Extracellular polymeric substances as paper coating biomaterials derived from anaerobic granular sludge

Recovering extracellular polymeric substances (EPS) from waste granular sludge offers a cost-effective and sustainable approach for transforming wastewater resources into industrially valuable products. Yet, the application potential of these EPS in real-world scenarios, particularly in paper manufacturing, remains underexplored. Here we show the feasibility of EPS-based biomaterials, derived from anaerobic granular sludges, as novel coating agents in paper production. We systematically characterised the rheological properties of various EPS-based suspensions. When applied as surface sizing agents, these EPS-based biomaterials formed a distinct, ultra-thin layer on paper, as evidenced by scanning electron microscopy. A comprehensive evaluation of water and oil penetration, along with barrier properties, revealed that EPS-enhanced coatings markedly diminished water absorption while significantly bolstering oil and grease resistance. Optimal performance was observed in EPS variants with elevated protein and hydrophobic contents, correlating with their superior rheological characteristics. The enhanced water-barrier and grease resistance of EPS-coated paper can be attributed to its non-porous, fine surface structure and the functional groups in EPS, particularly the high protein content and hydrophobic humic-like substances. This research marks the first demonstration of utilizing EPS from anaerobic granular sludge as paper-coating biomaterials, bridging a critical knowledge gap in the sustainable use of biopolymers in industrial applications.

A new strategy for accelerating recovery of anaerobic granular sludge after low-temperature shock: In situ regulation of quorum sensing microorganisms embedded in polyvinyl alcohol sodium alginate

Low-temperature could inhibit the performance of anaerobic granular sludge (AnGS). Quorum sensing (QS), as a communication mode between microorganisms, can effectively regulate AnGS. In this study, a kind of embedded particles (PVA/SA@Serratia) based on signal molecule secreting bacteria was prepared by microbial immobilization technology based on polyvinyl alcohol and sodium alginate to accelerate the recovery of AnGS system after low temperature. Low-temperature shock experiment verified the positive effect of PVA/SA@Serratia on restoring the COD removal rate and methanogenesis capacity of AnGS. Further analysis by metagenomics analysis showed that PVA/SA@Serratia stimulated higher QS activity and promoted the secretion of extracellular polymeric substance (EPS) in AnGS. The rapid construction of EPS protective layer effectively accelerated the establishment of a robust microbial community structure. PVA/SA@Serratia also enhanced multiple methanogenic pathways, including direct interspecies electron transfer. In conclusion, this study demonstrated that PVA/SA@Serratia could effectively strengthen AnGS after low-temperature shock.

Evaluating effects of tetrabromobisphenol A and microplastics on anaerobic granular sludge: Physicochemical properties, microbial metabolism, and underlying mechanisms

Tetrabromobisphenol A (TBBPA) and microplastics are emerging contaminants of widespread concern. However, little is known about the effects of combined exposure to TBBPA and microplastics on the physicochemical properties and microbial metabolism of anaerobic granular sludge. This study investigated the effects of TBBPA, polystyrene microplastics (PS MP) and polybutylene succinate microplastics (PBS MP) on the physicochemical properties, microbial communities and microbial metabolic levels of anaerobic granular sludge. The results showed that chemical oxygen demand (COD) removal of sludge was lowest in the presence of TBBPA alone and PS MP alone with 33.21% and 30.06%, respectively. The microorganisms promoted the secretion of humic substances under the influence of TBBPA, PS MP and PBS MP. The lowest proportion of genes controlling glycolytic metabolism in sludge was 1.52% when both TBBPA and PS MP were added. Microbial reactive oxygen species were increased in anaerobic granular sludge exposed to MPS. In addition, TBBPA treatment decreased electron transfer of the anaerobic granular sludge and disrupted the pathway of anaerobic microorganisms in acquiring adenosine triphosphate, and MPs attenuated the negative effects of TBBPA on the acetate methanogenesis process of the anaerobic granular sludge. This study provides a reference for evaluating the impact of multiple pollutants on anaerobic granular sludge.

Biogas upgrading performance and underlying mechanism in microbial electrolysis cell and anaerobic digestion integrated system

The productivity and efficiency of two-chamber microbial electrolysis cell and anaerobic digestion integrated system (MEC-AD) were promoted by a complex of anaerobic granular sludge and iron oxides (Fe-AnGS) as inoculum. Results showed that MEC-AD with Fe-AnGS achieved biogas upgrading with a 23%-29% increase in the energy recovery rate of external circuit current and a 26%-31% decrease in volatile fatty acids. The energy recovery rate of MEC-AD remained at 52%-57%, indicating a stable operation performance. The selectively enriched methanogens and electroactive bacteria resulted in dominant hydrogenotrophic and acetoclastic methanogenesis in the cathode and anode chambers. Mechanistic analysis revealed that MEC-AD with Fe-AnGS led to specifically upregulated enzymes related to energy metabolism and electron transfer. Fe-AnGS as inoculum could improve the long-term operation performance of MEC-AD. Consequently, this study provides an efficient strategy for biogas upgrading in MEC-AD.

Magnetite alleviating calcification of anaerobic granular sludge (AnGS): Electron transfer enhancement and ion competition

Calcification accompanied by deactivation of anaerobic granular sludge (AnGS) is a continuing challenge for high calcium wastewater treatment. The interaction between Ca2+ and extracellular polymeric substances (EPS) is a precondition for this problem. In this study, magnetite for activity recovery and calcification alleviation simultaneously of AnGS under high calcium stress was investigated. The results showed that, in the presence of magnetite, the relative biogas production increased by 13.2 % with the higher activities of key enzymes involved in methanogenesis. Methanosarcina turned into the dominant methanogens, and syntrophic bacteria such as Chloroflexi, Synergistota were enriched, which indicated the enhancement of electron transfer by magnetite, supported by an 18 % increase of the electron transfer system (ETS) activity. Further characterizations of AnGS suggested that the granule calcification was alleviated with a final decrease of 13-40 % calcium content of AnGS with particle size of 1-2.5 mm. Besides, calcium was partially substituted by iron in the EPS, and the secretion of EPS especially proteins decreased. Batch tests demonstrated the competition between Fe2+ dissolved from magnetite and Ca2+, which interfered the interaction between Ca2+ and EPS, so the granule calcification was prevented. Therefore, magnetite played a pluripotent role in the alleviation of granule calcification and deactivation in situ via (1) enhancing electron transfer, and (2) blocking the complex between Ca2+ and EPS. This study provides a novel insight into the application of conductive metal materials in biological wastewater treatment systems suffering from high calcium attack.

Comparative investigations on the incorporation of biogenic Fe products into anaerobic granular sludge of different sources: Fe loading capacity, physicochemical properties, microbial community and long-term methanogenesis performance

Anaerobic granular sludge (AGS) has been regarded as the core of lots of advanced anaerobic reactors. Formation of biogenic Fe products and their incorporation into AGS could influence interspecies electron transfer and methanogenesis performance. In this study, with anaerobic granular sludge (AGS) from different sources (brewery, chemical plant, paper mill, citric acid factory, and food factory) as the research targets, the formation of biogenic iron products in AGS through the biologically induced mineralization process was studied. Furthermore, the influences of physicochemical properties and microbial community on methanogenesis were investigated. Results showed that all the AGS of different sources possessed the capacity to form biogenic Fe products through dissimilatory iron-reduction process, and diverse Fe minerals including magnetite (Fe3O4), hematite (Fe2O3), goethite (FeOOH), siderite (FeCO3) and wustite (FeO) were incorporated into AGS. The AGS loaded with Fe minerals (Fe-AGS) showed increased conductivity, magnetism and zeta-potential comparing to the control. Those Fe-AGS of different sources demonstrated different methanogenesis performance during the long-term operation (50 days). Methane production was increased for the Fe-AGS of citric acid (6.99-32.50%), food (8.33-37.46%), chemical (2.81-7.22%) and brewery plants (2.27-2.81%), but decreased for the Fe-AGS of paper mill (54.81-72.2%). The changes of microbial community and microbial correlations in AGS as a response to Fe minerals incorporation were investigated. For the Fe-AGS samples with enhanced methane production capability, it was widely to find the enriched populations of fermentative and dissimilatory iron reducing bacteria Clostridium_sensu_stricto_6, Bacteroidetes_vadinHA17 and acetoclastic methanogens Methanosaeta, and positive correlations between them. This study provides comprehensive understanding on the effects of incorporation biogenic Fe products on AGS from different sources.

