Microbial Acclimation Research Articles

Microbial community response to temperature reduction during anaerobic treatment of long chain fatty acids-containing wastewater

Acclimating mesophilic biomass to low temperatures have been used to start-up psychrophilic anaerobic reactors, but limited microbial information is available during the acclimation. To investigate microbial responses to temperature reductions, duplicate lab-scale anaerobic digestion (AD) reactors were operated for 166 days, with the temperature being reduced from 37°C to 15°C, using synthetic long chain fatty acid (LCFA)-containing wastewater as the feedstock. The acclimated biomass at 15°C exhibited efficient removal of organic matter (total COD>75%, soluble COD>88%, and LCFA>99%). Temperature reductions lead to significant reductions in microbiome diversity. Fermentative bacteria were highly dynamic and functional redundant during temperature reductions. Smithella was the dominant syntrophic bacteria involved in LCFA degradation coupled with Methanothrix and Methanocorpusculum at 15°C. Membrane modifications and compatible cellular solutes production were triggered by temperature reductions as microbial response to cold stress. This study provided molecular insights in microbial acclimation to low temperatures for psychrophilic AD.

Exploring the impacts of steroid estrogens load and aeration intensity on the performance, membrane fouling characteristics, and bacterial community structure of the anoxic-oxic membrane bioreactor

Steroid estrogens (SEs) are typical endocrine-disrupting compounds, and they are inadequately eliminated in most wastewater treatment plants (WWTPs), contributing significantly to their environmental prevalence. In an effort to optimize the performance of membrane bioreactor (MBR) in mitigating SEs alike micropollutants, this study investigated the influences of influent loads of three typical SEs (estrone (E1), 17β-estradiol (E2), and 17α-ethynyestradiol (EE2)) and the aeration intensity on the pollutants removal performance, membrane fouling characteristics, and bacterial community structure in a lab-scale anoxic/oxic-MBR (A/O-MBR) process. The presence of SEs shed minimal impacts on the performance of A/O-MBR process as indicated by conventional water quality parameters due to gradual microbial acclimation. However, the presence and the rising input of SEs accelerated membrane fouling as a result of the enhanced EPS excretion and PN/PS ratio and the reduced floc size. The moderate aeration intensity was preferred from the perspectives of conventional pollutants removal, SEs biodegradation, biomass accumulation, and membrane fouling mitigation. Evolution of bacterial community structure and predominant genera were identified at different SEs loads and aeration intensities, with Candidatus Competibacter and Ferruginibacter detected as the predominant genera at different SEs input loads and Thiothrix, Azospira, and Saprospiraceae_norank at different aeration intensities with identical SEs input. The results demonstrated the potential of A/O-MBR as a promising barrier against SEs alike micropollutants through the regulation and control of aeration intensity.

Coupling of biogas residue biochar and low-magnitude electric fields promotes anaerobic co-digestion of sewage sludge and food waste.

Biochar-assisted anaerobic digestion (AD) remains constrained due to the inefficient decomposition of complex organics, even with the direct interspecies electron transfer (DIET) pathway. The coupling of electrochemistry with the anaerobic biological treatment could shorten lengthy retention time in co-digestion by improving electron transfer rates and inducing functional microbial acclimation. Thus, this work investigated the potential of improving the performance of AD by coupling low-magnitude electric fields with biochar derived from the anaerobically digested biogas residue. Different voltages (0.3, 0.6, and 0.9 V) were applied at various stages to assess the impact on biochar-assisted AD. The results indicate that an external voltage of 0.3 V, coupled with 5 g/L of biochar, elevates CH4 yield by 45.5% compared to biogas residue biochar alone, and the coupled approach increased biogas production by up to 143% within 10 days. This finding may be partly explained by the enhanced utilization of substrates and the increased amounts of specific methanogens such as Methanobacterium and Methanosarcina. The abundance of the former increased from 4.0 to 11.3%, which enhances the DIET between microorganisms. Furthermore, the coupling method shows better potential for enhancing AD compared to preparing iron-based biochar, and these results present potential avenues for its broader applications.

