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Microalgae are capable of assimilating nutrients from wastewater (WW), producing clean water and biomass rich in bioactive compounds that need to be recovered from inside the microalgal cell. This work investigated subcritical water (SW) extraction to collect high-value compounds from the microalga Tetradesmus obliquus after treating poultry WW. The treatment efficiency was evaluated in terms of total Kjeldahl nitrogen (TKN), phosphate, chemical oxygen demand (COD) and metals. T. obliquus was able to remove 77% TKN, 50% phosphate, 84% COD, and metals (48–89%) within legislation values. SW extraction was performed at 170 °C and 30 bar for 10 min. SW allowed the extraction of total phenols (1.073 mg GAE/mL extract) and total flavonoids (0.111 mg CAT/mL extract) with high antioxidant activity (IC50 value, 7.18 µg/mL). The microalga was shown to be a source of organic compounds of commercial value (e.g., squalene). Finally, the SW conditions allowed the removal of pathogens and metals in the extracts and residues to values in accordance with legislation, assuring their safety for feed or agriculture applications. [ABSTRACT FROM AUTHOR]

The objective of this review was to provide quantitative insights into algal growth and nutrient removal in anaerobic digestate. To synthesize the relevant literature, a meta-analysis was conducted using data from 58 articles to elucidate key factors that impact algal biomass productivity and nutrient removal from anaerobic digestate. On average, algal biomass productivity in anaerobic digestate was significantly lower than that in synthetic control media (p < 0.05) but large variation in productivity was observed. A mixed-effects multiple regression model across study revealed that biological or chemical pretreatment of digestate significantly increase productivity (p < 0.001). In contrast, the commonly used practice of digestate dilution was not a significant factor in the model. High initial total ammonia nitrogen suppressed algal growth (p = 0.036) whereas initial total phosphorus concentration, digestate sterilization, CO 2 supplementation, and temperature were not statistically significant factors. Higher growth corresponded with significantly higher NH 4 –N and phosphorus removal with a linear relationship of 6.4 mg NH 4 –N and 0.73 mg P removed per 100 mg of algal biomass growth (p < 0.001). The literature suggests that suboptimal algal growth in anaerobic digestate could be due to factors such as turbidity, high free ammonia, and residual organic compounds. This analysis shows that non-dilution approaches, such as biological or chemical pretreatment, for alleviating algal inhibition are recommended for algal digestate treatment systems. [Display omitted] • A meta-analysis was conducted on algal cultivation in anaerobic digestate. • Significant difference (p < 0.05) in algal growth in digestate vs. control media. • Chem/Bio pretreatment support (p < 0.05) algal productivity in digestate. • Non-dilution approaches are recommended for algae production from digestate. [ABSTRACT FROM AUTHOR]

The present study investigated the growth, harvesting, biocrude conversion, and recycling of the HTL aqueous phase for one self-settling (i.e., Chlorocystis sp.) and another non-settling (i.e., Picochlorum sp.) marine microalgae. Both the strains were grown simultaneously in 2 identical 25,000-L raceway ponds in the Qatari desert. The cell size of Picochlorum sp. was small (2–3 µm), and its biomass was harvested using a centrifuge. Cells of Chlorocystis sp. (6–9 µm) formed flocs that settled spontaneously in a sedimentation chamber. Harvested biomass of these two strains was then converted to biocrude oil, using a 500-mL Parr reactor. The biocrude yield of Picochlorum sp. and Chlorocystis sp. was 39.6 ± 1.15% and 34.8 ± 1.65%, respectively. The energy content of the biocrude oil was 32.78 and 33.38 MJ/kg for Chlorocystis sp. and Picochlorum sp., respectively. Both the strains were capable of efficiently utilizing more than 95% nitrogen of the HTL aqueous phase. Although lower biocrude yield was obtained from Chlorocystis sp., compared to Picochlorum sp., harvesting of Chlorocystis sp. would require much lower energy compared to Picochlorum sp. Therefore, a self-settling microalgae (e.g., Chlorocystis sp.) could potentially be a better candidate, over non-settling microalgae, for producing biofuel feedstock. [ABSTRACT FROM AUTHOR]

In this study, zeolite was employed for the separation and recovery of P from synthetic wastewater and its use as phosphorus (P) source for the cultivation of the green microalga Chlorella vulgaris and the cyanobacterium Arthrospira (Spirulina) platensis. At P-loaded zeolite concentration of 0.15–1 g/L, in which P was limited, the two species displayed quite different behavior regarding their growth and biomass composition. C. vulgaris preferred to increase the intracellular P and did not synthesize biomass, while A. platensis synthesized biomass keeping the intracellular P as low as possible. In addition under P limitation, C. vulgaris did display some little alteration of the biomass composition, while A. platensis did it significantly, accumulating carbohydrates around 70% from about 15%–20% (control). Both species could desorb P from zeolite biologically. A. platensis could recover over 65% and C. vulgaris 25% of the P bounded onto zeolite. When P-loaded zeolite concentration increased to 5 g/L, P was adequate to support growth for both species. Especially in the case of C. vulgaris, growth was stimulated from the presence of P-loaded zeolite and produced more biomass compared to the control.

