Mario Nieves

Growth of Scenedesmus sp. in artificial wastewater

The microalga Scenedesmus sp. was grown in artificial wastewater with 30 and 50% daily replacements of the culture volume and under continuous lighting. The biomass per unit volume was higher with the 30% dilution, but daily yields were better with 50%. In 24 h, phosphate removal was more than 50% in both cases. The total nitrogen removed, most of which was ammonia, was approximately 50 and 66% of the initial concentration for the 30 and 50% dilutions, respectively, and a nitrogen budget calculated using the total daily removal and the average algal protein harvested gave an imbalance of close to 65 and 75%, showing that ammonia stripping due to high pH values and aeration might play an important role in the biological tertiary treatment of wastewater with photosynthetic organisms.

Nitrogen budget in Scenedesmus obliquus cultures with artificial wastewater

Semicontinuous cultures of Scenedesmus obliquus in artificial wastewater, recycled into proteins about 33% and 25% of the dissolved nitrogen missing from the medium 24 h after harvesting 50% and 70% of the culture, and replacing the volume harvested with fresh medium. The residual dissolved nitrogen concentrations were 25% and 43% of the initial, respectively, with an imbalance in the mass budget close to 17 and 20 mg N l(-1) d-1. Most or all the nitrogen missing was found in an ammonia trap located at the air vent of the closed cultures, showing that an important role of microalgae in wastewater treatment is that of favouring NH3 stripping due to the photosynthesis-induced pH increases.

Zeolitic products as enrichment for cultures of a marine microalga

Abstract The cell yields of batch and semicontinuous cultures in f/2 medium of the marine diatom Chaetoceros sp., widely used in Mexican mariculture, may be improved by more than 30% by the addition of 10 mg l −1 of experimental zeolitic products to the medium. Over 3 days, the best yields are obtained with ZESTEC 56 and ZESEP 56, but ZEBEN 06 gives better results after 5 days, or in semicontinuous cultures.

The importance of acclimation for the evaluation of alternative media for microalgae growth

Important discrepancies were obtained in growth experiments run with two diatoms and three agricultural fertilizers, using different protocols. With a short preacclimation to the new media and small inocula, the growth of Chaetoceros sp. was stunted and the cells were heavier than those of the f/2-grown control cultures. Without acclimation, growth was acceptable in the short term, but the cells were unable to grow if used as starter cultures for a new experiment with the same medium. With Phaeodactylum tricornutum, one of the fertilizers gave consistently equal or even better results than the control medium; with the other two media, growth was poorer and inconsistent. As with Chaetoceros, growth-limiting media resulted in cells which were heavier than normal. The results show the importance of the choice of the experimental protocol in growth experiments aiming to evaluate alternative, cheaper formulations of media for mass cultures. In these cases, the protocol should reproduce as close as possible the routines used for commercial mass production.