The effects of plant roots on microbial community structure in aerated wastewater-treatment reactors

Hydroponic reactors are aerated tanks on top of which emergent macrophytes are grown with their roots developing freely into the wastewater, thus providing a support medium for attached microbial growth. The community structures of biofilms derived from the roots of two macrophyte species, Typha domingensis and Cyperus alopcuroides, were compared. The macrophytes were grown, hydroponically, in reactors treating public kitchen wastewater. Tuff particles served as a control. Microbial community structure was determined through community level physiological profiling using BIOLOG Ecoplates. The experimental system consisted of six parallel treatment trains, each composed of four consecutive aerated tanks inhabited by one plant species or unplanted. Retention time was 80 h. Biofilm samples were taken from the first and last reactors of each treatment train. Water analyses were also conducted. Wastewater treatment removed 97.7, 98.6, 99.98 and 73.1% of BOD, TSS, coliforms and TN, respectively. Support-medium type had no significant effect on any of these parameters. Ordination analyses showed a significant effect of support-medium type, treatment stage and reactor age on the physiological profile of biofilms. The effect of support-medium type on community structure remained significant across different treatment stages and reactor ages. Richness of well response was higher in the first reactors than in the last ones. Differences in richness between support-medium types were minor.