found to be an interesting green alternative to expand available oil sources for the chemical industry. Yeasts are considered a promising platform for sustainable lipid production. Remarkably, some oleaginous yeasts have even shown the ability to grow and accumulate lipids using unusual carbon sources derived from or...

This investigation evaluated the effect of process pH in the metabolite spectrum generated during the anaerobic fermentation (AF) of three carbohydrate-rich wastes (residual cucumber, tomato, and lettuce). For such a purpose, two groups of AF reactors were operated in parallel. One group was operated under inherent conditions of pH upon degradation...

Dry anaerobic digestion (D-AD) generates nitrogen-rich effluents that are normally neglected in the circular bioeconomy. The high turbidity and ammonium content hamper nitrogen recovery from these effluents via biological processes, such as microalgae culture. The goal of this study was to demonstrate microalgae growth viability in high-strength D-...

Microbial lipids are envisaged as promising alternatives for sustainable production of chemicals and fuels. Although sugar-based substrates are the most conventional carbon sources employed for this purpose, the use of low-cost feedstock, such as organic wastes, is crucial for an economically-viable process. In this study, volatile fatty acids (VFA...

Increasing yeast robustness against lignocellulosic-derived inhibitors and insoluble solids in bioethanol production is essential for the transition to a bio-based economy. This work evaluates the effect exerted by insoluble solids on yeast tolerance to inhibitory compounds, which is crucial in high gravity processes. Adaptive laboratory evolution...

The consortia formed by microalgae and bacteria developed during semi-continuous operation of photobioreactors treating domestic wastewater was characterized by means of flow cytometry and DGGE techniques. While microalgae population was dominated by the inoculated wild strain Chlorella sorokiniana, the bacterial community included as activated slu...

Carboxylic acids, traditionally produced from fossil fuels, might be generated from renewable biomass resources via anaerobic fermentation. Considering that the microbial activity of this bioprocess is ruled by the imposed hydraulic retention time (HRT), this investigation explored the relationship between process stability and microbial community....

To properly exploit short-chain fatty acids (SCFAs) in the chemical industry, it is of foremost importance to ensure stable SCFA profile production via anaerobic fermentation (AF). The different macromolecular distribution of food wastes (FWs) used as feedstock might be crucial for process outcome. Targeting at a specific SCFAs profile and yield, t...

In recent years, there has been a growing interest in the use of renewable sources for bio-based production aiming at developing sustainable and feasible approaches towards a circular economy. Among these renewable sources, organic wastes (OWs) can be anaerobically digested to generate carboxylates like volatile fatty acids (VFAs), lactic acid, and...

Unspecific microorganisms consortia are normally used in anaerobic biodegradation of solid wastes. However, these consortia can be tuned to optimally obtain determined bioproducts. In this study, high value-added products and biogas were obtained via an innovative two-stage anaerobic bioprocess from microalgae biomass. The anaerobic fermentation (A...

The organic fraction of municipal waste (OFMW), source-sorted (SS-OFMW) and non-sorted (NS-OFMW), was used as raw material for the sequential production of bioethanol and biogas. Non-isothermal and simultaneous saccharification and fermentation (NSSF) resulted in maximum ethanol concentrations of 51 g/L and 26 g/L for SS-OFMW and NS-OFMW samples, s...

Volatile fatty acids (VFAs) are platform molecules with numerous applications. They can be obtained by adjusting the operational conditions of anaerobic digestion to avoid methanogenesis while focusing on fermentative stages. There are gaps in the knowledge of how, from a life-cycle perspective, the fermentative process performs in VFAs production...

The organic fraction of municipal solid waste (OFMSW) is an appealing feedstock for bioethanol production due to its richness in cellulosic materials. After fermentation and distillation, the remaining residue constitutes a source of unconsumed carbohydrates, proteins and lipids. These macromolecules can be further used via anaerobic digestion (AD)...

Anaerobic degradation of enzymatically pretreated Chlorella vulgaris was aimed in an upflow anaerobic sludge blanket reactor (UASB) to evaluate the organic loading rate (OLR) effect on biomass valorization. Low OLRs resulted in high methane yields (171 mL CH4/g CODin) at low hydraulic retention time (HRT of 6 days). Firmicutes (35–43%), Bacteroidet...

Utilization of digestate as a source of nutrients must be understood in the context of their effects on light penetration. These conflicting consequences of digestate utilization were verified by growing the cyanobacterium Arthrospira platensis (Spirulina) in artificial seawater supplemented with 2.5%, 5%, 10% or 15% (v/v) of anaerobically digested...

