Macroalgal Biomass Research Articles

Environmental-friendly pretreatment and process optimization of macroalgal biomass for effective ethanol production as an alternative fuel using Saccharomyces cerevisiae

Abstract Fossil fuel depletion and gas limitations require tremendous efforts to the production of renewable energy from environmental-friendly and sustainable sources. The third-generation bioethanol from non-lignocellulosic biomass of macroalgae is an effective candidate for renewable and sustainable fuel–making that mainly involves pretreatment, enzyme hydrolysis, and microbial fermentation. Therefore, the purpose of this research was to develop a consolidated process for the effective conversion of macroalgal biomass into third-generation bioethanol. The pretreatment of two macroalgae biomasses (namely Ulva rigida and Ulva intestinalis) was optimized using a steam explosion, compared with ultrasonication, to maximize the fermentable reducing sugars yield. A condition of pressure at 25 psi and pretreatment time of 15 min by steam explosion pretreatment of U. intestinalis was the best condition for maximizing fermentable reducing sugars up to 5.41 g/L, generating 86.6 kJ/L of energy. In subsequent enzyme hydrolysis of pretreated biomass, using commercial cellulose enhanced the fermentable reducing sugars up to 6.18 g/L. Fermentation of the hydrolysate using yeast Saccharomyces cerevisiae produced 0.12 g–ethanol/g–fermentable reducing sugar in a short time with ethanol productivity of 2.54 mg–ethanol/g–fermentable reducing sugar/h. Interestingly, the produced ethanol can be converted into energy up to 21.91 kJ/L. This study demonstrates the macroalgal biomass is a suitable feedstock of non-lignocellulosic biomass for third-generation bioethanol production and the developed process confirmed the practical, low-cost, and non-polluting conversion of macroalgal biomass into bioethanol based renewable energy.

The neglected role of omnivore fish in the overgrazing of Mediterranean rocky reefs

Sea urchins are considered the most important grazers in Mediterranean shallow sublittoral rocky reef ecosystems, but fish can also have an important role in overgrazing and the reduction of habitat complexity. In this study, the trophic behavior of fish was recorded when provided access to experimental surfaces with increased macroalgal biomass and associated benthic fauna, created by herbivore exclusion cages. After a sufficient period for substantial algal growth, the cages were removed and the activity of fish on these surfaces was recorded for 3 h by an automated photographic camera system. Control surfaces with no restriction on grazers were defined on similar substrates for comparison. To quantify the effects of fish feeding activity on macroalgal coverage, photographic samples were taken immediately after the opening of the cages and after each 3 h recording. The response of fish when the cages were removed was immediate and intense. Feeding activity by 13 different fish species was recorded in total, of which the most frequent were the omnivores Diplodus vulgaris, Coris julis and Thalassoma pavo, and to a lesser extent the herbivore Sarpa salpa. The coverage of erect algae was substantially decreased on the experimental surfaces due to fish feeding activity. The algae were either directly consumed by the fish or cut off when the fish were feeding on macroinvertebrates. We conclude that in addition to grazing by herbivores, fish of higher trophic levels can also significantly affect macroalgal assemblages and restrict the recovery of erect algae in overgrazed reefs where prey is scarce.

Salinity tolerance of macroalgae Gracilaria birdiae

ABSTRACT: This study aimed to determining the manner in which salinity influenced the growth of the macroalgae Gracilaria birdiae, with the objective of identifying its tolerance limits to this abiotic variable. The specimens were submitted to nutrient-enriched water of varying salinities (0, 10, 20, 30, 40, 50, and 60 ppt) for a 30-day period. Initially, under extreme salinity conditions (0 and 60 ppt) the growth of the G. birdiae suffered a negative impact. The macroalgae biomass exposed to 0 and 10 ppt salinities showed a reduction from day six until the experiment was completed. The macroalgae biomass exposed to salinities 20, 30, 40, and 50 ppt showed an increase, with no significant differences between the four treatments. This suggested that this salinity range was comfortable for this species to develop. We concluded that salinity is a crucial parameter which controls the growth of the G. birdiae. This seaweed was negatively influenced when exposed to values equal to or below 10 ppt and equal to 60 ppt, demonstrating good tolerance to salinities of 20, 30, 40 and 50 ppt.

