Nutrient removal from activated sludge mixed liquor by wastewater protozoa in a laboratory scale batch reactor

The aim of the study was to investigate the nutrient removal rate of three wastewater protozoan isolates. The study was carried out in a laboratory-scale batch reactor for a period of 120 h. in a four batch study. Aliquot samples were withdrawn from the reactor every 24 h. for the analysis of phosphate, nitrate, nitrite, ammonia, chemical oxygen demand, dissolved oxygen and pH, using standard methods. The results obtained in the different batches among the three isolates showed PO₄^2- removal rate ranging from 0.04 to 0.52 mg-PO₄^2-/L/h. while NO₃^- nitrate removal rates ranged from 0.08 to 0.16 mg-NO₃^-/L /h. Also NO₂^- and NH₃^- rates were observed to range between 0.022 and 0.087 mg-NO₂^-/L /h. 0.05 and 0.16 mg-NH₃^-/L /h, respectively. For the physicochemical parameters, there was no observed COD decrease; rather there was an increase and this was irrespective of isolates and experimental batches. However, dissolved oxygen concentration decreased drastically (below 1 mg/L) at the end of each batch while pH show a decrease after an initial 24 h. period and thereafter increased. This trend was also irrespective of isolates and experimental batches. Overall, the study has been able to show the effect of the test isolates on nutrient removal rates and other physicochemical parameters (COD, DO and pH) in activated sludge mixed liquor.

Keywords
Phosphate, nitrite, nitrate, ammonia, chemical oxygen demand, dissolved oxygen