Solids and Plant Nutrient Content, and Settling Characteristics of Milking Centre Wastewater on a Grazing Dairy

Abstract

Large milking centre wastewater samples were collected from a storage pit on a grazing dairy farm in South Carolina on two different days. The samples were analysed to determine the concentrations of the following constituents: TS, VS, TKN, TAN (NH4+-N, + NH3-N), Org-N, NO3-N, total-P, total-K, Ca, Mg, S, Zn, Cu, Mn, and Na. The large amount of waste milk present on the second day (TS =7165 mg/L) resulted in significantly reduced solids and plant nutrient concentrations as compared to the sample collected on the first day (TS = 17,024 mg/L). Gravity settling and thickening experiments were performed for the two milking centre waste samples. Gravity settling was effective at removing a fraction of all of the defined constituents. The greatest mass removals were for TS, VS, Org-N, P2O5, S, Cu, and Zn. The mass removal efficiency for the soluble constituents, TAN, K2O, and Na, was a consequence of the liquid contained in the layer of settled material and not a result of a change in concentration. The data provided in this study can be used for design of primary treatment for milking centre wastewater, development of nutrient management plans, and to provide loading data for secondary treatment of the supernatant or settled solids.