Abstract

This paper describes the ability of microalgae Chlorella fusca (Chlorophyta) to bioremediate centrate obtained by the centrifugation of sludge from an urban wastewater treatment plant. Microalgae were grown under solar radiation in UV transparent cylindrical vessels in a batch culture for 35 days at different centrate concentrations (33%-66%-100%) and compared to microalgae grown in a Basal bold medium (BBM) with ammonium (BBM-NH4) or nitrate (BBM-NO3) as the inorganic nitrogen source. Biomass productivity was evaluated as cell weight and cell numbers. Photosynthetic activity was measured by in vivo chlorophyll a fluorescence associated with photosystem II. The ionic composition of the media, total internal carbon, nitrogen, protein and lipid content were evaluated. Culture growth in centrate treatments presented a lag phase, but reached, under 100% centrate, a higher number of cells (296.10(6) cellsmL(-1)) and equal biomass production (3.5 gL(-1)) than control treatment cultures in the stationary phase. The photosynthetic status, expressed as maximal quantum yield (Fv/Fm), was maintained high throughout time in BBM-NO3 treatment whereas under 100% centrate it reached similar values in the stationary phase. Maximal electron transport rate (ETRmax), estimator of photosynthetic capacity, was higher in BBM-NO3 (with a maximum value of 10.2 mmol e(-)m(-3)s(-1)), however 100%-C treatment reached similar values (8.6 mmol e(-)m(-3)s(-1)). Lipid and Protein productivities were higher under BBM-NO3 (58.8 mg(-1)L(-1)d(-1), 124.07 mg(-1)L(-1)d(-1)) and 100% centrate (42.5 mg(-1)L(-1)d(-1), 119.92 mg(-1)L(-1)d(-1)). Nitrogen deficiency in 66 and 100% centrate grown algae was related to an increase of the lipid to protein ratio. Centrate as the culture media was demonstrated to be a good candidate for biomass growth i.e. after a period of adaptation, photosynthetic state and productivity were similar to those in a traditional culture media. The reduction of N and P in centrate shows a promising application for the depuration of centrate with a reduction of costs.