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Article

Biorefinery of Beach Cast Seaweed in Brazil: Renewable Energy and Sustainability

by
Fernando Pinto Coelho
1,2,3,4,5,6,*,
Rômulo Simões C. Menezes
1,
Everardo Valadares de S. B. Sampaio
1,
Márcio Gomes Barboza
4,
Emerson Carlos Soares
6,7,
Elica Amara C. Guedes-Coelho
5,8,
Elvis J. de França
1,
Agnaldo J. dos Santos
2,4,
Marcelo F. de Lima
2,4,
Manoel Messias da S. Costa
9,
Natache Gonçalves de M. Ferrão
1,2,
Bruno M. Soares
5,
Diego M. do Nascimento
1,2,
Victor Andrei R. Carneiro
8 and
Cesar Augusto M. de Abreu
1
1
Graduate Program in Energy and Nuclear Technologies at the Federal University of Pernambuco (UFPE/PROTEN), National Nuclear Energy Commission, Recife 50740-540, Brazil
2
Research Nucleus in Energy Production of National Council for Scientific Research—CNPQ, Brasília 70070-010, Brazil
3
Geography Department, Campus do Sertão, Federal University of Alagoas, Delmiro Gouveia 57475-000, Brazil
4
Federal University of Alagoas Civil Engineering Technology Center, Maceió 57000-000, Brazil
5
Institute of Science, Technology and Innovation—Proalga Brazil, São Paulo 1109-060, Brazil
6
Expedition Scientific of San Francisco River—Brazil, Maceió 57000-000, Brazil
7
Federal University of Alagoas—Fishing Engineering, Rio Largo 57072-016, Brazil
8
Institute of Biological and Health Sciences, Federal University of Alagoas—ICBS/UFAL, Maceió 57000-000, Brazil
9
Federal Institute of Alagoas/IFAL/EAD, Brazilian Regional University UNIRB—Maceió, Maceió 57035-660, Brazil
*
Author to whom correspondence should be addressed.
Phycology 2024, 4(3), 394-413; https://doi.org/10.3390/phycology4030022
Submission received: 31 March 2024 / Revised: 5 June 2024 / Accepted: 17 June 2024 / Published: 13 August 2024
Browse Figures
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Abstract

:
Macroalgae are a natural oceanic resource of inexhaustible abundance for the biomass energy industry with growth rates that are three to four times greater than those of terrestrial plants. The objective of this study was to evaluate the sustainability of macroalgae as biomass for biorefining through two investigations. Firstly, the deposition of macroalgae was sampled through 28 collections on seven beaches in the city of Maceió, Brazil, over a two-year period using a zigzag sampling method, covering a deposition area of 135,000 m2. From this, it was estimated that daily collection would yield 5.03 t/ha of dry biomass. Secondly, the calorific values of macroalgal biomass energy and pellet compounds were calculated. The lower calorific value (8.82 MJ/kg) found from a compound of 13 species analyzed was similar to that of the main biomass used in Brazil to obtain energy, i.e., sugarcane bagasse, which has been evaluated as 8.91 MJ/kg. Macroalgal biomass in the form of condensed energy pellets was found to have a higher calorific value of 20.18 MJ/kg, i.e., 1.2% greater than the average for terrestrial biomass pellets. Based on the results obtained, it was observed that macroalgal biomass has the possibility of becoming a new renewable feedstock with potential for bioenergy. The estimates for the deposition of biomass show possibilities for producing biofuels from marine algal raw material, which provides scope for creating another sustainable alternative for global energy issues with a reduction in environmental problems.

1. Introduction

Industrial production systems for energy generation make intensive use of natural resources, and their consumtableption of the main raw materials found in nature gives rise to a variety of environmental impacts. Subsequent to the industrial revolution, concern for monitoring environment preservation, life protection and sustainable development has encouraged the creation of environmental legislation in different countries around the world. Thus, research and development relating to additional renewable energy sources is needed in order to meet the strongly increasing demand for energy worldwide. Energy consumption has increased by 65% over the last 30 years and will increase by another 40% by 2030 with investment reaching USD 600 billion per year [1].
Within this context, beach-cast marine macroalgal biomass is abundant and is freely deposited along coastlines. It has the potential to become an important raw material used for energy generation. The daily production of macroalgal biomass, with growth through photosynthesis, is four times greater than that of terrestrial plants [2,3,4], thus dispensing with the need for fertilizers or other agricultural inputs such as irrigation. Worldwide trade relating to the production of marine algae has reached USD 13.3 billion [5].
There are more than 20,000 species of macroalgae worldwide, but 85–90% of commercial production comes from only 221 species [6]. In 2018, the worldwide production of cultivated macroalgae was 32 million t/year [7]. Renewable energy from bioethanol, biobutanol, methanol, biodiesel, biogas or cogeneration products adds to the versatility of this biomass for the biorefining and bioenergy market. This provides high added value for industrial products such as coal, ethanol, diesel and butane gas [8,9].
Previous sampling studies conducted along the coasts of the states of Alagoas and Bahia, in Brazil, showed that high rates of daily deposition of macroalgal biomass occur on these coasts, ranging from 5.03 to 57.6 t/ha [10]. Therefore, the general objective of the present study was to evaluate the sustainability of natural biomass for use in biorefining processes and for manufacturing energy products associated with biofuels. The present research included two investigations with the following specific objectives: (1) to analyze the chemical composition of macroalgae species with a view to assessing the calorific value of macroalgae and their energetic viability for a new generation of pellet production as biofuel; and (2) to characterize sampled beach-cast seaweed deposits with a view to evaluating the sustainability of production of this biomass.
The information obtained in this study will help with understanding the processes inherent to environmental impacts generated by this biomass in soil, water and the atmosphere. Biomass waste that is discarded in public dumps and characterized in the state of Alagoas, Brazil, as unserviceable has consequences for bathers and tourists and gives rise to additional costs for the public administration. This study can contribute toward future research on marine biomass given that few studies on sampling macroalgal biomass with energy potential have yet been conducted in Brazil.