Coupling extracellular glycan composition with metagenomic data in papermill and brewery anaerobic granular sludges

Glycans are crucial for the structure and function of anaerobic granular sludge in wastewater treatment. Yet, there is limited knowledge regarding the microorganisms and biosynthesis pathways responsible for glycan production. In this study, we analysed samples from anaerobic granular sludges treating papermill and brewery wastewater, examining glycans composition and using metagenome-assembled genomes (MAGs) to explore potential biochemical pathways associated with their production. Uronic acids were the predominant constituents of the glycans in extracellular polymeric substances (EPS) produced by the anaerobic granular sludges, comprising up to 60 % of the total polysaccharide content. MAGs affiliated with Anaerolineacae, Methanobacteriaceae and Methanosaetaceae represented the majority of the microbial community (30-50 % of total reads per MAG). Based on the analysis of MAGs, it appears that Anaerolinea sp. and members of the Methanobacteria class are involved in the production of exopolysaccharides within the analysed granular sludges. These findings shed light on the functional roles of microorganisms in glycan production in industrial anaerobic wastewater treatment systems.

Enhancing methane production and interspecies electron transfer of anaerobic granular sludge by the immobilization of magnetic biochar

Supplementation of conductive materials has been proved to be a promising approach for enhancing microbial interspecies electron transfer (IET) in anaerobic digestion systems. In this study, magnetic bamboo-based biochar was prepared at temperatures of 400-800 °C via a ball milling/carbonization method, and it immobilized in mature anaerobic granular sludge (AGS) aimed to enhance methane production by improving the IET process between syntrophic microbial communities in the AGS. Results showed that the AGS with magnetic biochar immobilization demonstrated increased glucotrophic and acetotrophic methane production by 69.54-77.56 % and 39.96-54.92 %, respectively. Magnetic biochar prepared at 800 °C with a relatively higher Fe content (0.37 g/g magnetic biochar) displayed a stronger electron charge/discharge capacity (36.66 F/g), and its immobilization into AGS promoted methane production most. The conductivity of AGS increased by 52.13-87.32 % after incorporating magnetic biochar. Furthermore, the extracellular polymeric substance (EPS) of AGS showed an increased capacitance and decreased electron transfer resistance possibly due to the binding of magnetic biochar and more riboflavin secretion in EPS, which could contribute to the accelerated IET process in the inner AGS. In addition, the immobilization of magnetic biochar could promote the production of volatile fatty acids by 15.36-22.50 %. All these improvements may jointly lead to the enhanced methane production capacity of AGS. This study provided a fundamental understanding of the role of incorporated magnetic biochar in AGS in promoting anaerobic digestion performance.

Mediating the performance of anaerobic granular sludge by exogenous flavin supplementation: Flavin binding capacity and behavior, interspecies electron transfer, and methane production

Although flavins are known as effective electron mediators, the binding capacity of exogenous flavins by anaerobic granular sludge (AGS) and their role in interspecies electron transfer (IET) remains unknown. In this study, AGS was mediated by using three exogenous flavins of riboflavin (RF), flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). Results showed that the total amounts of flavins associated with extracellular polymeric substance (EPS) of AGS increased by 2.03-2.42 and 3.83-4.94 folds, after exposure to 50 and 200 μM of exogenous flavins, respectively. A large portion of FMN and FAD was transformed into RF by AGS. Exogenous flavin mediation also stimulated the production of EPS and cytochrome c (c-Cyts) as well as cytochrome-bound flavins. The increased abundance of these electron mediators led to a reduced electrochemical impedance of EPS and improved extracellular electron transfer capacity. The methane production of AGS after mediation with exogenous RF, FMN, and FAD increased by 19.03-31.71%, 22.86-26.04%, and 28.51-33.44%, respectively. This study sheds new light on the role of exogenous flavins in promoting the IET process of a complex microbial aggregate of AGS.

Temporal and spatial variations in the physical and chemical properties of anaerobic granular sludge within a Pilot Spiral Symmetry Stream Anaerobic Bioreactor

Anaerobic granular sludge (AGS) determines the high performance of the bioreactor. To study the regionalization of granular sludge in the bioreactor, a Pilot Spiral Symmetry Stream Anaerobic Bioreactor (P-SSSAB) was established over 216 days, divided into three zones (I, II, and III) from bottom to top. AGS at the bottom of P-SSSAB had a higher porosity (60.35 %-83.27 %) and more suitable settling velocity (60 m/h) when the particle size range was 1.0-2.0 mm. This proved the better metabolic activity and superior settling performance in zone I than in zones II and III. In addition, the elemental composition of AGS in various zones was analyzed. The relative content of iron (5.66 %, 3.36 %, and 1.38 %, respectively) and sulfur (2.47 %, 2.19 %, and 1.49 %, respectively) in zone I, II, and III tended to decrease with the height of P-SSSAB. This also verified the better mass transfer performance and operational stability in lower zone than in upper zone. However, the monitoring of bed temperature in various zones revealed that the microbial activity in zone I was 6.7×10-12~3.5×10-2 times and 1.8×10-15~1.4×10-3 times that in zones II and III, respectively, which indicated that the unit activity of AGS in zone I was the worst. It indicated that AGS in lower zone had poor unit activity but had the highest unit capacity due to the high sludge concentration. Besides, the unit capacity of the upper zone was too weak to produce enough alkalinity to neutralize acid produced by excessive hydrolysis and acidification in lower zone, resulting in the worst treatment efficiency of the upper zone. Therefore, temperature and concentration ratios under various spatial distributions in bioreactors are vital to the overall sewage treatment stability and efficiency of bioreactors in actual engineering applications.

Enhancing electricity-driven methanogenesis by assembling biotic-abiotic hybrid system in anaerobic membrane bioreactor

Biotic-abiotic hybrid systems are promising technologies to enhance methane production in anaerobic wastewater treatment. However, the dense structure of the extracellular polymeric substances (EPS) present in anaerobic granular sludge (AGS) poses challenges with respect to the implementation of hybrid systems and efficient interspecies electron transfer. In this study, the use of AGS with a Ni/Fe layered double hydroxide@activated carbon (Ni/Fe LDH@C-AGS) was investigated in an anaerobic membrane bioreactor (AnMBR). The hybrid system showed a significant increase of 82% in methane production. Further research revealed that Ni/Fe LDH@C regulated the dense structure of EPS, stimulated the production of cytochromes, and facilitated the decomposition of nonconductive substances. Surprisingly, the hybrid system also promoted resistance to membrane fouling and extended membrane life by 81%. This study provides insights into the operation of a biotic-abiotic hybrid system by regulating the dense structure of EPS ultimately resulting in an enhanced methane production.

Effects of microplastics on the properties of different types of sewage sludge and strategies to overcome the inhibition: A review

Microplastics have been identified as an emerging pollutant. When microplastics enter wastewater treatment plants, the plant traps most of the microplastics in the sludge during sewage treatment. Therefore, the effects of microplastics on sludge removal performance, and on the physical and chemical properties and microbial communities in sludge, have attracted extensive attention. This review mainly describes the presence of microplastics in wastewater treatment plants, and the effects of microplastics on the decontamination efficiency and physicochemical properties of activated sludge, aerobic granular sludge, anaerobic granular sludge and anaerobic ammonium oxidation sludge. Further, the review summarizes the effects of microplastics on microbial activity and microbial community dynamics in various sludges in terms of type, concentration, and contact time. The mechanisms used to strengthen the reduction of microplastics, such as biochar and hydrochar, are also discussed. This review summarizes the mechanism by which microplastics influence the performance of different types of sludge, and proposes effective strategies to mitigate the inhibitive effect of microplastics on sludge and discusses removal technologies of microplastics in sewage. Biochar and hydrochar are one of the effective measures to overcome the inhibition of microplastics on sludge. Meanwhile, constructed wetland may be one of the important choice for the future removal of microplastics from sewage. The goal is to provide theoretical support and insights for ensuring the stable operation of wastewater treatment plants and reducing the impact of microplastics on the environment.

Roles and regulation of quorum sensing in anaerobic granular sludge: Research status, challenges, and perspectives

Anaerobic granular sludge (AnGS) has a complex and important internal microbial communication system due to its unique microbial layered structure. As a concentration-dependent communication system between bacterial cells through signal molecules, QS (quorum sensing) is widespread in AnGS and exhibits great potential to regulate microbial behaviors. Therefore, the universal functions of QS in AnGS have been systematically summarized in this paper, including the influence on the metabolic activity, physicochemical properties, and microbial community of AnGS. Subsequently, the common QS-based AnGS regulation approaches are reviewed and analyzed comprehensively. The regulation mechanism of QS in AnGS is analyzed from two systems of single bacterium and mixed bacteria. This review can provide a comprehensive understanding of QS functions in AnGS systems, and promote the practical application of QS-based strategies in optimization of AnGS treatment process.

