Probing the robustness of Geobacter sulfurreducens against fermentation hydrolysate for uses in bioelectrochemical systems.

In this study, impacts of toxic ions/acids found in real fermentation-hydrolysate on the model exoelectrogenic G. sulfurreducens were investigated. Initially, different concentrations of acetate, butyrate, propionate, Na+, and K+ were tested, individually and in combination, for effects on the planktonic growth, followed by validation with diluted-hydrolysate. Meanwhile, it could be shown that (1) excess Na+ (≥100 mM) causes inhibition that can be reduced by K+ replacement, (2) butyrate (≥10 mM) induces higher toxicity than propionate, and (3) hydrolysate induces synergistic inhibition to G. sulfurreducens where organic constituents contributed more than Na+. Afterwards, compared with impacts on planktonic cells, the pre-enriched anodic biofilm of G. sulfurreducens in BESs showed higher robustness against diluted-hydrolysate, achieving current densities of 1.4-1.7 A/m2 (at up to ∼30 mM butyrate and propionate as well as ∼240 mM Na+). As a conclusion, using G. sulfurreducens in BESs dealing with fermentation-hydrolysate can be regulated for efficacious energy recovery.

Influence of cysteine, serine, sulfate, and sulfide on anaerobic conversion of unsaturated long-chain fatty acid, oleate, to methane.

This study aims to elucidate the role of sulfide and its precursors in anaerobic digestion (i.e., cysteine, representing sulfur-containing amino acids, and sulfate) on microbial oleate conversion to methane. Serine, with a similar structure to cysteine but with a hydroxyl group instead of a thiol, was included as a control to assess potential effects on methane formation that were not related to sulfur functionalities. The results showed that copresence of sulfide and oleate in anaerobic batch assays accelerated the methane formation compared to assays with only oleate and mitigated negative effect on methane formation caused by increased sulfide level. Nuclear magnetic resonance spectroscopy of sulfide-exposed oleate suggested that sulfide reaction with oleate double bonds likely contributed to negation of the negative effect on the methanogenic activity. Methane formation from oleate was also accelerated in the presence of cysteine or serine, while sulfate decreased the cumulative methane formation from oleate. Neither cysteine nor serine was converted to methane, and their accelerating effects was associated to different mechanisms due to establishment of microbial communities with different structures, as evidenced by high-throughput sequencing of 16S rRNA gene. These outcomes contribute with new knowledge to develop strategies for optimum use of sulfur- and lipid-rich wastes in anaerobic digestion processes.

Fatigue of anammox consortia under long-term 1,4-dioxane exposure and recovery potential: N-kinetics and microbial dynamics.

Long-term exposure of anammox process to 1,4-dioxane was investigated using periodic anammox baffled reactor (PABR) under different 1,4-dioxane concentrations. The results generally indicated that PABR (composed of 4 compartments) has robust resistance to 10 mg-dioxane/L. The 1st compartment acted as a shield to protect subsequent compartments from 1,4-dioxane toxicity through secretion of high extracellular polymeric substance (EPS) of 152.9 mg/gVSS at 10 mg-dioxane/L. However, increasing 1,4-dioxane to 50 mg/L significantly inhibited anammox bacteria; e.g., ~ 93% of total nitrogen removal was lost within 14 days. The inhibition of anammox process at this dosage was most likely due to bacterial cell lysis, resulting in the decrease of EPS secretion and specific anammox activity (SAA) to 105.9 mg/gVSS and 0.04 mg N/gVSS/h, respectively, in the 1st compartment. However, anammox bacteria were successfully self-recovered within 41 days after the cease of 1,4-dioxane exposure. The identification of microbial compositions further emphasized the negative impacts of 1,4-dioxane on abundance of C. Brocadia among samples. Furthermore, the development of genus Planococcus in the 1st compartment, where removal of 1,4-dioxane was consistently observed, highlights its potential role as anoxic 1,4-dioxane degrader. Overall, long-term exposure to 1,4-dioxane should be controlled not exceeding 10 mg/L for a successful application.

Unraveling the capability of graphene nanosheets and γ-Fe2O3 nanoparticles to stimulate anammox granular sludge.

