design: For microbial community analysis, 60 granular samples (4 granules for each diameter size multiply by 4 sizes and 3 height, with the addition of 4 total granular samples for each height) were subjected to DNA isolation by using FastDNA SPIN Kit for Soil (MP Biomedical, USA) according to the manufacturers protocol. Amplification of the V4 region of 16S rRNA gene was performed using the primer sets ArBa515F (5- GTGCCAGCMGCCGCGGTAA-3) and ArBa808R (5- GGACTACHVGGGTWTCTAAT -3).