Search

Objectives:The purpose of this study is to compare single models according to the missing value handling techniques for predicting leachate generation.Methods:Input factors such as landfill gas generation, and weather data (precipitation, wind speed, radiation, temperature, and relative humidity) were used from June 2002 to October 2018. Linear interpolation and mean method were used as the missing value handling technique. The experiment was conducted by dividing the data into train and test data according to the optimal ratio. Various single models were used, and the prediction performance of the model was compared and evaluated using coefficient of determination (R2).Results and Discussion:The gated recurrent unit (GRU) model was the best among the single models. In the GRU model, R2 was 0.867 for linear interpolation and R2 was 0.839 for the mean method, so that the GRU model using linear interpolation was most suitable for predicting leachate generation. In the ANN model, R2 of linear interpolation (0.862) was higher than that of mean method (0.828). In the long short-term memory (LSTM) model, R2 was 0.779 for linear interpolation and 0.762 for mean method. In the random forest (RF) model, R2 for linear interpolation (0.700) was also higher than that for the mean method (0.665). The model performance was excellent in the order GRU>ANN>LSTM>RF. The linear interpolation for the missing value handling technique was superior to the mean method in all models used in this experiment.Conclusion:The GRU using linear interpolation was the most suitable model for predicting landfill leachate generation.

Objectives : Photovoltaic power generation which significantly depends on meteorological conditions is intermittent and unstable. Therefore, accurate forecasting of photovoltaic power generation is a challenging task. In this research, random forest (RF), recurrent neural network (RNN), long short term memory (LSTM), and gated recurrent unit (GRU) are proposed and we will find an efficient model for forecasting photovoltaic power generation of photovoltaic power plants.Methods : We used photovoltaic power generation data from photovoltaic power plants at Gamcheonhang-ro, Saha-gu, Busan, and meteorological data from Busan Regional Meteorological Administration. We used solar irradiance, temperature, atmospheric pressure, humidity, wind speed, wind direction, duration of sunshine, and cloud amount as input variables. By applying the trial and error method, we optimized hyperparameters such as estimators in RF, and number of hidden layers, number of nodes, epochs, and validation split in RNN, LSTM, and GRU. We compared proposed models by evaluation indexes such as coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE).Results and Discussion : The best RF at 1,000 of number of decision tree achieved test R2=0.865, test RMSE=16.013, and test MAE=9.656. The best choice of RNN was 6 hidden layers and the number of nodes in each layer was 90. We set the epochs at 450. RNN achieved test R2=0.942, test RMSE=10.530, and test MAE=6.390. To find the best result of LSTM, we used 3 hidden layers, and the number of nodes was 600. The epochs were set to 200. LSTM achieved test R2=0.944, test RMSE=10.29, and test MAE=6.360. GRU was set to 3 hidden layer and the number of nodes was 450. The epochs were set to 500. GRU achieved test R2=0.945, test RMSE=10.189, and test MAE=5.968.Conclusions : We found RNN, LSTM, and GRU performed better than RF, and GRU model showed the best performance. Therefore, GRU is the most efficient model to predict photovoltaic power generation in Busan, Korea.

Ammonia (NH3) stripping by microwave irradiation was used to increase the efficiency of anaerobic digestion. The effects of final temperature (FT) (80 ≤ FT ≤ 100°C) and microwave irradiation time (...

This study developed a model to predict concentrations of chlorophyll-a ([Chl-a]) as a proxy for algal population with data from multiple monitoring stations in the Han river basin, by using machine-learning predictive models, then analyzed the relationship between [Chl-a] and the input variables of the optimized model. Daily water quality and meteorological data from 2012 to 2020 were collected from the real-time water quality information system and the meteorological administration of Korea. To quantify model accuracy, the coefficient of determination, root mean square error, and mean absolute error were applied. Among random forest (RF), support vector machine, and artificial neural network, the RF with random dataset showed the highest accuracy. The RF was optimized when 78 trees were applied to the model. Input variables for the best RF model were total organic carbon (feature importance: 27%), total nitrogen (19%), pH (13%), water temperature (8%), total phosphorus (8%), electrical conductivity (7%), dissolved oxygen (6%), minimum air temperature (AT) (4%), mean AT (3%), and maximum AT (3%). The feature-importance analysis showed that total organic carbon was the most important variable to predict [Chl-a] in the Han river basin. Total nitrogen was a more important variable than total phosphorus.

