A novel parameter for evaluating the influence of iron oxide on the methanogenic process

Persulfate-based strategy for promoted acesulfame removal during sludge anaerobic fermentation: Combined chemical and biological effects

The acesulfame (ACE) degradation in waste activated sludge (WAS) via direct anaerobic fermentation is difficult and the efficient elimination techniques are imperative for the ultimate safe WAS disposal. Persulfate (PS)-based approach was developed to promote the ACE removal during WAS anaerobic fermentation. Results demonstrated the effectiveness of PS-based treatments on ACE degradation, and the ACE removal efficiency was respectively 48.2% and 96.2% in the PS and PS/Fe-treated reactors while it was only 6.0% in the control reactor. Mechanism explorations revealed that the active free radicals (i.e. OH• and SO₄^•-) generated in the PS-based reactors were the key oxidative species for the ACE degradation. However, such effects were interfered by the released soluble substrates (i.e. protein, carbohydrate and inorganic ions) during anaerobic fermentation by competing and/or quenching free radicals, which caused the deceleration of the ACE removal efficiency. Moreover, the PS-based treatment facilitated the enrichment of functional microorganisms (i.e. Phyllobacteriaceae and Bradyrhizobiaceae) and upregulated the critical genes (i.e. pncB and nadE) involved in the ACE degradation. Based on the density functional theory (DFT) and metabolic intermediates analysis, the hydroxylation and oxidative ring-opening were the two main proposed metabolic pathways for ACE degradation. Overall, the combined chemical and biological metabolism effects collectively contributed to the efficient ACE degradation, and it provided a novel and effective strategy for refractory pollutants removal during WAS anaerobic fermentation.

Methanogenic biodegradation of iso-alkanes and cycloalkanes during long-term incubation with oil sands tailings

Microbes indigenous to oil sands tailings ponds methanogenically biodegrade certain hydrocarbons, including n-alkanes and monoaromatics, whereas other hydrocarbons such as iso- and cycloalkanes are more recalcitrant. We tested the susceptibility of iso- and cycloalkanes to methanogenic biodegradation by incubating them with mature fine tailings (MFT) collected from two depths (6 and 31 m below surface) of a tailings pond, representing different lengths of exposure to hydrocarbons. A mixture of five iso-alkanes and three cycloalkanes was incubated with MFT for 1700 d. Iso-alkanes were completely biodegraded in the order 3-methylhexane > 4-methylheptane > 2-methyloctane > 2-methylheptane, whereas 3-ethylhexane and ethylcyclopentane were only partially depleted and methylcyclohexane and ethylcyclohexane were not degraded during incubation. Pyrosequencing of 16S rRNA genes showed enrichment of Peptococcaceae (Desulfotomaculum) and Smithella in amended cultures with acetoclastic (Methanosaeta) and hydrogenotrophic methanogens (Methanoregula and Methanoculleus). Bioaugmentation of MFT by inoculation with MFT-derived enrichment cultures reduced the lag phase before onset of iso-alkane and cycloalkane degradation. However, the same enrichment culture incubated without MFT exhibited slower biodegradation kinetics and less CH₄ production, implying that the MFT solid phase (clay minerals) enhanced methanogenesis. These results help explain and predict continued emissions of CH₄ from oil sands tailings repositories in situ.

Exclusive microbially driven autotrophic iron-dependent denitrification in a reactor inoculated with activated sludge

Autotrophic iron-dependent denitrification (AIDD) is arising as a promising process for nitrogen removal from wastewater with a low carbon to nitrogen ratio. However, there is still a debate about the existence of such a process in activated sludge systems. This work provides evidence and elucidated the feasibility of autotrophic Fe(II)-oxidizing nitrate-reducing culture for nitrogen removal by long-term reactor operation, batch experimental verification, unstructured kinetic modeling and microbial community analyses. A relatively stable nitrate removal rate was achieved coupled with the oxidation of ferrous ions in 3-month operation of reactor. The kinetic modeling suggests that the iron oxidation was a growth-associated process in AIDD. Utilization of extracellular polymeric substances (and/or soluble microbial products) as electron donor for denitrification by heterotrophic denitrifiers was not mainly responsible for nitrogen removal in the reactor. After long-term operation of the reactor with activated sludge as inoculum, the enrichment culture KS-like consortium, dominated by Fe(II) oxidizer, Gallionellaceae, was successfully acclimated for autotrophic Fe(II)-oxidizing nitrate reduction. This work extents our understanding about the existence of such an autotrophic Fe(II)-oxidizing nitrate-reducing culture in both natural and engineered systems, and opens a door for its potential application in wastewater treatment.

Promotion of Para-Chlorophenol Reduction and Extracellular Electron Transfer in an Anaerobic System at the Presence of Iron-Oxides

Anaerobic dechlorination of chlorophenols often subjects to their toxicity and recalcitrance, presenting low loading rate and poor degradation efficiency. In this study, in order to accelerate p-chlorophenol (p-CP) reduction and extracellular electron transfer in an anaerobic system, three iron-oxide nanoparticles, namely hematite, magnetite and ferrihydrite, were coupled into an anaerobic system, with the performance and underlying role of iron-oxide nanoparticles elucidated. The reductive dechlorination of p-CP was notably improved in the anaerobic systems coupled by hematite and magnetite, although ferrihydrite did not plays a positive role. Enhanced dechlorination of p-CP in hematite or magnetite coupled anaerobic system was linked to the obvious accumulation of acetate, lower oxidation-reduction potential and pH, which were beneficial for reductive dechlorination. Electron transfer could be enhanced by Fe2+/Fe3+ redox couple on the iron oxides surface formed through dissimilatory iron-reduction. This study demonstrated that the coupling of iron-oxide nanoparticles such as hematite and magnetite could be a promising alternative to the conventional anaerobic reduction process for the removal of CPs from wastewater.