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The secondary fermentation stage is critical for stabilizing composting products and producing various secondary metabolites. However, the low metabolic rate of mesophilic bacteria is regarded as the rate-limiting stage in composting process. In present study, two indoleacetic acid (IAA)-producing bacteria (Bacillus safensis 33C and Corynebacterium stationis subsp. safensis 29B) were inoculated to strengthen the secondary fermentation stage to improve the plant-growth promoting potential of composting products. The results showed that the addition of IAA-producing bacteria promoted the assimilation of soluble salt, the condensation and aromatization of humus, and the accumulation of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC). The bioaugmentation strategy also enabled faster microbial community succession during the medium-late phase of secondary fermentation. However, the colonization of Bacillus and Corynebacterium could not explain the disproportionate increase of IAA yield, which reached up to 5.6 times compared to the control group. Deeper analysis combined with physicochemical properties and microbial community structure suggested that IAA-producing bacteria might induce the increase of salinity, which enriched halotolerant bacteria capable of producing IAA, such as Halomonas, Brachybacterium and Flavobacterium. In addition, the results also proved that it was necessary to shorten secondary fermentation time to avoid IAA degradation without affecting composting maturity. In summary, enhancing secondary fermentation of composting via adding proper IAA-producing bacteria is an efficient strategy for upgrading the quality of organic fertilizer.

Anaerobic digestion (AD) has been widely applied for the degradation of organic wastewater due to its advantages of high-load operation and energy recovery. However, some challenges, such as low treatment capacity and instability caused by the accumulation of volatile fatty acids, limit its further application. Here, S. wolfei and G. sulfurreducens were initially co-cultured in the anaerobic anode of bio-electrochemical system for degrading butyric acid. Butyrate degradation characteristics in different conditions were quantitatively described. Moreover, G. sulfurreducens simultaneously strengthened the consumption of H

The safe disposal of antibiotic mycelial residue (AMR), a hazardous waste, is a pressing problem owing to the spread of antibiotic and heavy metal pollution. In this study, AMR pyrolysis at different temperatures and heating rates was investigated to prepare valuable biochar for heavy metal immobilization. The results showed that AMR decomposition mainly involved three pseudo-reactions, with average activation energies of 252.4, 149.8, and 219.7 kJ/mol, that fitted a three-dimensional diffusion model. Increasing the pyrolysis temperature and heating rate decreased the yield and volatile matter content of biochar, but the ash content, fixed carbon content, and aromaticity increased. The AMR-derived biochar had a favorable fuel property (18.1-19.8 MJ/kg) and stability against degradation in soil. Calcium oxalate hydrate, a major mineral in AMR, degraded during biochar formation. Furthermore, high pyrolysis temperature promoted the residual fractions of Cr, Cu, Zn, Cd, and Pb in biochar, more so than did the heating rate, inducing a low potential ecological risk. In particular, the leaching rate of Zn decreased from 46.9% in AMR to 0.3% in biochar obtained at 700 °C with a heating rate of 10 °C/min. This study elucidates the formation process and physicochemical properties of AMR biochar, which helps in the harmless utilization of AMR as a carbon resource.

Constructed wetlands have been widely used for organic wastewater treatment owing to low operating costs and simple maintenance. However, there are some disadvantages such as unstable efficiency in winter. In this study, a microalgal electroactive biofilm-constructed wetland was coupled with anaerobic digestion for full-scale treatment of swine wastewater. In a 12-month outdoor trial, the overall removal efficiencies of chemical oxygen demand, ammonium, nitrate, total nitrogen, total phosphorus, and nitrite reached 98.26%/95.14%, 97.96%/92.07%, 85.45%/66.04%, 95.07%/91.48%, 91.44%/91.52%, and 85.45%/84.67% in summer/winter, respectively. Hydrolytic bacteria were dominant in the anaerobic digestion part, and Cyanobium, Shewanella, and Azoarcus were enriched in the microalgal electroactive biofilm. The operating cost of the entire system was approximately 0.118 $/m

The anionic detergent sodium dodecyl benzene sulfonate (SDBS) inhibits anaerobic solid waste fermentation process in mesophilic anaerobic digesters. In this study, the effect SDBS on the pe...

Supplementing nano zero valent iron (nZVI) is an attractive technology for wastewater treatment due to its advantages in accelerating the hydrolysis, fermentation and anaerobic digestion (AD) process. In this present study, nZVI was added to investigate its effects on enhancing tetracycline (TC) wastewater anaerobic treatment and the changes of microbial community, especially for underestimated syntrophic-methanogenic associations. The TC concentrations were 1, 10, 30, 50, 80, 100 and 150 mg/L with 0.38 g nZVI (with iron g/g VS of 0.50) complemented into reactors. Results revealed that nZVI could enhance AD process in both control and TC dosed systems, and the promoting effect on methanogenesis was more significant in systems of high concentration TC, with 100 and 150 mg/L. In addition, cumulative CH4 production for all TC added systems without nZVI were higher than the control indicating TC had positive effect instead of expected negative effect on AD process, high TC concentration of 100 and 150 mg/L only affecting the increase factor rather than causing inhibitory effect. After digestion, TC was largely removed in with/without nZVI systems. And also, nZVI evidently altered the bacterial and methanogenic community structure, with an increase abundance of syntrophic-methanogenic associations (Syntrophobacterales and Methanosarcinales) and resulting in the enhancement of methane generation. This research provides an efficient method for TC wastewater anaerobic treatment.

Acidic anaerobic digestion attracted much attention and interest due to its significant advantage in wastewater treatment. In the present study, methanogenic fermentation was successfully operated under acidic condition during treating wastewater containing oxytetracycline (OTC) in a scale up anaerobic baffled reactor (ABR). After start-up process, the pH value in the first compartment was 4.60 with high activity of methanogenesis. After stabilization, different OTC loading of 1.0, 3.3 and 5.0 g/m3/d was added in the influent for OTC removal. The resulted showed that OTC addition had little impact on the methane generation with whole COD and OTC removal rate of 95% and 60%, respectively. The microbial analysis, OTC addition could significantly influence the bacteria and archaea communities. To be more specific, Methanosaeta showed the highest relative abundance and tolerance to OTC under acidic condition. The present work supplied deeper insights into methane generation from acidic condition during wastewater containing OTC treatment.