This study detetmined optimal microwave irradiation (MI) conditions for removal of ammonia nitrogen (NH3-N) from swine wastewater. The wastewater was treated using a laboratory-scale indust...

Coagulation of titanium tetrachloride (TiCl4) and polytitanium tetrachloride (PTC) was studied at various conditions in treating wastewater that contained phosphorus (P). Jar-test experiments were performed at various chemical doses (0.02–0.49 mM), alkalinities (50 ≤ AT ≤ 150 mg CaCO3/L of NaHCO3), pH levels (3.0–8.5), and OH/Ti ratio (0.3 ≤ B ≤ 3.0) to determine the conditions at which P (2 mg/L) removal was most efficient. The TiCl4 concentration ([TiCl4]) required to achieve 98–99% P removal was 0.25 mM at 50 mg CaCO3/L, 0.31 mM at 100 mg CaCO3/L, and 0.49 mM at 150 mg CaCO3/L. Response surface analysis predicted that P removal would reach 100% at controlled pH = 3.5 with minimum [TiCl4] = 0.21 mM. PTC removed P most effectively at B = 0.3, and the optimal dose at B = 0.3 was 0.27 mM. Laboratory results and a pilot experiment will help to optimize use of Ti-based coagulants to remediate wastewater that contains P.

We investigated the effects of initial pH (2≤pH0≤6) and sewage sludge compost content (5≤[SSC]≤25 g/kg) on leaching characteristics of lead (Pb) and zinc (Zn) in contaminated field soil. pH0 and [SSC] significantly affected the leaching of Pb and Zn in soils contaminated with them. The pH in the solution increased as reaction time and [SSC] increased. The leached amounts of Pb and Zn were highest at pH0=2 and increased with reaction time. As [SSC] increased, the leached amount of Pb decreased (50.4 mg/kg at control condition ([SSC]=0 g/kg); 22.9 mg/kg at [SSC]=25 g/kg at pH0=2) and the leached amount of Zn increased (20.1 mg/kg at [SSC]=0 g/kg; 31.7 mg/kg at [SSC]=25 g/kg at pH0=2). The change increased as pH0 decreased. Within the design boundaries, minimum leaching of Pb (14.7 mg/kg) occurred at pH0=5.1 and [SSC]=25 g/kg, and minimum leaching of Zn (5.0 mg/kg) occurred at pH0=5.1 and [SSC]=5 g/kg.

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.

This study evaluates the efficacy of titanium tetrachloride (TiCl 4 ) on phosphorus (P) removal in synthetic wastewater. Jar test experiments were performed at various TiCl 4 concentration (0.25-0.59 mM), and intensities of slow (30-60 rpm) and rapid (100-250 rpm) mixings to determine the conditions at which P removal was most efficient. The P-removal efficiency was highest (about 99%) at TiCl 4 concentration ([TiCl 4 ])=0.39 mM with rapid-mixing intensity=100 rpm and slow-mixing intensity=30 rpm. The slow-mixing intensity was more sensitive than the rapid-mixing intensity to the P removal efficiency when [TiCl 4 ] was low (0.25≤[TiCl 4 ]≤0.27 mM). Key Words : Coagulation, Mixing Intensity, pH, Phosphorus, Titanium Tetrachloride 요약: 본 연구는 TiCl 4 의 농도(0.25-0.59 mM)와 급속교반속도(100-250 rpm), 완속교반속도(30-60 rpm)의 변화가 인 제거효율에 미치는 영향을 알아보고자 하였다. 응집제 농도가 0.25≤[TiCl 4 ]≤0.39 mM 범위에서 인 제거 효율은 TiCl 4 의 농도가 증가할수록 증가하였으며 처리후 인의 농도는 0.2 mg/L 이하였다. 응집제 농도 0.39 mM, 급속교반속도 100 rpm, 완속교반속도 30 rpm에서 인 제거효율이 약 99%로 가장 높았다. TiCl

