Revolutionizing sanitation: Valorizing fecal slags through co-digesting food waste at high-solid content and dosing metallic nanomaterials for anaerobic digestion stability.

To achieve the UN Sustainable Development Goals (SDGs) and the China Toilet Revolution on a global scale, it is crucial to implement a decentralized sanitation management system in developing countries. Fecal slags (FS) generated from septic tanks of toilets pose a challenge for remote villages. This study sought to resourcefully utilize FS through co-digesting with food waste (FW) under high-solid anaerobic co-digestion (HSAD). Besides, two metallic nanomaterials, nano-zerovalent iron (nZVI) and magnetite (Fe3O4), were employed to demonstrate the practical improvement of HSAD. The results showed that nZVI-dosed digesters produced the highest cumulative methane of 295.72 mL/gVS, 371.36 mL/gVS, 360.53 mL/gVS and 296.64 mL/gVS in 10%, 15%, 20% and 25% TS content, respectively, which was 1.15, 1.22, 1.16, 1.12 times higher than Fe3O4 dosed digesters. This increment could be ascribed to the simultaneous production of H2 from Fe2+ release from nZVI and the enrichment of homoacetogen. Changes in carbon degradation and methanogenic pathways, which facilitated stability under high TS contents, were observed. At low solid digestion (10% TS), Syntrophomonas cooperated with Methanosarcina and Methanobacterium to metabolize butyrate and propionate. However, due to the buildup of total ammonia nitrogen and volatile fatty acids, acetoclastic methanogens were inhibited in the high-solid digesters (15%, 20% and 25% TS). Consequently, a more resilient and highly tolerant Syntrophaceticus, alongside hydrogenotrophic methanogens such as Methanoculleus and Methanobrevibacter, maintained stability in the harsh environment.

Sustainability insights into the synthesis of engineered nanomaterials - Problem formulation and considerations.

Engineered nanomaterials (ENMs) have been introduced into the market for a wide range of applications. As per the literature review, the fabrication of new generations of ENMs is starting to comply with environmental, economic, and social criteria in addition to technical aspects to meet sustainability criteria. At this stage, identification of the appropriate criteria for the synthesis of ENMs is critical because the technologies already developed at the lab scales are being currently transferred to pilot and full scales. Hence, the development of scientific-based methodologies to identify, screen, and prioritize the involved criteria is highly necessary. In the present manuscript, a fuzzy-Delphi methodology is adopted to identify the main criteria and sub-criteria encompassing the sustainable fabrication of ENMs, and to explore the "degree of consensus" among the experts on the relative importance of the mentioned criteria. The "health and safety risks" respecting the equipment and the materials, solvent used, and availability of "green experts" were identified as the most critical criteria. Furthermore, although all the criteria were identified as being important, some criteria, such as "solvent" and "raw materials cost", raised a lower degree of consensus, indicating that various "degrees of uncertainties" still exist regarding the level of importance of the studied criteria.

Life cycle assessment of municipal biowaste management - a Czech case study.

As part of coming targets to transition to a sustainable society and actively set a circular economy, one of the EU objectives is to decrease the amount of municipal solid waste and initiate the separation of its organic fraction, i.e., biowaste. Consequently, the question of how to best manage biowaste at the municipal level is of high importance, and previous research has shown the strong influence of local factors on the most sustainable treatment option. Life Cycle Assessment is a valuable tool for comparison of waste management impacts and was used to assess environmental impacts of the current biowaste management in Prague and give insight for improvements. Different scenarios were created regarding EU and Czech biowaste targets for separated collection. Results show the significant influence of the source of energy that is substituted. Consequently, in the current situation of an energy mix highly based on fossil fuels, incineration is the most sustainable option in most impact categories. However, community composting was found to have a better potential to reduce ecotoxicity and resource use of minerals and metals. Furthermore, it could supply a significant proportion of the minerals need of the region while increasing the autonomy of the Czech Republic regarding mineral fertilisers. To meet targets of EU directives for separated collection of biowaste, a combination of anaerobic digestion, to avoid use of fossil fuels, and composting, to increase circular economy, is most likely the best option. The outputs of this project would be of great significance for municipalities.

Role of carrier characteristics affecting microbial density and population in enhanced nitrogen and phosphorus removal from wastewater.

