ABSTRACT
Microalgal-bacterial consortia have important advantages over conventional activated sludge systems by achieving full nitrification and organic carbon oxidation without the need of external oxygen supply. This study assessed the different ammonium removal mechanisms and oxygen production of a microalgal-bacterial consortium at the different solids retention times (SRT) of 52, 48, 26 and 17 days treating synthetic wastewater. The ammonium removal efficiency exceeded 94%, while the total nitrogen removal efficiency was higher than 70% at the different SRTs applied. The main nitrogen removal mechanism was through nitrification/denitrification, followed by algal cell synthesis and bacterial nitrogen growth requirements. Shorter SRTs favoured the nitrification/denitrification processes over the assimilation of nitrogen by algae. The highest volumetric ammonium removal rate observed was 2.12 mgNH4+ -N L−1 h−1 at an SRT of 17 d. The total gross oxygen production at the different SRTs ranged between 0.2 and 0.3 kg O2 m−3 d−1, reaching highest production at a 52 d SRT. The differences in oxygen production between the different SRTs are attributed to the algal biomass content and light attenuation. The oxygen consumption decreased at shorter SRTs due to a decrease in the respiration of the microalgal-bacterial biomass. This study showed that the SRT is a key operational parameter that allows to control the nutrient removal processes and observed growth of the microalgal-bacterial consortia.