2. Material and Methods

2.1. Macroalgae Sampling Methods on the Coast in Maceió, Brazil

A research area of 408,736 m2 covering seven beaches was georeferenced with geographic coordinates from the first beach (Sereia) at 9°35′17″ S/35°38′49″ W to the last beach (Pajuçara) at 9°40′53″ S/35°42′19″ W. These seven beaches (Sereia, Riacho Doce, Garça Torta, Guaxuma, Jatiúca, Ponta Verde and Pajuçara) are located on the north shore of the city of Maceió, state of Alagoas, Brazil (Figure 1). The size of the sampling area was calculated using georeferenced collection points within “My GPS Coordinates”, in the NOAA satellite image application (U.S. Navy, NGA, GEBECO), based on Google Maps. The sample collection techniques used in this study were based on the methodology of the Brazilian Agricultural Research Company (EMBRAPA).
A zigzag model of diagonal lines [11,12] (Figure 2) was used, each line covering a distance of 10 m from one end to the other. The collection procedure required 100 m from the first to the last collection point, and thus there were 10 collection points per beach (Figure 2). A total of four collections were performed on each beach, and thus there was a total of 40 collection points per beach. Over a two-year period, samples were obtained from 280 collection points, i.e., 28 collections on seven beaches. These collections were performed in the months of March, April, September and October, which were taken to represent the two climatic seasons that exist in northeastern Brazil, i.e., “summer” and “winter”, respectively.
The instrument used for collection was a polyethylene pipe (50 cm × 50 cm) set up to sample size. The sample collection locations were randomly chosen on each beach. The weight of the accumulated biomass around the sample perimeter was measured using a Roescht digital scale. The overall volume of deposition was calculated thus: the square sample measurement at each collection point per beach was multiplied by ten points for each location and then four collection locations per beach and seven beaches, i.e., respectively, 2500 cm2 × 10 × 4 × 7 = 700,000 cm2 or 70 m2 of the deposition area over the two-year period. The biomass weights and location coordinates were entered into spreadsheets.
The irregular area without linear deposition on the seven beaches was determined to have a horizontal length of 15 km with a vertical length of 9 m after wave breaking. The transect line measurements were obtained through field observations over the two-year period with four collections per beach. This can be represented as the following mathematical expression: A (area) = horizontal length × vertical length ⇨ 15,000 m × 9 m. Macroalgal deposition over the length of the transect was investigated between 1 and 21 m along the shoreline.
The timing of the collection periods was determined according to the phases of the moon, alternating between summer for waning and full moons and winter for new and waxing moons [13]. Each collection time of two hours was determined from the lowest point of the tide to form a macroalgal deposition transect line near the beach. The tidal data were provided by the Department of Hydrography and Navigation of the Brazilian Navy for the years 2015/2016 (Table 1).

2.1.1. Statistical Analyses on Biomass Deposition

Levene’s data test was used to assess normality and homogeneity. One-way ANOVA (analysis of variance) was used to test biomass during collection periods. Tukey’s pairwise multiple comparisons for Student–Newman–Keul’s test was applied to evaluate macroalgal biomass in the event of significant differences (p < 0.05). The PAST statistical software [14] was used for these procedures.

2.1.2. Macroalgal Biomass Processing

Macroalgae were collected manually along the shoreline and placed in 100-L plastic bags for weighing, using one for each collection point, to determine the gross weight per collection point, i.e., including any water, sand or residues. Afterwards, the material collected was washed with tap water in a stainless steel tank of dimensions 55 cm × 48 cm. A decantation method was used in which heavier solids such as sea sand were deposited at the bottom of the tank and rubbish was removed from the surface manually. Fine residual sand was removed by washing the macroalgae with running water delivered through a hose while laid out on 50/60 cm aluminum screens. After this process, the biomass was squeezed manually to extract as much water as possible and was then laid out in the open air to be sun-dried for three days. Assessments of biomass loss between the gross weight and net weight after removing the respective weights of water, sand and waste were made on three beaches (Jatiúca, Ponta Verde and Pajuçara) from a single collection by applying 1 m2 of polyethylene (pvc) material to the sample size on each beach. After determining the gross weight of the biomass, water was extracted through manual pressure, following the same methodology process as above and then reweighing.

2.2. Taxonomy and Laboratory Analysis

Out of the 26 macroalgae species classified through taxonomy, 13 species were randomly selected for characterization, from which the “aggregate biomass” was constituted. The specimens collected for the purpose of identification were packed in dark plastic bags that had previously been labeled and were fixed in 4% formalin. This material was then transported to the Phycology Laboratory of the Federal University of Alagoas. The taxonomic methodology used was based on descriptions in previous studies [15,16,17,18,19,20]. The scientific names identified for these species were confirmed through the Algae Database [21]. The taxonomic positions of the species and taxa synopses for nomenclatural review were as previously adopted [22].
The final drying stage was performed in the biomass laboratory of the Federal University of Pernambuco in an oven with an air circulation temperature of 65° C for 72 h. The biomass was weighed on a digital scale to determine the dry mass and moisture percentage. The samples were then ground up in a Willy mill such that the resultant grain diameter was <2 mm in order to determine the fiber content. The Ankon system methodology was applied: 0.5 g samples were placed in 6/5 cm HD polypropylene bags and were dried in a forced-circulation oven at 65 °C for 12 h [23]. The samples were then washed with neutral detergent (FDN), acid detergent (FDA) and lastly acetone to eliminate residues and enable faster drying. The reagents used in the FDA preparation were processed in a 0.255 N sulfuric acid solution, which was formed by dissolving 13.59 mL of H2SO4 PA in 2000 mL of distilled water. Then, a 0.313 N sodium hydroxide solution was formed by dissolving 12.50 g of NaOH PA in 2000 mL of distilled water.
The cellulose and ash contents were determined by calcining the samples in muffle crucibles for 2 h until reaching a temperature of 500° C. After 24 h, the crucibles were removed from the muffle and were weighed at room temperature. The cellulose content was calculated using the % FDA and % lignin contained in the samples. The total sample levels of C and N were obtained via combustion at 925 °C and determined in a CHNS-O element analyzer (Perkin Elmer PE-2400, Waltham, Ma, USA), using a thermo reference standard (1.755% C, 0.195% N and 0.039% S). The carbon samples were dried in an oven with air circulation at 65° C for 24 h and were passed through 100 mesh sieves. Approximately 3 mg of macroalgae sample was used.
Phosphorus and potassium analyses were performed at the Northeastern Regional Center for Nuclear Sciences (CRCN), using a dispersive energy X-ray fluorescence spectrophotometer (EDX 720, Shimadzu Corp., Kyoto, Japan) with a 10 mm polypropylene collimator for radiation control. The samples were placed in a container of diameter 31.6 mm and volumetric capacity of 10 mL, which was sealed with polypropylene film. The equivalent mass of each sample was 0.5–1 g. Each sample was irradiated with X-rays emitted from a tube, resulting in characteristic X-rays generated and detected in the sample (fluorescent X-rays) with reading times from 100 to 300 s. The respective reference materials were also tested (SRM 1570a, SRM 1547 and SRM 1515).