Enhancing microbial viability with biochar for increased methane production during the anaerobic digestion of chicken manure

This investigation explores the effects of integrating acid-alkali treated biochar into the anaerobic digestion of chicken manure. Digesters containing chicken manure with biochar addition exhibited an 8.4-fold improvement in methane production compared to untreated digesters. In addition, the porous structure of the biochar promoted microbial acclimation, facilitated direct interspecies electron transfer, and provided anchoring points for immobilisation. Anaerobic digesters containing chicken manure amended with biochar also demonstrated increased chemical oxygen demand removal, up to 81.8 %, and maintained lower total ammonia concentrations (2,478 mg/L) compared to levels in control reactors (4418 mg/L). In terms of the microbial community, the addition of propidium monoazide minimised errors in live microbial population estimation, providing new insights into the capacity of biochar to shield microbes from ammonia stress. These findings highlight biochar's quantitative benefits, emphasising its potential in enhancing methane production, mitigating ammonia stress, and promoting microbial resilience in anaerobic digestion.

Intact polar lipidome and membrane adaptations of microbial communities inhabiting serpentinite-hosted fluids.

The generation of hydrogen and reduced carbon compounds during serpentinization provides sustained energy for microorganisms on Earth, and possibly on other extraterrestrial bodies (e.g., Mars, icy satellites). However, the geochemical conditions that arise from water-rock reaction also challenge the known limits of microbial physiology, such as hyperalkaline pH, limited electron acceptors and inorganic carbon. Because cell membranes act as a primary barrier between a cell and its environment, lipids are a vital component in microbial acclimation to challenging physicochemical conditions. To probe the diversity of cell membrane lipids produced in serpentinizing settings and identify membrane adaptations to this environment, we conducted the first comprehensive intact polar lipid (IPL) biomarker survey of microbial communities inhabiting the subsurface at a terrestrial site of serpentinization. We used an expansive, custom environmental lipid database that expands the application of targeted and untargeted lipodomics in the study of microbial and biogeochemical processes. IPLs extracted from serpentinite-hosted fluid communities were comprised of >90% isoprenoidal and non-isoprenoidal diether glycolipids likely produced by archaeal methanogens and sulfate-reducing bacteria. Phospholipids only constituted ~1% of the intact polar lipidome. In addition to abundant diether glycolipids, betaine and trimethylated-ornithine aminolipids and glycosphingolipids were also detected, indicating pervasive membrane modifications in response to phosphate limitation. The carbon oxidation state of IPL backbones was positively correlated with the reduction potential of fluids, which may signify an energy conservation strategy for lipid synthesis. Together, these data suggest microorganisms inhabiting serpentinites possess a unique combination of membrane adaptations that allow for their survival in polyextreme environments. The persistence of IPLs in fluids beyond the presence of their source organisms, as indicated by 16S rRNA genes and transcripts, is promising for the detection of extinct life in serpentinizing settings through lipid biomarker signatures. These data contribute new insights into the complexity of lipid structures generated in actively serpentinizing environments and provide valuable context to aid in the reconstruction of past microbial activity from fossil lipid records of terrestrial serpentinites and the search for biosignatures elsewhere in our solar system.

Microbial community acclimatization enhances bioplastics biodegradation and biogas production under thermophilic anaerobic digestion

This paper reports the results of a novel study of microbial acclimatization for bioplastics anaerobic degradation and conversion into biogas. Three sequential anaerobic digestion (AD) runs were carried out to favour microbial acclimatization to two different bioplastics, starch-based (SBS) and polyactic-acid (PLA).AD of SBS and PLA bioplastics was favoured by the acclimatization of the inoculum to the substrate after each run of AD. SBS conversion into biogas increased by 52 % (from 94 to 143 NL kgVS-1) and it was correlated with the enhanced growth of starch degrading bacteria such as Hydrogenispora, Halocella and Haloplasma. PLA anaerobic degradation increased by 97 % (from 395 to 779 NLbiogas kgVS-1) and it was related to the acclimatization of known PLA-degraders such as Tepidimicrobium, Methanothermobacter and Tepidanaerobacter. Microbial acclimatization appears a suitable and low-cost strategy to enhance bioplastics circularity by promoting their anaerobic biodegradation and conversion into biogas.

