Mixotrophic denitrification of waste activated sludge fermentation liquid as an alternative carbon source for nitrogen removal: Reducing N2O emissions and costs.

Heterotrophic-sulfur autotrophic denitrification (HAD) has been proposed to be a prospective nitrogen removal process. In this work, the potential of fermentation liquid (FL) from waste-activated sludge (WAS) as the electron donor for denitrification in the HAD system was explored and compared with other conventional carbon sources. Results showed that when FL was used as a carbon source, over 99% of NO3--N was removed and its removal rate exceeded 14.00 mg N/g MLSS/h, which was significantly higher than that of methanol and propionic acid. The produced sulfate was below the limit value and the emission of N2O was low (1.38% of the NO3--N). Microbial community analysis showed that autotrophic denitrifiers were predominated in the HAD system, in which Thiobacillus (16.4%) was the dominant genus. The economic analysis showed the cost of the FL was 0.062 €/m3, which was 30% lower than that in the group dosed with methanol. Our results demonstrated the FL was a promising carbon source for the HAD system, which could reduce carbon emission and cost, and offer a creative approach for waste-activated sludge resource reuse.

Sulfate-reducing bacteria decreases fractional pressure of H2 to accelerate short-chain fatty acids production from waste activated sludge fermentation assisted with zero-valent iron activated sulfite pretreatment.

The production of short-chain fatty acids (SCFAs) is constrained by substrate availability and the increased fractional pressure of H2 emitted by acidogenic/fermentative bacteria during anaerobic fermentation of waste activated sludge (WAS). This study introduced a novel approach employing zero-valent iron (ZVI)-activated sulfite pretreatment combined with H2-consuming sulfate-reducing bacteria (SRB) mediation to improve SCFAs, especially acetate production from WAS fermentation. Experimental results showed that the combined ZVI-activated sulfite and incomplete-oxidative SRB (io-SRB) process achieved a peak SCFAs production of 868.11 mg COD/L, with acetate accounting for 80.55 %, which was 7.90- and 2.18-fold higher than that obtained from raw WAS fermentation, respectively. This could be firstly attributed to the SO4- and OH generated by ZVI-activated sulfite, which significantly promoted WAS decomposition, e.g., soluble proteins and carbohydrates increased 14.3- and 10.8-fold, respectively, over those in raw WAS. The biodegradation of dissolved organic matter was subsequently enhanced by the synergistic interaction and H2 transfer between anaerobic fermentation bacteria (AFB) and io-SRB. The positive and negative correlations among AFB, nitrate-reducing bacteria (NRB) and the io-SRB consortia were revealed by molecular ecological network (MEN) and Mantel test. Moreover, the expression of functional genes was also improved, for instance, in relation to acetate formation, the relative abundances of phosphate acetyltransferase and acetate kinase was 0.002 % and 0.005 % higher than that in the control test, respectively. These findings emphasized the importance of sulfate radicals-based oxidation pretreatment and the collaborative relationships of multifunctional microbes on the value-added chemicals and energy recovery from sludge fermentation.

Tannic Acid Modulation of Substrate Utilization, Microbial Community, and Metabolic Traits in Sludge Anaerobic Fermentation for Volatile Fatty Acid Promotion.

Anaerobic fermentation is a crucial route to realize effective waste activated sludge (WAS) resource recovery and utilization, while the overall efficiency is commonly restrained by undesirable disruptors (i.e., chemical dewatering agents). This work unveiled the unexpectedly positive effects of biodewatering tannic acid (TA) on the volatile fatty acids (VFAs) biosynthesis during WAS anaerobic fermentation. The total VFAs yield was remarkably increased by 15.6 folds with enriched acetate and butyrate in TA-occurred systems. TA was capable to disintegrate extracellular polymeric substances to promote the overall organics release. However, TA further modulated the soluble proteins structure by hydrogen bonding and hydrophobic interactions, resulting in the decrease of proteins bioavailability and consequential alteration of metabolic substrate feature. These changes reshaped the microbial community and stimulated adaptive regulatory systems in hydrolytic-acidogenic bacteria. The keystone species for carbohydrate metabolism (i.e., Solobacterium and Erysipelotrichaceae) were preferentially enriched. Also, the typical quorum sensing (i.e., enhancing substrate transport) and two-component systems (i.e., sustaining high metabolic activity) were activated to promote the microbial networks connectivity and ecological cooperative behaviors in response to TA stress. Additionally, the metabolic functions responsible for carbohydrate hydrolysis, transmembrane transport, and intracellular metabolism as well as VFA biosynthesis showed increased relative abundance, which maintained high microbial activities for VFAs biosynthesis. This study underscored the advantages of biodewatering TA for WAS treatment in the context of resource recovery and deciphered the interactive mechanisms.

