The disinhibition effect of iron-based particles on anaerobic digestion of florfenicol-containing cow manure: Performance and mechanism.

The overuse of antibiotics has caused problems such as environmental pollution, increased antibiotic resistance of pathogenic bacteria, and inhibition of engineered microbial processes such as anaerobic digestion (AD). At present, mitigating the inhibition of antibiotics on the process of microbial recycling of organic matter by using additives has always been a research hotspot. In this study, the effects of the addition of three iron-based particles including zero-valent iron (ZVI), Fe2O3 and Fe3O4 on the biogas yield during the AD of cow manure containing florfenicol (FLO) were studied. It was found that by alleviating the acid accumulation, the addition of low-concentration ZVI, Fe2O3 and high-concentration Fe3O4 enhanced the maximum methane production rate of FLO-containing cow manure during AD to 3.5, 1.7 and 3.6 times, respectively, while high concentration of ZVI will lead to the crash of the AD system due to the rise of pH. Within the concentration range of iron-based particles dosed in this study, the Fe3O4 dosage showed a significant positive correlation with the cumulative methane production enhancement rate (p < 0.01). The sum of the relative abundances of Limnobacter and Pseudomonas was correlated with the absolute abundance of floR gene with the Pearson correlation coefficient of 0.9457 (p < 0.01), indicating the possibility of these two genera being the potential host bacteria for floR gene.

Towards a better understanding of the anaerobic/oxic/anoxic-aerobic granular sludge process (AOA-AGS) for simultaneous low-strength wastewater treatment and in situ sludge reduction from ambient to winter temperatures.

The new anaerobic/oxic/anoxic-aerobic granular sludge (AOA-AGS) merits the advantages of effective carbon utilization and low-carbon treatment. However, low temperature poses stressing concerns and the resisting mechanism remains much unknown. Herein, an AOA-AGS process was configured for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) with low-strength wastewater from ambient (>15 °C) to winter temperatures (<15 °C). Results showed that simultaneously advanced nutrients removal, and dramatic in situ sludge reduction (Yobs of 0.093 g MLSS/g COD) were gained regardless of seasonally decreasing temperatures. Winter temperatures even amplified Candidatus Competibacter predominating from 20.11% to 34.74%, which laid the core basis for endogenous denitrification, sludge minimization and temperature resistance. A removal model was thus proposed given the observed functional groups, and doubts were also raised for future investigations. This study would aid a better understanding on the microbial ecology and engineering aspects of the new AOA-AGS process treating low-strength wastewater at low temperatures.

The role of hydrochloric acid pretreated activated carbon in chain elongation of D-lactate to caproate: Adsorption and facilitation.

Medium chain fatty acids (MCFA) generation is attracting growing interest due to fossil fuel depletion. To promote the production of MCFA, especially caproate, hydrochloric acid pretreated activated carbon (AC) was introduced into chain elongation fermentation. In this study, the role of pretreated AC on caproate production was investigated using lactate and butyrate as electron donor and electron acceptor, respectively. The results showed that AC did not improve the chain elongation reaction at beginning but promoted the caproate production at later stage. The addition of 15 g/L AC facilitated reactor reaching the peak of caproate concentration (78.92 mM), caproate electron efficiency (63.13%), and butyrate utilization rate (51.88%). The adsorption experiment revealed a positive correlation between the adsorption capacity of pretreated AC and the concentration as well as the carbon chain length of carboxylic acids. Moreover, the adsorption of undissociated caproate by pretreated AC contributed to a mitigated toxicity towards microorganisms, thereby facilitating the production of MCFA. Microbial community analysis revealed an increasing enrichment of key functional chain elongation bacteria, including Eubacterium, Megasphaera, Caproiciproducens, and Pseudoramibacter, but a suppression on acrylate pathway microorganism Veillonella, as the dosage of pretreated AC increasing. The findings of this study demonstrated the substantial impact of the adsorption effect of acid-pretreated AC on promoting caproate production, which would aid to the development of more efficient caproate production process.

