Research Articles (Chemical Engineering)

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Canary in the coliform mine : exploring the industrial application limits of a microbial respiration alarm system
(Public Library of Science, 2021-03-04) Stone, Wendy; Louw, Tobi M.; Booysen, Marthinus J.; Wolfaardt, Gideon M.; Zhang, Dawei
Fundamental ecological principles of ecosystem-level respiration are extensively applied in greenhouse gas and elemental cycle studies. A laboratory system termed CEMS (Carbon Dioxide Evolution Measurement System), developed to explore microbial biofilm growth and metabolic responses, was evaluated as an early-warning system for microbial disturbances in industrial settings: in (a) potable water system contamination, and (b) bioreactor inhibition. Respiration was detected as CO₂ production, rather than O₂ consumption, including aerobic and anaerobic metabolism. Design, thresholds, and benefits of the remote CO₂ monitoring technology were described. Headspace CO₂ correlated with contamination levels, as well as chemical (R² > 0.83–0.96) and microbiological water quality indicators (R² > 0.78–0.88). Detection thresholds were limiting factors in monitoring drinking water to national and inter- national standards (0 CFU/100 mL fecal coliforms) in both open- (>1500 CFU/mL) and closed-loop CO₂ measuring regimes (>100 CFU/100 mL). However, closed-loop detection thresholds allow for the detection of significant contamination events, and monitoring less stringent systems such as irrigation water (<100 CFU/mL). Whole-system respiration was effectively harnessed as an early-warning system in bioreactor performance monitoring. Models were used to deconvolute biological CO₂ fluctuations from chemical CO₂ dynamics, to optimize this real-time, sustainable, low-waste technology, facilitating timeous responses to biological disturbances in bioreactors.
Rational engineering of Saccharomyces cerevisiae towards improved tolerance to multiple inhibitors in lignocellulose fermentations
(BMC (part of Springer Nature), 2021-08-28) Brandt, Bianca A.; Garcia‑Aparicio, Maria D. P.; Gorgens, Johann F.; Van Zyl, Willem H.
Background: The fermentation of lignocellulose hydrolysates to ethanol requires robust xylose-capable Saccharomyces cerevisiae strains able to operate in the presence of microbial inhibitory stresses. This study aimed at developing industrial S. cerevisiae strains with enhanced tolerance towards pretreatment-derived microbial inhibitors, by identifying novel gene combinations that confer resistance to multiple inhibitors (thus cumulative inhibitor resistance phenotype) with minimum impact on the xylose fermentation ability. The strategy consisted of multiple sequential deltaintegrations of double-gene cassettes containing one gene conferring broad inhibitor tolerance (ARI1, PAD1 or TAL1) coupled with an inhibitor-specific gene (ADH6, FDH1 or ICT1). The performances of the transformants were compared with the parental strain in terms of biomass growth, ethanol yields and productivity, as well as detoxification capacities in a synthetic inhibitor cocktail, sugarcane bagasse hydrolysate as well as hardwood spent sulphite liquor. Results: The first and second round of delta-integrated transformants exhibited a trade-off between biomass and ethanol yield. Transformants showed increased inhibitor resistance phenotypes relative to parental controls specifically in fermentations with concentrated spent sulphite liquors at 40% and 80% v/v concentrations in 2% SC media. Unexpectedly, the xylose fermentation capacity of the transformants was reduced compared to the parental control, but certain combinations of genes had a minor impact (e.g. TAL1 + FDH1). The TAL1 + ICT1 combination negatively impacted on both biomass growth and ethanol yield, which could be linked to the ICT1 protein increasing transformant susceptibility to weak acids and temperature due to cell membrane changes. Conclusions: The integration of the selected genes was proven to increase tolerance to pretreatment inhibitors in synthetic or industrial hydrolysates, but they were limited to the fermentation of glucose. However, some gene combination sequences had a reduced impact on xylose conversion.
Incorporating anaerobic co-digestion of steam exploded or ammonia fiber expansion pretreated sugarcane residues with manure into a sugarcanebased bioenergy-livestock nexus
(Elsevier, 2019) Mokomelea, Thapelo; Da Costa Sousa, Leonardo; Balan, Venkatesh; Van Rensburg, Eugene; Dale, Bruce E.; Gorgens, Johann F.
