Pasture-Based Dairy and Water Hyacinth (Eichornia Crassipes) for Reduced Biological Oxygen Demand in Dairy Discharge Water

Abstract

Degradation of surface water quality through point and non-point source pollution is a major problem worldwide. Elevated biological oxygen demand (BOD5) in a waterbody results in the depletion of dissolved oxygen and subsequently adversely impacts on aquatic life. Discharge water from a dairy facility is enriched with oxygen-demanding substances such as total nitrogen (TN), total phosphorus (TP) or organic carbon, and has elevated BOD5. Therefore, it is important to have a sufficiently reduced BOD5 concentration in dairy discharge water prior to discharging it to the natural streams or waterways. The authors compared BOD5 in discharge water from confined dairy and pasture-based dairy, and assessed the effectiveness of the water hyacinth (Eichornia crassipes) for BOD5 reduction in dairy discharge water at UL Lafayette Research Farm in Cade, Louisiana. The dairy wastewater treatment system consisted of a first anaerobic lagoon and a second facultative lagoon. From 1985 to 2005, water samples were collected at least once a month by the grab method at the outlet of the facultative lagoon. These were analysed for BOD5, total suspended solids (TSS) and pH as per the compliance requirements of the Louisiana Department of Environmental Quality. In 2003, the second pond was divided into two halves and water hyacinths were introduced into one half of the pond. Water samples were collected for one year in seven sampling events by the grab method from the following four locations: inlet and outlet of the first pond, and each outlet of the divided second pond. Water samples were analysed in the lab for BOD5, TSS, total combustible solids (TCS), TN, nitrate/nitrite-N (NO3/NO2-N) and TP; while pH and temperature were determined in the field. Wastewater inflow data and dairy herd data were obtained from the records. The average BOD5 concentration of discharge water from pasture-based dairy was 28% lower compared with the confined dairy. Water hyacinths reduced BOD5 concentration by 30.2%, TN by 44% and TP by 19.4% compared with the pond without water hyacinths. Pasture-based dairy and the introduction of water hyacinths in the dairy wastewater treatment system show the potential for reducing BOD5 and oxygen-demanding substances, as well as minimizing surface water pollution and related environmental degradation from a dairy operation.