Impact and Control of Elevated Organic Acid Loadings on a Marginally Sized Activated Sludge Plant, 2002 Environmental Conference Proceedings

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The wastewater treatment plant (WWTP) at Mead Paper in Rumford, Maine has historically struggled with sludge bulking episodes. Recent mill changes, including the conversion to elemental chlorine free (ECF) bleaching and alkaline papermaking, exacerbated the problem. Microscopic examinations revealed that organic acids were the primary cause of bulking. This manifested itself mostly in the form of globular zoogleal bulking.

This paper discusses the successful development and implementation of the mill’s organic acid control program, and its impact on the activated sludge system. Testing throughout the mill indicated that roughly half of the organic acid loading was being generated in the primary clarifier. Various changes involving the primary clarifier were made based on this information. These changes included the discontinuance of co-settling, careful control of the clarifier sludge blanket, optimization of mechanical integrity, and bleaching of the sludge blanket.

The implementation of these modifications has decreased organic acid generation in the primary clarifier, and has led to a reduction in globular zooglea levels in the mixed liquor. The result is a much more stable, manageable secondary treatment system that is able to tolerate higher levels of filamentous organisms, while needing appreciably less sodium hypochlorite addition to the return activated sludge (RAS) for filament control.