ENGLISH ABSTRACT: The co-digestion of pretreated sugarcane lignocelluloses with dairy cow manure (DCM) as a bioenergy production and waste management strategy, for intensive livestock farms located in sugarcane regions, was investigated. Ammonia fiber expansion (AFEX) increased the nitrogen content and accelerated the biodegradability of sugarcane bagasse (SCB) and cane leaf matter (CLM) through the cleavage of lignin carbohydrate crosslinks, resulting in the highest specific methane yields (292–299 L CH4/kg VSadded), biogas methane content (57–59% v/v) and biodegradation rates, with or without co-digestion with DCM. To obtain comparable methane yields, untreated and steam exploded (StEx) SCB and CLM had to be co-digested with DCM, at mass ratios providing initial C/N ratios in the range of 18 to 35. Co-digestion with DCM improved the nutrient content of the solid digestates, providing digestates that could be used as biofertilizer to replace CLM that is removed from sugarcane fields during green harvesting.
Modelling the dynamics of granular particle interactions in a vortex reactor using a coupled DPM-KTGF model
(Elsevier, 2020) Oyegbile, B.; Akdogan, G.; Karimi, M.
ENGLISH ABSTRACT: In this work, a shear-driven two-phase particulate flow of monodispersed and polydispersed granular materials has been studied experimentally and numerically as a function of solids concentration and restitution coefficients for different operating speeds N (70 -130 rpm) in a lab-scale rotor-stator agglomeration reactor. A coupled computational fluid-particle dynamics (CFPD) model was developed consisting of a steady-state flow field of the continuous phase coupled to a transient particle tracking of the discrete phase. This was achieved via a one-way coupling between the continuous and the discrete phase by including the effect of drag, lift, pressure gradient, virtual mass forces, as well as granular collisional forces in describing the particle-particle, particle-wall and the fluid-particle interactions. The spatiotemporal evolution of the flow pattern, discrete phase properties, and influence of the operating conditions on the granular properties were characterized. The validation of the numerical model developed in this study was carried out based on the theoretical analysis of the rotor-stator flow and the PIV flow measurements. The results showed that the particle sizes were uniformly distributed within the reactor after steady-state conditions, while a small region of high particle concentration was observed near the rotor due to low vorticity and turbulent intensity around the region. In terms of the operating conditions, the restitution coefficients and the operating speeds do not have a significant influence on the granular properties apart from the small region around the shaft where there is a correlation between these parameters. The particle sizes, however, show a positive correlation with the granular properties. Also, a wider particle size distribution was observed axially towards the stator, which might be attributed to the pumping effect of the Batchelor flow in this direction. It was also concluded that the discrete phase velocity does not seem to vary significantly with the restitution coefficients. Furthermore, the vertical velocity and vorticity profiles give a reasonably good agreement between the CFPD model predictions and PIV measurements. The minor observed deviations were mainly due to some of the experimental limitations rather than the robustness of the CFPD model or the numerical code.
Cyanobacterial growth in minimally amended anaerobic digestion effluent and flue-gas
(MDPI, 2019) Beyl, Talita; Louw, Tobias M.; Pott, Robert W. M.
ENGLISH ABSTRACT: Anaerobic digestion (AD) is an important industrial process, particularly in a biorefinery approach. The liquid effluent and carbon dioxide in the off-gas, can be used to produce high-value products through the cultivation of cyanobacteria. Growth on AD effluent is often limited due to substrate limitation or inhibitory compounds. This study demonstrates the successful cultivation of Synechococcus on minimally amended AD effluent, supplemented with MgSO4 and diluted with seawater. An 8 L airlift reactor illustrated growth in a pilot scale setup. Higher biomass yields were observed for cyanobacteria grown in diluted AD effluent compared to minimal medium, with 60% total nitrogen removal in the effluent. It was demonstrated that controlling the pH, increasing dissolved salt concentrations and adding MgSO4 to the effluent allowed for the successful cultivation of the cyanobacterium, circumventing the addition of clean water for effluent dilution. This could ultimately increase the feasibility of anaerobic digestion-microalgae integrated biorefineries.

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