Conductive materials presented promising advantages for enhancing anaerobic digestion (AD) performance. This study evaluated the effects of activated carbon (AC) and nano-zero-valent iron (nZVI) on the acidogenesis and whole AD to explore their potential mechanisms. AC increased the content of lactic and propionic acids in acidogenesis. nZVI increased the production of formic acid, acetic acid and H2 in acidogenesis, thus significantly promoted the methane yield in the whole AD. Mechanism exploration proved that AC enriched Trichococcus, and norank_f__Bacteroidetes_vadinHA17, and then improved the activity of enzymes involved in the production of lactic and propionic acids. nZVI buffered the pH to increase the activity of pyruvate formate-lyase (PFL) in formic acid production. Furthermore, nZVI enriched the Methanobacterium which use H2 and formic acid as substrate. The research paves pathway for the efficient enhancement of conductive materials added novel AD process.

Acetate is a pivotal intermediate product during anaerobic decomposition of organic matter. Its generation and consumption network is quite complex, which almost covers the most steps in anaerobic digestion (AD) process. Besides acidogenesis, acetogenesis and methanogenesis, syntrophic acetate oxidation (SAO) replaced acetoclastic methanogenesis to release the inhibition of AD at some special conditions, and the importance of considering homoacetogenesis had also been proved when analysing anaerobic fermentations. Syntrophic acetate-oxidizing bacteria (SAOB), with function of SAO, can survive under high temperature and ammonia/ volatile fatty acids (VFAs) concentrations, while, homoacetogens, performed homoacetogenesis, are more active under acidic, alkaline and low temperature (10°C-20°C) conditions, This review summarized the roles of SAO and homoacetogenesis in AD process, which contains the biochemical reactions, metabolism pathways, physiological characteristics and energy conservation of functional bacteria. The specific roles of these two processes in the subprocess of AD (i.e., acidogenesis, acetogenesis and methanogenesis) were also analyzed in detail. A two phases anaerobic digester is proposed for protein-rich waste(water) treatment by enhancing the functions of homoacetogens and SAOB compared to the traditional two-phases anaerobic digesters, in which the first phase is fermentation phase including acidogens and homoacetogens for acetate production, and second phase is a mixed culture coupling syntrophic fatty acids bacteria, SAOB and hydrogenotrophic methanogens for methane production. This review provides a new insight into the network on production and consumption of acetate in AD process.

The accumulation of volatile fatty acids, particularly propionic acid, significantly inhibits the efficiency of the anaerobic digestion system. In propionate degradation metabolism, the unfavorable thermodynamics of syntrophic reactions, strict ecological niche of syntrophic priopionate oxidizing bacteria, and slow metabolic rate of methanogens are regarded as major limitations. In this study, Geobacter sulfurreducens was co-cultured with Syntrophobacter fumaroxidans in bioelelectrochemical cells to analyze the propionate degradation process, impact factor, mechanism metabolic pathways, and electron transfer comprehensively. The results revealed that the syntroph S. fumaroxidans and syntrophic partner G. sulfurreducens achieved more efficient propionate degradation than the control group, comprising S. fumaroxidans and methanogens. Moreover, the carbon resource concentration and pH were both significantly correlated with propionate degradation (P < 0.01). The results further confirmed that G. sulfurreducen strengthened the consumption of H2 and acetate via direct interspecific electron transfer in propionate degradation. These findings indicate that G. sulfurreducens plays an unidentified functional role in propionate degradation.

Anaerobic digestion (AD) is widely used on waste treatment for its great capability of organic degradation and energy recovery. Accumulation of volatile fatty acids (VFAs) caused by impact loadings often leads to the acidification and failure of AD systems. Bioaugmentation is a promising way to accelerate VFA degradation but the succession of microbial communities usually caused unpredictable consequences. In this study, we used the sludge previously acclimated with VFAs for the bioaugmentation of an acidified anaerobic digestion system and increased the methane yield by 8.03-9.59 times. To see how the succession of microbial communities affected bioaugmentation, dual-chamber devices separated by membrane filters were used to control the interactions between the acidified and acclimated sludges. The experimental group with separated sludges showed significant advantages of VFA consumption (5.5 times less final VFA residue than the control), while the group with mixed sludge produced more methane (4.0 times higher final methane yield than the control). Microbial community analysis further highlighted the great influences of microbial interaction on the differentiation of metabolic pathways. Acetoclastic methanogens from the acclimated sludge acted as the main contributors to pH neutralization and methane production during the early phase of bioaugmentation, and maintained active in the mixed sludge but degenerated in the separated sludges where interactions between sludge microbiotas were limited. Instead, syntrophic butyrate and acetate oxidation coupled with nitrate and sulfate reduction was enriched in the separated sludges, which lowered the methane conversion rate and would cause the failure of bioaugmentation. Our study revealed the importance of microbial interactions and the functionality of enriched microbes, as well as the potential strategies to optimize the durability and efficiency of bioaugmentation.

Ciprofloxacin is the most commonly prescribed antibiotic, and its widespread use poses threat to environmental safety. The removal of ciprofloxacin from contaminated water has remained a major challenge. The present study investigated adding nanoscale zero-valent iron (NZVI) and activated carbon (AC) on high-level ciprofloxacin removal in hydrolysis-acidogenesis stage of anaerobic digestion. The results showed that the degradation rate of ciprofloxacin increased from 22.61% (Blank group) to 72.41% after adding NZVI/AC with concentration of ciprofloxacin in effluent decreasing from 8.25 mg L−1 to 3.48 mg L−1. The volatile fatty acids (VFAs) yield increased by 173.7% compared with the Blank group. In addition, the NZVI/AC group achieved the highest chemical oxygen demand (COD) removal rate and acidogenesis rate. The microbial community analysis presented that hydrolytic and acidogenic bacteria and microorganisms related to degrading ciprofloxacin were obviously improved in the NZVI/AC group. Moreover, eleven transformation products and the main degradation pathways were proposed based on mass spectrometry information. In summary, the NZVI/AC addition supplied promising approach for ciprofloxacin wastewater treatment.

