Tangential flow separation and chemical enhancement to recover swine manure solids, nutrients and metals

Abstract

A mobile unit of a tangential flow separator (TFS) system was installed at a swine farm. System performance was evaluated through tests conducted on 11 different occasions between February and August of 1997 with flushed wastes and lagoon liquid. The TFS unit consists of a lime slurry tank, a pre-floc mixing tank, a TFS tank, a thickening tank and associated pumps and flow meters with a processing capacity of 110 m 3/d. Previously screened wastes were mixed with lime in the pre-floc tank, ferric chloride and polymer injected into the flow after pre-floc tank, and flow introduced to the TFS tank tangentially to the wall, creating a circular motion within the tank. The fluid dynamics tends to concentrate solids to the center of the tank where they settle to the bottom. Approximately 75% of incoming flow are discharged at the top as treated effluent, with reduced organic and nutrient content, and flow to a storage lagoon. The settled solids that accumulate at the bottom of the TFS tank flow into a thickening tank of similar design to the main unit in order to further concentrate the solid material (up to 5% total solids). System performance expressed as percentage reduction is better when flushed wastes are processed compared to lagoon liquid. Total phosphorus (Total-P) removal can be higher than 90% depending on the amount of chemicals used. The system can remove an average of 22% total Kjeldahl nitrogen (TKN), 49% chemical oxygen demand (COD), 50% volatile solids (VS), 82% total suspended solids (TSS) and 87% copper (Cu) and zinc (Zn). Percentage reductions obtained with lagoon liquid are generally lower than with flushed wastes. However, the concentrations in effluent from the TFS system are lower for lagoon liquid than for flushed wastes. Typical concentrations of chemicals are about 2000 mg/l of hydrated lime, 400 mg/l of ferric chloride, and 20 mg/l of polymer. Chemical costs can be significant and must be balanced with improvements in effluent quality and potential economic value of sludge.