Distribution and species diversity of the floating green macroalgae and micro-propagules in the Subei Shoal, southwestern Yellow Sea.

Massive floating green macroalgae have formed harmful green tides in the Yellow Sea since 2007. To study the early development and the associated environmental factors for the green tide, a field survey was carried out in the Subei Shoal, southwestern Yellow Sea. Multiple species were identified in both floating green macroalgae and micro-propagules , while their abundances showed distinct spatial variations. The floating macroalgal biomass was widespread in the northern Subei Shoal and most abundant at 34°N. Ulva prolifera dominated (91.2% in average) the floating macroalgae, and the majority (88.5%) of U. prolifera was the ‘floating type’. In comparison, the micro-propagules were most abundant around the aquaculture rafts, and decreased significantly with the distance to the rafts. The dominant species of micro-propagules was U. linza (48.5%), followed by U. prolifera (35.1%). Their distinct distribution patterns and species diversity suggested little direct contribution of micro-propagules for the floating macroalgae. The spatial variation of the floating macroalgae was probably a combined result from the biomass source and environmental factors, while the abundance of micro-propagules was closely associated with the rafts. A positive correlation between the floating macroalgae and DO was observed and suggested active photosynthesis of the initial biomass in Subei Shoal. This study revealed specific distributional pattern and relationships among the floating macroalgae, micro-propagules and the environmental factors in the source region, which helps understanding the early blooming dynamics of the green tides in Yellow Sea.

Biorefinery of marine macroalgae into high-tech bioproducts: a review

Pollution and climate change induced by fossil fuel usage are calling for the development of a circular bioeconomy based on carbon neutral resources such as marine macroalgae, also named seaweeds. Macroalgal biomass can generate biofuels and valuable bioproducts such as hydrocolloids and other unique biomolecules. Biorefinery of marine macroalgae involves a minimum use of energy and chemicals, and low waste generation, as demonstrated in recent laboratory-scale studies. Here, we review biorefinery of marine macroalgae with focus on non-energy bioproducts and advances in the separation of biomolecules. We found that metabolites with bioactive properties are in high demand for food, cosmetic, medicine and pharmaceutical industries. These metabolites can be obtained together with energy products to improve macroalgae valorization. Emerging extraction methods facilitate the generation of more qualitative bioproducts in higher yields with less energy.

Effects of geographical location on potentially valuable components in Ulva intestinalis sampled along the Swedish coast

ABSTRACT Macroalgal biomass has the potential to become an important source of chemicals and commodities in a future biorefinery. Currently, production of macroalgal biomass is expensive and the content of high-value compounds is often low. Therefore, in this study the biochemical composition of Ulva intestinalis along the Swedish west coast and the east coast up to Stockholm was assessed with the aim of determining how the content of potentially valuable compounds, such as rhamnose, iduronic acid and PUFAs, could be maximized by utilizing natural variation in the choice of marine cultivation site. Along the investigated coastline, the salinity dropped from 19.4‰ at high latitudes along the west coast to 5.4‰ at Stockholm. Nitrogen and phosphorus availability varied, while temperature was similar at all locations. The two major components of biomass, carbohydrates and ash, varied inversely with the highest content of ash in the west and carbohydrates in the east. In addition, total fatty acids were significantly higher in west coast samples at 3.2 g 100 g–1 dw, with a higher proportion of mono- and polyunsaturated fatty acids. Some health-beneficial fatty acids were found, including EPA and DPA, at 10–50 mg 100 g–1 dw, respectively. The metal content and elemental composition varied widely, probably due to the influence of specific local conditions. The P content was correlated with the phosphorus concentration in waters at the locations. In PCA analysis, the monosaccharides constituting the cell wall polysaccharide ulvan were found to vary by geographical location, with higher levels possibly associated with lower salinities. However, only glucuronic acid differed significantly between sites. These results show the considerable geographical variability in the composition of Swedish U. intestinalis and suggest that different salinities could be used to create a lipid- or carbohydrate-rich biomass.

