The effect of nutrient deficiency on removal of organic solvents from textile manufacturing wastewater during activated sludge treatment

Textile manufacturing wastewater is often deficient in nitrogen and phosphorus and contains hazardous solvents, including methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), toluene (TOL), and xylenes (XYL). The objectives of this study we e to evaluate the effectiveness of a short-term batch assay for predicting when a nutrient deficient condition exists in textile wastewater activated sludge, and to determine if nutrient deficiency affects biodegradation of MEK, MIBK, TOL, and p-XYL to a greater or lesser extent than bulk soluble chemical oxygen demand (sCOD). Addition of N + P significantly improved sCOD removal during treatment of textile wastewater in laboratory-scale sequencing batch reactors (SBRs). Batch tests using mixed liquor suspended solids (MLSS) from the SBRs correctly predicted the nutrient deficiency in the reactors that received unamended wastewater. During batch tests in sealed containers (to prevent volatilization) when N + P were added, the solvents biodegraded faster and to a greater extent than the bulk wastewater sCOD. MEK and MIBK were also completely consumed in MLSS from the SBR that received unamended wastewater, indicating that a shortage of nutrients did not significantly impact biodegradation of these ketones. However, nutrient deficient conditions significantly decreased the rate of TOL and p-XYL biodegradation. The difference in biodegradability of the ketones and monoaromatics under nutrient deficient conditions may be related to loss of plasmids required for aerobic catabolism of TOL and p-XYL. These results demonstrate that N + P addition to nutrient-deficient textile wastewater improves bulk sCOD removal and also significantly improves the biodegradability of TOL and p-XYL, thereby reducing the amount released to the atmosphere by volatilization.