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Applying the least squares method for the titrimetric determination of the concentration of VFA

Lee SK, Yeoh HK, Chua AS, Ngoh GC

Water Sci Technol, 2012;66(3):620-6.
PMID: 22744694 DOI: 10.2166/wst.2012.216

The titrimetric method is used for on-site measurement of the concentration of volatile fatty acids (VFAs) in anaerobic treatment. In current practice, specific and interpolated pH-volume data points are used to obtain the concentration of VFA by solving simultaneous equations iteratively to convergence (denoted as SEq). Here, the least squares method (LSM) is introduced as an elegant alternative. Known concentrations of VFA (acetic acid and/or propionic acid) ranging from to 200 to 1,000 mg/L were determined using SEq and LSM. Using standard numbers of data points, SEq gave more accurate results compared with LSM. However, results favoured LSM when all data points in the range were included without any interpolation. For model refinement, unit monovalent activity coefficient (f(m) = 1) was found reasonable and arithmetic averages of dissociation constants and molecular weight of 80 mol% acetic acid were recommended in the model for VFA determination of mixtures. An accurate result was obtained with a mixture containing more VFA (butyric acid and valeric acid). In a typical VFA measurement of real anaerobic effluent, a satisfactory result with an error of 14% was achieved. LSM appears to be a promising mathematical model solver for determination of concentration of VFA in the titrimetric method. Validation of LSM in the presence of other electrolytes deserves further exploration.
Interlinked population balance and cybernetic models for the simultaneous saccharification and fermentation of natural polymers

Ho YK, Doshi P, Yeoh HK, Ngoh GC

Biotechnol Bioeng, 2015 Oct;112(10):2084-105.
PMID: 25899009 DOI: 10.1002/bit.25616

Simultaneous Saccharification and Fermentation (SSF) is a process where microbes have to first excrete extracellular enzymes to break polymeric substrates such as starch or cellulose into edible nutrients, followed by in situ conversion of those nutrients into more valuable metabolites via fermentation. As such, SSF is very attractive as a one-pot synthesis method of biological products. However, due to the co-existence of multiple biochemical steps, modeling SSF faces two major challenges. The first is to capture the successive chain-end and/or random scission of the polymeric substrates over time, which determines the rate of generation of various fermentable substrates. The second is to incorporate the response of microbes, including their preferential substrate utilization, to such a complex broth. Each of the above-mentioned challenges has manifested itself in many related areas, and has been competently but separately attacked with two diametrically different tools, i.e., the Population Balance Modeling (PBM) and the Cybernetic Modeling (CM), respectively. To date, they have yet to be applied in unison on SSF resulting in a general inadequacy or haphazard approaches to examine the dynamics and interactions of depolymerization and fermentation. To overcome this unsatisfactory state of affairs, here, the general linkage between PBM and CM is established to model SSF. A notable feature is the flexible linkage, which allows the individual PBM and CM models to be independently modified to the desired levels of detail. A more general treatment of the secretion of extracellular enzyme is also proposed in the CM model. Through a case study on the growth of a recombinant Saccharomyces cerevisiae capable of excreting a chain-end scission enzyme (glucoamylase) on starch, the interlinked model calibrated using data from the literature (Nakamura et al., Biotechnol. Bioeng. 53:21-25, 1997), captured features not attainable by existing approaches. In particular, the effect of various enzymatic actions on the temporal evolution of the polymer distribution and how the microbes respond to the diverse polymeric environment can be studied through this framework.
Kinetic and stoichiometric characterization for efficient enhanced biological phosphorus removal (EBPR) process at high temperatures

Liau KF, Shoji T, Ong YH, Chua AS, Yeoh HK, Ho PY

Bioprocess Biosyst Eng, 2015 Apr;38(4):729-37.
PMID: 25381606 DOI: 10.1007/s00449-014-1313-3

A recently reported stable and efficient EBPR system at high temperatures around 30 °C has led to characterization of kinetic and stoichiometric parameters of the Activated Sludge Model no. 2d (ASM2d). Firstly, suitable model parameters were selected by identifiability analysis. Next, the model was calibrated and validated. ASM2d was found to represent the processes well at 28 and 32 °C except in polyhyroxyalkanoate (PHA) accumulation of the latter. The values of the kinetic parameters for PHA storage (q PHA), polyphosphate storage (q PP) and growth (μ PAO) of polyphosphate-accumulating organisms (PAOs) at 28 and 32 °C were found to be much higher than those reported by previous studies. Besides, the value of the stoichiometric parameter for the requirement of polyphosphate for PHA storage (Y PO4) was found to decrease as temperature rose from 28 to 32 °C. Values of two other stoichiometric parameters, i.e. the growth yield of heterotrophic organisms (Y H) and PAOs (Y PAO), were high at both temperatures. These calibrated parameters imply that the extremely active PAOs of the study were able to store PHA, store polyphosphate and even utilize PHA for cell growth. Besides, the parameters do not follow the Arrhenius correlation due to the previously reported unique microbial clade at 28 and 32 °C, which actively performs EBPR at high temperatures.
Left ventricular flow propagation velocity measurement: Is it cast in stone?

