Formation mechanism of persistent free radicals during pyrolysis of Fenton-conditioned sewage sludge: Influence of NOM and iron.

The present study provided an innovative insight into the formation mechanism of persistent free radicals (PFRs) during the pyrolysis of Fenton-conditioned sludge. Fenton conditioners simultaneously improve the dewatering performance of sewage sludge and catalyze the pyrolysis of sewage sludge for the formation of PFRs. In this process, PFRs with a total number of spins of 9.533×1019 spins/g DS could be generated by pyrolysis of Fenton-conditioned sludge at 400°C. The direct thermal decomposition of natural organic matter (NOM) fractions contributed to the formation of carbon-centered radicals, while the Maillard reaction produced phenols precursors. Additionally, the reaction between aromatic proteins and iron played a crucial role in the formation of phenoxyl or semiquinone-type radicals. Kinetics analysis using discrete distributed activation energy model (DAEM) demonstrated that the average activation energy for pyrolysis was reduced from 178.28 kJ/mol for raw sludge to 164.53 KJ/mol for Fenton conditioned sludge. The reaction factor (fi) indicated that the primary reaction in Fenton-conditioned sludge comprised of 27 parallel first-order reactions, resulting from pyrolysis cleavage of the NOM fractions, the Maillard reaction, and iron catalysis. These findings are significant for understanding the formation process of PFRs from NOM in Fenton-conditioned sludge and provide valuable insight for controlling PFRs formation in practical applications.

Revealing the roles of chemical communication in restoring the formation and electroactivity of electrogenic biofilm under electrical signaling disruption.

Electrogenic biofilms in microbial electrochemical systems have played significant roles in simultaneous wastewater treatment and energy recovery owing to their unique extracellular electron transfer. Their formation has been shown to be regulated by electrical and chemical communication, but the interaction between these signal communication pathways has not been studied. This research investigated the coordination between intracellular c-di-GMP signaling and reinforced quorum sensing with or without exogenous HSL (a common quorum sensing molecule), on the formation of mixed-cultured electrogenic biofilm under electrical signaling disruption by tetraethylammonium (TEA, a broad-range potassium channel blocker). Intracellular c-di-GMP was spontaneously reinforced in response to TEA stress, and metagenomic analysis revealed that the dominant DGC (the genes for producing c-di-GMP) induced the eventual biofilm formation by mediating exopolysaccharide synthesis. Meanwhile, reinforced quorum sensing by exogenous HSL could also benefit the biofilm restoration, however, it alleviated the TEA-induced communication stress, resulting in the weakening of c-di-GMP dominance. Interestingly, suppressing electrical communication with or without HSL addition both induced selective enrichment of Geobacter of 85.5% or 30.1% respectively. Functional contribution analysis revealed the significant roles of Geobacter and Thauera in c-di-GMP signaling, especially Thauera in resistance to TEA stress. This study proposed a potential strategy for electrogenic biofilm regulation from the perspectives of cell-to-cell communication.

Identification of Extracellular Key Enzyme and Intracellular Metabolic Pathway in Alginate-Degrading Consortia via an Integrated Metaproteomic/Metagenomic Analysis.

Uronic acid in extracellular polymeric substances is a primary but often ignored factor related to the difficult hydrolysis of waste-activated sludge (WAS), with alginate as a typical polymer. Previously, we enriched alginate-degrading consortia (ADC) in batch reactors that can enhance methane production from WAS, but the enzymes and metabolic pathway are not well documented. In this work, two chemostats in series were operated to enrich ADC, in which 10 g/L alginate was wholly consumed. Based on it, the extracellular alginate lyase (∼130 kD, EC 4.2.2.3) in the cultures was identified by metaproteomic analysis. This enzyme offers a high specificity to convert alginate to disaccharides over other mentioned hydrolases. Genus Bacteroides (>60%) was revealed as the key bacterium for alginate conversion. A new Entner-Doudoroff pathway of alginate via 5-dehydro-4-deoxy-d-glucuronate (DDG) and 3-deoxy-d-glycerol-2,5-hexdiulosonate (DGH) as the intermediates to 2-keto-3-deoxy-gluconate (KDG) was constructed based on the metagenomic and metaproteomic analysis. In summary, this work documented the core enzymes and metabolic pathway for alginate degradation, which provides a good paradigm when analyzing the degrading mechanism of unacquainted substrates. The outcome will further contribute to the application of Bacteroides-dominated ADC on WAS methanogenesis in the future.

Electricity production and microbial community in psychrophilic microbial fuel cells at 10 °C.

Psychrophilic microbial fuel cell (PMFC) offers an alternative method for low temperature wastewater treatment, but is seldom reported. In this study, the two-chamber PMFC was constructed at 10 °C using acetate as an electron donor. The maximum voltage under external resistance of 1000 Ω was around 550 mV. The columbic efficiency (CE) was 82.4% under external resistance of 100 Ω and the max power density was 582.4 mW/m2. After temperature decreasing to 4 °C, the maximum voltage also reached 530 mV and CE was 38.4%. The direct electron transfer was proposed in PMFC according to cyclic voltammetry curves. The short enriching time (~30 days) of biofilm in the anodic electrode may be due to the high activity of enriched novel exoelectrogens of M. fermentans (46.2%) and E. lemanii (15.4%). The development of PMFC involved biotechnologies in low temperature regions shall benefit for valuable chemicals production and energy generation in the future.

