Changes in Settling Characteristics and Fate of Solids in Dairy Manure Using Anaerobic Digestion, Mechanical Liquid-Solid Separation, and Electrocoagulation

Abstract

Manure from an 1,100 dairy in Weber County, Utah was treated first through anaerobic digestion in an Induced Blanket Reactor (IBR). Then the effluent passed through either a screw press separator or a two-stage dewaterer, to remove additional solids. On a laboratory scale, samples were also treated with an electrocoagulation (EC) unit to evaluate the potential for its use in a farm setting. Manure was taken between each unit operation and placed into a settling column seven feet high and twelve inches in diameter. Samples were taken from the column at time 0, 0.5, 1, 2, 4,8, 12, and 24 hours at depths 0, 1, 3, 5, and 6 ft (One foot of headspace was left in the top of the column to allow for mixing at time=0). Total solids (TS), volatile solids (VS), suspended solids (SS), and total suspended volatile solids (SVS) were determined for each depth at each time interval. Solids in the influent manure did not settle. Anaerobic stabilization removed 36% and 44% of the TS and VS respectively. The screw press removed 6% of the remaining TS. Use of a two-stage dewaterer was more effective, removing 38% of the TS. Two levels of EC treatment resulted in 78% and 89% removal of TS and VS respectively for the lower treatment, and 85% and 94% of the TS and VS respectively for the higher treatment level. The treatment system removed 87-91% of the TS and 95-97% of the VS depending on the level of treatment by electrocoagulation.