Refractory Organic Matters Research Articles

Combined electrochemical in-situ activated chlorine production and photocatalytic for degradation of dimethyl phthalate using membrane filtration recycle TiO2

The ultraviolet (UV)/chlorine advanced oxidation process (AOP), involving addition of activated chlorine to the UV irradiation system to generate hydroxyl radicals (HO·) and chlorine radicals (Cl·), is promising in addressing refractory organic matters. Herein, activated chlorine was electrochemically in-situ generated under low concentrations of chloride ions (Cl−), serving as the chlorine source. A UV/electrochemistry/titanium dioxide (UV/E/TiO2) system was established by coupled membrane filtration. TiO2 was separated and circulated to remove dimethyl phthalate (DMP). Impacts of catalyst (TiO2), Cl− concentrations, and initial pH on DMP degradation were investigated under different conditions. The results revealed that compared with E and UV/TiO2 systems, the UV/E/TiO2 system substantially enhanced the DMP degradation (from 5.11 % and 22.54 % to 78.33 %), with a synergistic factor of 1.16. Radical quenching experiments confirmed that HO·and Cl·were the primary reactive substances for DMP degradation in the UV/E/TiO2 system. Fluorescence probe experiments, coupled with HPLC and LC–MS analysis, revealed a continuous decrease in Cl− in the UV/E/TiO2 system due to ongoing photolysis, generating more HO·for DMP degradation in contrast to the E/TiO2 system. In conclusion, the coupled UV/E/TiO2 system can promote the degradation of refractory organic pollutants in water environments, showcasing significant potential.

Applying sludge hydrolysate as a carbon source for biological denitrification after composition optimization via red soil filtration

Sludge hydrolysate, the byproduct generated during sludge hydrothermal treatment (HT), is a potential carbon source for biological denitrification. However, the refractory organic matters and the nutrient substances are unfavorable to the nitrogen removal. In this study, effects of HT conditions on the hydrolysate properties, and the hydrolysate compositions optimization via red soil (RS) filtration were investigated. At HT temperature of 160–220 °C and reaction time of 1–4 h, the highest dissolution rate of organics from sludge to hydrolysate achieved 70.1 %, while the acetic acid dominated volatile fatty acids (VFAs) was no more than 5.0 % of the total organic matter content. The NH4+-N and dissolved organic nitrogen (DON) were the main nitrogen species in hydrolysate. When the hydrolysate was filtered by RS, the high molecular weight organic matters, DON, NH4+ and PO43− were effectively retained by RS, while VFAs and polysaccharide favorable for denitrification were kept in the filtrate. When providing same COD as the carbon source, the filtrate group (Fi-Group) introduced lower concentrations of TN and humic substances but higher content of VFAs. This resulted in TN removal rate (57.0 %) and denitrification efficiency (93.6 %) in Fi-Group higher than those in hydrolysate group (Hy-Group), 39.4 % and 83.7 %, respectively. It is noticeable that both Hy- and Fi- Groups up-regulated most of denitrification functional genes, and increased the richness and diversity of denitrifying bacteria. Also, more denitrifying bacteria genera appeared, and their relative abundance increased significantly from 3.31 % in Control to 21.15 % in Hy- Group and 31.31 % in Fi-Group. This indicates that the filtrate is a more suitable carbon source for denitrification than hydrolysate. Moreover, the pH rose from 4.6 ± 0.14 to 6.5 ± 0.05, and the organic carbon, TN, TP and cation exchange capacity (CEC) of RS increased as well after being filtered, implying that the trapped compounds may have the potential to improve soil quality. This study provides a new insight for hydrolysate application according to its composition characteristics, and helps make the most use of wasted sludge.

