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The influence of winery wastewater rich in organic carbon in lipids production from microalgae

Axaopoulou Vasiliki-Ariadni

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Summary

Microalgae have been extensively used for the production of lipids, which are subsequently used as prime material for the production of biodiesel. The growth of microalgae and the production and separation of lipids from the cultures pose a number of challenges, such as the maximization of biomass and lipids yield, the harvesting of microalgae from the culture and the extraction of lipids from the biomass. Microalgae can grow on carbon dioxide, however they may use organic carbon as an extra carbon source. Thus, the use of readily available and low cost carbon substrate for the maximization of microalgae production is an interesting alternative. Moreover, if wastewater can be used as substrate, then the process may serve a dual purpose: lipids production and wastewater bioremediation. In our laboratory, we have developed a novel process for microalgae growth and harvesting, which involves the growth of immobilized microalgae on flat solid surfaces, in shallow waters. Under the above conditions most of biomass is growing immobilized and can be easily separated using a scraper. Experiments were carried out on Stichococcus sp. monoculture, while lipids production was maximized by the application of nutrient starvation after full growth and prior to harvesting. In the present experiments, the effect of the type of growth media on the growth of immobilized Stichococcus sp., for the production of lipids, was examined. Three types of wastewater were used: (A) seawater with the addition nutrient salts, (B) seawater with the addition of diluted winery wastewater (1:600 wastewater : seawater) and (C) seawater with the addition of similar type diluted winery wastewater plus nutrient salts. Microalgae were grown on flat sand-blasted glass, in a photo bioreactor with working area of 0.14 m2, using simultaneously 2 types of fluorescent light sources (3500 and 5500 K). The level of culture media above the growth layer was 4 cm. Each microalgae cultivation in the photo-bioreactor was 18 days long (after inoculation), followed by 2 days of nutrient starvation. The average biomass growth at harvesting was measured as: 0.9, 1.1 and 1.2 mg/cm2 (dry basis) for culture media A, B and C, respectively. BOD reduction in the media used was also investigated for medium type B. In this case, the BOD was reduced from 385 mg/L to 42 mg/L after 18 days of cultivation, while it was further reduced to 30 mg/L, after the 2 days nutrient starvation period. The above indicates that organic carbon was utilized as substrate during all phases of cultivation. Following harvesting, the biomass underwent extraction process to separate and collect the lipids. A yield of 0.05-0.07 mglipids/mgdry biomass was calculated per 20 days growth/starvation cycle.

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