Wun Jern Ng

Optimization of agitation, aeration, and temperature conditions for maximum β-mannanase production

Abstract The effects of cultivation temperature, aeration rate, and agitation speed on the production of β-mannanase by Bacillus licheniformis NK-27 in a batch fermenter were investigated in this study. Results revealed that temperature was the most significant factor in terms of its effect on β-mannanase production. It influenced β-mannanase production by affecting the other parameters including bacteria growth, pH, dissolved oxygen, total and reducing sugars. Agitation speed and aeration rate could affect dissolved oxygen concentration which in turn affected cell growth and β-mannanase production. A maximum β-mannanase activity of 212.0xa0Uxa0ml−1 was attained in 36xa0h of cultivation when aeration rate, agitation speed, and temperature were controlled at 0.75xa0vvm, 600xa0rpm, and 30xa0°C, respectively. The maximum β-mannanase activity in the fermenter was close to that obtained from the shake flask fermentation study (198.2xa0Uxa0ml−1). However, the duration of fermentation cycle in the fermenter study was shorter than the corresponding duration obtained from the shake flask experiment by 12xa0h.

Use of Semiconductor Quantum Dots for Photostable Immunofluorescence Labeling of Cryptosporidium parvum

ABSTRACT Cryptosporidium parvum is a waterborne pathogen that poses potential risk to drinking water consumers. The detection of Cryptosporidium oocysts, its transmissive stage, is used in the latest U.S. Environmental Protection Agency method 1622, which utilizes organic fluorophores such as fluorescein isothiocyanate (FITC) to label the oocysts by conjugation with anti-Cryptosporidium sp. monoclonal antibody (MAb). However, FITC exhibits low resistance to photodegradation. This property will inevitably limit the detection accuracy after a short period of continuous illumination. In view of this, the use of inorganic fluorophores, such as quantum dot (QD), which has a high photobleaching threshold, in place of the organic fluorophores could potentially enhance oocyst detection. In this study, QD605-streptavidin together with biotinylated MAb was used for C. parvum oocyst detection. The C. parvum oocyst detection sensitivity increased when the QD605-streptavidin concentration was increased from 5 to 15 nM and eventually leveled off at a saturation concentration of 20 nM and above. The minimum QD605-streptavidin saturation concentration for detecting up to 4,495 ± 501 oocysts (mean ± standard deviation) was determined to be 20 nM. The difference in the enumeration between 20 nM QD605-streptavidin with biotinylated MAb and FITC-MAb was insignificant (P > 0.126) when various C. parvum oocyst concentrations were used. The QD605 was highly photostable while the FITC intensity decreased to 19.5% ± 5.6% of its initial intensity after 5 min of continuous illumination. The QD605-based technique was also shown to be sensitive for oocyst detection in reservoir water. This observation showed that the QD method developed in this study was able to provide a sensitive technique for detecting C. parvum oocysts with the advantage of having a high photobleaching threshold.

Effect of particles on the recovery of Cryptosporidium oocysts from source water samples of various turbidities

ABSTRACT Cryptosporidium parvum can be found in both source and drinking water and has been reported to cause serious waterborne outbreaks which threaten public health safety. The U.S. Environmental Protection Agency has developed method 1622 for detection of Cryptosporidium oocysts present in water. Method 1622 involves four key processing steps: filtration, immunomagnetic separation (IMS), fluorescent-antibody (FA) staining, and microscopic evaluation. The individual performance of each of these four steps was evaluated in this study. We found that the levels of recovery of C. parvum oocysts at the IMS-FA and FA staining stages were high, averaging more than 95%. In contrast, the level of recovery declined significantly, to 14.4%, when the filtration step was incorporated with tap water as a spiking medium. This observation suggested that a significant fraction of C. parvum oocysts was lost during the filtration step. When C. parvum oocysts were spiked into reclaimed water, tap water, microfiltration filtrate, and reservoir water, the highest mean level of recovery of (85.0% ± 5.2% [mean ± standard deviation]) was obtained for the relatively turbid reservoir water. Further studies indicated that it was the suspended particles present in the reservoir water that contributed to the enhanced C. parvum oocyst recovery. The levels of C. parvum oocyst recovery from spiked reservoir water with different turbidities indicated that particle size and concentration could affect oocyst recovery. Similar observations were also made when silica particles of different sizes and masses were added to seeded tap water. The optimal particle size was determined to be in the range from 5 to 40 μm, and the corresponding optimal concentration of suspended particles was 1.42 g for 10 liters of tap water.

Performance limitation of the full-scale reverse osmosis process

The mechanisms controlling the performance of a full-scale reverse osmosis (RO) process (typically a pressure vessel holding six 1 m long modules in series) under various operating conditions are carefully examined in this study. We demonstrate that thermodynamic equilibrium imposes a strong restriction on the performance of a full-scale RO process under certain circumstances. This thermodynamic restriction arises from the significant increase in osmotic pressure downstream of an RO membrane channel (owing to the phenomenon of salt accumulation within the RO channel as a result of permeate production). The behavior of the full-scale RO process under thermodynamic restriction is much different from that of the process when it is controlled by mass transfer. The conditions for an RO process to shift from mass transfer-controlled regime to thermodynamically restricted regime are delineated and discussed.

Removal of dissolved oxygen in ultrapure water production using microporous membrane modules

Abstract Dissolved oxygen is one of the major contaminants that have to be removed in the production of ultrapure water. The removal of dissolved oxygen from ultrapure water employing microporous hydrophobic membranes has been studied. The membranes have a negligible resistance to the passage of oxygen and provide a larger surface area per unit volume for gas-liquid contact. A study of the mass transfer in the membrane gas-liquid contactor showed that the resistance in the liquid film adjacent to the membrane phase controlled the rate of oxygen removal. The Leveque equation which describes adequately the observed overall mass transfer coefficients, fails to predict satisfactorily the dissolved oxygen concentrations in the parts per billion range. The experimental results also indicate that the membrane modules were capable of reducing the dissolved oxygen content in water to a level of around 8 ppb.

Removal of dissolved oxygen in ultrapure water production using a membrane reactor

Abstract Dissolved oxygen in water at parts per million (ppm) concentration range was reduced to a level less than 1.5 parts per billion (ppb) using a novel membrane reactor. The membrane reactor used was a polypropylene microporous hollow fibre membrane module packed with a palladium catalyst in the void space of the shell side. The saturated oxygen in water flowing in the shell side of the reactor was removed by purified hydrogen flowing in the fibre lumen. The hydrogen gas acted as both a reducing agent and a purge gas. Experimental results reveal that the rate of dissolved oxygen removal for both physical stripping and chemical reaction was controlled by the liquid film adjacent to the hollow fibre membrane and catalyst particles in the shell side. The removal of the dissolved oxygen was achieved by both the physical stripping and the chemical reaction at low catalyst loadings, whereas the chemical reaction became the dominant step at high catalyst loadings. A mass transfer correlation developed in this paper may be used in conjunction with available correlations for the design of a membrane deoxygenation reactor in the production of ultrapure water.