Optimization of cobalt, nickel, and iron supplement for mesophilic and thermophilic anaerobic digestion treating high-solid food waste.

ABSTRACTThe effects of trace metals (iron (Fe), cobalt (Co) + Fe, and Co + nickel (Ni) + Fe) on mesophilic and thermophilic anaerobic digestion of food waste were quantified experimentally. Supplementation with 0 ≤ [Co] ≤ 5 mg/L, 0 ≤ [Ni] ≤ 10 mg/L, or 0 ≤ [Fe] ≤ 200 mg/L can significantly improve the productivity of mesophilic (MD) and thermophilic (TD) digesters. Addition of micronutrients increased biogas production, but excessive addition of trace metals hindered the production. Supplementation with Fe + Co or Fe + Co + Ni increased biogas production more than the addition of only Fe did. Within the design boundaries, the optimal concentrations for supplementation with three trace metals in MD were [Co] = 0.33 mg/L, [Ni] = 0.43 mg/L, and [Fe] = 5.35 mg/L, and in TD were [Co] = 1.41 mg/L, [Ni] = 3.84 mg/L, and [Fe] = 200 mg/L. TD required larger amounts of the trace metals than MD (4.3-37.4 times). The results can give quantitative information on trace metal supplementation for successful anaerobic digestion.

Machine learning predictions of chlorophyll-a in the Han river basin, Korea.

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.

Improved mesophilic anaerobic digestion of swine wastewater by ammonia stripping with microwave irradiation.

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 (MIT) (2.5 ≤ MIT ≤ 5.5 min) of NH3 stripping, and hydraulic retention time (HRT) (7 ≤ HRT ≤ 20 d) in anaerobic digester were quantified. NH3 concentration decreased from 2794 to 140 mg/L within 5.5 min at FT = 100°C. The highest cumulative biogas production (>1800 mL/L) and efficiency of volatile solid removal (> 68%) were achieved at FT = 100°C and MIT = 5.5 min. The removal efficiency of volatile solid in digesters fed with untreated swine wastewater (control) and swine wastewater treated by NH3 stripping decreased as HRT decreased. The highest relative improvement of properties compared to the control occurred at 10 or 15 d HRT. Increases in biogas production compared to the control increased with the NH3 stripping as HRT was reduced to 10 d (243% higher at 10 d). The methane content of the produced biogas was 64-69% for control and 68-75% with NH3 stripping in the range of 10-20 d HRT. NH3 stripping using microwave irradiation is an effective pretreatment to improve the anaerobic digestion of swine wastewater.

Phosphorus Removal Characteristics of Titanium Salts Compared with Aluminum Salt.

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].

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.

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

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.

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.

Influence of Food Waste Compost on the Yield and Mineral Content of Ganoderma lucidum, Lentinula edodes, and Pholiota adipose Fruiting Bodies.

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.

Effect of microwave irradiation on cellular disintegration of Gram positive and negative cells.

This research investigated the effect of microwave irradiation (MWI) on cell disintegration in municipal secondary sludge (MSS). A representative MSS Gram-positive bacterium (Bacillus subtilis) and Gram-negative bacteria (Acinetobacter calcoaceticus and Pseudomonas aeruginosa) were pure cultured separately and treated using MWI. Compared to untreated controls, MWI significantly increased the soluble chemical oxygen demand (COD) (1.8-4.0-fold), soluble protein concentration (1.1-1.8-fold), and soluble carbohydrate concentration (3.2-14.1-fold), with greater increase in the Gram-negative bacteria. After MSS was MWI-treated with different irradiation times, from 0 to 9 min, soluble COD increased gradually from 0.14 to 2.38 g/L (i.e., 72-fold). Effective disintegration of Gram-negative cell walls and of MSS by MWI was confirmed by scanning electron microscopy. These findings suggest that MWI could be an effective pretreatment method for MSS that is dominated by Gram-negative microorganisms.

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.

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.

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.

Biokinetic evaluation and modeling of continuous thiocyanate biodegradation by Klebsiella sp.

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.

Modeling and biokinetics in anaerobic acidogenesis of starch-processing wastewater to acetic acid.

Starch-processing wastewater was anaerobically treated to produce acetic acid in laboratory-scale, continuously stirred tank reactors. The optimal conditions, in which the maximum acetic acid production occurred, were 0.56 d hydraulic retention time, pH 5.9, and 36.1 degrees C. Acetic acid production at the optimum conditions was 672 +/- 20 mg total organic carbon(equivalent) L(-)(1), which indicated a 75% conversion efficiency of influent total organic carbon into acetic acid. A fourth order Runge-Kutta approximation was used to determine the Monod kinetics of the acidogens by using unsteady-state data from continuous unsteady-state experiments at the optimum conditions. The model outputs and experimental data fit together satisfactorily, suggesting that the unsteady-state approach was appropriate for the evaluation of acidogenic biokinetics. These included micro(m), K(s), Y, and k(d), which were evaluated as being 0.13 h(-)(1), 25 mg total carbohydrate (TC) L(-)(1), 0.38 mg volatile suspended solid mg(-)(1) TC, and 0.002 h(-)(1), respectively.