2.3. Quantification of Calorific Value of Macroalgae

The higher calorific value (HCV) of the macroalgal biomass was determined from three replicates performed on the 13 selected species and from five replicates regarding the aggregate biomass of the samples. This was determined using a IKA-Werke (Staufen, Germany) calorimeter pump (C-2000) with samples of weights 0.6–1.0 g placed in crucibles that were then placed in a stainless-steel tank with a high-pressure (30.0 bar) oxygen atmosphere. This was closed and immersed in a double-wall vessel containing 4 L of water. The water temperature was programmed as a function of combustion time between 23.00 and 28.00 °C.
Standard measurements with vessel heats between 12 and 28 °C and water pressure between 1 and 1.5 bar enabled evaluation of the energy released during the combustion process.
The lower calorific value (LCV) of each species was evaluated using the ASTM Standard Method D-240-64 (ASTM, 2013) with hydrogen percentages evaluated in a CHNS-O analyzer (Perkin Elmer PE-2400) (Equation (1)). In this equation, LCV is the lower calorific value in calories per gram, HCV is the higher calorific value in calories per gram, and H is the hydrogen percentage of the sample.
LCV = HCV − 50, 68. H

Macroalgal Pellet Processing

Pellets were produced from these same 13 macroalgal species, after washing and drying the biomass. The method used consisted of placing 6 kg of dry biomass without milling and 50 mL of corn oil binder into a pelletizing machine (AKK-125). The pellets thus produced constituted a condensed biomass. These pellets were compacted by means of an extrusion process in the pelletizer, at an approximate pressure of 3059 kgf/cm2 and temperature of 120 °C, as described previously [24]. The average calorific power of the pellets was obtained through testing five samples in compacted and crushed forms in a calorimetric pump machine.
The higher calorific value of the aggregated biomass in pellet form was evaluated in the same calorimetric pump as mentioned above with insertion into the vessel wall in two ways: integral cylindrical form and manually ground form.

3. Results and Discussion

3.1. Macroalgal Biomass Sampling Survey

According to previous studies [8,25,26], few marine biomass sampling surveys have been conducted. The macroalgae deposition area results (Figure 3) were demarcated in vertical-band transects that were observed between 1 and 21 m along the shoreline.
The average was at 9 m, defining a demarcation area of 135,000 m2. Regarding the seasonality of collections in the present study (Table 2), there was greater macroalgae deposition in the months of March and April (dry season), in both of the years surveyed (2015 and 2016), and lower deposition in September and October. These latter months form a regional transition period between the rainy winter and dry summer. The survey results showed that the average daily deposition was 5.03 t/ha (Figure 4). The potentially productive area of 135,000 m2 (13.5 ha) therefore yielded an estimated an average daily deposition of 67.90 t/ha, which gives an annual projection of 24,785 t/ha of dry weight. Previously, significant results were found in the state of Bahia, with beach-cast seaweed deposition (dry weight) of 5765 g/m2 in 2007 for Itapuã beach and 2269.7 g/m2 for Pituba beach in 2010 [10]. Another study [27] conducted on four potential beaches in northeastern and southeastern Brazil, in the states of Ceará, Pernambuco and Espírito Santo, found that the average biomass deposition ranged from 732.0 to 1041.2 g/m2, from four collections conducted in the months of February, March, May and June, in which taxonomic classification was also used with twelve species analyzed. In Brazil, “bloom” occurrence in three phyla comprising chlorophytes, rhodophytes and ochrophytes [10,28,29] has been found to increase deposition in coastal areas. The evaluation of macroalgal deposition areas at high and low tide, taking the phases of the moon to be a strong deposition agent, has shown that major deposition occurs at the full and new moons. This productivity factor of macroalgal biomass can become greater at the daily periods of greatest deposition at low tide with collection twice a day according to the tide table. In this, collection can reach amounts of approximately 10.06 t/ha daily, i.e., a projection of 49,570 t/ha/year in the respective area. This enormous production comes with the invariable condition that marine macroalgal biomass is the only form of biomass worldwide from which two collections per day can be performed. This is an exponential advantage in comparison with terrestrial biomass.
On the other hand, macroalgal productivity in the coastal environment does not present deposition in continuous biomass bands. Empty sand intervals can be observed between transects, and this factor can therefore be considered to constitute a diminution of productivity.
In Table 2, it can be seen that there was no biomass deposition at some collection points in September and October. This result confirms that in the rainy season, beaches without a geological fringe coral reefs presented less biomass deposition than beaches with great coral formation near the coast. These are characteristics of benthic macroalgae that reproduce more intensively through improved photosynthesis in summer while located on coral fringe rock barrier substrates, which then may become dislodged through the force of the tides [30,31,32].
The most important biomass for food supply and biofuel in Brazil is sugarcane. Its annual productivity is 76.9 t/ha [33], considering crop production per 18 months. However, the estimated macroalgal biomass deposition over the same period that could be obtained through just one daily collection would be 35 times greater than the amount of biomass from sugarcane production. Based on productivity of 5.03 t/day × 547.5 days (18 months), the amount of macroalgal biomass would be 2691.50 t/ha/year (Figure 4). The main factor that differentiates the productivity of the respective biomasses is that sugarcane is harvested after eighteen months, while macroalgae can be collected daily [34]. Other advantages of macroalgae as a raw material collected in coastal regions include the facts that it is obtained through a free process, i.e., without agricultural costs due to inputs or irrigation. On the other hand, there are costs relating to washing processes, sea sand decantation, the separation of rubbish residues, drying machines and teams of workers needed for gathering the material every day [4,25].
According to one-way ANOVA statistical analysis [35,36], significant differences occurred, which were mainly through the absence of biomass observed on the beaches of Guaxuma, Garça Torta and Sereia (Table 2). The Newman–Kuels test [37] indicated that there were differences in the amount of biomass among the four collections performed with the highest amount of biomass (1.948 kg/m2) at Jatiúca beach (F = 5.774, p < 0.05). Tukey’s test [38] showed that there were significant differences in the amount of biomass in samples 1 and 2 compared with samples 3 and 4 (periods without macroalgal biomass deposition) (Table 2).

