The significance of slowly biodegradable COD on denitrification in the OAO process

The capacity of particulate organic matter to act as a carbon source for denitrification is a significant concern in wastewater treatment facilities. The biodegradability of particulate matter is essential to its applicability. This research aims to ascertain the role of particulate organic matter in denitrification by classifying COD, conducting pre and post denitrification tests, and analyzing the oxygen utilization rate (OUR) profile of respiration. A pilot plant was established and operated utilizing an Oxic-Anoxic-Oxic (OAO) system throughout four different loading stages, with unsettled raw wastewater as the influent. Following prolonged operation, the best removal efficiencies of OAO process for TCOD, BOD, TN, and NH₄⁺-N were 87.7 ± 5.3%, 90.1 ± 7.2%, 61.5 ± 7.3%, and 99.5 ± 0.2%, respectively. The COD classification of raw wastewater showed that readily biodegradable COD (RBCOD) makes up about 12.6% ± 3.8% of total COD (TCOD), while slowly biodegradable COD (SBCOD) makes up 45.6 ± 11.2% of TCOD. This could contribute to the explanation of the system's denitrification effectiveness. The post-specific denitrification rate was in the range of 0.32-0.70 mg NO₃^--N/gMLVSS.hr, which was higher than the endogenous denitrification. Furthermore, the observed re-increase in OUR tests explained the hydrolysis phenomena of SBCOD and demonstrated the viability of using adsorbed SBCOD as a carbon source for denitrification in the OAO process.