Determination of effects of thermophilic and hyperthermophilic temperatures on anaerobic hydrolysis and acidogenesis of pig manure through a one-year study

Improving hydrolysis and acidogenesis through thermophilic and hyperthermophilic temperatures is critical for enhancing the anaerobic decomposition of organic waste like pig manure. However, whether higher temperatures can provide more enhanced performance has not been elucidated experimentally. This study, therefore, conducted a 375-day continuous operation experiment at 55 and 70 °C with a 5-day hydraulic retention time. The two temperature reactors entered a stable state after about 200 days and long-term microbial acclimation markedly changed their performances. In the thermophilic and hyperthermophilic reactor, the hydrolysis efficiencies were obtained at 29.7 % and 27.3 % respectively, whereas the acidogenesis efficiency was relatively low at 1.0 % and 3.1 %. Due to the occurrence of methanogenesis, the volatile fatty acid concentration in the thermophilic reactor was only 45 % of that in the hyperthermophilic reactor. The thermophilic reactor exhibited higher bacterial diversity; however, this difference between the two reactors apparently did not correlate with hydrolysis and acidogenesis performance.

Optimizing total ammonia–nitrogen concentration for enhanced microbial fuel cell performance in landfill leachate treatment: a bibliometric analysis and future directions

Untreated landfill leachate can harm the environment and human health due to its organic debris, heavy metals, and nitrogen molecules like ammonia. Microbial fuel cells (MFCs) have emerged as a promising technology for treating landfill leachate and generating energy. However, high concentrations of total ammonia–nitrogen (TAN), which includes both ammonia and the ammonium ion, can impede MFC performance. Therefore, maintaining an adequate TAN concentration is crucial, as both excess and insufficient levels can reduce power generation. To evaluate the worldwide research on MFCs using landfill leachate as a substrate, bibliometric analysis was conducted to assess publication output, author-country co-authorship, and author keyword co-occurrence. Scopus and Web of Science retrieved 98 journal articles on this topic during 2011–2022; 18 were specifically evaluated and analysed for MFC ammonia inhibition. The results showed that research on MFC using landfill leachate as a substrate began in 2011, and the number of related papers has consistently increased every 2 years, totaling 4060 references. China, India, and the USA accounted for approximately 60% of all global publications, while the remaining 40% was contributed by 70 other countries/territories. Chongqing University emerged as one of the top contributors among this subject’s ten most productive universities. Most studies found that maintaining TAN concentrations in the 400–800 mg L−1 in MFC operation produced good power density, pollution elimination, and microbial acclimatization. However, the database has few articles on MFC and landfill leachate; MFC ammonia inhibition remains the main factor impacting system performance. This bibliographic analysis provides excellent references and future research directions, highlighting the current limitations of MFC research in this area.

Initial stage of innovative cell-entrapped biofilter start-up for removal of manganese in water: Treatment performance, manganese speciation, and microbial community

Manganese-contaminated groundwater as a drinking water source causes colored water, pipe clogging, and health problems. Manganese removal using biofilters is an effective process, but microbial acclimatization during the start-up period takes time. The aim of this study is to investigate the initial stage of an innovative cell-entrapped biofilter start-up for manganese removal. Streptomyces violarus SBP1 (SBP1) entrapped in barium alginate was incorporated into the biofilter to enhance manganese removal and cell retention. The manganese removal performance, microbial community, and manganese transformation were examined through dual media columns representing free cell-augmented (FC), entrapped cell-augmented (EC), and conventional biofilters at an initial manganese concentration of 1 mg/L. In a filtration experiment, EC achieved better removal performance (53 %) than FC (45 %) and conventional biofilter (39 %) because of higher manganese bio-oxidation. During the beginning period, manganese adsorption was predominant, whereas manganese bio-oxidation played a main role thereafter. A synchrotron-based analysis confirmed that most Mn(II) was oxidized to Mn(III) and Mn(IV). The amplicon sequencing results revealed that Proteobacteria-dominated natural biofilm in all three filters, while Streptomyces (expected as SBP1) was the major bacterial group in EC. This study demonstrated the feasibility of developing an innovative cell-entrapped biofilter.

