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 ± 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%).
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•Sufficient number of AnBR compartments for nitrogen removal varied depending on NLR.•High EPS and low PN/PS enhanced Anammox activity in the first compartment.•AnBR adapted-microbes dominated by Chloroflexi, Planctomycetes and Proteobacteria.•Behavior of nitrogen fractions in AnBR compartments was mathematically modeled.
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•Hythane production from anaerobic digestion of MEG-based substrate was examined.•Optimum H2 and CH4 production depended on inoculum-to-substrate ratio (ISR) and N/P.•CH4 yield peaked ...(152mL/gCODinitial) at ISR of 5.29gVSS/gCOD and N/P ratio of 5.5.•H2 yield at optimum ISR and N/P, further peaked at pH 5.0 using pre-treated sludge.•Regarding energy recovery, substantial economic/environmental profits were achieved.
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.
•Techno-economic feasibility of biogas production from saline effluent was studied.•Immobilized sludge anaerobic baffled reactor and salt-adapted culture were employed.•Temperature and OLR changes ...affected salt-tolerant bacterial/archaeal communities.•H2/CH4 yield increased at low OLR and 35 °C under high salinity (15–25 gNaCl/L).•Multivariable analysis showed the importance of OLR, temperature and configuration.
This study investigated the biogas (hydrogen and methane) production and microbial community dynamics in the anaerobic treatment of saline industrial effluents containing mono-ethylene glycol (MEG) as a major pollutant. An immobilized sludge anaerobic baffled reactor (ISABR) inoculated with salt-adapted mixed culture was developed as a lab-scale experiment, and effects of operational conditions (e.g., salinity, organic loading rates (OLRs), and temperature) on the system performance were examined. First, different OLRs of 0.64–2.34 gCOD/L/d, by increasing the initial MEG concentrations at a fixed hydraulic retention time (HRT) of 4.5 d, were examined from day 1 to 100 at lower salinity of 10 gNaCl/L and ambient temperature (25 ± 6 °C). Under such operational conditions, maximum methane yield (MY) of 165 mL CH4/gCODadd and hydrogen yield (HY) of 102 mL H2/gCODadd were achieved at the lowest OLR of 0.64 gCOD/L/d. Afterwards, impacts of higher salinities of 15–25 gNaCl/L were investigated from day 101 to 208 at a controlled mesophilic temperature of 35 °C and fixed OLR (0.64 gCOD/L/d). As a result, enhanced HY and MY (∼2-fold) at elevated salinities up to 25 gNaCl/L were obtained. Moreover, the compartment-wise water and gas analyses, for both experiments, revealed that hydrogen and methane peaked in former and latter compartments, respectively, and the peak location shifted depending on overall imposed OLR. The relative abundance of dominant salt-tolerant bacterial genus Desulfovibrio increased when OLR and operational temperature were increased, while dominant archaeal genera responded substantially when temperature was increased. Economic feasibility of ISABR for bioenergy recovery and treatment of MEG was evaluated by a cost-benefit analysis, suggesting that salinity level along with suitable operational temperature substantially affects the maximum net profit.
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.
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•Anammox bacteria revealed robust resistance for long-term exposure to 10 mg-dioxane/L•Most of N-removal was achieved in the first compartment of PABR•Process failure was noticed after 14 days of exposure to 50 mg-dioxane/L•Anammox process was self-recovered after 41 days of 1,4-dioxane non-exposure condition.•Planococcus shared microbial community with C. Brocadia due to 1,4-dioxane exposure
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•Anammox bacteria revealed robust resistance to the toxicity to 200 mg/L 1,4-dioxane.•1,4-Dioxane inhibition to anammox process was found to be substrate dependent.•Inactivation of ...HDH enzyme is the main anammox inhibition mechanism by 1,4-dioxane.•Candidatus Brocadia was adversely affected by increasing 1,4-dioxane concentration.