This study assessed the feasibility of melon and watermelon residues for the co-production of short-chain fatty acids (SCFAs) and hydrogen (H2) via single-stage anaerobic fermentation. The high content of carbohydrates and readily biodegradable organic matter in the wastes, along with the acid pH (5.6–5.8) imposed in the reactors, were key factors...

Arthrospira is the most widely cultivated strain of all microalgae and cyanobacteria. Arthrospira forms helical trichomes that, under certain circumstances, can switch to a straight morphology. This study compared harvesting using filtration and centrifugation between helical and straight Arthrospira strains. Filtration using woven nylon membranes...

Short-chain fatty acids (SCFAs) are considered building blocks for bioproducts in the so-called carboxylate platform. These compounds can be sustainably produced via anaerobic fermentation (AF) of organic substrates, such as microalgae. However, SCFAs bioconversion efficiency is hampered by the hard cell wall of some microalgae. In this study, one...

Using residual material instead of sugars as substrate for oleaginous microorganisms is a promising approach that may reduce the production costs of microbial lipid. In this study, five oleaginous yeasts were screened for their ability to grow and produce lipid utilizing volatile fatty acids (VFAs), generated from anaerobic fermentation of microalg...

Cellulose valorisation has been successfully addressed for years. However, the use of hemicellulosic hydrolysates is limited due to the presence of C5-sugars and inhibitors formed during pretreatment. Bacillus coagulans is one of the few bacteria able to utilize both C6- and C5-sugars to produce L-lactic acid, but its susceptibility to the lignocel...

This study assessed the potential of using microalgae anaerobic fermentation as a novel choice for producing microbial oils and biogas. Microalgae biomass (Chlorella vulgaris) was used for volatile fatty acids (VFAs) production at three organic loading rates (OLR = 6, 9, 12 g COD/Ld). Regardless of the OLR, anaerobic systems displayed similar organ...

The expansion of urban green areas has boosted the accumulation of gardening lignocellulosic residues that could be potentially used to produce platform chemicals like lactic acid. However, when using lignocelluloses, pretreatment step, such as steam explosion, is often needed to favour sugar release. Considering that the conversion of glucose from...

A wide range of biofuels and bio-based products can be produced from lignocellulose considering its high compositional diversity. Ethanol production by yeasts from cellulosic glucose is well-known, while hemicellulosic xylose utilization is still challenging. This work proposes the use the xylose for l-lactic acid fermentation. In this context, a s...

Disturbances in anaerobic digestion (AD) negatively impact the overall reactor performance. These adverse effects have been widely investigated for methane generation. However, AD recently appeared as a potential technology to obtain volatile fatty acids (VFAs) and thus, the impact of process disturbances must be evaluated. In this sense, microbial...

Volatile fatty acids (VFAs) are regarded as building blocks with a wide range of applications, including biofuel production. The traditional anaerobic digestion used for biogas production can be alternatively employed for VFAs production. The present study aimed at maximizing VFAs productions from Chlorella vulgaris through anaerobic digestion by a...

Volatile fatty acids (VFAs) are chemical building blocks for industries, and are mainly produced via the petrochemical pathway. However, the anaerobic fermentation (AF) process gives a potential alternative to produce these organic acids using renewable resources. For this purpose, waste streams, such as microalgae biomass, might constitute a cost-...

Transition into a circular economy based on sustainable use of resources is, nowadays, a main. Waste streams constitute a cost-effective raw material from which volatile fatty acids (VFAs) can be obtained through anaerobic digestion (AD). This chapter provides useful information involving VFAs production (operational conditions) as well as their se...

In the present study, anaerobic sludge was subjected to thermal and chemical pretreatments to favour VFAs production from a protein-rich waste (i.e. microalgae biomass). Sludge pretreatments have been previously used in hydrogen production; however, information about how they can affect VFAs production from microalgae is still lacking. Thermal pret...

FREE DOWNLOAD UNTIL JANUARY 6th, 2020): https://authors.elsevier.com/c/1a4xr,V9BZEXFx. The integrated production of biodiesel and biogas has been explored by using N. gaditana, I. galbana and A. platensis as substrate. Three fatty acid ethyl ester (FAEE) production approaches were assessed, namely an indirect process with previously extracted lipid...

This study evaluated the feasibility of the anaerobic digestion as a sustainable valorisation strategy for volatile fatty acids production from agroindustrial waste (cucumber, tomato and lettuce). High bioconversion efficiencies were reached by operating the reactors at 25 °C, 3 g VS·d-1·L-1 with pH adjustment. Cucumber fermentation achieved the hi...

Microalgae are a novel biomass feedstock for the production of biogas through anaerobic digestion. However, anaerobic digestion of microalgal biomass often suffers from low methane yields due to their rigid cell walls. In contrast to eukaryotic microalgae, prokaryotic cyanobacteria have a weaker cell wall and might be more attractive as feedstock f...

