Nitrogen dynamic in vitro using sludge of a sewage stabilization pond from Patagonia (Argentina).

A relevant and current aspect of wastewater treatment systems is related to the processes of the nitrogen cycle that results in its elimination in gaseous forms. In the present study, we report the first measurements of nitrate-reducing rate (NRR) at lab-scale, using the flow-through reactor technique with sludge of a sewage stabilization pond system located in Patagonia (Argentina). Sludge was collected from Inlet and Outlet areas, in winter and summer. The sludge was characterized by having high moisture content (>94%) and organic matter concentration greater than 37%. The nitrate reduction experimental dates fitted significantly to the Michaelis-Menten model, allowing the estimation of the parameters that regulate the NR kinetics. The maximum potential nitrate reduction rate (Rmax) showed great variability, registering a maximum of 131.6 µmol-N·gdw-1·h-1 (Outlet-Summer) and a minimum of 4.1 µmol-N·gdw-1·h-1 (Inlet-Winter). The lowest half saturation constant (Km) was recorded in the Inlet sludge during the winter (6.1 mg N-NO3-·L-1), which indicates a greater affinity for nitrate of this bacterial consortium. An unusually high activity of NR was registered, being higher with sludge from the Outlet zone and with summer temperature. In full-scale ponds, the NR activity could explain a relevant part of the nitrogen removal that involves the escape of gaseous forms.

Nutrient content in sludge profiles from a full-scale stabilization pond in a temperate location.

The inorganic nutrient concentrations in sludge profiles from a full-scale municipal facultative pond in Puerto Madryn City (Argentina) were measured. Sludge samples were collected with cores during autumn, winter, and summer at three sites: inlet, intermediate, and outlet. In general, the sludge accumulates NH4+ and PO4(3-), increasing their concentrations with depth. However, NH4+ presented a different behavior at the outlet station during the summer, when the lower concentrations were recorded. This finding reflects a nutrient release, originating in their greater demand from the water column. In the sludge, the NO3- followed the spatial and seasonal pattern recorded in the surface water: detectable concentrations in the warmer months at the outlet. The vertical reduction of NO3- could be an indication of denitrification. The study supported the hypothesis that the sludge can act as a nutrient trap or source, depending on factors such as the temperature, nutrients/oxygen concentration, mixing processes, and location.