Utilization of centrate from wastewater treatment for the outdoor production of Nannochloropsis gaditana biomass at pilot-scale

Abstract

In this work, the outdoor pilot-scale production of marine microalga Nannochloropsis gaditana using centrate from the anaerobic digestion of municipal wastewater was evaluated. For this, outdoor semi-continuous cultures were performed in both tubular and raceway reactors mixing seawater with different centrate percentages (15%, 20% and 30%) as culture medium. It was demonstrated that N. gaditana can be produced using centrate as the only nutrient source but at percentages below 30%. At this level inhibition was caused by an excess of ammonium in both photobioreactors, as confirmed by chlorophyll fluorescence and average irradiance data, thus reducing productivity. At 15% and 20% centrate percentages, biomass productivity was equal to that measured when using Algal culture medium, of 0.48 and 0.10 g L −1 day −1 for tubular and raceway reactors respectively. During the experiments nitrogen depuration decreased from 85% to 63% in tubular reactors with the increase of centrate percentage in the culture medium and the decrease in biomass productivity, while in raceway reactors an opposite behavior was observed due to ammonia stripping from the cultures. Phosphorus depuration from the culture medium was 85% whatever the system used and the centrate percentage in the culture medium indicating a phosphorus limitation into the cultures. By supplying additional phosphorus, to achieve an N:P ratio of 5, it was possible to enhance productivity and increase nitrogen depuration in both systems. The use of centrate is confirmed as a useful method for reducing microalgae production costs and for increasing process sustainability. Consequently, it is demonstrated that for the production of microalgae biomass, centrate from wastewater treatment plants can be used as the exclusive nutrient source, achieving high productivities and nutrient removal rates if using suitable strains and if the system is operated adequately.

Microalgae Cultivation on Anaerobic Digestate of Municipal Wastewater, Sewage Sludge and Agro-Waste

“…This result is in agreement with a previous report claiming strains related to these two species were the most efficient in growing in wastewater-derived substrates [39]. Only in the case of N. gaditana did it appear that any digestates could sustain algal growth, while previous works reported the possibility of using anaerobically digested municipal wastewater for N. gaditana [40] or Nannochloropsis salina [41,42] cultivation. The low salinity of the different digestates, especially upon dilution, is likely the main reason for the absence of growth of N. gaditana , since in a previous report it was found that the anaerobic digestates investigated were diluted with artificial salt water.…”

Phycoremediation of municipal wastewater by microalgae to produce biofuel

“…18 Seawater microalgae species have also been used to treat WW despite their salinity requirements. 19 Growth of microalgae in WW has been studied under various physiochemical conditions such as light, temperature, pH, CO 2 concentration, and nutrients, but the use of WW for the production of algal-based biofuel has not been explored extensively yet. 20,21 Thus, the scope of this study was to identify an algal strain that efficiently remediates municipal WW and can be used for biofuel production.…”

Lab‐scale testing of operation parameters for algae based treatment of piggery wastewater

“…As shown in Table , the amount of stripped N was lower with CO 2 supply and this is related to the better microalgae growth. The quantification of stripped N is an important aspect of microalgae‐based treatment to understand the N removal mechanism, as already demonstrated by Ledda et al …”