Johng-Hwa Ahn

Effect of output power, target temperature, and solid concentration on the solubilization of waste activated sludge using microwave irradiation.

In this paper, we quantify the effect of heating pretreatment on the degree of solubilization of waste activated sludge. The pretreatment process was carried out using a lab-scale industrial microwave unit (2450 MHz frequency). Response surface analysis was applied to determine the combination of output power (400-1600 W), target temperature (60-120 degrees C), and total solid concentration (1-3% total solid (TS)). The power, temperature, and TS concentration significantly affected the solubilization degree of sludge. Within the design boundaries, the conditions predicted to maximize the solubilization degree of 17.9% were determined to be 400 W, 102 degrees C, and 2.3% TS.

Effect of microwave pretreatment in presence of NaOH on mesophilic anaerobic digestion of thickened waste activated sludge.

This work experimentally determined the effect of microwave irradiation with NaOH pretreatment on anaerobic digestion of thickened waste activated sludge in semi-continuous mesophilic digesters at hydraulic retention times (HRT) of 15, 10, 7, and 5 days. The degree of substrate solubilization was 18 times higher in pretreated sludge (53.2%) than in raw sludge (3.0%). Removal efficiency of volatile solid in digesters fed with raw (control) and pretreated sludges (PD) decreased as HRT reduced. The highest relative improvement of properties compared with the control occurred at 5 day HRT. Improvements in biogas production compared with the control increased in the PD as HRT was reduced to 5 days (205% higher at 5 days). However, digested sludges in the control and PD increased capillary suction time compared with raw sludge. The results show that microwave irradiation combined with alkali pretreatment is effective in increasing mesophilic anaerobic biodegradability of sewage sludge.

Optimization of microwave pretreatment conditions to maximize methane production and methane yield in mesophilic anaerobic sludge digestion

The objective of this study was to find optimum microwave pretreatment conditions for methane production and methane yield in anaerobic sludge digestion. The sludge was pretreated using a laboratory‐scale industrial microwave unit (2450 MHz frequency). Microwave temperature increase rate (TIR) (2.9–17.1 °C/min) and final temperature (FT) (52–108 °C) significantly affected solubilization, methane production, and methane yield. Solubilization degree (soluble chemical oxygen demand (COD)/total COD) in the pretreated sludge (3.3–14.7%) was clearly higher than that in the raw sludge (2.6%). Within the design boundaries, the optimum conditions for maximum methane production (2.02 L/L) were TIR = 9.1°C/min and FT = 90 °C, and the optimum conditions for maximum methane yield (809 mL/g VSremoved) were TIR = 7.1 °C/min and FT = 92 °C.

Use of order-specific primers to investigate the methanogenic diversity in acetate enrichment system

The applicability of order-specific primers in minimizing the possible underestimation of microbial diversity was evaluated via denaturing gradient gel electrophoresis (DGGE) analysis of a lab-scale anaerobic digester. Initially, a population analysis with real-time quantitative PCR demonstrated the existence of three methanogenic orders—Methanobacteriales, Methanomicrobiales, and Methanosarcinales—throughout the reaction period. DGGE analyses with three pairs of order-specific primers yielded eight operational taxonomic units (OTUs), whereas DGGE analysis with two independent Archaea-specific primers identified only five. Moreover, the order-specific primers amplified at least one OTU affiliated with each order, whereas no members of Methanobacteriales or Methanomicrobiales were identified with Archaea-specific primers in most samples. These findings provide evidence that order-specific analysis can detect the diversity of methanogens in greater detail than conventional Archaea-specific analysis.

Biokinetic Evaluation and Modeling of Continuous Thiocyanate Biodegradation by Klebsiella sp.

Biokinetics for autotrophic degradation of thiocyanate using batch culture of Klebsiellasp. were evaluated both analytically and numerically. A sequential approach with an analytical method followed by a numerical approximation was used to evaluate and to ensure the accuracy of the parameter estimation. The nonlinear least‐squares method with a 95% confidence interval was employed. The growth conditions were maintained at pH 7 and 38 °C for all experiments. With an automated incubation and turbidity reader, a total of 16 different initial thiocyanate concentrations, ranging from 10 to 300 mg L−1, were used to develop a kinetic expression of specific growth rate as a function of substrate concentration. The biodegradation of thiocyanate with Klebsiellasp. followed a substrate inhibition pattern. Three identical automated bioreactors with working volumes of 1.5 L, equipped with sterilizable sampling ports, were also used for the numerical approximation of the biokinetic parameters in batch mode. A fourth order Runge‐Kutta method was used to approximate the substrate inhibition kinetics of the Klebsiellasp. utilizing thiocyanate. Although the kinetic coefficients estimated by analytical and numerical methods were not statistically different at a 0.05 α level, model responses of numerical approximation generated a better prediction of changes in thiocyanate and cell mass concentrations. The hypothetical maximum growth rate, μm, half saturation coefficient, Ks, microbial yield coefficient, Y, cell mass decay rate coefficient, kd, and substrate inhibition coefficient, Ksi, were evaluated as being 0.62 ± 0.05 d−1, 85 ± 8 mg SCN− L−1, 0.076 ± 0.011 mg cell mass (mg SCN)−1, 0.03 ± 0.002 d−1, and 131 ± 22 mg SCN− L−1, respectively. The calculated maximal substrate concentration, Sm, and apparent maximum specific growth rate, μ′m, were 105.5 ± 8.7 mg SCN− L−1 and 0.24 ± 0.01 d−1, respectively. Using these estimated parameters, the theoretical performance of the continuous operation was also illustrated, which depicts the residual thiocyanate and Klebsiella sp. concentrations in the non‐steady and steady states at different hydraulic retention times (HRTs). Assuming the influent concentration of 250 mg SCN− L−1, the expected treatment efficiency ranged from 94.9% to 69.4% between 20 and 5 days HRT, respectively. Klebsiellasp. was expected to be washed out at 4.8 days HRT, thus resulting in no treatment of thiocyanate.

