Sustainable microalgal production by recycling phosphorus and nitrogen from wastewaters : toward a next generation of sewage treatment plant – Phycover

Building on the existing heritage of natural lagoon-type rural sanitation facilities, processes can be modified to increase the algal population and improve gas exchange to accelerate carbon and nitrogen removal. Thus, with few modifications and simple operation, performance close to that of an activated sludge process may be possible. Coagulation combined with settling and a constructed wetland completes the treatment by removing phosphorus and particulate matter. This process makes it possible to intensify treatment and thus improve waste treatment capacity. The modelling of interactions between organisms that develop in high rate ponds makes it possible to propose scenarios for optimizing and managing the overall process.
Depending on the sludge treatment process, digestates can have nutritional qualities adapted to optimize the growth of high value-added microalgae. Thus, they can serve as new macro and micronutrient resources and lose their waste status to become a resource.

During the operation of high rate algal ponds, microalgae naturally provide the essential oxygen to the bacteria present, drastically reducing the usual energy consumption of wastewater treatment plants. However, the development of such a technology is hampered by the variability in sanitation efficiency due to climatic conditions, the very nature of the water to be treated and the presence of predators.
Digestates have proven to be a source of macronutrients and micronutrients (metals) relevant for the development of added value microalgae. Thus, digestates are not only an alternative way for recovering fertilisers, they are also opportunities to increase microalgae productivity and promote the economic profitability of the sector.

The limits of microalgae wastewater treatment are related to the uncontrolled presence of predators, the fragile balance between bacteria and microalgae and the low winter temperatures that require the development of new technological solutions.
On the other hand, digestate is a product that could quickly be made available to the microalgae industry. It however would require standardizing digestates, which can be costly and time-consuming. Perspectives in process innovation and less restrictive regulatory frameworks make it possible to demonstrate in the near future, the safety of such an approach and its economic and societal interest.

To date, the results obtained during the PHYCOVER project have been the subject of 28 articles published or submitted in international peer-reviewed journals, 13 papers in international conferences, 5 papers in national conferences, 2 doctoral theses and 8 Masters theses. No patents have been filed during the project.

The overall objective of the PHYCOVER project is to draw the scientific, technical and industrial contexts for an evolution of wastewater treatment plants, and urban wastewaters in particular. The project aims to identify an integrated and modular treatment process for the production of biogas while identifying opportunities to maximize the valorisation of residual material, the digestate. The method combines three modules. First, a high-rate algal pond is dedicated to the treatment of municipal wastewater. Then, an anaerobic digester capable of co- digesting biomass products (and others organic matter resources ) to significantly reduce biological and chemical contaminants while producing a sustainable energy as biogas is analysed. A final module aims to enhance the digestate valorisation to agricultural sectors (organic and mineral fertilizers) and cultures of high-value microalgae to aquaculture and green chemistry. Most recent studies indeed highlight the need to combine production of microalgae to liquid and gaseous effluents treatment, to decrease the cost and to limit the exogenous inputs of nitrogen, phosphorus and carbon. However, there is currently no technology optimized solution for combining water purification and production of microalgae, while complying with discharge standards. To further enlarge the potential of industrial applicability of this approach, it is important to control the fate of pathogens organisms in effluents and the project PHYCOVER will tackle these aspects. Finally, biotic and abiotic potential emissions to the atmosphere associated with the deployment of mass cultivation systems must be evaluated to enrich Life Cycle Analysis approaches. To assess the resource recovery from waste and wastewater using this innovative approach, the PHYCOVER project will work on a number of scientific and technological obstacles. First, the selection of algal communities demonstrating a strong effluent treatment capacity and resilience of productivity considering the environmental fluctuations will be performed in Task 1 and studied at pilot scale, representative of the industrial potential of sewage treatment and biogas production. The specific study of biotic and abiotic emissions to the atmosphere as well as the assessment of hygienisation of the integrated process will be the subject of the work done in Task 2. The management of organic matter through anaerobic digestion will addressed in Task 3. Management methods and opportunities for the valorisation of the digestate as agricultural fertilizer and microalgae nutriment for green chemistry will be studied in Task 4. The assessment and prediction of the overall performances in terms of environmental and energy outputs will be assessed in Task 5, together with the optimal process design. Finally, a techno-economical and environmental assessment of the sector as a whole will be given in Task 6. Overall, the project will lead to scientific, technical and economic achievements that will contribute to the establishment of a new and innovative chain for the treatment and valorization of urban waste and wastewater.