In this study, we investigated the potentials of nanomaterials to enhance anaerobic ammonium oxidation (anammox) process, in terms of nitrogen removal, microbial enrichment, and activity of key enzymes. Graphene nanosheets (GNs) and γ-Fe2O3 nanoparticles (NPs) were selected due to their catalytic functions as conductive material and electron shuttles, respectively. The obtained results revealed that the optimum dosage of GNs (10 mg/L) boosted the nitrogen removal rate (NRR) by 46 ± 3.1% compared to the control, with maximum NH4+-N and NO2--N removal of 86.5 ± 2.7% and 97.1 ± 0.5%, respectively. Moreover, hydrazine dehydrogenase (HDH) enzyme activity was augmented by 1.1-fold when using 10 mg/L GNs. The presence of GNs promoted the anammox granulation via enhancement of hydrophobic interaction of extracellular polymeric substances (EPS). Regarding the use of γ-Fe2O3 NPs, 100 mg/L dose increased NRR by 55 ± 3.8%; however, no contribution to HDH enzyme activity and a decrease in EPS compositions were observed. Given that the abiotic use of γ-Fe2O3 NPs further resulted in high adsorption efficiency (~92%), we conclude that the observed promotion due to γ-Fe2O3 NPs was mainly abiotic. Moreover, the 16S rRNA analysis revealed that the relative abundance of genus C. Jettenia (anammox related bacteria) increased from 11.9% to 12.3% when using 10 mg/L GNs, while declined to 8.3% at 100 mg/L γ-Fe2O3 NPs. Eventually, nanomaterials could stimulate the efficiency of anammox process, and this promotion and associated mechanism depend on their dose and composition.

Robustness of anaerobes exposed to cyanuric acid contaminated wastewater and achieving efficient removal via optimized co-digestion scheme.

The impact of various industrial pollutants on anaerobes and the biodegradation potentials need much emphasis. This study aims to investigate the response of anaerobic microbial systems to cyanuric acid (CA) exposure; CA is toxic and possible carcinogen. First, the long-term exposure of mixed culture bacteria (i.e., municipal sludge) to low-strength wastewater containing 20 mg/L CA was conducted in an up-flow anaerobic staged reactor. Stable performance and sludge granulation were observed, and the microbial community structure showed the progression of genus Acinetobacter known as CA degrader. Second, batch-mode experiment was performed to examine the CA biodegradability at higher doses (up to 250 mg/L of CA) in the absence and presence of glucose as a co-substrate; response surface-based optimization was used to design this experiment and to estimate the optimum CA-glucose combination. CA removal of 77-98% was achieved when CA was co-digested with glucose (250-1,000 mg/L), after 7 days-incubation at temperature of 37 °C, compared to 34% when CA was solely digested. Further, the obtained methane yield dropped when CA exceeded over 125 mg/L, though the deterioration was mitigated by addition of higher concentration of glucose. Overall, we conclude that CA is efficiently degraded under anaerobic conditions when being co-digested with readily assimilable substrate.

Regulating acidogenesis and methanogenesis for the separated bio-generation of hydrogen and methane from saline-to-hypersaline industrial wastewater.

Given the limitations of acidogens and methanogens activities under saline environments, this work aims to optimize the main operational parameters affecting hydrogen and methane production from saline-to-hypersaline wastewater containing mono-ethylene glycol (MEG). MEG is the main contaminant in several saline industrial effluents. Anaerobic baffled reactor (ABR), as a multi-stage system, was used at different temperatures (i.e., 19-31 °C [ambient] and 35 °C), organic loading rates (OLRs) of 0.6-2.2 gCOD/L/d, and salinity of 5-35 gNaCl/L. Mesophilic conditions of 35 °C substantially promoted MEG biodegradability (92-98%) and hydrogen/methane productivity, even at elevated salinity. Hydrogen yield (HY) and methane yield (MY) peaked to 258 and 140 mL/gCODadd, respectively, at OLR 0.64 gCOD/L/d and salinity up to 20-25 gNaCl/L. An immobilized sludge ABR (ISABR), packed with polyurethane media, was further compared with classical ABR, resulting in 1.8-fold higher MY, at 35 gNaCl/L. Microbial analysis showed that introducing attached growth system (ISABR) substantially promoted methanogens abundance, which was dominated by genus Methanosarcina. Among bacterial genera, Acetobacterium was dominant, particularly in 1st compartment, representing MEG-degrading/salt-tolerant genus. At high salinity up to 35 gNaCl/L, the multi-phase and attached growth configuration can efficiently reduce the induced salt stress, particularly on methanogens, towards balanced and separated acidogenesis/methanogenesis. Overall, producing hydrogen and methane from anaerobic treatment of MEG-based saline wastewater is feasible at optimized parameters and configuration.

Enhanced fermentative hydrogen production from industrial wastewater using mixed culture bacteria incorporated with iron, nickel, and zinc-based nanoparticles.

