Treatability of 2,4 Dinitrotoluene in Anaerobic/Aerobic Sequential Processes

Abstract

Lab-scale anaerobic upflow anaerobic sludge blanket (UASB) completely stirred tank (CSTR) activated sludge reactor system was used to investigate the treatability of 2,4 dinitrotoluene (DNT) using molasses as primary substrate in continuous fed mode. The treatment efficiencies in anaerobic and aerobic reactors were determined by monitoring the chemical oxygen demand (COD), DNT removals, total and methane gas productions. The effect of increasing DNT concentrations on bicarbonate alkalinity, volatile fatty acid accumulation and methane gas percentage were investigated in UASB reactor. Based on the anaerobic toxicity (ATA) test results, although 12 mg L−1 of DNT is toxic to unacclimatized partially granulated sludge; over 85 and 90% COD and DNT removal efficiencies were obtained at loadings rates of 250 mg DNT L−1 day−1 in anaerobic reactor at a HRT of 0.5 day. Total volatile fatty acid (TVFA) accumulation is associated with methane productions as low as 40% of total gas, at loading rate as high as 500 and 1000 mg DNT L−1 day−1 through anaerobic DNT biodegradation. The treatment efficiencies in the aerobic reactor were determined by monitoring the COD and DNT removals. The intermetabolite products released through anaerobic and aerobic phases were detected. The TVFA, total aromatic amines, ammonia, total nitrogen and toluene concentrations were monitored. The aerobic step was used for the ultimate mineralization of the remaining COD, DNT, toluene and aromatic amines from the anaerobic treatment. The specific methanogenic activity (SMA) of DNT degrading granules were 2.2 and 0.43 g CH4-COD g−1 VSS day−1 at DNT loading rates of 12 and 500 mg L−1 day−1, respectively. The anaerobic breakdown products of DNT were effectively oxidized in the CSTR reactor since the COD and DNT were ultimately mineralized under aerobic conditions. It can be suggested that DNT, the breakdown products and the COD were ultimately mineralized in combined UASB/CSTR reactor. More than 95% COD and DNT removal efficiencies were obtained in combined UASB/CSTR system at an initial DNT concentration of 125 mg/L−1 and a loading rate of 250 mg DNT L−1 day−1.