Performance and influence factors of completely autotrophic nitrogen removal over nitrite (CANON) process in a biofilter packed with volcanic rocks

<div><p>Completely autotrophic nitrogen removal over nitrite (CANON) process was considered as one of the most efficient and economical nitrogen removal processes, which was suitable for treating wastewater with low ratio of carbon to nitrogen. In this study, an enlarging start-up strategy for CANON process was proposed, and a 40-L CANON reactor was successfully started by seeding 2-L mature biofilm containing both aerobic ammonia-oxidizing bacteria (AerAOB) and anaerobic ammonia-oxidizing bacteria (AnAOB). The effects of dissolved oxygen (DO), ammonia loading rate and the ratio of air inflow to water inflow (<i>Q</i>_air/<i>Q</i>_water) on nitrogen removal performance were investigated. The distribution of AerAOB and AnAOB was analysed using fluorescence in situ hybridization (FISH) technique. The system reached a maximum NRR of 3.11 kg N m⁻³ d⁻¹ with a removal efficiency of 89.5%, and the average value in steady state was 2.42±0.26 and (83.07 ± 6.89)%, respectively. Analysis of influence factors showed the important role of high DO (around 5 mg L⁻¹), for the high-rate nitrogen removal, and the <i>Q</i>_air/<i>Q</i>_water should be controlled at 28–40 for stable operation. FISH results suggested that AerAOB and AnAOB predominated in the reactor, with proportions of 46.8% and 39.3%, respectively. This study demonstrated that the biofilter operated with high effluent DO was a feasible setup for CANON process.</p></div

Effect of 2,4-dichlorophenol on the production of methane from anaerobic granular sludge during anaerobic digestion through spectroscopy analysis

Chlorophenols in urban high organic wastewater increases, which plays an inhibitory role in the process of anaerobic fermentation and methanogenesis. The release rules of extracellular polymers (EPS) and soluble microbial products (SMP) and the production of methane from anaerobic granular sludge were evaluated by spectroscopic analysis. The methane production was reduced by 21.6%, 41.4% and 50.5% respectively by adding 2,4-DCP of different concentrations (25 mg/L, 50mg/L and 100 mg/L). Activity tests of methanogenic functional enzymes indicated that F420 was more susceptible to the toxic of 2, 4-DCP than Acetyl-CoA and NADH. The decrease in methane production was due to the reduction in the activity of conversion enzymes rather than the loss of crucial precursors for methanogenesis. 2,4-DCP disintegrated the protein ‘shell’ of anaerobic granular sludge by destroying α-helix and β-sheet structures. After the protein ‘shell’ in EPS was destroyed, 2, 4-DCP entered the interior of granular, which inhibited the activity of functional enzymes and affected the process of acidogenesis and methanogenesis. At the same time, due to the partial rupture of the cells after being affected by the toxicity of 2,4-DCP, the protein material could be dissolved into the aqueous phase and complexed with 2,4-DCP to reduce the toxic effect of 2,4-DCP.</p