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This study demonstrates the substantial role of bicarbonate within a zero-valent iron (ZVI) system in hydrogen evolution, demonstrating that heightened concentration levels notably enhance hydrogen output. The acetic acid performance production of seven different inocula was examined when exposed to ZVI and CO 2 as the sole carbon source, separately. Along the seven inocula, river and constructed wetland sludges show the highest production rates at 300 mg/L day -1 and 269 mg/L day -1 , respectively. Acetobacterium levels significantly rose in CO 2 -enriched environments, particularly in river and wetland sludges. Moreover, bacteria attached to ZVI showed accelerated hydrogen consumption and acetic acid production compared to their freely suspended or ZVI-detached counterparts when hydrogen was primarily added externally. This study highlighted the positive effect of high concentrations of soluble CO₂, which acted both as a reactant with ZVI for hydrogen production and as a substrate for homoacetogens, leading to high acetic acid generation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In the current study, treatment of undiluted real bilge water (BW) and the production of methane was examined for the first time using a membraneless single chamber Microbial Electrolysis Cell (MEC) with Anaerobic Granular Sludge (AGS) for its biodegradation. Initially, Anaerobic Toxicity Assays (ATAs) were used to evaluate the effect of undiluted real BW on the methanogenic activity of AGS. According to the results, BW shown higher impact to acetoclastics compared to hydrogenotrophic methanogens which proved to be more tolerant. However, dilution of BW caused lower inhibition allowing BW biodegradation. Maximum methane production (142.2 ± 4.8 mL) was observed at 50% of BW. Operation of MEC coupled with AGS, seemed to be very promising technology for BW treatment. During 80 days of operation in increasing levels of BW, R2 (1 V) reactor resulted in better performance than AGS alone. Exposure of AGS to gradual increase of BW content revealed that CH 4 production was possible and reached 51% in five days even after feeding with 90% of BW using simple commercial iron electrodes. Successful chemical oxygen demand (sCOD) removal (up to 70%) was observed after gradual biomass acclimatization. Among the different monitored volatile fatty acids (VFAs), acetic and valeric acids were the most frequently detected compounds with concentrations up to 2.79 and 1.81 g L -1 , respectively. The recalcitrant nature of BW did not allow the MEC-AD (anaerobic digester) to balance the consumed energy. Microbial profile analysis confirmed the existence of several methanogenic microorganisms of which Desulfovibrio and Methanobacterium presented significantly higher abundance in the cathodes compared to anodes and AGS., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

This paper deals with the development of a citrus peel waste (CPW) biorefinery that employs low environmental impact technologies for production of ethanol and methane. Three major yeasts were compared for ethanol production in batch fermentations using CPW pretreated through acid hydrolysis and a combination of acid and enzyme hydrolysis. The most efficient conditions for production of CPW-based hydrolyzates included processing at 116 °C for 10 min. Pichia kudriavzevii KVMP10 achieved the highest ethanol production that reached 30.7 g L -1 in fermentations conducted at elevated temperatures (42 °C). A zero-waste biorefinery was introduced by using solid biorefinery residues in repeated batch anaerobic digestion fermentations achieving methane formation of 342 mL g VS -1 (volatile solids). Methane production applying untreated and dried CPW reached a similar level (339-356 mL g VS -1 ) to the use of the side stream, demonstrating that the developed bioprocess constitutes an advanced alternative to energy intensive methods for biofuel production.