Jagannathan Krishnan

Start-up, performance and optimization of a compost biofilter treating gas-phase mixture of benzene and toluene

The performance of a compost biofilter inoculated with mixed microbial consortium was optimized for treating a gas-phase mixture of benzene and toluene. The biofilter was acclimated to these VOCs for a period of ∼18d. The effects of concentration and flow rate on the removal efficiency (RE) and elimination capacity (EC) were investigated by varying the inlet concentration of benzene (0.12-0.95g/m(3)), toluene (0.14-1.48g/m(3)) and gas-flow rate (0.024-0.072m(3)/h). At comparable loading rates, benzene removal in the mixture was reduced in the range of 6.6-41% in comparison with the individual benzene degradation. Toluene removal in mixture was even more affected as observed from the reductions in REs, ranging from 18.4% to 76%. The results were statistically interpreted by performing an analysis of variance (ANOVA) to elucidate the main and interaction effects.

Reliability, agreement, and validity of digital weighing scale with MatScan in limb load measurement

Limb loading measurements serve as an objective evaluation of asymmetrical weight bearing in the lower limb. Digital weighing scales (DWSs) could be used in clinical settings for measurement of static limb loading. However, ambiguity exists whether limb loading measurements of DWSs are comparable with a standard tool such as MatScan. A cross-sectional study composed of 33 nondisabled participants was conducted to investigate the reliability, agreement, and validity of DWSs with MatScan in static standing. Amounts of weight distribution and plantar pressure on the individual lower limb were measured using two DWSs (A, B) and MatScan during eyes open (EO) and eyes closed (EC) conditions. The results showed that intra- and interrater reliability (3, 1) were excellent (0.94-0.97) within and between DWS A and B. Bland-Altman plot revealed good agreement between DWS and MatScan in EO and EC conditions. The area under the receiver operating characteristic curve was significant and identified as 0.68 (p = 0.01). The measurements obtained with DWSs are valid and in agreement with MatScan measurements. Hence, DWSs could be used interchangeably with MatScan and could provide clinicians an objective measurement of limb loading suitable for clinical settings.

Enhancement of Oxygen Mass Transfer and Gas Holdup Using Palm Oil in Stirred Tank Bioreactors with Xanthan Solutions as Simulated Viscous Fermentation Broths

Volumetric mass transfer coefficient (k L a) is an important parameter in bioreactors handling viscous fermentations such as xanthan gum production, as it affects the reactor performance and productivity. Published literatures showed that adding an organic phase such as hydrocarbons or vegetable oil could increase the k L a. The present study opted for palm oil as the organic phase as it is plentiful in Malaysia. Experiments were carried out to study the effect of viscosity, gas holdup, and k L a on the xanthan solution with different palm oil fractions by varying the agitation rate and aeration rate in a 5 L bench-top bioreactor fitted with twin Rushton turbines. Results showed that 10% (v/v) of palm oil raised the k L a of xanthan solution by 1.5 to 3 folds with the highest k L a value of 84.44 h−1. It was also found that palm oil increased the gas holdup and viscosity of the xanthan solution. The k L a values obtained as a function of power input, superficial gas velocity, and palm oil fraction were validated by two different empirical equations. Similarly, the gas holdup obtained as a function of power input and superficial gas velocity was validated by another empirical equation. All correlations were found to fit well with higher determination coefficients.

Effect of Dopant Concentration of N, Fe Co-Doped TiO2 on Photodegradation of Methylene Blue under Ordinary Visible Light

The effect of dopant concentration on N, Fe co-doped TiO2 for photodegradation of methylene blue under ordinary visible light was investigated. The photocatalyst samples were prepared using solgel method with titanium tetraisopropoxide as precursor of titania. The dopant concentrations were varied from 0.50% and 1.0% and the calcinations temperature was fixed at 600oC. The prepared photocatalysts were characterized using XRD and FTIR to determine their physical properties. The results from XRD proved that photocatalyst with dopant concentration of 1.0% N, 1.0% Fe-TiO2 showing highly desirable properties in phase and crystal size. The results from FTIR revealed the presence of both the dopants in the samples. The effectivity of photocatalysts was tested by performing a standard batch photocatalytic degradation experiment with methylene blue as a model pollutant under ordinary visible light. The result showed that photocatalyst with high dopant concentration for both nitrogen and ferrum dopant (1.0 % N, 1.0% Fe-TiO2) yielded a maximum of 80.50% methylene blue degraded within five hours of irradiation time.

