Growth of Chlorella vulgaris and Nannochloris oculata in effluents of Tilapia farming for the production of fatty acids with potential in biofuels

The use of microalgae in wastewater treatment and its biotechnological exploitation for the production of biofuels is a potential environmental application. Some species of microalgae are notable due to their lipid composition and fatty acid profile suitable for biofuel production. During the present study, a factorial 23 experimental design was conducted, which assessed three factors: i) two species of microalgae (Chlorella vulgaris and Nannochloris oculata), ii) two types of culture media [wastewater of tilapia farming (WTF) and bold’s basal medium (BB)], and iii) two types of lighting (multi-LED lamps and white light). Microalgae were inoculated in photobioreactors in 6 L of medium (WTF or BBM) at an initial concentration of 1.0 × 106 cells ml-1 at 20 ± 2°C. The highest average cell density as well as the highest productivity of biomass observed in the treatments was C. vulgaris treatment in BBM and multi-LED lighting (8.83 × 107 cells ml-1 and 0.0854 g l-1 d-1, respectively). Although the majority of lipid productivity was obtained in the exponential phase of N. oculata cultivated in multi-LEDs in both treatments (BBM with 58% and WTF with 52%), cultivation of both species was generally maintained in WTF and were those that presented the major lipid productivity (2-18 mg l-1 d-1) in comparison with those cultivated in BBM. Palmitic, stearic, oleic, linoleic, linolenic and eicosanoic (C16–C20) fatty acids were present in both species of microalgae in concentrations between 26 and 74%. Based on the results of the present study, we conclude that cultivation of N. oculata and/or C. vulgaris in WTF illuminated with multi-LEDs is an economic and sustainable alternative for biodiesel production because it can represent up to 58% of lipids with a fatty acid profile optimal up to 74% of the total fatty acids.Key words: Chlorella vulgaris, Nannochloris oculata, production of fatty acids, wastewater of tilapia farming, production of biofuels

Comparison of two anaerobic coupled systems for biomethanization of the organic fraction of municipal solid wastes

Two lab-scale mesophilic systems for the anaerobic digestion of the organic fraction of municipal solid wastes (OFMSW) were compared. One system (RE-RE) consisted of two coupled reactors packed with OFMSW and the other (UASB-RE) consisted of an upflow anaerobic sludge blanket reactor (UASB) coupled to a packed reactor For the start-up phase, both leading reactors RE 1.1 and UASB 2.1 were inoculated with a mixture of non-anaerobic inocula and worked with leachate and effluent full recirculation. Once a full methanogenic regime was achieved in the leading reactors, their effluents were fed to fresh packed reactors RE 1.2 and RE 2.2. RE 1.1 reached its full methanogenic regime after 118 days (TMF time to achieve methanogenesis). At this point, its leachate had pH 7.05, alpha factor 0.35, volatile organic acids (VOA) 1405 mg/l HAc, COD 3080 mg/l and 62.02% methane in the biogas. The other leading reactor (UASB 2.1) reached its full methanogenesis regime after 34 days, and its effluent had pH 7.13, alpha 0.36, VOA 1289 mg/l HAc, COD 2280 mg/l, and 60.40% methane in the biogas. After coupling the leading reactors to the corresponding packed reactors, both coupled anaerobic systems showed similar performances regarding the degradation of OFMSW The UASB-RE system showed a faster overall start-up, a slightly higher reduction of organic matter (as volatile solids, VS) of the packed OFMSW and a higher biogas production than RE-RE. Removal efficiencies of VS and cellulose, and the methane pseudo yield were 85.95%, 80.88% and 0.1091 CH4/g-VSfed in RE-RE, and 88.75%, 82.61% and 0.1151 CH4/g-VSfed in RANMAL-RE