Effect of magnetite particle size on propionate degradation in the propionate-based anaerobic system

Fe3O4 nanoparticles promote methanogenesis in propionate acclimated system

Propionate accumulation is common in anaerobic digestion systems, while Fe3O4 nanoparticles (Fe3O4 NPs) show potential in steering direct interspecies electron transfer (DIET) to facilitate methanogenesis from propionate. However, the effect of Fe3O4 NPs in stable microbial communities remains unclear. This study demonstrated that 1.0 g/L Fe3O4 NPs enhanced propionate degradation and methane production by 220 % and 55 % of the propionate-acclimated microbial consortia post-shock loading, as evidenced by batch-test. High propionate concentrations suppressed Geobacter, yet Fe3O4 NPs enabled electron syntrophy between alternative DIET-participants (Arcobacter, Syntrophobacter) and methanogens (Methanothrix, Methanobacterium) serving as electron conduits. Network analysis further revealed that Fe3O4 NPs activated interactions among potential electroactive microbes, highlighting the potentially ubiquitous presence of electron syntrophy. Even in propionate-stressed microbial communities, such mutualism may be rapidly activated by Fe3O4 NPs, offering a practical solution for mitigating propionate accumulation and enhance digester performance.

Self-enhancement of bioenergy recovery from anaerobically digesting WAS with novel iron-based metal-organic framework assistance: Insights into electron transfer and metabolic pathways

Inadequate methane production and insufficient hydrolysis-acidification activity impede the practical application of anaerobic digestion (AD) of waste activated sludge (WAS). Recently, metal-organic framework (MOF) materials attains promising capability of controlling proton/electron transfer in AD processes. This study used a typical iron-based MOF and MIL-88A(Fe) to improve the methane production via digesting WAS. These materials were prepared via a one-step hydrothermal method. The findings indicated that the addition of 150 mg MIL-88A(Fe)/g WAS VS resulted in a 57.23% increase in accumulated methane production and a 43.84% increase in daily maximum methane production. The methane production rate (Rmax) also increased from 22.25 to 29.14 mL/g VS/d. The enhanced electron transfer capacity, improved hydrolysis of WAS, boosted acetate generation, and mitigated accumulation of volatile fatty acids (VFAs) collectively contributed to the better methane yield in the MIL-88A(Fe)-added system. The significant enrichment of Methanobacterium and Methanosaeta along with the up-regulation of key methanogenesis enzyme-encoding genes jointly suggested that the CO2 reduction and methanogenesis were strengthened. Moreover, MIL-88A(Fe) stimulated the production of c-type cytochrome and e-pili, facilitating direct interspecies electron transfer (DIET) between norank-f-SC-I-84 and Methanobacterium. This study provided new solutions for improving methane production and offered insights into the mechanism of enhanced methanogenesis of AD in the presence of MIL-88A(Fe).

Insight into the performance and microbial community of anaerobic digestion treating cow manure with a novel iron-functionalized activated biochar

The main objective of this research was to evaluate the impacts of FeCl3-activated biochar (FA-BC) on anaerobic digestion (AD) treating cow manure. The study focused on improving AD performance and understanding microbial community structure with the addition of FA-BC, while comparing FA-BC with other conductive additives, such as pristine biochar (P-BC), NaOH-activated biochar (NA-BC), and magnetite. Key findings indicated that FA- BC significantly enhanced the AD performance, supported by an increase in CH4 yield of 11-16% and a reduction in the lag phase by 51%. The high surface area and electrical conductivity of FA-BC synergistically facilitated direct interspecies electron transfer (DIET), leading to these improvements. On contrast, P-BC and NA-BC were not efficient in enhancing the AD performance due to relatively low electrical conductivity. P-BC also improved the CH4 yield, but less effectively than FA-BC. The effects of NA-BC varied with its dosage, showing inhibition at higher dosages due to excessive surface area. Magnetite, despite its high conductivity, made the limited enhancement in CH4 yield owing to its low surface area. Additionally, the statistical analyses revealed that each additive differently affected specific bacterial and archaeal groups depending on their physical and chemical properties. Thus, these findings suggest that FA-BC would be a highly promising additive for enhan cing AD systems, with potential applications in waste management and renewable energy production.

