Navid Moheimani

The effect of applied shear stress on Botryococcus braunii, in the presence of solvent is important to further understanding the mechanisms behind in-situ solvent extraction and will be critical in the design and scale up of an effective extraction process. This paper looks at the effect of various mixing rates on colony structure and culture photosynthetic activity in the presence of heptane. Partial colony disruption was found to occur at shear rates of 335 s -1, with the main mechanism of disruption believed to be microeddies generated by turbulence around the impeller. Photosynthetic activity was seen to drop by 55 % during the extraction period requiring a short recovery time of 3 days, reaching 66.5 % of its original value. These results provide valuable insight and data on the shear limits of B. braunii required in the design of a repeated milking process and will assist in the design and scale up of a viable milking process.

Learning Overview: After attending this presentation, attendees will understand newly explored factors that influence the persistence of diatoms as a form of physical trace evidence within different variations of clothing fabrics when subjected to environmental removal pressures and settings. This presentation will increase attendees’ awareness of diatoms, their potential applications, and their limit as trace evidence and factors affecting its role as such. Impact Statement: This presentation will impact the forensic science community by increasing awareness of the use of the diatoms in forensics, specifically as trace evidence, as well as exploring aspects of their persistence in common clothing fabrics in practical contexts.1,2 Aquatic crime scenes present a challenging environment for crime scene investigators to operate in. Generally, many conventional forms of evidence that are relied upon in terrestrial environments, such as trace evidence like fibers or hairs, are unavailable in aquatic environments due to their ephemeral nature and aquatic life therein. However, aquatic environments are host to organisms that can have evidential use in the absence of more traditional evidence. Diatoms are microscopic algae with cell walls composed of silica, initially largely used to aid in drowning diagnoses. More recent literature has shifted the attention of diatoms in forensics from the area of forensic pathology to that of trace evidence.3,4 So far, the research mostly centers on diatom transfer from environments to clothing and their subsequent extraction from clothing fabrics for analysis.2,5 Little research has yet been published concerning the persistence of diatoms in clothing fabrics. The aim of this study is to analyze the effects that various active (manual) and passive (natural) removal pressures have on the persistence of diatoms within various common clothing fabric of different constructions and compositions (pure cotton knit, denim weave, pure polyester knit). Fabrics were submerged in Diatom-Enriched Waters (DEW) prepared using 50:50 mixed cultures of native and common Australian diatom species (Chaetoceros muelleri and Navicula sp.). In the active experiment, the fabrics were washed in washing machines (top loader and front loader) at varying temperatures (cold and warm >40°C) for one, two, and three consecutive washes, to assess the persistence of diatoms in the fabric samples when subject to an attempt to remove them via machine washing actively. Additionally, some unsubmerged fabric samples were introduced to the washes to assess whether cross-contamination could occur. In the passive experiments, the fabrics were left in various environments (indoors and outdoors) and sampled at increasingly longer time intervals for three months to assess any passive reduction due to natural passive pressures without any active influence. This presentation will discuss the outcome of this study and provide interpretations and implications of the results in the light of future case work.