Long-Term Effects of Milking Centre Wastewater Application on Soil and Groundwater Quality

Abstract

If not managed properly, wastewater generated from milkroom cleaning activities on dairy farms may pose a risk to water resources. Vegetated infiltration areas have been recommended as a possible treatment/disposal method for milking centre wastewater. However, the long-term (> 20 years) ability of soil infiltration systems to treat milking centre wastewater constituents requires examination. In this study, groundwater and soil beneath a wastewater infiltration area that had received milking centre wastewater for approximately 30 years was characterized through the drilling and installation of shallow groundwater monitoring wells. The distribution of wastewater constituents within the soil profile was assessed through the collection and analysis of soil cores. Groundwater samples were collected over a six-month period from wells located within the treatment area and compared to background water quality data. The wastewater from the milkroom contained high concentrations of total phosphorus (TP > 100 mg L−1), chloride (Cl) and sulphate (SO4) and possessed a large biochemical oxygen demand (BOD5 > 1000 mg L−1). Compared to background conditions, a significant increase (p < 0.05) in groundwater concentrations of all major ions except phosphate was observed. However, the only wastewater constituent that had increased to levels exceeding aesthetic drinking water criteria was Cl. The majority of applied P was retained within the top 1 m of the soil profile. The Langmuir model was used to estimate P-adsorption maxima (Xmax) from batch experiments. Soils within the treatment area exhibited lower P-adsorption maxima than background soils that had not received wastewater, possibly due to competition with organic anions. Oxalate-extractable aluminum (Al) was a significant predictor of P-adsorption maxima (R2 = 0.804). Results from this study have indicated that soil infiltration systems have the ability to provide long-term treatment of milking centre wastewater.