Anammox process contaminated by 1,4-dioxane was evaluated using sets of batch experiments under different nitrogen loads and 1,4-dioxane concentrations. Toxicity of 1,4-dioxane to anammox consortia was negligible till the level of 200 mg-dioxane/L with a reduction in the total nitrogen (TN) removal efficiency, less than 8% at initial loads of <200 mgTN/L. However, 1,4-dioxane inhibition was also found to be substrate-dependent, where TN removal efficiency was declined by 19.3% at 500 mgTN/L and 200 mg-dioxane/L. The negative synergistic effect was exacerbated in the case of 500 mgTN/L and 2000 mg-dioxane/L, with the minimum TN removal efficiency of 24.1 ± 1.2%. Moreover, the impact of 1,4-dioxane on anammox activity was evaluated in terms of specific anammox activity (SAA), hydrazine dehydrogenase (HDH) activity, and extracellular polymeric substances (EPS). These parameters revealed a significant reduction when 1,4-dioxane surpassed 200 mg/L. Their lowest values of 0.90 ± 0.02 mgTN/gVSS/h (54.7% lower than control), 0.45 ± 0.03 µmol cytochrome-c reduced/min/mg protein (45.1% lower than control), and 74.8 ± 8.5 mg/gVSS (32.6% lower than control) were recorded when anammox bacteria were subjected to initial TN and 1,4-dioxane loads of 200 and 2000 mg/L, respectively. The inhibition mechanism of 1,4-dioxane on the anammox process was expected owing to HDH enzyme inactivation that led to a reduction in SAA and EPS secretion ability. Further, the 16S rRNA analysis revealed that the exposure to 1,4-dioxane caused a significant drop in the dominant anammox genus Candidatus Brocadia, along with a progression of denitrifying bacteria, particularly genus Limnobacter.
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.
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•Cysteine, serine, and sulfide accelerate conversion rate of oleate to methane.•Microbial community alters differently upon cysteine, serine, or sulfide amendments.•Sulfide has the potential to abiotically react with unsaturated bonds of LCFA.•Sulfide toxicity can be mitigated in the presence of unsaturated LCFA.
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.
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•H2/CH4 bio-production from hypersaline effluent (up to 35 gNaCl/L) was assessed.•Operational temperature and OLR were optimized to adapt different salinity levels.•H2/CH4 productivity peaked at low OLR and 35 °C under high salinity (20–25 gNaCl/L).•Employing attached growth reactor further promoted methane by 80%, at 35 gNaCl/L.•Acetobacterium and Methanosarcina dominated the bacterial and archaeal genera.
Hythane (H2 + CH4) production from petrochemical wastewater containing mono-ethylene glycol (MEG) via a novel stepped anaerobic baffled (SAB) reactor was investigated. The reactor was continuously ...operated for five months at constant hydraulic retention time (HRT) of 72 h and different organic loading rates (OLRs) of 0.33, 0.67 and 1.67 gCOD l−1 d−1. The maximum H2 yield of 359.01 ± 33.46 ml H2 gCODremoved−1 and H2 production rate of 5.12 ± 0.48 l d−1 were obtained at OLR of 1.67 gCOD l−1 d−1. Nevertheless, the maximum methane yield of 159.11 ± 14.72 ml CH4 gCODremoved−1 and methane production rate of 2.48 ± 0.22 l d−1 were recorded at OLR of 0.67 gCOD l−1 d−1. The maximum CH4 and H2 content of 52.08 and 49.84% were achieved at OLR of 0.33 and 1.67 gCOD l−1 d−1, respectively. Compartment-wise hythane profiles were assessed to optimize the production rate. Microbial community analysis was conducted and showed the dominant bacteria of Proteobacteria (44.3%), Firmicutes (28.9%), Chloroflexi (8.9%), Actinobacteria (5.7%), and Bacteroidetes (5.6%).
•Mono-ethylene glycol rich effluents proved a high potential for Hythane production.•New configuration of ABR showed uniform organic load distribution along its length.•The effect of organic loading rate on Hythane production was assessed.•Maximum hydrogen and methane yield of 359 and 159 mlgCODremoved−1 were achieved.
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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.
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