Hormesis-Like Effects of Tetrabromobisphenol A on Anaerobic Digestion: Responses of Metabolic Activity and Microbial Community

The Impact of Bisphenol A on the Anaerobic Sulfur Transformation: Promoting Sulfur Flow and Toxic H2S Production

Bisphenol A (BPA), as a typical leachable additive from microplastics and one of the most productive bulk chemicals, is widely distributed in sediments, sewers, and wastewater treatment plants, where active sulfur cycling takes place. However, the effect of BPA on sulfur transformation, particularly toxic H2S production, has been previously overlooked. This work found that BPA at environmentally relevant levels (i.e., 50-200 mg/kg total suspended solids, TSS) promoted the release of soluble sulfur compounds and increased H2S gas production by 14.3-31.9%. The tryptophan-like proteins of microbe extracellular polymeric substances (EPSs) can spontaneously adsorb BPA, which is an enthalpy-driven reaction (ΔH = -513.5 kJ mol-1, ΔS = -1.60 kJ mol-1K -1, and ΔG = -19.52 kJ mol-1 at 35 °C). This binding changed the composition and structure of EPSs, which improved the direct electron transfer capacity of EPSs, thereby promoting the bioprocesses of organic sulfur hydrolysis and sulfate reduction. In addition, BPA presence enriched the functional microbes (e.g., Desulfovibrio and Desulfuromonas) responsible for organic sulfur mineralization and inorganic sulfate reduction and increased the abundance of related genes involved in ATP-binding cassette transporters and sulfur metabolism (e.g., Sat and AspB), which promoted anaerobic sulfur transformation. This work deepens our understanding of the interaction between BPA and sulfur transformation occurring in anaerobic environments.

Surfactant-mediated bio-manufacture: A unique strategy for promoting microbial biochemicals production

Biochemicals are widely used in the medicine and food industries and are more efficient and safer than synthetic chemicals. The amphipathic surfactants can interact with the microorganisms and embed the extracellular metabolites, which induce microbial metabolites secretion and biosynthesis, performing an attractive prospect of promoting the biochemical production. However, the commonness and differences of surfactant-mediated bio-manufacture in various fields are largely unexplored. Accordingly, this review comprehensively summarized the properties of surfactants, different application scenarios of surfactant-meditated bio-manufacture, and the mechanism of surfactants increasing metabolites production. Various biochemical productions such as pigments, amino acids, and alcohols could be enhanced using the cloud point and the micelles of surfactants. Besides, the amphiphilicity of surfactants also promoted the utilization of fermentation substrates, especially lignocellulose and waste sludge, by microorganisms, indirectly increasing the metabolites production. The increase in target metabolites production was attributed to the surfactants changing the permeability and composition of the cell membrane, hence improving the secretion ability of microorganisms. Moreover, surfactants could regulate the energy metabolism, the redox state and metabolic flow in microorganisms, which induced target metabolites synthesis. This review aimed to broaden the application fields of surfactants and provide novel insights into the production of microbial biochemicals.

Deciphering the core bacterial community structure and function and their response to environmental factors in activated sludge from pharmaceutical wastewater treatment plants

Pharmaceutical wastewater is recognized for its heightened concentrations of organic pollutants, and biological treatment stands out as an effective technology to remove these organic pollution. Therefore, a comprehensive exploration of core bacterial community compositions, functions, and their responses to environmental factors in pharmaceutical wastewater treatment plants (PWWTPs) is important for understanding the removal mechanism of these organic pollutants. This study comprehensively investigated 36 activated sludge (AS) samples from 15 PWWTPs in China. The results revealed that Proteobacteria (45.41%) was the dominant phylum in AS samples, followed by Bacteroidetes (19.54%) and Chloroflexi (4.13%). While the dominant genera were similar in both aerobic and anaerobic treatment processes, their relative abundances exhibited significant variations. Genera like HA73, Kosmotoga, and Desulfovibrio were more abundant during anaerobic treatment, while Rhodoplanes, Bdellovibrio, and Hyphomicrobium dominated during aerobic treatment. 13 and 10 core operational taxonomic units (OTUs) were identified in aerobic and anaerobic sludge, respectively. Further analysis revealed that core OTUs belonging to genera Kosmotoga, Desulfovibrio, Thauera, Hyphomicrobium, and Chelativorans, were associated with key functions, including sulfur metabolism, methane metabolism, amino acid metabolism, carbohydrate metabolism, toluene degradation, and nitrogen metabolism. Furthermore, this study highlighted the crucial roles of environmental factors, such as COD, NH4+-N, SO42-, and TP, in shaping both the structure and core functions of bacterial communities within AS of PWWTPs. Notably, these factors indirectly affect functional attributes by modulating the bacterial community composition and structure in pharmaceutical wastewater. These findings provide valuable insights for optimizing the efficiency of biochemical treatment processes in PWWTPs.

