The continued growth and evolving lifestyles of the human population require the urgent development of sustainable production in all its aspects. Microalgae have the potential of the sustainable production of various commodities; however, the energetic requirements of algae cultivation still largely contribute to the overall negative balance of many operation plants. Here, we evaluate energetic efficiency of biomass and lipids production by Chlorella pyrenoidosa in multi-tubular, helical-tubular, and flat-panel airlift pilot scale photobioreactors, placed in an indoor environment of greenhouse laboratory in Central Europe. Our results show that the main energy consumption was related to the maintenance of constant light intensity in the flat-panel photobioreactor and the culture circulation in the helical-tubular photobioreactor. The specific power input ranged between 0.79 W L−1 in the multi-tubular photobioreactor and 6.8 W L−1 in the flat-panel photobioreactor. The construction of multi-tubular photobioreactor allowed for the lowest energy requirements but also predetermined the highest temperature sensitivity and led to a significant reduction of Chlorella productivity in extraordinary warm summers 2018 and 2019. To meet the requirements of sustainable yearlong microalgal production in the context of global change, further development towards hybrid microalgal cultivation systems, combining the advantages of open and closed systems, can be expected.

Phosphorus is one of the non-renewable natural resources. High concentration of phosphorus in surface water leads to undesirable eutrophication of the water ecosystem. It is therefore necessary to develop new technologies not only for capturing phosphorus from wastewater but also for phosphorus recovery. The aim of the study was to propose three different integration scenarios for a microalgal biofilm system for phosphorus removal in medium and small wastewater treatment plants, including a comparison of area requirements, a crucial factor in practical application of microalgal biofilm systems. The area requirements of a microalgal biofilm system range from 2.3 to 3.2 m2 per person equivalent. The total phosphorus uptake seems to be feasible for construction and integration of microalgal biofilm systems into small wastewater treatment plants. Application of a microalgal biofilm for phosphorus recovery can be considered one of the more promising technologies related to capturing CO2 and releasing of O2 into the atmosphere.

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