Microalgae population dynamics in photobioreactors with secondary sewage effluent as culture medium

Nitrogen and phosphorus present in sewage can be used for microalgae growth, possibiliting cost reduction in the production of microalgae at the same time that it decreases the eutrophication potential of the effluent. This research aimed at monitoring the native community of microalgae and coliform bacteria in a secondary effluent from anaerobic municipal sewage treatment. Two treatments (aerated and non-aerated) were performed to grow microalgae under semi-controlled conditions in semi-closed photobioreactors in a greenhouse. The results showed no significant pH and coliforms (total and Escherichia coli) variation between treatments. Nutrient concentrations were reduced supporting microalgae growth up to 107 cells.mL−1 independent of aeration. Exponential growth was obtained from the first day for the non-aerated, but a 5 day lag phase of growth was obtained for the aerated. Chlorella vulgaris was the dominant microalgae (99.9%) in both treatments. In the aerated, 5 algae classes were detected (Chlorophyceae, Cyanophyceae, Chrysophyceae, Bacillariophyceae and Euglenophyceae), with 12 taxa, whereas in the non-aerated, 2 classes were identified (Chlorophyceae and Cyanophyceae), with 5 taxa. We concluded that effluent is viable for microalgae growth, especially Chlorella vulgaris, at the same time that the eutrophication potential and coliforms are decreased, contributing for better quality of the final effluent.

Glycolytic activities in size-fractionated water samples: emphasis on rhamnosidase, arabinosidase and fucosidase activities

Glycolytic activities of eight enzymes in size-fractionated water samples from a eutrophic tropical reservoir are presented in this study, including enzymes assayed for the first time in a freshwater environment. Among these enzymes, rhamnosidase, arabinosidase and fucosidase presented high activity in the free-living fraction, while glucosidase, mannosidase and galactosidase exhibited high activity in the attached fraction. The low activity registered for rhamnosidase, arabinosidase and fucosidase in the attached fraction seemed contribute to the integrity of the aggregate and based on this fact, a protective role for these structures was proposed. The presented enzyme profiles and the differences in the relative activities probably reflected the organic matter composition as well as the metabolic requirements of the bacterial community, suggesting that bacteria attached to particulate matter had phenotypic traits distinct from those of free-living bacteria.

Carboidratos dissolvidos do reservatório de Barra Bonita (Estado de São Paulo, Brasil) e sua relação com as algas fitoplanctônicas abundantes / Dissolved carbohydrates from Barra Bonita Reservoir (São Paulo State, Brazil) and its relationships with phytoplanktonic abundant algae

O estudo dos carboidratos dissolvidos e sua relação com as algas abundantes no reservatório de Barra Bonita, foi realizado em coletas mensais (junho de 2002 a janeiro de 2004), em seis profundidades na coluna d'água, cujos valores variaram dependendo da estação do ano e do nível do reservatório, num ponto fixo, localizado 3 km a montante da barragem. Aproximadamente 90 por cento dos carboidratos dissolvidos neste reservatório foram constituídos por carboidratos poliméricos hidrolisáveis (polissacarídeos ou oligossacarídeos). A análise de variância detectou variabilidade entre as concentrações dos carboidratos dissolvidos apenas em escala temporal (p < 0,05), sendo que no eixo vertical, as concentrações destes açúcares apresentaram-se homogêneas (p > 0,05). A composição monossacarídica dos açúcares encontrados no reservatório foi galactose, ramnose, glicose e fucose. Na maioria dos meses amostrados, as concentrações de carboidratos dissolvidos, a maioria deles poliméricos, ocorreram concomitantemente ao registro de florescimentos das espécies abundantes, principalmente cianofíceas, que provavelmente foram as principais fontes de polissacarídeos extracelulares para o sistema.

Dissolved carbohydrates and abundant algae of Barra Bonita Reservoir were studied monthly from June 2002 to January 2004 in six depths whose values vary depending on the seasons and the water level at a sampling site located 3 km upstream the Reservoir dam. Nearly 90 percent of the dissolved carbohydrates were constituted of polymeric hydrolysable carbohydrates (polysaccharides or oligosaccharides). Analysis of variance detected variability among concentrations of dissolved carbohydrates only in temporal scale (p < 0.05), whereas in vertical axis the concentrations of these sugars were uniform (p > 0.05). The monosaccharide composition of the sugars found in the reservoir was galactose, rhamnose, glucose e fucose. During the sampling period, higher concentrations of dissolved carbohydrates, mostly polymeric, occurred together with large phytoplanktonic blooms, predominantly cyanobacteria, which probably were the main source of extracellular polysaccharides in the system.

Limnological characteristics and seasonal changes in density and diversity of the phytoplanktonic community at the Caçó pond, Maranhäo State, Brazil

Seasonal changes of the phytoplanktonic community and limnological abiotic characteristics of Caçó pond (Maranhäo State, Brazil) was evaluated from two field researches during the rainy (April 1999) and dry (November 1999) seasons. Measurements of twelve chemical and physical variables and phytoplankton collections were carried out at eight sampling stations. The Chlorophyceae and Cyanobacteria groups were in highest fractions during the rainy and dry seasons, respectively. The limnological abiotic variables showed a homogenous spatial distribution. The cluster analysis, using Bray-Curtis distance, distinguished two major groups, represented by the most common and abundant species in both the periods. The results showed that the climate regime, due to the seasonal changes in pluviosity, was a determinant over the phytoplanktonic community structure at Caçó pond