Microbial oils are proposed as a suitable alternative to petroleum‐based chemistry in terms of environmental preservation. These oils have traditionally been studied using sugar‐based feedstock, which implies high costs, substrate limitation, and high contamination risks. In this sense, low‐cost carbon sources such as volatile fatty acids (VFAs) ar...

This investigation compared the digestion in completely stirred tank reactor (CSTR) of Spirulina platensis at two digestion temperatures (25 and 35 °C). This comparison was conducted in terms methane production, organic matter (COD) removal, volatile fatty acids (VFAs) production and nitrogen mineralization. In mesophilic range, 42%tCOD removal and...

Abstract Lignocellulosic ethanol production requires high substrate concentrations for its cost-competitiveness. This implies the presence of high concentrations of insoluble solids (IS) at the initial stages of the process, which may limit the fermentation performance of the corresponding microorganism. The presence of 40–60% IS (w/w) resulted in...

Since xylose is the second most abundant sugar in lignocellulose, using microorganisms able to metabolize it into bio-based chemicals like lactic acid is an attractive approach. In this study, Lactobacillus pentosus CECT4023T was evolved to improve its xylose fermentation capacity even at acid pH by adaptive laboratory evolution in repeated anaerob...

BACKGROUND Anaerobic digestion (AD) could be designed as a source of volatile fatty acids (VFAs). However, acidogenesis optimization for novel substrates such as Chlorella vulgaris biomass needs to be investigated considering parameters such as temperature (T), organic loading rate (OLR), hydraulic retention time (HRT) and the adaptation of the slu...

Lactic acid is a versatile chemical that can be produced via fermentation of lignocellulosic materials. The heterolactic strain Lactobacillus pentosus CECT 4023 T, that can consume glucose and xylose, was studied to produce lactic acid from steam exploded wheat straw prehydrolysate. The effect of temperature and pH on bacterial growth was analyzed....

Volatile fatty acids (VFAs) produced via anaerobic digestion (AD) are regarded as a low cost production process of building blocks of interest for the chemical industry. In this study, VFAs and methane production were assessed in batch reactors at different temperature ranges (psychrophilic 25°C, mesophilic 35°C, thermophilic 50°C) and different pH...

The techno-environmental performance of a medium-scale wastewater treatment system using high-rate algal ponds was evaluated through mass and energy balances and life cycle assessment. The system involves wastewater primary treatment, microalgae-based secondary treatment, thermal hydrolysis with steam explosion of microalgae, anaerobic co-digestion...

Background Microalgae biomass is regarded as a potential feedstock for bioenergy purposes through anaerobic digestion (AD). Even though AD is a well-proven technology, the use of new feedstocks requires in-depth studies. A lot of research has been conducted assessing methane yield without paying attention to the anaerobic microbiome and their activ...

Biogas generation is the least complex technology to transform microalgae biomass into bioenergy. Since hydrolysis has been pointed out as the rate limiting stage of anaerobic digestion, the main challenge for an efficient biogas production is the optimization of cell wall disruption/hydrolysis. Among all tested pretreatments, enzymatic treatments...

During the last decade, a lot of research has been focused on identifying the methane yields achievable when using microalgae biomass (fresh and pretreated) as a substrate in anaerobic digestion. Encountered differences are frequently attributed to the different microalgae strains (cell walls and macromolecular profiles) or the different metabolic...

The production of high added-value products from lignocellulose is proposed as a suitable alternative to petroleum-based resources in terms of environmental preservation, sustainability, and circular economy. Lactic acid is a versatile building block that can be produced via fermentative routes by several groups of microorganisms, including yeasts...

The unsustainable use of fossil fuels has led to environmental concerns, energy crises, and global climate change. Microalgae have been pointed out as a potential feedstock to cope with all those issues. In this chapter recent investigations dealing with microalgae biomass for biogas production has been reviewed. Two of the main limiting steps rela...

Acclimatized anaerobic communities to high ammonia levels can offer a solution to the ammonia toxicity problem in biogas reactors. In the current study, a stepwise acclimation strategy up to 10g NH4(+)-N L(-1), was performed in mesophilic (37±1°C) continuously stirred tank reactors. The reactors were co-digesting (20/80 based on volatile solid) cat...

The potential of co-producing two different biofuels from a lignocellulosic substrate (wheat straw), according to a biorefinery concept, has been investigated. For such a purpose, simultaneous saccharification and fermentation (SSF) from the hemicellulosic and cellulosic fractions was performed for maximizing bioethanol production. The non-washed w...

