Using headspace gas monitoring to determine available carbon source (sodium acetate) in a biological nutrient removal process

A utilizable carbonaceous substance is essential in the biological nutrient removal (BNR) of wastewater treatment, for denitrification and phosphorus removal. Accurate and prompt determination of these available carbon sources in each BNR stage is beneficial for operating control and process optimization. A new method and apparatus were developed using the carbon dioxide (CO 2 ) detected in the headspace of a batch reactor, to estimate the carbon source available in the BNR process. Experimental results showed that detectable changes of CO 2 concentration in the headspace reflected the sodium acetate utilization in the anaerobic and anoxic conditions, i.e., the P release and denitrification reactions. A series of clean water and activated sludge sample tests also verified that the headspace CO 2 profiles were induced by the carbon utilization in BNR reactions. In the CO 2 profiles of activated sludge sample with carbon source addition, the elapsed time (E Time) of CO 2 evolution changes, during BNR reactions, was found proportional to the initial amount of carbon source added in solution. The E Time was also inversely proportional to the sludge concentration or the mixed liquor volatile suspended solids (MLVSS), at a constant carbon source addition. Results suggested that this E Time approach, using the headspace CO 2 information, is capable of on-line determining the carbon source available in BNR reactions, as well as monitoring system performance.