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The main objective is to promote the sustainability of the maritime aquaculture sector through the implementation of an innovative process for the recovery of algae through its transformation into biofuels that make it possible to obtain renewable energy.
To achieve this, VALORALGAE will introduce new technical-scientific and organizational knowledge in the sector to promote the sustainable use of available resources and thus reduce its environmental footprint.
The selected recovery options are: transformation into a gaseous renewable fuel (biogas) through anaerobic digestion, and the use of algae as solid fuel (pellets) in a boiler. Both fuels will be used to generate renewable energy with neutral emissions.
In addition, the feasibility of taking advantage of this renewable gas and/or pellets as a source of energy for fish markets, ports or guilds will be studied, thus complying with the philosophy of circular economy in the marine aquaculture sector.

Specific objectives of the project:

-To detail the current problems of arribazón algae and to expand the end uses of the cleaning equipment developed in the GESTALGAR project.
-Develop and validate specific processes for the energy recovery of algae by transforming it into gaseous biofuel.
-Evaluate the process of co-digestion of algae with other organic by-products of the sector, such as fish discards, to increase resource efficiency and generation of gaseous biofuel.
-Develop and validate specific processes for the energy recovery of algae by transforming it into solid biofuel.
-Evaluate different mixtures of algae with biomass materials, to increase resource efficiency and the generation of solid biofuel.
-To evaluate the economic viability of the implementation of the new processes and equipment in fish markets, ports and guilds.
-Promote and disseminate the sustainable use of seaweed among entities in the marine aquaculture sector.

A1 “Boundary Conditions”

A2 “Obtaining gaseous biofuel (biogas)

A3 “Obtaining solid biofuel (pellets)

A4 “Technical-economic feasibility

A5 “Dissemination and dissemination actions

The results achieved have been as follows:

1. Location selection and collection of the algae

Within Activity 1, entitled Boundary Conditions, the potential of algae present in the Autonomous Communities under study, i.e. Galicia and Asturias, has been determined in order to reflect the magnitude of the available resource suitable for energy recovery. Likewise, within this same activity and based on the data collected, the algae sampling sites were selected for their subsequent characterization and energy recovery.

According to data obtained through different contacts with the brotherhoods of Galicia and Asturias, it was estimated that the amount of algae present on the Galician coasts ranges between 5,000-7,000 t/year. On the Asturian coasts, the amount of this resource ranges between 3,500-6,500 t/year, with the time for its harvest being from May to September.

In Galicia the presence of the arribazones affects the economy to a large extent due to the large number of shellfish guilds on foot that can be found, something that does not happen in Asturias. For this reason, two beaches located on the west coast of Galicia were selected for the sampling: the beach of the shellfish bank of A Barra (Redondela) and the beach of the shellfish bank Castelete-O Rego (Vilanova de Arousa).

The main species collected were: Ulva Lactuca, Gracilaria spp., and Ulva Intestinalis.

The quantities collected in each of the selected sites (between 0.5-2.5 kg/m2) allow us to glimpse the potential of the existing resource per year that is currently not used and that could be used to obtain sustainable energy.

2. Physicochemical characterization and determination of the methanogenic potential of the collected algae

The objective of Activity 2 of the project is to obtain a gaseous bifuel (biogas). So far, the physicochemical composition of the species of algae collected from the selected washed and unwashed beaches has been analysed and their methanogenic potential has been established.

It has been seen that the physicochemical characteristics of the studied algae vary between the different species studied and that, when washed, the inorganic content decreases and the volatile solids content increases. For example, with Ulva Intestinalis you go from 5.2% volatile solids to 12%.

As for the methanogenic potential, it has also been seen that it is different for each species. The values range from 16-30Nm3CH4/tonne, a range in the range of other studies that have been carried out with algae.

In addition, an attempt has been made to improve this potential by co-digesting Ulva Lactuca (the most abundant species on the Galician coasts) with fish and organ discards.

In this way, the methanogenic potential of the samples is increased to values close to 44 Nm3 CH4/tonne.

From the results obtained after the physicochemical characterization and the determination of the methanogenic potential tests, it is concluded that the algae studied have value as a source of methane production.

However, in order to use them in an anaerobic digestion process, it will be necessary to eliminate the inorganic compounds present, mainly sands, as they could cause operational problems.

3. Energy potential of selected algae in thermochemical recovery processes

The objective of Activity 3 of the project is to obtain a solid bi-fuel in the form of pellets. To this end, the washed collected algae have been physicochemically characterised in order to glimpse its potential as a fuel in combustion processes with its moisture content, volatiles, ashes and calorific value.

The data obtained have made it possible to verify the high moisture and ash content of the species studied, something that makes a drying process necessary, which is why two experiences of drying by natural aeation and forced drying have been carried out with the algae under study. Likewise, the calorific values obtained are between 8.77-15.44 MJ/kg, being moderate if compared to a reference fuel (19.91 MJ/kg for pine, highly used in combustion processes).

After drying, pelletization was carried out on the species mostly observed on the Galician coasts (Ulva Lactuca). To do this, an annular pellet machine was used after conditioning the particle size of the samples (blade mill).

The physicochemical characteristics of the pellet obtained improve in terms of the moisture content of the initial algae but the ash content is still very high, so they do not comply with the minimum quality established in current regulations (UNE EN ISO 17225:2014). That is why it has been tested to densify this algae with other biomass cosubstrates available within the studied territory: kiwi pruning remains and xesta.

From the results obtained after carrying out the immediate, elemental analysis and the determination of the calorific value of the pellets obtained as a result of mixing algae (Ulva Lactuca) with kiwi and xesta in different proportions, it is determined that, the higher the percentage of co-substrate in the mixture, the better the properties of the pellets obtained both in terms of ash content and calorific value and a lower presence of elements that can be the precursors of the formation of pollutants in combustion processes. However, the pellets obtained still do not meet the minimum quality specifications required according to current regulations, which indicates that they could only be used in combustion facilities that have been specially designed and adjusted for this type of pellets.

4. Technical-economic feasibility

Energy consumption and waste generation in entities in the aquaculture sector have been evaluated through visits and surveys via telephone and email. The results obtained allow us to determine that the renewable energy potential generated by the combustion and anaerobic digestion of the algae studied would allow to cover a large part of the electricity demand of the entities studied.