Indole-3-acetic acid regulating the initial adhesion of microalgae in biofilm formation.

Regulating the microalgal initial adhesion in biofilm formation is a key approach to address the challenges of attached microalgae cultivation. As a type of phytohormone, Indole-3-acetic acid (IAA) can promote the growth and metabolism of microalgae. However, limited knowledge has been acquired of how IAA can change the initial adhesion of microalgae in biofilm formation. This study focused on investigating the initial adhesion of microalgae under different IAA concentrations exposure in biofilm formation. The results showed that IAA showed obvious hormesis-like effects on the initial adhesion ability of microalgae biofilm. Under exposure to the low concentration (0.1 mg/L) of IAA, the initial adhesion quantity of microalgae on the surface of the carrier reached the highest value of 7.2 g/m2. However, exposure to the excessively high concentration (10 mg/L) of IAA led to a decrease in the initial adhesion capability of microalgal biofilms. The enhanced adhesion of microalgal biofilms due to IAA was attributed to the upregulation of genes related to the Calvin Cycle, which promoted the synthesis of hydrophobic amino acids, leading to increased protein secretion and altering the surface electron donor characteristics of microalgal biofilms. This, in turn, reduced the energy barrier between the carriers and microalgae. The research findings would provide crucial support for the application of IAA in regulating the operation of microalgal biofilm systems.

Deep insights into the roles and microbial ecological mechanisms behind waste activated sludge digestion triggered by persulfate oxidation activated through multiple modes.

Persulfate oxidation (PS) is widely employed as a promising alternative for waste activated sludge pretreatment due to the capability of generating free radicals. The product differences and microbiological mechanisms by which PS activation triggers WAS digestion through multiple modes need to be further investigated. This study comprehensively investigated the effects of persulfate oxidation activated through multiple modes, i.e., ferrous, zero-valent iron (ZVI), ultraviolet (UV) and heat, on the performance of sludge digestion. Results showed that PS_ZVI significantly accelerated the methane production rate to 12.02 mL/g VSS. By contrast, PS_Heat promoted the sludge acidification and gained the maximum short-chain fatty acids (SCFAs) yield (277.11 ± 7.81 mg COD/g VSS), which was 3.41-fold compared to that in PS_ZVI. Moreover, ferrous and ZVI activated PS achieved the oriented conversion of acetate, the proportions of which took 73% and 78%, respectively. MiSeq sequencing results revealed that PS_Heat and PS_UV evidently enriched anaerobic fermentation bacteria (AFB) (i.e., Macellibacteroides and Clostridium XlVa). However, PS_Ferrous and PS_ZVI facilitated the enrichment of Woesearchaeota and methanogens. Furthermore, molecular ecological network and mantel test revealed the intrinsic interactions among the multiple functional microbes and environmental variables. The homo-acetogens and sulfate-reducing bacterial had potential cooperative and symbiotic relationships with AFB, while the nitrate-reducing bacteria displayed distinguishing ecological niches. Suitable activation modes for PS pretreatments resulted in an upregulation of genes expression responsible for digestion. This study established a scientific foundation for the application of sulfate radical-based oxidation on energy or high value-added chemicals recovery from waste residues.

Simultaneous volatile fatty acids promotion and antibiotic resistance genes reduction in fluoranthene-induced sludge alkaline fermentation: Regulation of microbial consortia and cell functions.

