The effects of hydraulic and organic loadings on the performance of a full-scale facultative pond in a temperate climate region (Argentine Patagonia)

Abstract

This work focuses on the performance of a primary facultative pond, in a full-scale waste stabilization pond system, located in a temperate climate region (average air temperature in winter, 7.7°C; spring and autumn, 14.0°C; and summer, 19.9°C) in Puerto Madryn city - Argentine Patagonia (42°45'S; 65°05;W). Experimental work was conducted for 43 months in seven sampling points. During the experimental time frame, the influent flow rate increased from 12,000 to 15,500 m 3/day; the surface organic loading ranged from 55 to 68 kg BOD 5/ha·day and the theoretical retention time decreased from 31 to 24 days. The results indicate that a primary facultative pond performing in this region, to keep predominant facultative conditions and acceptable filtered biochemical oxygen demand (BOD 5) removal, should be loaded with an organic loading rate of up to 60 kg BOD 5/ha·day. The flow and organic loading increase affected the ammonium removal process, extending the period time in which ammonium removal was less than 50% and nitrate was not detectable; at first, this period occurred during winter strictly and then covered part of autumn and part of spring, too. Ammonium removal was clearly temperature dependent and directly related to chlorophyll a and nitrate concentrations (i.e. higher ammonia removals were reported under summer conditions when chlorophyll a and nitrate concentrations were higher), but was not linked with high pH values. The ammonium volatilization as a predominant removal process could be discarded, while ammonium nitrification-denitrification and algal nitrogen uptake seems to be the dominant mechanisms.