In-situ methane enrichment in anaerobic digestion of food waste slurry by nano zero-valent iron: Long-term performance and microbial community succession

In this work, nano zero-valent iron (nZVI) was added to a lab-scale continuous stirring tank reactor (CSTR) for food waste slurry treatment, and the effect of dosing rate and dosage of nZVI were attempted to be changed. The results showed that anaerobic digestion (AD) efficiency and biomethanation stability were optimum under the daily dosing and dosage of 0.48 g/gTCOD. The average daily methane (CH4) yield reached 495.38 mL/gTCOD, which was 43.65% higher than that at control stage, and the maximum CH4 content reached 95%. However, under single dosing rate conditions, high nZVI concentrations caused microbial cell rupture and loosely bound extracellular polymeric substances (LB-EPS) precipitation degradation. The daily dosing rate promoted the hydrogenotrophic methanogenesis pathway, and the activity of coenzyme F420 increased by 400.29%. The microbial analysis indicated that daily addition of nZVI could promote the growth of acid-producing bacteria (Firmicutes and Bacteroidetes) and methanogens (Methanothrix).

A comprehensive review on the preparation of biochar from digestate sources and its application in environmental pollution remediation

The preparation of biochar from digestate is one of the effective ways to achieve the safe disposal and resource utilization of digestate. Nevertheless, up to now, a comprehensive review encompassing the factors influencing anaerobic digestate-derived biochar production and its applications is scarce in the literature. Therefore, to fill this gap, the present work first outlined the research hotspots of digestate in the last decade using bibliometric statistical analysis with the help of VOSviewer. Then, the characteristics of the different sources of digestate were summarized. Furthermore, the influencing factors of biochar preparation from digestate and the modification methods of digestate-derived biochar and associated mechanisms were analyzed. Notably, a comprehensive synthesis of anaerobic digestate-derived biochar applications is provided, encompassing enhanced anaerobic digestion, heavy metal remediation, aerobic composting, antibiotic/antibiotic resistance gene removal, and phosphorus recovery from digestate liquor. The economic and environmental impacts of digestate-derived biochar were also analyzed. Finally, the development prospect and challenges of using biochar from digestate to combat environmental pollution are foreseen. The aim is to not only address digestate management challenges at the source but also offer a novel path for the resourceful utilization of digestate.

Benzethonium chloride affects short chain fatty acids produced from anaerobic fermentation of waste activated sludge: Performance, biodegradation and mechanisms

Benzethonium chloride (BZC) is viewed as a promising disinfectant and widely applied in daily life. While studies related to its effect on waste activated sludge (WAS) anaerobic fermentation (AF) were seldom mentioned before. To understand how BZC affects AF of WAS, production of short chain fatty acids (SCFAs), characteristics of WAS as well as microbial community were evaluated during AF. Results manifested a dose-specific relationship of dosages between BZC and SCFAs and the optimum yield arrived at 2441.01 mg COD/L with the addition of 0.030 g/g TSS BZC. Spectral results and protein secondary structure variation indicated that BZC denatured proteins in the solid phase into smaller proteins or amino acids with unstable structures. It was also found that BZC could stimulate the extracellular polymeric substances secretion and reduce the surface tension of WAS, leading to the enhancement of solubilization. Beside, BZC promoted the hydrolysis stage (increased by 7.09 % to 0.030 g/g TSS BZC), but inhibited acetogenesis and methanogenesis stages (decreased by 6.85 % and 14.75 % to 0.030 g/g TSS BZC). The microbial community was also regulated by BZC to facilitate the enrichment of hydrolytic and acidizing microorganisms (i.e. Firmicutes). All these variations caused by BZC were conducive to the accumulation of SCFAs. The findings contributed to investigating the effect of BZC on AF of WAS and provided a new idea for the future study of AF mechanism.

Effects of Mixtures of Engineered Nanoparticles and Cocontaminants on Anaerobic Digestion

The widespread application of nanotechnology inevitably leads to an increased release of engineered nanoparticles (ENPs) into the environment. Due to their specific physicochemical properties, ENPs may interact with other contaminants and exert combined effects on the microbial community and metabolism of anaerobic digestion (AD), an important process for organic waste reduction, stabilization, and bioenergy recovery. However, the complicated interactions between ENPs and other contaminants as well as their combined effects on AD are often overlooked. This review therefore focuses on the co-occurrence of ENPs and cocontaminants in the AD process. The key interactions between ENPs and cocontaminants and their combined influences on AD are summarized from the available literature, including the critical mechanisms and influencing factors. Some sulfides, coagulants, and chelating agents have a dramatic "detoxification" effect on the inhibition effect of ENPs on AD. However, some antibiotics and surfactants increase the inhibition of ENPs on AD. The reasons for these differences may be related to the interactive effects between ENPs and cocontaminants, changes of key enzyme activities, adenosine triphosphate (ATP) levels, reactive oxygen species (ROS) production, and microbial communities. New scientific opportunities for a better understanding of the coexistence in real world situations are converging on the scale of nanoparticles.