Redox mediators stimulated chain elongation process in fluidized cathode electro-fermentation systems for caproate production.

Medium chain fatty acids (MCFAs), the secondary products of traditional anaerobic fermentation, can be produced via chain elongation (CE), a process often retarded due to the difficulty during interspecies electron transfer (IET). This study employed redox mediators, neutral red (NR), methyl viologen (MV), and methylene blue (MB) as electron shuttles to expedite the electro-fermentation for caproate production by improving IET. Results showed that MV increased the MCFAs production by promoting acetate to ethanol conversion, leading to the highest MCFAs selectivity of 68.73%. While NR was indicated to improve CE by encouraging H2 production, and the biocathode had the highest electrical activity due to the smallest internal resistance and largest capacitance increase of 96% than the control. A higher proportion of Sutterella, Prevotella, and Hydrogenophaga, linked with the H2 mediated interspecies electron transfer (MIET) during CE process, was observed across redox mediators supplied groups compared to the control. The presence of mediators led to an elevated abundance of key enzymes for enhanced CE process and electron transfer. This study provided the perspective of the stimulated electron transfer for improved MCFAs production in electro-fermentation systems.

Characterization, risk assessment and resource potential of sediments in the black-odor water in Hunan, China.

The black-odor water in urban water bodies is increasingly found, resulting in serious atrophy of water bodies and degradation of water ecosystems. At present, the pollution status of the sediments as an internal source still remains much unknown. In order to assess the pollution status of black-odor water sediments, the content of total nitrogen, total phosphorus, organic matter and heavy metals in the sediments were determined by taking the black-odor water sediments in urban areas of Hunan Province as the research object. Geoaccumulation and potential ecological risks index methods were used to evaluate heavy metal pollution in the sediments, and comprehensive pollution index method was used to evaluate nitrogen and phosphorus nutrient pollution in the sediments so as to provide pertinent information for urban black-odor water treatment. Finally, resource recovery potentials of sediments in black-odor water were revealed. The results could be beneficial for evaluation of sediments in black-odor water bodies.

Lotus seedpod as a low-cost biomass for potential methylene blue adsorption.

The adsorption of methylene blue (MB) by low cost biomass lotus seedpod (LSP) was optimized by a central composite design combined with response surface methodology in aqueous solution. Solution pH, initial dye concentration and adsorbent dosage were studied as independent variables at five levels each, respectively. Analysis of variance suggested the validity of the regression model. LSP was characterized by Fourier transform infrared spectra and energy dispersive spectroscopy. The kinetics revealed that the adsorption behavior followed the pseudo-second-order model. Langmuir and Freundlich isotherm models were used to evaluate the adsorption, and the experimental data were better fitted by the Langmuir isotherm than the Freundlich isotherm. The maximum monolayer adsorption capacity of the LSP was 157.98 mg g-1 at 30 °C for MB adsorption. In addition, 0.2 M HCl solution could be used for reusability of LSP via desorption tests. LSP was proven to be an available and effective biosorbent for MB removal from aqueous solution.

Microbial community in a hydrogenotrophic denitrification reactor based on pyrosequencing.

Effects of some key factors on hydrogenotrophic denitrification were investigated in lab-scale bioreactors. Results indicated that optimum biomass loading, pH value, temperature, nitrate loading, and C/N ratio in this study were optical density at 600 nm (OD600) of 0.173, 6.0∼7.0, 35 °C, 105 mg L(-1), and 30, respectively. To obtain a better understanding of microbial community in the bioreactors, the 454-pyrosequencing technology was used to characterize the 16S ribosomal RNA (16S rRNA) gene of bacteria in selected samples Y1 and Y2, in which a total of 62,559 effective sequences (36,445 in Y1 and 26,114 in Y2) were obtained. The taxonomic complexities in two samples were compared at phylum/class/genus levels. In total, 41 bacterial phyla, 43 bacterial classes, and 312 genera were detected, where phylum Firmicutes, class Clostridia were most abundant. Genus Proteiniclasticum was predominant among the top 100 genera. This work aims to add some novel insights into hydrogenotrophic denitrification process and its microbial community structures in bioreactors.

