| A high performing wastewater treatment system at a bleached kraft pulp mill was evaluated to understand the efficiency of adsorbable organic halogen (AOX) removal. A hydraulic retention study was initially undertaken so that wastewater testing could follow the flow of wastewater through the system and evaluate removal across each unit process. AOX removal efficiency was compared to removal efficiency of other wastewater parameters, to operating conditions, and to other wastewater characteristics. It was found that AOX removal was occurring in all stages of the wastewater treatment system. In particular, removal in the primary clarifiers was very high (43%) and the activated sludge treatment process was performing at a very high level (70% removal). Neutralization using caustic, the return of waste activated sludge (WAS) to the front of the system, and the high sludge age are believed to be major factors in the systems performance. |
