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Primary Sludge Fermentation: A Sustainable and Economic Process of Supplementing Carbon for Short Cut Nitrogen Removal Open Access

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This study evaluates the selection for partial denitrification (PdN, NO3 NO2) and coupling with anammox as an alternative route of achieving short-cut nitrogen removal at Blue Plains advanced wastewater treatment plant. The use of primary sludge fermentate was evaluated as a cheaper and viable option of providing soluble chemical oxygen demand (sCOD) as well as volatile fatty acids (VFA) for PdN control. The overall objective of this research was to explore the solids retention time (SRT) conditions needed to reach required sCOD and VFA yields as well as the concurrent nutrient release during fermentation. Batch fermentation tests showed yield in g sCOD per gram volatile suspended solids (VSS) increased until a 2 day SRT, but then it flattened out, demonstrating that there is no need to go any further in terms of SRT. The increase in orthophosphate, OP-P (mg P/L) with SRT followed a linear trend, whereas the increase in ammonia, NH4 (mg NH4-N/L) had a higher rate of increase at longer SRT. Therefore, 2 day SRT should be sufficient to provide a reasonably high yield without sending excess nutrients back to the mainstream system at least for the spring-summer period. Proof of principle with mainstream pilot showed that a sCOD:N:P ratio of fermentate of 100:1.7:1 is suitable to provide sufficient sCOD to drive PdN, without posing detrimental effect on the effluent quality in terms of NH4-N and OP-P. Overall, significant cost saving for nitrogen removal were proven without any nitrite oxidizing bacteria (NOB) out-selection using simple PdN approach coupled with anammox.

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