Caproate production from xylose by mesophilic mixed culture fermentation.

Caproate production by mixed culture fermentation (MCF) is economically attractive. Xylose is known as the second most abundant sugar in nature, however, producing caproate from xylose is never reported. In this study, caproate production from xylose by mesophilic MCF was firstly investigated. The results showed that as pH decreasing to 5.0, the caproate concentration was 2.06 g/L in a batch reactor and was between 0.45 and 1.07 g/L in a continuously stirred reactor. Microbial analysis illustrated that Caproiciproducens and Clostridium_sensu_stricto_12, as two main identified caproate producers, occupied over 50% and around 10% of mixed culture, respectively. Thus, caproate production from xylose was proposed via the fatty acid biosynthesis pathway, not the well-known reverse ß-oxidation pathway. These unexpected differences from literatures gains more understanding about caproate production from organic substrates via MCF.

Stimulation of methane production from benzoate with addition of carbon materials.

Huge amounts of wastewater that contain aromatic compounds such as benzene and phenols are discharged worldwide. Benzoate is a typical intermediate in the anaerobic transformation of those aromatic compounds. In this study, electrically conductive carbon-based materials of granulated activated carbon (GAC), multiwalled carbon nanotubes (MwCNTs), and graphite were evaluated for the ability to promote the benzoate degradation. The results showed that 82-93% of the electrons were recovered in CH4 production from benzoate. The carbon materials stimulated benzoate degradation in the sequence of GAC (5 g/L) > MwCNTs (1 g/L) ~ Graphite (0.1 g/L) > Control. Acetate was the only detected intermediate in the process of benzoate degradation. Taxonomic analyses revealed that benzoate was degraded by Syntrophus to acetate and H2, which were subsequently converted to methane by Methanosarcina (both acetoclastic methanogens and hydrogenotrophic methanogens) and Methanoculleus (hydrogenotrophic methanogens), and direct interspecies electron transfer (DIET) of Desulfovibrio and Methanosarcina. Thus, these results suggest a method to effectively enhance the removal of aromatic compounds and methane recovery.

Microbial electrochemical stimulation of caproate production from ethanol and carbon dioxide.

The production of value added chemicals from CO2 is of critical importance for the practical application of microbial electrosynthesis (MES). Here, a binary electron donor (ED) design (using electrode and ethanol) was introduced to provide an efficient caproate production with the bioconversion of both CO2 and ethanol. A maximum caproate production rate of 2.41 ±â€¯0.69 g L-1 d-1, and a final concentration of 7.66 ±â€¯1.38 g L-1 was achieved. Caproate production selectivity based on the substrate increased to 91.47 ±â€¯0.58% (Binary EDs) from 32.22 ±â€¯32.58% (open circuit Electrode ED). An observed amount of 23.43 ±â€¯0.69% of carbon within the final binary ED products originated from the CO2. This work proves for the first time the potential of caproate production from CO2 utilization and ethanol upgrading using solid electrodes to regulate the chain elongation process.

Decolorization of Acid Orange 7 by extreme-thermophilic mixed culture.

Although a large amount of textile wastewater is discharged at high temperatures, azo dye reduction under extreme-thermophilic conditions by mixed cultures has gained little attention. In this study, Acid Orange 7 (AO7) was used as the model azo dye to demonstrate the decolorization ability of an extreme-thermophilic mixed culture. The results showed that a decolorization efficiency of over 90% was achieved for AO7. The neutral red (NR, 0.1 mM) could promote AO7 decolorization, in which the group of Cell + NR offered the highest decolorization rate of 1.568 1/h and t1/2 was only 0.44 h, whereas after CuCl2 addition, the decolorization rate (0.141 1/h) was lower and t1/2 (4.92 h) was much longer. Thus, CuCl2 notably inhibited this process. Caldanaerobacter (64.0%) and Pseudomonas (25.4%) were the main enriched bacteria, which were not reported to have the ability for dye decolorization. Therefore, this study extends the application of extreme-thermophilic biotechnology.

Synergetic alginate conversion by a microbial consortium of hydrolytic bacteria and methanogens.

Sludge, of which alginate-like biomaterial is a major organic component, is an increasing environmental problem. Thus, efficient anaerobic degradation of alginate provides a new method for sludge utilization. In this study, anaerobic alginate hydrolytic bacteria (AHB) were proposed to enrich with methanogens synergetically to reduce the inhibition of intermediate metabolites. The COD of produced methane reached 80.7 ±â€¯1.9% (n = 4) of initial alginate COD. After considering the microbial growth (8%-18% of COD), a good COD balance indicated that alginate was fully consumed and the main final metabolites were methane and CO2. Methanogenesis could promote alginate conversion by AHB. The enriched bacteria for alginate degradation in this study were different from that of former known AHB. The metabolic pathway of alginate degradation was revealed by metagenomics, in which oligo-alginate lyase was detected in twelve bacteria, and typical carbon metabolic pathways to convert alginate to methane were identified. More studies of bacterial isolation and biofuel production are still needed in the future.