Jae K. Park

Characterization of thermal reaction by peak temperature and height of DTG curves

Abstract A relationship between the peak temperature and height in derivative thermogravimetry (DTG) curves was explored to seek their specific combination for addressing the uniqueness of a thermal reaction. The functional relationship between the peak temperature and height was closely related to the activation energy and reaction order, but rarely affected by the preexponential factor and heating rate. Determining peak temperature and height at a heating rate was enough to characterize a thermal reaction of first-order kinetics or known reaction order, but was insufficient to specify a reaction without knowing the shifting pattern of either peak temperature or peak height with heating rate. The peak temperature and height varied with the heating rate according to the kinetic parameters. The shifting pattern of the peak temperature with the heating rate was related to the activation energy, while that of the peak height was confined by the reaction order together with the activation energy.

Competition between polyphosphate- and glycogen-accumulating organisms in enhanced-biological-phosphorus-removal systems: Effect of temperature and sludge age

Temperature and sludge age were found to be important factors in determining the outcome of competition between polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating non-polyphosphate organisms (GAOs) and the resultant stability of enhanced-biological-phosphorus removal (EBPR). At 20 degrees C and a 10-day sludge age, PAOs were dominant in an anaerobic/aerobic (A/O) sequencing-batch reactor (SBR), as a result of their higher anaerobic-acetate-uptake rate and aerobic-biomass yield than GAOs. However, at 30 degrees C and a 10-day sludge age, GAOs were able to outcompete PAOs in the A/O SBR because of their higher anaerobic-acetate-uptake rate than PAOs. At 30 degrees C and a 5-day sludge age, GAOs coexisted with PAOs in the A/O SBR, resulting in unstable EBPR performance. At 30 degrees C, reducing the sludge age from 5 to 3 days improved the EBPR efficiency drastically, and the EBPR performance was stable. The maximum specific-anaerobic-acetate-uptake rates of GAO-enriched sludge were affected by temperature with the Arrhenius temperature coefficient theta of 0.042 (degrees C(-1) between 10 and 30 degrees C. The effect of sludge age (5 and 10 days) on the maximum specific-anaerobic-acetate-uptake rates of GAO-enriched activated sludge, however, was not significant. For the PAO-enriched activated sludge, the maximum specific-anaerobic-acetate-uptake rate did not change significantly between 20 and 30 degrees C, but significantly increased from 0.38 to 0.52 mmol-C/ mmol-C/h as the sludge age decreased from 10 to 3 days at 30 degrees C.

Removal of polychlorinated phenols in sequential anaerobic-aerobic biofilm reactors packed with tire chips

Scrap vehicle tire chips were used as packing material for sequential anaerobic-aerobic biofilm reactors to remove persistent chlorinated hydrocarbons. Adsorption capacity of scrap tires was greater under acidic conditions than under basic conditions. However, it was only approximately 0.04 to 0.3% of that of activated carbon. The amount of biomass that attached to the surface of scrap tires was 3.16 and 3.72 mg volatile suspended solids/cm{sup 2} after 14 and 37 days, respectively. Two laboratory-scale, down-flow anaerobic-aerobic biofilm reactors packed with tire chips were operated to remove 2,4-dichlorophenol (DCP) and 4-chlorophenol (CP). More than 98% of DCP was dehalogenated to CP in the anaerobic reactor, 70 to 98% of which was subsequently degraded in the aerobic reactor. Scrap tires did not cause any operational problems when used as biofilter media.

Removal efficiencies of endocrine disrupting chemicals by coagulation/flocculation, ozonation, powdered/granular activated carbon adsorption, and chlorination

Removal efficiencies of endocrine disrupting chemicals (EDCs), bisphenol A and nonylphenol, during various types of water treatment processes were evaluated extensively using laboratory- and pilot-scale experiments. The specific processes of interest were coagulation/flocculation sedimentation/filtration (conventional water treatment process), powdered activated carbon (PAC), granular activated carbon (GAC), ozonation and chlorination. Batch sorption tests, coagulation tests, and ozone oxidation tests were also performed at higher concentrations with 14 EDCs including bisphenol A. The conventional water treatment process had very low removal efficiencies (0 to 7%) for all the EDCs except DEHP, DBP and DEP that were removed by 53%, 49%, and 46%, respectively. Ozonation at 1 mgO3/ L removed 60% of bisphenol A and 89% of nonylphenol, while chlorination at 1 mg/L removed 58% and 5%, respectively. When ozone and chlorine doses were 4 and 5 mg/L, respectively, both EDCs were not detected. PAC removal efficiencies ranged from 15% to 40% at 3 to 10 mg/L of PAC with a contact time of 15 minutes. In the high concentration batch sorption tests, EDC removal efficiencies by PAC were closely related to octanol-water partition coefficient (Kow). GAC adsorption was very effective water treatment process. The type and service time of GAC did not affect EDC removal efficiencies. The combination of ozonation and GAC in series appears to remove EDCs effectively to safe levels while conventional water treatment could not.

Enhanced anaerobic biodegradability and inactivation of fecal coliforms and Salmonella spp. in wastewater sludge by using microwaves.