The impact and mechanism of fluoranthene (Flr), a typical polycyclic aromatic hydrocarbon highly detected in sludge, on alkaline fermentation for volatile fatty acids (VFAs) recovery and antibiotic resistance genes (ARGs) transfer were studied. The results demonstrated that VFAs production increased from 2189 to 4272 mg COD/L with a simultaneous reduction of ARGs with Flr. The hydrolytic enzymes and genes related to glucose and amino acid metabolism were provoked. Also, Flr benefited for the enrichment of hydrolytic-acidifying consortia (i.e., Parabacteroides and Alkalibaculum) while reduced VFAs consumers (i.e., Rubrivivax) and ARGs potential hosts (i.e., Rubrivivax and Pseudomonas). Metagenomic analysis indicated that the genes related to cell wall synthesis, biofilm formation and substrate transporters to maintain high VFAs-producer activities were upregulated. Moreover, cell functions of efflux pump and Type IV secretion system were suppressed to inhibit ARGs proliferation. This study provided intrinsic mechanisms of Flr-induced VFAs promotion and ARGs reduction during alkaline fermentation.

Dynamic microbiome disassembly and evolution induced by antimicrobial methylisothiazolinone in sludge anaerobic fermentation for volatile fatty acids generation.

In the post-COVID-19 pandemic era, various antimicrobials have emerged and concentrated in waste-activated sludge (WAS), affecting the biological treatment of WAS. However, there is still a knowledge gap in the dynamic response and adaptive mechanism of anaerobic microbiome under exogenous antimicrobial stress. This study found that methylisothiazolinone (MIT, as a typic antimicrobial) caused an interesting lag effect on the volatile fatty acids (VFAs) promotion in the WAS anaerobic fermentation process. MIT was effective to disintegrate the extracellular polymeric substances (EPS), and those functional anaerobic microorganisms were easily exposed and negatively impacted by the MIT interference after the loss of protective barriers. Correspondingly, the ecological interactions and microbial metabolic functions related to VFA biosynthesis (e.g., pyruvate metabolism) were downregulated at the initial stage. The syntrophic consortia gradually adapted to the interference and attenuated the MIT stress by activating chemotaxis and resistance genes (e.g., excreting, binding, and inactivating). Due to the increased bioavailable substrates in the fermentation systems, the dominant microorganisms (i.e., Clostridium and Caloramator) with both VFAs production and MIT-tolerance functions have been domesticated. Moreover, MIT disrupted the syntrophic interaction between acetogens and methanogens and totally suppressed methanogens' metabolic activities. The VFA production derived from WAS anaerobic fermentation was therefore enhanced due to the interference of antimicrobial MIT stress. This work deciphered dynamic changes and adaptive evolution of anaerobic syntrophic consortia in response to antimicrobial stress and provided guidance on the evaluation and control of the ecological risks of exogenous pollutants in WAS treatment.

Novel calcium oxide activated peroxymonosulfate system for methylene blue removal: Identification of key influencing factors, transformation pathway and toxicity assessment.

The activation of peroxymonosulfate (PMS) has gained significant interest in the removal of organic pollutants. However, traditional methods usually suffer from drawbacks such as secondary contamination and high energy requirements. In this study, we propose a green and cost-effective approach utilizing calcium oxide (CaO) to activate PMS, aiming to construct a simple and reliable PMS based advanced oxidation processes (AOPs). The proposed CaO/PMS system achieved fast degradation of methylene blue (MB), where the degradation rate of CaO/PMS system (0.24 min-1) was nearly 2.67 times that of PMS alone (0.09 min-1). Under the optimized condition, CaO/PMS system exhibited remarkable durability against pH changes, co-exists ions or organic matters. Furthermore, singlet oxygen (1O2) was identified as the dominant reactive oxygen species by electron paramagnetic resonance (EPR) and quenching tests. Accordingly, the degradation pathways of MB are proposed by combing the results of LC/MS analysis and density functional theory (DFT) calculations, and the predicted ecotoxicity of the generated byproducts evaluated by EOCSAR could provide systematic insights into the fates and environmental risks of MB. Overall, the study provides an eco-friendly and effective strategy for treating dyeing wastewater, which should shed light on the application of PMS based AOPs.