Distinct effects of chemical- and bio- flocculants on the sludge acidogenic fermentation for volatile fatty acids production by affecting the acidogenic steps, microbial community structure and metabolic functions

Flocculants play crucial roles in sludge treatment, while the specific impact of chemical and bio-flocculants on sludge anaerobic fermentation was unknown. This study unveiled the contrasting effects of chitosan (CTS) and poly‑aluminum chloride (PAC) on volatile fatty acids (VFAs) generation during sludge fermentation. CTS supplementation resulted in 17.2 % increase in VFAs production, while PAC exposure led to 7.6 % reduction compared to the control. Further investigation revealed that CTS facilitated sludge solubilization and hydrolysis, thus providing sufficient organic substrates for VFAs generation. Additionally, environmental-friendly CTS exposure positively influenced the abundance and activity of functional anaerobes, as well as the expression of genes associated with VFAs biosynthesis. In contrast, PAC exposure resulted in the formation of larger sludge flocs, which hindered WAS solubilization and hydrolysis. Meanwhile, its potential microbial toxicity also impeded the microbial metabolic activity (i.e., genetic expressions), resulting in unsatisfactory VFAs production.

Percarbonate-strengthened ferrate pretreatment for enhancing short-chain fatty acids production from sewage sludge

Sewage sludge management poses a pressing environmental challenge, demanding the implementation of sustainable solutions to facilitate resource recovery. Short-chain fatty acids (SCFAs) serve as valuable chemicals and renewable energy sources, underscoring the importance of maximizing their production to achieve sustainable waste management. Therefore, this study proposes a novel and green strategy, i.e., percarbonate-strengthened ferrate pretreatment to enhance SCFAs synthesis from sewage sludge, because percarbonate could activate ferrate oxidation through providing (bi) carbonate and hydrogen peroxide. Results show that percarbonate largely reduces the required ferrate dosage for fermentation improvement, and their combination exhibits obvious synergistic effects on SCFAs accumulation and sludge reduction. Under the optimal pretreatment conditions, SCFAs production is promoted to 3670.2 mg COD/L, representing a remarkable increase of 5512.4 %, 156.0 % or 395.1 % compared to the control, percarbonate alone or ferrate alone, respectively. Mechanism explorations demonstrate that percarbonate-strengthened ferrate pretreatment significantly enhances sludge solubilization, elevates substrate biodegradability, and alters the physiochemical properties of sludge to favor organics fermentation. The synergistic effects on solid organics release and sludge properties can be attributed to the combined mechanisms of enhanced oxidation and alkaline hydrolysis. Further investigations on metabolic pathways reveal that the combination substantially improves key enzyme activities associated with hydrolysis and SCFAs formation, while severely inhibits that of SCFAs consumption. These findings are further supported by the functional genes coding relevant enzymes. Moreover, the combination alters microbial structures and compositions, leading to the screening and enrichment of key microbes that facilitate SCFAs accumulation. This innovative strategy holds significant promise in advancing sewage sludge management towards a more circular and resource-efficient paradigm.

Advances in responses of microalgal-bacterial symbiosis to emerging pollutants in wastewater

Nowadays, emerging pollutants are widely used and exist in wastewater, such as antibiotics, heavy metals, nanoparticle and microplastic. As a green alternative for wastewater treatment, microalgal-bacterial symbiosis has been aware of owning multiple merits of low energy consumption and little greenhouse gas emission. Thus, the responses of microalgal-bacterial symbiosis to emerging pollutants in wastewater treatment have become a hotspot in recent years. In this review paper, the removal performance of microalgal-bacterial symbiosis on organics, nitrogen and phosphorus in wastewater containing emerging pollutants has been summarized. The adaptation mechanisms of microalgal-bacterial symbiosis to emerging pollutants have been analyzed. It is found that antibiotics usually have hormesis effects on microalgal-bacterial symbiosis, and that microalgal-bacterial symbiosis appears to show more capacity to remove tetracycline and sulfamethoxazole, rather than oxytetracycline and enrofloxacin. Generally, microalgal-bacterial symbiosis can adapt to heavy metals at a concentration of less than 1 mg/L, but its capabilities to remove contaminants can be significantly affected at 10 mg/L heavy metals. Further research should focus on the influence of mixed emerging pollutants on microalgal-bacterial symbiosis, and the feasibility of using selected emerging pollutants (e.g., antibiotics) as a carbon source for microalgal-bacterial symbiosis should also be explored. This review is expected to deepen our understandings on emerging pollutants removal from wastewater by microalgal-bacterial symbiosis.