Calcium peroxide mediated sustainable microalgal-bacterial consortium system: Role and significance of configured anaerobic fermentation

Microalgal-bacterial consortium (MBC) is an effective way to meet increasingly stringent standards in wastewater treatment, with advantages in nutrient removal, resource recovery, and energy conservation. The efficient and stable operation of the MBC sewage treatment system is generally limited by the insufficient and unstable carbon source in the influent. In this study, a calcium peroxide-mediated anaerobic fermenter was configured to transfer the MBC sludge into the preferred carbon source, short-chain fatty acids (SCFAs) in-situ, to alleviate the limitations. Experimental results showed that after 4-day 0.15 g/g VS calcium peroxide mediated anaerobic fermentation, the production of SCFAs and the proportion of acetic acid reached 514.8 mg COD/g VS and 59 %, respectively. Scanning electron microscopy, COD mass balance analysis, and lactate dehydrogenase assays jointly showed that calcium peroxide effectively promoted the breakdown of MBC sludge cells, which led to the release of large amounts of organic matter and could be attributed to the released OH–, ·OH and ·O2– from calcium peroxide, thereby providing more bioavailable substrates for SCFAs production. Microbial community analysis indicated that the anaerobes associated with hydrolysis and degradation of refractory organic matters were enriched in the mediated fermenter and had positive correlation with SCFAs production. Using such fermentation liquid as an additional carbon source for influent sewage, the MBC process performance was significantly promoted, with phosphorus and COD removal and sludge settleability reaching 84.7 %, 96.1 %, and 33 %, respectively. Configuring calcium peroxide-mediated anaerobic fermentation may thus become a sustainable strategy to strengthen the MBC sewage treatment system, thus providing new ideas for wastewater treatment to reduce inputs and improve performance.

Advanced synergetic nitrogen removal of municipal wastewater using oxidation products of refractory organic matters in secondary effluent by biogenic manganese oxides as carbon source.

Due to the high operational cost and secondary pollution of the conventional advanced nitrogen removal of municipal wastewater, a novel concept and technique of advanced synergetic nitrogen removal of partial-denitrification anammox and denitrification was proposed, which used the oxidation products of refractory organic matters in the secondary effluent of municipal wastewater treatment plant (MWWTP) by biogenic manganese oxides (BMOs) as carbon source. When the influent NH4+-N in the denitrifying filter was about 1.0, 2.0, 3.0, 4.0, 5.0 and 7.0mg/L, total nitrogen (TN) in the effluent decreased from about 22mg/L to 11.00, 7.85, 6.85, 5.20, 4.15 and 2.09mg/L, and the corresponding removal rate was 49.15, 64.82, 69.40, 76.70, 81.36 and 90.58%, respectively. The proportional contribution of the partial-denitrification anammox pathway to the TN removal was 12.00, 26.45, 39.70, 46.04, 54.97 and 64.01%, and the actual CODcr consumption of removing 1mg TN was 0.75, 1.43, 1.26, 1.17, 1.08 and 0.99mg, respectively, which was much lower than the theoretical CODcr consumption of denitrification. Furthermore, CODcr in the effluent decreased to 8.12mg/L with a removal rate of 72.40%, and the removed organic matters were mainly non-fluorescent organic matters. Kinds of denitrifying bacteria, anammox bacteria, hydrolytic bacteria and manganese oxidizing bacteria (MnOB) were identified in the denitrifying filter, which demonstrated that the advanced synergetic nitrogen removal was achieved. This novel technology presented the advantages of high efficiency of TN and CODcr removal, low operational cost and no secondary pollution.

