CSS3: Current and Future Challenges
January 27, 2023

Authors: Alberto Reis, Luísa Gouveia & Rafał Łukasik

The partners and other stakeholders involved in FRONTHSH1P CSS3 will be challenged with several potential threats to the well-timed progress of the project. The challenges brought by CSS3 can be summarised in two categories. First, those related to technical and scientific barriers (bottlenecks) and lastly those inherent to organisational activities in the framework of the implementation plan.

Concerning strictly the technical/scientific issues, several potential barriers are expected from the biochemical nature of the feedstocks. Flue gases and wastewater hold a wide range of toxic compounds that may trigger different levels of microalgal growth inhibition or under extreme conditions, culture death. This detrimental effect is strain-specific and should be evaluated timely before launching pilot-scale trails. Other potential threats may arise from the well-known fluctuating composition of wastewater reflecting different societal and industrial dynamics. These fluctuations can be hourly, weekly and/or seasonal, making the efficient conversion of wastewater to microalgal biomass more difficult to achieve and optimise to meet the requirements of the project. The adoption of an equalisation tank for storing larger volumes of wastewater can solve or alleviate the problem of chemical composition heterogeneity. Other key problems that may arise are listed as follows: mass microalgae cultures may deal with the occurrence of different levels of competition from other algae, infestation, contamination, and predation (grazing) that may put at risk the performance of the whole system. However, the closed photobioreactor supplied by STAM for piloting trials is expected to minimise this risk.

The EU Algae Initiative identified several problems concerning the current EU algae sector and its potential for sustainable growth: high production costs, low-scale production, limited knowledge of the markets and consumers’ needs, limited knowledge of the risks and environmental impacts of algae cultivation, and fragmented governance framework. The major economic factor for microalgal production, which is costly has been the feedstock cost, which accounts for 60-80% of the total costs. Substantial cost reductions may be expected if CO2, nutrients, and water can be obtained at a low cost. Although phytoremediation of wastewater and CO2 sequestration using microalgae are well reported to decrease biomass production cost significantly, the final product faces legal constraints concerning its application in human nutrition, and pharmaceutic markets, among others.

Harvesting and drying the microalgal biomass following cultivation is energetically and economically costly, due to the need to process large volumes of water, the small size of microalgal cells and their similar density to that of water, as is downstream processing, which can represent 20-40% of the total product costs. The economic and energetic viability of microalgal biofuels and other biobased products is limited by all associated costs and nutrient sources. Rather than harvesting and drying the biomass and extracting a part of the whole biomass, it is better to process the whole wet biomass to produce biofuel directly (biomethane) through anaerobic digestion or as biostimulant with concomitant energy and process time trimmings. However, the whole wet biomass could become highly perishable if not conditioned properly, increasing logistic complexity.

Concerning the anaerobic digestion of freshwater microalgae two factors explain the so-far reported low methane yields and productivity. First, the tick microalgal cell wall acts as a barrier for the hydrolysis stage, being the limiting step. Cell disruption methods which can overcome this are extremely energy demanding thus compromising the overall energy balance Second, the high protein content of the algal biomass leads to a high ammonium release, which could induce inhibition of some of the anaerobic bacterial populations. In addition, anaerobic digestion envisages some problems, such as time consumption, the need for microorganisms’ acclimation, is specie-dependent based on cell rupture efficiency, the need for a high C/N ratio (optimal around 20-30), inhibition due to ammonia and volatile acids accumulation, high dependence of the quality of biomass (i.e. organic loadings). Biomethane production is also directly affected by the temperature, pH and retention time of the digester, and therefore requires a significant land area and infrastructure investment.

The description of the challenges specific to CSS3 goes beyond the technical aspects. Organisational challenges arise from engagement barriers between project partners and local stakeholders with different goals and expectations. While the containerised solution delivered by STAM is expected to minimise plant transport problems, the management of logistics can be a burden in the scheduled transport of the equipment among countries, due to frequent disturbances in international delivery due to the current crisis and Ukrainian war, and some delays in CSS3 timeline can appear, which should be included in FRONTSH1P CSS3 risk assessment and mitigation plan. Finally, a strong effort should be carried out to put together different integration approaches for setting up plants in the expected European replication locations as well as the required commissioning dealing with different specificities.