This research aims to improve simultaneous nitrification-denitrification and phosphorus removal (SNDPR) using novel carriers and to demonstrate the effect of carrier characteristics on nutrient removal in a biofilm reactor. For this purpose, biofilms enriched with both polyphosphate-accumulating organisms (PAOs) and nitrifiers were cultivated in two parallel sequencing batch reactors containing conventional moving bed bioreactor carriers (MBBR) and a novel type of carriers (carbon-based moving carriers (CBMC)). The new carriers were produced based on recycled waste materials via a chemical-thermal process and their specific surface area were 10.4 times higher than typical MBBR carriers of similar dimensions. The results showed that the use of CBMC carriers increased bacterial adhesion by about 18.5% and also affected the microbial population inside the biofilms, leading to an increase in PAOs abundancy and thus an increase in biological phosphorus removal up to 12.5%. Additionally, it was corroborated that the volume of the anoxic zones with dynamic behavior is strictly influenced by the carrier structure and biofilm thickness due to a limitation in oxygen penetration. Accordingly, the formation of broader anoxic zones and shrinkage of these zones to a lesser extent resulted in the continuation of anoxic reactions for longer periods using the novel carriers. Thereby, an increase in nitrogen removal by about 15% was obtained mainly by denitrifying PAOs. The results also exhibited that a higher simultaneous nitrification-denitrification (SND) efficiency can be achieved by selecting an appropriate aeration program influencing the dynamic changes of anoxic zones. Overall, a biofilm system using the new carriers, with phosphorus and nitrogen removal efficiencies of 97.5% and 92.3%, was presented as an efficient, compact, and simple operation SNDPR process.

Adsorption of acid fuchsine dye from wastewater by Mg-ferrite particles.

Adsorption is a widely applied waste water treatment technology, especially for removing micro-pollutants and dyes of industrial effluents. Over the past decade, adsorbing metal oxide micron- and nano-particles have been successfully developed and investigated as adsorbents. In the present research, Mg-ferrite adsorbent particles were synthesized and their properties were fully determined. The pore volume is 0.139 cm3/g. The BET analysis reveals a surface area of 94.4 m2/g. The porosity is of meso- and microporous nature. The adsorbent was used to adsorb acid fuchsine, an important industrial dye. The equilibrium adsorption capacity was 796.4 mg/g, with an adsorption yield of 78.7-82.0%. The adsorption kinetics can be adequately fitted by a pseudo-second-order model. The isotherms of both Langmuir and Freundlich are applicable. The stability, recovery and reuse of the ferrite particles were proven in multi-cycle experiments, and the adsorption activity decreased by less than 3% between the first and fifth cycle. Experimental and fitting results were finally used to design a batch adsorber to remove a given concentration of acid fuchsine from different volumes of wastewater.

Producing hydrogen by catalytic steam reforming of methanol using non-noble metal catalysts.

Current energy systems have a significant environmental impact and contribute to the climate change. The future energy systems must call upon clean and renewable sources, capable of producing energy with low CO2 emission, hence partly decarbonizing the energy sector. Producing H2 by catalytic steam reforming of methanol (CSRM) is gaining interest for its specific applications in fuel cells, in a decentralized H2 production, or to locally boost the heat content of e.g. natural gas. Supported metal catalysts enhance the endothermic steam-driven methanol conversion. The paper discusses the CSRM manufactures and assesses 2 novel, cheap and efficient catalysts (Co/α-Al2O3 and MnFe2O4). The performance of the Co/α-Al2O3 catalyst is significantly superior to MnFe2O4. The methanol conversion exceeds 95% with high H2 yields (>2.5 mol H2/mol CH3OH) and low CO and CO2 by-product formation. The methanol reaction is very fast and a nearly constant product distribution is achieved for gas-catalyst contact times in excess of 0.3 s. The catalyst maintains its efficiency and selectivity for several days of reaction. The hydrogen productivity of the Co/α-Al2O3 is about 0.9 L H2 gcat-1 h-1., nearly a fourfold of the MnFe2O4 alternative. The different occurring reactions are combined in a kinetics analysis and demonstrate the high rate of reaction and the predicted product distribution. A catalytic sintered metal fleece reactor is finally developed, mostly in view of its integration with a solid oxide fuel cell (SOFC). The assessed CSRM system clearly merits further pilot plant research.

Changes in the microbiota during biological treatment of palm oil mill waste: A critical review.

