Soil Nutrient Load and Drain Water Quality in Seepage Fields Receiving Milk House Wastewater

Abstract

The large volume of wastewater generated on dairy farms from the cleaning of milk pipelines and milking equipment contains nutrients and microorganisms that could pollute waterways if discharged without treatment. The objective of this study was to evaluate a modified septic tank-seepage field system for disposing of milk house wastewater, by measuring the accumulation of nutrients in the soil and monitoring the water drained from the seepage field. The study was conducted on two small dairy farms (40–50 milking cows) in south-west Quebec, Canada. After passing through a sediment and milk fat trap and then the septic tank, the milk house wastewater was drained into a 0.45 ha experimental seepage field under pasture or arable cropped land. Much larger than a conventional seepage bed (0.025 ha), the experimental seepage field was designed to remain recycle the wastewater nutrients and water, while preventing soil saturation. Annual nutrient loading from milk house wastewaters were, on average, 60 kg total N ha−1, 50 kg total P ha−1 and 80 kg total K ha−1. The concentrations of plant-available nutrients increased when milk house wastewater entered the seepage field, but the magnitude of change was farm-specific, due to the unique topography and soil characteristics offered by each farm. For instance, the P concentration was unchanged on one farm, but there was rapid and significant accumulation of P in the 20–60 cm depth of the soil profile on the second farm. There was an increase in Ca and Mg concentrations in the soil profile on both farms, but soil salinity remained <4 dS m−1 during this study. Water drained from the experimental seepage fields was similar in quality to that drained from a control area, indicating that the seepage fields were sufficiently large to adsorb and treat the nutrients contained in milk house wastewater in the short-term. Assessment of the cation and anion adsorption capacity of soils on these farms will be necessary to verify the treatment capacity and effective lifespan of the seepage fields.