Degradation bensulfuron-methyl by magnetic CoFe alloy@N-doped graphitized carbon derived from CoFe2O4 activated by peroxymonosulfate

Magnetic CoFe alloy@N-doped graphitized carbon nano-catalyst (CoFe@N-GC) was synthesized by hydrothermal method and chemical deposition method, which could couple with peroxymonosulfate (PMS) to degrade herbicide bensulfuron-methyl (BSM). CoFe alloy nanoparticles were encapsulated in N-doped graphitized carbon yarn-like material, providing strong stability and high corrosion resistance properties of them. Furthermore, CoFe alloy can make great improvement of degradation performance via tuning metal site’s intrinsic performance of the Fermi energy level density of states. CoFe@N-GC (k = 0.4 min−1) displayed better catalytic performance than CoFe2O4 (k = 0.14 min−1) because of the intrinsic strengths of each component, synergy between cobalt and iron, doping of nitrogen atoms and graphitized carbon and unique electronic properties. 10 mg·L−1 bensulfuron-methyl was degraded completely by the combination of CoFe@N-GC and PMS within 10 min at pH 7. Magnetic CoFe@N-GC could be separated from solution by an external magnet, thus making convenience to collect catalyst and avoiding second pollution. After 15 recycling use of CoFe@N-GC, the BSM degradation efficiency could still be maintained at 95%. CoFe@N-GC/PMS system exhibited stable degradation ability over a wide pH range (3–8) and displayed strong tolerance to real water samples. The main active species, possible BSM degradation pathways and potential reaction mechanism of CoFe@N-GC/PMS were systematically explored. Thus, our finding can provide an environmental friendly, efficient and easy recycle catalyst to degrade refractory organic matters by PMS activation.

Persulfate activation by Fe3O4-doped biochar synthesized from Fenton sludge and sewage sludge for enhanced 1-H-1,2,4-triazole degradation

A novel composite biochar synthesized from Fenton sludge (FS) and sewage sludge (SS) was employed to catalyze persulfate for the removal of 1-H-1,2,4-triazole (TZ). The optimized conditions for the synthesis and operating process were identified through response surface methodology as follow: SS/FS mass ratio = 5:1, catalyst dosage = 0.9 g L−1 and PDS concentration = 0.5 g L−1. The removal efficiencies of TZ, TOC and organic nitrogen were found to be as high as 97.6%, 80.33% and 100%, respectively, with the addition of Fe3O4-doped biochar in persulfate catalytic system. Besides, Fe3O4-doped biochar exhibited superior stability and tolerance to wide range of pH (2–12), temperature (15–45 °C) and co-existing substrate. The reactive oxygen species, which resulted in the catalytic degradation of TZ followed the order of SO4∙− > ∙OH > O2∙− >1O2, were identified by electron spin resonance and quenching tests. It demonstrated that the radical pathway accomplished with non-radical pathway contributed to the enhanced degradation of TZ, which was further identified by electrochemical experiments. Moreover, the possible degradation pathway of TZ was ascertained and proposed through DFT calculation and LC-MS analysis. These findings illustrated that the novel magnetic biochar would be a promising persulfate catalyst for the treatment of refractory organic matters. In addition, it also provided a new alternative method for the resource utilization of FS and SS.

Advanced nitrogen removal performance and microbial community structure of a lab-scale denitrifying filter with in-situ formation of biogenic manganese oxides

Advanced nitrogen removal faces the challenges of high operational cost resulted from the additional carbon source and secondary pollution caused by inaccurate carbon source dosage in municipal wastewater. To address these problems, a novel carbon source was developed, which was the oxidation products of refractory organic matters in the secondary effluent of municipal wastewater treatment plant (MWWTP) by in-situ generated biogenic manganese oxides (BMOs) in the denitrifying filter. In the steady phase, the effluent chemical oxygen demand (CODcr), NO3−-N and total nitrogen (TN) in the denitrifying filter 2# with BMOs was 11.27, 9.03 and 10.36 mg/L, and the corresponding removal efficiency was 54.79%, 51.85% and 48.03%, respectively, which was significantly higher than those in the control denitrifying filter 1# that the removal efficiency of CODcr, NO3−-N and TN was only 32.30%, 28.58% and 29.36%, respectively. Kinds of denitrifying bacteria (Candidatus Competibacter, Defluviicoccus, Dechloromonas, Candidatus Competibacter, Dechloromonas, Pseudomonas, Thauera, Acinetobacter, Denitratisoma, Anaerolineae and Denitratisoma) and anammox bacteria (Pirellula, Gemmata, Anammoximicrobium and Brocadia) were identified in the denitrifying filters 1# and 2#, which explained why the actual CODcr consumption (1.55 and 1.44 mg) of reducing 1 mg NO3−-N was much lower than the theoretical CODcr consumption. While manganese oxidizing bacteria (MnOB, Bacillus, Crenothrix and Pedomicrobium) was only identified in the denitrifying filter 2#. This novel technology presented the advantages of no additional carbon source, low operational cost and no secondary pollution. Therefore, the novel technology has superlative application value and broad application prospect.