Palm oil mill waste has a complex cellulosic structure, is rich in nutrients, and provides a habitat for diverse microbial communities. Current research focuses on how the microbiota and organic components interact during the degradation of this type of waste. Some recent studies have described the microbial communities present in different biodegradation processes of palm oil mill waste, identifying the dominant bacteria/fungi responsible for breaking down the cellulosic components. However, understanding the degradation process's mechanisms is vital to eliminating the need for further pretreatment of lignocellulosic compounds in the waste mixture and facilitating the commercialization of palm oil mill waste treatment technology. Thus, the present work aims to review microbial community dynamics via three biological treatment systems comprehensively: composting, vermicomposting, and dark fermentation, to understand how inspiration from nature can further enhance existing degradation processes. The information presented could be used as an umbrella to current research on biological treatment processes and specific research on the bioaugmentation of indigenous microbial consortia isolated during the biological degradation of palm oil mill waste.

Indicators for resource recovery monitoring within the circular economy model implementation in the wastewater sector.

The European Union is currently in the process of transformation toward a circular economy model in which different areas of activity should be integrated for more efficient management of raw materials and waste. The wastewater sector has a great potential in this regard and therefore is an important element of the transformation process to the circular economy model. The targets of the circular economy policy framework such as resource recovery are tightly connected with the wastewater treatment processes and sewage sludge management. With this in view, the present study aims to review existing indicators on resource recovery that can enable efficient monitoring of the sustainable and circular solutions implemented in the wastewater sector. Within the reviewed indicators, most of them were focused on technological aspects of resource recovery processes such as nutrient removal efficiency, sewage sludge processing methods and environmental aspects as the pollutant share in the sewage sludge or its ashes. Moreover, other wide-scope indicators such as the wastewater service coverage or the production of bio-based fertilizers and hydrochar within the wastewater sector were analyzed. The results were used for the development of recommendations for improving the resources recovery monitoring framework in the wastewater sector and a proposal of a circularity indicator for a wastewater treatment plant highlighting new challenges for further researches and wastewater professionals.

ZnO/γ-Fe2O3/Bentonite: An Efficient Solar-Light Active Magnetic Photocatalyst for the Degradation of Pharmaceutical Active Compounds.

For applications related to the photocatalytic degradation of environmental contaminants, engineered nanomaterials (ENMs) must demonstrate not only a high photocatalytic potential, but also a low tendency to agglomeration, along with the ability to be easily collected after use. In this manuscript, a two-step process was implemented for the synthesis of ZnO, ZnO/Bentonite and the magnetic ZnO/γ-Fe2O3/Bentonite nanocomposite. The synthesized materials were characterized using various techniques, and their performance in the degradation of pharmaceutical active compounds (PhACs), including ciprofloxacin (CIP), sulfamethoxazole (SMX), and carbamazepine (CBZ) was evaluated under various operating conditions, namely the type and dosage of the applied materials, pH, concentration of pollutants, and their appearance form in the medium (i.e., as a single pollutant or as a mixture of PhACs). Among the materials studied, ZnO/Bentonite presented the best performance and resulted in the removal of ~95% of CIP (5 mg/L) in 30 min, at room temperature, near-neutral pH (6.5), ZnO/Bentonite dosage of 0.5 g/L, and under solar light irradiation. The composite also showed a high degree of efficiency for the simultaneous removal of CIP (~98%, 5 mg/L) and SMX (~97%, 5 mg/L) within 30 min, while a low degradation of ~5% was observed for CBZ (5 mg/L) in a mixture of the three PhACs. Furthermore, mechanistic studies using different types of scavengers revealed the formation of active oxidative species responsible for the degradation of CIP in the photocatalytic system studied with the contribution of h+ (67%), OH (18%), and ·O2- (10%), and in which holes (h+) were found to be the dominant oxidative species.

Reviewing the thermo-chemical recycling of waste polyurethane foam.

The worldwide production of polymeric foam materials is growing due to their advantageous properties of light weight, high thermal insulation, good strength, resistance and rigidity. Society creates ever increasing amounts of poly-urethane (PU) waste. A major part of this waste can be recycled or recovered in order to be put into further use. The PU industry is committed to assist and play its part in the process. The recycling and recovery of PU foam cover a range of mechanical, physical, chemical and thermo-chemical processes. In addition to the well-documented mechanical and chemical processing options, thermo-chemical treatments are important either as ultimate disposal (incineration) or towards feedstock recovery, leading to different products according to the thermal conditions of the treatment. The review focuses on these thermo-chemical and thermal processes. As far as pyrolysis is concerned, TDI and mostly polyol can be recovered. The highest recovery yields of TDI and polyols occur at low temperatures (150-200 °C). It is however clear from literature that pure feedstock will not be produced, and that a further upgrading of the condensate will be needed, together with a thermal or alternative treatment of the non-condensables. Gasification towards syngas has been studied on a larger and industrial scale. Its application would need the location of the PU treatment plant close to a chemical plant, if the syngas is to be valorized or considered in conjunction with a gas-fired CHP plant. Incineration has been studied mostly in a co-firing scheme. Potentially toxic emissions from PU combustion can be catered for by the common flue gas cleaning behind the incineration itself, making this solution less evident as a stand-alone option: the combination with other wastes (such as municipal solid waste) in MSWI's seems the indicated route to go.