Allometric models effectively predict Saccharina latissima (Laminariales, Phaeophyceae) fresh weight at local scales

Obtaining reliable estimates of algal biomass is key to assessing the contributions of macroalgae to nearshore ecosystems and to monitoring the effects of environmental change on macroalgal-dominated reefs. Using non-destructive methods to estimate macroalgal biomass leaves algal beds intact but requires precise allometric models (e.g., length–weight relationships). In this study, we established allometric relationships for the widespread kelp, Saccharina latissima, in the Salish Sea. Thalli were harvested from five sites across two regions in Southern British Columbia and the abilities of four non-destructive metrics (stipe length, blade length, blade width, and total thallus length) to predict thallus fresh weight were compared. Allometric models were developed for each region for all combinations of thallus metrics to explain thallus fresh weight and models were ranked based on their AICc scores. Finally, using our largest sample (n = 114 individuals), we performed a resampling experiment to determine the appropriate sample size for constructing local models. These models can be developed from as little as 2 hours of field data collection and are inexpensive and effective methods for non-destructively estimating S. latissima biomass.

Macroalgal Blooms Trigger the Breakdown of Seagrass Blue Carbon.

Intensive macroalgal blooms, a source of labile organic carbon (LOC) induced by coastal nutrient loading in some seagrass ecosystems, create ideal conditions for enhanced recalcitrant organic carbon (ROC) loss via the cometabolism effect. Here, we carried out a 62-day laboratory experiment to see if density-dependent addition of macroalgal biomass can influence the seagrass decomposition process, including seagrass detritus carbon chemistry, greenhouse emissions, and bacterial communities. We found that higher density macroalgal addition stimulated microbes to decompose ∼20% more of the seagrass biomass compared to other treatments, which was also reflected in enhanced (∼twofold) greenhouse gas emissions. Although the composition of the seagrass-associated microbiome communities was unaffected by the addition of macroalgae, we showed that high macroalgal addition caused a relative depletion in the ROC as lignin and lipid compounds, as well as δ13C depletion and δ15N enrichment of the seagrass detritus. These results suggest that macroalgal blooms may stimulate the remineralization of recalcitrant components of seagrass detritus via cometabolism, possibly through providing available energy or resources for the synthesis of ROC-degrading enzymes within the resident microbial population. This study provides evidence that cometabolism can be a mechanism for leading to reduced seagrass blue carbon sequestration and preservation.

Macroalgae-A Sustainable Source of Chemical Compounds with Biological Activities.

Nowadays, one of the most important research directions that concerns the scientific world is to exploit the earth’s resources in a sustainable way. Considering the increasing interest in finding new sources of bioactive molecules and functional products, many research studies focused their interest on demonstrating the sustainability of exploiting marine macroalgal biomass as feedstock for wastewater treatment and natural fertilizer, conversion into green biofuels, active ingredients in pharmaceutical and nutraceutical products, or even for the production of functional ingredients and integration in the human food chain. The objective of the present paper was to provide an overview on the recent progress in the exploitation of different macroalgae species as a source of bioactive compounds, mainly emphasizing the latter published data regarding their potential bioactivities, health benefits, and industrial applications.

Application of macroalgal biomass derived biochar and bioelectrochemical system with Shewanella for the adsorptive removal and biodegradation of toxic azo dye

The present study aimed towards adsorptive removal of the toxic azo dye onto biochar derived from Eucheuma spinosum biomass. Characterization of the produced biochar was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). Eucheuma spinosum biochar (ES-BC) produced at 600 °C revealed a maximum adsorption capacity of 331.97 mg/g towards reactive red 120 dye. The adsorption data fitted best to the pseudo-second order kinetics (R2 > 0.99) and Langmuir isotherm (R2 > 0.98) models. These adsorption models signified the chemisorption mechanism with monolayer coverage of the adsorbent surface with dye molecules. Furthermore, the adsorption process was mainly governed by electrostatic interaction, ion exchange, metal complexation, and hydrogen bonding as supported by the solution pH, FTIR, XPS, and XRD investigation. Nevertheless, alone adsorption technology could not offer a complete solution for eliminating the noxious dyes. Therefore, the bioelectrochemical system (BES) equipped with previously isolated marine Shewanella marisflavi BBL25 was intended for the complete remediation of azo dye. The BES II demonstrated highest dye decolorization (97.06%) within 48 h at biocathode where the reductive cleavage of the azo bond occurred. Cyclic voltammetry (CV) studies of the BES revealed perfect redox reactions taking place where the redox mediators shuttled the electrons to the dye molecule to accelerate the dye decolorization. Besides, the GC-MS analysis revealed biotransformation of the dye into less toxic metabolites as tested using a phyto and cytogenotoxicity.