Comparison of prokaryotes between Mount Everest and the Mariana Trench

BackgroundMount Everest and the Mariana Trench represent the highest and deepest places on Earth, respectively. They are geographically separated, with distinct extreme environmental parameters that provide unique habitats for prokaryotes. Comparison of prokaryotes between Mount Everest and the Mariana Trench will provide a unique perspective to understanding the composition and distribution of environmental microbiomes on Earth.ResultsHere, we compared prokaryotic communities between Mount Everest and the Mariana Trench based on shotgun metagenomic analysis. Analyzing 25 metagenomes and 1176 metagenome-assembled genomes showed distinct taxonomic compositions between Mount Everest and the Mariana Trench, with little taxa overlap, and significant differences in genome size, GC content, and predicted optimal growth temperature. However, community metabolic capabilities exhibited striking commonality, with > 90% of metabolic modules overlapping among samples of Mount Everest and the Mariana Trench, with the only exception for CO2 fixations (photoautotrophy in Mount Everest but chemoautotrophy in the Mariana Trench). Most metabolic pathways were common but performed by distinct taxa in the two extreme habitats, even including some specialized metabolic pathways, such as the versatile degradation of various refractory organic matters, heavy metal metabolism (e.g., As and Se), stress resistance, and antioxidation. The metabolic commonality indicated the overall consistent roles of prokaryotes in elemental cycling and common adaptation strategies to overcome the distinct stress conditions despite the intuitively huge differences in Mount Everest and the Mariana Trench.ConclusionOur results, the first comparison between prokaryotes in the highest and the deepest habitats on Earth, may highlight the principles of prokaryotic diversity: although taxa are habitat-specific, primary metabolic functions could be always conserved.8c6sxptuhXFJaznJoiBvg_Video abstract.

Composition, distribution, and source of organic carbon in surface sediments of Erhai Lake, China

Lake sediment is an important organic carbon (OC) sink. Nevertheless, few studies have been conducted on sediment organic carbon (SOC) in lakes, and the effects of environmental variables on SOC pools remain poorly understood. We combined physicochemical and spectroscopic analyses to investigate the composition, distribution, and source of OC in surface sediments of Erhai Lake, southwest China, and explored the relationships between environmental variables and its SOC pool. The SOC pool consists of relatively high proportions of labile organic carbon fractions, mainly from algal production, which are rapidly decomposed and exhibit high turnover rates. The relative content of humus carbon ranges from 13.5 % to 20.5 %, with fulvic acid carbon predominating (average 52.95 %), indicating weak humification and a relatively active humus carbon pool. The dissolved organic matter in water column and sediments of Erhai Lake is largely influenced by endogenous production, with a great contribution from phytoplankton. Surface sediments contained more protein-like components than overlying waters (80.0 % vs. 63.0 %), attributed mainly to abundant algal deposition and intense bacterial metabolism. Among environmental variables, sediment chlorophyll a showed the strongest relationship with the SOC pool, and was associated with rapid decomposition and promotion of the humification process, which supported the conclusion that algae had an important influence on the SOC pool. The SOC pool in the southern region of the lake is mainly contributed by algae, other microorganisms, and sewage, exhibiting a greater potential to release organic matters into the water column. The center and northern SOC pools show relatively stable characteristics and stronger OC sink capacity, mainly because of the input of terrestrial refractory organic matters from runoff. Our data shed light on the OC storage mechanisms in the surface sediments of Erhai Lake and provide theoretical bases for enhancing the OC sink of sediments in the lake.

