Bioindicators of community structure in microalgae-bacteria processes

Abstract

For many decades, microalgae biomass has been representing a valuable resource for anthropic ecosystems. An important step was achieved in microalgae-based technologies field once with finding that relationship established between microalgae and activated sludge could revolutionize conventional wastewater treatment systems, with establishment of the sustainable treatment strategies. In conventional activated sludge processes, protozoan species represent indicators of the operating conditions and treatment performance. However, low level of knowledge was found to be addressed to bioindicators in microalgae-bacteria processes. Thus, the study focused on investigating protozoa dynamics during low strength wastewater treatment using microalgae-bacteria system. Experiments were performed using a photobioreactor operated in sequential batch operation mode. During the first treatment batches, protozoan community was characterized by a high species richness represented by ciliates and testate amoebae, small free swimming ciliates being the prevalent taxa- diversity comparable with that reported in the early stage of the activated sludge development. A transition stage of the protozoan community followed once with biomass development, the disappearance of testate amoeba and development of stalked ciliates populations being noticed. However, a reduction of species richness was recorded after transition stage, a tendency that has led to a complete elimination of the protozoan community. Taking into consideration operating conditions, it was concluded that microalgae-bacteria processes are different from those of activated sludge regarding protozoan community structure. However, microalgae-bacteria processes sustained the development of metazoan community, a high abundance of rotifers populations being recorded at the end of experiments.