Simultaneous methane production and atmospheric carbon fixation during nutrient recycling from yellow wastewater in a continuously fed PBR-UASB system

The use of wastewater as raw material for feeding biorefinery systems is gaining importance as the advances in the technical viability of producing biofuels enhances the overall economic viability. The present study evaluates the performance of one of such biorefinery systems, consisting on a photobioreactor treating a semi-synthetic wastewater (tap water human urine) while producing microalgal biomass, which is then processed in a UASB reactor for producing biogas and nutrient-rich digestate. It is to be noted that microalgae methanization has been reported in several studies but the experimental setup is usually based on a microalgae batch culture, microalgae biomass harvest, and batch anaerobic digestion of the microalgae. This research attempts to go a step further in the scalability of the process by connecting a continuously fed photobioreactor to a UASB reactor, and skipping the intermediate microalgal biomass harvesting step. The proposed biorefinery system was able to use the nutrients from urine to grow microalgae while fixing atmospheric carbon up to an equivalent chemical oxygen demand of 1118 mgCOD L-1. Later on, this microalgal biomass was converted to biogas with an efficiency of 60%. These results show the technical viability of a continuously fed system for obtaining biogas from atmospheric carbon while treating wastewater and recovering nutrients. It is a first step on the scalability of the process and the system can still be improved with respect to microalgae pretreatments to increase the biogas production efficiency. [Display omitted] •The utilization of algae biomass is employed for the production of methane as an energy source.•The cultivation of algae in contaminated waters constitutes an effective method of bioremediation.•Anaerobic processes implemented through activated sludge reactors prove to be advantageous in the acquisitin of methane.•Flow cytometry is effective for quantifying or determining the viability of Chlorella vulgaris after a treatmente.