Unravelling the resilience of magnetite assisted granules to starvation and oxytetracycline stress

Starvation and antibiotics pollution are two frequent perturbations during breeding wastewater treatment process. Supplying magnetite into anaerobic system has been proved efficient to accelerate microbial aggregates and alleviate the adverse effect caused by process disturbance. Nevertheless, whether these magnetite-based granules are still superior over normal granules after a long-term starvation period remains unknown, the responsiveness of these granules to antibiotics stress is also ambiguous. In current study, we investigated the resilience of magnetite-based anaerobic granular sludge (AnGS) to starvation and oxytetracycline (OTC) stress, by unravelling the variations of reactor performance, sludge properties, ARGs dissemination and microbial community. Compared with the AnGS formed without magnetite, the magnetite assisted AnGS appeared more robust defense to starvation and OTC stress. With magnetite supplement, the average methane yield after starvation recovery, 50 mg/L and 200 mg/L OTC stress was enhanced by 48.95%, 115.87% and 488.41%, respectively, accompanied with less VFAs accumulation, improved tetracycline removal rate (76.3-86.6% vs. 51.0-53.5%) and higher ARGs reduction. Meanwhile, magnetite supplement effectively ameliorated the potential sludge breakage by triggering more large granules formation. Trichococcus was considered an important impetus in maintaining the stability of magnetite-based AnGS process. By inducing more syntrophic methanogenesis partnerships, especially for hydrogenotrophic methanogenesis, magnetite ensured the improved reactor performance and stronger resilience at stress conditions.

Ecological distribution of anaerobic granular sludge towards efficient anaerobic reactor

Anaerobic reactors often underperform compared to expectations. To identify the key factors, an ecological anaerobic reactor (EAR) with vertical partitions was developed and compared to a physical anaerobic reactor (PAR) as the control. It was observed that EAR achieved a much higher organic loading rate (OLR) compared to PAR (>100 vs 45 kg/m3·d). The different vertical distribution characteristics of anaerobic granular sludge could be ascribed to two vertical distribution patterns dominated in EAR and PAR, i.e., ecological and physical distributions. It was revealed that ecological distribution was formed by the habitat selection, resulting in promoted substrate availability and higher OLR. While physical distribution was mainly affected by hydraulic selection via granule settleability, causing declined substrate availability and lower OLR. Consequently, the promoted ecological distribution and weakened hydraulic selection in EAR contributed to its good performance. Overall, these findings could offer novel concepts for the development of reactors towards high performance.

Magnetic anaerobic granular sludge for sequestration and immobilization of Pb

The development of magnetic adsorbents with high capacity to capture heavy metals has been the subject of intense research, but the process usually involves costive synthesis steps. Here, we propose a green approach to obtaining a magnetic biohybrid through in situ grown anaerobic granular sludge (AGS) with the help of magnetite, constituting a promising adsorbent for sequestration and immobilization of Pb in aqueous solutions and soils. The resultant magnetite-embedded AGS (M-AGS) was not only capable of promoting methane production but also conducive to Pb adsorption because of the large surface area and abundant function groups. The uptake of Pb on M-AGS followed the pseudo-second order, having a maximum adsorption capacity of 197.8 mg gDS^-1 at pH 5.0, larger than 159.7, 170.3, and 178.1 mg gDS^-1 in relation to AGS, F-AGS (ferrihydrite-mediated), and H-AGS (hematite-mediated), respectively. Mechanistic investigations showed that Pb binding to M-AGS proceeds via surface complexation, mineral precipitation, and lattice replacement, which promotes heavy metal capture and stabilization. This was evident from the increased proportion of structural Pb sequestrated from the aqueous solution and the enhanced percentage of the residual fraction of Pb extracted from the contaminated soils.

Insights into biodegradation behaviors of methanolic wastewater in up-flow anaerobic sludge bed (UASB) reactor coupled with in-situ bioelectrocatalysis

Granular sludge disintegration and washing out pose a challenge to up-flow anaerobic sludge bed (UASB) reactor treating methanolic wastewater. Herein, in-situ bioelectrocatalysis (BE) was integrated into UASB (BE-UASB) reactor to alter microbial metabolic behaviors and enhance the re-granulation process. BE-UASB reactor exhibited the highest methane (CH₄) production rate of 388.0 mL/L_reactor/d and chemical oxygen demand (COD) removal of 89.6 % at 0.8 V. Sludge re-granulation was strengthened with particle size over 300 µm of up to 22.4%. Bioelectrocatalysis stimulated extracellular polymeric substances (EPS) secretion and formation of granules with rigid [-EPS-cell-EPS-] matrix by enhancing the proliferation of key functional microorganisms (Acetobacterium, Methanobacterium, and Methanomethylovorans) and diversifying metabolic pathways. Particularly, a high Methanobacterium richness (10.8%) drove the electroreduction of CO₂ into CH₄ and reduced its emissions (52.8%). This study provides a novel bioelectrocatalytic strategy for controlling granular sludge disintegration, which will facilitate the practical application of UASB in methanolic wastewater treatment.

Multiple microplastics induced stress on anaerobic granular sludge and an effectively overcoming strategy using hydrochar

Previous studies mostly focused on the responses of anaerobic granular sludge (AGS) to one kind of microplastics during wastewater treatment. However, a wide variety of microplastics has been detected in wastewater. The multiple microplastics induced stress on AGS and the effectively mitigating strategy still remain unavailable. Herein, this work comprehensively excavated the influences of multiple microplastics (i.e., polyethylene terephthalate (PET), polystyrene (PS), polyethylene (PE) and polypropylene (PP)) coexisting in the wastewater on AGS system from macroscopic to microcosmic aspects. Experimental results illustrated that microplastics decreased AGS granule size, increased cell inactivation and caused deteriorative methane recovery from wastewater. As such, this study then put great emphasis on proposing a mitigating strategy using hydrochar and disclosing the role of hydrochar in overcoming the stress induced by coexisting microplastics to AGS system. Physiological characterization and microbial community analysis demonstrated that hydrochar effectively mitigated the reductions in methane production by 50.6% and cell viability by 68.8% of microplastics-bearing AGS and reduced the toxicity of microplastics to microbial community in the AGS. Mechanisms investigation by fluorescence tagging and excitation emission matrix fluorescence spectroscopy with fluorescence regional integration (EEM-FRI) analysis revealed that hydrochar adsorbed/accumulated microplastics and enhanced microplastics-bearing AGS to secrete extracellular polymeric substance (EPS) with more humic acid generation, thus reducing the direct contact between microplastics and AGS. In addition, hydrochar weakened the AGS intracellular oxidative stress induced by microplastics, thereby completely eliminating the inhibition of microplastics on acidification efficiency of AGS, and partially mitigating the suppression on methanation.

Evaluating the role of biochar in mitigating the inhibition of polyethylene nanoplastics on anaerobic granular sludge

The extensive application of anaerobic granular sludge (AGS) to wastewater treatment for methane recovery has drawn considerable attention to the system performances affected by the presence of emerging contaminants in wastewater such as nanoplastics. However, effective strategies on how to mitigate the inhibition caused by nanoplastics remained unavailable. In this study, a novel strategy using biochar to mitigate the inhibition on the AGS performances caused by polyethylene nanoplastics (PE-NPs) was proposed and the corresponding mitigating mechanisms involved were explored. The PE-NPs solely decreased the level of methane recovery of AGS to 71.3 ± 2.7% of control, which was subsequently increased to 85.6 ± 0.8% of control with the presences of both biochar and PE-NPs, although biochar solely showed no obvious effect on methane production. The addition of biochar also elevated the granule size of AGS, along with AGS integrity based on the morphological observation. Moreover, the distributions of live cells and functional microbes related to acidification and methanation increased with biochar addition compared to sole PE-NPs exposure. More extracellular polymeric substance (EPS) was secreted when biochar was involved in AGS systems, with more protein being detected to maintain the granule structure of AGS. Evaluation of adsorption tests indicated that biochar possessed stronger affinity for PE-NPs than AGS, thus capturing the PE-NPs that would originally contact AGS and posing less toxicity to microorganisms.

