Electro-Coagulation of Meat Processing Wastewater

Blood wastewater is a significant by-product of the meat processing industry with a solids concentration of 7% and 13% by weight. The blood is typically collected and steam coagulated at rendering facilities before dewatering. It is then either dried separately to produce bloodmeal or rendered with meat and bone to produce meat and bone meal. However, steam coagulation typically requires 200-250 kg of steam per tonne of blood, which can represent a problem if the rendering facility has insufficient steam capacity. A potential alternative is electro-coagulation. Electro-coagulation uses metal electrodes submerged in the wastewater to pass a current through the water, which results in the dissolution of metal at the anode. The metal ions that are liberated then coagulate the dissolved solids. A laboratory scale study was undertaken to examine the treatment performance, electrode requirements and configuration and costs associated with this treatment option for comparison with steam coagulation. Bench top prototype units were built consisting of up to nine pairs of aluminium electrodes submerged in a vessel operated in batch and continuous modes. These units were trialled examining the effect of voltage, electrode type and area, blood concentration, pH and flowrate on solids removal, foaming, amount of electrode consumed, and power consumption. Foaming was significant resulting in a foam with the similar water content to the blood wastewater, and needed dewatering. The electro-coagulation prototype combined with dewatering achieved solids removal rates up to 58% after 2 hours of treatment. The aluminium electrode consumption rate was 0.01 g/amp.min and was independent of the starting concentration of the blood wastewater. The mass of aluminium required to remove the solids varied from 0.5 g/g solids removed with a starting concentration of 0.2% solids, to 0.04 g/g solids at 11.5% starting concentration. Aluminium in the solids was estimated to be between 8-9% and the operating cost of the plant (aluminium electrodes and power) was calculated to be between 2.5 to 5 times that of steam coagulation.