Pilot-scale evaluation of ozone as a polishing step for the removal of nonylphenol from tank truck cleaning wastewater.

The presence of nonylphenol (NP) in the wastewater of the tank truck cleaning industry is a major concern because of its endocrine disruptive properties. In this paper, the use of ozone for degrading NP from tank truck cleaning wastewater was investigated by operating a pilot-scale biological wastewater treatment in combination with an ozonation unit. The impact of the added ozonation step on the removal of NP, soluble chemical oxygen demand (sCOD) and total organic carbon (TOC) was monitored over one year. sCOD and TOC removal were not significantly enhanced, but the NP peak concentrations in the effluent were significantly lower than those obtained after biological treatment only: a relatively low NP concentration was observed, even when peak loads were present in the influent of the pilot-scale biological wastewater treatment plant (influentbio). Contrariwise, the effluent of the sole biological treatment follows the peak load trends of the influentbio. During the ozonation period, the average NP concentration in the combined biological-ozone unit was 0.29 µg/L, compared to 1.89 µg/L for the effluent obtained after a sole biological treatment, resulting in an improved average removal efficiency of 32%.

Prospects and perspectives foster enhanced research on bio-aviation fuels.

Bio-aviation fuels are a major research and development topic, with strong interests from the aviation sector, the public, lawmakers and potential producers. Yet the development and market penetration in the air-transportation sector is slow, despite proven environmental benefits. Bio-fuels can indeed mitigate the environmental impact of the aviation sector mostly due to their low carbon intensity and favourable chemical structure. Such bio-aviation fuels must have "drop-in" characteristics with specifications and compatibility with the combustion behaviour of kerosene. The ASTM approval procedures are an important guarantee in this respect. Additional emission reductions rely on the production pathways, while optimum flight-related strategies are an additional benefit. An analysis of both the production pathways, and the environmental and Life Cycle Assessment findings delineates important research directions to enhance the production and use of bio-aviation fuels. Towards specific environmental issues, target research topics should include various topics. A better quantification of particulate and soot emissions, condensation contrails and NOx are of primary concern. The impact of geographic parameters on the bio-aviation fuel benefits should be investigated towards using bio-aviation fuels primarily in specific climate zones. Emission prediction models should be further developed. LCA approaches should be extended. More on-flight emission patterns should be measured to provide relevant data for the above considerations; Towards bio-aviation fuel characterization, safety and reliability are major criteria of the ASTM approval. Towards production pathways, the technical viability studies of synthesis pathways should be combined with economic assessments. Towards fuel costs, the reason for the high production cost of bio-aviation fuel is at least partly due to the oxygen-rich bio-polymer nature of biomass with unsuitable carbon chain length. In order to reduce the cost of bio-aviation fuel, several research directions are encouraged and discussed in the paper.

Combining microwave irradiation with sodium citrate addition improves the pre-treatment on anaerobic digestion of excess sewage sludge.

This study investigated the synergistic effect of sodium citrate (SC; Na3C3H5O(COO)3) and microwave (MW) treatment on the efficiency of the anaerobic digestion of excess sewage sludge. In terms of the methane yield, an increase of the digestion's efficiency was observed. Taking into account the cost for the MW energy supplied to the system, the optimum treatment conditions were a MW energy input of 20 MJ/kg TS and a SC concentration of 0.11 g/g TS, obtaining a methane yield of 218.88 ml/g VS, i.e., an increase of 147.7% compared to the control. MW treatment was found to break the sludge structure, thereby improving the release of extracellular polymeric substances (EPS) and volatile fatty acids (VFAs). The treatment of sodium citrate further strengthened the breakage of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound extracellular polymeric substances (TB-EPS). The increased VFA content stressed the improved digestion by this pretreatment. Furthermore, the preliminary economic analysis showed that at this point in the research, only operational but no financial gains were achieved.