Advanced oxidation processes and selection of industrial water source: A new sight from natural organic matter

Natural organic matter (NOM) refers to the dissolved organic matter in natural water that can pass through 0.45μm filter membrane. As a pivotal role in the surface water body, it has a significant effect on the efficiency of AOPs. In this study, Excitation emission matrix - parallel factor (EEM-PARAFAC) analysis is used to elucidate the changes of NOM fluorescence peaks after electrochemical oxidation process, two-dimensional correlation spectroscopy (2D-FTIR-COS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) are utilized to clarify the molecular characteristics of NOM in surface water and the effects of electrochemical oxidation on NOM molecules. The results indicate that parts of NOM molecules are mineralized into simple compounds and precursors of refractory organic matters produced by some NOM molecules after AOPs. It is concluded that the precursors of these refractory organic matters may belong to terrestrial humus (C2). Therefore, for the purpose of avoiding more refractory organic pollutants produced by NOM which can reduce the performance of AOPs in the water treatment process, factories should choose water sources with less humus as industrial water supply, or degrade humus by physical or chemical methods before industrial water supply.

Transformation and toxicity dynamics of polycyclic aromatic hydrocarbons in a novel biological-constructed wetland-microalgal wastewater treatment process

In this study, a novel wastewater treatment process combining sequencing batch reactor, constructed wetland and microalgal membrane photobioreactor (BCM process) was proposed, and its performance on removal, transformation and toxicity reduction of polycyclic aromatic hydrocarbons (PAHs) was intensively explored. Satisfactory PAHs removal (90.58%–97.50%) was achieved and molecular weight had significant impact on the removal pathways of different PAHs. Adsorption dominated the removal of high molecular weight PAHs, while the contribution ratio of microbial degradation increased with the decrease of molecular weight of PAHs. More importantly, it was reported for the first time that substituted PAHs (SPAHs) produced by microbial degradation of PAHs would lead to increased toxicity during the BCM process. High PAHs (75.37%–88.52%) and SPAHs removal (99.56%–100.00%) were achieved in the microalgae unit due to its abundant cytochrome P450 enzyme, which decreased the bacterial toxicity by 90.93% and genotoxicity by 93.08%, indicating that microalgae played significance important role in ensuring water security. In addition, the high quantitative relationship (R2 = 0.98) between PAHs, SPAHs and toxicity exhibited by regression model analysis proved that more attention should be paid to the ecotoxicity of derivatives of refractory organic matters in wastewater treatment plants.

Impact of different organic matters on the occurrence of antibiotic resistance genes in activated sludge

The occurrence of antibiotic resistance genes (ARGs) in various environments has drawn worldwide attention due to their potential risks. Previous studies have reported that a variety of substances can enhance the occurrence and dissemination of ARGs. However, few studies have compared the response of ARGs under the stress of different organic matters in biological wastewater treatment systems. In this study, seven organic pollutants were added into wastewater treatment bioreactors to investigate their impacts on the ARG occurrence in activated sludge. Based on high-throughput sequencing, it was found that the microbial communities and ARG patterns were significantly changed in the activated sludge exposed to these organic pollutants. Compared with the non-antibiotic refractory organic matters, antibiotics not only increased the abundance of ARGs but also significantly changed the ARG compositions. The increase of Gram-negative bacteria (e.g., Archangium, Prosthecobacter and Dokdonella) carrying ARGs could be the main cause of ARG proliferation. In addition, significant co-occurrence relationships between ARGs and mobile genetic elements were also observed in the sludge samples, which may also affect the ARG diversity and abundance during the organic matter treatment in the bioreactors. Overall, these findings provide new information for better understanding the ARG occurrence and dissemination caused by organic pollutants in wastewater treatment systems.