Disinfectant sodium dichloroisocyanurate synergistically strengthened sludge acidogenic process and pathogens inactivation: Targeted upregulation of functional microorganisms and metabolic traits via self-adaptation.

Harmless and resourceful treatment of waste activated sludge (WAS) have been the crucial goal for building environmental-friendly and sustainable society, while the synergistic realization approach is currently limited. This work skillfully utilized the disinfectant sodium dichloroisocyanurate (NaDCC) to simultaneously achieve the pathogenic potential inactivation (decreased by 60.1 %) and efficient volatile fatty acids (VFAs) recovery (increased by 221.9 %) during WAS anaerobic fermentation in rather cost-effective way (Chemicals costs:0.4 USD/kg VFAs versus products benefits: 2.68 USD/kg chemical). Mechanistic analysis revealed that the C=O and NCl bonds in NaDCC could spontaneously absorb sludge (binding energy -4.9 kJ/mol), and then caused the sludge disintegration and organic substrates release for microbial utilization due to the oxidizability of NaDCC. The disruption of sludge structure along with the increase of bioavailable fermentation substrates contributed to the selectively regulation of microbial community via enriching VFAs-forming microorganisms (e.g., Pseudomonas and Streptomyces) and reducing VFAs-consuming microorganisms, especially aceticlastic methanogens (e.g., Methanothrix and Methanospirillum). Correspondingly, the metabolic functions of membrane transport, substrate metabolism, pyruvate metabolism, and fatty acid biosynthesis locating in the central pathway of VFAs production were all upregulated while the methanogenic step was inhibited (especially acetate-type methanogenic pathway). Further exploration unveiled that for those enriched functional anaerobes were capable to activate the self-adaptive systems of DNA replication, SOS response, oxidative stress defense, efflux pump, and energy metabolism to counteract the unfavorable NaDCC stress and maintain high microbial activities for efficient VFAs yields. This study would provide a novel strategy for synergistic realization of harmless and resourceful treatment of WAS, and identify the interrelations between microbial metabolic regulations and adaptive responses.

Prediction of biological nutrients removal in full-scale wastewater treatment plants using H2O automated machine learning and back propagation artificial neural network model: Optimization and comparison.

The effective control of total nitrogen (ETN) and total phosphorus (ETP) in effluent is challenging for wastewater treatment plants (WWTPs). In this work, automated machine learning (AutoML) (mean square error = 0.4200 âˆ¼ 3.8245, R2 = 0.5699 âˆ¼ 0.6219) and back propagation artificial neural network (BPANN) model (mean square error = 0.0012 âˆ¼ 6.9067, R2 = 0.4326 âˆ¼ 0.8908) were used to predict and analyze biological nutrients removal in full-scale WWTPs. Interestingly, BPANN model presented high prediction performance and general applicability for WWTPs with different biological treatment units. However, the AutoML candidate models were more interpretable, and the results showed that electricity carbon emission dominated the prediction. Meanwhile, increasing data volume and types of WWTP hardly affected the interpretable results, demonstrating its wide applicability. This study demonstrated the validity and the specific advantages of predicting ETN and ETP using H2O AutoML and BPANN model, which provided guidance on the prediction and improvement of biological nutrients removal in WWTPs.

Valorization of sewage sludge for facile and green wood bio-adhesives production.

A method is presented herein for the design of wood bio-adhesives using sewage sludge extracts (SSE). SSE was extracted from SS using deep eutectic solvents and processed with glycerol triglycidyl ether (GTE) to disrupt the secondary structure of proteins. An additive was also used to improve mechanical performance. The resulting bio-adhesive (SSE/GTE@TA) had a wet shear strength of 0.93 MPa, meeting the Chinese national standard GB/T 9846-2015 (≥0.7 MPa). However, the high polysaccharide content in SSE would weaken the mechanical properties of wood bio-adhesives. The key to improve bio-adhesive quality was the formation of a strong chemical bond via Maillard reaction as well as higher temperatures (140 °C) to reduce polysaccharide content via dehydration. This approach has lower environmental impact and higher economic efficiency compared to incineration and anaerobic digestion of sewage sludge. This work provides a new perspective on the high-value utilization of SS and offers a novel approach to developing bio-adhesives for the wood industry.