Optimization of hydrothermal conversion of bamboo (Phyllostachys aureosulcata) to levulinic acid via response surface methodology.

In this study, the dilute acid hydrolysis of lignocellulosic bamboo (Phyllostachys aureosulcata) particles to levulinic acid in a hydrothermal synthesis reactor is reported. The aim of the study was to optimize the reaction conditions for maximum levulinic acid production in terms of reaction time (t), reaction temperature (T) and HCl concentration (cHCl) via Response Surface Methodology (RSM). A maximum levulinic acid yield of 9.46 w% was predicted at the following reaction conditions: t of 3 h, T of 160 °C and cHCl of 0.37 M. A maximal experimental yield of levulinic acid of 10.13 w% was observed, which in respect to the cellulose fraction of the bamboo particles corresponds to 34.60 w% or 48.05 mol%. Furfural, which is formed by the hemicellulose fraction of bamboo, has not been observed within the boundaries of the RSM model, since it is already degraded under the given reaction conditions. The conversion of levulinic acid and furfural occurred more or less simultaneously, however, furfural was more vulnerable to degradation reactions at the given process conditions. Therefore, if both fractions (cellulose + hemicellulose) are required to be valorized, further optimization is required. However, the global results of this study provide insight in the potential of lignocellulosic bamboo as an alternative platform to fossil sources.

Evaluation of the effects of low energetic microwave irradiation on anaerobic digestion.

The present study investigates the effects of microwave irradiation on the performance of anaerobic digestion processes. A first set of experiments is performed to distinguish the upper limit of the applied energy levels. Secondly, the effects of these treatments on the performance of the digestion process are evaluated in 3 experimental setups: (i) monitoring the acetic acid degradation, (ii) performing a biological methane potential (BMP) assay and (iii) conducting a specific methanogenic activity (SMA) test. The solubilisation experiment reveals a limited degree of disintegration of anaerobic biomass up to a microwave treatment of 10000 kJ/kg TS. Above this threshold value the soluble COD level started to rise, with up to 350% at 30000 kJ/kg TS regardless of the microwave output power. Because solubilisation of the biomass increases the easily degradable content, this would lead to false observations regarding increased activity. Therefore, solubilisation is minimized by limiting the microwave treatment to a maximum of 6000 kJ/kg TS during the second part of the experiments. Monitoring the degradation of acetic acid after a low intensity microwave treatment, reveals that microwave irradiation shortens the lag phase, e.g., from 21 to 3 h after a microwave treatment of 1000 kJ/kg TS at 100 W. However most treatments also result in a decrease of the maximum degradation and of the degradation rate of acetic acid. BMP assays are performed to evaluate the activity and performance of the entire anaerobic community. Every treatment results in a decreased biogas production potential and decreased biogas production rate. Moreover, each treatment induced an increase of the lag phase. The SMA experiments show no influence of the microwave irradiation in terms of biogas or methane production.

Selective electrochemical degradation of 4-chlorophenol at a Ti/RuO2-IrO2 anode in chloride rich wastewater.

The electrochemical degradation of 4-chlorophenol (4-CP) in the presence of chlorides by the use of a Ti/RuO2-IrO2 anode was investigated under different operational parameters such as applied current density (J) and chloride concentration ([NaCl]). By performing a design of experiments, a model for the removal of 4-chlorophenol under these circumstances was obtained. To investigate matrix effects for this oxidation process, the influence of various biodegradable substrates (such as glucose, a complex synthetic wastewater and a pilot-scale UASB effluent) on the degradation profile of 4-chlorophenol was investigated. The 4-CP degradation was hardly affected by the presence of glucose, which was itself only limitedly degraded (max. 5%). This indicates a selective degradation for the phenolic compound, independent of the values of the operational parameters. The presence of a more complex synthetic wastewater, however, resulted in a decrease in 4-CP degradation rate up to a factor 7. The biodegradable substrates are in this case also degraded by the electrochemical treatment. In the case where 4-CP was added to a pilot-scale UASB effluent and this wastewater was afterwards treated, the degradation rate of 4-CP only decreased by a factor 2. After 2 h of treatment, a full mineralization was obtained in this experiment. The latter observation suggests the suitability of the technique as an effluent polishing step after a biological treatment or as a treatment in recycle over a biological reactor.

Microwave and ultrasound pre-treatments influence microbial community structure and digester performance in anaerobic digestion of waste activated sludge.

