Effect of mechanical elutriation on carbon source recovery from primary sludge in a novel activated primary tank

A novel activated primary tank (APT) with an elutriation unit was developed for recovering carbon by the fermentation and elutriation of primary sludge, and the mechanical elutriation mechanism was analysed by conducting a batch fermentation experiment to improve carbon source recovery. The results indicated that a high stirring velocity gradient could cause sludge disintegration, which could not only shorten the fermentation time, but also increase the production of soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) by 8.3% and 9.5%, respectively. Moreover, mechanical elutriation could also promote the release of SCOD from sludge to water, resulting in an increase in the yield of SCOD by 9.2%, it was observed that elutriation intensity plays a more important role than the elutriation time. The microbial community structure of the fermentation system was influenced by the stirring intensity. The relative abundance of fermentative bacteria in the reactor with a stirring intensity (G) of 160 s⁻¹ was 13.8%, which was significantly higher than that in the reactor with G = 31 s⁻¹ (8.037%), so the accumulation of VFAs and SCOD in the reactor with G = 160 s⁻¹ was improved.