Enhanced sludge solubilization by a fluidized electrode: Granular activated carbon promoted electrochemical oxidation.

Electrochemical sludge pretreatment is receiving increasing attention because of its small footprint and higher environmental compatibility. However, the limited effective area of electrode plates and the low conductivity of sludge hinder the widespread application of electrochemical pretreatment. In this study, granular activated carbon (GAC) was employed to construct a fluidized electrode electrochemical system (FEE) to promote electrochemical pretreatment. Under the optimal operating parameters, the FEE system could effectively facilitate sludge decomposition, indicated by 126% increase in soluble chemical oxygen demand (SCOD) and 23.1% reduction in sludge volume. Mechanism study revealed that the addition of GAC significantly enhanced the conductivity of sludge, thereby promoting the oxidation capacity of FEE system. Furthermore, continuously generated H2O2 in FEE further promoted sludge solubilization. GAC offered an effectively, green and sustainable enhancement approach for sludge electrochemical pretreatment.

Effects of successional sulfadiazine exposure on biofilm in moving bed biofilm reactor: Secretion of extracellular polymeric substances, community activity and functional gene expression.

The effects of sulfadiazine (SDZ) on responses of biofilm in a moving bed biofilm reactor were explored with emphasis on the changes in extracellular polymeric substances (EPS) and functional genes. It was found that 3 to 10 mg/L SDZ reduced the protein (PN) and polysaccharide (PS) contents of EPS by 28.7%-55.1% and 33.3%-61.4%, respectively. The EPS maintained high ratio of PN to PS (10.3-15.1), and the major functional groups within EPS remained unaffected to SDZ. Bioinformatics analysis showed that SDZ significantly altered the community activity such as increased expression of s_Alcaligenes faecali. Totally, the biofilm held high SDZ removal rates, which were ascribed to the self-protection by secreted EPS, and genes levels upregulation of antibiotic resistance and transporter protein. Collectively, this study provides more details on the biofilm community exposure to an antibiotic and highlights the role of EPS and functional genes in antibiotic removal.

Advanced low-strength wastewater treatment, side-stream phosphorus recovery, and in situ sludge reduction with aerobic granular sludge.

Modern paradigm has upgraded wastewater treatment plants (WWTPs) to water resources recovery facilities (WRRFs), where aerobic granular sludge (AGS) is a sewage treatment technology with promising phosphorus recovery (PR) potential. Herein, the AGS-based simultaneous nitrification, denitrification, and phosphorus removal coupling side-stream PR process (AGS-SNDPRr) was developed with municipal wastewater. Results revealed that AGS always maintained good structural stability, and pollutant removal was unaffected and effective after 40 days of anaerobic phosphorus-rich liquid extraction (fixed rate of 30%). The AGS-SNDPRr achieved a stable phosphorus recovery efficiency of 63.40%, and the side-stream PR further exaggerated in situ sludge reduction by 7.7-10%. Apart from responses of extracellular polymeric substances (EPS), the Matthew effect of typical denitrifying glycogen accumulating organisms (DGAOs) Candidatus_Competibacter up to 67.40% mainly contributed to enhanced performance of this new process. This study demonstrated a new approach for simultaneous advanced wastewater treatment, phosphorus recovery, and excess sludge minimization.

Performance of anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal system overwhelmingly dominated by Candidatus_Competibacter: Effect of aeration time.

The anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal process (AOA-SNDPR) is a promising technology for enhanced biological wastewater treatment and in situ sludge reduction. Herein, effects of aeration time (90, 75, 60, 45, and 30 min, respectively) on the AOA-SNDPR were evaluated including simultaneous nutrients removal, sludge characteristics, and microbial community evolution, where the role of a denitrifying glycogen accumulating organisms, Candidatus_Competibacter, was re-explored given its overwhelming dominance. Results revealed that nitrogen removal was more vulnerable, and a moderate aeration period of 45-60 min favored nutrients removal most. Low observed sludge yields (Yobs) were obtained with decreased aeration (as low as 0.02-0.08 g MLSS/g COD), while MLVSS/MLSS got increased. The dominance of Candidatus_Competibacter was identified as the key to endogenous denitrifying and in situ sludge reduction. This study would aid the low carbon- and energy-efficient aeration strategy for AOA-SNDPR systems treating low-strength municipal wastewater.

Metagenomic insights into the effects of various biocarriers on moving bed biofilm reactors for municipal wastewater treatment.

Preferable biocarrier is vital for start-up and operation of moving bed biofilm reactor (MBBR). Effects of three separate biocarriers - PPC, PU, and PP on MBBRs were systematically investigated including nutrients removal performances, biomass attachment, microbial community, and relevant functional genes. Results showed that three biocarriers achieved similar removal efficiencies for chemical oxygen demand (COD) and total phosphorus (TP), though much higher biomasses were found attached onto PPC and PU carriers. PPC and PU performed better than PP for ammonia nitrogen (NH4+-N) removal. However, PPC exhibited the greatest and most reliable denitrifying efficiency, mainly due to stronger simultaneous nitrification and denitrification during better micro-anoxic-environment created within PPC carriers than others. Further studies by 16S rRNA gene and metagenomic sequencing analysis uncovered the bacterial diversity and structures, and relevant functional genes for nitrogen-transformation and pathways of nitrogen metabolisms, which laid the biological basis for the best performances via biocarrier PPC. This study inspired a feasible approach for municipal wastewater treatment through PPC filled MBBR.

Rapid start-up and stable operation of an aerobic/oxic/anoxic simultaneous nitrification, denitrification, and phosphorus removal reactor with no sludge discharge.

An anaerobic/aerobic/anoxic mode simultaneous nitrification, denitrification, and phosphorus removal system was visited for enhanced low-strength wastewater treatment and dramatic in situ sludge reduction. Results showed that rapid start-up was achieved with conventional activated sludge after 15 days, with effluent ammonia nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand being 0.25, 7.89, 0.12, 24.37 mg/L, respectively. A two-stage biomass growth rate was observed with the sludge yield of 0.285 (day 1-50) and 0.017 g MLSS/g COD (day 51-110) without sludge discharge. Dynamics of bacterial community has been identified with outstanding accumulation of Candidatus_Competibacter up to 29.06 %, which contributed to both simultaneous nutrients removal and sludge reduction. Further analysis via PICRUSt2 revealed the main pathway of nitrogen metabolism, while proposed mechanism for phosphorus removal with no sludge discharge was analyzed from the intracellular and extracellular perspectives. Overall, this study provided guidance and reference for the development and application of A/O/A-SNDPR technology.

Distinct responses of aerobic granular sludge sequencing batch reactors to nitrogen and phosphorus deficient conditions.

