The influence of hydraulic retention time (HRT

24

18

15 and 12 h) on the performance of double circle (DC) anaerobic reactor for treating traditional Chinese medicine wastewater was investigated. Additionally

the characteristics of granular sludge were studied

including particle size distribution (PSD)

extracellular polymeric substances (EPS)

and distribution of microbial communities. When HRT was reduced from 24 h to 12 h

the DC anaerobic reactor demonstrated good COD removal of 90%. Although concentration of acetate increased to 339.69 mg·L-1

the process was operating favorably without acidification. But humic acid-like and fulvic acid-like absorption peaks were stronger and coenzyme F420 absorption was weaker in the EEM spectra of soluble microbial products (SMP) at HRT 12 h. It was not recommended to further reduce HRT. The contents of EPS

protein

and polysaccharide decreased in the sludge at HRT 12 h

and tyrosine played an important role in maintaining stability of the sludge. The phospholipid fatty acids analysis showed that reducing HRT affected significantly distribution of microbial community in the second reaction area of the DC anaerobic reactor. Gram-positive bacteria decreased from 44.24% to 32.69%

while gram-negative bacteria increased from 32.69% to 38.66%.