Composition and Settling Characteristics of Milking Center Wastewater: A Case Study

Abstract

Milking center wastes are often included with manure from the animal housing areas for treatment, storage, and land application. On a grazing dairy, milking center wastewater is often handled independent of other manure generated on farm. Very little data are available on the composition and settling characteristics of milking center wastewater. Large milking center wastewater samples were collected from a storage pit on a grazing dairy farm in South Carolina on two different days. The samples were analyzed 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 day 2 resulted in significantly higher dry basis concentrations for most constituents than on day 1. In particular, the waste milk introduced 217% more Na, 75% more Ca, and 51% more P. Gravity settling and thickening experiments were performed for the two milking center waste samples (7165 and 17,024 mgTS/L). 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 volume fractionalization and not a change in concentration.