Co-Metabolic Biodegradation of Nitrified Old Landfill Leachate with Nitrate-N in Anoxic Sequencing Batch Biofilm Reactors (ASBBRs)

In consideration of the high concentration of ammonia and refractory organics, co-metabolic biotreatment system of old landfill leachate after bio-nitrification was constructed in ASBBRs with nitrate-N as growth substrate. Under the conditions of 0.25 kg COD/(m³·d) and 0.20 kg NO₃^--N/(m³·d), the degradation rates of chemical oxygen demand (COD), total organic carbon (TOC), NO₃^--N and colour index, after the operation for 67 d were 67.60%, 53.78%, 45.54% and 53.57%, respectively, while the BOD₅/COD value of old landfill leachate was 0.068. Analyses of molecular weight cut off (MWCO) showed that micro-molecular refractory organics of 5~10 KDa in inflow were effectively degraded, of which parts of organics became more difficult to be biodegraded with smaller molecular weight. Fourier transforms infrared spectroscopy (FTIR) analysis demonstrated that aldehydes, aliphatics, phenols and alcohols, etc. decreased and O-H functional group increased in the effluent. A majority of bacteria in the co-metabolic system were discovered to be globular and short-bar-shaped, with a few disc-shaped bacteria by scanning electric microscopy (SEM) testing. Moreover, benzene and toluene, as particular pollutants in old landfill leachate, were researched in different co-metabolic systems with nitrate-N. The result showed that the dehydrogenase concentration might accelerate the degradation of refractory organics.