Nutrient Content in Sludge Profiles from a Full-Scale Stabilization Pond in a Temperate Location
FALESCHINI, MAURICIO; ESTEVES, JOSÉ LUIS
WATER ENVIRONMENT RESEARCH
WATER ENVIRONMENT FEDERATION
Lugar: Virginia; Año: 2014
The inorganic nutrient concentrations in sludge profiles from a full-scale municipal facultative pond in Puerto Madryn City (Patagonia, Argentina) were measured. Sludge samples were collected using acrylic cores during the autumn, winter and summer at three sites: one near the entrance of the raw wastewater, one in the middle of the pond and one near the exit. In general, the sludge accumulates total NH4+ and PO43-, increasing their concentrations with depth. An exception was observed for NH4+ during the summer at the Outlet station, which had the lowest concentrations. This finding reflects a rapid nutrient release from the pond bottom, originating in the greater demand for NH4+ from the water column (maximum nitrification rate and phytoplankton development). This situation would establish a concentration gradient that supports NH4+ diffusion from sludge to the water column. The NO3- behaviour in the sludge followed the spatial and seasonal pattern recorded in the surface water: detectable concentrations in the warmer months at the Outlet station, with the maximal concentration found in the surface sludge layer. The vertical reduction of NO3- could be an indication of denitrification processes. The present study supported the hypothesis that the sludge in stabilisation ponds can act as a nutrient trap or sink, depending on such factors as the seasonality (directly related to temperature), nutrients/ oxygen concentration in the water column, intensity of the mixing processes and location within the pond. Benthic metabolism in sludge may play an important role in the control of nutrient concentration in the water column.