An integrated constructed wetland to treat contaminants and nutrients from dairy farmyard dirty water

Abstract

Water pollution by agriculture can include inappropriately managed dairy farmyard dirty water. In Ireland, dairy farmyard dirty water includes farmyard runoff, parlour washings, and silage/farmyard manure effluents. The objectives of this study were to determine (i) the quality and quantity of dirty water generated at a farm-scale and (ii) the seasonal effectiveness of a constructed wetland to treat farmyard dirty water. The wetland system was 4800 m 2 in area and treated dirty water from a 42-cow organic dairy unit with an open yard area of 2031 m 2. Monthly dirty water inflow rate to the wetland ranged between 3.6 and 18.5 m 3 d −1. Farmyard dirty water accounted for 27% of hydrological inputs to the wetland, whereas rainfall on wetland, along with wetland bank inflows accounted for 45 and 28%, respectively. Farmyard dirty water quality and quantity did not vary with season. Yearly mass loads discharged to the wetland were 47 ± 10 kg yr −1 of soluble reactive phosphorus (SRP), 128 ± 35 kg yr −1 of NH 4 +, 5484 ± 1433 kg yr −1 of organic material as measured by five-day biological oxygen demand (BOD 5), and 1570 ± 465 kg yr −1 of total suspended solids (TSS). Phosphorus retention by the wetland varied with season (5–84%) with least amounts being retained during winter.