Biology subjects

Ahrens, L.

Publications and source records attributed to Ahrens, L..

3 recordsLinked to original sources

bioRxiv2025

Scaling down-Evaluation of start-up and microbial stabilisation dynamics in five parallel laboratory-scale CSTR biogas system

Laboratory-scale continuous stirred tank reactors (CSTRs) are commonly used to study and optimise anaerobic digestion (AD), yet the time required for such systems to become representative of full-scale processes remains unclear. This study investigated start-up and stabilisation dynamics in five parallel 10-L CSTRs operated as direct scale-downs of a full-scale agricultural biogas plant, using identical inoculum, substrate composition, organic loading rate (2.57 g VS L-1 day-1), hydraulic retention time (55 days), and temperature (37 {degrees}C). The reactors were monitored for 213 days (3.9 HRTs), with one reactor operated for an additional 330 days. All reactors showed highly reproducible behaviour but experienced a transient disturbance, characterised by volatile fatty acid (VFA) accumulation and fluctuating methane production after approximately one HRT. This disturbance was likely caused by a higher effective daily organic loading rate compared to full scale, resulting from once-daily feeding excluding weekends. Increasing the feeding frequency led to VFA degradation and recovery, and stable process performance was achieved after approximately three HRTs, with methane yields of 285 {+/-} 21 NL CH4 kg-1 VS. The microbial community showed pronounced dynamics during start-up, including major genus-level shifts within Cloacimonadia and a transition in aceticlastic methanogens from Methanothrix to Methanosarcina compared to the full-scale system. Although microbial composition stabilised after about three HRTs, it remained dynamic during prolonged operation and diverged from the original inoculum. These results demonstrate that even direct scale-down reactors require extended stabilisation and may develop microbial communities that differ from the full-scale process, raising questions about their representativeness.

microbiology↗

bioRxiv2023

Accumulation of per- and polyfluoroalkyl substances (PFAS) in a terrestrial food web

Per- and polyfluoroalkyl substances (PFAS) are synthetic organofluorine chemical compounds that are broadly used in amongst others aqueous firefighting foam, cosmetics, textiles, carpets, coatings, plastics, and ski wax. Their chemical properties make them persistent organic pollutants that are potential bioaccumulative and toxic. Most studies on PFAS have been performed in groundwater, surface water and aquatic biota. Our knowledge on the terrestrial fate of PFAS is therefore limited. We sampled soil, berries, mushrooms, and wildlife on the island Froson, central Sweden, in 2021 and 2022, to study the fate of 22 PFAS in a terrestrial food web. Groundwater, surface water and fish on Froson have previously shown high PFAS concentrations. Soil, berries, and mushrooms were also concurrently sampled in a reference area in northern Sweden. Overall, concentrations of the sum of PFAS were low in berries and mushrooms. In moose (Alces alces), roedeer (Capreolus capreolus), and bank vole (Myodes glareolus), concentrations were highest in liver. The maximum levels for PFOS in offal as set by the European Commission (50 ng/g ww) were exceeded in the liver of two of 10 roedeer. Bank voles (n = 12 pools) that were sampled in the vicinity of a firefighting training site showed partly extreme concentrations with none of the samples having liver concentrations <474 ng/g ww (maximum 11,600 ng/g ww). Bioaccumulation factors (BAFs) for multiple PFAS in bank voles were higher for the studied mushrooms and soil compared to studied berries and were >100 for 27 out of 265 calculated BAFs. BAFs in the ungulate species were generally lower than those for bank voles but were >1 for several PFAS from the mushroom. The exact origin of PFAS in bank voles could not be identified in our study, but the BAFs are supported by the feeding and behaviour ecology of bank voles, i.e., there is likely bioaccumulation and biomagnification from soil and mushrooms to bank voles. The measured PFAS concentrations and BAFs, especially those in bank voles are worrying from an ecosystem and One Health perspective considering that voles are staple food for multiple predators.

ecology↗

bioRxiv2022

Towards 3D-bioprinting of osseous tissue of pre-defined shape using single-matrix cell-bioink constructs

Engineering living bone tissue of defined shape on-demand has remained a challenge. 3D-bioprinting (3DBP), a biofabrication process capable of yielding cell constructs of defined shape, when combined with developmental engineering can provide a possible path forward. Through the development of a bioink possessing appropriate rheological properties to carry a high cell load and concurrently yield physically stable structures, printing of stable, cell-laden, single-matrix constructs of anatomical shapes was realized without the need for fugitive or support phases. Using this bioink system, constructs of hypertrophic cartilage of predesigned geometry were engineered in vitro by printing human MSCs at a high density to drive spontaneous condensation and implanted in nude mice to evoke endochondral ossification. The implanted constructs retained their prescribed shape over a 12-week period and underwent remodeling to yield ossicles of the designed shape with neovascularization. Micro-CT, histological and immunohistochemistry assessments confirmed bone tissue characteristics and the presence of human cells. These results demonstrate the potential of 3DBP to fabricate complex bone tissue for clinical application.

bioengineering↗