Deciphering the fate of osmotic stress priming on enhanced microorganism acclimation for purified terephthalic acid wastewater treatment with high salinity and organic load

Osmotic stress priming (OSP) was an effective management strategy for improving microbial acclimation to salt stress. In this study, the interaction between pollutants and microbiota, and microbial osmoregulation were investigated triggered by OSP (alternately increasing salinity and organic loading). Results showed that OSP significantly improved COD removal from 31.53 % to 67.99 % and mitigated the terephthalate inhibition produced by toluate, decreasing from 1908.08 mg/L to 837.16 mg/L compared with direct priming. Due to an increase in salinity, Pelotomaculum and Mesotoga were enriched to facilitate terephthalate degradation and syntrophic acetate oxidation (SAO). And organic load promoted acetate formation through syntrophic metabolism of Syntrophorhabdus/Pelotomaculum and SAO-dependent hydrogenotrophic methanogenesis. K+ absorbing, proline and trehalose synthesis participated in osmoregulation at 0.5 % salinity, while only ectoine alleviated intracellular osmolarity under 1.0 % salinity with OLR of 0.44 kg COD /m3. This study provided in-depth insight for microbial acclimation process of anaerobic priming of saline wastewater.

Anaerobic–anoxic–oxic biological treatment of high-strength, highly recalcitrant polyphenylene sulfide wastewater

This paper outlines an integrated anaerobic–anoxic–oxic (A2O) treatment scheme for high-strength, highly recalcitrant wastewater from the production of polyphenylene sulfide (PPS) resins and their composite chemicals. An integrated anaerobic granular sludge blanket (GSB) and anoxic–oxic (AO) reactor indicated that the A2O removed chemical oxygen demand (COD) of up to 7,043 mg/L with no adverse impact from high total dissolved solids (25,000 mg/L) on the GSB COD removal and effluent suspended solids. At a Total Kjeldahl Nitrogen (TKN) nitrification load of 0.11 g TKN/L.d and 400 mg NH3/L, almost 99 % of the NH3 was degraded with effluent NH3 < 5 mg/L, meeting the limit of 35 mg/L. High S2- levels of up to 1470 mg/L can be transformed through aerobic microbial degradation to meet a limit of 1.0 mg/L. With proper microbial acclimation and process designs, the integrated A2O scheme offers a resilient and robust treatment for high-strength recalcitrant PPS wastewater.

Soil warming decreases carbon availability and reduces metabolic functions of bacteria

Plastic film mulch (PFM) is effective to save soil water and increase temperature and consequently, to increase crop yield. Therefore, PFM has become one of the most widely used on-farm management practices for maize cultivation in semi-arid regions. The effects of PFM-induced warming on the labile carbon (C) pools and microorganisms remain unclear. We used high-throughput genomic sequencing to assess bacterial community structure and metabolic functions in soils after short- (2 years) and long-term (10 years) cover with PFM in a dryland agriculture system. Strong decrease of dissolved organic C (DOC) pool (14–18 % less than in Control soil) by warming (2.4 °C) raised bacterial ⍺-diversity. The short-term mulch reduced the absolute abundance of bacteria by 36–43 % due to the temperature rise and labile C reduction. Bacteria developed with lower abundance (e.g., smaller colonies) but with higher diversity in soils with less available resources. During the long-term mulching and microbial acclimation to increased temperature and the reduced labile C, the bacterial community strongly changed towards an oligotrophic life history. The PFM increased the abundance of bacterial species with high nutrient uptake (e.g. Patescibacteria increased by 83 %), while chemotrophs that prefer eutrophic conditions were reduced in the PFM soil (e.g. Actinobacteriota by 11 %). The PFM increased the complexity of co-occurring networks of bacterial communities and decreased their stability. Almost all bacterial marker taxa screened by random forest algorithm differed between Control and Mulch soils. Long-term mulching reduced the rate of bacterial metabolism associated with organic matter degradation, such as metabolism of carbohydrates, esters (propanoate and butanoate decreased strongly), lipids (the greatest reduction was for fatty acids), and amino acids (lysine, valine, leucine, and isoleucine degradation pathways dropped the most). Structural equation modeling indicated that bacterial metabolism was mainly influenced by bacterial community structure. Consequently, the metabolic functions of bacteria were reduced after the decrease of C availability induced by warming under PFM, and this reduction was dependent on the duration of PFM application.

