ABSTRACT

Respirometric tests (RT) are a common tool for assessment of microbiological processes in wastewater. Respirometric tests were used in this chapter on microalgal bacterial biomass previously cultivated in a flat panel photobioreactor. The RTs were performed successfully showing a high ammonium removal by algal uptake, reaching up to 60% of the total ammonium removed. The removal of ammonium by algae was identified to have a higher rate than nitrification mainly due to the ammonium storage capacity of the microalgae. The storage of nitrogen (ammonium) by microalgae was modelled by adapting the model presented in Chapter 6, including two new processes: (i) nitrogen algal uptake and (ii) phototrophic growth on stored nitrogen. The model was calibrated for ammonium, nitrite, nitrate and oxygen concentrations resulting in small errors (indexes of agreement exceeding 0.8). The maximum nitrogen stored was 0.3 g Nsto gVSS−1 of algal biomass, while the maximum specific phototrophic growth was 3.5 and 1.2 d−1 for the growth on extracellular nitrogen and the growth on stored nitrogen, respectively. The maximum growth of ammonium oxidising bacteria and nitrite oxidising bacteria was 0.50 and 0.76 d−1, respectively.