3.2. Sampling of Biomass: Losses and Gains

The percentage loss in the weight of biomass collected on three beaches (Figure 5) between the net and gross weights was found to depend on some influential factors at the time of collection, such as the weight of water when the macroalgae are in the wet stage and the amounts of sea salt, garbage and sea sand aggregation on the biomass. The average general loss was 7.5 kg/m2 i.e., 64.3%, but this differed between the beaches (Figure 5). Ponta Verde and Jatiúca beaches showed similar proportional losses, while Pajuçara beach showed a high rate through water losses. This difference occurred due to the accumulation of water on some points of continental shelf formation, with different elevations at some parts of the coastal terrain, which may give rise to unequal water flows in tidal movements at the time of biomass collection, such that the biomass may become damper or drier at different points of beaches along the coastline (Figure 5).

3.3. Factors Involved in Macroalgal Deposition

Some depositional factors, such as photosynthesis, sea water tidal strength, ocean water temperature, surface aquatic nutrients, climatic variations and the extent of coral reefs, can change the biomass volume and deposition area [39]. Photosynthesis is an element of sustainability for macroalgae growth and deposition along the coastline. The photosynthetic efficiency of marine macroalgae (6–8%) is superior to that of terrestrial biomass (1.8–2.2%) [2,40,41]. This feature means that macroalgal biomass requires less energy to develop than terrestrial plants, which promotes the advantage of growing faster than any terrestrial plant species [42,43,44].
Seasonal macroalgae collections in the summer can yield better results with high biomass deposition [39,45,46,47]. The macroalgae collected on beaches such as Ponta Verde reached productivity levels of 20.3 t/ha in summer (Figure 6), with a discontinuous transect deposition area of 1.85 ha (Figure 7). The average deposition (9.1 t/ha) (Figure 6) shows that summer production is more pronounced. This can be attributed in part to the greater proximity of the sun to our planet in January (in the southern hemisphere), which is a period characterized as the “perihelion”. Better photosynthesis is favored through greater solar radiation and increased water temperature, creating better conditions for biomass reproduction [37,40,48]. There is a 3.3% difference in the Earth–sun distance between the aphelion and perihelion [49], which means that the top of the atmosphere intercepts about 6.7% more solar radiation at the perihelion than at the aphelion 50,51]. This factor increases the incident global solar radiation to an insolation rate of 6% in relation to the aphelion period in June. The Earth’s position at the summer solstice extends the length day in Maceió to 14 h 10 min, while at the winter solstice, it is 10 h 10 min. The perihelion factor may contribute to increasing the ocean water temperature [50] and enabling a greater input of energy to macroalgae in their natural environment. This favors improvement of the conditions for better photosynthesis and facilitates the absorption of organic nutrients for macroalgae reproduction, which gives rise to their best development during this period.
Macroalgal species in tropical climates have a greater euphotic margin in the oceans. This combines favorably with the greater proximity to equatorial zone, such that the insolation rates in the northeastern region of Brazil yield 8 h in summer and 6 h in winter [51]. This has consequences regarding photosynthesis variations, pigmentation, and nutrients associated with water temperature and morphological structure, leading to significant growth [48,52]. Because of the city of Maceió’s position in the tropical zone, it has intense solar radiation that enables the incidence of a large euphotic zone with low turbidity in coastal marine waters, which favors the appearance of algal species in the phylum Chlorophyta.
The sustainability of benthic species is conditioned by coral reef ecosystems (Figure 8). In these, macroalgae are attached to rocks in accordance with their genetics and natural habitat. They are influenced by cyclical seasonality, such that they may have greater or lower exposure to solar radiation at different water temperatures [19,29,52].
For Ponta Verde beach, with macroalgae deposition of 37.63 t/day and 13,737 t/year, even if an estimate of 50% average loss due to discontinuous areas is projected, the annual deposition may reach 6868 t/year. This percentage difference between continuous and discontinuous areas was assessed previously [53], in a study conducted in Odawa Bay, Japan, on the macroalgal seagrass carpet species Zostera marina Linnaeus, Zostera japonica Ascherson & Graebner and Halophila ovalis (R.Br.) Hook. Deposition varied by more than 100% across the research area. In an actual study, three random collections were carried out on Cruz das Almas and Jacarecica beaches, which do not have barrier reefs along their shorelines. A total absence of biomass deposition was observed on these beaches. This marginal coastal strip on the urban perimeter was displayed through different transects of biomass deposition. It represents relief transformations in the continental shelf region, in which marine macroalgae are found in different topographic formations. These irregular biomass accumulations interspersed along the coastal strip with sand may be associated with morphological accommodations of terrain and unequal arrangements of rocky beds in the barrier reef on these beaches. Prolonged coral formation favors benthic macroalgal development aggregated to the rocky substratum and provides ideal habitats for macroalgal growth (Figure 8).
Another factor that may have an impact on the reproduction of marine macroalgae is dynamic ocean surface air masses, which may form different streams over water and provoke erosional forces on reefs that are the natural habitat of marine macroalgae. This continuous cyclical movement may accelerate the process of transporting marine benthic macroalgal biomass from the ocean surface to the shoreline. The influences of air masses and their climatic characteristics are defined as a “tropical coastal climate” in the northeastern region of Brazil. Climatic studies [54] have characterized the wind regime in this region as one of trade winds that reach this area and blow toward the equator, deviating to the left due to Coriolis force and giving rise to southeasterly winds. In the area of the present study, winds blow predominantly from the east between September and April and from the southeast between May and August. In the summer season (from October to March), the wind speed can produce dynamic forces and displace floating marine biomass with greater intensity. In a previous study [31], values between 6.94 and 10.19 m/s for northeasterly winds were obtained; in contrast, weaker southeasterly winds from 4.22 to 6.07 m/s were recorded, following the influence of the South Atlantic anticyclone region, from the late autumn, which marks the ending of the rainy season.
The influence of marine streams on macroalgal biomass deposition remains an abiotic system. Three marine streams have been investigated at the regional scale [54]: the northern current of Brazil, coastal drift currents and tidal currents. These marine currents can move benthic macroalgae and disperse beach-cast seaweed along coastal beaches, causing greater biomass deposition. The relative dominance of each of these current systems at any given point will be determined mainly as a function of the distance from the coast and some aspects of coastal geometry. This means that further away from the shoreline, the influence of the northern current of Brazil will be increases. This current flows northwestwards, being driven by the prevailing trade winds from the southeast. Closer to the continental shelf, the influence of coastal drift and tidal currents becomes greater. The coastal drift has a preferential east-to-west direction, mainly motivated by coastline orientation, which along this stretch of the coast is east–west, such that waves that reach the coastline preferentially come from the northeast and east. Tidal currents are perpendicular to the shoreline and have an influence approximately as far as the 10 m isobath. The longshore drift is significant, with its main currents flowing west–northwest, induced by dominant forces with regular waves providing sediment transportation, comprising of the order of 100 m3/day of marine biomass deposition to the west [31,32].
Macroalgal rafts with floating navigation characteristics are extensive on the surface of the Pacific Ocean and the eastern China Sea [47,52,55]. In India, these species of “drifting seaweed” have been found to give rise to a deposition of 126.81 kg/km2 (wet weight) over an area of 6.14 km2. These have been classified as species of Sargassum C. Agardh, and their characteristics of floating of the sea surface are due to gas storage vesicles in their membrane that enable them to remain on the surface [19,22]. Sargassum species with the same gas storage vesicles were found in the present study, in which 26 taxonomic macroalgal species were classified (Table 3).

