@article{SandmannMuenzbergBresseletal.2022,
  author    = {Sandmann, Michael and M{\"u}nzberg, Marvin and Bressel, Lena and Reich, Oliver and Hass, Roland},
  title     = {Inline monitoring of high cell density cultivation of Scenedesmus rubescens in a mesh ultra-thin layer photobioreactor by photon density wave spectroscopy},
  series = {BMC Research Notes / Biomed Central},
  volume    = {15},
  journal   = {BMC Research Notes / Biomed Central},
  number    = {1},
  publisher = {Biomed Central (London)},
  address   = {London},
  issn      = {1756-0500},
  doi       = {10.1186/s13104-022-05943-2},
  pages     = {7},
  year      = {2022},
  abstract  = {Objective Due to multiple light scattering that occurs inside and between cells, quantitative optical spectroscopy in turbid biological suspensions is still a major challenge. This includes also optical inline determination of biomass in bioprocessing. Photon Density Wave (PDW) spectroscopy, a technique based on multiple light scattering, enables the independent and absolute determination of optical key parameters of concentrated cell suspensions, which allow to determine biomass during cultivation. Results A unique reactor type, called "mesh ultra-thin layer photobioreactor" was used to create a highly concentrated algal suspension. PDW spectroscopy measurements were carried out continuously in the reactor without any need of sampling or sample preparation, over 3 weeks, and with 10-min time resolution. Conventional dry matter content and coulter counter measurements have been employed as established offline reference analysis. The PBR allowed peak cell dry weight (CDW) of 33.4 g L-1. It is shown that the reduced scattering coefficient determined by PDW spectroscopy is strongly correlated with the biomass concentration in suspension and is thus suitable for process understanding. The reactor in combination with the fiber-optical measurement approach will lead to a better process management.},
  language  = {en}
}
@article{HartwigHass2018,
  author    = {Hartwig, Anne and Hass, Roland},
  title     = {Monitoring lactose crystallization at industrially relevant concentrations by photon density wave spectroscopy},
  series = {Chemical engineering \& technology},
  volume    = {41},
  journal   = {Chemical engineering \& technology},
  number    = {6},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0930-7516},
  doi       = {10.1002/ceat.201700685},
  pages     = {1139 -- 1146},
  year      = {2018},
  abstract  = {Lactose is of great industrial importance and its production includes the cooling crystallization from highly concentrated solutions. Monitoring the crystallization process is essential to ensure reproducible product quality. Photon density wave (PDW) spectroscopy enables in-line monitoring of highly concentrated processes in liquid dispersions. It was applied to the determination of the solubility and nucleation points of lactose monohydrate in water, sizing of lactose crystals, and to dissolution as well as crystallization monitoring. Other process analytical technologies (focused-beam reflectance measurement, particle vision and measurement) were used as reference, and the comparison indicates that PDW spectroscopy is very robust against probe fouling and is, thus, a useful tool for monitoring crystallization processes in concentrated suspensions.},
  language  = {en}
}
@article{HaeneBruehwilerEckeretal.2019,
  author    = {Haene, Janick and Bruehwiler, Dominik and Ecker, Achim and Hass, Roland},
  title     = {Real-time inline monitoring of zeolite synthesis by Photon Density Wave spectroscopy},
  series = {Microporous and mesoporous materials : zeolites, clays, carbons and related materials},
  volume    = {288},
  journal   = {Microporous and mesoporous materials : zeolites, clays, carbons and related materials},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1387-1811},
  doi       = {10.1016/j.micromeso.2019.109580},
  pages     = {6},
  year      = {2019},
  abstract  = {The formation process of zeolite A (Linde Type A) was monitored inline at 1.5 L scale by Photon Density Wave (PDW) spectroscopy as novel process analytical technology for highly turbid liquid suspensions. As a result, the reduced scattering coefficient, being a measure for particle number, size, and morphology, provides distinct process information, including the formation of amorphous particles and their transfer into crystalline zeolite structures. The onset and end of the crystallization process can be detected inline and in real-time. Analyses by powder X-ray diffraction and electron microscopy, based on a sampling approach, support the interpretation of the results obtained by PDW spectroscopy. In addition, the influence of the molar water content was investigated, indicating a linear increase of the time needed to reach the end of the zeolite A crystallization with increasing molar water content. Further experiments indicate a strong influence of the silica source on the course of the crystallization. The applicability of PDW spectroscopy under even more demanding chemical and physical conditions was investigated by monitoring the synthesis of zeolite L (Linde Type L).},
  language  = {en}
}