Nitrogen removal during summer and winter in a primary facultative waste stabilization pond: preliminary findings from ¹⁵N-labelled ammonium tracking techniques

Nitrogen removal mechanisms and pathways within WSP have been the focus of much research over the last 30 years. Debates and theories postulated continue to refine our knowledge regarding the cycling and removal pathways for this important nutrient, but a succinct answer has yet to be provided for holistic nitrogen removal. In this study, two experimental runs using labelled ¹⁵N as a stable isotope tracking technique were conducted on a pilot-scale primary facultative WSP in the UK; one in the summer of 2006, and the other in the winter of 2007. An ammonium chloride (¹⁵NH⁴Cl) spike was prepared as the slug for each experimental run, which also contained rhodamine WT to act as a dye tracer enabling the hydraulic characteristics of the pond to be mapped. Initial results from the study are reported here, and findings are compared and contrasted. Preliminary findings reveal that a greater proportion of ¹⁵N is incorporated into the algal biomass by assimilation and subsequent release as soluble organic nitrogen in summer than in winter. ¹⁵N ammonium passes out of the system much sooner and in a much higher proportion in the winter than in summer.