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

A real scale hybrid constructed wetland (CW) system (656 m(2)), 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 m(3)d(-1) of high strength milking parlor wastewater under colder climate. Annual mean air temperature at site was recorded as 6.4 degrees C (extremes vary as -22.8 degrees C at lowest and 30.6 degrees C at highest). From the monthly sampling from November 2006 to January 2010, average loading and removal rates of TSS, CODcr, 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.