Studies On The Removal Of α-pinene From Waste Gases By Biofiltration

α-Pinene (C10H16), with a maximum water solubility of 5–10 mg L^-1, is a hydrophobic and recalcitrant volatile organic compounds (VOCs), which could cause serious health and environmental problems. Becasuse troposphericα-pinene is believed to be the daytime oxidation with hydroxyl radicals and reaction with nitrate radicals during the night, leading to the formation of photochemical smog. Moreover, it also could destroy ozonosphere via reacting with ozone throughout the day.A biofilter (BF) packed with wood chip/peat and a biotrickling filter (BTF) packed with ether-based polyurethane foam were employed to removeα-pinene from waste gases. The start-up time and reactor performance were investigated for both reactors. The start-up procedures of the BF and the BTF were finished by joint gas-liquid phase inoculation within 21 d and 27 d, respectively. The changing tendency of biomass concentrations and pressure drop can be used to evaluate the start-up status of the biofilter. Scanning electron microscopy (SEM) revealed that bacterial communities grew well on the carriers, and bacilli and cocci may be the dominant bacteria. Under the conditions of inletα-pinene concentrations of 80²200 mg·m^-3 and empty bed residence time (EBRT) of 29¹02 s, both BF and BTF could effectively degradeα-pinene, and the maximum elimination capacities were 50 g·m^-3·h^-1and 43 g·m^-3·h^-1 respectively. The mass ratio of carbon dioxide produced to theα-pinene removed was approximately linear, and the mineralization rates ofα-pinene in the BF and BTF obtained were 74% and 68%, respectively. The results indicated that theα-pinene was removed mainly via biodegradation. Colony forming unit (CFU) analysis showed that the biomass concentration in the BF and BTF increased during the start-up stages of operation, and increased with EBRT during the steady-state operation. When EBRT was set at 102 s, biomass concentrations in the BF and BTF reached 5.52×10¹⁴cfu·m^-3 and 1.84×10¹⁴ cfu·m^-3, respectively. The pressure drop and shock loads analysis showed that the pressure drops in the BF and BTF were not high, however, the former was higher than the latter. Both BF and BTF could recover the elimination capacity rapidly in response to shock loads.Process parameters, such asα-pinene inlet loading, inlet concentration, EBRT, moisture content, pH and spraying volume had effects on theα-pinene removal efficiency. A moisture content ranging from 46% to 62% and from 53% to 67% were proper to the BF and BTF for a long-term operation, respectively. The effect of pH on the activity ofα-pinene-oxided bacteria was not obvious, and the optimum pH was ranged from 5 to 7. The BTF maintained better elimination capacity with spraying volume of 180 mL·min^-1.The fingerprints of PCR-DGGE indicated that microbial population differed obviously during the start-up period. The bacterial communities had rich microbial population and stable community structure, implying little variation about the composition and diversity of microorganisms during the stable operation period. The sequencing results showed that in the BF the dominant organisms responsible forα-pinene degradation were closely related to Pseudomonas fluorescens, Comamonadaceae bacterium, Mycobacterium nonchromogenicum, Mycobacterium neoaurum, Pseudomonas veronii, Benzene-decomposing bacterium and Mycobacterium terrae. And in the BTF the dominant organisms were closely related to Pseudomonas fluorescens, Comamonadaceae bacterium, Pseudomonas veronii, Benzene-decomposing bacterium, Mycobacterium terrae and Acidovorax caeni. Some researchers reported that Pseudomonas fluorescens and Pseudomonas veronii were the dominant bacterias which could degrade effectivelyα-pinene, and the former was consistent with the preselected bacteria which inoculated during the start-up process.