Nitrification performance for secondary effluent from MWTP using bio-zeolite constructed wetland

The bio-zeolite constructed wetland (CW) pilot plant receiving a real secondary effluent of the municipal wastewater treatment plant(WWTP) was set up. The performance of bio-zeolite CW enhancing the nitrification of the WWTP secondary effluent and the effect of temperature on nitrification rate were explored during 273 days. The results indicated that the N ${\mathrm{H}}_4^{+}$ from secondary effluent was removed rapidly and effectively. Average removal rate of N ${\mathrm{H}}_4^{+}$ was 90.5% and the concentration of N ${\mathrm{H}}_4^{+}$ in the effluent was lower than 0.5 mg/L in the normal operation phase. After a short recovery period of 12 days, the average removal rate of N ${\mathrm{H}}_4^{+}$ was higher than 70%. The average removal rate of N ${\mathrm{H}}_4^{+}$ still remained at a relative high level as 67.6% in the low temperature stage (below 13 ℃). The temperature had signi?cant impact on the nitrification, and the average nitrification rate increased from 28% to 62% as the water temperature rose slowly from below 15 ℃ to above 25 ℃ in bio-zeolite CW. No obvious accumulation of nitrite nitrogen was found in the effluent of bio-zeolite CW except the low temperature stage, and the average concentration of nitrite nitrogen in the effluent was 0.16 mg/L. N ${\mathrm{H}}_4^{+}$ was mainly nitrified by microorganisms and transformed into nitrate.