Tertiary microscreening of poultry processing wastewater
Kiepper, Brian Harry
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Two series of experiments were conducted to measure the effects of tertiary microscreening (screen gaps <200 micron) on conventional wastewater constituents, chemical composition and particulate matter in poultry processing wastewater (PPW). The first series of experiments utilized a bench-scale wet sieving apparatus designed to microscreen PPW from three broiler slaughter plants to 50 micron. Results showed that chemical oxygen demand (COD) had the highest (2733) pre-sieve mean concentration (mg/L), followed by total solids (TS) (2304), total volatile solids (TVS) (1822), total suspended solids (TSS) (1129), and total Kjeldahl nitrogen (TKN) (161). Microscreening reduced the concentration of TSS 30%, TVS 19%, TS 16%, and TKN and COD 8% each. Mean concentrations (mg/L) of chemical elements for pre-sieved samples were sodium (Na) 120, potassium (K) 61, phosphorus (P) 34, calcium (Ca) 26, silicon (Si) 14, magnesium (Mg) 9.0, iron (Fe) 2.0, aluminum (Al) 0.6, zinc (Zn) 0.3, copper (Cu) 0.2, manganese (Mn) 0.1, boron (B) 0.4, molybdenum (Mo) 0.02, nickel (Ni) 0.02, and chromium (Cr) 0.01. The percent (%) fat, protein, crude fiber and ash on a dry weight basis of the recovered particulate solids were 55.3, 27.1, 4.1 and 6.1, respectively. The second series of experiments involved utilizing a pilot-scale vibratory microscreen within the wastewater treatment area of a broiler slaughter plant. Secondary-screened PPW was microscreened using three screen gap sizes: 212, 106 and 45 micron. Results showed that COD (3686) had the highest pre-screen mean concentration (mg/L), followed by TS (2726), TVS (2495), TSS (1353), FOG (fat, oil and grease) (848), and TKN (154). Vibratory microscreening reduced TSS 29%, TKN 27%, FOG 25%, COD 13%, and TKN 5%. The mean moisture for all screened samples collected was 79%. The mean percent (%) fat, protein, crude fiber and ash on a dry weight basis, were 64, 18, 5.0 and 1.5, respectively. Results indicate that tertiary microscreening is not effective at reducing chemical elements present in PPW. There were no significant differences in the removal, reduction or recovery rates of the three microscreen gap sizes.