Deciphering the role of polystyrene microplastics in waste activated sludge anaerobic digestion: Changes of organics transformation, microbial community and metabolic pathway

Microplastics are ubiquitous in the natural environment, which inevitably affect the relevant biochemical process. Nevertheless, the knowledge about the impacts of microplastics on organics transformation and corresponding microbial metabolism response in anaerobic environment is limited. Here, polystyrene (PS) microplastics were selected as model microplastics to explore their potential impacts on organics transformation, microbial community and metabolic pathway during sludge anaerobic digestion system operation. The results indicated that the PS microplastics exhibited the dose-dependent effects on methane production, i.e., the additive of 20-40 particles/g TS of PS microplastics improved the maximum methane yield by 3.38 %-8.22 %, whereas 80-160 particles/g TS additive led to a 4.78 %-11.04 % declining. Overall, PS microplastics facilitated the solubilization and hydrolysis of sludge, but inhibited the acidogenesis process. Key functional enzyme activities were stimulated under low PS microplastics exposure, whereas were almost severely inhibited due to the increased oxidative stress induced from excess PS microplastics. Microbial community and further metabolic analysis indicated that low PS microplastics improved the acetotrophic and hydrogenotrophic methanogenesis, while a high level of PS microplastics shifted methanogenesis from acetotrophic to hydrogenotrophic pathway. Further analysis showed that the reacted PS microplastics exhibited greater toxicity and ecological than the raw PS microplastics due to that they are more likely to adsorb contaminants. These findings revealed the dosage-dependent relationships between microplastics and organics transformation process in anaerobic environments, providing new insights for assessing the impact of PS microplastics on sludge anaerobic digestion.

Endogenous biopolymer hydrolysis for enhancing short-chain fatty acids recovery from excess sludge: Combination of lysozyme-catalyzing and cation exchange resin-mediated metal regulation

In decades, anaerobic fermentation with short-chain fatty acids (SCFAs) recovery from excess sludge have attained rising attention. However, rigid particulate organic matter (POMs) structure with slow hydrolysis limited anaerobic fermentation performance of excess sludge. Remarkable sludge hydrolysis performance was supposed to be achievable by the synchronous EPS repture and microbial cell lysis. This study clarified the improvement of overall anaerobic fermentation performance by combination treatment of lysozyme (Lyso) catalysis and metal regulation (MR). The Lyso + MR treatment triggered EPS rupture by protein structure deflocculation while catalyzing microbial cell lysis, which promoted massive extracellular and intracellular POMs hydrolysis. As a result, a significant amount of SCOD (5646.67 mg/L) was produced. Such endogenous organic matters hydrolysis led to considerable SCFAs accumulation (3651.14 mg COD/L) through 48-h anaerobic fermentation at 1.75 g/g SS cation-exchange resin and Lyso dosage of 10% (w/w), which was 5.945 times higher than that in the control. Additionally, it suggested that most of the recovered SCFAs remained in fermentative liquid after chemical conditioning and mechanical dewatering towards solid-liquid separation, which provided considerable economic benefit of 363.6-1059.1 CNY/ton SS.

Impact of sertraline on biohydrogen production from alkaline anaerobic fermentation of waste activated sludge: Focusing on microbial community and metabolism

Nowadays, antidepressants are massively consumed worldwide, inevitably bringing about the concern for their latent hazard to the natural environment. This research focused on exploring the effect of sertraline (SET, a typical antidepressant) on hydrogen yields from alkaline anaerobic fermentation of waste activated sludge (WAS). The hydrogen accumulation reached the peak of 14.73 mL/g VSS (volatile suspended solids) at a SET dosage of 50 mg/kg TSS (total suspended solids), i.e., 1.90 times of that in the control fermenter. The data of Illumina high-throughput sequencing demonstrated that SET promoted the expression of genes regulating the membrane transport. Microbial community analysis suggested that some species that could degrade refractory substances were enriched after SET exposure. Finally, metabolic pathways of hydrogen production and consumption were found to be significantly affected with SET addition. This study would deepen the concept of typical antidepressants influencing energy recovery from WAS.

Atomic hydrogen-mediated enhanced electrocatalytic hydrodehalogenation on Pd@MXene electrodes

In this study, a Pd@MXene catalyst was synthesized to enhance the electrocatalytic hydrodehalogenation (ECH) of emerging halogenated organic pollutants (HOPs) by improving the dispersibility, catalytic activity, and stability of palladium (Pd). The average size of Pd nanoparticles (NPs) was reduced to 3.62 ± 0.34 nm with a more intensive peak of Pd (111), which facilitated atomic hydrogen (H*) production. The Pd@MX/CC electrode demonstrated superior ECH activity for diclofenac (DCF) degradation, with a reaction rate constant (kobs) 2.48 times higher than that of Pd/CC (without MXene). The satisfactory ECH performance of Pd@MX/CC remained consistent within a wide range of initial DCF concentrations (5-100 mg/L), and no significant ECH attenuation was observed even after up to 10 batches. Furthermore, the high activity of Pd@MX/CC was also observed in the ECH of other halogenated organic pollutants (levofloxacin, tetrabromobisphenol A, and diatrizoate). Density functional theory (DFT) calculations revealed that electronic configuration modulation of the Pd@MXene catalyst optimized binging energies to H* , DCF, and dechlorinated products, thereby enhancing the ECH efficiency of DCF.