Comparative analyses of bacterial and archaeal community structures and dynamics in three biogas digesters during start-up and subsequent operation using microwaved, ultrasonicated or untreated waste activated sludge were performed based on 454 pyrosequencing datasets of part of 16S ribosomal RNA sequences and quantitative PCR. The pre-treatment increased the solubility, and thus the availability of the substrate for microbial degradation and significantly affected the succession of the anaerobic community structure over the course of the digestion. Bacteroidetes, Proteobacteria and Firmicutes were the dominant phyla in all digesters throughout operation. Proteobacteria decreased in relative abundance from 23-26 % to 11-13 % in association with enhanced substrate availability. Negative correlations between relative abundance of Alpha-, Beta- and Gammaproteobacteria and the substrate availability and/or biogas production were disclosed in statistical analyses. Clostridiales was the dominant order in Firmicutes, and Clostridiales, Clostridia and Firmicutes relative abundance and richness were shown to positively correlate with substrate availability and biogas generation. Methanogenic communities had a fairly restricted structure, highly dominated by Methanosaeta and Methanobrevibacter phylotypes. A gradual decline in Methanobrevibacter and increased representation of Methanosaeta concilii over time were particularly apparent in the digester receiving untreated waste activated sludge, whereas more diversified archaeal communities were maintained in the pre-treatment digesters. The quantitative PCR analyses revealed a methanogenic community distribution that coincided with the 454 pyrosequencing data.

Bioethanol from lignocellulosic biomass: current findings determine research priorities.

"Second generation" bioethanol, with lignocellulose material as feedstock, is a promising alternative for first generation bioethanol. This paper provides an overview of the current status and reveals the bottlenecks that hamper its implementation. The current literature specifies a conversion of biomass to bioethanol of 30 to ~50% only. Novel processes increase the conversion yield to about 92% of the theoretical yield. New combined processes reduce both the number of operational steps and the production of inhibitors. Recent advances in genetically engineered microorganisms are promising for higher alcohol tolerance and conversion efficiency. By combining advanced systems and by intensive additional research to eliminate current bottlenecks, second generation bioethanol could surpass the traditional first generation processes.

A review on co-metabolic degradation of organic micropollutants during anaerobic digestion: Linkages between functional groups and digestion stages.

The emerging presence of organic micropollutants (OMPs) in water bodies produced by human activities is a source of growing concern due to their environmental and health issues. Biodegradation is a widely employed treatment method for OMPs in wastewater owing to its high efficiency and low operational cost. Compared to aerobic degradation, anaerobic degradation has numerous advantages, including energy efficiency and superior performance for certain recalcitrant compounds. Nonetheless, the low influent concentrations of OMPs in wastewater treatment plants (WWTPs) and their toxicity make it difficult to support the growth of microorganisms. Therefore, co-metabolism is a promising mechanism for OMP biodegradation in which co-substrates are added as carbon and energy sources and stimulate increased metabolic activity. Functional microorganisms and enzymes exhibit significant variations at each stage of anaerobic digestion affecting the environment for the degradation of OMPs with different structural properties, as these factors substantially influence OMPs' biodegradability and transformation pathways. However, there is a paucity of literature reviews that explicate the correlations between OMPs' chemical structure and specific metabolic conditions. This study provides a comprehensive review of the co-metabolic processes which are favored by each stage of anaerobic digestion and attempts to link various functional groups to their favorable degradation pathways. Furthermore, potential co-metabolic processes and strategies that can enhance co-digestion are also identified, providing directions for future research.

Mild alkaline conditions affect digester performance and community dynamics during long-term exposure.

This paper examines the adaptive responses of microbial communities to gradual shifts in pH toward the mild alkaline range in anaerobic digestion (AD) systems. The results indicate that a pH of 8.0 serves as a critical upper limit for stable AD operation, beyond which microbial efficiency declines, underscoring the importance of microbial resilience against elevated pH stress. Specifically, hydrolysis genera, e.g. Eubacterium and Anaerobacterium, and syntrophic bacteria were crucial for reactor stability. Fibrobacter had also been shown to play a key role in the accumulation of propionate, thus leading to its dominance in the volatile fatty acid profile throughout the experimental phases. Overall, this investigation revealed the potential adaptability of microbial communities in AD systems to mild alkaline pH shifts, emphasizing the hydrolysis bacteria and syntrophic bacteria as key factors for maintaining metabolic function in elevated pH conditions.