Using microalgae and bacteria consortium for urban wastewater treatment of small communities

Abstract

Small communities, those which have less than 2000 e-h, are the most forgotten in terms of wastewater treatment. A great amount of the global population (over 28% of the EU population, in 2015 (EUROSTAT, 2017) are disperse in villages and the discharge of contaminants in their natural waters suppose an important pressure for the quality of the ecosystems surrounding leading, sometimes, to eutrophication phenomena. Intensive technologies, such as activated sludge systems, are not suitable for the particular case of small communities, in those cases extensive technologies are applied due to their simplicity, effectiveness and a great integration with the environment. The downside of these technologies is the vast space they need to fulfil the discharge limits of contaminants collected by the European legislation (Directive 91/271) and their poor effectiveness in the reduction of nutrients from the water. Among the different paths of research, the use of the biotechnology of microalgae for the urban wastewater treatment of small communities is giving promising results as a new option sustainable, simple and suitable for the peculiarities of these cases. Due to the high organic matter concentration in these effluents, bacteria also grow in consortia with the microalgae. This consortium improves the metabolism of both kind of microorganism enhancing significantly the kinetics of the culture when it is compared with the kinetics of a microalgae monoculture (3 days of hydraulic retention time, HRT, against 7 days (Arbib et al., 2017)).