Aiming at relieving acid accumulation in anaerobic digestion (AD), syntrophic associations of syntrophic fatty acid-oxidation bacteria and H

Physical structures of sludge are critical factors determining the performance of the anaerobic digestion process, especially for the rate-limiting step, methanogenesis. Thus, to evaluate the effect of granular physical structure on methanogenesis and methanogenic community variation, intact and disintegrated granules were applied as inocula with formate, hydrogen and acetate as sole substrates in batch reactors. Kinetics results revealed that the physical structure of sludge had little impact on methane yield potential from three substrates, while a significantly different impact on methanogenesis rates of formate, hydrogen and acetate. The methanogenesis rate of formate in disintegrated granules was higher than that in the intact granular system, the methanogenesis rate of H2/CO2 in the intact granular system was higher than that in the disintegrated granules and the methanogenesis rate of acetate was similar with the in intact and disintegrated granular systems. Besides, in both intact and disintegrated granular systems, methanogenesis rates of formate were the highest, then followed the H2/CO2 and acetate was the lowest, indicating formate consumption has an advantage over hydrogen in the studied system. A microbial assay indicated that Methanobacteriales, Methanosarcinales and Methanomicrobiales are dominant methanogens on the order level, and the physical structure of granular sludge has little influence on methanogenic communities on the order level but showed significant influence on the species level. It enlightens us that the physical structure of sludge could be considered for regulating the anaerobic digestion via influencing the methanogenesis rates.

Enriching suitable fermentative products by optimizing operation conditions could effectively improve the efficiency of anaerobic digestion. In the present study, pH (5.0-6.0) and hydraulic retention time (HRT) (2 h-12 h) were regulated for volatile fatty acids (VFAs) production during glucose fermentation in acidogenic continuous stirred tank reactor (CSTR). Results showed that acetate and butyrate dominated during pH regulation. HRT reduction favored butyrate production and formate retainment. Maximum total VFAs production with highest acetate content was achieved at pH of 6.0 and HRT of 6 h. Microbial analysis revealed that Clostridium_sensu_stricto_1 was predominant butyrate producer during pH regulation, and Bacteroides was main contributor when HRT shorter than 6 h. In addition to acetyl-CoA pathway, acetate could also be produced via homoacetogenesis by Parabacteroides, UCG-004 and norank_f__Acidaminococcaceae. These results give guidance for enhancing targeted VFAs products by optimizing operational parameters or bio-augmentation with specific bacteria.

Composting, as an effectively bio-oxidative process, has been widely used for converting organic waste to organic fertilizer. However, the low fertilizer efficiency of composting product limited its application in agriculture. To improve the growth-promoting effect of composting product, the present study investigated the bioaugmentation strategy of inoculating indole-3-acetic-acid (IAA)-producing bacteria. Firstly, two IAA-producing bacteria (Bacillus safensis 33C and Rhodococcus rhodochrous YZ) were isolated from composting products with high IAA yields of 39.18 and 16.32 μg mL-1, respectively. Secondly, the microbial inoculants were prepared with 33C, YZ and a previously isolated IAA-producing strain Corynebacterium stationis 29B. To increase the accumulation of microbial secondary metabolites, microbial inoculants were amended at the secondary fermentation stage of composting. Physicochemical characterization showed that the maturity of composting product was significantly promoted by inoculating microbial inoculants prepared with 33C and 29B (single and combined inoculants). Finally, bioaugmentation with 33C and 29B increased the IAA contents of composting products by 2.9-5.2 times, which benefited the germination and early vegetative growth of plants. In summary, inoculating proper IAA-producing bacteria during secondary fermentation of composting could improve the quality of composting product and expand its application.

In this study, the performances of a conventional anaerobic baffled reactor (ABR) and an ABR combined with microbial electrolysis cells (MECs) for enhancing degradation of volatile fatty acids (VFAs) were evaluated in 55°C. The ABR-MECs system achieved a total chemical oxygen demand (COD) removal rate of 97.2% and a methane yield of 236 ± 5 mL g-1 CODremoved at organic loading rate (OLR) of 6.9 kg COD m-3 d-1, which were higher than those of the ABR with 77.6% and 207 ± 5 mL g-1 CODremoved, respectively, at OLR of 5.1 kg COD m-3 d-1. The pyrosequencing analysis confirmed that the introduction of MECs into ABR was conducive to establishing stable functional communities of syntrophic fatty acids oxidizing bacteria (SFOB), exoelectrogens and hydrogenotrophic methanogens, such as Syntrophobacter (5.4%), Thermodesulfovibrio (2.0%), Methanobacterium (43.8%), Methanolinea (20.4%). The content of unclassified bacteria increased from 12.4% in the ABR system to 52.3% in the ABR-MECs system. In contrast, the proportion of aceticlastic methanogens decreased from 50.1% in the ABR to 24.5% in the ABR-MECs system. The improved performance of the thermophilic ABR-MECs system resulted from phase separation, wide ecological niche and intensification of methanogenesis process via functional microbes, which significantly enhanced the degradation of propionic acid and acetic acid.

Surfactants are widely used and discharged into wastewater treatment plants, which might influence the anaerobic digestion (AD) treatment of municipal waste. In this study, the effects of typical anionic surfactants sodium dodecyl benzene6 sulfonate (SDBS) and non-ionic surfactants APG, on mesophilic anaerobic co-digestion of sludge, food waste, and green waste were investigated. Results indicated that at 5 mg/g, the biogas production was inhibited in SDBS supplemented systems while stimulated in APG-added reactors, with the methane yield of 146.58 L/g VS consumed. At 15 mg/g, the biogas production in both SDBS and APG supplemented reactors was both inhibited. It means the negative or positive effect of APG on AD depends on the dose of APG supplementation. The 16S rRNA gene analysis demonstrated the microbial community structure in the digester was changed due to the addition of surfactant.

