Natural　ventilation　trickling　filters　(NVTFs)　with　three　different　carriers　(sponge,　zeolite　and　ceramsite)　were　used　to　treat　domestic　wastewater.　All　NVTFs　with　different　biofilm　carriers　showed　stable　capability　of　COD　removal　and　ammonia　nitrification.　The　nitrification　rate　(NR),　oxygen　uptake　rate　(OUR),　dehydrogenase　enzyme　activity　(DHA)　of　biofilms　were　measured　to　investigate　microorganism　activity　and　polymerase　chain　reaction-denaturing　gradient　gel　electrophoresis　(PCR-DGGE)　analysis　was　conducted　to　investigate　the　microorganism　biodiversity.　It　was　found　that　greater　amount　of　biomass　was　attached　on　the　sponge　than　those　attached　on　ceramsite　and　zeolite,　due　to　the　large　specific　surface　area　of　sponge.　Large　biomass　may　decrease　the　biofilm　activity　in　the　NVTFs.　Compared　with　inoculated　sludge,　the　biofilm　in　NVTFs　had　more　abundant　biodiversity　after　long-time　domestication.　Major　DGGE　bands　of　NVTFs　were　phylogenetically　related　to　class　Proteobacteria　followed　by　Bacteroidetes,　Nitrospirae,　Cyanobacteria　and　Actinobacteria.　The　microorganism　distribution　in　biofilm　of　zeolite　NVTF　was　more　similar　with　ceramsite,　compared　with　sponge.　As　a　biofilm　carrier,　zeolite　showed　no　outstanding　superiority　on　pollutants　removal　or　nitrifying　bacteria　growing.　(c)　2015　Elsevier　B.V.　All　rights　reserved.