Effects of tertiary microsieving on the composition of poultry processing wastewater

Abstract

SUMMARY Experiments were conducted to establish baseline values and processing plant variability in the reduction in concentrations of 5 wastewater parameters and 15 minerals after bench-scale tertiary microsieving of poultry processing wastewater (PPW) to 53 µm. Most US poultry processing plants currently use a 2-stage series of primary and secondary mechanical screens in the Fine (1,500 to 6,000 µm) and Very Fine (250 to 1,500 µm) micron range to remove gross offal before the wastewater enters advanced treatment systems. Poultry processors could receive substantial economic and environmental benefits by reducing the amount of fine particulate matter in PPW entering advanced wastewater treatment systems through the use of tertiary microscreening, which is the physical screening of PPW below 250 µm. This would increase the volume of offal recovered while decreasing associated wastewater treatment costs. Composite samples of PPW from 3 US broiler slaughter plants were collected after secondary rotary screening and analyzed for mean concentrations (mg/L) of chemical oxygen demand (2,733 mg/L), total solids (2,304 mg/L), total volatile solids (1,822 mg/L), total suspended solids (1129 mg/L), and total Kjeldahl nitrogen (161 mg/L). Tertiary microsieving reduced total suspended solids by 27 to 37%, total volatile solids by 16 to 22%, total solids by 16%, total Kjeldahl nitrogen by 8%, and chemical oxygen demand by 7%. The PPW samples were also analyzed for mean concentrations (mg/L) of sodium (119.9), potassium (61.0), phosphorus (33.5), calcium (26.2), silicon (13.9), magnesium (8.9), iron (1.8), aluminum (0.6), zinc (0.3), copper (0.16), manganese (0.102), boron (0.036), molybdenum (0.019), nickel (0.016), and chromium (0.013). Four of the 7 elements with mean concentrations >1 mg/L (sodium, potassium, phosphorus, and magnesium) were generally unaffected by microsieving.