Conductive material assisted anaerobic digestion presented much interest and promising prospect in pollutant removal during wastewater treatment. The present study deeply investigated the effect iron/carbon in anaerobic digestion for dichlorophen (DCP) degradation and methane production in synthetic DCP wastewater treatment. Results showed that nano-zero valent iron/activated carbon (nZVI/AC) and zero valent iron/activated carbon (ZVI/AC) gave higher chemical oxygen demand (COD) conversion (42.18% and 42.61%) and DCP removal (98.49 wt% and 99.00 wt%) in acidification step with better methane production from anaerobic digestion of the pretreated effluent. Same phenomenon occurred in the direct anaerobic degradation process due to the formation of galvanic cells between iron and carbon. In comparison, applying iron/carbon in acidification as pretreatment strategy plus following effluent anaerobic degradation showed higher efficiency in methane production and DCP removal than that of direct anaerobic degradation. Specifically, the methane production was 253.70 mL and 253.41 mL in subsequent anaerobic digestion system after nZVI/AC and ZVI/AC acidification pre-treatment, which was higher than 224.37 mL and 246.31 mL in direct anaerobic digestion system. Microbial community analysis showed that Clostridium_sensu_stricto_1 was the dominated bacteria due to its important role in DCP wastewater treatment. Both acetoclastic and hydrogenotrophic methanogens were enhanced in iron/carbon added systems, which was also agreement with the strengthen in related genes involved in methanogenesis. In conclusion, the present work systematically investigated the enhancement role of iron/carbon system in anaerobic digestion for DCP wastewater treatment and paved way for future application.

In this study, an anaerobic baffled reactor (ABR) coupled with a microbial electrolysis cell (MEC) was set up to treat carbohydrate-containing wastewater at 55 ± 1 °C. The MEC was employed to accelerate the degradation of volatile fatty acids (VFAs). The removal of chemical oxygen demand (COD) and production of methane and the corresponding kinetics were determined for different organic load rates (OLRs). The highest COD removal rate was 95.8% at an OLR of 7.0 kg COD m−3 d−1, but it declined to 90.4% when the OLR was 19.4 kg COD m−3 d−1 and finally stabilized at 65.3% when the OLR was increased to 34.3 kg COD m−3 d−1. The volumetric production of methane was 1.5 L (L−1 d−1) when the OLR was 7.0 kg COD m−3 d−1 and increased to 4.1 L (L−1 d−1) at an OLR of 34.3 kg COD m−3 d−1, when the methane yield stabilized at 0.20-0.25 L g−1 CODremoved. The kinetics and predictions according to the Stover-Kincannon and Van der Meer-Heertjes models closely agreed with the experimental data for the removal of COD and volumetric production of methane, respectively. An analysis of the microbial community suggested that hydrolytic bacteria, syntrophic fatty acid-oxidizing bacteria (SFOB), exoelectrogens and hydrogenotrophic methanogens achieved a significant synergistic effect and enhanced the degradation of VFAs, which made the thermophilic anaerobic system stable and efficient at high OLRs.

In this study, anaerobic batch experiments were conducted to investigate the effect of carbon-based (biochar) and metal-based (nanoscale zero-valent iron, NZVI and zero valent iron, ZVI) mediators on the AD process treating phenolic wastewater. Fresh apricot shell- and wood-derived biochar (BiocharA, BiocharB) could remove the phenol efficiently (77.1% and 86.2%), suggesting that biodegradation cooperated with adsorption had advantage in phenol removal. BiocharB, NZVI and ZVI enhanced the methane production by 17.6%, 23.7% and 23.2%, respectively. Apart from serving as carrier for microbial growth, BiocharB might promote the direct interspecies electron transfer (DIET) since the Anaerolineaceae/Clostridium sensu stricto, which have potential for DIET, were enriched. NZVI and ZVI added systems mainly enhanced the abundance of Clostridium sensu stricto (24.5%, 37.6%) and Methanosaeta. Interestingly, BiocharA inhibited the methanogenesis completely. An inhibitory mechanism was proposed: the exposure of absorbed microbes on the BiocharA to the highly concentrated phenol in biochar' pores resulted in the inhibition of methanogens, especially for Methanosarcina. In conclusion, this study showed that suitable biochar (BiocharB) could serve as an alternative redox mediator for realizing simultaneously the efficient phenol removal and methane production.

The anaerobic bio-treatment of lower COD/SO42- ratio wastewater constitutes a bottle-aqneck due to the limited carbon source. In this type of environment, interactions between acidogenic fermentation bacteria and methane-producing bacteria (MPB) are aided by syntrophic fatty acid oxidation bacteria present in the functional niche; MPB and sulfate-reducing bacteria (SRB) compete with each other due to the availability of sulfate. Therefore, introduction of syntrophic fatty acid oxidation bacteria into an SRB dominated culture can achieve maximum utilization of the substrate, weakening the competition of MPB. In this study, the mixed culture of dominant syntrophic propionate oxidation bacteria (SPOB) and SRB was established and characterized at 35°C. The dominant SPOB and SRB were enriched in a continuous flow stirred-tank reactor and in batch experiments, respectively. Subsequently, an equal proportion of the enriched sludge was mixed and incubated in conical flasks with propionate as the sole substrate. S...

Sludge filtrate is a kind of special organic wastewater generated from hydrothermally pretreated sewage sludge. The efficient treatment of sludge filtrate can promote the development of sludge recycling technology. Herein, the anaerobic baffled reactor (ABR) assisted by symbionts of short chain fatty acid-oxidation syntrophs (SFAS) and exoelectrogens was applied to treat the sludge filtrate. The influence of fermentation temperature and promotion of methanogenesis via symbionts were focused. The results showed that the COD removal efficiency and methane yield of the ABR system assisted by symbionts at 35 °C (R3) were 11.7% and 11.0% higher than the one at 55 °C (R2), respectively. And the COD removal efficiency and methane yield of the R2 system were 9.1% and 12.9% higher than the traditional ABR system at 55 °C (R1), respectively. Large abundances of exoelectrogens such as Thermincola and Geobacter were found in the R2 and R3 systems, respectively. Moreover, ample Syntrophobacter, Syntrophomonas and Methanobacterium were detected in both R2 and R3 systems. The present research revealed the importance of SFAS, exoelectrogens and hydrogenotrophic methanogens for the improvement of methanogenesis. Besides, the mesophilic condition is conducive to enhancing the methanogenesis rate of sludge filtrate.