Microbial and physicochemical responses of anaerobic hydrogen-producing granular sludge to polyethylene micro(nano)plastics

Micro(nano)plastics is an emerging contaminant in wastewater that has showed significant impacts on various biological treatment processes. Nevertheless, the underlying effects of micro(nano)plastics with different concentrations and sizes on the anaerobic hydrogen-producing granular sludge (HPG) were still unclear. This work firstly attempted to illustrate the microbial and physicochemical responses of HPG to a shock load of polyethylene microplastics (PE-MPs) with varied concentrations and sizes. The results revealed that the PE-MPs inhibitory effect on hydrogen production by HPG was both concentration- and size-dependent. Specifically, the increase of PE-MPs concentration and the decline of PE-MPs size to nano-sized plastics (NPs) significantly decreased the hydrogen yield, downgraded to 79.9 ± 2.6% and 63.0 ± 3.9% (p = 0.001, and 0.0002) of control, respectively, at higher MPs concentration and the smaller MPs size (i.e., NPs). The higher PE-MPs concentration and PE-NPs also suppressed extracellular polymeric substances (EPS) generation more severely. The critical bio-processes involved in hydrogen production were disturbed by PE-MPs, with the extent of negative impacts depending on the dosage and size of PE-MPs. These adverse impacts further manifested as granule disintegration and loss of cellular activity. Mechanism analysis highlighted the roles of oxidative stress, leachate released from PE-MPs, interaction between PE-NPs and granules inducing physical crushing of HPG that led to possible direct contact between cells and toxic substances.

Different sizes of polystyrene microplastics induced distinct microbial responses of anaerobic granular sludge

Recent investigations confirmed the inhibitory effect of microplastics with single sizes on the anaerobic granular sludge (AGS) wastewater treatment system. However, the differences of toxicity from different sizes of microplastics toward AGS and their underlying mechanism are still unclear. In this work, the responds of AGS exposed to different particle sizes of polystyrene microplastics (PS-MPs) were reported. The results showed that the increasing particle sizes (from 0.5 μm to 150 μm) of PS-MPs induced a gradually increasing and distinct inhibitory (from 6.7% to 16.2%) effect on the cumulative methane production by AGS, accompanied by the similar decreasing organic carbon degradation trends. Correspondingly, the integrity and the cell viability of the AGS granules were damaged and the populations of the key acidogens and methanogens were reduced when exposed to PS-MPs, which was particularly evident in the reactors affected by the larger micron-sized PS-MPs. The zeta potential and contact angle indicated that the larger-sized PS-MPs had the stronger dispersive properties and affinity for AGS, causing the higher oxidative stress and leachates toxicity. Further investigation revealed that the tolerance of AGS to PS-MPs toxicity also exhibited size-dependent trend. Larger particles (e.g., 150 μm) of PS-MPs inhibited extracellular polymeric substance (EPS) secretion, while smaller particles (e.g., 0.5 μm) promoted EPS generation with the release of more humic acid, alleviating their toxicity.

Effects of PFOA on the physicochemical properties of anaerobic granular sludge: Performance evaluation, microbial community and metagenomic analysis

The impact of perfluorooctanoic acid (PFOA) on the anaerobic granular sludge was evaluated through a sequential batch experiment. Results showed that PFOA inhibited the chemical oxygen demand (COD) removal rate of the sludge and the dosage of 100 mg/L PFOA was more obvious. However, this negative effect would gradually weaken with the adaptation of microorganisms. For the 50 mg/L PFOA experimental group, the proteins content in the extracellular polymeric substances (EPS) of the anaerobic granular sludge increased from 1.53 mg/g to 3.65 mg/g. Meanwhile, PFOA inhibited the 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT) activity of the anaerobic granular sludge. Furthermore, 100 mg/L PFOA reduced the relative abundance of Proteobacteria by 5.99% and Longilinea by 1.11%. 100 mg/L PFOA mainly restricted COD removal by affecting the glycolysis process, with the abundances of glucokinase and pyruvate kinase reduced by 8% and 28.1%, respectively. Compared with the control group, the relative abundance of the methyl-coenzyme M reductase alpha subunit increased by 84%, respectively, under 100 mg/L PFOA.

Enhancing methanogenesis of anaerobic granular sludge by incorporating Fe/Fe oxides nanoparticles aided with biofilm disassembly agents and mediating redox activity of extracellular polymer substances

Anaerobic granular sludge (AGS) is a promising technology for organic wastewater treatment and energy recovery. In this study, three different kinds of Fe and Fe oxides nanoparticles (Fe₃O₄, Fe₂O₃ and ZVI) were tried to be incorporated into AGS through direct loading or aided with biofilm disassembly agents of norspermidine and D-tyrosine, which was aimed to enhance methane production capacity of AGS via increasing redox activity of extracellular polymer substance (EPS) and interspecies electron transfer. Despite the loading methods, incorporation of Fe and Fe oxides nanoparticles into AGS increased methane production capacity remarkably, with an enhancement of 36.49-85.17%, 20.37-204.95% and 189.71-243.32%, respectively, for the Fe₃O₄, Fe₂O₃ and ZVI loaded AGS. Pretreatment of AGS using biofilm disassembly agents helped to incorporate more Fe and Fe oxides into the inner structure of AGS, which further enhanced methane production capacity by 48.68% and 184.58%, respectively, for the Fe₃O₄ and Fe₂O₃ loaded AGS. Loading Fe and Fe oxides into AGS not only introduced exogenous conductive substances and Fe(III)/Fe(II) redox couples into EPS matrix of AGS, but also stimulated the production of redox active components of flavins and c-Cyts. All these factors may contribute to the reduced resistance of EPS, enhanced interspecies electron transfer and methane production capacity of AGS. This study provides a novel strategy and facile method to accelerate interspecies electron transfer and enhance methane production for matured AGS.

Underlying function regulators of anaerobic granular sludge: Starvation and dormancy

Anaerobic granular sludge (AnGS) is the core of anaerobic granular sludge bed system. In this study, the effect and its mechanism of stopping substrate supply on function of AnGS were investigated. The cutoff of exogenous substrate supply triggered AnGS to enter the dormant state. Some methanization microorganisms sporulated. The number and activity of methanization microorganisms based on 16S rDNA and 16S rRNA/16S rDNA ratio declined and stayed at 45.5% and 0.06% (bacteria), 48.7% and 0.39% (archaea) of the initial vegetative value, respectively. The resuming of exogenous substrate supply promoted AnGS to restore the vegetative state. The spores disappeared. The specific methanization activity of AnGS returned to the original level of 35.82 mL-CH4/g-VSS·d, but the delay time for gas production (DTGS) was prolonged from 9.54 to 18.04 h (0-132 d). The dormancy of methanization microorganisms was the main cause for the fluctuation of apparent function and the stability of intrinsic function of AnGS under starvation stress. The dormancy stabilized the structure and sustained the methanization community of AnGS via the reduction of EPS (structure binder/energy reserve) consumption.

Evaluation of characteristics and microbial community of anaerobic granular sludge under microplastics and aromatic carboxylic acids exposure

The influences of polyether sulfone (PES) microplastics and different structures aromatic carboxylic acids such as benzoic acid (BA), phthalic acid (PA), hemimellitic acid (HA), and 1-naphthoic acid (1-NA) on the performances and characteristics of anaerobic granular sludge as well as the microbial community were investigated. The chemical oxygen demand (COD) removal efficiency was the highest in the experimental group with 40 mg/L BA, reaching 90.1%. The inhibitory effect of aromatic carboxylic acids addition on the 2,3,5-triphenyltetrazolium chloride (TTC) activity was more obvious than that on 2-para (iodo-phenyl)-3(nitrophenyl)-5(phenyl) tetrazolium chloride (INT) activity. Compared with the control group (only 0.5 g/L PES microplastics, 60.6 mg TF·g TSS·h^-1), the inhibition effect of TTC activity was 32.5 mg TF·g TSS·h^-1 and 44.3 mg TF·g TSS·h^-1 in the 40 mg/L HA and 40 mg/L 1-NA experimental groups, respectively. When aromatic carboxylic acids were added, the activities of acetate kinase and coenzyme F₄₂₀ in the anaerobic granular sludge decreased. The excitation-emission matrix (EEM) fluorescence spectra indicated that loosely bound extracellular polymeric substances (LB-EPS) began to decay. After the addition of different aromatic carboxylic acids, the CC and CH functional groups of the anaerobic granular sludge increased, suggesting that aromatic carboxylic acids migrated to the surface of anaerobic granular sludge, such a transfer would lead to changes in anaerobic granular sludge performance. High-throughput sequencing technology showed that the dominant microbial communities in the anaerobic granular sludge were Proteobacteria, Methanothrix, and Methanomicrobia. After the addition of aromatic carboxylic acids, the relative abundances of Proteobacteria, Methanobacterium, and Methanospirillum increased. In the presence of PES, 1-NA had the most serious toxicity to the anaerobic granular sludge.