The nutrients availability determines efficiency of biological treatment systems, along with the structure and metabolism of microbiota. Herein nutrients deficiencies on aerobic granular sludge were comparatively evaluated, treating wastewater with mass ratios of chemical oxygen demand : nitrogen : phosphorus being 200:20:4, 200:2:4, and 200:20:0.4 (deemed as nutrient-balanced, nitrogen-deficient, and phosphorus-deficient), respectively. Results revealed that both nitrogen and phosphorus deficiencies significantly raised the effluent qualities especially nitrogen removal. However, nitrogen deficiency aroused considerable growth of filamentous bacteria, while granules kept compact structure under phosphorus deficient condition. Extracellular polymeric substances (EPS) also varied in contents and structures in response to different wastewaters. Microbial community structure analysis demonstrated that nitrogen deficiency led to lower richness and higher diversity, while the reverse was observed under phosphorus deficient condition. Nitrogen deficiency mainly induced decrease of nitrifying bacteria, while similarly phosphorus deficiency led to loss of phosphorus accumulating organisms. Dramatic enrichment Candidatus_Competibacter and filamentous Thiothrix were found under nutrients deficiencies, in which the latter explained and indicated filamentous bulking potential especially under nitrogen limited condition. Bacterial metabolism patterns verified the functions of microbial community responding to nutrients via PICRUSt2 prediction mainly by up-regulating cell motility, and cellular processes and signaling. This study could aid understanding of long-term stability of aerobic granular sludge for low-strength wastewater treatment.

Anaerobic caproate production on carbon chain elongation: Effect of lactate/butyrate ratio, concentration and operation mode.

The objective of this study was to understand how lactate-to-butyrate ratio and substrates concentrations affect the caproate production and product structure. The results showed that a higher butyrate-to-lactate ratio is beneficial to caproate production at low initial lactate concentration. Low pH (5.0) and low substrate concentration (20 mM and 40 mM) effectively decreased propionate production via restrained acrylate pathway, resulting in higher electron efficiency of caproate. With the optimum mole ratio of lactate to butyrate (1:4) and 80 mM initial butyrate concentration, the electron efficiency of caproate reached the maximum (43.10%). Moreover, high butyrate concentration suppressed the production of odd-carbon-number carboxylates while promoting the production of caproate. Compared with the batch operation, the caproate production in semi-continuous operation was enhanced by 3.45 times to 30.91 ± 1.07 mM as the acrylate pathway was successfully inhibited in semi-continuous experiments due to low pH and low lactate concentration.

Efficient heavy metal removal from water by alginate-based porous nanocomposite hydrogels: The enhanced removal mechanism and influencing factor insight.

Novel porous alginate-based nanocomposite hydrogels were prepared by incorporating polyaniline-polypyrrole modified graphene oxide (GO@PAN-PPy) as reinforcing fillers into the alginate matrix (GO@PAN-PPy/SA) for Cr(VI) and Cu(II) removal from water. Different in-situ co-polymerization functionalized GO with Py-to-An mass ratios of monomers (from nil to 1:1) and contents of GO@PAN-PPy (from nil to 2.0%(w/v)) were embedded into the alginate backbone to improve the sorption performance. Key factors, such as pH, coexisting metal ions, and swelling states were investigated in batch adsorption modes. The synergistic effect combined from polymer backbone and fillers could lower the impact of the pH-dependent adsorption reaction. With an adsorption ability superior to that of plain SA and GO/SA, the optimized GO@PAN-PPy-2(1)/SA exhibited good experimental maximum adsorption capacities for Cr(VI) (~133.7 mg/g) and Cu(II) (~87.2 mg/g) at pH 3.0, which were better than those of many other similar sorbents. The sorbents possessed excellent adaptability for 0.2 M salt for Cr(VI) removal but poor for Cu(II) removal. Pre-swelling treatment and co-adsorption could enhance the adsorption performance. The excellent reusability of hydrogel was demonstrated after five cycles in single/binary system. Overall, this work reveals that the resultant hydrogel holds potential as candidate sorbent to remove anionic-cationic heavy metal ions from water.

Insights into the simultaneous nitrification, denitrification and phosphorus removal process for in situ sludge reduction and potential phosphorus recovery.