Simultaneous effect of temperature, cyanide and ammonia-oxidizing bacteria concentrations on ammonia oxidation

For biological nitrification, a set of experiments were carried out to approximate the response of lag period along with ammonia oxidation rate with respect to different concentrations of cyanide (CN−) and ammonia-oxidizing bacteria (AOB), and temperature variation in laboratory-scale batch reactors. The effects of simultaneous changes in these three factors on ammonia oxidation were quantitatively estimated and modeled using response surface analysis. The lag period and the ammonia oxidation rate responded differently to changes in the three factors. The lag period and the ammonia oxidation rate were significantly affected by the CN− and AOB concentrations, while temperature changes only affected the ammonia oxidation rate. The increase of AOB concentration and temperature alleviated the inhibition effect of cyanide on ammonia oxidation. The statistical method used in this study can be extended to estimate the quantitative effects of other environmental factors that can change simultaneously.

Effect of Food Waste Compost on the Antler-Type Fruiting Body Yield of Ganoderma lucidum

Abstract The effects of the composition of a mixture containing food waste compost (FWC), rice bran (RB), and oak sawdust (SD) on the antler-type fruiting body (FB) yield of Ganoderma lucidum were studied. Experiments were performed using 0 (control), 5, 10, 15, 20, 25, 30, 35, and 40% (w/w) FWC added to a basal growth medium consisting of 20% (w/w) RB and 80% (w/w) SD. The content of 15% FWC gave the highest FB yield (27.0 ± 1.3 g/bottle), which was 44% higher than the yield (18.6 ± 2.8 g/bottle) of the control treatment. However, FWC contents of 20~40% showed reduced yield (2.4~23.0 g/bottle), partly because FWC had a high Na concentration (0.6%). These results demonstrate the potential for use of FWC as a component of a growth medium for production of G. lucidum FBs.

Changes of absorption spectra, SUVA254, and color in treating landfill leachate using microwave-assisted persulfate oxidation

We experimentally determined the effects of microwave-assisted persulfate oxidation (MAPO) on absorbance spectra, specific ultraviolet absorbance at a wavelength of 254 nm (SUVA254), and color in treating landfill leachate. The effects of treatment temperature (60≤T≤90 °C) and sodium persulfate (SPS) concentration (0.05≤[SPS]≤0.3 M) were characterized. An absorbance band in the visible region disappeared after MAPO, but the absorbance in UV region remained. SUVA254 of treated leachate varied from 2.3 to 14.7 L/mg·m. Color number (CN) removal of 99% (CN=0.004 cm−1) was achieved within 30min with MAPO at 80 °C and [SPS]=0.2 M. As T and [SPS] increased, CN and total organic carbon decreased, but SUVA254 increased.

High-Temperature Microwave NaOH Pretreatment of Waste-Activated Sludge for Anaerobic Digestion

AbstractThe research reported in this paper determined the effect of combined microwave irradiation and NaOH pretreatment on solubilization and biodegradation in anaerobic digestion of waste-activated sludge (WAS). Solubilization increased significantly with NaOH concentration (20–60  meqNaOH/L) and microwave final temperature (100–170°C). However, the experimental trials did not adequately approximate the response surface for volatile solids reduction, cumulative biogas production, and biogas yield. Within the design boundaries, the maximum solubilization degree (72%) of WAS occurred at 60  meq/L and 170°C. The highest volatile solids removal efficiency (62.4%) was achieved at 40  meq/L and 170°C. Cumulative biogas production and yield were 2.3–5.7  L/L and 154–393  mL/g added volatile solids, respectively, and both parameters were highest at 20  meq/L and 135°C.

Evaluation of a microwave-heating anaerobic digester treating municipal secondary sludge.

This work experimentally determined the effect of microwave irradiation on the anaerobic digestion of municipal secondary sludge in semi-continuous mesophilic digesters at hydraulic retention times (HRT) of 15, 10 and 5 days when microwaves were used as a heating source. A microwave-heating anaerobic digester (MHAD) was compared with a water-heating reactor (control). Biogas production increased in both digesters as the HRT decreased except for the control with a HRT of 5 days. Improvement in removal efficiency of volatile solid and biogas production of the MHAD relative to the control increased as the HRT decreased. The results show that the MHAD was more effective than the control in increasing mesophilic anaerobic biodegradability and biogas production treating secondary sludge.