Analysis of environmental variables on population dynamic change of Haliscomenobacter hydrossis, the bulking causative filament in Macau wastewater treatment plant

Macau Peninsula wastewater treatment plant (WWTP) is experiencing filamentous bulking in recent years, which is caused by overgrowth of filamentous bacteria of Haliscomenobacter hydrossis, thus interfering the settling of activated sludge. Previous studies using molecular techniques have been widely used for identifying and quantifying the dominant filaments. However, the mechanisms caused by various environmental variables have not yet been completely understood to form the deterministic cause-effect relationship. In this study, principal component analysis (PCA) and generalized linear model (GLM) were used to analyze various environmental variables on the population dynamic changes of H. hydrossis identified and quantified as the dominant bulking causative filament using quantitative real-time PCR (qPCR). Our results showed that the qPCR was successful for identifying and quantifying the H. hydrossis. Correlation analysis indicated that ammonia nitrogen sources and sludge volume index (SVI) have strongly positive correlations with H. hydrossis. PCA can explain 75.21% of the variance from the total data in PC1-PC4 and GLM revealed a unimodal relationship between the overall H. hydrossis gene copies number and three environmental variables. Besides, the quadratic increases in the number of H. hydrossis copies were observed with the increasing gradient of SVI, TN, and NH3-N, suggesting that H. hydrossis played an important role in filamentous bulking of the WWTP.