Feasibility of nitrogen and phosphorus removal from treated wastewater using microalgae and potential microalgae use as biofertilizer

Abstract

ABSTRACT: Wastewater treatment plants reduce the impact of eutrophication; however, alternatives or complements are needed because their efficiency is limited to 50 % by outdated guidelines and lack of technologies. This research determines the economic feasibility of microalgae treatments to bioremediate and valorize nitrogen (N) and phosphorus (P) from various wastewater sources in Antioquia, Colombia as a microalgae biofertilizer. Chlorella Sorokiniana (Chl), Spirulina Platensis (Spi) and Scenedesmus sp. (Scn) were cultured in 250 mL Erlenmeyer flasks with blends of inoculum, synthetic and real wastewater, 12:12 white light photoperiod (110 μM m−2 s−1), 120 rpm and different concentrations of N:P. Synthetic wastewater and inoculum blends indicate that ammonia was consumed (up to 98.9 %) and oxidized to nitrite, which accumulates (up to 7.58 mg N/L), forming toxic aquatic environments, fluctuating pH and inhibiting nitrate uptake by microalgae (<14 % removal) and growth. The blends show high N and P consumption in most cases (73–99 % for both), nitrite removal (>98 %), high nitrate consumption and higher biomass yields of 882, 1197 and 1040 mg/L for Chl, Scn and Spi respectively. Blends in 20 L photobioreactors with 2:8 inoculum-wastewater ratios determine that the main operating expenses are energy for the 4 L/min air pump 50 %, 20 % for collection and 15 % for labor. The fastest growing microalgae was Scenedesmus, with annual profits of $4 M USD and OPEX 1.0 USD/Kg when processing 5184m3 of effluent from a municipal wastewater plant, with a sales price of $22 USD/Kg microalgae. A limitation in its large-scale application is the space needed for greater effluent collection.