A simultaneous nitrification-denitrification and phosphorus removal (SNDPR) system operated in an alternating anaerobic/aerobic/anoxic (A/O/A) mode was revisited from new perspectives of sludge reduction and potential phosphorus recovery. Reliable and robust removal performance was obtained even under winter temperatures, with average removal efficiency of COD, TP, NH4+-N and TIN being 89.68%, 93.60%, 92.15% and 79.01% at steady state, respectively. Inoculated sludge got enhanced in biomass density, settleability, and bioactivity. And relatively stable amounts of extracellular polymeric substances (EPS) with a stable protein/ polysaccharide (PN/PS) ratio were observed over operation. Meanwhile, a low observed sludge yield (Yobs) of 0.083 g MLSS/g COD (0.082 g MLVSS/g COD) was obtained. A maximum anaerobic phosphorus release up to 43.54 mg/L was found, thus providing phosphorus-rich and low-turbidity stream for further phosphorus recovery. Overall, the SNDPR system deserved attention for in situ sludge reduction and potential phosphorus recovery, beyond reliable and stable wastewater treatment.

Effects of phenol on extracellular polymeric substances and microbial communities from aerobic granular sludge treating low strength and salinity wastewater.

The effects of phenol on aerobic granular sludge including extracellular polymeric substances (EPS) and microbial community were investigated for low strength and salinity wastewater treatment. Elevated phenol over 20 mg/L stimulated biological phosphorus removal mainly via co-metabolism with nearly complete phenol degradation, whereas resulted in significant accumulation of nitrate around 4 mg/L. Aerobic granules kept structural stability via enhancing production of extracellular polymeric substances (EPS), especially folds of polysaccharides (PS) and varying functional groups identified through EEM, FTIR and XPS spectral characterizations at increasing phenol loads. Illumina MiSeq sequencing results indicated that elevated phenol decreased the bacterial diversity and richness, and caused remarkable variations in structural and compositions of microbial population. Multiple halophilic bacteria including Stappia, Luteococcus, and Formosa laid the biological basis for stability of aerobic granules and efficient biological nutrients and phenol removal. Redundancy analysis (RDA) suggested the key role of phenol in shaping the relative abundances and predominant genera. This study proved that aerobic granular sludge was feasible for low-saline and phenol-laden low-strength wastewater treatment.

Interaction and removal of oxytetracycline with aerobic granular sludge.

Aerobic granular sludge as a promising technology showed great resistance to adverse conditions. However, the interaction between oxytetracycline (OTC) and granular sludge was not studied sufficiently. This study therefore investigated OTC-tolerance ability of incomplete and complete granulation sludge from aspects of simultaneous nutrients removal, sludge characteristics, microbial activity, community changes, and vice versa OTC removal performance. Incomplete granulation sludge showed better denitrification performance and resistance. Whereas, denitrification and phosphorus removal of complete granulation sludge suffered a permanent collapse under 5 mg/L OTC. OTC could be removed by rapid adsorption and slow biodegradation via granular sludge. The EPS, especially TB-PS, played a significant role during the operational period subjected to OTC. The major genera of Lysobacter and Candidatus_Competibacter laid the biological basis for stability and functionality of granules, which acted as the putative contributors for resisting and removing OTC. This study showed that incomplete-granulated sludge qualified more promising application prospect.

Research on the aerobic granular sludge under alkalinity in sequencing batch reactors: Removal efficiency, metagenomic and key microbes.

Effects of additional alkalinity on the performance of aerobic granular sludge (AGS) in sequencing batch reactors (SBR) performing simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) were evaluated. Results showed that COD and ammonia-N (NH4+-N) were slightly stimulated and remained high and stable with the increase of alkalinity up to 750 mg/L, while denitrification was boosted and total inorganic nitrogen (TIN) removal efficiency increased from 60.46% to 98.62% with an additional alkalinity of 750 mg/L. However, total phosphorus (TP) removal stayed unaffected and efficient. Illumina MiSeq sequencing revealed that microbial diversity and richness shifted mostly with 500 mg/L exterior alkalinity addition. Additional alkalinity altered the bacterial compositions within aerobic granules at various levels and the enrichment of Thiothrix and Acinetobacter was accounted for the promotion of COD and TIN removal.