Recent advances in anaerobic digestion of lipid-rich waste: Challenges and potential of seaweeds to mitigate the inhibitory effect

• Lipid-rich waste (LRWs) represents a potential feedstock for biogas production. • Microbial structure and activity play a significant role in LRWs digestion and biogas yield. • Foaming, fatty acids accumulation, and nutrients imbalance are the main challenges. • Seaweeds provide a complementary co-substrate and a synergistic action to mitigate the effect. • Co-digestion of LRWs and seaweeds enhance the economic feasibility up to 18.9-times. Considerable attention has been devoted towards anaerobic digestion of lipid-rich waste (LRWs) due to their higher energy content comparing to other waste rich in carbohydrates and proteins. However, there are still many challenges for LRWs anaerobic digestion which are mainly attributed to floatation, foaming, long-chain fatty acids (LCFAs) accumulation, and nutrients imbalance resulting in reactor instability and failure. The present review aims to report the recent progress in LRWs production, with a special focus on the main challenges for anaerobic digestion and the recent advances to enhance the digestion process including pretreatment, microbial acclimatization, dosing of trace elements, carrier addition, and co-digestion. Regarding the later, main characteristics and potential of seaweeds to mitigate the toxic effect of LRWs towards enhanced anaerobic digestion through cascading approach was discussed. Considering the low nitrogen content in LRWs and moderate nitrogen content in seaweeds with very low lipid content and negligible lignin, seaweeds could be a potential co-substrate for anaerobic digestion with LRWs. Co-digestion of seaweeds with LRWs results in synergistic action leading to nutrient balance and enhanced anaerobic performance. In addition, developing a cascading approach for high bioenergy recovery from LRWs through co-digestion with seaweeds/residues could further provide optimum conditions for enhanced biogas production and economic feasibility. The economic analysis estimated US$ 15.27 million annual net profit from co-digestion of LRWs and seaweeds, which was 1.0- and 18.9-times higher than that from mono-digestion of LRWs or seaweeds, respectively. The present article suggests a new perspective for efficient anaerobic digestion of LRWs towards enhanced energy recovery through integrated cascading approaches.

Growth rate-dependent coordination of catabolism and anabolism in the archaeon Methanococcus maripaludis under phosphate limitation.

Catabolic and anabolic processes are finely coordinated in microorganisms to provide optimized fitness under varying environmental conditions. Understanding this coordination and the resulting physiological traits reveals fundamental strategies of microbial acclimation. Here, we characterized the system-level physiology of Methanococcus maripaludis, a niche-specialized methanogenic archaeon, at different dilution rates ranging from 0.09 to 0.003 h-1 in chemostat experiments under phosphate (i.e., anabolic) limitation. Phosphate was supplied as the limiting nutrient, while formate was supplied in excess as the catabolic substrate and carbon source. We observed a decoupling of catabolism and anabolism resulting in lower biomass yield relative to catabolically limited cells at the same dilution rates. In addition, the mass abundance of several coarse-grained proteome sectors (i.e., combined abundance of proteins grouped based on their function) exhibited a linear relationship with growth rate, mostly ribosomes and their biogenesis. Accordingly, cellular RNA content also correlated with growth rate. Although the methanogenesis proteome sector was invariant, the metabolic capacity for methanogenesis, measured as methane production rates immediately after transfer to batch culture, correlated with growth rate suggesting translationally independent regulation that allows cells to only increase catabolic activity under growth-permissible conditions. These observations are in stark contrast to the physiology of M. maripaludis under formate (i.e., catabolic) limitation, where cells keep an invariant proteome including ribosomal content and a high methanogenesis capacity across a wide range of growth rates. Our findings reveal that M. maripaludis employs fundamentally different strategies to coordinate global physiology during anabolic phosphate and catabolic formate limitation.