Species-specific biomass drives macroalgal benthic primary production on temperate rocky reefs

Temperate rocky reefs dominated by the giant kelp, Macrocystis pyrifera, support diverse assemblages of benthic macroalgae that provide a suite of ecosystem services, including high rates of primary production in aquatic ecosystems. These forests and the benthic macroalgae that inhabit them are facing both short-term losses and long-term declines throughout much of their range in the eastern Pacific Ocean. Here, we quantified patterns of benthic macroalgal biomass and irradiance on rocky reefs that had intact kelp forests and nearby reefs where the benthic macroalgae had been lost due to deforestation at three sites along the California, USA and Baja California, MEX coasts during the springs and summers of 2017 and 2018. We then modeled how the loss of macroalgae from these reefs impacted net benthic productivity using species-specific, mass-dependent rates of photosynthesis and respiration that we measured in the laboratory. Our results show that the macroalgal assemblages at these sites were dominated by a few species of stipitate kelps and fleshy red algae whose relative abundances were spatially and temporally variable, and which exhibited variable rates of photosynthesis and respiration. Together, our model estimates that the dominant macroalgae on these reefs contribute 15 to 4,300 mg C m−2 d−1 to net benthic primary production, and that this is driven primarily by a few dominant taxa that have large biomasses and high rates of photosynthesis and / or respiration. Consequently, we propose that the loss of these macroalgae results in the loss of an important contribution to primary production and overall ecosystem function. Key words: benthic production; ecosystem function; kelp forest; macroalgae; primary production

Object-Based Modeling of Marine Phytoplankton and Seaweeds

The aim of this work is to simulate the dissolved oxygen deficiency in the coastal zone that sometimes occurs during the summer water stagnation. We consider the main components of the marine ecosystem that play a major role in such processes—concentrations of nitrogen, phosphorus and sulfur compounds in water, dissolved and particular organic matter, oxygen, biomass of phytoplankton and macroalgae. We use the object-based modeling technique to simulate the spatio-temporal variability of the ecosystem in a 2D domain. In comparison with the traditional approach, it gives several advantages: more precise parametrizations of the biological components’ functionality; higher spatial resolution; possibility to account for the individual variability of hydrobionts; easy inclusion of an arbitrary number of species in the model. Our model included three species of phytoplankton and seven macroalgae. Individual-based modules control their functionality. Species of phytoplankton and seaweeds chosen for simulations are typical for the coastal zone of Crimea. In the simulations, we study the contribution of micro- and macroalgae to the processes of self-purification of a semi-enclosed basin in case of a sharp increase in nutrient concentration in water.

Sargassum-based potential biosorbent to tackle pollution in aqueous ecosystems – An overview

The uncontrolled release of toxic pollutants related to anthropogenic processes has threatened biodiversity and the ecological integrity of aqueous ecosystems during years. The bioaccumulation and biomagnification of toxic pollutants at different trophic levels have raised concern. Several bioremediation approaches have been tested for efficient mitigation and removal of toxic compounds such as metal ions from aquatic environments. Biosorption by biodegradable and renewable sources such as micro and macroalgae biomass has an increasing scope. However, the biosorption mechanisms of Sargassum spp. have not been completely elucidated, and there are still some drawbacks to overcome. Sargassum spp. biomass has been recognized to be a natural, renewable, and cost-effective material to arrest pollutants from aqueous systems. This mini-review is a compendium that spotlights the potentialities of Sargassum-based biosorbents as an alternative for the removal of toxic contaminants from aquatic environments. Main biosorption mechanisms, key factors influencing biosorption, and the challenges regarding its implementation are highlighted with suitable examples.