Revealing the mechanism of quartz sand seeding in accelerating phosphorus recovery from anaerobic fermentation supernatant through vivianite crystallization.

The recovery of phosphorus (P) through vivianite crystallization offers a promising approach for resource utilization in wastewater treatment plants. However, this process encounters challenges in terms of small product size and low purity. The study aimed to assess the feasibility of using quartz sand as a seed material to enhance P recovery and vivianite crystal characteristics from anaerobic fermentation supernatant. Various factors, including seed dosage, seed size, Fe/P ratio, and pH, were systematically tested in batch experiments to assess their influence. Results demonstrated that the effect of seed enhancement on vivianite crystallization was more pronounced under higher seed dosages, smaller seed sizes, and lower pH or Fe/P ratio. The addition of seeds increased P recovery by 4.43% in the actual anaerobic fermentation supernatant and also augmented the average particle size of the recovered product from 19.57 to 39.28 µm. Moreover, introducing quartz sand as a seed material effectively reduced co-precipitation, leading to a notable 12.5% increase in the purity of the recovered vivianite compared to the non-seeded process. The formation of an ion adsorption layer on the surface of quartz sand facilitated crystal attachment and growth, significantly accelerating the vivianite crystallization rate and enhancing P recovery. The economic analysis focused on chemical costs further affirmed the economic viability of using quartz sand as a seed material for P recovery through vivianite crystallization, which provides valuable insights for future research and engineering applications.

Influence of C/N ratio and ammonia on nitrogen removal and N2O emissions from one-stage partial denitrification coupled with anammox.

The development of low carbon treatment processes is an important issue worldwide. Partial denitrification coupled with anammox (PD/A) is a novel strategy to remove nitrogen and reduce N2O emissions. The influence of C/N ratio and NH4+ concentration on nitrogen removal and N2O emissions was investigated in batch reactors filled with PD/A coupled sludge. A C/N ratio of 2.1 was effective for nitrogen removal and N2O reduction; higher ammonia concentration might make anammox more active and indirectly reduce N2O emissions. Long-term operation further confirmed that a C/N ratio of 2.1 resulted in a minimum effluent N2O concentration (mean value of 0.94 µmol L-1); as the influent NH4+ concentration decreased to 50 mg L-1 (NH4+-N/NO3--N: 1), the nitrogen removal rate increased to 82.41%. Microbial analysis showed that anammox bacteria (Candidatus Jettenia and Ca. Brocadia) were enriched in the PD/A system and Ca. Brocadia gradually dominated the anammox community, with the relative abundance increasing from 1.69% to 18.44% between days 97 and 141. Finally, functional gene analysis indicated that the abundance of nirS/K and hao involved in partial denitrification and anammox, respectively, increased during long-term operation of the reactor; this change benefitted nitrogen metabolism in anammox, which could indirectly reduce N2O emissions.

Surfactant and antibiotic co-occurrence reshaped the acidogenic process for volatile fatty acids production during sludge anaerobic fermentation.

The overuse of surfactants and antibiotics has led to their high concentration in waste activated sludge (WAS), and these exogenous pollutants have been shown to pose various influences on the subsequent anaerobic treatment process. Previous works have primarily concerned the impacts of individual pollutants on WAS anaerobic fermentation process. This work revealed the synergetic effects of sodium dodecyl benzene sulfonate (SDBS) and sulfadiazine (SDZ) co-occurrence in WAS on the biosynthesis of volatile fatty acids (VFAs). The addition of SDBS in the SDZ reactor significantly increased VFAs generation, and this increase was correlated with the concentration of SDZ. The VFAs production exhibited a 200.0-211.9 % and 5.9-20.4 % increase in comparison with the sole SDZ and SDBS reactor, respectively. The SDBS and SDZ co-occurrence facilitated the solubilization, hydrolysis, and acidification stages of WAS fermentation synchronously. SDBS was effectively to disintegrate the cemented structure of extracellular polymeric substances and meanwhile improve the SDZ solubilization, which increase the SDZ bioavailability as well as biotoxicity to the anaerobic species. Herein, the anaerobic consortia structure was evidently reshaped, and the keystone microbes Acetoanaerobium and Fususibacter, as well-tolerated hydrolytic-acidogenic bacteria, were greatly enriched. Furthermore, the functional microbial metabolic traits responsible for the substrate extracellular hydrolysis (e.g., glsA and MAN2C1), intracellular metabolism (e.g., ALDO and asdA), and fatty acid generation (e.g., aarC) were all upregulated in the SDBS/SDZ co-occurrence reactor.