Microalgae-Based Biofuels and Bioproducts: From Feedstock Cultivation to End Products compiles contributions from authors from different areas and backgrounds who explore the cultivation and utilization of microalgae biomass for sustainable fuels and chemicals. With a strong focus in emerging industrial and large scale applications, the book summar...

As a result of the increasing population and industrial development, there is an enormous energy demand worldwide. For this reason, the research on the potential of microalgae (including also cyanobacteria) as a third-generation feedstock for bioenergy production has markedly increased. Besides biofuels (biogas, bioethanol, biodiesel, etc.), algae...

Three low-grade carbonaceous materials from biomass (Scenedesmus algae and wheat straw) and waste treatment (sewage sludge) have been selected as feedstock for solar-driven thermochemical processes. Solar-driven pyrolysis and gasification measurements were conducted directly irradiating the samples in a 7 kWe high flux solar simulator and the relea...

Microalgae biomasses are considered promising feedstocks for biofuel and methane productions. Two Continuously Stirred Tank Reactors (CSTR), fed with fresh (CSTR-C) and heat pre-treated (CSTR-T) Chlorella biomass were run in parallel in order to determine methane productions. The methane yield was 1.5 times higher in CSTR-T with regard to CSTR-C. A...

This study investigated the ability of an ammonia-acclimatized inoculum to digest efficiently protein-rich microalgae for continuous 3rd generation biogas production. Moreover, we investigated whether increased C/N ratio could alleviate ammonia toxicity. The biochemical methane potential (BMP) of five different algae (Chlorella vulgaris)/manure (ca...

The addition of laccase enzymes reduces the amount of phenols present in lignocellulosic pretreated materials and increases their fermentability. However, laccase addition in combination with cellulases reduces hydrolysis yields. In this work, hybrid hydrolysis and fermentation (HHF) configuration allowed overcoming the negative effect of laccase t...

Anaerobic digestion of microalgae is hampered by its complex cell wall. Against this background, cyanobacteria cell walls render this biomass as an ideal substrate for overcoming this drawback. The aim of the present study was to compare the growth of two cyanobacteria (Aphanizomenon ovalisporum and Anabaena planctonica) and a microalga (Chlorella...

When laccases are applied for detoxifying steam-exploded slurries, enzymatic hydrolysis is affected. In this study, 10% (w/v) of dry weight (DW) slurry or water insoluble solid fraction were subjected to 48 h enzymatic hydrolysis in the presence of different laccase loadings (0.1, 0.5, 5 or 10 IU/g DW). All laccase dosages higher than 0.1 IU/g DW s...

This book chapter deals with the production of biogas coupled with the use of waste effluents for microalgae biomass growth. Biogas production through anaerobic digestion of microalgae uses the whole organic content of microalgae to produce energy. Furthermore, biogas generation seems to be the least complex of the different energy conversion route...

Phenols are known as inhibitors for cellulases and fermentative microorganisms in bioethanol production processes. The addition of laccases removes the phenolic compounds and subsequently reduces the lag phase of the fermentative microorganism. However, the application of laccases diminishes glucose release during the enzymatic hydrolysis. In this...

Integration of anaerobic digestion (AD) with microalgae processes has become a key topic to support economic and environmental development of this resource. Compared with other substrates, microalgae can be produced close to the plant without the need for arable lands and be fully integrated within a biorefinery. As a limiting step, anaerobic hydro...

Cell disruption is one of the most critical steps affecting the economy and yields of biotechnological processes for producing biofuels from microalgae. Enzymatic cell disruption has shown competitive results compared to mechanical or chemical methods. However, the addition of enzymes implies an associated cost in the overall production process. Re...

When employing biotechnological processes for the procurement of biofuels and bio-products from microalgae, one of the most critical steps affecting economy and yields is the “cell disruption” stage. Currently, enzymatic cell disruption has delivered effective and cost competitive results when compared to mechanical and chemical cell disruption met...

BACKGROUND The hard cell wall of some microalgae hampers an efficient methane production when using those substrates. The present study investigated the effect of two groups of biocatalysts, namely carbohydrases and proteases, applied to Chlorella vulgaris and Scenedesmus sp. for microalgae hydrolysis prior anaerobic digestion.RESULTSC. vulgaris su...

The presence of inhibitors compounds after pretreatment of lignocellulosic materials affects the saccharification and fermentation steps in bioethanol production processes. Even though, external addition of laccases selectively removes the phenolic compounds from lignocellulosic prehydrolysates, when it is coupled to saccharification step, lower hy...

Among the biofuel production processes using different substrates, the biogas generation process is one of the simplest. Compared with bioethanol or biodiesel production processes, anaerobic digestion is a process where all the organic matter (carbohydrates , lipids and proteins) can be biologically degraded for methane production. Biological degra...