A review of application of combined biochar and iron-based materials in anaerobic digestion for enhancing biogas productivity: Mechanisms, approaches and performance

Strengthening direct interspecies electron transfer (DIET), via adding conductive materials, is regarded as an effective way for improving methane productivity of anaerobic digestion (AD). Therein, the supplementation of combined materials (composition of biochar and iron-based materials) has attracted increasing attention in recent years, because of their advantages of promoting organics reduction and accelerating biomass activity. However, as far as we known, there is no study comprehensively summarizing the application of this kind combined materials. Here, the combined methods of biochar and iron-based materials in AD system were introduced, and then the overall performance, potential mechanisms, and microbial contribution were summarized. Furthermore, a comparation of the combinated materials and single material (biochar, zero valent iron, or magnetite) in methane production was also evaluated to highlight the functions of combined materials. Based on these, the challenges and perspectives were proposed to point the development direction of combined materials utilization in AD field, which was hoped to provide a deep insight in engineering application.

Surfactant enhances anaerobic fermentative hydrogen sulfide production: Changes in sulfur-containing organics structure and microbial community

The presence of surfactants in waste activated sludge (WAS) system is generally regarded as beneficial to sludge treatment such as enhancing sludge dewatering and improving value-added fermentation products generation. However, in this study, it was firstly found that sodium dodecylbenzene sulfonate (SDBS, a typical surfactant) obviously increased toxic hydrogen sulfide (H₂S) gas production from WAS anaerobic fermentation at environmentally relevant concentrations. Experimental results showed that H₂S production from WAS significantly increased from 53.24 × 10^-3 to 111.25 × 10^-3 mg/g volatile suspended solids (VSS) when SDBS level increased from 0 to 30 mg/g total suspended solid (TSS). It was found that SDBS presence destroyed WAS structure and enhanced sulfur containing organics release. SDBS reduced the proportion of α-helix structure, damaged disulfide bridges and protein conformation, and effectively destroyed protein structure. SDBS promoted sulfur containing organics degradation and provided more readily hydrolyzed micro-molecule organics for sulfide production. Microbial analysis showed that SDBS addition enhanced the abundance of functional genes encoding protease, ATP-binding cassette transporters, and amino acids lyase, enhanced the activities and abundance of hydrolytic microbes, thus increased sulfide production from the hydrolysis of sulfur containing organics. Compared with the control, 30 mg/g TSS SDBS increased organic sulfurs hydrolysis and amino acids degradation by 47.1 % and 63.5 %, respectively. Key genes analysis further showed that SDBS addition promoted sulfate transport system and dissimilatory sulfate reduction. SDBS presence also lowered fermentation pH, promoted the chemical equilibrium transformation of sulfide, thus increased H₂S gas release.

Low-dose chemical stimulation and pest resistance threaten global crop production

Pesticide resistance increases and threatens crop production sustainability. Chemical contamination contributes to the development of pest resistance to pesticides, in part by causing stimulatory effects on pests at low sub-toxic doses and facilitating the spread of resistance genes. This article discusses hormesis and low-dose biological stimulation and their relevance to crop pest resistance. It highlights that a holistic approach is needed to tackle pest resistance to pesticides and reduce imbalance in accessing food and improving food security in accordance with the UN's Sustainable Development Goals. Among others, the effects of sub-toxic doses of pesticides should be considered when assessing the impact of synthetic and natural pesticides, while the promotion of alternative agronomical practices is needed to decrease the use of agrochemicals. Potential alternative solutions include camo-cropping, exogenous application of phytochemicals that are pest-suppressing or -repelling and/or attractive to carnivorous arthropods and other pest natural enemies, and nano-technological innovations. Moreover, to facilitate tackling of pesticide resistance in poorer countries, less technology-demanding and low-cost practices are needed. These include mixed cropping systems, diversification of cultures, use of 'push-pull cropping', incorporation of flower strips into cultivations, modification of microenvironment, and application of beneficial microorganisms and insects. However, there are still numerous open questions, and more research is needed to address the ecological and environmental effects of many of these potential solutions, with special reference to trophic webs.

Revealing an unrecognized role of free ammonia in sulfur transformation during sludge anaerobic treatment

Free ammonia (FA), the unionized form of ammonium, is presented in anaerobic fermentation of waste activated sludge (WAS) at high levels. However, its potential role in sulfur transformation, especially H₂S production, during WAS anaerobic fermentation process was unrecognized previously. This work aims to unveil how FA affects anaerobic sulfur transformation in WAS anaerobic fermentation. It was found that FA significantly inhibited H₂S production. With an increase of FA from 0.04 to 159 mg/L, H₂S production reduced by 69.9%. FA firstly attacked tyrosine-like proteins and aromatic-like proteins in sludge EPSs, with CO groups being responded first, which decreased the percentage of α-helix/(β-sheet + random coil) and destroyed hydrogen bonding networks. Cell membrane potential and physiological status analysis showed that FA destroyed membrane integrity and increased the ratio of apoptotic and necrotic cells. These destroyed sludge EPSs structure and caused cell lysis, thus strongly inhibited the activities of hydrolytic microorganisms and sulfate reducing bacteria. Microbial analysis showed that FA reduced the abundance of functional microbes (e.g., Desulfobulbus and Desulfovibrio) and genes (e.g., MPST, CysP, and CysN) involved in organic sulfur hydrolysis and inorganic sulfate reduction. These findings unveil an actually existed but previously overlooked contributor to H₂S inhibition in WAS anaerobic fermentation.

