Investigating the reduction of BTEX in automotive paint sludge combined with biological sludge by vermicomposting process using Eisenia fetida

Background: Due to the fact that in the process of car painting in the automotive industry, sludge containing dangerous compounds of benzene, toluene, ethylbenzene, xylene which cannot be released into the environment without purification, is inevitably produced, this study was conducted to investigate the feasibility of removing BTEX (benzene, toluene, ethylbenzene, and xylene) from the paint sludge of Saipa Automotive Company using Eisenia fetida worms. Methods: This is an experimental study. First, mixtures with different proportions of sludge were prepared and loaded in suitable boxes. After preparing the desired sludge, their quantitative and qualitative characteristics were determined in terms of type and amount of BTEX, volatile materials, moisture content, and C/N ratio. Then, to check the changes in BTEX, sampling was performed on different days during 90 days. BTEX measurements were performed using GC-MS method (NIOSH Method 1501). Results: The results showed that in the best mixing ratio of sludge, the amount of benzene decreased from 3 mg to less than 0.01 mg in 30 days, toluene decreased from 1.5 mg to zero over a 45-day period, ethyl benzene was reduced from 7 mg to zero mg over 70 days, and xylene decreased from 18 mg to 0.9 mg over 90 days. In addition, in the same optimal mixing ratio, the amount of volatile organic matter, pH, and C/N ratio also had a decreasing trend in the vermicomposting process. Conclusion: According to the results, E. fetida worms are able to work in mixed sludge and have the ability to break down BTEX.