Microalgae biomass production using wastewater: treatment and costs: scale-up considerations

Abstract

This work is part of a LIFE project to treat urban wastewater from Águas da Figueira (AdF, Figueira da Foz, PT) using a vertical tubular photobioreactor (PBR) prototype (150 L), to be scaled up and integrated in a waste water treatment plant (WWTP). The PBR was inoculated with three different microalgae: Chlorella vulgaris (Cv), Scenedesmus obliquus (Sc) and Consortium C (ConsC), isolated from the effluent. The study intends to find the best microalga in terms of wastewater remediation, biomass productivity and quality, for further uses, such as biofuel, biofertilizer and bioplastic production.

The experiments achieved volumetric productivities of 0.1 g/L·d (Cv), 0.4 g/L·d (Sc) and 0.9 g/L·d (ConsC). The maximum removals attained by Cv, Sc and ConsC were: 84, 95 and 98% for total nitrogen; 95, 92 and 100% for phosphorus; and 36, 63 and 64% for COD, respectively. The treated water had values that are in accordance with environmental legislation (Directive 98/15/CE).

Electrocoagulation was tested and resulted in an energy saving of 89%, compared with centrifugation alone. For drying the biomass, a solar dryer was used. Costs of overall processes versus conventional technologies are discussed and compared with other facilities and target values.