Copper multifaceted interferences during swine wastewater treatment in high-rate algal ponds: alterations on nutrient removal, biomass composition and resource recovery.

Microalgae cultivation in swine wastewater (SW) allows the removal of nutrients and biomass production. However, SW is known for its Cu contamination, and its effects on algae cultivation systems such as high-rate algal ponds (HRAPs) are poorly understood. This gap in the literature limits the proposition of adequate concentrations of Cu to optimise SW treatment and resource recovery in HRAPs. For this assessment, 12 HRAPs installed outdoors were operated with 800 L of SW with different Cu concentrations (0.1-4.0 mg/L). Cu's interferences on the growth and composition of biomass and nutrient removal from SW were investigated through mass balance and experimental modelling. The results showed that the concentration of 1.0 mg Cu/L stimulated microalgae growth, and above 3.0 mg Cu/L caused inhibition accompanied by an accumulation of H2O2. Furthermore, Cu affected the contents of lipids and carotenoids observed in the biomass; the highest concentration was observed in the control (16%) and 0.5 mg Cu/L (1.6 mg/g), respectively. An innovative result was verified for nutrient removal, in which increased Cu concentration reduced the N-NH4+ removal rate. In contrast, the soluble P removal rate was enhanced by 2.0 mg Cu/L. Removal of soluble Cu in treated SW reached 91%. However, the action of microalgae in this process was not associated with assimilation but with a pH increase resulting from photosynthesis. A preliminary evaluation of economic viability showed that the commercialisation of biomass considering the concentration of carotenoids obtained in HRAPs with 0.5 mg Cu/L could be economically attractive. In conclusion, Cu affected the different parameters evaluated in this study in a complex way. This can help managers consort nutrient removal, biomass production, and resource recovery, providing information for possible industrial exploitation of the generated bioproducts.

Swine wastewater treatment in high rate algal ponds: Effects of Cu and Zn on nutrient removal, productivity and biomass composition.

This study aimed to evaluate the simultaneous interferences of Cu and Zn found in swine wastewater (SW) in the development of microalgae considering real conditions of cultivation in high rate algal ponds (HRAPs). Ten HRAPs on a pilot scale were fed with SW with different mixtures of Cu (0.5-3.0 mg/L) and Zn (5.0-25.0 mg/L). The interferences of these metals in removing nutrients (N-NH4+ and soluble phosphorus (Ps)) from the SW were determined. In addition, this study evaluated the effects on biomass growth and biochemical composition. Chlorella sp. was dominant in all HRAPs and the condition that potentiated its growth occurred in medium containing 1.8 mg Cu/L + 15.0 mg Zn/L, while higher concentrations conferred inhibition. Only Cu compromised the removal rates of N-NH4+ while the effects of Zn were not significant. Contrary, Zn interfered with Ps removal rates, but the impact of Cu was not significant. The greatest Cu applications increased the protein levels by biomass (50.5-55.2 %). Carbohydrate accumulation was favored by conditions that inhibited the development of microalgae due to either limitation or excess of metals. Copper and Zn compromised the levels of lipids, and the control treatment had the highest content (24.5 %). The presence of Cu and Zn changed the dynamics of HRAPs regarding nutrient removal, productivity, and biochemical composition of the biomass.

Alternative fertilizer-based growth media support high lipid contents without growth impairment in Scenedesmus obliquus BR003.

Nitrogen (N) sources have been target in microalgae cultivation studies, considering their nutritional impact on growth and high costs. Here, we have evaluated the growth of Scenedesmus obliquus BR003, applying alternative low-cost culture media containing ammonium and urea, or combinations of both N sources. The culture media were applied for indoor and outdoor cultivation, followed by growth analyses and metabolic characterization. The alternative culture media B4 and L4 supported higher biomass production (1.4 g L-1) compared to BG11 (nitrate-based medium). In addition, the lipid percentage was higher for B4 (ammonium-based culture medium), reaching up to 25% DW. High contents of carbohydrates (60%) and proteins (40%) were also obtained in media with ammonium and urea, respectively. Considering the lower costs of alternative fertilizer-based media, using ammonium and/or urea as N sources, and the high lipid content observed, we suggest these media as viable for large-scale production of S. obliquus.

Combination of trace elements and salt stress in different cultivation modes improves the lipid productivity of Scenedesmus spp.

The genus Scenedesmus harbors around 120 species, and some strains have been successfully used for mass culture and biotechnological applications. Considering the potential of this genus as a promising feedstock for production of biofuels, mainly biodiesel, it was evaluated the combined effects of trace elements, salinity stress and different cultivation modes (single batch, semi-continuous, and two-stage batch) on lipid productivity of the freshwater strains S. obliquus BR003 and S. bajacalifornicus BR024. Cultivation of BR003 and BR024 applying culture medium supplemented with trace elements and salt stress sustained a higher production of lipids. However, S. obliquus BR003 and S. bajacalifornicus BR024 showed different concentrations of neutral and total lipids when cultivated in batch-based and semi-continuous modes, and the batch-based modes were preferred for the production of lipids and carbohydrates. Consequently, different cultivation strategies coupled with slight salt stress improve the lipid productivity in Scenedesmus strains.

Increased urea availability promotes adjustments in C/N metabolism and lipid content without impacting growth in Chlamydomonas reinhardtii.

INTRODUCTION: The use of urea as a nitrogen (N) source by Chlorophytes usually enhances biomass and lipid production when compared to ammonium (NH4+). However, the metabolic shifts displayed by Chlamydomonas reinhardtii growing with this organic N source are not known. OBJECTIVES: This study aimed: (i) to characterize the metabolism of C. reinhardtii cultivated in media containing only urea as N source as well as combined with different NH4+ ratios; (ii) to understand how metabolism respond to urea availability. METHODS: Specific quantification of metabolites using 96-well microplates, and high-performance liquid chromatography combined with non-targeted metabolite profiling by gas chromatography (GC)-time-of-flight (TOF)-mass spectrometry (MS) were used in this study. In addition, GC analysis was used to determine fatty acid profiling. RESULTS: The use of urea did not alter the growth rate in comparison with NH4+. Interestingly, the cell number decreased and the cell size increased proportionally with urea availability. Furthermore, chlorophyll, protein and lipid contents increased with the amount of urea. Regarding the fatty acid profile, oleic acid (C18:1 w8) decreased with amount of urea, while linoleic acid (C18:2 w6) doubled in urea-containing medium. CONCLUSIONS: These results indicate that urea promotes remarkable adjustments in metabolism, without drastic changes in biomass, promoting changes in carbohydrate and amino acid metabolism, as well as in lipids production and fatty acid profile.