Song J, Kinney K A
Environmental and Water Resources Engineering, Department of Civil Engineering, ECJ 8.6, University of Texas at Austin, 78712, USA.
Biotechnol Bioeng. 2000 Jun 5;68(5):508-16. doi: 10.1002/(sici)1097-0290(20000605)68:5<508::aid-bit4>3.0.co;2-p.
Excess biomass accumulation and activity loss in vapor-phase bioreactors (VPBs) can lead to unreliable long-term operation. In this study, temporal and spatial variations in biomass accumulation, distribution and activity in VPBs treating toluene-contaminated air were monitored over a 96-day period. Two laboratory-scale bioreactors were subjected to a toluene loading rate of 45.8 g/m(3)-h with one VPB operating in a unidirectional (UD) mode and a second identical VPB operating in a directionally switching (DS) mode. In the UD bioreactor, the contaminated air stream was continuously fed to the bottom of the reactor, while, in the DS bioreactor, the direction of the contaminated gas flow was reversed every three days. Overall, the DS system performed better with respect to biomass distribution and microbial activity across the bioreactor, resulting in more stable bioreactor performance. In contrast, most of the biomass accumulation and activity was confined to the front half of the UD bioreactor column which caused high pressure drops, rapid activity loss and eventually toluene breakthrough. A carbon balance reveals that excess biomass accumulated continuously in both bioreactors, and biomass yield coefficients were very similar (0.59 g dry biomass/g toluene for the UD and 0.63 g dry biomass/g toluene for the DS). The viable biomass population remained relatively constant in both bioreactors over the operational period, while the inactive biomass fraction steadily increased over the same time frame. Biodegradation activity determined by the dehydrogenase enzyme activity assay was found to be a function of biomass accumulation and reflected pollutant removal profiles along the columns. In addition, biomass activity correlated well with the toluene-degrading fraction of the total bacterial population.
气相生物反应器（VPB）中过量的生物质积累和活性损失会导致长期运行不可靠。在本研究中，对处理甲苯污染空气的VPB中生物质积累、分布和活性的时空变化进行了为期96天的监测。两个实验室规模的生物反应器的甲苯加载速率为45.8 g/m³·h，其中一个VPB以单向（UD）模式运行，另一个相同的VPB以方向切换（DS）模式运行。在UD生物反应器中，受污染的空气流连续进料到反应器底部，而在DS生物反应器中，受污染气流的方向每三天反转一次。总体而言，DS系统在整个生物反应器中的生物质分布和微生物活性方面表现更好，从而使生物反应器性能更稳定。相比之下，大多数生物质积累和活性局限于UD生物反应器柱的前半部分，这导致了高压降、活性快速损失并最终导致甲苯穿透。碳平衡表明，两个生物反应器中都持续积累了过量的生物质，并且生物质产率系数非常相似（UD为0.59 g干生物质/g甲苯，DS为0.63 g干生物质/g甲苯）。在运行期间，两个生物反应器中活生物质数量保持相对恒定，而无活性生物质部分在同一时间范围内稳步增加。通过脱氢酶活性测定法确定的生物降解活性是生物质积累的函数，并反映了沿柱的污染物去除情况。此外，生物质活性与总细菌群体中甲苯降解部分密切相关。