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 poly­aluminum 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.

Phosphorus recovery from synthetic anaerobic fermentation supernatant via vivianite crystallization: Coupling effects of various physicochemical process parameters.

Recovery of phosphorus (P) via vivianite crystallization is an effective strategy to recycle resources from the anaerobic fermentation supernatant. However, the presence of different components in the anaerobic fermentation supernatant (e.g., polysaccharides and proteins) might alter conditions for optimal growth of vivianite crystals, resulting in distinct vivianite characteristics. In the present study, the effect of different components on vivianite crystallization was explored. Then, the reaction parameters (pH, Fe/P, and stirring speed) for P recovery from synthetic anaerobic fermentation supernatant as vivianite were optimized using response surface methodology, and the relationship between crystal properties and supersaturation was elucidated using a thermodynamic equilibrium model. The optimized values for pH, Fe/P, and stirring speed were found to be 7.8, 1.74, and 500 rpm respectively, resulting in 90.54 % P recovery efficiency. Moreover, the variation of reaction parameters did not change the crystalline structure of the recovered vivianite but influenced its morphology, size, and purity. Thermodynamic analysis suggested the saturation index (SI) of vivianite increased with increasing pH and Fe/P ratio, leading to a facilitative effect on vivianite crystallization. However, when the SI was >11, homogenous nucleation occurred so that the nucleation rate was much higher than the crystal growth rate, causing a smaller crystal size. The findings presented herein will be highly valued for the future large-scale application of the vivianite crystallization process for wastewater treatment.

N-acyl homoserine lactone mediating initial adhesion of microalgal biofilm formation.

While pioneering methods have demonstrated that bacterial N-acyl homoserine lactone (AHL) signaling molecules can influence the growth and self-aggregation of suspended microalgae, whether AHLs can affect the initial adhesion to a carrier has remained an open question. Here we revealed that the microalgae exhibited different adhesion potential under AHL mediation, where the performance was affiliated to both AHL types and concentrations. The result can be well explained by the interaction energy theory, where the energy barrier between the carriers and the cells varied due to AHL mediation. Depth analyses revealed that AHL acted through modifying the properties of the surface electron donor of the cells, which were dependent upon three major components, i.e., extracellular protein (PN) secretion, the PN secondary structure, and the PN amino acid composition. These findings expand the known diversity of AHLs mediation on microalgal initial adhesion and metabolisms, which may interface with other major cycles and become helpful to theoretically guide the application of AHLs in microalgal culture and harvesting.

Boosting short-chain fatty acids production from co-fermentation of orange peel waste and waste activated sludge: Critical role of pH on fermentation steps and microbial function traits.

The anaerobic co-fermentation of orange peel waste (OPW) and waste activated sludge (WAS) for useful short-chain fatty acids (SCFAs) generation presents an environmentally friendly and efficient method for their disposal. This study amied to investigate the effects of pH regulation on OPW/WAS co-fermentation, and found that the alkaline pH regulation (pH 9) significantly enhanced the promotion of SCFAs (11843 ± 424 mg COD/L), with a high proportion of acetate (51%). Further analysis revealed that alkaline pH regulation facilitated solubilization, hydrolysis, and acidification while simultaneously inhibiting methanogenesis. Furthermore, the functional anaerobes, as well as the expressions of corresponding gene involved in SCFAs biosynthesis, were generally improved under alkaline pH regulation. Alkaline treatment might played a critical role in alleviating the toxicity of OPW, resulting in improving microbial metabolic activity. This work provided an effective strategy to recover biomass waste as high-value products, and insightful understanding of microbial traits during OPW/WAS co-fermentation.

