Evaluation of in-situ sludge reduction and enhanced nutrient removal in an integrated repeatedly coupling aerobic and anaerobic and oxic-setting-anaerobic system

Aiming to achieve simultaneous good performances of in-situ sludge reduction and effluent quality, an integrated repeatedly coupling aerobic and anaerobic and oxic-setting-anaerobic system (rCAA+OSA) is developed to reduce sludge production and enhance nutrient removal. Considering the mechanism of in-situ sludge reduction in this rCAA+OSA system, the combined effect of energy uncoupling metabolism and sludge cryptic growth maybe attributed to the higher reduction of biomass. Results show that the maximal sludge reduction in this rCAA+OSA system is obtained when the hydraulic retention time (HRT)is controlled at 6.5 h, which an increase in 16.67% reduction in excess sludge is achieved compared with OSA system (HRT of 6.5 h). When compared the performances of effluent qualities, the enhanced nutrient removal efficiencies also can be observed in this rCAA+OSA system. Three-dimensional excitation emission matrix (3D-EEM) fluorescence spectroscopy is applied to characterize the effluent organic matters (EfOM) under different HRTs in the OSA and the rCAA+OSA systems. Analyses of 3D-EEM spectra show that more refractory humic-like and fulvic-like components are observed in the effluent of the OSA system. On the basis of these results, simultaneous enhanced in-situ sludge reduction and improved nutrient removal can be obtained in the rCAA+OSA systems.