Use of Steel Slag to Reduce Phosphorus Loading in Animal Waste Handling Systems.

A bench-scale study examines the feasibility of using electric arc furnace (EAF) steel slag to remove phosphorus from animal waste effluent.  Dairies in Utah often have limited acreage close to the dairy.  Manures are typically separated and the effluent is used for irrigation and crop needs on the adjacent ground. As soil phosphorus levels climb with continued application, producers are facing the challenge of how to continue using the effluent for irrigation needs and nitrogen content, yet minimize the phosphorus application. Previous studies have indicated that EAF steel slag has good phosphorus binding properties in some municipal waste water systems.  Effluent from animal waste has more organic matter than in the municipal waste water studies.  It is unknown whether the organic matter will interfere with the phosphorus binding capacity of steel slag. This study examines the phosphorus removal capability of the EAF steel slag under four treatments (warm temperature, cold temperature, high organic matter content, control) with three replications.  Effluent is collected from a dairy monthly and three composite samples are collected from each batch of effluent. Effluent is released from reservoirs at a flow rate of 2.1-2.8 ml/min into treatment columns 15.2 cm in diameter and 30 cm in height.   Each column is filled with steel slag or gravel (control) to a height of approximately 22.86 cm allowing for a standard 12 hr retention time.  Effluent leaving the treatment column is collected after 1 day and then weekly for 16 weeks.  All samples are analyzed for pH and orthophosphorus to determine phosphorus removal from the effluent.