Chang Gyun Kim

Decomposition of 1,4-Dioxane by Advanced Oxidation and Biochemical Process

This study was undertaken to determine the optimal decomposition conditions when 1,4-dioxane was degraded using either the AOP S (Advanced Oxidation Processes) or the BAC-TERRA microbial complex. The advanced oxidation was operated with H2O2, in the range 4.7 to 51 mM, under 254 nm (25 W lamp) illumination, while varying the reaction parameters, such as the air flow rate and reaction time. The greatest oxidation rate (96%) of 1,4-dioxane was achieved with H2O2 concentration of 17 mM after a 2-hr reaction. As a result of this reaction, organic acid intermediates were formed, such as acetic, propionic and butyric acids. Furthermore, the study revealed that suspended particles, i.e., bio-flocs, kaolin and pozzolan, in the reaction were able to have an impact on the extent of 1,4-dioxane decomposition. The decomposition of 1,4-dioxane in the presence of bio-flocs was significantly declined due to hindered UV penetration through the solution as a result of the consistent dispersion of bio-particles. In contrast, dosing with pozzolan decomposed up to 98.8% of the 1,4-dioxane after 2 hr of reaction. Two actual wastewaters, from polyester manufacturing, containing 1,4-dioxane in the range 370 to 450 mg/L were able to be oxidized by as high as 100% within 15 min with the introduction of 100:200 (mg/L) Fe(II):H2O2 under UV illumination. Aerobic biological decomposition, employing BAC-TERRA, was able to remove up to 90% of 1,4-dioxane after 15 days of incubation. In the meantime, the by-products (i.e., acetic, propionic and valeric acid) generated were similar to those formed during the AOPS investigation. According to kinetic studies, both photo-decomposition and biodegradation of 1,4-dioxane followed pseudo first-order reaction kinetics, with k = 5 × 10−4 s−1 and 2.38 × 10−6 s−1, respectively. It was concluded that 1,4-dioxane could be readily degraded by both AOP S and BAC-TERRA, and that the actual polyester wastewater containing 1,4-dioxane could be successfully decomposed under the conditions of photo-Fenton oxidation.

Optimization of biological wastewater treatment conditions for 1,4-dioxane decomposition in polyester manufacturing processes.

The solvent stabilizer 1,4-dioxane could have harmful effects on an ecosystem. The discharge limit of 1,4-dioxane in a body of water will be regulated at 5 mg/L in Republic of Korea. Thus, the currently operating activated sludge used in the manufacture of polyester should be properly treated to meet the regulations. Accordingly, the removal rate of 1,4-dioxane and its microbial properties was assessed at K, H and T corporations. The highest removal efficiencies were recorded at H. However, the concentration of 1,4-dioxane in the effluent of T exceeded the criterion. In addition, a microbial degradation test was conducted on 100 mg/L of 1,4-dioxane inoculated with the activated sludge from each of the three corporations. After 7 days, the 1,4-dioxane was completely removed with the H sludge and efficiencies were 67% in the T sludge and 52% in the K sludge. These results confirm that the biodegradability of 1,4-dioxane may vary in relation to the microbial properties. The microbial diversity of activated sludge of each company was therefore investigated by 16S rDNA cloning methods. In conclusion, the activated sludge of H is the most effective for the biodegradation of 1,4-dioxane. This fact is of significant concern for the industrial sector.

Comparative enzyme inhibitive methanol production by Methylosinus sporium from simulated biogas.

Methane in a simulated biogas converting to methanol under aerobic condition was comparatively assessed by inhibiting the activity of methanol dehydrogenase (MDH) of Methylosinus sporium using phosphate, NaCl, NH4Cl or EDTA in their varying concentrations. The highest amount of methane was indistinguishably diverted at the typical conditions regardless of the types of inhibitors: 35°C and pH 7 under a 0.4% (v/v) of biogas, specifically for <40 mM phosphate, 50 mM NaCl, 40 mM NH4Cl or 150 µM EDTA. The highest level of methanol was obtained for the addition of 40 mM phosphate, 100 mM NaCl, 40 mM NH4Cl or 50 µM EDTA. In other words, 0.71, 0.60, 0.66 and 0.66 mmol methanol was correspondingly generated by the oxidation of 1.3, 0.67, 0.74 and 1.3 mmol methane. It gave a methanol conversion rate of 54.7%, 89.9%, 89.6% and 47.8%, respectively. Among them, the maximum rate of methanol production was observed at 6.25 µmol/mg h for 100 mM NaCl. Regardless of types or concentrations of inhibitors differently used, methanol production could be nonetheless identically maximized when the MDH activity was limitedly hampered by up to 35%.

