Leaching Toxicity Of Unfired Bricks Prepared From The Sludge Derived From Dyestuff-Making Wastewater Coagulation

The utilization of sludge for brick is a potential way of recycling. However, there is a serious problem, that is, lack of integrated leaching toxicity assessment methodology. As the leaching tests published are mainly for heavy metals or other inorganic pollutants and there is litter work on organics, the research work on the leaching behavior of organic pollutants is important to the environment protection.This work investigated the leaching behavior of aniline, m-phenylenediamine, nitroaniline, acrylonitrile and chloropropene in the sludge derived from dyestuff-making wastewater coagulation and the sludge unfired bricks based on the Chinese standard, that is, Test Method Standard for Leaching Toxicity of Solid Wastes:Horizontal Oscillation Leaching Procedure (HJ557-2009) coupled with Solid Waste Extraction Procedure for Leaching Toxicity Sulfuric Acid and Nitric Acid Method (HJ/T299-2007). We developed the accurate HPLC-DAD method that simultaneously determinates aniline, m-phenylenediamine and nitroaniline and the accurate GC-FID method that simultaneously determinates acrylonitrile and chloropropene.The concentrations of nitroaniline, aniline, m-phenylenediamine, acrylonitrile in leachates were determined by spectrophotometric method and chemical titration. The experiment results exhibited that the leaching toxicity of the organic compounds in the dye wastewater coagulation sludge was dramatically decreased after solidification/stabilization using cements as binders. The average recoveries for five organic pollutants were more than 90% with the relative standard deviations (RSD) of more than 5%. The HPLC-DAD method that determinates the concentrations of aniline, m-phenylenediamine, nitroaniline more accurately was developed. The type of the solid phase exaction column, elution velocity, the proportion and dosage of elution agents were examined. It was found that the optimal extraction conditions of there organics were as follows: column: Waters Oasis HLB; elution velocity: 5mL.min-1; the proportion of elution agents: methanol of 100%; and the dosage of elution agents,6 mL. The optimal operational conditions of HPLC-DAD were: column:Eclipse XDB-C18 (4.6mm×150mm,5um); mobile phase:0-5-10 min,5%-5%-10% (methanol/water); detection wavelength:254nm; and flow rate:1.0mL.min-1. The average recoveries for three organic pollutants were in the range of 92.0%～93.3%. The repeated RSDs of peak areas for a certain concentration of mixed standard three organic pollutants were 1.08%-1.65%, and the limits of detection of three organic pollutants were 0.025-0.05μg.mL-1 (SNR is 3).The GC-FID method that determinates the concentrations of acrylonitrile and chloropropene was also developed. The chromatographic conditions were optimized. At the temperature of vaporizing chamber and inspection room,150℃; the column temperature,35℃; the flow rate of carrier gas,10mL.min-1, the repeated RSDs of peak areas for a certain concentration of mixed standard two organic pollutants were 1.19% and 3.16%, and the limits of detection of two organic pollutants were 0.25μg.mL-1 and 0.15μg.mL-1 (SNR is 3).The concentrations of five organic pollutants in leachates were determined with the established chromatographic methods. The experimental results exhibited that the concentrations of the organic compounds were much lower than the limited concentration of the Chinese standard. It is concluded that the unfired bricks made from the sludge were friendly to environment, which may not cause the secondary pollution in use.