DOC dynamics and bacterial community succession during long-term degradation of Ulva prolifera and their implications for the legacy effect of green tides on refractory DOC pool in seawater

Under climate warming and coastal eutrophication, outbreaks of green tides have increased in recent decades; e.g., the world's largest green tide caused by Ulva prolifera has occurred in the Yellow Sea for 13 consecutive years. The massive assemblage of macroalgae absorbs large amounts of atmospheric CO2 and converts it into biomass. After the green tide, millions of tons of the macroalgal biomass sink to the seabed to be degraded eventually; this inevitably has a significant impact on the coastal organic carbon pool and microbial community. However, this impact is poorly understood. Here, the degradation of Ulva prolifera over 520 days revealed that relatively sufficient degradation of the macroalgae occurred at ca. 7 months. The rapid release of dissolved organic carbon (DOC) mainly occurred in the first week, which not only increased the size and diversity of the DOC pool in a short time but also promoted the rapid growth of bacteria and led to hypoxia and acidification of the seawater. After that, the labile portion of DOC was gradually used up by bacteria within one month, while the degradation of semi-labile or semi-refractory DOC occurred in half a year. The remaining DOC existed in the form of refractory DOC (RDOC), resisting bacterial consumption and remaining stable for 10 months. During the long-term degradation process, bacterial community structure and metabolic function showed obvious successional characteristics, driving the gradual transformation of DOC from labile to refractory through the microbial carbon pump mechanism. After the long-term degradation, the remaining RDOC accounted for approximately 1.6% of the macroalgal carbon biomass. As RDOC can maintain long-term stability, we propose that the frequent outbreaks of green tides not only affect microbial processes but also may have an important cumulative effect on the coastal RDOC pool.

The Biogeochemistry of Marine Polysaccharides: Sources, Inventories, and Bacterial Drivers of the Carbohydrate Cycle.

Polysaccharides are major components of macroalgal and phytoplankton biomass and constitute a large fraction of the organic matter produced and degraded in the ocean. Until recently, however, our knowledge of marine polysaccharides was limited due to their great structural complexity, the correspondingly complicated enzymatic machinery used by microbial communities to degrade them, and a lack of readily applied means to isolate andcharacterize polysaccharides in detail. Advances in carbohydrate chemistry, bioinformatics, molecular ecology, and microbiology have led to new insights into the structures of polysaccharides, the means by which they are degraded by bacteria, and the ecology of polysaccharide production and decomposition. Here, we survey current knowledge, discuss recent advances, and present a new conceptual model linking polysaccharide structural complexity and abundance to microbially driven mechanisms of polysaccharide processing. We conclude by highlighting specific future research foci that will shed light on this central but poorly characterized component of the marine carbon cycle.

Facultative scavenging feeding habits in Acanthurus chirurgus (Bloch, 1787) (Acanthuriformes: Acanthuridae).

The family Acanthuridae is a key component of coral reef ecosystems as it controls macroalgae biomass buildup. During routine monitoring of benthic communities in the Mexican Caribbean, we observed unusual behaviour of a group of Acanthurus chirurgus, which were feeding on a tuna head left on site by travel tour personnel. This phenomenon has been documented in other herbivorous fish species, especially in places where tourism is a major coastal activity. Although many Acanthurus seek additional sources of protein by feeding on detritus, it is unusual for them to feed directly on fish flesh. Acanthurus chirurgus will incorporate proteins from animal tissues whenever the opportunity arises. Such opportunities occurred rarely in the past, but have become more frequent recently, related to increasing tourism activities where flesh is used as bait to attract the surrounding fauna.

Sustainable and economic analysis of marine macroalgae based chemicals production - Process design and optimization

This work proposes a Mixed Integer Nonlinear Programming (MINLP) model to determine the optimal design of macroalgae based chemicals production plants. The superstructure considers two brown marine macroalgae species (Macrocystis pyrifera and Lessonia vadosa) that are used to produce sorbitol for further transformation. Two additional alternatives are included: corn starch as the traditional feedstock to obtain the corresponding sugars and directly buying sorbitol from market. Sorbitol is transformed into isosorbide, a platform molecule, which can be converted into a drug for heart disease (isosorbide dinitrate), a flame retardant, a biopolymer and a biosolvent (dimethyl isosorbide). The Renewable Process Synthesis Index Metric (RePSIM) is used as objective function to address sustainability. Alternatively, Net Present Value (NPV) is also considered to obtain a detailed economic analysis. In terms of sustainability, the production of isosorbide dinitrate is the optimal pathway, albeit it shows a negative RePSIM of −4.30 million USD/yr. On the other hand, the production of dimethyl isosorbide is the optimal configuration taking into account the economic objective function. Its NPV is 44.31 million USD with a production cost of 6.97 USD/kg. It is worth mentioning that the social and environmental aspect of the dimethyl isosorbide production process is positive. In this sense, this chemical can be obtained from marine macroalgae biomass in a profitable way with a process that is socially and environmentally beneficial.