3.4. Macroalgal Thermal Capacity: HCV and LCV

Previous studies [40] on macroalgae found that they presented HCV values of 17.6 MJ/kg and 21.7 MJ/kg, respectively. These results are superior to the HCV of many terrestrial biomasses. Pyrolysis on the macroalgal species Laminaria japonica Areschoug, Fucus serratus L. and Porphyra tenera Kjellman, i.e., heating the macroalgal biomass to 500° C, showed HCV results of 33.57 MJ/kg, 32.46 MJ/kg and 29.74 MJ/kg, respectively [56]. Thus, macroalgae show biodiversity in terms of diverse chemical compositions, treatment methodologies, seasonality, natural environment, endemic species and different genetic evolution. Hence, the energy potential will vary depending on the species evaluated [4,57]. The respective upper and lower calorific power of macroalgae were in the ranges 6.3–12 MJ/kg and 5.9–10.8 MJ/kg, i.e., below those of most terrestrial biomasses, which present HCV values of 17–18 MJ/kg [2,8]. However, in the present study, macroalgal biomass compounds with an average LCV of 8.82 MJ/kg were identified (Table 4). This was similar to that of the main biomass in Brazil, sugarcane bagasse, which has a value of 8.91 MJ/kg [46,57]. Among the characteristics that have been compared between macroalgae and terrestrial biomass, the absence of lignin in the composition of macroalgae [56,58] increases its degradation and facilitates its combustion. However, the levels of carbon contrast and hydrogen molecules in terrestrial biomass are higher than those in macroalgal biomass [52,59], and these factors provide higher calorific power. On the other hand, a selected combination of species consisting of 25% Sargassum sp., 35% Cryptonemia crenulata, 10% Gracilaria sp. and 30% Sargassum vulgare may have an estimated HCV of 11.29 MJ/kg, i.e., about 11.2% higher than an aggregated compound of macroalgal biomass (10.03 MJ/kg). Thus, there is a possibility that the selective collections of species, or combinations of different biomasses of macroalgae, may give rise to better yields and greater energy potential [60,61,62]. In another study [63], the phyla Chlorophyta and Ochrophyta were found to have high calorific values of 8–13 MJ/kg and 9–11 MJ/kg respectively. Those results were equivalent to those of the present survey for species in the phyla Chlorophyta and Ochrophyta (Table 4). The species of the phylum Rhodophyta reached the highest calorific values of 11.4–12.0 MJ/kg.

3.4.1. Evaluation of Heat Capacity Produced by Pellets

Cylindrical pellets of diameter 3–5 mm and length 8–23 mm were produced with specific mass of 680 kg/m3. Corn oil was input as a binder, of volume 50 mL, equivalent to 1.88 MJ/kg, with performance of 6 kg of dry biomass, thus resulting in 1.28 kg of pellets. The high calorific value (HCV) obtained was 20.19 MJ/kg (Figure 9). The ligand participated in the PCS, representing 9.35%, plus the average biomass moisture (17.61%). The total calorific value of 26.96% was attributed to the binder and moisture. Corn oil was chosen because of the sustainability of this agricultural product, given that Brazil is the world’s third largest producer of corn, thus enabling a greater availability of raw material with low production costs. Corn oil can add nutritional value to the pellets produced without negative environmental impacts that could interfere with the production process. Studies [3,64,65] have shown that increased abrasion resistance to reduce wear on equipment for producing biofuel pellets can be achieved through the addition of natural binders such as corn, potato starch, cane molasses, vegetable oil and sulfonated lignin (waste from the pulp and paper industry). It has been reported [64,65] that additive use should be analyzed cautiously because sulfonated lignin, for example, increases the sulfur content, which causes undesirable gas emissions when pellets are burned with environmental implications. There is no consensus about these binders. These additives are not used in the United States and Italy for high-quality pellets. In Sweden, the use of these binders must be informed on product packaging. Research carried out in Sweden [64,65] showed that producers used 0.5–2.0% potato starch in wood pellets. The ash content found in pellets is similar to that found in relation to macroalgal species. because it is the same raw material aggregated in a compound.
A comparison with the higher calorific value of terrestrial biomass [60,66] condensed into energetic composites such as in briquette form (Figure 10) showed that it ranged from 9.83 to 20.51 MJ/kg with an average of around 17.61 MJ/kg. This was 11.46% lower than the higher calorific value of macroalgae aggregated into condensed pellets, as determined from five samples evaluated in the present study, which was 20.19 MJ/kg (Figure 10). The lower calorific values of the pellets and briquettes were equivalent, without significant difference when analyzed for the same biomasses, given that the compression and moisture suppression processes for these two cylindrical formats are similar. The average HCV for terrestrial pellets (19.96 MJ/kg), as evaluated in two previous studies [63,67], was 1.15% lower than that of macroalgae pellets (20.19 MJ/kg) (Table 5).
The average LCV of pellets from 17 terrestrial species was found to be 16.10 MJ/kg [68], which was 11.6% lower than the average for macroalgae pellets (18.76 MJ/kg). Both indicators (HCV and LCV) showed that it was more efficient to generate energy using macroalgal biomass than using the majority of terrestrial pellets [69]. The chemical structure and composition of the biomass underwent changes through pelletization. Likewise, the physical structure, such as the porosity and surface morphology of the biomass, are compacted in cylindrical concentrated compounds. Consequently, the thermal characteristics of biomass pellets differ from those of the feedstock that is received [62].