The present study assessed the efficiency of utilizing mixed culture bacteria (MCB) incorporated with individual nanoparticles (NPs), i.e., hematite (α-Fe2O3), nickel oxide (NiO), and zinc oxide (ZnO), dual NPs (α-Fe2O3 + NiO, α-Fe2O3 + ZnO, and NiO + ZnO), and multi-NPs (α-Fe2O3 + NiO + ZnO) for hydrogen production (HP) from industrial wastewater containing mono-ethylene glycol (MEG). When MCB was individually supplemented with α-Fe2O3 (200 mg/L), NiO (20 mg/L), and ZnO NPs (10 mg/L), HP improved significantly by 41, 30, and 29%, respectively. Further, key enzymes associated with MEG metabolism, such as alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and hydrogenase (hyd), were rapidly and substantially enhanced in the medium. NiO and ZnO NPs notably promoted ADH and ALDH activities, respectively, while α-Fe2O3 exhibited superior impact on hyd activity. Maximum hydrogen production rate was concomitant with higher acetic acid production and lower residual acetaldehyde and ethanol. HP using MCB supplemented with individual NiO (20 mg/L) and ZnO NPs (10 mg/L) further improved by 8.0%-14% when dual and multi-NPs were used; the highest HP was recorded when multi-NPs were used. In addition, NPs incorporation resulted in substantial increase in the relative abundance of Clostridiales (belonging to family Clostridiaceae; > 83%). Overall, this study provides significant insights into the impact of NPs on hydrogen production from MEG-contaminated wastewater.

Physico-chemical and microbial characterization of compartment-wise profiles in an anammox baffled reactor.

In this study, compartment-wise investigation of an anammox baffled reactor (AnBR) was performed. The AnBR achieved steady-state conditions after a start-up period of ∼50 days and achieved NH4 and NO2 conversion percentages of 88.5 and 99.3%, respectively. Examination of the nitrogen mass balance revealed that an AnBR with a two-compartment configuration was sufficient for nitrogen loading rates (NLRs) ranging from 0.125 to 1.975 kg N/m3/d and resulted in a nitrogen removal efficiency (NRE) of 86.7-93.7%. Higher NLRs (4.04-5.05 kg N/m3/d) required four compartments to achieve an NRE of 82.2-87.1%. Further, an overall NLR increase of up to 5.93 ±â€¯0.23 kg N/m3/d resulted in complete AnBR failure. The maximum nitrogen removal rate was consistently recorded in the 1st compartment for all NLRs examined; as a result, this compartment exhibited the highest bacterial activity. Biomass concentration, specific anammox activity, extracellular polymeric substances, and average granule diameter in the 1st compartment with an overall NLR of 0.05 kg N/m3/d were estimated to be 11.2 gVSS/L, 0.03 mg N/gVSS/h, 84.3 mg/gVSS, and 0.65 mm, respectively. These values increased to 26.1 gVSS/L, 11.80 mg N/gVSS/h, 242.1 mg/gVSS, and 2.31 mm, respectively, when the overall NLR was incremented to 4.04 kg N/m3/d. However, a gradual reduction in bacterial activity was observed from the 1st to the 5th compartment. The microbial community analysis indicated that the dominant phyla in the 1st compartment (NLR of 0.252 kg N/m3/d) with the highest nitrogen removal were Chloroflexi (38.13%), Planctomycetes (22.62%), and Proteobacteria (14.75%).

Factors affecting on hythane bio-generation via anaerobic digestion of mono-ethylene glycol contaminated wastewater: Inoculum-to-substrate ratio, nitrogen-to-phosphorus ratio and pH.

This study aims to assess the effect of inoculum-to-substrate ratio (ISR) and nitrogen-to-phosphorus balance on hythane production from thermophilic anaerobic decomposition of mono-ethylene glycol (MEG) contaminated wastewater. ISRs ranging from 2.65 to 13.23gVSS/gCOD were employed, whereas the tested N/P ratios varied from 4.6 to 8.5. Maximum methane and hydrogen yields (MY and HY) of 151.86±10.8 and 22.27±1.1mL/gCODinitial were achieved at ISRs of 5.29 and 3.78gVSS/gCOD, respectively. HY increased 1.45-fold by decreasing N/P from 8.5 to 4.6, while MY improved 1.6-fold by increasing N/P from 4.6 to 5.5. Methane production was strongly influenced by initial NH4-N, compared to initial PO4-P. Optimal HY of 47.55mL/gCODinitial was achieved at pH 5.0 and ISR of 3.78gVSS/gCOD using thermal-treated sludge. Three-dimensional regression model was applied for the combined effect of initial MEG, NH4-N and PO4-P on hythane production. Potential economic benefits of hythane production from MEG contaminated wastewater were assessed.