Efforts to Predict BOD for Process Control, 2003 Environmental Conference Proceedings

For many mills, reliable compliance with both BOD₅ and nutrient discharge limits would be greatly aided by a realtime surrogate that would dependably signal significant shifts in BOD₅ loading. For mills addressing water quality based BOD₅ discharge limits that vary directly with flow or other conditions of the receiving water, reliable compliance with the varying BOD₅ discharge limit would also be greatly aided by a real-time surrogate that would dependably predict the final effluent BOD₅ concentration. If future limits for both nutrient and BOD₅ discharges are generally lowered, the feasibility of reliably adjusting the biological treatment process to variations in inlet loading is placed at greater risk, as is the feasibility of reliably generating an effluent with a realistic safety factor below water-quality-based BOD₅ limits.

Seven tests of possible BOD₅ surrogates have been conducted in recent years at mills. For the normal working range of conditions, reasonable correlations were identified in a few cases. But no surrogate measurements have been identified that reliably alert operators in a timely manner to adjust to normal loading changes. Even for large BOD changes and reasonable overall correlations, surrogate performance could not be considered reliable from a process risk management perspective.