Effect of Calcination Temperature on Synthesis of N-Fe-TiO2 for Photocatalytic Degradation of Methylene Blue under Visible Light

Effect of calcination temperature on the synthesis of N, Fe codoped TiO2 for the photodegradation of methylene blue under ordinary visible lamps was investigated. The photocatalyst were prepared using solgel method where titanium isopropoxide was used as precursor of titania. The calcination temperatures were varied from 450 to 600°C. The prepared photocatalysts were characterized by using XRD, FE-SEM and FTIR to determine their physical properties. The results from XRD proved that photocatalysts calcined at 600°C possessed perfect properties in phase and crystal size. FE-SEM image analysis revealed the formation of the fine spherical particles and the FTIR analysis verified the presence of dopants at various calcination temperatures. The effectivity of photocatalysts was tested by performing a standard batch photocatalytic degradation experiment with methylene blue as a model pollutant under ordinary visible light. The result showed that N and Fe codoped photocatalyst calcined at 600°C (1.0 % N, Fe-TiO2-600) yielded a maximum of 80.50% methylene blue degraded within five hours of irradiation time.

Preparation, characterization and effectivity of N, Fe-TiO2 as a visible light active photocatalyst

Surface modification of the titanium dioxide by doping and co-doping with nitrogen and iron in order to make the photocatalyst active under visible light was investigated. Solgel method was adapted for the preparation of surface modified titanium dioxide, where tetra titanium isopropoxide, ammonium nitrate and ferric nitrate were used as precursors while maintaining the dopant concentration and calcination temperature at 0.75% and 600°C, respectively. The prepared photocatalyst samples were characterized by XRD, FE-SEM and FTIR in order to study their physical properties. The results from XRD confirmed that all prepared photocatalyst were of anatase phase. FE-SEM image analysis revealed the formation of fine particles and the FTIR analysis verified the presence of dopants. The effectivity of photocatalysts was tested by performing a standard batch photocatalytic degradation experiment with methylene blue as a model pollutant under visible light. The result showed that co-doped photocatalyst (0.75% N, 075% Fe-TiO2-600) yielded a maximum of 76% methylene blue degraded within three hours of irradiation time.

Recovery of Xanthan Gum from Palm Oil-Based Fermentation Broth by Diafiltration with Flat Polysulfone Microfiltration (MF) Membrane

Xanthan gum is a pseudoplastic biopolymer used as stabilizing agent in food, beverages, pharmaceutical, and cosmetic products, as well as drilling fluid in oil recovery.1 A major hurdle for optimum Xanthan yield is poor oxygen transfer due to viscosity increase over fermentation hours that restrict crucial oxygen transfer for cell’s metabolism. The use of bubble column and centrifugal fibrous-bed fermenter improved oxygen transfer slightly, resulting in Xanthan yield of 25–35 g L–1 compared to 22 g L–1 of conventional fermenter. Others resorted to biphasic water-in-oil (W/O) broth that successfully reduced Xanthan viscosity by dispersing Xanthan molecules within aqueous phase, resulting in Xanthan yield up to 65–75 g L–1.2 The prospect optimum, industrial scale of Xanthan production utilizing W/O broth requires a feasible separation to replace the costly conventional separation and purification method that is attributed to energy-intensive centrifugation for cell separation from the whole broth, and massive amount of alcohol to separate Xanthan from liquid broth, i.e. at 1:3 of liquid: alcohol ratio.2,3 The potential substitute for conventional method of Xanthan recovery is membrane filtration. Previously, ultrafiltration (UF) was used to dewater and concentrate Xanthan solution,4 whereas electrofiltration was used to concentrate Xanthan by electrophoretic effect.5 In fact, membrane filtration is already common in the recovery and purification of other bioproducts, such as surfactin (biosurfactant),6 fumaric acid,7 alginate,8 penicillin G9 and enzymes.10 More extensive application of membrane was shown during purification of protein implementing microfiltration (MF) for cell separation from whole broth followed by-product’s concentration by UF or nanofiltration (NF).11 To the best of our knowledge, similar strategy was never adopted for Xanthan recovery, except in our recent work employing hollow fibre MF membrane that results in 64 % recovery.12 This work demonstrated the feasibility of MF for Xanthan recovery from palm oil based (W/O) fermentation broth by optimizing the membrane filtration parameters using Taguchi method; transmembrane pressure (TMP), crossflow velocity (CFV) and ionic strength (IS) with diafiltration factor (DF) as additional parameter. Recovery of Xanthan Gum from Palm Oil-Based Fermentation Broth by Diafiltration with Flat Polysulfone Microfiltration (MF) Membrane