Effect and mechanism of benzalkonium bromide on short chain fatty acid production from anaerobic sludge fermentation process

Quaternary ammonium compounds (QACs) was frequently detected in wastewater treatment plants and leads to potential toxicity to the related biological processes. In this study, the effect of benzalkonium bromide (BK) on anaerobic sludge fermentation process for short chain fatty acid (SCFAs) production was investigated. Batch experiments indicated that BK exposure significantly enhanced the SCFAs production from anaerobic fermentation sludge and the maximum concentration of total SCFAs increased from 474.40 ± 12.35 mg/L to 916.42 ± 20.35 mg/L with BK increasing from 0 to 8.69 mg/g VSS. Mechanism exploration exhibited that the presence of BK enhanced much more bioavailable organic matters release, little affected on hydrolysis, acidification, but seriously inhibited methanogenesis. Microbial community investigation revealed that BK exposure importantly enhanced the relative abundances of hydrolytic-acidifying bacteria and also improved the metabolic pathways and functional genes for sludge lysis. This work further supplement the information for environmental toxicity of emerging pollutants.

Exploration of the mechanism of 2-CP degradation by Acinetobacter sp. stimulated by Lactobacillus plantarum fermentation waste: A bio-waste reuse

Green and economical pollution management methods which reusing bio-waste as biostimulant to effectively improve the removal of target pollutants are receiving more and more attention. In this study, Lactobacillus plantarum fermentation waste solution (LPS) was used to investigate its facilitative effect and the stimulation mechanisms on the degradation of 2-chlorophenol (2-CP) by strain Acinetobacter sp. Strain ZY1 in terms of both cell physiology and transcriptomics. The degradation efficiency of 2-CP was improved from 60% to >80% under LPS treatment. The biostimulant maintained the morphology of strain, reduced the level of reactive oxygen species, and recovered the cell membrane permeability from 39% to 22%. It also significantly increased the level of electron transfer activity and extracellular polymeric substances secretion and improved the metabolic activity of the strain. The transcriptome results revealed the stimulation of LPS to promote biological processes such as bacterial proliferation, metabolism, membrane structure composition, and energy conversion. This study provided new insights and references for the reuse of fermentation waste streams in biostimulation methods.

Insights into high-solids anaerobic digestion of food waste concomitant with sorbate: Performance and mechanisms

High-solids anaerobic digestion (HS-AD) of food waste is increasingly applied commercially. Sorbate, a food preservative extensively used in the food industry, induces potential environmental risks. Results indicated sorbate at 0-10 mg/g VS slightly inhibited methane production, and the cumulative methane yield suggested a negative correlation with 25 mg/g VS sorbate, with a reduction of 15.0% compared to the control (from 285.7 to 253.6 mL CH₄/g VS). The reduction in methane yield could be ascribed to the promotion of solubilization and inhibition of acidogenesis and methanogenesis with sorbate addition. Excessive sorbate (25 mg/g VS) resulted in the inhibition of aceticlastic metabolism and the key enzymes activities (e.g., acetate kinase and coenzyme F₄₂₀). This study deeply elucidated the response mechanism of HS-AD to sorbate, supplemented the potential ecological risk assessment of sorbate, and could provide insights to further prevent the potential risk of sorbate in anaerobic digestion of FW.

Insights into the Occurrence, Fate, Impacts, and Control of Food Additives in Food Waste Anaerobic Digestion: A Review

The recovery of biomass energy from food waste through anaerobic digestion as an alternative to fossil energy is of great significance for the development of environmental sustainability and the circular economy. However, a substantial number of food additives (e.g., salt, allicin, capsaicin, allyl isothiocyanate, monosodium glutamate, and nonnutritive sweeteners) are present in food waste, and their interactions with anaerobic digestion might affect energy recovery, which is typically overlooked. This work describes the current understanding of the occurrence and fate of food additives in anaerobic digestion of food waste. The biotransformation pathways of food additives during anaerobic digestion are well discussed. In addition, important discoveries in the effects and underlying mechanisms of food additives on anaerobic digestion are reviewed. The results showed that most of the food additives had negative effects on anaerobic digestion by deactivating functional enzymes, thus inhibiting methane production. By reviewing the response of microbial communities to food additives, we can further improve our understanding of the impact of food additives on anaerobic digestion. Intriguingly, the possibility that food additives may promote the spread of antibiotic resistance genes, and thus threaten ecology and public health, is highlighted. Furthermore, strategies for mitigating the effects of food additives on anaerobic digestion are outlined in terms of optimal operation conditions, effectiveness, and reaction mechanisms, among which chemical methods have been widely used and are effective in promoting the degradation of food additives and increasing methane production. This review aims to advance our understanding of the fate and impact of food additives in anaerobic digestion and to spark novel research ideas for optimizing anaerobic digestion of organic solid waste.