Response of a Coastal Microbial Community to Olivine Addition in the Muping Marine Ranch, Yantai

Spreading olivine powder in seawater to enhance alkalinity through weathering reactions has been proposed as a potential solution to control atmospheric CO2 concentration. Attention has usually been paid to the chemical properties of seawater after the addition of olivine within lab and modeling studies. However, both microbial acclimation and evolution in such manipulated natural environments are often overlooked, yet they are of great importance for understanding the biological consequences of whether olivine addition is a feasible approach to mitigating climate change. In this study, an olivine addition experiment was conducted to investigate variation in bacterial diversity and community composition in the surface and bottom seawater of a representative marine ranch area in the Muping, Yantai. The results show that the composition of the particle-attached microbial community was particularly affected by the application of olivine. The relative abundance of biofilm-forming microbes in particle-attached fraction increased after the addition of olivine, while no significant variation in the free-living bacterial community was observed. Our study suggests that olivine addition would reshape the bacterial community structure, especially in particle-attached microenvironments. Therefore, the risk evaluation of alkalinity enhancement should be further studied before its large-scale application as a potential ocean geoengineering plan.

Glucose Addition Enhanced the Advanced Treatment of Coking Wastewater

Biological processes have high removal efficiencies and low operational costs, but the secondary effluent of coking wastewater (CWW), even at a low concentration, is difficult for microorganisms to degrade directly. In this study, glucose was used as a carbon source and co-metabolic substrate for microbial acclimation in order to enhance the advanced treatment of coking wastewater (CWW). The removal performance of the pollutants, especially recalcitrant compounds, was studied and the changes in the microbial community structure after activated sludge acclimation were analyzed. The effect of glucose addition on the secondary biochemical effluent of coking wastewater (SBECW) treatment by the acclimated sludge was further studied by a comparison between the performance of two parallel reactors seeded with the acclimated sludge. Our results showed that the concentrations of chemical oxygen demand (COD), total organic carbon (TOC), and UV absorption at 254 nm (UV254) of the wastewater decreased in the acclimation process. Refractory organic matter, such as polycyclic aromatic hydrocarbons and nitrogen-containing heterocyclics, in the SBECW was effectively degraded by the acclimated sludge. High-throughput sequencing revealed that microbes with a strong ability to degrade recalcitrant compounds were enriched after acclimation, such as Thauera (8.91%), Pseudomonas (3.35%), and Blastocatella (10.76%). Seeded with the acclimated sludge, the reactor with the glucose addition showed higher COD removal efficiencies than the control system without glucose addition (p &lt; 0.05). Collectively, glucose addition enhanced the advanced treatment of coking wastewater (CWW).

Long-term warming\xa0and nitrogen fertilization affect C-, N- and P-acquiring hydrolase and oxidase activities in winter wheat monocropping soil

The enzymatic activities and ratios are critical indicators for organic matter decomposition and provide potentially positive feedback to carbon (C) loss under global warming. For agricultural soils under climate change, the effect of long-term warming on the activities of oxidases and hydrolases targeting C, nitrogen (N) and phosphorus (P) and their ratios is unclear, as well as whether and to what extend the response is modulated by long-term fertilization. A 9-year field experiment in the North China Plain, including an untreated control, warming, N fertilization, and combined (WN) treatment plots, compared the factorial effect of warming and fertilization. Long-term warming interacted with fertilization to stimulate the highest activities of C, N, and P hydrolases. Activities of C and P hydrolase increased from 8 to 69% by N fertilization, 9 to 53% by warming, and 28 to 130% by WN treatment compared to control, whereas the activities of oxidase increased from 4 to 16% in the WN soils. Both the warming and the WN treatments significantly increased the enzymatic C:N ratio from 0.06 to 0.16 and the vector length from 0.04 to 0.12 compared to the control soil, indicating higher energy and resource limitation for the soil microorganisms. Compared to WN, the warming induced similar ratio of oxidase to C hydrolase, showing a comparable ability of different microbial communities to utilize lignin substrates. The relationship analyses showed mineralization of organic N to mediate the decomposition of lignin and enzyme ratio in the long-term warming soil, while N and P hydrolases cooperatively benefited to induce more oxidase productions in the soil subject to both warming and N fertilization. We conclude that coupled resource limitations induced microbial acclimation to long-term warming in the agricultural soils experiencing high N fertilizer inputs.

