Australian Centre for Water and Environmental Biotechnology, The University of Queensland, Brisbane, QLD, 4072, Australia; CRETUS, Department of Chemical Engineering, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain.
Australian Centre for Water and Environmental Biotechnology, The University of Queensland, Brisbane, QLD, 4072, Australia.
Water Res. 2022 Jul 1;219:118572. doi: 10.1016/j.watres.2022.118572. Epub 2022 May 9.
Light attenuation in enriched purple phototrophic bacteria (PPB) cultures has not been studied, and its understanding is critical for proper process modelling and reactor design, especially for scaled systems. This work evaluated the effect of different biomass concentrations, reactor configurations, wastewater matrices, and growth conditions, on the attenuation extent of near infra-red (NIR) and ultraviolet-visible (UV-VIS) light spectra. The results show that increased biomass concentrations lead to higher light attenuation, and that PPB absorb both VIS and NIR wavelengths, with both fractions of the spectrum being equally absorbed at biomass concentrations above 1,000 g COD·m. A flat plate configuration showed less attenuation compared with cylindrical reactors illuminated from the top, representative for open ponds. Neither a complex wastewater matrix nor the presence of polyhydroxyalkanoates (under nutrient limited conditions) affected light attenuation significantly. The pigment concentration (both bacteriochlorophyll and carotenoids) however, had a strong effect, with significant attenuation in the presence of pigments. Attenuation predictions using the Lambert-Beer law (excluding scattering) and the Schuster model (including scattering) indicated that light scattering had a minimal effect. A proposed mathematical model, based on the Lambert-Beer law and a Monod function for light requirements, allowed effective prediction of the kinetics of photoheterotrophic growth. This resulted in a half saturation coefficient of 4.6 W·m. Finally, the results showed that in dense outdoor PPB cultures (≥1,000 g COD·m), effective light penetration is only 5 cm, which biases design away from horizontal lagoons, and towards non-incident multi-panel systems such as flat plate reactors.
富营养化紫色光合细菌（PPB）培养物中的光衰减尚未得到研究，而了解这一点对于正确的过程建模和反应器设计至关重要，尤其是对于规模化系统而言。本工作评估了不同生物质浓度、反应器构型、废水基质和生长条件对近红外（NIR）和紫外可见（UV-VIS）光谱光衰减程度的影响。结果表明，生物质浓度的增加会导致更高的光衰减，并且 PPB 吸收 VIS 和 NIR 波长，在生物质浓度高于 1,000 g COD·m 时，两个光谱部分的吸收相等。与从顶部照明的圆柱形反应器相比，平板构型显示出较低的衰减。复杂的废水基质或在营养有限条件下存在聚羟基脂肪酸酯（PHA）都不会显著影响光衰减。然而，色素浓度（细菌叶绿素和类胡萝卜素）对光衰减有很大影响，存在色素时会有明显的衰减。Lambert-Beer 定律（不包括散射）和 Schuster 模型（包括散射）的衰减预测表明，光散射的影响很小。基于 Lambert-Beer 定律和光需求的 Monod 函数的拟数学模型允许对光异养生长动力学进行有效预测。这导致半饱和系数为 4.6 W·m。最后，结果表明，在密集的户外 PPB 培养物（≥1,000 g COD·m）中，有效的光穿透仅为 5 cm，这使得设计偏向于非水平池塘，而不是非入射多面板系统，如平板反应器。