Simultaneous removal of lead and selenium through biomineralization as lead selenide by anaerobic granular sludge

This study demonstrated the simultaneous removal of lead (Pb) and selenium (Se) as lead selenide biomineralization using anaerobic granular sludge. The microbial community of the granular sludge was first enriched for 140 days in the presence of Pb(II) only, selenate and selenite only, Pb(II)+selenate, and Pb(II)+selenite. In the absence of Se, removal of Pb(II) mainly occurred via biosorption and deposited on the biomass as lead oxide and lead carbonate. The Pb removal efficiency (94% of initial 50 mg L^-1) was reduced to 90% and 86% in the presence of selenate and selenite, respectively, due to biosorption. Addition of Pb(II) didn't exert any toxic effect on the Se-reducing microbial community, on the contrary: Pb(II) addition improved the Se removal efficiency for selenate from 85% to 90%, but did not affect selenite removal after 14 d of incubation. The bioreduction of the Se-oxyanions produced elemental Se (Se(0)) and selenide, which later interacted with Pb(II) to produce lead selenide (PbSe). Adsorption of Pb(II) onto the Se(0) nanoparticles and precipitation as the Se(0)-Pb complex might also have contributed to the simultaneous removal of Pb and Se. XPS and XRD analysis further confirmed the immobilization of Pb as PbSe, PbO and PbCO₃ in the biomass.

Response of anaerobic granular sludge to long-term loading of roxarsone: From macro- to micro-scale perspective

Extensive use of organoarsenic feed additives such as roxarsone has caused organoarsenicals to occur in livestock wastewater and further within anaerobic wastewater treatment systems. Currently, information on the long-term impacts of roxarsone on anaerobic granular sludge (AGS) activity and the underlying mechanisms is very limited. In this study, the response of AGS to long-term loading of roxarsone was investigated using a laboratory up-flow anaerobic sludge blanket reactor spiked with 5.0 mg L^-1 of roxarsone. Under the effect of roxarsone, methane production decreased by ∼40% due to the complete inhibition on acetoclastic methanogenic activity on day 260, before being restored eventually. Over 30% of the influent arsenic was accumulated in the AGS and the capability of AGS to prevent intracellular As(III) accumulation increased with time. The AGS size was reduced by ∼30% to 1.20‒1.26 mm. Based on morphology and confocal laser scanning microscopy analysis, roxarsone exposure stimulated the excretion of extracellular polymeric substances and the surface spalling of AGS. High-throughput sequencing analysis further indicated roxarsone initially altered the acidogenic pathway and severely inhibited the acetoclastic methanogen Methanothrix. Acetogenic bacteria and Methanothrix were finally enriched and became the main contributor for a full restoration of the initial methane production. These findings provide a deeper understanding on the effect of organoarsenicals on AGS, which is highly beneficial for the effective anaerobic treatment of organoarsenic-bearing wastewater.

Effects of reflux ratio on the anaerobic sludge and microbial social behaviors in an expanded granular sludge bed reactor: From the perspective of acyl-homoserine lactones-mediated quorum sensing

Performance of anaerobic sludge and microbial social behaviors in an expanded granular sludge bed (EGSB) were evaluated by increasing reflux ratio from 50% to 500% stage by stage, with a constant influent chemical oxygen demand (COD) of 5500 mg/L at hydraulic retention time 12 h. The results indicated that the reflux ratio of 100% - 200% was more favorable for the EGSB with a methane production of 2.4 m³/m³·d. It was found that acyl-homoserine lactones (AHLs)-mediated quorum sensing (QS) could balance various microbial populations in the anaerobic digestion process. C₄-HSL and C₈-HSL were identified as the specific AHLs in enhancing granulation of anaerobic sludge by stimulating protein secretion into extracellular polymeric substances (EPS). 3-oxo-C₆-HSL and 3-oxo-C₁₄-HSL were verified for the enhancement of methanogenesis. The present study showed a novel perspective on the performance of EGSB with reflux ratios based on the AHLs-mediated QS.

In-situ formation and self-immobilization of biogenic Fe oxides in anaerobic granular sludge for enhanced performance of acidogenesis and methanogenesis

Addition of ferric oxides into flocculent anaerobic sludge was reported to enhance methanogenesis due to accelerated direct interspecies electron transfer (DIET) between syntrophic microbial communities. However, it is generally hard to incorporate Fe oxides into already matured anaerobic granular sludge (AGS) due to its special aggregated structure. In this study, a novel method was attempted to fast incorporate Fe oxides into AGS through in-situ microbial formation and immobilization of biogenic Fe oxides. Factors influencing the formation of Fe oxides were investigated and effects of Fe oxides on the acidogenic and methanogenic performance of AGS were assessed. Results showed that AGS could form Fe oxides mainly in the form of magnetite and hematite through biological reduction of Fe(III) oxyhydroxide. A maximum loading amount of 83.9 mg Fe/g MLVSS was obtained at pH 7 after contacting with 60 mM Fe(III) oxyhydroxide. The efficiency of electron donors which supported Fe(III) reduction followed the order of pyruvate > propionate > glucose > acetate > lactate > formate. Addition of electron transfer mediators (ETMs) promoted the formation of Fe oxides and their performance followed the order of AQDS > AQC > humics > FMN > riboflavin. Presence of Fe oxides in AGS (134.6 Fe/g VSS) increased the production of volatile fatty acids (VFAs) and methane by 16.28% and 41.94% respectively, comparing to the control. The enhancement may be attributed to increased conductivity and stimulated growth of exoelectrogens (Clostridium and Anaerolinea) and methanogenic endoelectrogens Methanosaeta in granular sludge which may strengthen direct interspecies electron transfer between syntrophic microbial communities. Overall, this study provides an alternative strategy to improve the digestion performance of AGS through in-situ formation and immobilization of biogenic Fe oxides.

Comparison of different cultures and culturing conditions for the biological deterioration of organic load from real saline bilge wastewater: microbial diversity insights and ecotoxicity assessment

Bilge wastewater is a high strength, typically saline wastewater, originating from operation of ships. In this study, the treatment of real bilge wastewater was tested using pure isolated aerobic strains and mixed cultures (aerobic and anaerobic). The Chemical Oxygen Demand (COD) and ecotoxicity decrease were monitored over time, while the microbial dynamics alterations in mixed cultures were also recorded. The isolated strains Pseudodonghicola xiamenensis, Halomonas alkaliphila and Vibrio antiquaries were shown to significantly biodegrade bilge wastewater. Reasonable COD removal rates were achieved by aerobic mixed cultures (59%, 9 days), while anaerobic mixed cultures showed lower performance (34%, 51 days). The genus Pseudodonghicola was identified as dominant under aerobic conditions both in the mixed cultures and in the control sample (raw wastewater), after exposure to bilge wastewater, demonstrating natural proliferation of the genus and potential contribution to COD reduction. Biodegradation rates were higher when initial organic load was high, while the toxicity of raw wastewater partially decreased after treatment.

Anaerobic biodegradation of soybean-process wastewater: Operation strategy and sludge bed characteristics of a high-performance Spiral Symmetric Stream Anaerobic Bioreactor

A 300m3/d demonstration project of soybean-process wastewater has been established recently with a Spiral Symmetric Stream Anaerobic Bioreactor (SSSAB) as the core. In order to obtain the optimal operation strategy for a full-scale SSSAB and to make it run efficiently and stably in a demonstration project, a Pilot-scale SSSAB (P-SSSAB, effective volume 100 L) was performed for the treatment of soybean-process wastewater over 216 days. The volumetric load rate (VLR) range of the P-SSSAB was 0.32~27.17 kg COD/(m3·d), where the highest VLR [27.17 kg COD/(m3·d)] was 2.01 times to the highest value [13.5 kg COD/(m3·d)] reported. The pH and VFA/ALK of the effluent from the P-SSSAB were in the range of 6.9 up to 9.2 and 0.03 up to 0.17, respectively. The methane yield of the P-SSSAB increased from 0.03 m3/kg COD to 0.47 m3/kg COD, which was 3.36 times to the maximum value (0.14 m3/kg COD) reported. To meet the influent requirement of the aerobic biological treatment in demonstration project (influent COD ≤ 1.5 g/L), the maximum VLR of SSSAB was optimal at about 22 kg COD/(m3·d). By analyzing the sludge bed characteristics of the P-SSSAB, it was obvious that zone I (the bottom of the bed) was the major contributor of the COD removal, while zone III (the upper part of the bed) was the major contributor for the NH4+-N increase. The anaerobic granular sludge (AGS) in the bed showed a good granulation. The average MLVSS/MLSS value in sludge bed was about 0.7, and PN/PS in TB-EPS (zone I, II and III) increased to 6.830, 4.257, and 3.747, respectively. SMA and coenzyme F420 values of zone III were the maximum [666.35 ml CH4/(g VSS·d) and 0.690 mol/g VSS, respectively]. According to the analysis obtained from the 16S rRNA high-throughput sequencing, the microbial community in the AGS had been more specific to the soybean-process wastewater since the bacteria Firmicutes were increased. The relative abundance of microbe which perform direct interspecies electron transfer (DIET) for the syntrophic degradation of VFAs and production of the methane has been increased significantly, such as the bacteria Syntrophomonas and archaea Methanosaeta.