Decomposition of 1,4-dioxane by photo-Fenton oxidation coupled with activated sludge in a polyester manufacturing process

The cyclic ether 1,4-dioxane is a synthetic industrial chemical that is used as a solvent in producing paints and lacquers. The EPA and the International Agency for Research on Cancer(IARC) classified 1,4-dioxane as a GROUP B2(probable human) carcinogen. 1,4-dioxane is also produced as a by-product during the manufacture of polyester. In this research, a polyester manufacturing company (i.e. K Co.) in Gumi, Korea was investigated regarding the release of high concentrations of 1,4-dioxane (about 600 mg/L) and whether treatment prior to release should occur to meet with the level of the regulation standard (e.g., 5 mg/L in 2010). A 10 ton/day pilot-scale treatment system using photo-Fenton oxidation was able to remove approximately 90% of 1,4-dioxane under the conditions that concentrations of 2800 ppm H(2)O(2) and 1,400 ppm FeSO(4) were maintained along with 10 UV-C lamps (240 microW/cm(2)) installed and operated continuously during aeration. However, the effluent concentration of 1,4-dioxane was still high at about 60 mg/L where TOC concentration in the effluent had been moreover increased due to decomposed products such as aldehydes and organic acids. Thus, further investigation is needed to see whether the bench scale (reactor volume, 8.9 L) of activated sludge could facilitate the decomposition of 1,4-dioxane and their by-products (i.e., TOC). As a result, 1,4-dioxane in the effluent has been decreased as low as 0.5 mg/L. The optimal conditions for the activated sludge process that were obtained are as follows: DO, 3-3.5 mg/L; HRT, 24 h; SRT 15 d; MLSS, 3,000 mg/L. Consequently, photo-Fenton oxidation coupled with activated sludge can make it possible to efficiently decompose 1,4-dioxane to keep up with that of the regulation standard.

Resource recovery of sludge as a micro-media in an activated sludge process

Abstract An experiment was conducted to evaluate the feasibility of sludge reuse as a micro-medium in an activated sludge (AS) process. Two experimental protocols were employed. A conventional activated sludge was tested as a control, while the other involved addition of clinoptilolite (ZR) of which 4000 mg/l was unvaryingly sustained in an aeration basin. Two experiments were performed for ZR. In one, clinoptilolite was used as micro-media for 60 days (Model 1). The other used dried excess sludge for 55 days (Model 2). For sludge being recovered as micro-media, organic matter in the sludge was eliminated by 86% at 300 °C. It was completely removed at 500 °C within 30 min, which was regarded as the optimal drying condition. For Model 1, the concentration of biomass was increased by 4720 mg MLVSS/l. It was greater by a factor of two than that of the control. Moreover, it is shown that organic matter could be removed up to 95%. In addition, the sludge settling properties were greatly enhanced by clinoptilolite being implemented as floc seeds. Nitrification was considerably improved by more than 90%, due to the high concentration of nitrifiers attached to micro media. For Model 2, the improved performance was sustained on applying burned sludge into the AS. It was concluded that dried sludge could be reused as micro-media in an activated sludge process.

Hybrid Treatment of Tetramethyl Ammonium Hydroxide Occurring from Electronic Materials Industry

TMAH (tetramethyl ammonium hydroxide) originating from etching and photo-developing processes was treated with Fenton oxidation followed by an activated sludge. Additionally, a Microtox test was performed to address any potential toxicity of TMAH against mixed cultures of microorganisms in the activated sludge. The Microtox test revealed that toxicity of TMAH againstPhotobacterium phosphoreum was highly effective showing 5% of EC50, but its toxicity was completely dissipated showing 100% of EC50 being recovered after being treated with Fenton reagents. BOD5 test showed that acclimated cultures to TMAH could readily decompose TMAH in an order of magnitude higher than that of not-acclimated culture. Feasibility tests showed that TMAH was readily biodegraded after being oxidized by the Fenton process, while TMAH fed directly into the activated sludge was laggardly decomposed during longer adaptation period. In the presence of acetic acid, activity of acclimated mixed cultures to TMAH was considerably reduced by dominant presence of predators competitively utilizing acetic acid.

The removal of 1,4-dioxane from polyester manufacturing process wastewater using an up-flow Biological Aerated Filter (UBAF) packed with tire chips

1,4-Dioxane is one of the by-products from the polyester manufacturing process, which has been carelessly discharged into water bodies and is a weak human carcinogen. In this study, a laboratory-scale, up-flow biological aerated filter (UBAF), packed with tire chips, was investigated for the treatment of 1,4-dioxane. The UBAF was fed with effluent, containing an average of 31 mg/L of 1,4-dioxane, discharged from an anaerobic treatment unit at H Co. in the Gumi Industrial Complex, South Korea. In the batch, a maximum of 99.5 % 1,4-dioxane was removed from an influent containing 25.6 mg/L. In the continuous mode, the optimal empty bed contact time (EBCT) and air to liquid flow rate (A:L) were 8.5 hours and 30:1, respectively. It was also found that the removal efficiency of 1,4-dioxane increased with increasing loading rate within the range 0.04 to 0.31 kg 1,4-dioxane/m3·day. However, as the COD:1,4-dioxane ratio was increased within the range 3 to 46 (mg/L COD)/(mg/L 1,4-dioxane), the removal efficiency unexpectedly decreased.

