Bio-photovoltaic cells (BPVs) are a new photo-bio-electrochemical technology for harnessing solar energy using the photosynthetic activity of autotrophic organisms. Currently power outputs from BPVs are generally low and suffer from low efficiencies. However, a better understanding of the electrochemical interactions between the microbes and conductive materials will be likely to lead to increased power yields. In the current study, the fresh-water, filamentous cyanobacterium Pseudanabaena limnetica (also known as Oscillatoria limnetica) was investigated for exoelectrogenic activity. Biofilms of P. limnetica showed a significant photo response during light-dark cycling in BPVs under mediatorless conditions. A multi-channel BPV device was developed to compare quantitatively the performance of photosynthetic biofilms of this species using a variety of different anodic conductive materials: indium tin oxide-coated polyethylene terephthalate (ITO), stainless steel (SS), glass coated with a conductive polymer (PANI), and carbon paper (CP). Although biofilm growth rates were generally comparable on all materials tested, the amplitude of the photo response and achievable maximum power outputs were significantly different. ITO and SS demonstrated the largest photo responses, whereas CP showed the lowest power outputs under both light and dark conditions. Furthermore, differences in the ratios of light : dark power outputs indicated that the electrochemical interactions between photosynthetic microbes and the anode may differ under light and dark conditions depending on the anodic material used. Comparisons between BPV performances and material characteristics revealed that surface roughness and surface energy, particularly the ratio of non-polar to polar interactions (the CQ ratio), may be more important than available surface area in determining biocompatibility and maximum power outputs in microbial electrochemical systems. Notably, CP was readily outperformed by all other conductive materials tested, indicating that carbon may not be an optimal substrate for microbial fuel cell operation.

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Extended or repeated heating of food fats promotes polymerisation reactions that produce difficult-to-remove soil layers. Cleaning of these baked-on/burnt-on fat deposits was investigated using model layers generated by baking lard on 316 stainless steel discs. Rigorous characterisation of the layer material was difficult, as it was insoluble in most solvents. Cleaning was studied using the scanning fluid dynamic gauging technique developed by Gordon et al. (Meas Sci Technol 21:85–103, 2010), which provides non-contact in situ measurement of layer thickness at several sites on a sample in real time. Tests at 50 C with alkali (sodium hydroxide, pH 10.4–11) and three surfactant solutions indicated two removal mechanisms, related to the (1) roll-up and (2) dispersion mechanisms reported for oily oils, namely (1) penetration of solvent at the soil–liquid interface, resulting in detachment of the soil layer as a coherent film, observed with linear alkylbenzene sulfonic acid (LAS) and Triton X-100 and aqueous sodium hydroxide at pH 10.4–11; and (2) the breakdown promoted by the agent penetrating through the layer, observed with cetyl trimethyl ammonium bromide (CTAB), in which CTAB antagonised the cleaning action of LAS.

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We report proof-of-concept results for a fluid dynamic gauging (FDG) device for measuring the thickness and strength of soft solid fouling layers immersed in an opaque liquid in situ and in real time at elevated pressures and temperatures. The device reported here is configured to make measurements on the inner rod of an annular flow test section but the concept is generic. Data are presented from tests using mineral oil at temperatures and pressures up to 140 °C and 10 bara, respectively. Problems with the prototype hardware prevented testing up to the design limits of 270 ºC and 30 bara. The practical working range of the gauge, i.e. 0.10 < h/d t < 0.25, proved to be unaffected by the pressure and temperature. h is the nozzle-surface clearance and d t the nozzle throat diameter. At smaller h/d t values the pressure drop across the nozzle is very high and this can serve as an alarm for close approach. The range of discharge coefficient, C d, values obtained is sensitive to flow rate when the Reynolds number at the throat, Re t , falls below 20. A useful range of C d values is obtained when Re t > 40. Computational fluid dynamics (CFD) simulations of the gauging flow in these quasi-static experiments (no bulk liquid flow) gave good agreement with experimental data for the cases tested. The CFD results showed that the low Re t regime is related to creeping flow in the nozzle. CFD calculations of the shear stress being imposed on the surface being gauged gave good agreement with an analytical model for flow between parallel discs, indicating that the latter can be used to estimate the maximum shear stress imposed by the gauging flows measurements.