Enhanced biological nutrient removal in a simultaneous fermentation, denitrification and phosphate removal reactor using primary sludge as internal carbon source

The production of volatile fatty acids (VFAs) from primary sludge and the subsequent application to improve biological nutrient removal has drawn much attention. In this study, a novel approach of using primary sludge as an additional carbon source was conducted in batch tests. The nitritation effluent was directly injected into the sludge fermentation reactor to achieve nitrogen removal. Complete denitrification could be realized in the combined reactor. Moreover, injecting nitrite not only promoted the sludge stabilization process, but also reduced the release of phosphate and ammonium during sludge stabilization. The novel process was further evaluated in a continuous system by treating sludge dewatering liquors. Under optimum conditions, 85% removal of ammonium and 75% of total nitrogen could be obtained using primary sludge, resulting in the suitable effluent for recycling into the inlet of the wastewater treatment plant.

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► Fermentation, denitrification and phosphorus removal were achieved simultaneously.
► Injecting nitrite into fermentation phase promoted the sludge degradation process.
► Nutrients released during sludge fermentation were significantly reduced.
► Nitrogen removal was enhanced using primary sludge as the external carbon source.