During continuous operation of three mesophilic-anaerobic digesters, the effect of microwave irradiation, as sludge thermal pretreatment (60 to 65 degrees C), was studied. The fecal coliforms log inactivation for microwaved/digested sludge was 4.2 +/- 0.4, whereas for conventionally heated/digested sludge and control were 2.9 +/- 0.5 and 1.5 +/- 0.5, respectively. In the case of Salmonella spp., no colonies were detected in 85% of the microwaved/digested samples. Considering the detection limit, the log inactivation of these samples was greater than 2.0 +/- 0.3. The conventionally heated/digested sludge and control showed log inactivations of 1.9 +/- 0.2 and 1.1 +/- 0.3, respectively. At the 95% confidence level, microwaved/digested sludge increased the biogas production by 16.4 +/- 5.6% and 6.3 +/- 2.4%, as compared to control and conventionally heated/digested sludge, respectively. When thermally treated sludge was analyzed for soluble chemical oxygen demand, microwaved waste-activated sludge showed considerable solubilization between 37 and 60 degrees C. Microwaved/digested sludge showed a reduction of capillary suction times by 11.1 +/- 5.9% and 10.7 +/- 5.6%, as compared to control and conventionally heated/digested sludge, respectively.

Activity, structure, and stratification of membrane-attached methanotrophic biofilms cometabolically degrading trichloroethylene

A membrane-attached methanotrophic biofilm reactor was developed for the cometabolic degradation of trichloroethylene (TCE). In this reactor, CH4 and O2 are supplied to the interior of the biofilm through the membrane, while TCE-contaminated water is supplied to the exterior, creating a “counter-diffusional” effect that minimizes competitive inhibition between TCE and CH4. In addition, this novel design provides 100% CH4 and O2 transfer efficiencies, promotes the development of a thick biofilm, and minimizes the negative effects of TCE byproduct toxicity. The reactor sustained 80-90% TCE removals at TCE loading rates ranging from 100-320 μmol/m2/d. Chloride mass balances demonstrated that 60-80% of the TCE removed was mineralized. The maximum TCE transformation yield was 1.8 mmol of TCE removed per mole of CH4 utilized, although higher transformation yields are expected at higher TCE loading rates. The CH4 utilization rate was 0.20 mol/m2/d. Scanning electron microscopy (SEM) revealed a dense biofilm with a thickness of at least 400 μm. SEM and transmission electron microscopy (TEM) analyses indicated that the “holdfast” material associated with rosette formation in planktonic Methylosinus trichosporium OB3b ( M.t. OB3b) cells might also contribute to pure-culture biofilm development. In addition, fimbriae-like structures not commonly associated with methanotrophic bacteria were observed in pure-culture M.t. OB3b biofilms. Finally, fluorescent in situ hybridization (FISH) analyses showed the presence of discrete microcolonies of serine-pathway methanotrophs within mixed-culture biofilms.

Electrochemical mechanisms of corrosion influenced by sulfate-reducing bacteria in aquatic systems

Abstract It has been recognized that sulfate-reducing bacteria (SRB) play a significant role in corrosion by accelerating the electrochemical processes whenever environmental conditions are favouable. In this study, the polarization test and the dual-cell test were conducted to result in a better fundamental understanding of corrosion influenced by SRB. The polarization test showed that the effects of SRB and anodic or cathodic depolarization on corrosion were insignificant when 1.5 mM of CaCO 3 was added to the solution. The instantaneous corrosion rates of steel coupons immersed in the SRB-inoculated solution were 1.5–2.5 times greater than those obained in the sterile solution. The polarization curves obtained in the SRB-inoculated solution with 0.5 mM sulfate concentration indicated that both anodic and cathodic depolarization occurred on steel coupons. However, only cathodic depolarization was obtained in the SRB-inoculated solution with 0.1 mM sulfate concentration, due to low hydrogen sulfide production. From the dual-cell test, the electron was transferred from the steel coupon in the sterile solution toward the steel coupon immersed in the SRB-inoculated solution, probably due to the electron consumption by SRB. When CaCO 3 was added to the same solution, no reactions occurred on the coupons exposed to either the SRB-inoculated solution or the sterile solution after 20 h of inoculation.

Effect of wastewater composition on microbial populations in biological phosphorus removal processes

Bench-scale sequential batch reactors (SBRs) were fed with glucose- and acetate-containing synthetic wastewaters to evaluate microbial population dynamics and types of phosphorus-accumulating organisms (PAOs) using a cellular fatty acid profile analysis. The phosphorus content in the sludge was 38% (w/w) for the acetate-fed SBR and 20% (w/w) for the glucose-fed SBR with a VSS/TSS ratio of 50%. Glucose-fed PAOs were found to remove phosphorus with accumulation of glycogen in cells without synthesizing poly-β-hydroxybutyrate (PHB) at influent phosphorus concentration Acinetobacter, Pseudomonas, Arthrobacter, Aeromonas, and Micrococcus ), only Arthrobacter spp. had the biomarker of fatty acid a15:0, indicating that Arthrobacter spp. may be one of the PAOs existing in the glucose-fed bioreactors.

Effects of volatile organic compounds on clay landfill liner performance

Clay borrow materials intended for use in a clay liner system were found to be contaminated by low concentrations of volatile organic chemicals (VOCs). The suspected source of contaminants was a ne...

Statistics-based classification of microbially influenced corrosion in freshwater systems

Abstract This paper describes work aimed at developing a statistics-based approach to classify water sites of an unknown biocorrosive class. Field surveys were performed at over 40 sites throughout Wisconsin for 2 years to investigate microbially influenced corrosion. More than 20 water-related variables were measured. Aerobic bacteria and sulfate-reducing bacteria were isolated and their numbers in the water sample were counted. Steel coupons were installed and the corrosion rates were estimated using a gravimetric method. A visual examination rating system was adopted to evaluate the microbial corrosion rate and results showed that the visual examination rating was in agreement with the measured corrosion rate. Based on the stepwise regression analysis and discriminant analysis results, a set of classification rules was developed. By using these practical rules, the biocorrosive tendency of freshwater sites could be predicted. Furthermore, some valuable implications obtained from field surveys were summarized and explored.