Periodic Reporting for period 1 - ALGALVANISE (ALGAL biorefinery of biogas digestate to high VAlue fuNctional IngredientS through circular approachEs)
Okres sprawozdawczy: 2020-04-01 do 2022-03-31
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.
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.
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.