A CFD study of the effect of venturi geometry on high pressure wet gas metering

Venturi meter is increasingly being preferred as wet gas flow meter because of its simple construction and ease of operation. It has been found that the performance of venturi in single phase gas is very different from that of water. In this work, with a view to optimise the design, the effects of diameter, diameter ratio and convergent angle on the performance of a venturi meter for wet gas metering has been studied by CFD modelling of the high pressure wet gas flow. The performance of eight wet gas correlations for flow prediction has also been studied. Simulation results reveal that a convergent angle of 10.5 deg to be a better choice for wet gas metering. Homogeneous flow model, Steven’s and De Leeuw’s correlations are found to be better than the other correlations. While homogeneous flow model performs consistently, Steven’s and De Leeuw’s performance drops at 40 bar.

Comparison of pretreatment methods for the enhancement of fermentable sugar production from kitchen waste

The effect of different chemicals (H<inf>2</inf>SO<inf>4</inf>, NaOH and H<inf>2</inf>O<inf>2</inf>) pretreatments at various concentrations and microwave-assisted chemical (NaOH, H<inf>2</inf>SO<inf>4</inf> + NaOH and H<inf>2</inf>SO<inf>4</inf> + NaOH + H<inf>2</inf>O<inf>2</inf>) pretreatments on conversion of lignocelluloses in kitchen waste for maximum glucose yield were comparatively investigated. Overall, pretreatment by dilute H<inf>2</inf>SO<inf>4</inf> (2%) achieved the highest glucose yield of 39.43 g/L with glucose recovery of 98.86%. Alkali pretreatment using NaOH at different concentration shows no significant effect on the glucose generation (0.61–1.13 g/L) when NaOH concentration was increased. However, the combination of alkali pretreatment with microwave treatment resulted in a drastic increase of glucose yield in kitchen waste sample. Meanwhile, H<inf>2</inf>O<inf>2</inf> pretreatment seems to have little effect on the glucose yield (1.53–3.05 /L) when the concentration of H<inf>2</inf>O<inf>2</inf> was increased. But when this oxidizing agent was added to H<inf>2</inf>SO<inf>4</inf> and NaOH -microwave treatment, it increases the glucose yield from 10.36 to 13.31 g/L. With respect to glucose recovery, all microwave-assisted chemical pretreatment achieved the value of more than 90% glucose recovery.

Effect of N, S Co-doped TiO2 concentration on photocatalytic degradation of phenol

The effect of N, S Co-doped TiO2 concentration on photocatalytic degradation of phenol was investigated. The photocatalyst were prepared using sol-gel method with different concentration of dopant ranging from 0.5% to 1.0%. The precursor of titania was Titanium (IV) isopropoxide (TTIP) while the sources of nitrogen and sulfur were ammonium nitrate and thiourea respectively. The precursors were mixed to obtain a gel. The gel was dried, ground and calcined at 600 °C. The characterization of the photocatalyst using XRD showed the presence of anatase phase only and dopant concentration of 1.0% had the smallest size of crystallite which is 24 nm. The performance of the photocatalyst was tested under visible light for five hours of irradiation time. The highest degradation efficiency of phenol was at 81.8% by dopant concentration of 1.0%.