Search

Nitrogen (N) limitation is considered as the most efficient strategy to induce the accumulation of lipids, carbohydrates or other target compounds in microalgal biomass. However, along with biomass biochemical composition, alterations in N limitation affect the photosynthetic apparatus and result in decreased growth. In this study, Chlorella vulgaris was cultivated in semi-continuous mode with different degrees of N limitation and chlorophyll (Chl) fluorescence analyses were used to investigate the effect of N limitation on photosystem II (PSII) performance, in terms of structural and functional heterogeneity. As expected, N limitation resulted in the decrease of quantum yield and calculated OJIP parameters related to PSII performance. N limitation resulted in a significant increase of trapped energy per reaction center (RC) and subsequently to higher dissipation of excess energy. However, despite the negative effect of N limitation on the number of RCs, the electron transport beyond QA as well the capacity of reducing/re-oxidation of plastiquinone were not negatively affected, implying that performance of RCs was not affected by N limitation. Photochemical quenching (qp) increased of as N limitation increased while the curve of non-photochemical quenching (NPQ) was unimodal, i.e. increased up to a level of N limitation and then decreased as N limitation degree increased further. The overall results of the present study suggest that the decrease of PSII performance was due to a reduction of the number of RCs accompanied with higher energy dissipation a probable outcome of the decreased need for reductant by cells due to lower metabolic activity under N limitation.

The detection of new pollutants, stricter environmental regulations, and advancements in treatment technologies are driving improvements in bioprocesses for treating wastewater. Specifically, special concern is being placed on phosphorus and nitrogen forms, which spur eutrophication of water bodies, and emerging micropollutants such as pharmaceuticals and person-care products. Algae and cyanobacteria cultivation requirements include water and nutrient sources that currently are supplied by fertilizers, which provide poor sustainability and economics. Using wastewater as a source of nitrogen and phosphorus represents an attractive option to cultivate microalgae simultaneous with contaminant removal. Phycoremediation refers to the assimilation or disintegration of organic and inorganic compounds (carbon, nitrogen, or phosphorus), metals, and emerging contaminants in wastewater by microalgae – algae and cyanobacteria. In addition, added value comes when the microalgae are harvested to become feedstock for biofuels such as biogas. Although promising studies have been published for algal growth in wastewater while simultaneously removing contaminants, limitations in the scale-up process still have to be addressed. In this work, we summarize biological mechanisms by which nutrients and contaminants are removed by microalgae. We specifically address the interactions that the microalgae have with other microorganisms and the production of extracellular polymeric substances, a mechanism well known in the literature, but hardly studied in microalgae. Finally, we discuss different strategies reported to improve the scale up of microalgae cultivation in wastewater.

Although ammoniacal nitrogen is the preferred nitrogen source for microalgae/cyanobacteria, at elevated concentrations and high pH values it may negatively impact photosynthesis and growth. Chlorophyll (Chl) fluorescence analysis is a useful tool to monitor the influence of various stress conditions on the photosynthetic activity of plants or microalgae/cyanobacteria. In this study, we investigated the effect of ammoniacal nitrogen on Chl fluorescence in microalgae/cyanobacteria. Chl fluorescence analysis revealed that the parameters related to flux ratios and specific energy fluxes of photochemistry were gradually inhibited as the free ammonia (FA) concentration increased. Photosynthetic electron transport activity was measured using artificial electron acceptors, donors or inhibitors. These analyses suggest that ammonia has multiple impacts on the photosynthetic apparatus; photosystems I (PSI) and II (PSII), the electron transport chain, the oxygen-evolution complex (OEC) as well the dark respiration were gradually inhibited by increasing FA concentration. At high FA concentration, the PSI/PSII activity increased, suggesting that PSI was more tolerant to FA than PSII. Non-photochemical quenching (NPQ) decreased to zero at elevated FA concentrations. The Chl fluorescence data obtained in the presence of DCMU (diuron) suggest that the decrease of NPQ under ammonia inhibition/toxicity is due to the increase of PSI/PSII activity. The rapid response of Chl fluorescence transients to increases in FA may allow one to use pulse amplitude modulation (PAM) fluorescence as a tool to monitor ammonia inhibition/toxicity in cultures of microalgae/cyanobacteria.

In the present paper, the use of raw poultry litter (PL) as a nutrient source for the cultivation of Arthrospira platensis and Chlorella vulgaris was investigated. PL was added to acid solution (62.5 mM H 2 SO 4 ) for the extraction of nutrients contained in PL. After settling, the supernatant, called PL leachate (PLL) was diluted 25 ×, 20 ×, 15 ×, and 10 × and used as a medium for the cultivation of A. platensis and C. vulgaris . A. platensis could not survive in 15 × and 10 × diluted leachate and while in 20 × and 25 × dilutions the biomass production was only half of that in a control medium (Zarrouk). The biomass composition had a high carbohydrate content (37–44%), which suggests that A. platensis was stressed due to nutrient limitation. C. vulgaris grew well in PLL-based media and the biomass production was higher than in the control medium (BG-11). Biomass composition of C. vulgaris in PLL-based media had lower protein content and higher carbohydrate and lipid content than in the control medium. The overall process for producing microalgal biomass from PL that we propose includes: (i) acid extraction of nutrients through the generation of PL leachate (PLL), (ii) indoor PL composting and recovery of stripped ammonia and CO 2 , and (iii) use of recovered ammonia and CO 2 along with the PLL for the cultivation of microalgae and cyanobacteria for the production of biomass.

In this study, the cyanobacterium Arthrospira platensis, commonly known as Spirulina, was cultivated utilizing phosphorus in the form of struvite recovered from effluents of a biogas plant treating municipal and agro-industrial wastes. Under the specific experimental conditions, providing sterilized struvite at about 120 mg/L (or 15 mg-P/L) gave the same results in terms of biomass production and biochemical composition as the control cultures (with KH2PO4 as a P source). Struvite sterilization was found to be an important step because its original microbial load had a negative effect on the biomass production and resulted in biomass with lower value (lower protein and phycocyanin content). P from struvite was almost complete released upon adding it in the cultivation medium after 90 min, where parameters, such as medium pH, struvite particle size and medium reusing cycles had no effect on the kinetics of P release, indicating that P is almost immediately available for cell uptake. Since struvite was generated from effluents of a biogas plant treating municipal and agro-industrial wastes, the potential of its contamination with hazardous compounds was examined in order to assess the safety of the produced biomass. Unwanted compounds like heavy metals, bisphenol A (BPA), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) were calculated to be at levels significantly lower than those of the maximum levels allowed in the European Union regulation for feedstuff safety, while neither veterinary drugs nor Escherichia coli were detected in the struvite. Results suggest that struvite recovered from biogas plants could be used as P source for the cultivation of A. platensis for feed or food quality.