Ma Eugenia Martínez

Nitrogen and phosphorus removal from urban wastewater by the microalga Scenedesmus obliquus

Abstract The removal of phosphorus and nitrogen by the freshwater alga Scenedesmus obliquus, cultured in urban wastewater, previously submitted to secondary sewage treatment, was studied under different conditions of stirring and temperature. In all cases, the amount of NH3 lost, as well as biomass productivity and its biochemical composition, were evaluated. The specific growth rates proved greatest in the stirred cultures, the highest μ value being 0.0438 h−1 at 30°C. The stirring increased biomass productivity (PB) in the linear growth phase after exponential growth, with the optimum appearing at 25°C. For the temperatures studied stirring was not necessary to provide the highest percentage of P elimination (%Pmax), but did reduce the time needed to reach that percentage (tmax). The highest %Pmax value, 98%, within the shortest time period, tmax=94.33 h, was found in the culture with stirring at 25°C. Ammonium removal was determined by two factors – the consumption of ammonium for growth and elimination by desorption as ammonia. The highest percentage of ammonium removal (%Nmax), 100%, resulted at the final culture time (tf) of 188.33 h, in the stirred culture at 25°C. The biochemical composition of the biomass gave the normal values for this microalga reported by other authors. The protein content was notably low, around 11.8% by weight, and the polyunsaturated-fatty-acid content was high. The N:P ratio of the culture medium was 12.9. Finally, we proposed a dilution factor for the treated wastewater (f) to be dumped in order to regulate operation conditions and time for an optimal removal of nitrogen and phosphorus.

Influence of phosphorus concentration and temperature on growth and phosphorus uptake by the microalga Scenedesmus obliquus

The growth of the freshwater microalga Scenedesmus obliquus has been studied in a mineral medium with P concentrations of between 0 and 372 μM and temperatures of 20, 25, 30 and 35°C. At all the temperatures, growth was inhibited by the P. The inhibition by P was highly dependent on temperature, detected at concentrations on the order of 1 μM at 35°C, 2 μM at 20 and 25°C, and 350 μM at 30°C. The greatest specific growth rate, 0.047 h−1, was registered at 30°C. The specific growth rates were adjusted to a semistructured model of inhibition by the substrate. The inhibition constants, K1 (μM), increased with rising temperatures from 20 to 25 and 30°C, and decreased at higher temperatures. At 35°C, the lowest value was recorded for K1 1.20 μM, and thus the inhibitory effect was the most pronounced. At 30°C, within the interval of P concentrations of 0–300 μM, it was possible for the variation in μS0 to be fitted to a semistructured Monod kinetic model of limitation by the substrate. Yield of biomass varied with temperature. The highest yields were reached at 20°C. The specific rates of P consumption increased with S0, tending towards a constant value. The highest values, obtained at 30°C and 35°C, were practically the same, and the lowest were obtained at 20°C.

Influence of temperature on growth of Scenedesmus obliquus in diluted olive mill wastewater as culture medium

Scenedesmus obliquus can help to reduce the environmental impact of industrial olive mill wastewater from olive oil extraction in the three‐phase system. This work examines the effect of temperature changes (288–308 K) on algal growth, culture medium, and biochemical composition of S. obliquus. The maximum specific growth rate of 0.024 h−1 occurred at an optimal temperature of 302.7 K. The apparent activation energies of cell growth and cell death were determined as 61.8 and 142.8 kJ/mol, respectively. At the end of culture the percentages of pigments, proteins, and carbohydrates were greater at the two ends of the temperature range studied, as it was also observed for the maximum elimination of biochemical oxygen demand (BOD5). The mono‐ and polyunsaturated fatty acid content of the biomass was greater at the lowest temperature used (288 K).

Growth and biochemical composition with emphasis on the fatty acids of Tetraselmis sp.

SummaryThe influence of temperature (15–32°C) and the ratio of nitrogen to phosphorus (N/P) in the culture medium (0.5–80) on the growth kinetics and protein, chlorophyll, lipid and fatty acid content of the marine microalga Tetraselmis sp. have been studied. Below an N/P of 20, growth was determined by N limitation and above 20 by P limitation. Protein increased with a rise in N content at any test temperature. The chlorophyll content increased with temperature, with maximum values at 25°C. The lipid content decreased with increasing N/P ratio above 20°C. The polyunsaturated fatty acid content tends to be inversely proportional to the growth rate within the N/P range 20–80. The quotient of the n3 and n6 polyunsaturated-fatty-acid fractions, an indicator of the nutritive value of microalgae, was found to be within the range 2–3. These values were obtained either between 25 and 28°C independent of the N/P ratio used at 20°C for N/P ratios higher than 40.0.

Continuous culture of the marine microalga Tetraselmis sp. — productivity analysis

Camacho, F., Mohna, E., Martinez, Ma. E., Sanchez, S. and Garcia, F., 1990. Continuous culture of the marine? microalga Tetraselmis sp. - productivity analysis. Aquaculture, 90: 75-84. An outdoor experimental system for continuous culture of the marine microalga Tetraselmis sp. is described. The influence of dilution rate, initial biomass concentration and the intensity of solar radiation on the amount of biomass obtained was examined. The average rate of production of cells, G,. is a parabolic function of the dilution rate and reached a maximum value at D=O.O9 h-‘. The intensity of light, I,, influences productivity up to approximately 100 W/m*, above which saturation was observed. The experimental results G,-I, were adjusted to an exponential model for light-restricted growth. The average rate of production of cells, versus the initial biomass concentration, C,, reached a maximum value. G,,, decreased as C,, increased to high cell density values due to light limitation and when C, decreased to low cell density values due to decreased efficiency in the use of incident solar radiation.

The influence of flow rate and the composition of supplied CO2/air mixtures on discontinuous growth of Tetraselmis sp.

SummaryThis paper studies the influence of the flow rate of gaseous mixtures on the kinetics of growth and the fatty acid composition of Tetraselmis sp. at CO2/air ratios of 3 × 10−4 and 2 × 10−5. The specific growth rate rises with increased flow rate up to values of approximately 0.086 h−1 and 0.063 h−1 at CO2/air ratios of 3 × 10−4 and 2 × 10−5 respectively, when the flow rate is approximately 3 v/v per minute. At higher flow rates, the specific growth rate decreases. The polyunsaturated fatty acid content decreases slightly as the gaseous mixture flow rate increases, whereby the ratio ω3/ω6 remains between 2 and 3, indicating good nutritional values.

The influence of culture media and aeration rate on the growth and fatty-acid content of Skeletonema costatum

The growth of the marine microalga Skeletonema costatum in a batch photobioreactor has been studied to determine the influence of the culture medium and aeration rate on the growth rate and fatty-acid composition of the biomass. The most favourable conditions for high biomass production with a good nutritive value were achieved with Walne medium at 1% stock solution and an aeration rate of 1·5 vv−1 min−1. The specific growth rate reached μm = 0·04 h−1, a biomass productivity of 2·2 × 10−3 g litre−1 h−1, and the lipid fraction contained 44·1% polyunsaturated fatty acids, 30·7% essential fatty acids, and 6·2% Σn−3 highly unsaturated fatty acid (HUFA).