ALGAL biorefinery of biogas digestate to high VAlue fuNctional IngredientS through circular approachEs

Project Information

ALGALVANISE

Grant agreement ID: 898560

DOI

10.3030/898560

Project closed

EC signature date 20 March 2020

Start date 1 April 2020

End date 31 March 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 184 590,72

EU contribution

€ 184 590,72

Coordinated by

CELIGNIS LIMITED
Ireland

Periodic Reporting for period 1 - ALGALVANISE (ALGAL biorefinery of biogas digestate to high VAlue fuNctional IngredientS through circular approachEs)

Reporting period: 2020-04-01 to 2022-03-31

Summary of the context and overall objectives of the project

ALGALVANISE was aimed at addressing the challenges associated with digestate originating from anaerobic digestion (AD) plants. A major problem with digestates comes from their high phosphorous contents which can lead to eutrophication issues in areas with a large number of anaerobic digesters. Hence, often digestate has to be treated for disposal causing further environmental and economic challenges for AD plant operators. ALGALVANISE considers this phosphorus as a source of nutrients, using microalgae as a tool for phosphate recovery, while addressing the challenges associated with high upstream and downstream costs of microalgae cultivation.

The effluent stream of high-rate anaerobic digestion systems that treat dairy process water (DPW) waste and the digestate from an anaerobic digestion facility that treats municipal solid waste (MSW digestate) were used to study the potential of biogas-microalgae integrated biorefineries. In order to understand the feasibility of this biorefinery, the work is divided into the following specific objectives:

1) Identification and selection of algal strains capable of yielding high biomass with efficient nutrient recovery.
2) Optimised process conditions for luxurious uptake of nutrients by selected algal strain in untreated digestate with the use of minimum quantities of enzymes.
3) Determination of minimum chitosan dosage to enhance bacterial flocculation in terms of yield and quality of the biomass without using any alkali agents.
4) Profile of algal chemical composition and the properties of the products (lipids, proteins, carbohydrates, pigments) produced and harvested under different process conditions.
5) Predictive models developed from large sets of lab-scale experimental and pilot-scale operational data that are used to relate process conditions and variations in digestate composition with yields and quality of the algae.

The two years project has resulted in some significant outcomes that might make the biogas-microalgae biorefinery a possibility in the near future. Enzymes are efficient in treating the digestate to increase the transparency of the digestate for efficient light penetration for microalgae cultivation. The mixed algal culture of Scendesmus and Hematococcus species grow efficiently in both MSW (enzyme-treated) and DPW digestates and produce valuable compounds such as astaxanthin in high concentrations. The cultivation is mixotrophic with no additional supplementation of nutrients which significantly bring down the production costs. The mixed culture can be flocculated using natural flocculating agents which makes the downstream processing quite efficient compared to conventional membranes and centrifuges.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The effluent stream of high-rate anaerobic digestion systems that treats dairy process water (DPW) waste and the digestate from an anaerobic digestion facility that treats municipal solid waste (MSW digestate) were used to grow the microalgae strains isolated from various sources. The selection of mixed culture systems was done after adaptation of the strains to the digestate and effluent streams.

MSW digestate is treated with enzymes to reduce the colour of the digestate and to allow light penetration for microalgal growth. The effluent stream from DPW high-rate digester did not need any pretreatment, while the digestate from MSW required pretreatment to reduce the colour of the stream. The enzyme treatment was optimised to increase the microalgae growth by >200%.

The natural flocculant chitosan was used for microalgae flocculation together with microbial granules to achieve microalgae flocculation and the same was optimised to achieve harvesting efficiency >95%.

The process conditions that favour microalgae growth together with phosphate accumulation and astaxanthin accumulation were developed and a phosphate removal of 83.2% was achieved. The red stage culture has accumulated astaxanthin up to 4% of dry biomass, while protein and fat accumulation was 25 and 36% respectively in enzyme-treated MSW digestate stream.

The predictive models for digestate and microalgae composition are created by using near infrared spectra. The models are generated for phosphate and nitrogen concentrations in the digestate and for the protein and astaxanthin contents of microalgae. The models fit all the analytes, except for phosphate.

Based on the preliminary techno-economic analysis conducted in the project, without any nutrients supplementation, by growing the algae in MSW digestate stream will result in microalgae production with minimum biomass selling price (MBSP) of €1108/ Dry Tonne at IRR of 10%, assuming a cultivation area of 50 acres. This is without considering the new harvesting technology developed as part of the project. If the cultivation area is increased to 100 acres, the MBSP will come down to approx. (MBSP) of €717/ Dry Tonne. Considering the presence of valuable compounds such as astaxanthin in the product, carefully handled product can be of very high value and can be additional economic benefit for the biogas plant operators.

Microalgae are excellent phytoremediators and will add great value when it is integrated with industries producing liquid waste streams rich in nutrients.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Currently, digestate streams are considered as waste and the nutrient recovery is mostly by chemical means to be used as fertilisers. Without a doubt, the chemical technologies are playing a significant role in expanding the product spectrum of biogas plants and may win the battle to treat the digestate to meet the environment regulations. However, chemical technologies are not an option for all types of streams and if the sludge produced cannot be used as a fertliliser or for other applications, the biogas plant will have to face sludge disposal costs. ALGALVANISE has demonstrated that it is possible to grow microalgae in complex waste streams such as MSW digestate and can obtain a product of high value. This will have both high environment and economic impact on the biogas plants. Biogas plants are mostly rurally operated on a variety of waste streams and this integrated biorefinery will allow creation of new jobs. This process will also allow circularity, where the liquid waste streams originating from the farms can be pumped to central microalgae cultivation facility that will in return produce feed to the local poultry or fishery. The efficient harvesting system developed in this project by using a bioflocculant will allow the operations to run without the need of highly qualified engineers. These farms will also add additional knowledge and skillset to the local community, as happened with the biogas industry.

Through the dissemination and communication activities of the project, the benefits of microalgal systems integrated with biogas plants, food and beverage producers are presented and advocated. This has brought interest and new project collaborations for Celignis. At Celignis, we hope the network of microalgae technology developers and industries producing liquid waste streams will lead to a new wave of circular technologies that will make the industries highly sustainable and environment friendly.

Microalgae strain producing astaxanthin in MSW Digestate