Hydrochar mediated anaerobic digestion of bio-wastes: Advances, mechanisms and perspectives

Bio-wastes treatment and disposal has become a challenge because of their increasing output. Given the abundant organic matter in bio-wastes, its related resource treatment methods have received more and more attention. As a promising strategy, anaerobic digestion (AD) has been widely used in the treatment of bio-wastes, during which not only methane as energy can be recovered but also their reduction can be achieved. However, AD process is generally disturbed by some internal factors (e.g., low hydrolysis efficiency and accumulated ammonia) and external factors (e.g., input pollutants), resulting in unstable AD operation performance. Recently, hydrochar was wildly found to improve AD performance when added to AD systems. This review comprehensively summarizes the research progress on the performance of hydrochar-mediated AD, such as increased methane yield, improved operation efficiency and digestate dewatering, and reduced heavy metals in digestate. Subsequently, the underlying mechanisms of hydrochar promoting AD were systematically elucidated and discussed, including regulation of electron transfer (ET) mode, microbial community structure, bio-processes involved in AD, and reaction conditions. Moreover, the effects of properties of hydrochar (e.g., feedstock, hydrothermal carbonization (HTC) temperature, HTC time, modification and dosage) on the improvement of AD performance are systematically concluded. Finally, the relevant knowledge gaps and opportunities to be studied are presented to improve the progress and application of the hydrochar-mediated AD technology. This review aims to offer some references and directions for the hydrochar-mediated AD technology in improving bio-wastes resource recovery.

Thiosulfate pretreatment enhancing short-chain fatty acids production from anaerobic fermentation of waste activated sludge: Performance, metabolic activity and microbial community

A novel strategy based on thiosulfate pretreatment for enhancing short-chain fatty acids (SCFAs) from anaerobic fermentation (AF) of waste activated sludge (WAS) was proposed in this study. The results showed that the maximal SCFA yield increased from 206.1 ± 4.7 to 1097.9 ± 17.2 mg COD/L with thiosulfate dosage increasing from 0 to 1000 mg S/L, and sulfur species contribution results revealed that thiosulfate was the leading contributor to improve SCFA yield. Mechanism exploration disclosed that thiosulfate addition largely improved WAS disintegration, due to thiosulfate serving as a cation binder for removing organic-binding cations, especially Ca²⁺ and Mg²⁺, dispersing the extracellular polymeric substance (EPS) structure and further entering into the intracellularly by stimulated carrier protein SoxYZ and subsequently caused cell lysis. Typical enzyme activities and related functional gene abundances indicated that both hydrolysis and acidogenesis were remarkably enhanced while methanogenesis was substantially suppressed, which were further strengthened by the enriched hydrolytic bacteria (e.g. C10-SB1A) and acidogenic bacteria (e.g. Aminicenantales) but severely reduced methanogens (e.g. Methanolates and Methanospirillum). Economic analysis confirmed that thiosulfate pretreatment was a cost-effective and efficient strategy. The findings obtained in this work provide a new thought for recovering resource through thiosulfate-assisted WAS AF for sustainable development.

Benzo[a]pyrene stress impacts adaptive strategies and ecological functions of earthworm intestinal viromes

The earthworm gut virome influences the structure and function of the gut microbiome, which in turn influences worm health and ecological functions. However, despite its ecological and soil quality implications, it remains elusive how earthworm intestinal phages respond to different environmental stress, such as soil pollution. Here we used metagenomics and metatranscriptomics to investigate interactions between the worm intestinal phages and their bacteria under different benzo[a]pyrene (BaP) concentrations. Low-level BaP (0.1 mg kg^-1) stress stimulated microbial metabolism (1.74-fold to control), and enhanced the antiphage defense system (n = 75) against infection (8 phage-host pairs). Low-level BaP exposure resulted in the highest proportion of lysogenic phages (88%), and prophages expressed auxiliary metabolic genes (AMGs) associated with nutrient transformation (e.g., amino acid metabolism). In contrast, high-level BaP exposure (200 mg kg^-1) disrupted microbial metabolism and suppressed the antiphage systems (n = 29), leading to the increase in phage-bacterium association (37 phage-host pairs) and conversion of lysogenic to lytic phages (lysogenic ratio declined to 43%). Despite fluctuating phage-bacterium interactions, phage-encoded AMGs related to microbial antioxidant and pollutant degradation were enriched, apparently to alleviate pollution stress. Overall, these findings expand our knowledge of complex phage-bacterium interactions in pollution-stressed worm guts, and deepen our understanding of the ecological and evolutionary roles of phages.

Microplastics decrease the toxicity of cadmium to methane production from anaerobic digestion of sewage sludge

Microplastics (MPs) and Cd have been proven to inhibit methane production from anaerobic digestion of sewage sludge. However, the published studies mainly focused on their single inhibition. This cannot reflect the real-world situations where MPs and Cd co-exist. This study therefore aims to reveal the combined effect of MPs and Cd on anaerobic digestion of sewage sludge. Experimental results showed that PVC-MPs at environmentally relevant levels (e.g., 1, 10 particles/g total solids (TS)) did not affect methane yield but decrease the toxicity of Cd. When PVC-MPs were 30 particles/g TS, the cumulative methane production recovered from 58.8 % (in the presence of 5 mg Cd/g TS) to 89.7 % of the control. Organic fluxes were significantly increased compared with the control, particularly affecting the content of dissolved substances and short-chain fatty acids during anaerobic digestion. Mechanistic exploration showed that the adsorption of Cd by PVC-MPs was higher than that of sludge-substrate, which reduced the bioavailability of Cd by anaerobes, as evidenced by the increased anaerobes driven carbon flux from solid-phase to bio-methane during anaerobic digestion. Overall, these findings identified important factors in determining the toxicity of pollutants on anaerobic digestion process, providing precise data for toxicity evaluation of MPs and metals in anaerobic environment.