The growing amount of sewage sludge from wastewater treatment plant is an emerging challenge in China. The efficient anaerobic digestion of sludge filtrate generated from hydrothermally pretreated sewage sludge can promote the disposal of sewage sludge. Herein, a pilot-scale anaerobic baffled reactor (ABR) assisted by symbionts of short chain fatty acid-oxidation syntrophs (SFAS) and exoelectrogens was developed to improve its stability and efficiency for filtrate treatment. The results demonstrated that the symbionts of exoelectrogens and SFAS, which were enriched by introduction of electrodes in the ABR system, promoted the degradation of butyric, propionic and acetic acids. Therefore, the COD removal efficiency increased from 74.1% to 86.6% and the methane content increased from 81.5% to 92.2% with methane production rising from 241 to 282 mL/g CODremoved. Furthermore, the economic evaluation indicated that the energy consumption of electrodes was 0.600 kWh/m3 of sludge filtrate, the net energy profited from increased methane was 2.344 kWh/m3 of sludge filtrate. These results confirmed that the ABR system assisted by symbionts of SFAS and exoelectrogens was feasible for treatment of sludge filtrate in terms of both technical and economic level through pilot-scale verification.

Hydrothermal pretreatment was used for dewatering food waste digestate residue, and biochar/biogas were generated from the separated solid and liquid phases via pyrolysis and anaerobic digestion, respectively. Increasing hydrothermal pretreatment temperature (110–200 °C) clearly improved dewaterability, whereas enhancing treatment duration (30–90 min) had little impact. The optimal condition of 160 °C/30 min gave the best dewatering performance with relative lower energy consumption and was chosen for pilot-scale verification achieving 61.7 wt% dry weight content after mechanical squeezing. Moreover, the filtrate and filter cake obtained at optimal condition were applied for biogas and biochar production in lab scale. The methane yield of the filtrate was 335 mL/g COD. Pyrolysis temperature of 500 °C gave better biochar performance and was verified in a pilot scale test. Additionally, the heavy metals in digestate were effectively immobilized during hydrothermal dewatering and pyrolysis processes. In the end, mass/energy balance calculated using pilot-scale data presented the combined systems provided a promising strategy for accomplishing energy recovery and resource reuse of digestate residue.

Anaerobic co-digestion (AcoD) is proved as an effective approach to solving a bottleneck problem of the low biogas yield in agricultural biomass waste treatment with anaerobic digestion (AD) technology. The present study investigated the effect of C/N radio, organic loading rate (OLR) and total solids (TS) contents on reactor performance in AcoD of pig manure and corn straw for simultaneous biogas and biogas slurry production. It was found that the highest biogas production was obtained at C/N ratio of 25, while the best biogas slurry performance was achieved at C/N ratio of 35. And high OLR and TS resulted in good performances in both biogas production and biogas slurry. At last, the microbial community analysis suggested that Bacteroidetes played a significant role in AcoD process. Acetoclastic methanogenesis was the main pathway for methane production in the stable system. And changing operational parameters could transform and shift the microbial community.

This study employed high-throughput quantitative PCR and 16S rRNA sequencing to evaluate the effect of temperature and residual antibiotics on the dynamics of antibiotic resistance genes (ARGs) and microbial communities during anaerobic digestion of swine manure. The abundances of total ARGs and 16S rRNA genes significantly decreased in all of four treatments (25°C, 37°C, and 37°C with 50 mg of wet weight antibiotics of body weight, and 55°C). The abundances of most ARG types were significantly correlated with those of the 16S rRNA gene and transposase gene (P < 0.01). However, the abundances of total ARGs at 55°C were much higher than those of other treatments. Meanwhile, the microbial communities at 55°C, where the Streptococcus pathogen remained at a relatively high abundance and cellulose degraders and hydrogen producers, such as Ethanoligenens and Coprococcus bacteria, increased, were markedly different from those of other treatments. Redundancy analysis indicates that temperature, pH, and the genus Streptococcus had the highest explanation for ARG variation among experimental factors, chemical properties, and representative genera, respectively. Network analysis further showed that the genus Streptococcus contributed greatly to the higher ARG abundance at 55°C. The moderate antibiotic residue only caused a slight and transitory inhibition for microbially diverse populations and promotion for ARG abundance, probably due to the degradation of antibiotics and microbial adaptability. Our results clarify the cooperativity of gene transfer-related items on ARG variation and intensively prove that higher temperature cannot always achieve better ARG removal in anaerobic digestion unless pathogens and gene transfer elements are more efficiently inhibited. IMPORTANCE Antibiotic resistance genes (ARGs) are frequently detected with high abundance in manure-applied soils. Anaerobic digestion is one of widely used processes for animal waste treatment. Thus, it is critical to understand the potential of anaerobic digestion to attenuate ARGs. Although some previous studies recommended thermophilic digestion for ARG removal, they did not get sufficient evidence to support this view. The antibiotics applied to animals are mostly excreted through feces and urine because of incomplete metabolism. It is indispensable to know whether residual antibiotics in manure will hinder ARG attenuation in anaerobic digesters. The significance of our research is in comprehensively understanding the evolution and mechanism of ARGs in anaerobic digestion of swine manure affected by temperature and residual antibiotics, which will allow the development of an ARG elimination strategy before their release into the environment.

Interspecies electron transfer (IET) between syntrophic fatty-acid oxidizing bacteria (SFOBs) and methanogens decided the performance of anaerobic digestion. Electron shuttles, as potential IET accelerators, were controversial concerning their influences on methanogenesis. In this study, concentration-dependent effects of anthraquinone-2-sulfonate (AQS) and cysteine on glucose digestion were firstly demonstrated: low dosage of AQS and cysteine (50 and 100 µM, respectively) had highest methane yield (133.5% and 148.6%, respectively). Using butyrate as substrate, distinct tendencies towards the enrichment of methanogenic community were further revealed. Cysteine just acted as a reductant which lowered ORP quickly and enriched most methanogens. It benefited methanogenesis right until methanogenic substrates accumulated. AQS, however, showed characteristic features of electron shuttles: it was firstly oxidized by SFOBs and then reduced by hydrogenotrophic methanogens, which accelerated methanogenic butyrate degradation. This study showed wide spectrum of SFOBs and methanogens benefited from the addition of electron shuttles, which laid foundation for future application.