Landfill leachate treatment in-depth by bio-chemical strategy: microbial activation and catalytic ozonation mechanism

The combination of activated sludge process and catalytic ozonation technology was used to treat the landfill leachate as bio-chemical strategy in this study. The technology of activated sludge pretreatment and catalytic ozonation post-treatment coupled with baffled membrane bioreactor (MBR) system was proposed. The COD, ammonia nitrogen and phosphate were removed in anaerobic and aerobic environments. At the same time, catalytic ozonation could significantly remove COD, colority, UV254, ammonia nitrogen, 3D fluorescence peak value, and fluorescence regional integration (FRI) of organic pollutants from landfill leachate. Ultimately, the maximum removal efficiencies of COD, ammonia nitrogen and phosphate were 98.46 ± 0.28%, 99.92 ± 0.01%, and 79.71 ± 1.62%, respectively. The heavy metal contents met the emission standards after treatment with this strategy. The removal of pollutants in landfill leachate could be attributed to the positive effect of microorganism in sludge and catalyst in ozonation: (1) The microorganism found in sludge all played different roles, Proteobacteria and Bacteroidetes accounted for the most, they could degrade organisms and even refractory organic matters. Though the number of Thauera, Acinetobacter, Nitrospira and Nitrosomonas was small, they played an important role on denitrification. (2) During catalytic ozonation, the hydroxyl radical (OH) produced by ozone would combine with oxygen to generate hydrogen peroxide radical (OOH) during the reaction, while unpaired electrons were trapped by surface adsorbed oxygen on the catalysts to produce superoxide radical (O2–). In addition, the active metal components, such as Ce4+/Ce3+ redox pair, Mn2+, Mn3+ and Mn4+ on the catalyst surface were able to transform synergistically, which was able to maintain the catalyst activity and realize the removal of contaminants.

Interface engineering strategy of a Ti4O7 ceramic membrane via graphene oxide nanoparticles toward efficient electrooxidation of 1,4-dioxane

Although Ti4O7 ceramic membrane has been recognized as one of the most promising anode materials for electrochemical advanced oxidation process (EAOP), it suffers from relatively low hydroxyl radical (•OH) production rate and high charge-transfer resistance that restricted its oxidation performance of organic pollutants. Herein, we reported an effective interface engineering strategy to develop a Ti4O7 reactive electrochemical membrane (REM) doped by graphene oxide nanoparticles (GONs), GONs@Ti4O7 REM, via strong GONs–O–Ti bonds. Results showed that 1% (wt%) GON doping on Ti4O7 REM significantly reduced the charge-transfer resistance from 73.87 to 8.42 Ω compared with the pristine Ti4O7 REM, and yielded •OH at 2.5–2.8 times higher rate. The 1,4-dioxane (1,4-D) oxidation rate in batch experiments by 1%GONs@Ti4O7 REM was 1.49×10−2 min−1, 2 times higher than that of the pristine Ti4O7 REM (7.51×10−3 min−1) and similar to that of BDD (1.79×10−2 min−1). The 1%GONs@Ti4O7 REM exhibited high stability after a polarization test of 90 h at 80 mA/cm2, and within 15 consecutive cycles, its oxidation performance was stable (95.1–99.2%) with about 1% of GONs lost on the REM. In addition, REM process can efficiently degrade refractory organic matters in the groundwater and landfill leachate, the total organic carbon was removed by 54.5% with a single-pass REM. A normalized electric energy consumption per log removal of 1,4-D (EE/O) was observed at only 0.2–0.6 kWh/m3. Our results suggested that chemical-bonded interface engineering strategy using GONs can facilitate the EAOP performance of Ti4O7 ceramic membrane with outstanding reactivity and stability.