Evaluation of increased denitrification in an anoxic activated sludge using zeolite

Zeolite added activated sludge unit (ZU) under anoxic conditions improved nitrate removal efficiency by 48% (i.e., equivalent to approximately 10 mg//) greater than that of a conventional activated sludge unit (CU) regardless of varying C/N ratio ranging from 0 to 4.8. For a C/N ratio of 4, no significant differences of denitrification rate were found between two units showing a range of 6.7 to 6.9 mg NO3--N/g VSS (volatile suspended solids) hr. However, a C/N ratio decrease to 1.6 was ascribed to considerable differences in denitrification rate showing 4.15 mg NO3--N/g VSS ·hr for the ZU, which was 39% greater than that of the CU presenting at 2.98 mg NO3--N/g VSS ·hr. It was decided that the presence of greater concentration of MLVSS (mixed liquor suspended solids) in the ZU can be efficiently used for enhanced denitrification as a potential carbon source due to autolysis, although a lower concentration of COD (i.e., less than 1.6 of C/N ratio) is introduced.

Comment on "the interaction of humic substances with cationic polyelectrolytes".

Kam and Gregory (Water Research 35(2001) 3557– 3566) reported on the removal of humic substances (HS) in the coagulation and flocculation process using cationic polyelectrolytes. The investigation was devoted to the dominant mechanism of HS removal in the process. The HS elimination was compared in a Jar test performed with cationic polymers of different charge and molecular weight under constant pH of 7. The experimental results showed that charge neutralization was a significant factor for the removal of aquatic HS in the coagulation/flocculation process, monitored by the colloid titration and the streaming current procedures, and indicated that a bridging mechanism was unlikely to play a major role in this process. The authors concluded that the key mechanism of charge neutrality was applied to the HS removal in the coagulation process of metal coagulants used, as well as cationic polymers. However, the former is questionable. In coagulation using metal coagulants, three kinds of mechanisms were commonly referred for the HS removal: (1) charge neutralization, (2) complexation, and (3) adsorption [1,2]. A dominant mechanism depends on the pH of a solution. Gregor et al. [2] noted that cationic Al ions formed complexes combined with acidic functional groups (carboxylic and phenolic groups) of HS in the pH condition below 5.5, and that the function (defined as complexation) prevalently attributed to the HS reduction under the pH region. The complexation was differentiated from charge neutralization in that the complex would be precipitated due to size increase rather than charge neutrality [2]. On the other hand, Bell-Ajy et al. [3] recently reported that at low pH conditions insoluble complexes could be established through charge neutralization between negative HS and cationic metal hydrolysis products. It is likely that at low pH values the key mechanism of the HS removal is not clarified yet in the coagulation process. It was reported that the adsorption of humic substances to alum flocs played a major role in the HS removal under pH 6–7 favoring Al hydroxide precipitation [4,5]. The adsorption of HS to Al hydroxide occurs through surface complexation or ligand exchange [6]. Here, the surface complexation means interactions between functional groups of HS and surface hydroxyl on Al hydroxide [7,8]. Bose and Reckhow [9] also suggested that the adsorption of HS to Al hydroxide floc was a prevalent process in removing aquatic HS. In this paper, it was concluded that charge neutralization was the key mechanism in the coagulation process using cationic polymers, and the phenomenon extended to the HS removal in the coagulation of metal salts employed without experimental validation. However, it has been demonstrated that the dominant mechanism for the HS removal seriously varies depending on the pH of the solution in the coagulation/flocculation process when metal salts are used as coagulants. It is likely that a supplementary experiment is required to evaluate the HS removal mechanism in the coagulation using metal coagulants.

Degradation of the long-resistant pharmaceutical compounds carbamazepine and diatrizoate using mixed microbial culture

ABSTRACT The microbial degradation of two recalcitrant pharmaceutical compounds, carbamazepine (CBZ) and diatrizoate (DTZ), was studied in laboratory batch experiments. We used a defined mixed microbial culture comprising four distinct microbial species that were previously known to have high decomposition capacity toward recalcitrant substances. Biological decomposition in liquid phase cultures for either CBZ or DTZ, or in a combination of the two, was conducted for 12 days. DTZ and CBZ were degraded by 43.2% and 60%, respectively from an initial concentration of 100 µg L−1. When degradation was assessed using a mixture of the two compounds, the initial degradation rates of CBZ and DTZ were lower than those observed in the single-compound study. However, the final cumulative removal efficiency was very similar. The extent of dissolved organic carbon (DOC) removal was correlated with the degradation of the pharmaceuticals.