This work experimentally determined the effect of a combination of microwave irradiation (MWI) and sodium persulfate (Na 2 S 2 O 8 , SPS) on decolorization and decomposition of methylene blue (C 16 H 18 N 3 SCl, MB). The effects of treatment temperature (70–100 °C, T ) and SPS concentration (1–5 g l −1 ) at 8-min MWI time were characterized. The conversion rate of MB (50 mg l −1 ) was increased and accelerated by MWI, reaching 99.9% after heating for 8 min at 90 °C and 600-W MW power in the presence of 5 g l −1 of SPS; this is higher than the conversion rate (98.3%) of treatment by conventional heating for 30 min. The MB decolorization increased with T ( p = 0.002) and initial SPS ( p = 0.006). The total organic carbon (TOC) removal also increased with T ( p = 0.004). Within the design boundaries, full decolorization was achieved at T ≥ 93 °C and SPS ≥3.5 g l −1 . The TOC removal level reached 100% at T ≥ 95 °C and SPS = 5 g l −1 . The results show that MWI combined with SPS is effective in decolorization and degradation of MB due to advantages of fast and effective processing.

This study evaluates the efficacy of titanium tetrachloride (TiCl4) and titanium sulfate [Ti(SO4)2] on phosphorus (P) removal in synthetic wastewater compared with aluminum sulfate [Al2(SO4)3]. Jar test experiments were performed at various chemical doses and initial pH (pHi) levels to determine the conditions at which P removal was most efficient. The doses with 99% P removal were 0.31 to 0.34 mM for TiCl4, 0.15 mM for Ti(SO4)2, and 0.19 mM for Al2(SO4)3 as Al at 2 mg P/L, 100 mg CaCO3/L, and pHi = 7.0 to 8.0. The optimum pHi was 7 for TiCl4, 5.5 for Ti(SO4)2, and 7 for Al2(SO4)3. The P-removal efficiencies were Ti(SO4)2 > Al2(SO4)3 > TiCl4 at pHi 5.5, and TiCl4 ≈ Al2(SO4)3 > Ti(SO4)2 at pHi 7 and 8.5. P-removal ability of TiCl4 decreased as alkalinity increased. Quadratic models successfully approximated the response surface for P removal efficiency with simultaneous changes in pHi and chemical concentrations [TiCl4 and Al2(SO4)3].

The objectives of this study were to evaluate applicability of food waste compost (FWC) as a substrate for cultivation of Ganoderma lucidum, Lentinula edodes, and Pholiota adipose, and to determine contents of Ca, Mg, Na, and K in fruiting bodies (FB). FB yield per substrate in FWC-free controls was 53 ± 4 g/kg for G. lucidum, 270 ± 90 g/kg for L. edodes, and 1,430 ± 355 g/kg for P. adipose. Substrates supplemented with FWC showed the highest FB production at FWC content of 10% for G. lucidum (64 ± 6 g/kg), and 13% for L. edodes (665 ± 110 g/kg) and P. adipose (2,345 ± 395 g/kg), which were 1.2~2.5 times higher than the values for the controls. P. adipose contained higher amounts of mineral elements than the other species. Ca, Mg, Na, and K content in FB did not show a significant relation to FWC content.

The objective of this study was to find optimum rice bran (RB) and food waste compost (FWC) contents in culture medium for mycelial growth rate and fruit body yield of oyster mushroom, Pleurotus ostreatus . RB (0–20%) and FWC (20–40%) contents significantly affected the fruit body yield of P. ostreatus . Within the design boundaries, the optimum conditions for maximum mycelial growth rate (14.8 cm 20 d −1 ) were 9.3% RB and 24% FWC. The optimum conditions for maximum fruit body yield (91 g bottle −1 ) were 12% RB and 25% FWC, which was 153% higher than value (36 ± 11 g bottle −1 ) at the control condition of 80% w/w sawdust and 20% w/w RB. Our results proved a good potential of FWC to serve as an alternative growth medium for cultivating oyster mushroom, P. ostreatus . This may improve the production efficiency of edible mushrooms to help minimize production costs and maximize farm profits.