3.4.2. Heat Capacity of Seaweed from Nutrient/Fiber Analysis

Materials with high carbon and hydrogen content keep high calorific value, while the presence of oxygen has the opposite effect [70,71]. The results from the present study confirm this theory. The macroalgal species Ulva lactuca and Hypnea pseudomusciformis have carbon concentrations of, respectively, 50.08% and 61.87%, which are the highest percentages of all types of macroalgal biomass. The HCV of Ulva lactuca is 1.43 MJ/kg, which thus has potential for the energy industry (Table 6). The high carbon content of some macroalgal species may be due to the presence of several sulfated polysaccharides (PSs) in their composition [68]. Thus, the species H. pseudomusciformis is characterized as a carrageenan. This family of PSs undergoes several variations originating from free hydroxyl substitutions. Repetitive disaccharide units form these polymers.
Macroalgae with low lignin content have reduced calorific values in relation to terrestrial biomasses and generally lower calorific values than those of biomasses with higher lignin content and high cellulose content [72]. Lignin should be considered as having an average HCV (0.025 MJ/kg) compared with 0.015 MJ/kg for celluloses. It is known that a lignin polymer contains less oxygen than the polysaccharides present in cellulose [59], which is a factor that influences the HCV. The species Ulva lactuca has low lignin content (9.13%) (Table 7) but was found to have the second largest HCV (11.43 MJ/kg). This was comparable with previous results from the same species, with HCV of 12.89 MJ/kg [73], thus confirming the theory of low lignin x high calorific value.
The macroalgal ash content is higher than that of terrestrial biomass [2,40,59]. In a previous study [74], ash content ranging from 14 to 39.7% was found, among the 10 species that were analyzed, while a range from 3.3 to 46% was found among four species in another study [75]. Those findings differed from the results from the present study in which the range was from 1.86 to 10.56% among 12 species that were analyzed (Table 7). However, the species were not the same and may have physiologically distinct genetic development, which would influence their fiber concentrations. Variations in ash composition are influenced by seasonality [40,41], such that higher ash concentrations can be found at certain times of the year. The environmental impact of ash resulting from macroalgal combustion processes may vary depending on the specific characteristics of the ash and the context within which it is generated. The composition of macroalgal ash contains a variety of chemical elements, including oxides of silicon, aluminum, iron, calcium, potassium and magnesium [76]. To mitigate environmental impacts, it is important to consider viable alternatives for reusing ash. Some studies have explored the possibility of using ash in other applications, such as construction materials or as soil-improver fertilizers [77].
In summary, the environmental impact of macroalgal ash combustion depends on several factors, including the ash composition, treatment process and the way in which it is reused or discarded. It is important to consider strategies that minimize negative impacts and promote sustainability.
Reduced cellulose indices (11.28%) can facilitate combustion processes (Table 7). According to previous studies [72,78], the cellulose glucose polymer is present in the macroalgae of the phyla Ochrophyta, Chlorophyta and Rhodophyta in amounts of less than 10%.

4. Conclusions

The results from the present sampling study on marine macroalgal biomass deposition confirm that this biomass has 35 times more productivity than any terrestrial biomass. The sustainable raw material from this macroalgal biomass presented productivity estimated at 5.03 kg/ha, which defines the potential of the biomass for biorefining processes with energy-generating purposes. Evaluation of the lower calorific value (LCV) of the macroalgae, compared with energy from terrestrial biomasses such as sugar cane bagasse, showed that the result of 8.82 MJ/kg for macroalgae was near or almost equivalent to terrestrial biomass. However, seasonality and environmental abiotic factors that affect the growth of benthic macroalgae can become influential conditioning factors for biomass production. The comparative costs of the marine macroalgal biomass biorefining process, like the desiccator machine, washing process and labor, were found to be lower than the known costs of terrestrial biomass, such as irrigation, fertilization, extensive land areas, pest control, labor and agricultural machines. The present study proved the capacity of this biomass to generate bioenergy in pellet form, and its higher calorific value (HCV) of 20.19 MJ/kg was compatible with and superior to the average HCV of terrestrial biomasses in pellet form. Pellets produced from macroalgae may constitute an innovative element for renewable energy and biofuels that can be promoted as an environmentally sound alternative to fossil fuels. Macroalgal biorefining reduces the environmental liability of needing to deposit accumulated biomass in sanitary landfills, improving the efficiency of public policy relating to solid waste management. The regular collection of this biomass for energy-biorefining purposes promotes a condition with unique characteristics of low environmental impact while also eliminating the discomfort of accumulated biomass on coastal beaches that makes it difficult for bathers and tourists to walk along sandy beaches.

Author Contributions

Conceptualization, F.P.C. and M.G.B.; Methodology, R.S.C.M., E.V.d.S.B.S., E.A.C.G.-C., E.J.d.F., A.J.d.S., M.F.d.L., M.M.d.S.C., N.G.d.M.F., D.M.d.N., V.A.R.C. and C.A.M.d.A.; Software, E.J.d.F., A.J.d.S., M.F.d.L., M.M.d.S.C. and D.M.d.N.; Validation, R.S.C.M. and C.A.M.d.A.; Formal analysis, E.A.C.G.-C., M.F.d.L., M.M.d.S.C. and D.M.d.N.; Investigation, F.P.C., E.V.d.S.B.S., E.A.C.G.-C., B.M.S., V.A.R.C. and C.A.M.d.A.; Resources, M.G.B., N.G.d.M.F. and B.M.S.; Data curation, A.J.d.S. and D.M.d.N.; Writing—original draft, F.P.C.; Writing—review & editing, E.C.S., E.A.C.G.-C., V.A.R.C. and C.A.M.d.A.; Supervision, F.P.C., E.J.d.F., A.J.d.S. and B.M.S.; Project administration, F.P.C., R.S.C.M. and C.A.M.d.A. All authors have read and agreed to the published version of the manuscript.

