Potential of hybrid constructed wetland system in treating milking parlor wastewater under cold climatic conditions in northern Hokkaido, Japan

A real scale hybrid constructed wetland (CW) system (656 m²), with a configuration of VFA-VFB-HF beds constructed in series is operating since November 2006 in northern Hokkaido, Japan. The system was experimented to assess its capability in purifying 4.5 m³d⁻¹ of high strength milking parlor wastewater under colder climate. Annual mean air temperature at site was recorded as 6.4 ^oC (extremes vary as -22.8 ^oC at lowest and 30.6 ^oC at highest). From the monthly sampling from November 2006 to January 2010, average loading and removal rates of TSS, COD_cr, BOD₅, TN and TP were 5.4 g m⁻² d⁻¹ (98%), 30.3 g m⁻² d⁻¹ (88%), 11.5 g m ² d⁻¹ (89%), 1.2 g m⁻² d⁻¹ (76.4%) and 0.2 g m⁻² d⁻¹ (76%). System did not stop for a single day, efficiently worked even during snow covered periods and was tolerant to the load fluctuations.