Influence of lincomycin on anaerobic digestion: Sludge type, biogas generation, methanogenic pathway and resistance mechanism

This study investigated the tolerance, defensive response and methanogenic pathways of anaerobic granular slugde and anaerobic suspended sludge (AGS and ASS) exposed to different LCM concentrations. AGS presented a higher tolerance to LCM stress, accompanied with 20.8 ± 2.6% enhancement in methane production at 1000 mg/L LCM, which was likely attributed to the less cell deaths and extracellular polymeric substances (EPSs) protection. In the acidification stage, acetate accumulation was stimulated and the activity of acetate kinase was promoted by LCM. In the methanogenesis stage, propionate and butyrate utilization for methane production were impaired after LCM addition. LCM also improved the activity of pyruvate-ferredoxin oxidoreductase and strengthened the process of hydrogenotrophic methanogenesis, likely by accelerating interspecies electron transfer mediated by hydrogen. ErmB and ermF were the dominate LCM resistance genes in AGS under LCM pressure conferring the resistance mechanism of ribosomal protection.

Optimization of a newly developed electromethanogenesis for the highest record of methane production

The development of an effective biocathode with high catalytic ability and dense biomass is a major challenge for the industrial applications of electromethanogenesis (EM) process. In our previous study, intact anaerobic granular sludge (AnGS) biocathode and EM hybrid system (AnGS-EM) showed superior ability and stability when treating raw biogas, but its maximum CO₂-to-CH₄ conversion potential and the response to different operating conditions are still unknown. Herein, we optimized the performance of the AnGS-EM system and explored its maximum CH₄ production capacity. The AnGS-EM system achieved a maximum methane production rate of 202.15 L CH₄/m²cat_proj/d, which is over 3 times higher than the maximum value reported so far. Within a certain range, the methane production rate increased with the buffer concentration, applied voltage, and bicarbonate concentration. Excessive applied voltage and carbonate concentration not only led to resource waste but also inhibited methanogen performance. The AnGS biocathode could withstand oxygen exposure for 24 h, the acidic (pH of 5.5), and alkaline conditions (pH over 9). Illumina sequencing results showed that hydrogenotrophic methanogen (especially Methanobacterium) were dominant. This work using AnGS as biocathode for CH₄ synthesis offers insight into the development of scalable, efficient, and cost-effective biocathode for biofuels and value-added chemicals production.

Effects of anaerobic granular sludge towards the treatment of flowback water in an up-flow anaerobic sludge blanket bioreactor: Comparison between mesophilic and thermophilic conditions

Cost-effective treatment of flowback water remains a challenge for the sustainability of shale gas development. This study evaluated the efficiency of anaerobic granular sludge (AnGS) technology for flowback water treatment under mesophilic and thermophilic conditions. The granule characteristics and metagenomic characterization were also investigated. Thermophilic AnGS achieved 70.9% of COD removal and 362 NmL/d of methane production, higher than those for mesophilic AnGS (60.0% and 241 NmL/d). Thermophilic AnGS had higher extracellular polymeric substances content but low granular size and settleability. Metagenomic analysis revealed the genes related to hydrolysis acidification and carbohydrate metabolism were upregulated during thermophilic condition. Thermophilic condition most likely improved the hydrolysis of complex organics in the flowback water such as guar gum and hydrolyzed polyacrylamide, and led to higher COD removal and methane production. These results suggest that AnGS technology is a promising alternative for the treatment of flowback water, particularly when operated at thermophilic condition.

Exogenous N-acyl-homoserine lactones promote the degradation of refractory organics in oligotrophic anaerobic granular sludge

For refractory industrial wastewaters, anaerobic granular sludge technology cannot be widely used because of its limited treatment capacity, so strengthening the anaerobic degradation of refractory organics should be discussed. In this paper, the feasibility of adding exogenous N-acyl-homoserine lactones (AHLs) to promote the degradation of refractory organics in oligotrophic anaerobic granular sludge was addressed. The results showed that, after easily-degradable organics were completely metabolized, exogenous AHLs strengthened the further degradation of refractory organics and improved the methanogenic activity of anaerobic granular sludge. In addition, adding AHLs could promote the secretion of more extracellular polysaccharides and proteins by anaerobic microorganisms to resist the oligotrophic environment. Microbiological analysis showed that adding AHLs significantly optimized the microbial community in oligotrophic anaerobic granular sludge. With the regulation of AHLs, the abundance proportion of hydrolytic acidifying bacteria for refractory organics in bacterial community and the abundance proportion of acetotrophic methanogens in methanogens community increased obviously. Exogenous AHLs showed concentration-related effects on the optimization of bacteria and methanogens, and AHLs of higher concentration were beneficial to the succession of community structure in a better direction. Exogenous regulation of AHLs-mediated QS provided an attractive strategy for enhancing the anaerobic degradation of refractory organics, and proposed a technical idea for the application of anaerobic granular sludge technology in refractory industrial wastewaters.

Improvement in calcified anaerobic granular sludge performance by exogenous acyl-homoserine lactones

Given the high content of Ca²⁺ in waste paper recycling wastewater, the anaerobic granular sludge (AnGS) undergoes calcification during wastewater treatment and affects the treatment efficiency. To restore the activity of calcified AnGS and improve the performance of AnGS, four types of N-acyl-homoserine lactones (AHLs) were added to the AnGS system while papermaking wastewater treatment. The addition of N-butyryl-DL-homoserine lactone(C4-HSL) and N-octanoyl-DL-homoserine lactone (C8-HSL) had an inhibitory affect the COD removal efficiency and SMA of sludge at the inception. The addition of N-hexanoyl-L-homoserine lactone (C6-HSL) has no obvious effect on the COD removal efficiency, but can improve the SMA of sludge more obviously. The addition of N-(β-ketocaproyl)-DL-homoserine lactone (3O-C6-HSL) can increased COD removal efficiency and promoted SMA together obviously. The addition of C6-HSL and 3O-C6-HSL can increase volatile suspended solid (VSS)/total suspended solid (TSS), and regulate extracellular polymeric substance (EPS) secretion in AnGS. Analysis of microbial sequencing revealed changes in the microbial community structure following AHL addition, which enhanced the methane metabolism pathway in sludge. The addition of C6-HSL, C8-HSL, and 3O-C6-HSL increased Methanosaeta population, thus increasing the aceticlastic pathway in sludge. Thus, exogenous AHLs can play an important role in regulating microbial community structure, and in improving the performance of AnGS.

The removal of copper and zinc from swine wastewater by anaerobic biological-chemical process: Performance and mechanism

Copper and zinc are often used as feed additives and frequently detected in swine wastewater. Anaerobic granular sludge (AnGS) plays an important role in high-rate anaerobic methanation biotechnologies which are widely applied to treat swine wastewater. The removal of Cu²⁺ and Zn²⁺ by AnGS was investigated in the batch and continuous systems. The results of batch experiments showed the adsorption by AnGS could be a significant method for Cu²⁺ and Zn²⁺ removal with efficiencies of 99 % and 49 % respectively. The sulfide precipitation mediated by AnGS could be another significant pathway for Zn²⁺ removal with efficiency of 18-27 % in Protein/M²⁺ experiments and 16-46 % in SO₄^2-/M²⁺ experiments (M²⁺ represents the total concentration of Cu²⁺ and Zn²⁺). The results of continuous experiment showed, with SO₄^2-/M²⁺ larger than 1.5, the influent Cu²⁺ and Zn²⁺ could be effectively removed in an anaerobic methanation bioreactor and its effluent Cu²⁺and Zn²⁺concentrations were below 1 mg/L and 2 mg/L separately. The main removal mechanism of Cu²⁺and Zn²⁺ in the anaerobic methanation system was that the biological production of sulfide from sulfate was followed by chemical precipitation and reduction. It is helpful for the removal of Cu²⁺ and Zn²⁺ with organic pollutants simultaneously to eliminate environmental risk of swine wastewater.

Performance of DOuble Circulation Anaerobic Sludge bed reactor: Biomass self-balance

The calcification of Anaerobic Granular Sludge is a serious problem in the application of anaerobic methanization biotechnology. Regular replacement of calcified sludge with exogenous sludge is an effective method, but it is costly and troublesome. A new DOuble Circulation Anaerobic Sludge bed reactor was developed for the enhanced production of endogenous sludge to self-balance the discharge of calcified sludge. The sludge washout rate was demonstrated to fall by 45% and the sludge proliferation rate was shown to rise by 230%, offsetting the regular discharge of calcified sludge. The zoogloea in 100 μm dimension was revealed to be the intermediate component of sludge. The sludge proliferation mode was proposed as follows: (i) Growth of sludge; (ii) Self-cracking of sludge to release fragmental sludge; (iii) Migration of fragmental sludge by self-floatation; (iv) Accumulation of suspended sludge in the sedimentation chamber; (v) Re-granulation of suspended sludge with the aid of Venturi effect.