Funding

No funding was received to assist in the preparation of this manuscript. No funding or grants or third-party resources were received by any authors. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Institutional Review Board Statement

The authors are responsible for the accuracy of the statements provided in the manuscript and confirm the authenticity and originality of the research. The studies carried out were conducted within the ethical principles of scientific research.

Data Availability Statement

The results of this research can be publicly consulted in: “Digital Repository Data of Pernambuco Federal University” at the link: https://repositorio.ufpe.br/handle/123456789/30792, accessed on 9 August 2024. All statistical and methodological data of research were actualized and confirmed with consent of all authors. The authors declare that they had support of Federal University of Pernambuco, Federal University of Alagoas and Northeast Regional Centre for Nuclear Sciences to carry out laboratory research and chemical analysis of the raw material.

Acknowledgments

My best regards and thanks to Federal University of Alagoas (UFAL), Federal University of Pernambuco (UFPE), Regional Centre for Nuclear Sciences of the Northeast (CRCN), my master’s and doctoral supervisors, all professors who contributed to my teaching, all my team researcher who helped me in this paper and to my family and friends who always believed in me.

Conflicts of Interest

The authors declare that there was no conflict of interest involving financial resources or copyright disputes.

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Phycology 04 00022 g001
Figure 1. Map of geographical research area—Maceió—AL. Source: Brazilian Institute of Statistical Geography (2015).
Figure 1. Map of geographical research area—Maceió—AL. Source: Brazilian Institute of Statistical Geography (2015).
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Figure 2. Sample collection points/zigzag method.
Figure 2. Sample collection points/zigzag method.
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Figure 3. Estimate macroalgae biomass deposition band area in 4 collections per beach C1–C4.
Figure 3. Estimate macroalgae biomass deposition band area in 4 collections per beach C1–C4.
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Figure 4. Statistics of macroalgae biomass deposition in research area/ha (Maceió—Al).
Figure 4. Statistics of macroalgae biomass deposition in research area/ha (Maceió—Al).
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Figure 5. Analysis of loss weight after cleaning, washing and biomass drying.
Figure 5. Analysis of loss weight after cleaning, washing and biomass drying.
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Figure 6. Average daily deposition of macroalgae biomass in summer/t/ha—Maceió.
Figure 6. Average daily deposition of macroalgae biomass in summer/t/ha—Maceió.
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Figure 7. Deposition band by beach cast seaweed in Ponta Verde beach.
Figure 7. Deposition band by beach cast seaweed in Ponta Verde beach.
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Figure 8. Deposition area macroalgae biomass in Ponta Verde beach with collection points near coral reefs. Source: Google Earth, (2022).
Figure 8. Deposition area macroalgae biomass in Ponta Verde beach with collection points near coral reefs. Source: Google Earth, (2022).
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Figure 9. Marine macroalgae pellets of aggregated biomass.
Figure 9. Marine macroalgae pellets of aggregated biomass.
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Figure 10. Energetic condensed composites from different biomass-HCV.
Figure 10. Energetic condensed composites from different biomass-HCV.
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Table 1. Tide table on the days of macroalgae collections.
Table 1. Tide table on the days of macroalgae collections.
DateHoursTide Height/mMoon Phases
12 March 201513.47 min0.6full moonPhycology 04 00022 i001
4 April 20159.47 min0.2full moonPhycology 04 00022 i002
5 April 201510.15 min0.2full moonPhycology 04 00022 i003
5 March 20167.11 min0.6waning moonPhycology 04 00022 i004
12 March 201612.09 min0.1new moonPhycology 04 00022 i005
17 September 201610.00 min0.0full moonPhycology 04 00022 i006
15 October 20168.56 min0.0waxing moonPhycology 04 00022 i007
16 October 20169.38 min0.0full moonPhycology 04 00022 i008
Table 2. Four collect of macroalgae in each beach /m2 = 28 collects.
Table 2. Four collect of macroalgae in each beach /m2 = 28 collects.
BeachesCollect 1Collect 2Collect 3Collect 4Media of 28 Collection in All Beach
DateHourBiomass kg/m2DateHourBiomass kg/m2DateHourBiomass kg/m2DateHourBiomass kg/m2Biomass kg/m2
Pajuçara12 March 201513:300.41612 March 201612:000.21017 September 201610:000.01615 October 201608:450.27560.229
Ponta Verde12 March 201514:101.87612 March 201612:302.17617 September 201610:300.32415 October 201609:300.07201.112
Jatiúca12 March 201514:501.94812 March 201613:000.14817 September 201611:000.02815 October 201610:000.03200.539
Guaxuma4 April 201509:300.70812 March 201613:300.04017 September 201611:300.000 **16 October 201609:350.00400.188
Garça Torta4 April 201510:101.36012 March 201614:001.86417 September 201612:000.01616 October 201610:150.0000 **0.810
Riacho Doce4 April 201510:500.41212 March 201614:300.25617 September 201612:150.02016 October 201611:000.41600.276
Sereia5 August 201513:301.3045 June 201609:400.16417 September 201612:300.000 **16 October 201611:300.0000 **0.367
AVERAGE 1.146 * 0.694 * 0.058 * 0.114 *0.503
ANOVASum of sqrsdfMSFpTukey’s
5.5977331.865915.7740.00404Collect 3, Collect 4 < Collect 2, Collect 1
* Significant differences by test for Tukey’s (p < 0.05), ** absence of biomass.
Table 3. Taxonomic identification of the macroalgae arriving from research area–Maceió.
Table 3. Taxonomic identification of the macroalgae arriving from research area–Maceió.
Phylum ChlorophytaPhylum RhodophytaPhylum Ochrophyta
Anadyomene stellata (Wulfen) C. AgardhBotryocladia occidentalis (Boergesen) Kylin Canistrocarpus cervicornis (Kutz) J.C. de Paula & De Clerck
Boodleopsis pusilla (Collins) W. R. Taylor, A.B. Joly & BernatorwiczCryptonemia crenulata—J. AgardhCalpomenia sinuosa (Mertens ex Roth) Derbés & Solier
Bryopsis pennata J.V.LamarouxCryptonemia seminervis (C.Agardh) J. AgardhLobophora variegata (J. V. Lamouroux) Womersley ex E. C. Oliveira
Caulerpa chemnitzia (Esper) J.V. LamarouxDigenea simplex (Wulfen) C. AgardhPadina gymnospora (Kützing) Sonder
Caulerpa microphysa (Weber Bosse) FeldmannGracilaria caudata J. AgardhSargassum cymosum C. Agardh
Caulerpa racemosa—(Forssk) J. AgardhGracilaria sp.—GrevilleSargassum vulgare—C. Agardh
Ulva lactuca LinnaeusHalymenia elongata C. AgardhSpatoglossum schroederi—(C. Agardh) Kützing
Hypnea pseudomusciformis Nauer, Cassano & M.C. Oliveira
Jania subulata—Ellis & Solander
Osmundaria obtusiloba (C.Agardh) R. Norris
Palisada perforata (Bory) K.W.Nam.
Tricleocarpa cylindrica (J. Elis & Solander) Huisman & Borowitzka
Table 4. High calorific value (HCV) and lower caloric value (LCV) of macroalgae.
Table 4. High calorific value (HCV) and lower caloric value (LCV) of macroalgae.
SpeciesPhylumHCV/MJ/KgLCV/MJ/Kg
Cryptonemia sp.Rhodophyta11.4310.04
Sargassum sp.Ochrophyta10.689.67
Ulva fasciataChlorophyta8.216.76
Cryptonemia crenulataRhodophyta12.0210.87
Lobophora variegataOchrophyta10.589.58
Gracilaria spRhodophyta11.149.91
Cryptonemia seminervisRhodophyta9.678.99
Ulva lactucaChlorophyta11.439.38
Hydropuntia corneaRhodophyta11.429.86
Padina sp.Ochrophyta8.327.31
Caulerpa microphysaChlorophyta6.375.97
Hypnea pseudomusciformisRhodophyta8.736.51
Sargassum vulgareOchrophyta11.199.79
Average Calorific Value—10.098.82
Table 5. Higher calorific value of pellets.
Table 5. Higher calorific value of pellets.
Types of PelletsH.C.V. MJ/KGReferences
Wood of Denmark20.08Bruhn et al. (2011) [48]
Wood of Belgium 20.31V.K. Verma et al. (2012) [49]
Finland peat 21.63V.K. Verma et al. (2012) [49]
Reed canary grass pellets of Finland19.25V.K. Verma et al. (2012) [49]
Poland apple juice from Industrial waste20.68V.K. Verma et al. (2012) [49]
Pectin from citrus shell—Denmark 19.24V.K. Verma et al. (2012) [49]
Sunflower husks—Ukraine 20.27V.K. Verma et al. (2012) [49]
Belgium wheat straw 18.25V.K. Verma et al. (2012) [49]
Macroalgae—Brazil20.19Coelho, F.P. (2018)
Table 6. Nutrients seaweed concentrations deposited in coastal beaches of Maceió, Alagoas, Brazil. (%) *.
Table 6. Nutrients seaweed concentrations deposited in coastal beaches of Maceió, Alagoas, Brazil. (%) *.
Species/BiomassWeight/gCHNPK
Cryptonemia sp. 3.137.946.543.740.7303.113
Sargassum sp. 3.128.994.781.300.04819.869
Ulva fasciata3.129.516.861.620.2365.691
Cryptonemia crenulata2.830.425.443.030.5828.022
Lobophora variegata3.130.624.721.190.4707.606
Gracilaria sp. 2.933.625.82.550.22534.872
Cryptonemia seminervis3.020.603.222.351.2556.197
Ulva lactuca2.950.089.644.180.3014.819
Hydropuntia cornea3.141.977.330.95ND34.014
Padina sp. 3.128.214.791.590.2849.181
Caulerpa microphysa3.016.581.880.981.1861.466
Hypnea pseudomusciformis3.061.8710.444.790.65850.068
Sargassum vulgare2.938.606.63.330.5959.412
Aggregate biomass2.943.976.734.530.598.795
* The samples weight for elements P and K were 0.5–1 g in XRF-EDX, and the results are g/kg.
Table 7. Lignin, cellulose, ashes of seaweeds and aggregate biomass (%).
Table 7. Lignin, cellulose, ashes of seaweeds and aggregate biomass (%).
Seaweed-SpeciesPhylumLignin (%)Cellulose (%)Ashes (%)
Sargassum sp.Ochrophyta9.4111.768.06
Cryptonemia crenulataRhodophyta2.449.272.46
Lobophora variegataOchrophyta5.2723.294.04
Gracilaria sp.Rhodophyta1.987.173.16
Cryptonemia seminervisRhodophyta4.118.333.86
Ulva lactucaChlorophyta9.139.574.15
Hydropuntia corneaRhodophyta0.315.131.86
Padina sp.Ochrophyta12.7210.4210.56
Caulerpa microphysaChlorophyta13.7413.929.79
Hypnea pseudomusciformisRhodophyta8.588.237.32
Sargassum vulgareOchrophyta7.1317.724.33
Aggregate biomass -7.2912.013.75
Overallaverage 6.8111.285.30
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MDPI and ACS Style