Rapid initiation of methanogenesis in the anaerobic digestion of food waste by acclimatizing sludge with sulfidated nanoscale zerovalent iron

Although coupling of sulfidated nanoscale zero-valent iron (S-nZVI) into anaerobic digestion of food waste (FW) for improving methanogenesis has been reported, the specific role of S-nZVI during start-up process and its influence on subsequent methanogenesis and system stability remains unknown. In this study, S-nZVI was added into the unacclimatized sludge system to investigate its influence on microbial acclimatization and methanogenic performance. During acclimatization phase, CH4 production improved and VFAs transformation facilitated with the addition of S-nZVI. Furthermore, enzymatic activity analysis and electrochemical measurements presented direct evidence that electron transfer capacity of acclimatized sludge was significantly improved. S-nZVI favored the transition of microbial community to a robust and specialized population. During evaluation phase, acclimatized sludge still exhibited strong methanogenic ability, but the microbial community inevitably changed under the stress of FW. This research provides a novel perspective on initiating anaerobic digestion of FW for shorter start-up time and stronger methanogenesis.

Biomethane potential test reveals microbial adaptation and increased methane yield during anaerobic co-digestion

The study explored anaerobic co-digestion of waste activated sludge (WAS) with food waste and fats, oils and grease (FOG) at 25%, 50% and 75% VS fractions using short-term biomethane potential (BMP) tests to assess if prior exposure of the inoculum to co-substrates induced microbial adaptation and enhanced methane yield. The study also assessed if the addition of co-substrates changed the microbial community structure. Mono-digestion of WAS produced the lowest methane yield of 74.9 ± 6.5 NmL CH4/gVS. Co-digestion of food waste and FOG significantly increased methane yield, with 75% FOG fraction yielding the highest methane of 878.2 ± 25.2 NmL CH4/gVS without microbial acclimation. Prior acclimation of the inoculum to co-substrates further enhanced methane production by up to 0.2-fold. The dominant microbial taxa remained constant irrespective of the different co-substrates. The bacterial community had a substantial abundance of syntrophic fatty acid oxidizers, while hydrogenotrophic methanogens, particularly Methanolinea, was the predominant methanogen.

System integration of hydrothermal liquefaction and anaerobic digestion for wet biomass valorization: Biodegradability and microbial syntrophy

Sewage sludge treatment & disposal pose environmental challenges in populated-dense urban environments. Due to its poor digestibility and dewaterability, sewage sludge contains high water content and concentrated nutrients (carbon, nitrogen, and phosphorus) even after conditioning and mechanical thickening. Regarding this, a pretreatment step and downstream anaerobic digestion (AD) are often required. To meet our societal goal towards a circular economy, system integration of hydrothermal pretreatment and AD now present an attractive approach for recovering resources from the wet sewage sludge biomass. In this study, such system integration together with struvite precipitation was applied for valorizing sewage sludge. Firstly, hydrothermal conditions of different temperatures (160 °C–230 °C) and duration (2 h–12 h) were compared to their performance of nutrients solubilization. Subsequently, the hydrothermal condition of 220°C-3 h was selected for further investigations of struvite recovery and bioenergy production. Through AD comparisons, the integrated process improved the ultimate biomethane yield by 38%. Interestingly, a lag phase occurred in the midst of the AD, which indicated the need for microbial acclimatization after the hydrothermal process. The long-term microbial monitoring revealed the efficient biomethane re-generation was closely related to the late enrichment of Syntrophus for potential H2-syntrophy. Therefore, on one hand, this study investigated an efficient and integrated approach of sewage sludge valorization. On other hand, it uncovered the microbial bottlenecks and potential biotechnological means for further system improvement. Further research about nutrients speciation in the integrated system would be desired.