COD and ammonia removal from landfill leachate by UV/PMS/Fe2+ process: ANN/RSM modeling and optimization

Landfill leachate is a highly contaminated liquid generated in municipal solid waste landfills. The application of sulfate radical-based advanced oxidation processes (SR-AOP) in landfill leachate treatments is emerging due to their ability to degrade both organic refractory matters and ammonia nitrogen. In this paper, application of peroxymonosulfate (PMS), activated by Fe2+ and UV was used as an economical and environmentally friendly approach for treatment of landfill leachate. Chemical oxygen demand (COD) and ammonia removals were measured as the two primary responses of landfill leachate to UV/PMS/Fe2+ treatment system. The main parameters (pH, PMS/Fe2+ mass ratio, Fe2+ dosage) affecting this system were modeled by two approaches; Response Surface Method (RSM) and Artificial Neural Network (ANN). Although RSM has an acceptable prediction performance (R2pred = 0.87–0.92), and the models are well fitted (R2 = 0.95–0.96), ANN can deliver a more precise estimate of the experimental targets (53% and 79% less root mean square error for COD and ammonia removals, respectively). The modeling results confirmed that ANN could be trained satisfactorily using data obtained from the CCD experimental design. Sensitivity analysis emphasized the importance of pH and PMS/Fe2+ mass ratio in COD removal and the significant influence of pH on ammonia removal. Multi-objective optimization and experimental results at optimal conditions confirmed that maximum COD and ammonia removal with minimum catalyst consumption are 80.8% and 25.6%, respectively. The results show that hybrid activation of PMS can remarkably enhance the removal of refractory organic matters in landfill leachate compared to the previously studied SR-AOP systems. FTIR spectra results indicate that after 60 min of treatment by UV/PMS/Fe2+ process, the carbonyl groups disappeared, and the amount of C-O-C in aliphatic ethers increased due to chemical oxidation. In addition, the transmittance of the bands corresponding to aromatic CC and asymmetric stretch of COO- decreased significantly, suggesting that the degree of leachate humification has changed. The BOD/COD ratio of the final effluent improved from 0.52 to 0.99, meaning that the treated leachate has higher capability to be treated via biological methods.

Enhanced anaerobic digestion of tar solution from rice husk thermal gasification with hybrid upflow anaerobic sludge-biochar bed reactor

Tar generated as a by-product during biomass gasification contains a high concentration of refractory organic matters. In this study, a hybrid upflow anaerobic sludge-biochar bed reactor was established for tar treatment, and the methane yield was 120–154 NmL-CH4/g-CODinf, 20–30% higher than the control reactor. COD removal and methane production significantly decreased in both reactors when the influent tar concentration was doubled from 4954 mg-COD/L to 9964 mg-COD/L. When the influent concentration was reduced, the biochar packed reactor showed a faster recovery. Batch tests confirmed that higher tar concentration inhibited methane production and induced longer lagphase. Biochar addition effectively relieved the inhibition and prolonged the retention of organic matters. SEM observation and 16S rRNA analysis suggested that biochar also acted as the microbe’s carrier, and promoted the growth of some microbes. The results of this study provide new ideas for tar treatment.

Characteristics of microbial community in EGSB system treating with oxytetracycline production wastewater

In order to realize the efficient and stable operation of anaerobic digestion for oxytetracycline (OTC) production wastewater which contains high concentration refractory organic matters and antibiotic residues, two laboratory-scale EGSB reactors (the experimental reactor and the control reactor) were constructed for pre-treating OTC production wastewater and the complex characteristics and connections among anaerobic fermentative bacteria, methanogens and fungi were analyzed. The experimental reactor gradually increased OTC doses of 0–200 mg/L by four phases compared with the control reactor which was fed without OTC addition during 280 days’ operation. The average COD removal efficiency of 91.44% with the average OTC removal efficiency of 27.90% was achieved at OTC concentration of 200 mg/L. The addition of OTC did not affect the preponderant methanogen type, and Methanosaeta, a strict aceticlastic methanogen genus, was dominant both in working and controlling reactors on day 280. Redundancy analysis revealed that OTC and VFAs were the main environmental factors affecting the microbial communities and molecular ecological networks analysis indicated that the key genera principally belonged to Methanosaeta, Proteobacteria and Apiotrichum. Additionally, the fungi genus Apiotrichum might be related to the degradation of complex organic contaminants in OTC production wastewater treatment system.

