Abstract
The use of microorganisms to clean up wastewater provides a cheaper alternative to the conventional treatment plant. The efficiency of this method can be improved by the choice of microorganism with the potential of removing contaminants. One such group is photosynthetic bacteria. Rhodobacter capsulatus is a purple non-sulfur bacterium (PNSB) found to be capable of different metabolic activities depending on the environmental conditions. Cell growth in different media and conditions was tested, obtaining a concentration of about 108 CFU/mL under aerobic-dark and 109 CFU/mL under anaerobic-light conditions. The biomass was then used as a bioremediation agent for denitrification and nitrification of municipal wastewater to evaluate the potential to be employed as an additive in biological wastewater treatment. Inoculating a sample of mixed liquor withdrawn from the municipal wastewater treatment plant with R. capsulatus grown in aerobic-dark and anaerobic-light conditions caused a significant decrease of N-NO3 (>95%), N-NH3 (70%) and SCOD (soluble chemical oxygen demand) (>69%), independent of the growth conditions. A preliminary evaluation of costs indicated that R. capsulatus grown in aerobic-dark conditions could be more convenient for industrial application.
Highlights
Wastewater treatment and reuse is not new, and knowledge on this topic has evolved and advanced in the past years
Biological treatments have many advantages because they are cheaper, more reliable, can be done on site and their efficiency can be improved by the choice of a variety of microorganisms [4]
Taking into account its proven versatile metabolic behavior depending on environmental conditions [22], the aim of this study was to compare R. capsulatus cell growth in anaerobic-light and aerobic-dark conditions, using appropriate culture media
Summary
Wastewater treatment and reuse is not new, and knowledge on this topic has evolved and advanced in the past years. The general purpose of wastewater treatments is to remove pollutants that can harm the aquatic environment and natural ecosystems in case they are discharged. Because of the deleterious effects of the low concentration of dissolved oxygen in aquatic life, wastewater treatment has been historically focused on the removal of pollutants that would deplete dissolved oxygen and favor eutrophication in receiving waters [2]. Both chemical and biological treatments or a combination of them have been employed [3]. Bioremediation processes explore the use of biological mechanisms to destroy, transform or immobilize environmental contaminants
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