Formation of soluble microbial products and their contribution as electron donors for denitrification

- SMP serve as substitutive carbon source in biological wastewater treatment.
- Portions of BAP are biodegradable under famine and denitrification conditions.
- Considerable TN removal is attributed to SMP as electron donors.
- The existence of oxidation nitrogen can activate transformation from EPS to SMP.

Soluble microbial products (SMP) cause major soluble chemical oxygen demands (sCOD) in secondary effluent and significantly affect effluent quality. However, SMP can be also treated as new organic carbon resource, which can provide electrons for denitrification under anoxic conditions. This work investigated contribution of SMP as electron donors during denitrification under different conditions (feast, feast-famine, and famine). Only fraction of utilization-associated products could be adopted as electron donors for denitrification in feast condition because of sufficient organic carbon supply. Most biomass-associated products remained in water. In feast-famine condition, the nitrogen (nitrate and nitrite) reduction using influent TOC and SMP as electron donors were 86.4 and 55.2 mg N/L respectively. SMP accounted for 33.6% and 39.0% of total nitrogen (TN) removal and total nitrogen (nitrate and nitrite) reduction, respectively. Only SMP can be adopted as sole electron donors in famine condition. Approximately 128.7 mg N/L of nitrogen (nitrate and nitrite) reduction was calculated. Nitrate and TN removal were 91.4% and 51.7%, respectively. As electron acceptors under anoxic conditions, nitrate or nitrite can stimulate SMP generation from hydrolysis of extracellular polymeric substances.

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