Pollutant removal from landfill leachate via two-stage anoxic/oxic combined membrane bioreactor: Insight in organic characteristics and predictive function analysis of nitrogen-removal bacteria

A two-stage anoxic/oxic combined membrane bioreactor (A/O-A/O-MBR) was operated for 81 d to treat landfill leachate under different reflux ratios (R). The best performance was found under R = 150%, where the chemical oxygen demand (COD), ammonium (NH4+-N) and total nitrogen (TN) removal was 85.6%, 99.3%, and 80.7%, respectively. Particularly, the highest pollutant removal was achieved in the second-stage A/O, where the COD and TN removal capacity was 78.88 and 11.74 g/d, respectively. Meantime, DOM removal was 83.9%, where the removal of aromatic protein substances I and II, fulvic acids-like compounds, soluble microbial products and humic acids-like compounds was 93.4%, 86.4%, 72.0%, 86.6% and 59.4%, respectively. The gene functions of microbial community in the process showed that amoA, hao, nirK and nosZ, etc. were the core genes for nitrification and denitrification. The carbon source for denitrification might come from the conversion of refractory organic matters in landfill leachate.

Removing organic matters from reverse osmosis concentrate using advanced oxidation-biological activated carbon process combined with Fe3+/humus-reducing bacteria

The high-concentration wastewater produced in the industrial reverse osmosis (RO) process contains a large amount of refractory organic matters, which will have serious impacts on the natural environment and human health. Among them, contaminants can be transformed by humus-reducing bacteria based on humus. In this study, O3- assisted UV-Fenton method was applied as pretreatment. Biological activated carbon (BAC) technology in which humus-reducing bacteria were the dominant bacteria, enhanced by electron donor and Fe3+, was used to dispose of RO concentrate (ROC). The results showed that water treatment process combining oxidation with biological filtration had a positive effect on the removal of stubborn contaminants in ROC. The system was strengthened by adding electron donor and Fe3+, and the chemical oxygen demand (COD) removal efficiency was up to 80.1%. However, when the removal efficiency of UV254 absorbing pollutants reached optimal value (87.3%), that means only Fe3+ was added.

Enhancing swine wastewater hydrolysis with thermophilic bacteria and assisted pretreatments.

Slow degradation rate of swine wastewater, which is mainly caused by particulate and refractory organic matters, is the main drawback of anaerobic digestion. Therefore, it is necessary to improve the hydrolysis of swine wastewater. In this study, different pretreatments were used to hydrolyze swine wastewater, including thermophilic bacteria (TB), alkali, acid, ultrasound (UL), and ultrasonic-combined thermophilic bacteria (UL-TB) pretreatment. The hydrolysis effect was investigated by analyzing the changes of pretreated soluble chemical oxygen demand (SCOD), soluble protein, and carbohydrate. The experimental results showed that effect of different pretreatments on swine wastewater hydrolysis had the following order: TB=alkali>UL-TB>UL>acid. Alkali pretreatment was effective for the release of protein from swine wastewater, and TB pretreatment was advantageous for carbohydrate release during hydrolysis. The results could provide valuable information for the disposition of swine wastewater as well as the application of TB-related pretreatments. PRACTITIONER POINTS: TB and alkali pretreatment exhibited the highest hydrolysis ability. The release of carbohydrate by TB was higher than other pretreatments. Ultrasonic assistance generated inhibition on the hydrolysis of TB.