Deciphering Fe@C amendment on long-term anaerobic digestion of sulfate and propionate rich wastewater: Driving microbial community succession and propionate metabolism

This study evaluated the reflection of long-term anaerobic system exposed to sulfate and propionate. Fe@C was found to efficiently mitigate anaerobic sulfate inhibition and enhance propionate degradation. With influent propionate of 12000mgCOD/L and COD/SO42- ratio of 3.0, methane productivity and sulfate removal were only 0.06 ± 0.02L/gCOD and 63 %, respectively. Fe@C helped recover methane productivity to 0.23 ± 0.03L/gCOD, and remove sulfate completely. After alleviating sulfate stress, less organic substrate was utilized to form extracellular polymeric substances for self-protection, which enhanced mass transfer in anaerobic sludge. Microbial community succession, especially for alteration of key sulfate-reducing bacteria and propionate-oxidizing bacteria, was driven by Fe@C, thus enhancing sulfate reduction and propionate degradation. Acetotrophic Methanothrix and hydrogenotrophic unclassified_f_Methanoregulaceae were enriched to promote methanogenesis. Regarding propionate metabolism, inhibited methylmalonyl-CoA degradation was a limiting step under sulfate stress, and was mitigated by Fe@C. Overall, this study provides perspective on Fe@C's future application on sulfate and propionate rich wastewater treatment.

Harnessing iron materials for enhanced decolorization of azo dye wastewater: A comprehensive review

Highly colored azo dye-contaminated wastewater poses significant environmental threats and requires effective treatment before discharge. The anaerobic azo dye treatment method is a cost-effective and environmentally friendly solution, while its time-consuming and inefficient processes present substantial challenges for industrial scaling. Thus, the use of iron materials presents a promising alternative. Laboratory studies have demonstrated that systems coupled with iron materials enhance the decolorization efficiency and reduce the processing time. To fully realize the potential of iron materials for anaerobic azo dye treatment, a comprehensive synthesis and evaluation based on individual-related research studies, which have not been conducted to date, are necessary. This review provides, for the first time, an extensive and detailed overview of the utilization of iron materials for azo dye treatment, with a focus on decolorization. It assesses the treatment potential, analyzes the influencing factors and their impacts, and proposes metabolic pathways to enhance anaerobic dye treatment using iron materials. The physicochemical characteristics of iron materials are also discussed to elucidate the mechanisms behind the enhanced bioreduction of azo dyes. This study further addresses the current obstacles and outlines future prospects for industrial-scale application of iron-coupled treatment systems.

Insight into the effect of rice-straw ash on enhancing the anaerobic digestion performance of high salinity organic wastewater

Anaerobic digestion is an economic method for treating high salinity organic wastewater (HSOW), but performance enhancement is needed because of the inhibitory effect of high salinity. In this study, rice-straw ash (RSA) was applied to alleviate the inhibitory effect during HSOW anaerobic digestion. The results showed that, when the NaCl content increased from 0% to 3.0%, the methane production decreased by 87.35%, and the TOC removal rate decreased to 34.12%. As a K+ and alkalinity source, RSA addition enhanced the anaerobic digestion performance, and the optimal dosage was 0.88 g/L. Under this dosage, the methane production increased by 221.60%, and TOC removal rate reached 66.42% at 3.0% salinity. The addition of RSA increased the proportion of living cells in the high salinity environment, and enhanced the activity of key enzymes and electron transfer efficiency in the anaerobic digestion process. The addition of RSA with a dosage of 0.88 g/L promoted the accumulation of acetoclastic methanogen Methanothrix. The abundance of substrate transporters, ion transporters and electron transfer related functional genes were enriched, which might be key for promoting HSOW anaerobic digestion performance. The results also showed that RSA addition played an important role in maintaining the stability of the anaerobic digestion system, and it could be a potential strategy for enhancing the anaerobic digestion performance under high salinity conditions.

Effects of upward flow rate and modified biochar location on the performance and microecology of an anaerobic reactor treating kitchen waste

Increasing the value of food waste through anaerobic digestion is an attractive strategy. Meanwhile, the anaerobic digestion of kitchen waste also faces some technical challenges. In this study, four EGSB reactors were equipped with Fe-Mg-chitosan bagasse biochar at different locations, and the reflux pump flow rate was increased to change the upward flow rate of the reactor. The effects of adding modified biochar at different locations under different upward flow rate on the efficacy and microecology of anaerobic reactors treating kitchen waste were investigated. Results showed that Chloroflexi was the dominant microorganism when the modified biochar was added to the lower, middle, and upper parts of the reactor and mixed in the reactor, accounting for 54%, 56%, 58%, and 47%, respectively, on day 45. With the increased upward flow rate, the abundance of Bacteroidetes and Chloroflexi increased, while Proteobacteria and Firmicutes decreased. It was worth noting that the best COD removal effect was achieved when the anaerobic reactor upward flow rate was v2 = 0.6 m/h and the modified biochar was added in the upper part of the reactor, during which the average COD removal rate reached 96%. In addition, mixing modified biochar throughout the reactor while increasing the upward flow rate provided the greatest stimulus for the secretion of tryptophan and aromatic proteins in the sludge extracellular polymeric substances. The results provided a certain technical reference for improving the efficiency of anaerobic digestion of kitchen waste and scientific support for the application of modified biochar to the anaerobic digestion process.