Microalgal nutrients recycling from the primary effluent of municipal wastewater and use of the produced biomass as bio-fertilizer

Abstract

Availability of N, P and other trace metals in municipal wastewater (MWW) makes it very attractive to produce microalgae biomass using MWW. Although limited organic carbon is available in MWW, supplementing flue gas as CO2 sources may enhance both the biomass production and recycling of nutrients. Five microalgae strains were grown in the primary effluent of MWW, in a small-scale indoor experiment, to compare their nitrogen and phosphorus recovery abilities. From this study, two potential strains (Chlorella sp., and Scenedesmus sp.) were selected for the large-scale (i.e., 200 L) outdoor experiment. Each of these strains was grown in four different conditions: (1) MWW without any CO2 source, (2) MWW with pure CO2, (3) MWW with simulated flue gas (SFG), and (4) modified BG-11 medium with pure CO2. For both strains, injection of either CO2 or SFG in the MWW cultures resulted in faster growth rates, and higher biomass productivities compared to cultures that did not receive CO2 or SFG. Furthermore, recovery of TN from the MWW was ≥ 95% for the microalgae cultures that received either CO2 or SFG; however, in all cases, phosphorus recovery was less than 15% of the initial concentration. Both the MWW grown microalgae biomass (MWGMB) were used as bio-fertilizer to grow the wheat plant. Both the Number of leaves and the average size of the leaves of the plants were higher for both the MWGMB compared to conventional NPK fertilizer.