The Medium- and Long-Term Mass Balance in the Multi-Stage Constructed Wetland Treating Milking Parlor Wastewater and the Effect of Vegetation

Abstract

　In this research work, the medium- and long-term mass balance in the multi-stage constructed wetland （MS－CW） treating milking parlor wastewater was estimated and the effect of vegetation on the sediment formation and mass balances for carbon, nitrogen and phosphorus were elucidated. The sediment formation for BOD removed at 1st filtration bed where the raw wastewater received was 1069 cm³/kg－BOD, while the sediment formation for SS removed was 1430 cm³/kg－SS. The increment of the sediment formation by the vegetation for the BOD was negligible and for the SS was around 20%. The residual organic matter per BOD removed in the MS－CW was 0.057 kg－VSS/kg－BOD and its increment due to vegetation was 40%. The loss ratio of nitrogen removed in the MS－CW was approximately 75%, resulting in 25% of nitrogen retention and its increment by the vegetation reached 55%. On the other hand, the phosphorus retention ratio in the MS－CW was approximately 50% and it was not affected by the vegetation. The estimated discharge load increased 20% considering transpiration and precipitation amount, however, the removal efficiency and residual ratio almost did not vary because of much higher removal load compared to discharge load.