Mushroom research and production have received increased attention in recent years because of the recognition that mushrooms are a nutritious food with health-stimulating properties and medicinal effects [1]. In Korea, China, Japan, and Taiwan, Ganoderma lucidum has long been a popular traditional or Oriental medicine used for treatment of various human diseases including hepatitis, hypertension, hypercholesterolemia, and gastric cancer [1, 2]. This species normally forms shelf-like fruiting bodies (FBs) on tree-trunks, but when grown in darkness and poor ventilation conditions some strains produce an antler-type FB [3] that is rarely found in the wild. In modern production systems, G. lucidum is cultivated on a mixture of sawdust (SD) and wood-chips in bottles or bags [3]. During G. lucidum production, raw materials and the preparation of selective compost for FB production are major cost inputs. Therefore, growers are seeking ways to reduce their production costs by increasing bio-efficiency [4]. Recently, the addition of food waste to the G. lucidum growth medium has been considered because this practice has the dual benefits of increasing FB yield and disposing of organic wastes [1]. In Korea, large amounts of food wastes are produced. Currently, such waste is recycled as fertilizer. Food waste compost (FWC) is a nutritionally rich and complex product low in toxic constituents that can be fed to heterotrophic organisms such as fungi [5]. A mixture of SD and rice bran (RB) is one of a variety of possible substrates for mushroom production. Therefore, several types of mushrooms including G. lucidum are commercially cultivated in SD media consisting of a mixture of SD and RB. However, little information is available regarding how addition of FWC to growth media affects mushroom production. Thus, the objectives of this study were to evaluate the applicability of FWC as a substrate for G. lucidum cultivation and estimate the FWC content at which FB production is greatest.

This work determined the effect of a combination of microwave irradiation and sodium persulfate (Na2S2O8, SPS) on the decomposition of landfill leachate. The effect of treatment temperature, T(60–90°C), SPS concentration, [SPS], (0.05–0.30 M), and solution pH (3.0–8.4) were characterized. As T increased from 60 to 90°C, the observed degradation rate constant of total organic carbon (TOC), kobs, in landfill leachate increased from 0.0032 to 0.0704 min−1. The value kobs fitted the Arrhenius equation and yielded an apparent activation energy of 104 kJ/mol. As [SPS] increased from 0.05 to 0.3 M, kobs increased from 0.0075 to 0.0974 min−1. It decreased as pH increased. Within the design boundaries, T (p 0.05). The results demonstrate that microwave-assisted persulfate oxidation can adequately remove organics from landfill leachate.

This work experimentally determined the effect of microwave treatment on the disintegration and acidogenesis of waste-activated sludges (WAS) from municipal and coke wastewater treatment plants. Sludge samples (500 g) were heated for 0, 3, 5, 7, 9, 11, and 15 min in a microwave oven (2,450 MHz, 700 W). The degree of sludge solubilization [soluble chemical oxygen demand (SCOD)/COD] increased asymptotically with microwave irradiation time from 1.5% at 0 min to 22.3% at 15 min for WAS from a municipal wastewater treatment plant (WASM) and 1.5% to 5.1% for WAS from a coke wastewater treatment plant of a steel manufacturing industry (WASC). The calcium concentrations in both sludges also increased with microwave irradiation time. The biochemical acidogenic potentials (BAP) increased from 3.70 to 4.44 g COD L-1 for WASM and 1.19 to 1.67 g COD L-1 for WASC. The results show that microwave irradiation increases the solubilization and BAP of sludges and that WASM had a higher degree of solubilization and BAP tha...

This work experimentally determined the effect of thermal and microwave pretreatments on the anaerobic digestion of mixtures of municipal primary and secondary sludges in semi-continuous mesophilic digesters at hydraulic retention times (HRT) of 20, 15, 10, 7, and 5 days. The ratio of soluble chemical oxygen demand (COD) to total COD in thermally pretreated and microwaved sludges at 80°C was 2.7 and 3.2 times higher than that of raw sludge, respectively. The volatile solids (VS) and COD removal efficiencies in all three di gesters fed with raw (control), thermally pretreated (TM), and microwaved (MW) sludges decreased as the HRT was reduced. The highest relative improvement in VS removal compared to the control occurred at the HRT of 5 days in the TM and MW (29 and 41% higher than the control, respectively). At this HRT, improvement in the COD removal efficiencies in the TM and MW compared to the control was 28 and 53%, respectively. Improvements in biogas production compared with the control increased in both the TM and MW as the HRT was reduced to 5 days. The relative improvement in daily biogas production compared to the control from the TM and MW was 33 and 53% higher than the control at the HRT of 5 days, respectively. The results show that microwave pretreatment is more effective than thermal pretreatment in increasing the solubilization degree and mesophilic anaerobic biodegradability of sewage sludge.

