| Hazardous waste composting is a demonstrated technology for many types of organic contaminants. However, treatment outcome is often uncertain for hydrophobic compounds and treatability studies are needed to predict performance. A composting pilot study was conducted to determine the treatability of substituted aromatic hydrocarbons in two 15 m3 samples of tar-like dye manufacturing waste sludge. Performance over a 49-day period was characterized for mixtures of 17 aromatic compounds using first-order kinetics. Half-life was generally lower (8- 18 days) for chlorobenzene, xylenes, nitrobenzene, aniline, toluene, and ethylbenzene when initially present at relatively high mass (above 10%). Nitrobenzene did not degrade in material with a carbon to nitrogen ratio of 18:1 but did degrade in material with a ratio of 98:1. Although 50% to 75% of the contaminant mass was degraded, benzene, nitrobenzene, N-nitrodiphenylamine, naphthalene, and benzo(a)anthracene concentrations were above regulatory standards in finished compost. A fugacity analysis showed that compounds partitioned significantly (rho<0.05) to the organic fraction and non-aqueous phase liquid of the composting material. Application of Fenton reaction to improve treatment was more effective after bulking. No significant (rho<0.05) differences between biotreatment alone and biotreatment with pre and post Fenton oxidation were observed. Alkaline hydrolysis using 5% w/w CaMg(OH)4 removed nearly all of 25,000 mg/kg tetryl in soil. Picric acid and N-methylpicramide were tentatively identified as treatment products. Biotransformation of the nitroaromatic compound RDX was determined by comparing kinetic meta-data obtained from 42 studies. Degradation rates were statistically faster for aerobic and anaerobic bacteria than for fungi. Results of this study show that biodegradability, bioavailability, and kinetics are critical elements of a treatability analysis and can identify the need for additional treatment processes. Processes can be integrated into biotreatment using cost effective reagents that enhance compound removal. Additional research is needed to define the chemical, biological, and physical interface of the integrated system to improve process outcome. |
