Pre treatment of Duckweed Biomass, Obtained from Wastewater Treatment Ponds, for Biogas Production

Considering the capacity of duckweed to treat wastewater and to produce valuable biomass, the present study aimed to highlight the potential of duckweed biomass harvested from wastewater treatment plant for biogas (methane) production. In this way a pilot system, comprising an anaerobic pretreatment and two duckweed ponds designed in series (10 m2 each), was operated with real domestic sewage. The treatment efficiency was evaluated through the monitoring of conventional physical–chemical water quality variables sach as Temperature, pH, total phosphorus (TP), phosphate (PO4), total nitrogen (TN), ammoniacal nitrogen (NH4+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{NH}_{4}^{+}$$\end{document}–N) and chemical oxygen demand (COD). Simultaneously the excess of biomass produced during the treatment was submitted to Biochemical Methane Potential test (BMP) carried out in a multi-batch reactor system. Three pretreatment approaches (fermentative, drying and alkaline) were performed in triplicate to evaluate their influence on methane production. Findings showed that the duckweed ponds removed the organic matter and nutrients from the wastewater (TN = 94%, TP = 92% and COD = 91%). Moreover, the biomass submitted to a fermentative pretreatment returned higher gas production (0.39 Nm³biogas/kgVSfed) compared with the anaerobic digestion (AD) of unpretreated biomass (0.25 Nm³biogas/kgVSfed). These results highlight the potential of duckweed ponds technologies to treat wastewater and produce clean energy simultaneously.