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.

This work experimentally determined the effect of microwave treatment on the disintegration and acidogenesis of municipal secondary sludge. Sludge samples (500 g) were heated for 0, 3, 5, 7, 9, 11, and 15 min in a microwave oven (2450 MHz, 700 W). The solubilization degree (soluble chemical oxygen demand (SCOD)/COD) of sludge increased asymptotically with microwave irradiation time from 2% at 0 min to 22% at 15 min. The concentrations of soluble protein, carbohydrate, lipid, and calcium also increased with microwave irradiation time. The biochemical acidogenic potentials (BAP) of sludge increased from 3.58 to 4.77 g COD l −1 . The results show that microwave irradiation increases the solubilization degree and BAP of municipal secondary sludge.

Solubilization of sewage sludge creates favorable conditions for anaerobic microorganisms to produce biogas. In this paper, we quantify the effect of heating pretreatment on the degree of solubilization of sewage 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 temperature-increase rate (ramp rate) (2.9 to 17.1℃/min) and terminal temperature (52 to 108℃). Both ramp rate and temperature significantly affected the solubilization degree of sludge. Within the design boundaries, the conditions predicted to maximize the solubilization degree of 15.8% were determined to be 2.9℃/min and 104℃.

This study determined the minimum nitrogen concentration at which the mesophilic and thermophilic upflow anaerobic filters treating a simulated papermill wastewater could operate efficiently. For this purpose, the chemical oxygen demand (COD) to nitrogen ratio in both digesters was increased in five consecutive steps, from 94: 5 to 363: 5. The maximum COD to nitrogen ratios that provided satisfactory operation were 283: 5 (30mg N/L) and 363: 5 (23 mg N/L) for the mesophilic and thermophilic reactors, respectively. The nitrogen consumption of bacteria in the thermophilic digester was lower than that in the mesophilic digester. The operational efficiency of the thermophilic digester was higher than that of the mesophilic one regardless of the COD to nitrogen ratio.

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.

The 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.

A series of experiments with 0, 1, 3, 5, and 7 g Ca 2+ /l using calcium chloride were performed to evaluate the effect of various calcium concentrations on anaerobic digestion of swine wastewater. The addition of 3 g/l gave the best performance. On the other hand, the calcium concentrations of 5–7 g/l had an inhibitory effect on anaerobiosis. The lag phase durations expected in biogas production were 28–31 days with the addition of 0–3 g/l of calcium, and 43–52 days for calcium concentrations of 5 g/l or more. The concentrations of total volatile fatty acids decreased to less than 100 mg/l with calcium concentrations of 3–7 g/l. On the other hand, propionate and i -valerate concentrations remained over 4 and 0.8 g/l, respectively, when 1 g/l or less of calcium was added.

The fourth order Runge-Kutta approximation was used to determine the substrate inhibition kinetics of Klebsiella sp. utilizing thiocyanate in batch culture. The hypothetical maximum growth rate, half saturation-, microbial yield-, biomass decay rate-, and substrate inhibition-coefficients were evaluated as being 0.62 ± 0.05 day −1 , 85 ± 8 mg SCN l −1 , 0.076 ± 0.011 mg dry cell weight mg −1 SCN, 0.03 ± 0.002 day −1 , and 131 ± 22 mg SCN l −1 , respectively. The apparent maximum specific growth rate and maximal substrate concentration resulting in apparent maximum growth rate were calculated to be 0.24 ± 0.01 day −1 and 106 ± 9 mg SCN l −1 , respectively.

Biokinetics for autotrophic degradation of thiocyanate using batch culture of Klebsiella sp. 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 degrees 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 Klebsiella sp. 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 Klebsiella sp. utilizing thiocyanate. Although the kinetic coefficients estimated by analytical and numerical methods were not statistically different at a 0.05 alpha level, model responses of numerical approximation generated a better prediction of changes in thiocyanate and cell mass concentrations. The hypothetical maximum growth rate, micro m, 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, micro'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. Klebsiella sp. was expected to be washed out at 4.8 days HRT, thus resulting in no treatment of thiocyanate.

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.