This work evaluates the use of native microalgae consortia for a dual role: polishing treatment of municipal wastewater effluents and microalgae biomass feedstock potential for biodiesel or biofertilizer production. An initial screening was undertaken to test N and P removal from secondary effluents and biomass production by 12 consortia. A subsequent treatment was performed by selected consortia (01 and 12) under three operational conditions: stirring (S), S+12 h of daily aeration (S+ A) and S+ A enriched with CO2 (S+ AC). All treatments resulted in compliance with environmental regulations (e.g. Directive 91/271/EEC) and high removal efficiency of nutrients: 64-79% and 80-94% of total N and PO4 3--P respectively. During the experiments it was shown that pH alkalinization due to microalgae growth benefits the chemical removal of ammonia and phosphorus. Moreover, advantages of pH increase could be accomplished by intermittent CO2 addition which in this research (treatment S + AC) promoted higher yield and lipid concentration. The resulting dry biomass analysis showed a low lipid content (0.5-4.3%) not ideal for biodiesel production. Moreover, the high rate of ash (29.3-53.0%) suggests that biomass could be readily recycled as a biofertilizer due to mineral supply and organic constituents formed by C, N and P (e.g. carbohydrate, protein, and lipids). [ABSTRACT FROM AUTHOR]

In this study, zeolite was employed for the separation and recovery of P from synthetic wastewater and its use as phosphorus (P) source for the cultivation of the green microalga Chlorella vulgaris and the cyanobacterium Arthrospira (Spirulina) platensis. At P-loaded zeolite concentration of 0.15-1 g/L, in which P was limited, the two species displayed quite different behavior regarding their growth and biomass composition. C. vulgaris preferred to increase the intracellular P and did not synthesize biomass, while A. platensis synthesized biomass keeping the intracellular P as low as possible. In addition under P limitation, C. vulgaris did display some little alteration of the biomass composition, while A. platensis did it significantly, accumulating carbohydrates around 70% from about 15%-20% (control). Both species could desorb P from zeolite biologically. A. platensis could recover over 65% and C. vulgaris 25% of the P bounded onto zeolite. When P-loaded zeolite concentration increased to 5 g/L, P was adequate to support growth for both species. Especially in the case of C. vulgaris, growth was stimulated from the presence of P-loaded zeolite and produced more biomass compared to the control. [ABSTRACT FROM AUTHOR]

A wastewater-fed, partly indoor aquaculture plant (36 basins, 360 m2 and 420 m3 in total) was designed in Otelfingen/Zurich, Switzerland. It was charged with the effluent from a methanization plant processing organic household waste and started operation in spring 1998. The aim of the successive arrangement of the different modules and steps was to efficiently recycle water-borne nutrients in the form of aquatic biomass products, such as floating (ornamental) macrophytes, fish, zoo- and phytoplankton, suitable for selling on the Swiss market. Besides treating the effluent (total organic carbon [TOC], total nitrogen, nitrate [NO3-N], ammonium [NH4-N], and total phosphorus concentrations being 670 g/m3, 255 g/m3, 150 g/m3, 95 g/m3, and 52 g/m3, respectively) according to Swiss law requirements, the research focused on the search for suitable aquatic organisms and their testing at different environmental conditions. During the 16-week experimental period, a total of 2,150 kg fresh weight (FW) of biomass (97% as floating macrophytes) was harvested. This way, 176 g/week nitrogen and 47 g/week phosphorus were eliminated by assimilation, corresponding to 25-35% of the system's inflow. Due to relatively high evapotranspiration rates (on average 35.4 mm/week) and for water reconditioning purpose in the fish stocking basins, fresh water was added. Nevertheless, the system's final effluent was very low (21% of total inflow plus rainfall) and was carrying only about 2% and 0.5% of the input loads of nitrogen and phosphorus, respectively. Hence, the elimination rate was significantly above the average performance of a conventional system normally applied in Middle Europe, although the concentration values of most parameters in the outflow were comparable. Macrophyte production (and thus nutrient assimilation) was close to theoretical maxima in basins with high nutrient levels. Both plankton and fish growth were, at their best, only moderately satisfying. The semi-continual planktonic microalgae culture, and therefore also zooplankton culture, could be improved if the light absorbing humic substances were removed in a pre-treatment. Under given conditions (i.e., temperate climate) fish would rather play an accompanying role in the ecological production process. A wastewater-fed aquaculture facility resembles an integrated production plant rather than a wastewater disposal site. In addition to that, it has potential to prove advantageous over the highly developed conventional wastewater treatment plants established in Middle Europe. Further research in this field is essential and also recommended, considering political programs like Agenda 21, which contemplate the need for sustainable strategies for handling resources. [ABSTRACT FROM PUBLISHER]