The Effects of Different Substrates on Ammonium Removal in Constructed Wetlands: A Comparison of Their Physicochemical Characteristics and Ammonium-Oxidizing Prokaryotic Communities

A vertical flow constructed wetland (VFCW) filled with natural zeolite had higher ammonium removal (82.4-94.0%) than another VFCW filled with volcanic rock (51.3-69.4%) treating piggery wastewater under any of three recirculation ratios. To reveal the underling reasons, physicochemical characteristics and ammonium-oxidizing prokaryotes (AOPs) of two substrates were determined. The calculated maximum ammonium adsorption of zeolite (11.6mg g(-1)) was remarkably higher than that of volcanic rock (0.21mg g(-1)), mainly because the former contains two cationic binding crystalline species, AlSi3O8- and montmorillonite. Quantitative analyses indicated that ammonium-oxidizing archaea (AOA) are the dominant AOP of zeolite and ammonium-oxidizing bacteria (AOB) are the dominant AOP of volcanic rock respectively. Diversity and phylogenetic analysis further showed that both AOB and AOA communities were significantly different between two substrates. Nitrosospira-like AOB (92.6%) and sediment/soil clade AOA (71.4%) were the main components of AOB and AOA in natural zeolite, whereas Nitrosomonas-like AOB (76.1%) and water/sediment clade AOA (77.1%) dominated the AOB and AOA in volcanic rock. These results suggest that the substrates show high selectivity to AOP community. Thus, in addition to physicochemical characteristics, the AOP of substrates is very likely to affect ammonium removal in VFCWs.