The COD was measured using the potassium dichromate method, i.e., the alkaline potassium persulfate digestion-UV spectrophotometric method; NH3eN was measured using Nessler's reagent colorimetric method; NO2eN using the spectrophotometric method and the phenol disulfonic acid spectrophotometric method; TP using the ammonium molybdate spectrophotometric method; Suspended solids (SS) the gravimetric method; pH the electrode method; and the dissolved
oxygen (DO) immediately measured using a YSL 5000 DO meter after on-site sampling. The number of nitrifying bacteria in the constructed wetland substrates was measured using the FISH method; and the number of denitrifying bacteria was measured using MPN method