Coelho, F.P.; Menezes, R.S.C.; Sampaio, E.V.d.S.B.; Barboza, M.G.; Soares, E.C.; Guedes-Coelho, E.A.C.; França, E.J.d.; Santos, A.J.d.; Lima, M.F.d.; Costa, M.M.d.S.; et al. Biorefinery of Beach Cast Seaweed in Brazil: Renewable Energy and Sustainability. Phycology 2024, 4, 394-413. https://doi.org/10.3390/phycology4030022

AMA Style

Coelho FP, Menezes RSC, Sampaio EVdSB, Barboza MG, Soares EC, Guedes-Coelho EAC, França EJd, Santos AJd, Lima MFd, Costa MMdS, et al. Biorefinery of Beach Cast Seaweed in Brazil: Renewable Energy and Sustainability. Phycology. 2024; 4(3):394-413. https://doi.org/10.3390/phycology4030022

Chicago/Turabian Style

Coelho, Fernando Pinto, Rômulo Simões C. Menezes, Everardo Valadares de S. B. Sampaio, Márcio Gomes Barboza, Emerson Carlos Soares, Elica Amara C. Guedes-Coelho, Elvis J. de França, Agnaldo J. dos Santos, Marcelo F. de Lima, Manoel Messias da S. Costa, and et al. 2024. "Biorefinery of Beach Cast Seaweed in Brazil: Renewable Energy and Sustainability" Phycology 4, no. 3: 394-413. https://doi.org/10.3390/phycology4030022

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