Performance of aerobic granular sludge in a sequencing batch bioreactor for slaughterhouse wastewater treatment

• Biological nutrient removal was positive correlated to sludge granulation.
• The external feature of granular sludge was studied by 3D-EEM and EPS.
• Particle size distribution showed the superior size for AOB and NOB growth.
• The SOUR was used to analyze the activity of AOB and NOB.

Lab-scale experiment was conducted to investigate the formation and characteristics of aerobic granular sludge for biological nutrient removal of slaughterhouse wastewater. Experimental results showed that removal performances of chemical oxygen demand (COD), ammonia and phosphate were enhanced with sludge granulation, and their removal efficiencies reached 95.1%, 99.3% and 83.5%, respectively. The aerobic granular sludge was matured after 90 days cultivation, and protein-like substances were the main components. Simultaneously, the mass ratio of proteins and polysaccharides (PN/PS) was enhanced to 2.5 from 1.7. The granules with particle sizes of 0.6–1.2 and 1.2–1.8 mm, accounting for 69.6%, were benefit for the growth of ammonia oxidizing bacteria (AOB) and nitrate oxidizing bacteria (NOB), and corresponding specific oxygen demand rates (SOUR) of AOB and NOB were 31.4 and 23.3 mgO2/gMLSS h, respectively.