Organic Carbon and Nitrogen Removal in Attached-Growth Circulating Reactor (AGCR)

Abstract
Experiments on attached-growth circulating reactor (AGCR) were conducted to investigate its efficiencies on organic carbon and nitrogen removal (through denitrification). A laboratory-scale AGCR, made of serpentine channel with a total length of 180.0 m, was fed with a synthetic wastewater at the chemical oxygen demand (COD) and total nitrogen (TN) loading rates of 3.56-10.16 and 0.30 - 0.91 g/(m2.d), respectively. The reactor effluent was recycled back to the influent feeding point and the dissolved oxygen (DO) concentrations along the channel length were controlled by means of air diffusion. It was found that the COD loading rate of 5 g/(m2. d) corresponding to the TN loading rate of 0.54 g/(m2.d) gave the optimal COD and TN removal rates of 4.8 and 0.43 g/(m2.d), respectively. The overall AGCR performance was limited by the nitrification efficiency at the high TN loading rates. The biofilm accumulation and thickness were found to be relatively high in the first-half portion of the channel length where carbon oxidation and denitrification were predominant. The second-half portion where nitrification mainly occurred had much less biofilm accumulation and thickness.

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