Influence of polyether sulfone microplastics and bisphenol A on anaerobic granular sludge: Performance evaluation and microbial community characterization

The retention of polyether sulfone (PES) and bisphenol A (BPA) in wastewater has received extensive attention. The effects of PES and BPA on the removal of organic matter by anaerobic granular sludge were investigated. We also analyzed the changes in the electron transport system and the effects on the composition of extracellular polymeric substances (EPS), as well as alternations of the microbial community in the anaerobic granular sludge. In the experimental groups which received BPA, the removal of the chemical oxygen demand (COD) were significantly suppressed, which an average removal efficiency of less than 65%, 30% lower than that of the control group. In the loosely-bound EPS (LB-EPS) excitation-emission matrix (EEM) spectra, the absorption peak of tryptophan disappeared when the BPA pollutants was added, which it was present in the control group without added pollutants. The addition of PES and BPA also affected protease, acetate kinase, and coenzyme F₄₂₀ activities in the anaerobic granular sludge. Especially, the coenzyme F₄₂₀ reduced from 0.0045 to 0.0017 μmol/L in the presence of PES and BPA. The relative abundance of Spirochaetes decreased in the presence of PES and BPA, while the relative abundance of Bacteroidetes increased from 12.98% to 22.87%. At the genus level, in the presence of PES and BPA, the relative abundance of Acinetobacter increased from 2.20% to 9.64% and Hydrogenophaga decreased sharply from 15.58% to 0.12%.

Cadmium Selenide Formation Influences the Production and Characteristics of Extracellular Polymeric Substances of Anaerobic Granular Sludge

Feeding cadmium (II) and selenium (IV) simultaneously to anaerobic granular sludge with the aim of synthesizing cadmium selenide (CdSe) nanoparticles induces compositional changes in the extracellular polymeric substances (EPS) matrix of this sludge. A methanogenic anaerobic granular sludge was repeatedly exposed to Cd(II) (10-50 mg L^-1) and selenite (79 mg L^-1) for 300 days at pH 7.3 and 30 °C in a fed-batch feeding regime for enrichment of Se-reducing bacteria and synthesis of CdSe nanoparticles. EPS fingerprints of the granular sludge, obtained by size exclusion chromatography coupled to a fluorescence detector, showed a significant increase in the intensity of protein-like substances with > 100 kDa apparent molecular weight (aMW) upon repeated exposure to Cd(II) and Se(VI). This was accompanied by a prominent decrease in protein-like substances of aMW < 10 kDa. The fingerprint of the humic-like substances showed emergence of a new peak with aMW of 13 to 300 kDa in the EPS extracted from the Cd/Se fed granular sludge. Experiments on metal(loid)-EPS interactions showed that the CdSe nanoparticles interact mainly with loosely bound EPS (LB-EPS). This study showed that the formation of Se(0) and CdSe nanoparticles occurs in the LB-EPS fraction of the granular sludge and repeated exposure to Cd and Se induces compositional changes in the EPS matrix.

A novel thermophilic anaerobic granular sludge membrane distillation bioreactor for wastewater reclamation

Membrane distillation (MD) has a high heat requirement. Integrating MD with thermophilic bioreactors could remedy this problem. A laboratory-scale thermophilic anaerobic granular sludge membrane distillation bioreactor (ThAGS-MDBR) was used to treat wastewater with a high organic loading rate (OLR). Waste heat from ThAGS was used directly for the MD process to reduce energy consumption. The result demonstrated that the ThAGS-MDBR system achieved a high-efficiency removal of chemical oxygen demand (more 99.5%) and NH₄⁺-N (96.4%). Furthermore, the highest methane production from the proposed system was 332 mL/g COD_removed at OLR of 16 kg COD/m³/day. Specifically, an aggregate of densely packed diverse microbial communities in anaerobic granular sludge was the main mechanism for the enhancement of bioreactor tolerance with environmental changes. High-quality distillate water from ThAGS-MDBR was reclaimed in one step with total organic carbon less than 1.7 mg/L and electrical conductivity less than 120 μS/cm. Furthermore, the result of the DNA extraction kit recorded that Methanosaeta thermophila was a critical archaea for high COD removal and bioreactor stability.

A comprehensive study of volatile fatty acids production from batch reactor to anaerobic sequencing batch reactor by using cheese processing wastewater

Volatile fatty acids (VFAs) has great potential for closed-loop production in dairy industries via resource recovery from waste-streams. In the current study, the transition of VFA production from batch reactor to anaerobic sequencing batch reactor (ASBR) by using cheese industry wastewater under alkali pH was evaluated with respect to seed sludge structure, microbial diversity and reactor type. The transition from the batch reactor to the ASBR demonstrated that the maximum VFA production yield (g COD/g SCOD) was comparable in two reactors (batch: 0.97; ASBR: 0.94), whereas, the dominant acid type was different (batch: 49% lactic acid; ASBR: 80% propionic acid). There was a significant correlation between the productions of butyric acid with Gracilibacteraceae and Desulfovibrionaceae; propionic acid with Desulfovibrionaceae and Synergistaceae; lactic acid with Pseudomonadaceae and Rhodocyclaceae. The high VFA production efficiency can be achieved by long term reactor operation, which enables the shift from industrial waste-streams to biorefineries.

Developing a high-quality catalyst from the pyrolysis of anaerobic granular sludge: Its application for m-cresol degradation

This study proposes a novel approach for utilizing granular sludge discharged from anaerobic reactors to prepare an effective and stable catalyst for the removal of refractory contaminants in catalytic wet peroxide oxidation (CWPO). By implementing the response surface methodology, the experimental conditions for m-cresol degradation in CWPO with a HNO₃-modified sludge carbon (GSC-M) as catalyst were explored. The removal efficiencies for m-cresol and total organic carbon (TOC) were 100% and 91.4%, respectively, at the optimal conditions of 60 °C for 120 min with a pH of 3, H₂O₂ dosage of 1.85 g/L, and catalyst dosage of 0.75 g/L. A continuous experiment was conducted for 6 d to investigate the durability and catalytic performance of GSC-M, resulting in a TOC removal above 90% with the catalyst maintaining its original morphology. GSC-M catalyst exhibited excellent stability and low iron leaching (0.34%). The high catalytic degradation could be attributed to a high content of iron species, various types of surface functional groups, porous structures, and the π-π interaction between aromatic clusters in sludge carbon and the benzene ring of m-cresol. Interestingly, GSC-M catalyst exhibited magnetic properties which are beneficial for recycling. Based on the identified intermediates, a possible degradation pathway of m-cresol was proposed.

Polystyrene nanoplastics reshape the anaerobic granular sludge for recovering methane from wastewater

Wastewater has been identified as an important carrier for nanoplastics, which could elicit unintended impacts on critical microbial processes. However, the long-term impacts of nanoplastics on anaerobic granular sludge (AGS) for methane recovery from wastewater and the mechanisms involved remains unclear. In this study, we investigated the long term exposure-response relationship between polystyrene nanoplastics (Nano-PS) and AGS. In continuous test over 120 days with 86 days' Nano-PS exposure, feeding wastewater with 10 μg/L of Nano-PS had no significant impacts on the AGS performance. In comparison, higher levels (i.e., 20 and 50 μg/L) of Nano-PS decreased methane production and chemical oxygen demand (COD) removal by 19.0-28.6% and 19.3-30.0%, respectively, along with volatile fatty acids (VFA) accumulation. More extracellular polymeric substance (EPS) was induced by 10 μg/L of Nano-PS as a response to protect microbes, but higher levels (i.e., 20 and 50 μg/L) of Nano-PS decreased EPS generation, causing a decline in granule size and cell viability. Fluorescence tagging found that a large number of Nano-PS agglomerated/accumulated on the outer layer of AGS and even transferred into deeper layers of AGS over exposure time, producing toxic effects to adherent microorganisms, e.g., Longilinea sp., Paludibacter sp. and Methanosaeta sp.. The oxidative stress induced by Nano-PS was revealed to be a key factor for reshaping the AGS, reflected by the increased reactive oxygen species (ROS) generation and lactate dehydrogenase (LDH) release. The sodium dodecyl sulfate (SDS) leached from Nano-PS was also demonstrated to restrain the activities of antioxidant enzymes, thereby further lessening resistance to oxidative stress induced by Nano-PS. This work improves our ability to predict the risks associated with this ubiquitous contaminant in the environment.