Zinc pyrithione induced volatile fatty acids promotion derived from sludge anaerobic digestion: Interrelating the affected steps with microbial metabolic regulation and adaptive responses.

The massive use of zinc pyrithione (ZPT, as broad-spectrum bactericides) resulted in its high levels in waste activated sludge (WAS) and affected subsequent WAS treatment. This work revealed the effects of ZPT on the volatile fatty acids (VFAs) during WAS anaerobic digestion, in which VFAs yield was enhanced by approximately 6-9 folds (from 353 mg COD/L in control to 2526-3318 mg COD/L with low level of ZPT (20-50 mg/g TSS)). The ZPT occurred in WAS enabled the acceleration of solubilization, hydrolysis and acidification processes while inhibited the methanogenesis. Also, the low ZPT contributed to the enrichment of functional hydrolytic-acidifying microorganisms (e.g., Ottowia and Acinetobacter) but caused the reduction of methanogens (e.g., Methanomassiliicoccus and Methanothrix). Meta-transcriptomic analysis demonstrated that the critical genes relevant to extracellular hydrolysis (i.e. CLPP and ZapA), membrane transport (i.e. gltI, and gltL), substrates metabolisms (i.e. fadj, and acd), and VFAs biosynthesis (i.e. porB and porD) were all upregulated by 25.1-701.3% with low level of ZPT. Specifically, the ZPT stimulus on amino acids metabolism for VFAs transformation was prominent over carbohydrates. Moreover, the functional species enabled to regulate the genes in QS and TCS systems to maintain favorable cell chemotaxis to adapt the ZPT stress. The cationic antimicrobial peptide resistance pathway was upregulated to blunt ZPT with the secretion of more lipopolysaccharide and activate proton pumps to maintain ions homeostasis to antagonize the ZPT toxicity for high microbial activities, the abundance of related genes was up-regulated by 60.5 to 524.5%. This work enlightened environmental behaviors of emerging pollutants on WAS anaerobic digestion process with interrelations of microbial metabolic regulation and adaptive responses.

Proteomic profiling of robust acetoclastic methanogen in chrysene-altered anaerobic digestion: Global dissection of enzymes.

Methanogen is a pivotal player in pollution treatment and energy recovery, and emerging pollutants (EPs) frequently occur in methanogen-applied biotechnology such as anaerobic digestion (AD). However, the direct effect and underlying mechanism of EPs on crucial methanogen involved in its application still remain unclear. The positive effect of chrysene (CH) on semi-continuous AD of sludge and the robust methanogen was dissected in this study. The methane yield in the digester with CH (100 mg/kg dry sludge) was 62.1 mL/g VS substrate, much higher than that in the control (46.1 mL/g VS substrate). Both methane production from acetoclastic methanogenesis (AM) and the AM proportion in the methanogenic pathway were improved in CH-shaped AD. Acetoclastic consortia, especially Methanosarcina and functional profiles of AM were enriched by CH in favor of the corresponding methanogenesis. Further, based on pure cultivation exposed to CH, the methanogenic performance, biomass, survivability and activity of typical Methanosarcina (M. barkeri) were boosted. Notably, iTRAQ proteomics revealed that the manufacturing (transcription and translation), expression and biocatalytic activity of acetoclastic metalloenzymes, particularly tetrahydromethanopterin S-methyltransferase and methyl-coenzyme M reductase with cobalt/nickel-cofactor (F430 and cobalamin), and acetyl-CoA decarbonylase/synthase with cobalt/nickel-active site, of M. barkeri were upregulated significantly with fold changes in the range of 1.21-3.20 due to the CH presence. This study shed light on EPs-affecting industrially crucial methanogen at the molecular biology level during AD and had implications in the technical relevance of methanogens.