Hydrocarbon and lipid extraction from Scenedesmus sp. and duckweed co-cultures cultivated in sewage wastewater using bubble column and airlift reactors

Abstract

Fossil fuel depletion and the remediation of industrial wastewater can be solved simultaneously through cultivating microalgal biomass to produce biofuels. This study's objective focuses on the monoculture and coculture of Scenedesmus sp. and Lemna sp. (Duckweed) for hydrocarbon and lipid recovery by employing a pilot plant study in a real industrial wastewater setting. This study aimed to quantify the extracted lipids and valuable hydrocarbons. When compared to Scenedesmus monoculture, the results showed that co-cultivation with duckweed significantly increased biomass productivity by 90 %, possibly due to an improved oxygen balance and synergistic nutrient uptake. Cultivation was performed in a 3-column bubble photobioreactor with controlled pH, light, growth medium, nitrogen and CO2 aeration regulation. Harvested biomass underwent a combination of solid-liquid extraction techniques for the extraction of lipids and hydrocarbons. SEM revealed the surface morphology and efficient extraction of the algal biomass. The biomass TGA and DSC thermograms indicated that it was thermally stable up to 250 °C, with different decomposition patterns associated with different lipid fractions. FTIR spectra identified clustered functional groups around 1,000 – 1,300 cm-1 and ~1,460 cm-1 linked to long-chain hydrocarbons, esters, alkanes, and aromatic hydrocarbons. Alkanes, alkenes, and long-chain fatty acid methyl esters were identified by GC-MS as the dominant fractions in the extracts from the co-cultures (57.68 % FFA’s, 10.84 % MAG’s, 21.48 % DAG’s and 7.85 % TAG’s), showing a richer hydrocarbon profile and a higher yield of total hydrocarbons and lipid derivatives (27.6 % dry weight).