Performance of Lemna gibba bioreactor for nitrogen and phosphorus retention, and biomass production in Mediterranean...

Lemna gibba (Lemnaceae) had been experimented in Morocco to develop macrophyte-based wastewater treatment systems adapted to the local climatic and socio-economic circumstances. This species growing on pre-treated urban wastewater, in a lagoon (Lemna bioreactor) operating in fed-batch, generates a net productivity of 28.39 t dw.ha^-1.yr^-1, through regular harvest of the biomass produced. In wet seasons the roots of this macrophyte generally exceed 10 cm. The Lemna lagoon clearly reduces plankton production, especially during the vegetative period, when compared to the bioreactor without macrophytes (lagoon; chlorophyll-a concentration of 86.4 ± 168 μg. l^-1). The Lemna bioreactor also removes more particulate nitrogen (N) and phosphorus (P), and shows a highly significant total P and significant non-particulate P retention, in comparison with the lagoon. L. gibba can export daily the equivalent of 13.2% of N and 19.9% of P entering the bioreactor. The algal flora is dominated throughout the year by phytoplanktonic populations of Euglenophyceae and Chlorophyceae. Branchiopoda (Daphniidae), Insecta (Dytiscidae Chironomidae, Culicidae and Heteroptera), and Gastropoda are the main taxa of animalia developing in the Lemna bioreactor. In the Mediterranean climate, the L. gibba bioreactors would be more profitable in the tertiary wastewater treatment, especially P removal, provided regularly collect of the biomass produced.