Electrocoagulation is showing promise as an alternative to dissolved air flotation tank treatments for scalder water at Tyson Foods Inc. The process is not temperature sensitive and is very effective for removing metals.
“Electrocoagulation kills bacteria, reduces Kjehdahl nitrogen (TKN) by 74 percent, phosphorous by 93 percent and copper by 90 percent,” says John Askegaard, new technology manager and wastewater specialist, Tyson Foods, Inc. Askaard says that electrocoagulation raises the potential for recycling scalder water.
Electrocoagulation is expensive, but shows promise. And he added that it could be cost effective for plants with high nutrient loads.
How it works
Coagulation is one of the most important physiochemical operations used in water treatment. This process is used to cause the destabilization and aggregation of smaller particles into larger particles. Water contaminants such as ions, heavy metals, and colloids, both organic and inorganic, are primarily held in solution by electrical charges. Colloidal systems can be destabilized by the addition of ions having a charge opposite to that of the colloid. The destabilized colloids can be aggregated and subsequently removed by sedimentation and or filtration.
Coagulation can be achieved by chemical or electrical means. In the electrocoagulation process, direct electrical current is introduced into water via parallel metal plates. The two most common plate materials are iron and aluminum. Metal ions are split off the plates and are sacrificed into the liquid medium. These metal ions tend to form metal oxides that electromechanically attract contaminants that have been destabilized. As this occurs, the contaminants form hydrophobic entities that precipitate and can easily be removed by a number of secondary separation techniques.
Most meat and poultry plant wastewater pretreatment operations use a dissolved air floatation (DAF) tank with some sort of chemical, pH and or polymer addition. DAF biosolids are a byproduct of this process and it has generally been accepted that hauling away these skimmings for either rendering or land application is a necessity. Tyson has been exploring some alternatives to the traditional DAF system.
One third of the total TKN, consisting of organically-bound nitrogen and ammonia, in a poultry plant’s wastewater, comes from the scalder.