Metabolism and kinetic study of bioH 2 production by anaerobic sludge under different acid pretreatments

Artificial intelligence modeling to predict transmembrane pressure in anaerobic membrane bioreactor-sequencing batch reactor during biohydrogen production

The complex nature of wastewater treatment has led to search for alternative strategies such as different artificial intelligence (AI) techniques to model the various operational parameters. The present work is aimed at predicting the transmembrane pressure (TMP) as a key operational parameter in the case of anaerobic membrane bioreactor-sequencing batch reactor (AnMBR-SBR) during biohydrogen production using the adaptive neuro-fuzzy inference systems (ANFIS) and artificial neural network (ANN). In both the models, organic loading rates (OLR) ranging from 0.5 to 8.0 g COD/L/d, effluent pH (3.6-6.9), mixed liquor suspended solid (4.6-21.5 g/L) and mixed liquor volatile suspended solid (3.7-15.5 g/L) were used as the input parameters to test TMP as an output parameter. The ANFIS model was trained using the hybrid algorithms for TMP prediction. The higher prediction performance was obtained by using the Gauss membership function with four membership numbers. A back-propagation algorithm was also employed for the feed forward training of ANN model; the best structure was a Levenberg-Marquardt training algorithm with nine neurons in the hidden layer. By employing ANFIS and ANN models, relatively a good prediction of TMP was obtained with the R² values of 0.93 and 0.88, respectively while the calculated mean square error for TMP in the ANFIS model (7.3 × 10^-3) was lower than that of ANN model (8.02 × 10^-3). The higher R² and lower MSE values for the ANFIS model exhibited a better TMP prediction performance than the ANN model. Finally, it was observed that in the sensitivity analysis of ANN model, OLR was the most important input parameter on the variation of TMP.

Electron flow of biological H2 production by sludge under simple thermal treatment: Kinetic study

Mixed culture sludge has been widely used as a microbial consortium for biohydrogen production. Simple thermal treatment of sludge is usually required in order to eliminate any H₂-consuming bacteria that would reduce H₂ production. In this study, thermal treatment of sludge was carried out at various temperatures. Electron flow model was then applied in order to assess community structure in the sludge upon thermal treatment for biohydrogen production. Results show that the dominant electron sink was acetate (150-217 e- meq/mol glucose). The electron equivalent (e- eq) balances were within 0.8-18% for all experiments. Treatment at 100 °C attained the highest H₂ yield of 3.44 mol H₂/mol glucose from the stoichiometric reaction. As the treatment temperature increased from 80 to 100 °C, the computed acetyl-CoA and reduced form of ferredoxin (Fd_red) concentrations increased from 13.01 to 17.34 e- eq (1.63-2.17 mol) and 1.34 to 4.18 e- eq (0.67-2.09 mol), respectively. The NADH₂ balance error varied from 3 to 10% and the term e-(Fd↔NADH₂) (m) in the NADH₂ balance was NADH₂ consumption (m = -1). The H₂ production was mainly via the Fd:hydrogenase system and this is supported with a good NADH₂ balance. Using the modified Gompertz model, the highest maximum H₂ production potential was 1194 mL whereas the maximum rate of H₂ production was 357 mL/h recorded at 100 °C of treatment.

Biohydrogen production from alkaline wastewater: The stoichiometric reactions, modeling, and electron equivalent

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The average of hydrogen production at studied alkalinity 670, 1325, 2232, and 2678 mg/L as CaCO₃, were 57.91, 220.02, 204.65, and 92.51 mL/d.

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As the ALK/COD ratio was 0.3, the highest hydrogen yield (0.6 mmol H₂/g COD_in) was achieved.

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The required ALK/COD ratio for methanogenic and hydrogenogenic processes was about alike.

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The highest H₂ fraction was coinciding with high eˉeq of acetate.

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When the initial alkalinity was 1325 and 670 mg/L, the highest and lowest H₂ eˉeq was occurred, respectively.

Hydrogen gas (H₂) is the cleanest energy carrier with 142 kJ/g energy content and without toxic byproducts release during combustion. There is interest to H₂ production by biological process from sustainable resources including municipal and industrial wastewater and also solid waste. Here, we describe the biohydrogen production that involves first survey the effect of alkalinity on biohydrogen production based on stoichiometric reaction, followed by the electron equivalent balances determination and examination of prediction capability of Gamperts model for biohydrogen production.

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The method uses a dark fermentation biological process for H₂ production from wastewater.

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As the influent alkalinity increased, the hydrogen production increased and then promptly descended.

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The predicted gas volume, based on Gamperts model confirmed good agreement with experimental value.

Biohydrogen production under hyper salinity stress by an anaerobic sequencing batch reactor with mixed culture

BACKGROUND

This study investigated the effect of organic loading rate (OLR) and NaCl concentration on biohydrogen production by preheated anaerobic sludge in a lab scale anaerobic sequencing batch reactor (ASBR) fed with glucose during long time operation.

METHODS

During ASBR operation, the OLR was increased in steps from 0.5 to 5 g glucose/L.d and NaCl addition started at an OLR of 5 g glucose/L.d, to obtain NaCl concentrations in the reactor in the range of 0.5-30 g/L.

RESULTS

With an increasing OLR from 0.5 to 5 g glucose/L.d, the biohydrogen yield increased and reached 0.8 ± 0.4 mol H₂/mol glucose at an OLR of 5 g glucose/L.d. A NaCl concentration of 0.5 g/L resulted in a higher yield of biohydrogen (1.1 ± 0.2 mol H₂/mol glucose). Concentrations above 0.5 g/L NaCl led to decreasing biohydrogen yield and the lowest yield (0.3 ± 0.1 mol H₂/mol glucose) was obtained at 30 g/L of NaCl. The mass balance errors for C, H, and O in all constructed stoichiometric reactions were below 5%.

CONCLUSIONS

The modified Monod model indicated that r (H2)max and Ccrit values were 23.3 mL H2/g VSS/h and 119.9 g/L, respectively. Additionally, ASBR operation at high concentrations of NaCl shifted the metabolic pathway from acidogenic toward solventogenic.