Growing environment problem and emphasis of environmental protection motivate intense research efforts in exploring technology to improve treatment efficiency on refractory organic pollutants. Hence, finding a method to make up for the deficiency of anaerobic digestion (AD) is very attractive and challenging tasks. The recent spark in the interest for the usage of some nanomaterials as an additive to strengthen AD system. The adoption of iron compounds can influence the performance and stability in AD system. However, different iron species and compounds can influence AD system in significantly different ways, both positive and negative. Therefore, strengthening mechanism, treatment efficiency, microbial community changes in Nanoscale Zero Valent Iron (nZVI) and Fe3O4 nanoparticles (Fe3O4 NPs) added AD systems were summarized by this review. The strengthening effects of nZVI and Fe3O4 NPs in different pollutants treatment system were analyzed. Previous study on the effects of nZVI and Fe3O4 NPs addition on AD have reported the concentration of nZVI and Fe3O4 NPs, and the types and biodegradability of pollutants might be the key factors that determine the direction and extent of effect in AD system. This review provides a summary on the nZVI and Fe3O4 NPs added AD system to establish experiment systems and conduct follow-up experiments in future study.

Anaerobic methane production from paddy soils plays an important role in global methane emissions. Syntrophic-methanogenic associations have been viewed as a key regulator of methane generation in paddy fields. However, the effects of rice phenology on the diversity and abundance of syntrophic and methanogenic communities remain largely unknown. This study investigated the changes in syntrophic-methanogenic associations at different rice growth by comparing the 16S RNA sequences of total (DNA-based) and active (RNA-based) microbial communities in rhizosphere and bulk soils. Moreover, the concentrations of specific syntrophs and methanogens were quantified using qPCR assay. Statistical significant differences in the alpha and beta diversities were observed between DNA-based and RNA-based syntrophic communities. The relative abundance of syntrophs in rhizosphere soil was significantly higher at RNA level compared to that at DNA level, indicating that syntrophs display considerably high specific activities. Syntrophic bacteria accounted for 6.23–6.81% of the active communities in rhizosphere soil and 6.12–6.71% in bulk soil. Besides, the quantities of methanogens increased over the entire period of rice growth, and peaked at flowering stage. Such changing pattern was consistent with the total number of short-chain fatty acids-degrading syntrophs at flowering stage, suggesting that rice phenology can affect both syntrophic and methanogenic activities. Furthermore, not only environmental factors (e.g., pH and SOC), but also organic acids (e.g., citrate and succinate), shaped the composition and abundance of syntrophic and methanogenic communities in paddy soils.

For evaluating the methanogenesis from typical methanogenic precursors (formate, acetate and H2/CO2), CH4 production kinetics were investigated at 37±1°C in batch anaerobic digestion tests and stimulated by modified Gompertz model. The results showed that maximum methanation rate from formate, acetate and H2/CO2 were 19.58±0.49, 42.65±1.17 and 314.64±3.58NmL/gVS/d in digested manure system and 6.53±0.31, 132.04±3.96 and 640.16±19.92NmL/gVS/d in sewage sludge system during second generation incubation. Meanwhile the model could not fit well in granular sludge system, while the rate of formate methanation was faster than from H2/CO2 and acetate. Considering both the kinetic results and microbial assay we could conclude that H2/CO2 methanation was the fastest methanogenic step in digested manure and sewage sludge system with Methanomicrobiales as dominant methanogens, while granular sludge with Methanobacteriales as dominant methanogens contributed to the fastest formate methanation.

Aiming at relieving acid accumulation in anaerobic digestion (AD), syntrophic associations of syntrophic fatty acid-oxidation bacteria and H2/formate-scavenging methanogens were enriched by feeding propionate, butyrate and formate in an up-flow anaerobic sludge blanket (UASB) reactor. Results showed that methane yield increased by 50% with increasing formate concentration (0–2000 mg COD/L). In addition, the abundance and quantity of SFOB (Syntrophobacter, Smithella and Syntrophomonas) and H2/formate-scavenging methanogens (Methanobacteriales and Methanomicrobiales) were increased after microbial acclimation. The enriched syntrophic associations showed higher propionate and butyrate removal efficiencies of 98.48 ± 1.14% and 99.71 ± 0.71%, respectively. Furthermore, encoding genes of formate dehydrogenase and hydrogenases presented higher abundances after microbial enrichment, which suggested that the enhancements of interspecies formate transfer and interspecies hydrogen transfer between syntrophic associations benefited volatile fatty acids (VFAs) conversion. This research provided an effective strategy to relieve acid accumulation.

The response of characteristics and microbial resistance of aerobic granules to sulfamethazine, oxytetracycline, and ciprofloxacin at ppb level in swine wastewater was investigated in this study. Results showed that no significant changes in physical strength, average granules size, and settling property of aerobic granules were observed with target antibiotics exposure (p > 0.05). However, compared to the control group, the protein/polysaccharide ratio and zeta potential of aerobic granules in treatment groups showed a higher level (p

Antibiotics and antibiotic resistance genes (ARGs) pollution in animal feeding farms received more public attention recently. Livestock wastewater contains large quantities of antibiotics and ARGs even after traditional lagoon treatment. In this study, the performance of vertical up-flow constructed wetlands (VUF-CWs) on swine wastewater containing tetracycline compounds (TCs) and tet genes was evaluated based on three aspects, TCs and tet genes removal efficiencies, residual TCs and tet genes in soils and plants, and the effect of TCs accumulation on nutrients removal and tet genes development. High removal efficiencies (69.0-99.9%) were achieved for oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) with or without OTC spiked in the influent additionally. TCs concentrations in surface soils increased at first two sampling periods and then decreased after plants were harvested. Satisfactory nutrients removal efficiencies were also obtained, but TN and NH4-N removal efficiencies were significantly negative correlated with total concentration of TCs (∑TCs) in the soils (p 0.01). The absolute abundances of all the target genes (tetO, tetM, tetW, tetA, tetX and intI1) were greatly reduced with their log units ranging from 0.26 to 3.3. However, the relative abundances of tetO, tetM and tetX in some effluent samples were significantly higher than those in the influent (p 0.05). The relative abundances of tet genes except for tetO were significantly correlated with ∑TCs in the soils (p 0.05). In summary, the proposed VUF-CWs are effective alternative for the removal of TCs and tet genes. But it is of great importance to prevent large accumulation of TCs in the soils.

