R2 (Figure ) showed slight temporal changes in microbial communities, with relatively low dissimilarity values ranging from 0.20 to 0.27 between samples taken from the same reactor positions over time. However, R2 displayed moderate spatial variation, with certain reactor positions maintaining different microbial communities. Shifts in composition between reactor positions were gradual, showing moderate dissimilarity values between the top, middle, and bottom sections on the same day, ranging from 0.17 to 0.54 on day 79 and from 0.12 to 0.33 on day 112. This gradual shift suggests a combination of stable and adaptive microbial structures within R2, where some positions show higher diversity while others maintain more consistent community compositions. The observed dissimilarity in R2 microbial communities, especially between the bottom and sump positions, may be due to the variations in nutrient concentrations and biofilm structure. These differences likely drove different adaptations in microbial composition, resulting in moderate spatial variation despite stable overall conditions in the reactor.