For the rapid granulation and enrichment of denitrifying phosphate accumulating organisms (DPAOs)

taking flocculent activated sludge and granular sludge stored at low temperature as inoculated sludge and synthetic water as treatment object

four groups of SBR were operated under constant hydraulic retention time (HRT) mode and alternating long/short HRT mode with different ratios. The impact of starvation under the alternating long/short HRT mode on DPAOs enrichment and granulation was explored. Results showed that the granular sludge under alternating long/short HRT mode had higher DPAOs proportion

better nitrogen and phosphorus removal capacity

better sedimentation capacity

and dense structure. The pollutant removal capacity of simultaneous nitrification-denitrification and phosphorus removal (SNDPR) particles was the best when the ratio of alternating long/short HRT mode was 12 h/6 h. The removal rates of COD

TN

and TP reached 93%

96%

and 98% in the long cycle

and 95%

90%

and 93% in the short cycle

which was mainly due to the comprehensive effect of anoxic zone formed in large size particles

the secretion of EPS under starvation

and the utilization of soluble microbial products (SMP) by denitrifying bacteria. When the ratio of HRT increased to 13.5 h/4.5 h

too high a level of SMP accumulation and too short anaerobic time led the effluent COD and TP concentrations to exceed the standard; when the ratio of HRT decreased to 10.5 h/7.5 h

the proportion of DPAOs decreased by 18%

and the TN removal rate of effluent also reduced

which indicated that 12 h/6 h was a reference value for the operation of alternating long/short HRT mode.