Effect of different carbon substrates on the removal of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) by anaerobic mesophilic granular sludge

The influence of carbon substrate supplement on the degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) by anaerobic mesophilic granular sludge was investigated. Batch experiments were carried to evaluate the biodegradation performance in the presence of acetate, ethanol, glucose and soluble starch. The results of specific methanogenic activity tests showed that RDX and HMX at concentration of 139 and 20 μmol L^-1, respectively, had no major inhibitory effect on the bioactivity of anaerobic granular sludge. Glucose and acetate could better facilitate the degradation of RDX and HMX when compared with ethanol and soluble starch. The concentration of carbon substrate was considered critical for enhancing the transformation of RDX and HMX. As carbon substrate concentration increased up to 50 mmol chemical oxygen demand (COD) L^-1, there was a major stimulatory effect of the amended carbon substrates, while a slight inhibitory effect was also found at some concentrations. These results indicate that adding suitable carbon substrates may be an important strategy for stimulating the anaerobic biotransformation of high-energetic ammunition compounds in bioreactors.