Solution-state behaviour of algal mono-uronates evaluated by pure shift and compressive sampling NMR techniques

Sodium salts of the algal uronic-acids, d-mannuronic acid (HManA) and l-guluronic acid (HGulA) have been isolated and characterised in solution by nuclear magnetic resonance (NMR) spectroscopy. A suite of recently-described NMR experiments (including pure shift and compressive sampling techniques) were used to provide confident assignments of the pyranose forms of the two uronic acids at various pD values (from 7.5 to 1.4). The resulting high resolution spectra were used to determine several previously unknown parameters for the two acids, including their pKa values, the position of their isomeric equilibria, and their propensity to form furanurono-6,3-lactones. For each of the three parameters, comparisons are drawn with the behaviour of the related D-glucuronic (HGlcA) and D-galacturonic acids (HGalA), which have been previously studied extensively. This paper demonstrates how these new NMR spectroscopic techniques can be applied to better understand the properties of polyuronides and uronide-rich macroalgal biomass.

Integration of Marine Macroalgae (Chaetomorpha maxima) with a Moving Bed Bioreactor for Nutrient Removal from Maricultural Wastewater.

Rather than direct nutrient removal from wastewaters, an alternative approach aimed at nutrient recovery from aquacultural wastewaters could enable sustainable management for aquaculture production. This study demonstrated the feasibility of cultivating marine macroalgae (Chaetomorpha maxima) with a moving bed bioreactor (MBBR-MA), to remove nitrogen and phosphorus in aquaculture wastewater as well as to produce macroalgae biomass. MBBR-MA significantly increased the simultaneous removal of nitrate and phosphate in comparison with only MBBR, resulting in an average total nitrogen (TN) and total phosphorus (TP) removal efficiency of 42.8 ± 5.5% and 83.7 ± 7.7%, respectively, in MBBR-MA while MBBR had no capacity for TN and TP removal. No chemical oxygen demand (COD) removal was detected in both reactors. Phosphorus could be a limiting factor for nitrogen uptake when N : P ratio increased. The recovered nitrogen and phosphorus resulted in a specific growth rate of 3.86%–10.35%/day for C. maxima with an uptake N : P ratio of 6. The presence of macroalgae changed the microbial community in both the biofilter and water by decreasing the relative abundance of Proteobacteria and Nitrospirae and increasing the abundance of Bacteroidetes. These findings indicate that the integration of the macroalgae C. maxima with MBBR could represent an effective wastewater treatment option, especially for marine recirculating aquaculture systems.

Bioethanol production from Codium tomentosum residue

ABSTRACT The present study investigated the feasibility of using residual biomass of marine macroalgae (Codium tomentosum) for bioethanol production. Influence of various parameters was analyzed for optimization of bioethanol production. Pre-treatment was performed with different acids, H2SO4 concentrations, temperatures, and reaction times. Maximum reducing sugar yield achieved was 16.45 ± 0.33 g/l with 4% of H2SO4 at 100°C for 60 min. Cellulase produced from Trichoderma reesei is used for the hydrolysis of biomass. Cellulase activity was estimated at various pH, temperatures, and reaction times. The partially purified cellulase was found to have more activity at 30°C for 48 h of cultivation at pH 5. Enzymatic hydrolysis was analyzed with various biomass concentrations, enzyme concentrations, temperatures, and reaction times. Fermentable sugar yield of 17.05 ± 0.25 g/l was obtained using 5% (w/v) biomass with 4% (w/v) enzyme at 50°C for 48 h. The fermentable sugar was converted to bioethanol by fermentation using Saccharomyces cerevisiae with different parameters such as different pH, temperatures, and reaction times were executed. The maximum bioethanol yield of 4 ± 0.33 g/l was obtained at 30°C for 72 h at pH 5. Further, the bioethanol content was characterized using GC-MS. Thus, the results shows that Codium tomentosum is an excellent biomass resource that can be used as a renewable feedstock for the production of bioethanol.