Seasonal efficiency of a hybrid sub-surface flow constructed wetland system in treating milking parlor wastewater at northern Hokkaido

This paper presents the effects of seasonal variations on the purification and removal efficiencies of a hybrid sub-surface CW system (VF-VF-HF) treating milking parlor wastewater at northern Hokkaido, Japan. VF(a) and VF(b) are gravel beds, each 160 m2 in size whereas HF is sand bed and 336 m2 in size. Daily mean air temperature at site showed a difference of 16 °C between warm (May–October) and cold (November–April) periods. Average influent concentrations for cold and warm periods were: CODCr: 3749 and 4988 mg L−1; BOD5: 1637 and 1395 mg L−1; TSS: 661 and 862 mg L−1; TN: 161 and 194 mg L−1; TP: 23.9 and 31.9 mg L−1 and total carbon: 1212 and 1715 mg L−1. Average purification rates of BOD5, TSS, TP, PO4–P and total carbon fluctuated <2.5% between both periods. However purification rates of NH4–N and Organic-P decreased by 9.5% and 12% respectively during warm period. Average removal rates of TSS and BOD5 were unaffected between both periods, while that of CODCr, TN, total carbon increased by 3–4% during warm period. Hybrid sub-surface CW system achieved purification and removal rates of >95% for TSS and total coliform; >89% for CODCr and BOD5; >76% for TN and >72% for TP during both cold and warm periods.

► A hybrid CW consisting vertical and horizontal beds was operated for milking parlor wastewater treatment. ► We assessed seasonal variations in treatment efficiency of hybrid CW. ► Hybrid CW achieved removal rates of >95% for TSS, >89% for BOD5, >76% for TN during cold and warm periods. ► Hybrid CW can treat wastewater under adverse conditions i.e., heavy snow, high inflow etc.