Four pilot-scale constructed wetlands (free water surface, SF; horizontal subsurface flow, HSF; vertical subsurface flows with different water level, VSF-L and VSF-H) were operated to assess their ability to remove sulfamethazine (SMZ) and tetracycline (TC) from wastewaters, and to investigate the abundance level of corresponding resistance genes (sulI, sulII, tetM, tetW and tetO) in the CWs. The results indicated that CWs could significantly reduce the concentration of antibiotics in wastewater, and the mass removal rate range of SMZ and TC were respectively 11%-95% and 85%-95% in the four systems on the basis of hydraulic equilibrium; further relatively high removal rate was observed in VSF with low water level. Seasonal condition had a significant effect on SMZ removal in the CWs (especially SMZ in SF), but TC removal in VSFs were not considered to have statistically significant differences in winter and summer. At the end period, the relative abundances of target genes in the CWs showed obvious increases compared to initial levels, ranging from 2.98 × 10(-5) to 1.27 × 10(-1) for sul genes and 4.68 × 10(-6) to 1.54 × 10(-1) for tet genes after treatment, and those abundances showed close relation to both characteristic of wastewater and configuration of CWs.

Anaerobic baffled reactor (ABR) processes play an increasingly important role in wastewater treatment and resource recycling by its ingenious construction and excellent performance. The authors aim to introduce new research progresses and applications of ABR in the last two decades, focusing mainly on the following aspects: presenting and comparing its development and application instances, discussing the optimization of operating regulation and mathematical models, stating existing problems in current researches, suggesting possible improvements, and proposing future research perspectives. The contributions of this review involve enhancing ABR treatment efficiency and operation stability to provide information for colleagues.

Bio-hydrogen (H2) and methane (CH4) co-production from soybean protein processing wastewater (SPPW) was examined using a four-compartment anaerobic baffled reactor (ABR) with the active reactor volume (34 L) under continuous flow condition in this present study. At steady state, the ABR achieved H2 yields of 25.67 L/d, specific hydrogen production rate of anaerobic activated sludge was 0.28 L/g MLVSS d, CH4 yields of 13.89 L/d, and chemical oxygen demand (COD) removal of 95% when operated at the organic loading rate of 1.9–2.6 kg COD/m3 d, hydraulic retention time of 48 h, and temperature of (35 ± 1) °C, respectively. The results showed that the niches of the bio-hydrogen-producing phase and the methane-producing phase in the ABR are different. A high alkalinity in the methanogenic compartment of the ABR was able to secure the pH neutral and methane generation. In general, the ABR proved to be a stable, reliable, and effective process for energy recovery and stabilization treatment of SPPW.

In the process of fermentative bio-hydrogen production, organic matter is degraded into volatile fatty acids and ethanol, and consequently thermodynamic constraints prevent the further spontaneous reactions. Moreover, the anaerobic baffled reactor (ABR) with the advantage of phase separation could realize the acetic acid accumulation via acid-producing bacteria. The microbial electrolysis cell (MEC) could convert the acetic acid into hydrogen furthermore. Considering this, the ABR coupled with MEC has been operated to strengthen the hydrogen production. This study was designed regarding orthogonal experiments to operate the four-compartment ABR with a hydraulic retention time (HRT) = 24 h, influent COD ∼ 4600 mg/L, temperature = 35 ± 1 °C, and discovered the optimal parameters with pH = 7, C/N = 44, and 2-bromoethanesulfonate (BES) concentration = 20 mmol/L to achieve the high acetic acid accumulation of effluent. The single-chamber membranless MEC with carbon anode and Ni-catalyst stainless steel cathode (liquid volume = 85 mL) fed with the ABR effluent with applied voltage = 0.6 V and electric conductivity = 7.45 mS/cm, achieved 99.0 ± 0.3% total COD removal efficiency, 1.31 ± 0.04 m 3 H 2 /m 3 d hydrogen production, 2.78 ± 0.11 mLH 2 /mgCOD hydrogen yield and 138.63 ± 3.11% electrical energy efficiency. Therefore the ABR-MEC system could overcome the “fermentation barrier” to achieve higher hydrogen production and organic matter degradation.

Breaking through the “fermentation barrier” bottleneck of conventional biological hydrogen production technology, achieving the depth use of carbon source, and obtaining the higher hydrogen production, bioelectrocatalysis technology assisted fermentation process has vast prospective of applications. The main technical route is the microbial electrolysis cell (MEC). Based on the cutting-edge researches carried out by worldwide scholars, this paper focuses on the comprehensive discussion of MEC design, substrate selection, electrode materials, performance optimization, microbiology, as well as the main problems of the corresponding research. The review also presents recommendations and solutions accordingly. Finally, the prospects of microbial electrocatalysis assisted technology in the field of environmental pollution control and energy recovery application have been disclosed.

This paper investigated the efficiency of two vertical flow constructed wetlands characterized by volcanic (CW1) and zeolite (CW2) respectively, at removing three common antibiotics (ciprofloxacin HCl, oxytetracycline HCl, and sulfamethazine) and tetracycline resistance (tet) genes (tetM, tetO, and tetW) from swine wastewater. The result indicated that the two systems could significantly reduce the wastewater antibiotics content, and elimination rates were in the following sequence: oxytetracycline HCl>ciprofloxacin HCl>sulfamethazine. The zeolite-medium system was superior to that of the volcanic-medium system vis-a-vis removal, perhaps because of the differing pH values and average pore sizes of the respective media. A higher concentration of antibiotics accumulated in the soil than in the media and vegetation, indicating that soil plays the main role in antibiotics removal from wastewater in vertical flow constructed wetlands. The characteristics of the wetland medium may also affect the antibiotic resistance gene removal capability of the system; the total absolute abundances of three tet genes and of 16S rRNA were reduced by 50% in CW1, and by almost one order of magnitude in CW2. However, the relative abundances of target tet genes tended to increase following CW1 treatment.

This study evaluated the physicochemical properties and phosphorus adsorption capacities for oyster shell (OS), broken bricks, volcanics, and zeolite when used as substrates for swine wastewater treatment. All substrates, with the exception of volcanics, proved to be appropriate for microorganism and plant growth enrichment within water treatment systems. Meanwhile, phosphorus adsorption tests indicated that OS was most effective in phosphorus removal. Significant phosphorus removal was achieved in pilot tests when OS was used as a substrate in vertical-flow wetlands treating swine wastewater from an anaerobic tank. The pilot tests also indicated that both soluble reactive phosphorus (SRP) and total phosphorus (TP) removal rates increased when the HRT was prolonged. Overall, the study results showed that OS could be used for phosphorus removal in constructed wetlands, and such use carries the added benefits of reuse of a by-product that promotes sustainability.

