Ki-Hoon Kang

Reaction kinetics and transformation products of 1-naphthol by Mn oxide-mediated oxidative-coupling reaction

In this study, the transformation of 1-naphthol via oxidative-coupling reaction was investigated using Mn oxides. 1-Naphthol was transformed completely by birnessite, which is one of the natural Mn oxides present in soil. The surface area-normalized specific rate constant, k(surf), for 1-naphthol was determined to be 9.66 x 10(-4)L/m(2)min using observed pseudo-first-order rate constants with respect to birnessite loading. The transformation of 1-naphthol was dependent on the solution pH, and the pseudo-first-order rate constants increased from 0.028 at pH 11 to 0.075 at pH 2 at a birnessite loading of 0.625 g/L. GC and LC mass spectroscopic analysis of the supernatants were performed after separating the reaction solution into hydrophobic and hydrophilic fractions by solvent extraction. The major transformation products were found to be 1,4-naphthoquinone(1,4-NPQ) and naphthol polymerized products with a molecular weight (m/z) ranging from 400 to 2000. Transformation of 1,4-NPQ, to the polymerized products by an additional birnessite loading was also verified. The DOC concentrations of the supernatants before and after the reaction were analyzed and the rate of oligomeric precipitate formation was measured.

A novel solution for hydroxylated PAHs removal by oxidative coupling reaction using Mn oxide

In this study, removals of 1-naphthol by oxidative-coupling reaction using birnessite, one of the natural Mn oxides present in soil, was investigated in various experimental conditions (reaction time, Mn oxide loadings, pH). The removal efficiency of 1-naphthol by birnessite was high in all the experimental conditions, and UV-visible and mass spectrometric analyses on the supernatant after reaction confirmed that the reaction products were oligomers formed by oxidative-coupling reaction. Pseudo-first order rate constants, k, for the oxidative transformation of 1-naphthol by birnessite was derived from the kinetic experiments under various amounts of birnessite loadings, and using the observed pseudo-first order rate constants with respect to birnessite loadings, the surface area normalised specific rate constant, k(surf), was also determined to be 9.3 x 10(-4) (L/m(2).min) for 1-naphthol. In addition, the oxidative transformation of 1-naphthol was found to be dependent on solution pH, and the pseudo-first order rate constants were increased from 0.129 at pH 10 to 0.187 at pH 4.

Analysis of extracellular polymeric substance (EPS) release in anaerobic sludge holding tank and its effects on membrane fouling in a membrane bioreactor (MBR)

Amongst sludge reduction strategies, the anaerobic side-stream sludge holding tank (SHT) is of particular interest because it has shown significant sludge reduction efficiency. However, due to the anaerobic and starving environment of the SHT, the release of extracellular polymeric substance (EPS) may be stimulated, and it may hamper the application of the SHT to the membrane bioreactor. In order to investigate the effect of sludge storage on EPS release, sludge samples from a pilot-scale sequencing batch reactor coupled with SHT was incubated in a series of bench-scale SHT reactors for different periods of time (0-24 h). The increase in EPS was not significant until 12 h of incubation (9.3%), while 40.9% of the increase was observed in the sample incubated for 24 h. The rapid increase in EPS concentration after 12 h indicates a greater rate of cell lysis than that with EPS consumption as substrate. Since inducing the initial stage of the endogenous phase within microorganisms is a key factor for the successful operation of the SHT for sludge reduction, the retention time for the SHT should be shorter than the time for the sudden increase in EPS release.

Evaluation of WAS reduction efficiency using kinetic parameters in pilot-scale SBR operated with anaerobic sludge holding tank.

By evaluating microbial kinetic parameters of a pilot sludge blanket reactor (SBR) plant operated with an anaerobic sludge holding tank (SHT), it was found that the sludge production was reduced by 63.5%. According to the theory of uncoupling metabolism, the microorganisms were induced to the initial stage of the endogenous phase in SHT, which resulted in the reduction of yield coefficient. For the determination of optimal retention time in SHT without causing a significant decay of microorganisms, ammonia concentration was monitored with time at specific temperature and mixed liquor suspended solids concentrations. In a long-term (>1 yr) operation of the pilot plant, no deterioration of the effluent water quality was observed. Considering phosphorus removal, an extended sludge retention time of 60-70 days (due to the reduced yield coefficient) did not significantly affect the efficiency relative to typical biological nutrient removal (BNR) processes. According to the findings of this study, anaerobic SHT can be applied for BNR processes with reduced production of sludge, and this will help to minimize environmental and economic problems pertaining to the final disposal of sludge.

Reduced sludge production in a membrane bioreactor by uncoupling metabolism and its effect on phosphorus accumulation in the biomass

ABSTRACT Due to its limited recycling or reuse, treatment and disposal of excess waste activated sludge has been a major challenge. As a preemptive method, therefore, uncoupling metabolism for reduced sludge production has been investigated recently. In this study, we operated a pilot-scale A2O-membrane bioreactor (MBR) system incorporating an anaerobic sludge holding tank (SHT) in a sludge recycling line to induce uncoupling metabolism, and investigated sludge production and treatment efficiency. After operation for ≥1 year, the Yobs value was estimated to be 0.041 g mixed liquor suspended solid (MLSS)/g chemical oxygen demand with 198.7 days of solids retention time (SRT). This Yobs value was markedly lower than those reported previously. Since MBR can be operated with a relatively high MLSS and prolonged SRT, the greatest reduction was achieved by combination with uncoupling metabolism. Phosphate fractionation experiments of the MLSS from the pilot MBR suggested the total phosphate content of microorganisms was 47.0 mg P/g mixed liquor volatile suspended solid; 83% higher than that of the activated sludge process and 49% higher than that of the conventional A2O process. Of the increased phosphate contents, that of the acid-insoluble polyphosphate (AISP) fraction was greatest, suggesting that growth inhibition by uncoupling metabolism stimulates AISP synthesis, which can be utilized under growth-limiting conditions. Abbreviations: AISP: acid-insoluble polyphosphate; ASP: acid-soluble polyphosphate; BNR: biological nutrients removal; EPS: extracellular polymeric substance; LMH: L/m2 h; MBR: membrane bioreactor; OST: oxic-settling-anaerobic; PAO: phosphate accumulation organism; PCA: perchloric acid; SBR: sequencing batch reactor; SHT: sludge holding tank; SRT: solids retention time; TN: total nitrogen; TP: total phosphate; WAS: waste activated sludge

Fouling Mitigation for Pressurized Membrane of Side-Stream MBR Process at Abnormal Operation Condition

Pressurized membrane used for side-stream MBR process requires fouling control strategy both for normal and abnormal operation conditions for stable operation of the facilities. In this study, 85 m/day of pilot-scale side-stream MBR process was constructed for the evaluation of fouling mitigation by air bubble injection into the membrane module. In addition, fouling phenomena at abnormal operation conditions of low influent and/or loading rate were also investigated. Injection of air bubble was found to be effective in delaying transmembrane pressure (TMP) increase mainly due to scouring effect on the membrane surface, resulting in expanded filtration cycle at a high flux of 40 L/m・h (LMH). At abnormal operation condition, injection of PACl (53 mg/L as Al) into the bioreactor showed 19% reduction of TMP increase. However, inhibition of nitrifying bacteria by continuous PACl injection was observed from batch experiments. In contrast, injection of powdered activated carbon (PAC, 0.6 g/L) was able to maintain the initial TMP of 0.2 kg/cm for 5 days at the abnormal conditions. It may have been caused from the adsorption of extracellular polymeric substances (EPS), which was known to be excessively released during growth inhibition condition and act as the major foulants in MBR operations.