Biological treatment of wastewater from urea plants of Kuwait

Abstract

A qualitative and quantitative study of the pollutants in the hydrolyzer effluent of the Petrochemical Industries Company (PIC) was undertaken.This task involved flow measurements coupled with a routine and intensive collection of wastewater samples, a comprehensive analysis for the determination of a set of 6–11 parameters and 10 heavy metals, and statistical analysis of the results.The results showed that despite process optimization of the hydrolyzer plant, the average concentration of ammonia and urea in the hydrolyzer effluent were 100 and 130 mg/l, respectively. The biological treatment studies were aimed at removing urea and ammonia in batch and continuous systems.Biological treatment in the batch system indicated that hydrolyzer effluent was a nutritionally deficient medium to sustain microbial growth, hence supplementation with optimum levels of nutrients was a prerequisite for high treatment efficiency. Kinetic studies were undertaken to optimize nitrification — denitrification and urea biodegradation. The observed rates of nitrification, denitrification, urea and combined nitrogen bio-oxidation rates were comparable to or sometimes better than the corresponding rates reported in the literature.In a continuous biological treatment system urea and ammonia could be completely removed from the hydrolyzer effluent at a hydraulic retention time of 20–24 hours and a solids retention time in excess of 30 days.The average concentrations of ammonia, nitrite, nitrate and urea in the final effluent were 0.3, 0.21, 0.4 and 0.0 mg/l, respectively; the total dissolved solids were 450 mg/l.