Biomedical subjects

Deokjin Jahng

Publications and source records attributed to Deokjin Jahng.

4 recordsLinked to original sources

PubMed2006

Enhanced methane production from anaerobic digestion of disintegrated and deproteinized excess sludge.

To improve biogas yield and methane content in anaerobic digestion of excess sludge from the wastewater treatment plant, the sludge was disintegrated by using various methods (sonication, alkaline and thermal treatments). Since disintegrated sludge contains a high concentration of soluble proteins, the resulting metabolite, ammonia, may inhibit methane generation. Therefore, the effects of protein removal from disintegrated sludge on methane production were also studied. As a result, an obvious enhancement of biogas generation was observed by digesting disintegrated sludge (biogas yield increased from 15 to 36 ml/g COD(added).day for the raw excess sludge and the sonicated sludge, respectively). The quality of biogas was also improved by removing proteins from the disintegrated sludge. About 50% (w/w) of soluble proteins were removed from the suspension of disintegrated sludge by salting out using 35 g MgCl(2) x 6H(2)O/l and also by isoelectric point precipitation at pH 3.3. For deproteinized sludge, methane production increased by 19%, and its yield increased from 145 ml/g COD(removed) to 325 ml/g COD(removed). Therefore, the yield and quality of biogas produced from digestion of excess sludge can be enhanced by disintegrating the sludge and subsequent protein removal.

Anaerobiosis↗

PubMed2005

A rapid and simple respirometric biosensor with immobilized cells of Nitrosomonas europaea for detecting inhibitors of ammonia oxidation.

As obligate chemolithotrophs, ammonia-oxidizing bacteria (AOB) grow very slowly and are known to be extremely sensitive to a wide variety of inhibitors. Since it is generally accepted that inhibition of ammonia oxidation by AOB results in a total failure of nitrogen removal, it is necessary to develop a method to detect inhibitors of ammonia oxidation in wastewater. Since ammonia oxidation accompanies oxygen consumption, ammonia oxidation can be easily evaluated by measuring oxygen consumption rate using a dissolved oxygen (DO) probe. In this study, a rapid and simple respirometric biosensor using the pure culture of Nitrosomonas europaea was developed. N. europaea was cultivated in a continuous fermentor operating at the dilution rate of 0.008 h(-1) to obtain physiologically constant cells and was immobilized onto the dialysis membrane through filtration. DO, determined by the biosensor, started to increase 30 s later after ammonia oxidation inhibitor was fed, and a new steady-state DO was obtained in 10-30 min. For this DO profile, steady-state kinetics was applied to evaluate ammonia oxidation efficiency. The concentration of a toxic compound causing 50% decrease of oxygen-consumption activity (EC50) was determined for different chemicals. The EC50 values obtained with the biosensor (0.018 mg l(-1) for allylthiourea, 0.027 mg l(-1) for thioacetamide, 1.10 mg l(-1) for phenol and 0.0 1mg l(-1) for thiourea) indicated that the developed biosensor was highly sensitive to a variety of the inhibitors. It was also shown that the biosensor is applicable for on-line real time monitoring.

Ammonia↗

PubMed2004

A novel continuous toxicity test system using a luminously modified freshwater bacterium.

An automated continuous toxicity test system was developed using a recombinant bioluminescent freshwater bacterium. The groundwater-borne bacterium, Janthinobacterium lividum YH9-RC, was modified with luxAB and optimized for toxicity tests using different kinds of organic carbon compounds and heavy metals. luxAB-marked YH9-RC cells were much more sensitive (average 7.3-8.6 times) to chemicals used for toxicity detection than marine Vibrio fischeri cells used in the Microtox assay. Toxicity tests for wastewater samples using the YH9-RC-based toxicity assay showed that EC50-5 min values in an untreated raw wastewater sample (23.9 +/- 12.8%) were the lowest, while those in an effluent sample (76.7 +/- 14.9%) were the highest. Lyophilization conditions were optimized in 384-multiwell plates containing bioluminescent bacteria that were pre-incubated for 15 min in 0.16 M of trehalose prior to freeze-drying, increasing the recovery of bioluminescence and viability by 50%. Luminously modified cells exposed to continuous phenol or wastewater stream showed a rapid decrease in bioluminescence, which fell below detectable range within 1 min. An advanced toxicity test system, featuring automated real-time toxicity monitoring and alerting functions, was designed and finely tuned. This novel continuous toxicity test system can be used for real-time biomonitoring of water toxicity, and can potentially be used as a biological early warning system.

Biological Assay↗

PubMed2004

Nitrogen control in AO process with recirculation of solubilized excess sludge.

In order to establish a sludgeless process with a nitrogen-controlled effluent, batch and continuous experiments in a lab scale anoxic-oxic (AO) process were carried out to investigate the possibility of ozonized sludge (OS) usage as a denitrification energy source. Through ozonation at an ozone dose of 1.2g O(3)/g MLVSS, 63.2% of treated MLVSS was solubilized, 12.7% of COD was lost (probably due to complete oxidation to CO(2)), and soluble COD/TN ratio of OS appeared to be only about 10.78 because ozonation released cellular proteins and other nitrogenous substances. In oxic conditions, incubation of OS supernatant with activated sludge generated nitrate without significant ammonia accumulation, which meant that rapid nitrification occurred following ammonia generation from heterotrophic degradation of nitrogen-bearing cellular substances. In anoxic conditions, externally supplied nitrate was removed at the expense of organic carbons in the OS supernatant. However, ammonia was accumulated as anoxic incubation proceeded probably because of heterotrophic degradation of nitrogenous materials as in oxic conditions. Thus it was appeared that solubilized excess sludge acted as a reducing power for denitrification but also as a nitrogen source. In addition, 24-41% of COD contained in OS supernatant were found to be consumed for denitrification. But the remaining COD was not assimilated further even in the presence of nitrate. It was concluded by a nitrogen balance analysis that the energy source contained in OS was not sufficient to completely reduce the nitrogen that was originated from OS itself to nitrogen gas.

Ammonia↗