Chan BT, Yeoh HK, Liew YM, Aziz YFA, Sridhar GS, Hamilton-Craig C, et al.

Med Biol Eng Comput, 2017 Oct;55(10):1883-1893.
PMID: 28321684 DOI: 10.1007/s11517-017-1639-5

This study aims to investigate the measurement of left ventricular flow propagation velocity, V p, using phase contrast magnetic resonance imaging and to assess the discrepancies resulting from inflow jet direction and individual left ventricular size. Three V p measuring techniques, namely non-adaptive (NA), adaptive positions (AP) and adaptive vectors (AV) method, were suggested and compared. We performed the comparison on nine healthy volunteers and nine post-infarct patients at four measurement positions, respectively, at one-third, one-half, two-thirds and the conventional 4 cm distances from the mitral valve leaflet into the left ventricle. We found that the V p measurement was affected by both the inflow jet direction and measurement positions. Both NA and AP methods overestimated V p, especially in dilated left ventricles, while the AV method showed the strongest correlation with the isovolumic relaxation myocardial strain rate (r = 0.53, p
Tropical-based EBPR process: The long-term stability, microbial community and its response towards temperature stress

Poh PK, Ong YH, Arumugam K, Nittami T, Yeoh HK, Bessarab I, et al.

Water Environ Res, 2021 Nov;93(11):2598-2608.
PMID: 34260796 DOI: 10.1002/wer.1611

Temperature is known to influence the operational efficiency of enhanced biological phosphorus removal (EBPR) systems. This study investigated the impact of thermal stress above 30°C on the properties of an EBPR community established with tropical inoculum. The results confirmed the stability of the 30°C EBPR system with high P-removal efficiency over 210 days. Accumulibacter was abundant in the community. When the EBPR sludge was subjected to a sudden temperature increase to 35°C under multiple cycles of anaerobic-aerobic phases, each lasting 4 h, high P-removal was maintained over 2 days, before gradually failing when the Competibacter appeared to outcompete Accumulibacter. These data suggested that the EBPR capacity is robust when subjected to occasional thermal stress. However, it could not be maintained even for a short time under temperature stress at 40°C. Thus, the threshold temperature for tropical EBPR failure is between 35°C and 40°C. PRACTITIONER POINTS: EBPR was stably maintained at 30°C with Accumulibacter being dominant. Good EBPR activities persisted for a short period at 35°C. EBPR was deteriorated at 40°C. The threshold temperature for tropical EBPR failure is between 35°C and 40°C.
Quantitative analysis of intraventricular flow-energetics and vortex in ischaemic hearts

Chan BT, Yeoh HK, Liew YM, Dokos S, Al Abed A, Chee KH, et al.

Coron Artery Dis, 2018 06;29(4):316-324.
PMID: 29261521 DOI: 10.1097/MCA.0000000000000596

OBJECTIVE: This study investigated the intraventricular flow dynamics in ischaemic heart disease patients.
PATIENTS AND METHODS: Fourteen patients with normal ejection fraction and 16 patients with reduced ejection fraction were compared with 20 healthy individuals. Phase-contrast MRI was used to assess intraventricular flow variables and speckle-tracking echocardiography to assess myocardial strain and left ventricular (LV) dyssynchrony. Infarct size was acquired using delayed-enhancement MRI.
RESULTS: The results obtained showed no significant differences in intraventricular flow variables between the healthy group and the patients with normal ejection fraction group, whereas considerable reductions in kinetic energy (KE) fluctuation index, E' (P<0.001) and vortex KE (P=0.003) were found in the patients with reduced ejection fraction group. In multivariate analysis, only vortex KE and infarct size were significantly related to LV ejection fraction (P<0.001); furthermore, vortex KE was correlated negatively with energy dissipation, energy dissipation index (r=-0.44, P=0.021).
CONCLUSION: This study highlights that flow energetic indices have limited applicability as early predictors of LV progressive dysfunction, whereas vortex KE could be an alternative to LV performance.