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COD fractionation and biological treatability of mixed industrial wastewaters

Fall, C., Millán-Lagunas, E., Bâ, K.M., Gallego-Alarcón, I., García-Pulido, D., Díaz-Delgado, C., Solís-Morelos, C.
Journal of environmental management 2012 v.113 pp. 71-77
activated sludge, biochemical oxygen demand, biodegradation, chemical oxygen demand, color, environmental impact, fractionation, industry, laws and regulations, molasses, rivers, salinity, salts, wastewater, wastewater treatment
This study was conducted at a centralized wastewater treatment plant that receives discharges from nearly 160 industries. The chemical oxygen demand (COD) was fractionated for two objectives: delineation of the limits of the activated sludge process being used at the plant, and evaluation of the potential environmental impact of the treated effluent. Physico-chemical analyses, respirometric and biodegradation tests, as well as COD fractionation were carried out. Molasses-wastewaters were determined to be the major contribution to the plant. The influent was dark brown in color, with a relatively high content of both organics (2503 mg/L COD) and salts (5459 μS/cm conductivity), but a low biochemical oxygen demand (568 mg/L BOD₅) and BOD₅/COD ratio (0.24). The degradability of the organics was limited by the high content of inert soluble COD (SI). The COD fractionation pattern was 40–20–40% for SI, XI (inerts) and SH (soluble hydrolyzable), respectively. More than 90% BOD₅ removal was obtained, which was sufficient for the plant to meet the national Standards. However, the effluent discharged into the river was intensely colored and polluted (>1000 mg/L COD, >5000 μS/cm), emphasizing the need for legislation regulating COD, color and salinity, and for upgraded treatment methods worldwide for molasses wastewaters.