Potential effect of ciprofloxacin HCl (CIP), oxytetracycline HCl (OTC) and sulfamethazine (SM2) on the common wetland plant (Phragmites australis) was evaluated by measuring root activity, antioxidant enzymes and chlorophyll in leaf, and a study of the accumulation of antibiotics in plant was also included. Plants were incubated in six containers for 62 days and exposed to antibiotics at concentrations of 0, 0.1, 1, 10, 100, and 1000 μg/L in nutrient solutions. Results illustrated that high antibiotics concentrations (>10 μg/L) had a toxic effect on root activity and leaf chlorophyll, while hormesis occurred at low antibiotics concentrations (0.1–1 μg/L). As antibiotics dosages increased, superoxide dismutase and catalase activity significantly declined (5–55% and 9–58%), while peroxidase activity significantly increased. P. australis accumulated antibiotics via passive absorption, exposure to 1000 μg/L concentrations led to higher CIP, OTC, and SM2 contents in plants (13,834, 6901 and 2047 ng/g dry weight, respectively) than did exposure to 0.1 μg/L concentrations (345, 165, and 24 ng/g dry weight, respectively). The total antibiotics content in all plants followed the sequence CIP > OTC > SM2, and the distribution of all antibiotics followed the sequence root > leaf > stem. These preliminary results indicated that P. australis could both absorb and tolerate antibiotics concentrations typically found in wastewater.

This study designed two vertical flow constructed wetlands (VFCW) as a secondary treatment for piggery wastewater. The effect of effluent recirculation and substrate type on treatment efficiency of constructed wetlands on piggery waster was firstly investigated. Recirculation considerably improved the removal of NH4-N, total nitrogen (TN), and total phosphorus (TP), but not that of chemical oxygen demand (COD). The natural zeolite-based VFCW performed better than volcanic rock-based VFCW for all four parameters. At the highest recirculation ratio, the average treatment efficiencies of natural zeolite-based VFCW reached 50.7, 91.6, 48.3, and 80.7% for COD, NH4-N, TN, and TP, respectively. The diversity and composition of total bacteria and ammonia-oxidizing bacteria (AOB) in the bioflim of natural zeolite and volcanic rock were then determined. Both total bacteria and AOB in biofilm of natural zeolite were more diverse than those in biofilm of volcanic rock. Phylogenetic analyses further revealed ...

A vertical flow constructed wetland (VFCW) filled with natural zeolite had higher ammonium removal (82.4–94.0%) than another VFCW filled with volcanic rock (51.3–69.4%) treating piggery wastewater under any of three recirculation ratios. To reveal the underling reasons, physicochemical characteristics and ammonium-oxidizing prokaryotes (AOPs) of two substrates were determined. The calculated maximum ammonium adsorption of zeolite (11.6 mg g−1) was remarkably higher than that of volcanic rock (0.21 mg g−1), mainly because the former contains two cationic binding crystalline species, and montmorillonite. Quantitative analyses indicated that ammonium-oxidizing archaea (AOA) are the dominant AOP of zeolite and ammonium-oxidizing bacteria (AOB) are the dominant AOP of volcanic rock respectively. Diversity and phylogenetic analysis further showed that both AOB and AOA communities were significantly different between two substrates. Nitrosospira-like AOB (92.6%) and sediment/soil clade AOA (71.4%) were the main components of AOB and AOA in natural zeolite, whereas Nitrosomonas-like AOB (76.1%) and water/sediment clade AOA (77.1%) dominated the AOB and AOA in volcanic rock. These results suggest that the substrates show high selectivity to AOP community. Thus, in addition to physicochemical characteristics, the AOP of substrates is very likely to affect ammonium removal in VFCWs.

A low pH, ethanol-type fermentation process was evaluated for wastewater treatment and bio-hydrogen production from acidic beet sugar factory wastewater in a continuous stirred tank reactor (CSTR) with an effective volume of 9.6 L by anaerobic mixed cultures in this present study. After inoculating with aerobic activated sludge and operating at organic loading rate (OLR) of 12 kgCOD·m−3·d−1, HRT of 8h, and temperature of 35°C for 28 days, the CSTR achieved stable ethanol-type fermentation. When OLR was further increased to 18 kgCOD·m−3·d−1 on the 53rd day, ethanol-type fermentation dominant microflora was enhanced. The liquid fermentation products, including volatile fatty acids (VFAs) and ethanol, stabilized at 1493 mg·L−1 in the bioreactor. Effluent pH, oxidation-reduction potential (ORP), and alkalinity ranged at 4.1–4.5, −250-(−290) mV, and 230–260 mgCaCO3·L−1. The specific hydrogen production rate of anaerobic activated sludge was 0.1 L·gMLVSS−1·d−1 and the COD removal efficiency was 45%. The experimental results showed that the CSTR system had good operation stability and microbial activity, which led to high substrate conversion rate and hydrogen production ability.

Fermentative H(2) production from soybean protein processing wastewater (SPPW) was investigated in a four-compartment anaerobic baffled reactor (ABR) using anaerobic mixed cultures under continuous flow condition in the present study. After being inoculated with aerobic activated sludge and operated at the inoculants of 5.98 gVSS L(-1), COD of 5000 mg L(-1), HRT of 16 h and temperature of (35 ± 1) °C for 22 days, the ABR achieved stable ethanol-type fermentation. The specific hydrogen production rate of anaerobic activated sludge was 165 LH(2)kg MLVSS(-1) day(-1), the substrate conversion rate was 600.83 LH(2)kg COD(-1)and the COD removal efficiency was 44.73% at the stable operation status. The ABR system exhibited a better stability and higher hydrogen yields than continuous stirring tank reactor under the same operational condition. The experimental data documented the feasibility of substrate degradation along with molecular H(2) generation utilizing SPPW as primary carbon source in the ABR system.

Correction for ‘Impact of physical structure of granular sludge on methanogenesis and methanogenic community structure’ by Xiaofang Pan et al., RSC Adv., 2019, 9, 29570–29578.