1-Butyl-3-methylimidazolium Chloride Affects Anaerobic Digestion through Altering Organics Transformation, Cell Viability, and Microbial Community

1-Butyl-3-methylimidazolium chloride (BmimCl), an imidazolium-based ionic liquid, is considered the representative emerging persistent aquatic pollutant, and its environmental toxicity has attracted a growing concern. However, most of the investigations focused on monocultures or a single organism, with little information available on the complex syntrophic consortium that dominates the complex and successional biochemical processes, such as anaerobic digestion. In this study, the effect of BmimCl at environmentally relevant levels on glucose anaerobic digestion was therefore investigated in several laboratory-scale mesophilic anaerobic digesters to provide such support. Experimental results showed that BmimCl at 1-20 mg/L inhibited the methane production rate by 3.50-31.03%, and 20 mg/L BmimCl inhibited butyrate, hydrogen, and acetate biotransformation by 14.29%, 36.36%, and 11.57%, respectively. Toxicological mechanism studies revealed that extracellular polymeric substances (EPSs) adsorbed and accumulated BmimCl through carboxyl, amino, and hydroxyl groups, which destroyed the EPSs' conformational structure, thereby leading to the inactivation of microbial cells. MiSeq sequencing data indicated that the abundance of Clostridium_sensu_stricto_1, Bacteroides, and Methanothrix decreased by 6.01%, 7.02%, and 18.45%, respectively, in response to 20 mg/L BmimCl. Molecular ecological network analysis showed that compared with the control, the lower network complexity, fewer keystone taxa, and fewer associations among microbial taxa were found in the BmimCl-present digester, indicating the reduced stability of the microbial community.

Iron-rich digestate biochar toward sustainable peroxymonosulfate activation for efficient anaerobic digestate dewaterability

In this study, a suite of Fe-rich biochars derived from Fenton-like treated digestate (Fe-BC) were fabricated under different pyrolysis temperatures (300, 500, and 800 °C), which were firstly utilized as peroxymonosulfate (PMS) activators for promoting digestate dewaterability with wide applicability. Results showed that compared to the Fe-BC₃₀₀/Fe-BC₅₀₀ + PMS treatments, Fe-BC₈₀₀ + PMS process performed superior digestate dewaterability in which specific resistance to filtration reduction and water content reduction improved by > 12.5% and > 130%, respectively, under the optimal conditions. Mechanistic results demonstrated that in Fe-BC₈₀₀ + PMS system, HO• and SO₄^•- oxidation played a pivotal role on promoted digestate dewaterability, while HO• and ¹O₂ oxidation was dominated in Fe-BC₃₀₀/Fe-BC₅₀₀ + PMS treatments. Fe-BC₈₀₀ containing higher Fe and CO contents could efficiently interact with PMS to generate numerous HO• and SO₄^•- via iron cycle. These highly reactive oxygen species proficiently reduced the hydrophilic biopolymers, protein molecules, and amino acids in extracellular polymeric substances, leading to remarkable decrease in particle size, hydrophilicity, adhesion, network strength, and bound water of digestate. Consequently, the flowability and dewaterability of digestate could be significantly enhanced. The cost-benefit result indicated the Fe-BC + PMS treatment possessed desirable reusability, applicability, and economic viability. Collectively, the Fe-BC + PMS is a high-performance and eco-friendly technique for digestate dewatering, which opens a new horizon towards a closed-loop of digestate reutilization.

Advances in pretreatment strategies to enhance the biodegradability of waste activated sludge for the conversion of refractory substances

Anaerobic digestion (AD) is a low-cost technology widely used to divert waste activated sludge (WAS) to renewable energy production, but is generally restricted by its poor biodegradability which mainly caused by the endogenous and exogenous refractory substances present in WAS. Several conventional methods such as thermal-, chemical-, and mechanical-based pretreatment have been demonstrated to be effective on organics release, but their functions on refractory substances conversion are overlooked. This paper firstly reviewed the presence and role of endogenous and exogenous refractory substances in anaerobic biodegradability of WAS, especially on their inhibition mechanisms. Then, the pretreatment strategies developed for enhancing WAS biodegradability by facilitating refractory substances conversion were comprehensively reviewed, with the conversion pathways and underlying mechanisms being emphasized. Finally, the future research needs were directed, which are supposed to improve the circular bioeconomy of WAS management from the point of removing the hindering barrier of refractory substances on WAS biodegradability.