The objective of the present study was to use a test system for clustering and characterizing the bacterial populations in five wastewater infiltration systems ranging in size from 12 m2 to 1960 m2 (corresponding to the demand for 4-500 population equivalents). From each system two sand samples were taken and from each sample 88 bacterial isolates were collected. Every isolate was exposed to 52 physiological and biochemical tests. The resulting 880 objects × 52 variable data matrix was subjected to principal components analysis (PCA). After a variable reduction the PCA model revealed a scattered bacteria pattern (score plot) in parts of the sand filters expected to have high loading rates of wastewater, e.g. at the inlet of the filters. This indicates that a diverse bacterial population had developed in response to the carbon and energy source in the wastewater. In contrast to this pattern a more narrow bacteria pattern had developed in low loaded parts of the sand filter. The most important variables explaining the structure of the microbial biofilm at high wastewater load were the ability to ferment sugars and the capacity to sustain different pH levels. The potential to ammonify and grow on nutrient broth was also an important feature. In conclusion, the bacterial test system together with PCA seems to be a useful tool to evaluate the function of a bacterial sand-filter ecosystem.
- sand filter
- principal components analysis
- wastewater treatment
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