Wastewater Treatment for Chicken Processing Plants

Clarified water is discharged or recycled at the plant for purposes such as washing.
Using ferric sulfate during wastewater treatment in chicken processing plants provides several process benefits, says two scientists. Ricardo Camacho and Luis Huerta from Optar S.A. de C.V., Mexico, assert those benefits include precipitation of sulfur compounds, increased efficiency in TSS and BOD5 elimination, reduction in energy consumption in the biological process, lower corrosion and longer life for the mechanical equipment in the plant compared to the use of ferric chloride.

Chicken processing plants (CPPs) use large quantities of clean water in processing and production, and more than 90 percent of clean water is converted into wastewater. The basic functions of water at these types of processing plants include cleaning the animal channels during the process and afterwards; cooling the channels after taking out the internals (guts); and cleaning the installation in general. Camacho and Huerta have researched using ferrite sulfate as a treatment for CPP wastewater and published the results.

Wastewater generated at the CPP has a high concentration of colloidal suspended solids, and waste, BOD5, (biochemical oxygen demand for 5 days), grease and oils, and coloring. (In Mexico, commercial chickens are colored to have a yellowish appearance.) It is best to treat the wastewater as soon as possible to prevent the dissolving of pollutants that can be removed in a physical/chemical treatment process.

The first part of the treatment consists of screening to separate coarser materials, during which most guts and feathers are removed. (Most modern CPPs separate the feathers, which contain effluents). This separation stage normally is achieved using equipment supplied by the same company that supplies the chicken processing equipment, and sometimes this separation equipment is not considered as part of the wastewater treatment process. However, this separation has a fundamental influence on the functioning of all the wastewater treatment processes.

The next step consists of filtering the water through a curved or drum screen with a fine slot width with openings of 0.02" (0.5 mm) to separate all larger particles, cleaning the effluent for the next treatment step.

Once the water has been screened, it can be treated by physical/chemical processes or by biological treatment. Camacho and Huerta say the chemical treatment process is the most suitable because it requires less space, is easier to operate and is less sensitive. However, best results are achieved with a combination of physical, chemical and biological processes, say the scientists.

For CPP effluent, Camacho and Huerta recommend a chemical process that consists of flocculation pipe and a flotation unit that uses dissolved air, and chemical dosing units. The most common biological treatment method is the activated sludge process. They note that biggest problem in chemical treatment is the selection of the chemicals, including a suitable coagulant, to add to the wastewater to separate the dispersed pollutants. The coagulant must be easy to handle, store and prepare, and it must achieve the required degree of removal of the pollutants.

According to Camacho and Huerta, ferric sulfate with the right polymer is an efficient coagulant for CPPs. Ferric sulfate is a primary coagulant in granular form based on trivalent iron (Fe+3), and it can be dissolved to give an iron content of 10 percent to 11.8 percent. This coagulant works well in a wide range of pH and does not have operational problems associated with ferric chloride.

In a physical/chemical process for a CPP, the ferric sulfate acts principally on coloring, TSS, BOD5 and turbidity. The sludge generated in the wastewater treatment plant where ferric sulfate is used as a coagulant is easier to dewater than sludge generated with other products. Sludge coming from a treatment process where ferric sulfate is used requires only one cationic polymer to improve the dewatering characteristics. In processes where other coagulants are used, it normally requires three or more chemicals for dewatering the sludge. ical equipment in the plant compared to the use of ferric chloride. Also, the authors say there is less maintenance work and expense at the plant.