Nutrient uptake in activated sludge mixed liquor: A case study of two protozoa in a laboratory-scale reactor

Wastewater effluents are major contributors to the eutrophication of water bodies. This study was aimed at investigating the role of two protozoa (Trachelophyllum and Peranema) in the removal of phosphate and nitrogen compounds from activated sludge mixed liquor. The study was carried out in a laboratory-scale batch reactor that was operated over four batches under aerobic conditions. During each experimental batch, which ran for 120 h, aliquot samples were removed from the reactor for the analysis of phosphate, nitrate, ammonia, nitrite and chemical oxygen demand (COD), using standard methods. The results revealed simultaneous phosphate and nitrogen removal in presence of the two isolates. In the presence of Trachelophyllum and Peranema, phosphate concentrations were observed to decrease from an initial range of 53.90–57.83 to a final range of 6.89–34.87 mg/L and from an initial range of 54.29–58.58 mg/L to a final range of 17.77–53.12 mg/L, respectively. Similarly, nitrate concentrations decreased from initial ranges of 12.82–14.69 mg/L and 12.79–13.79 mg/L to final ranges of 0.52–4.32 mg/L and 0.05–1.59 mg/L in the presence of Trachelophyllum sp and Peranema sp, respectively. Although remarkable nitrogen removal was observed during the different experimental batches, phosphate removal was only observed to be remarkable during the first two batches. Also, the COD concentration in mixed liquor was observed to show a steady increase with time. This was irrespective of experimental batch and isolate used. The result of the study will help to understand and explain more of the observations made in microbial life in wastewater treatment systems. The knowledge of this will help in evaluating the possibility of creating enabling environment for the proliferation of the test isolates in wastewater treatment systems.