Laboratory and full-scale performances of integrated anaerobic granule-aerobic biofilm-activated sludge processes for high strength recalcitrant paint wastewater

Sustainable treatment of wastewaters generated from paint production is increasingly posing an environmental concern. Recalcitrant paint wastewaters are mostly treated by energy and cost intensive physicochemical methods like incineration, distillation or advanced oxidation. This paper reported for the first time a case study applying biological treatment processes to properly handle a high-strength recalcitrant paint wastewater with 5-day biochemical oxygen demand (BOD₅)/chemical oxygen demand (COD) less than 0.02. A biological treatment scheme integrating anaerobic granular sludge blanket reactor, aerobic carrier biofilm reactor and aerobic activated sludge bioreactor was proposed and examined. Laboratory and full-scale trials demonstrated satisfactory operation with overall COD removal up to 99%. Besides yielding consistent effluent quality conforming to the discharge limits, the full-scale plant gained considerable savings in operating cost over a 5-year operation. With proper microbial adaptation and cultivation, as well as adequate reactor and process designs, the scheme offers a good feasibility for efficient and cost-effective treatment of the high strength and recalcitrant paint wastewater.

Insights into the microbial response of anaerobic granular sludge during long-term exposure to polyethylene terephthalate microplastics

The negative effects of ubiquitous microplastics on wastewater treatment have attracted increasing attention. However, the potential impacts of microplastics on anaerobic granular sludge (AGS) remain unknown. To fill this knowledge gap, this paper investigated the response of AGS to the exposure of model microplastics (polyethylene terephthalate (PET-MPs)) and provided insights into the mechanisms involved. The 84 days' long-term exposure experiments demonstrated that PET-MPs, at relatively low level (15 MP L^-1) did not affect AGS performance during anaerobic wastewater treatment, while 75-300 MP L^-1 of PET-MPs caused the decreases of COD removal efficiency and methane yields by 17.4-30.4% and 17.2-28.4%, accompanied with the 119.4-227.8% increase in short-chain fatty acid (SCFA) accumulation and particle breakage. Extracellular polymeric substances (EPS) analysis showed that dosage-dependent tolerance of AGS to PET-MPs was attributed to the induced EPS producing protection role, but PET-MPs at higher concentrations (75-300 MP L^-1) suppressed EPS generation. Correspondingly, microbial community analysis revealed that the populations of key acidogens (e.g., Levilinea sp.) and methanogens (e.g., Methanosaeta sp.) decreased after long-term exposure to PET-MPs. Assessment of the toxicity of PET-MPs revealed that the leached di-n-butyl phthalate (DBP) and the induced reactive oxygen species (ROS) by PET-MPs were causing toxicity towards AGS, confirmed by the increases in cell mortality and lactate dehydrogenase (LDH) release. These results provide novel insights into the ecological risk assessment of microplastics in anaerobic wastewater treatment system.

Cation exchange membrane behaviour of extracellular polymeric substances (EPS) in salt adapted granular sludge

This paper aims to elucidate the role of extracellular polymeric substances (EPS) in regulating anion and cation concentrations and toxicity towards microorganisms in anaerobic granular sludges adapted to low (0.22 M of Na⁺) and high salinity (0.87 M of Na⁺). The ion exchange properties of EPS were studied with a novel approach, where EPS were entangled with an inert binder (PVDF-HFP) to form a membrane and characterized in an electrodialysis cell. With a mixture of NaCl and KCl salts the EPS membrane was shown to act as a cation exchange membrane (CEM) with a current efficiency of ∼80%, meaning that EPS do not behave as ideal CEM. Surprisingly, the membrane had selectivity for transport of K⁺ compared to Na⁺ with a separation factor ( [Formula: see text] ) of 1.3. These properties were compared to a layer prepared from a model compound of EPS (alginate) and a commercial CEM. The alginate layer had a similar current efficiency (∼80%.), but even higher [Formula: see text] of 1.9, while the commercial CEM did not show selectivity towards K⁺ or Na⁺, but exhibited the highest current efficiency of 92%. The selectivity of EPS and alginate towards K⁺ transport has interesting potential applications for ion separation from water streams and should be further investigated. The anion repelling and cation binding properties of EPS in hydrated and dehydrated granules were further confirmed with microscopy (SEM-EDX, epifluorescence) and ion chromatography (ICP-OES, IC) techniques. Results of specific methanogenic activity (SMA) tests conducted with 0.22 and 0.87 M Na⁺ adapted granular sludges and with various monovalent salts suggested that ions which are preferentially transported by EPS are also more toxic towards methanogenic cells.

A full-scale study of high-rate anaerobic bioreactors for whiskey distillery wastewater treatment with size fractionation and metagenomic analysis of granular sludge

Two full-scale high-rate bioreactors, i.e. external circulation sludge bed (ECSB) and expanded granular sludge bed (EGSB), were monitored for three years. Their performances for treating wastewater in a whiskey distillery were compared in terms of COD, pH, alkalinity and VFA. Even though feed flowrate highly fluctuated, COD removals of ECSB and EGSB were both excellent (95.7 ± 1.3% and 94.8 ± 3.0%, respectively). The influent and effluent characteristics of ECSB reactor were profiled and urea and urethane were also detected. High-strength properties of raw spent wash were exhibited in TOC, soluble COD and BOD5,20°C of 13500, 37750, and 1950 mg·L-1, respectively and characterized by GC-MS. Anaerobic granular sludge sampled from different heights of ECSB reactor were fractionated for demonstrating vertical size distributions. Moreover, major species found by next-generation sequencing technique were archaea, i.e. Methanosaeta and Methanolinea, while major bacteria were Bacteroidetes with minor Nitrospiraceae. This metagenomic analysis provided an insight of anaerobic microbial consortium.

Enhanced 2,4,6-trichlorophenol degradation and biogas production with a coupled microbial electrolysis cell and anaerobic granular sludge system

A coupled microbial electrolysis cell - anaerobic granular sludge system (MEC-AGS) was established to explore the degradation efficiency of 2,4,6-trichlorophenol (TCP) with synchronous biogas production. Results showed that MEC-AGS yielded a higher proportion of CH₄ than MEC (83.8 ± 0.4% vs 82.0 ± 1.0%, P < 0.05) with sodium acetate (NaAc) as the only carbon source. Moreover, MEC-AGS had higher tolerance to the addition of TCP, with the highest TCP degradation efficiency of 45.5 ± 0.5% under 5 mg L^-1 of TCP addition in 24 h. Furthermore, microbial community structures were significantly changed based on community composition, hierarchical cluster and PCoA analysis, which proved that MEC-AGS favored the enrichment of dechlorination-related microbes such as Pseudomonas, Desulfovibrio and Longilinea, as well as their syntrophic bacteria of Anaerolineacea, Syntrophobacter, Arcobacter, etc. The coupled system provides a promising strategy for biogas production from wastewater with recalcitrant organics.

Effects of biogenic nanopalladium precipitation on the performance and microbial community structure of anaerobic granular sludge

Biogenic nanopalladium (BioPd) catalysts have drawn increasing attentions recently as a combination of metal catalyst over the support of biomass. Anaerobic granular sludge (AGS), as a special microbial granule, demonstrates a strong potential to reduce Pd(II) and precipitate Bio-Pd in the sludge body. The problem how the Bio-Pd precipitates would influence the function and microbial community of the Pd hosting AGS (Pd-AGS) remains unknown. In this study, Pd-AGS with different Bio-Pd loadings (1.7, 3.0, 4.4 and 8.0 wt% of Pd) was obtained through bio-reduction at different Na₂PdCl₄ concentrations. Effects of Bio-Pd precipitates on acidogenesis and methanogenesis of AGS were assayed. Response of bacterial and archaeal community of AGS towards Bio-Pd precipitation were also revealed based on high-throughput sequencing data on Illumina Miseq platform. Results showed that Bio-Pd precipitates affected the acidogenesis and methanogenesis process of the Pd-AGS, as the produced total volatile fatty acids (VFA) and methane were reduced by 25.8-53.0% and 33.9-87.7%, respectively, comparing to the native AGS. Bio-Pd precipitation resulted in microbial community shift and a decrease in the microbial diversity. The bacterial community suffered more influence than the archaeal community. Hydrogenotrophic methanogens were more sensitive to the toxicity of Pd(II)/Bio-Pd than acetotrophic methanogens. Overall, when the heterogeneous Pd-AGS catalyst is designed to possess both the function of microbial metabolism and Pd catalysis, it is necessary to control a suitable Pd(II) concentration during reduction process and the final Bio-Pd loading in AGS (<4.4 wt% of Pd).