Search

Aiming to reveal the humification process of organic waste and its contribution to the heavy metal behaviour affected by earthworm activity, it was studied about the variation of humic acid (HA) and heavy metal behaviour during vermicomposting of the mixed pig manure and 13C-labelled rice straw. The results showed that earthworms could well adapt to the culturing environment and feed organic matter for its growth and reproduction, the vermicomposting process increased the content of humic substances (HS), HA, and fulvic acid (FA) in substrate residues, but led to less transformation of HA into FA. The elemental, ultraviolet absorption spectroscopy, Fourier transform infrared (FTIR) and fluorescence excitation–emission matrix (EEM) analysis indicated that vermicomposting led to more aromatic structures and much higher humification degree in HA, whereas less protein, FA-like substances and plastein in HA. Vermicomposting could enhance the total Cu content and decrease Cu/Zn bioavailability in the substrate residues, and vermicomposting especially can help stabilize Cu in the substrate residues by forming more complexed HA–Cu.

The response of anaerobic ammonium oxidation (anammox) process and granular sludge in the upflow anaerobic sludge blanket reactor was analyzed under long-term exposure to MnO2 nanoparticles (NPs) (1–200 mg L−1). The addition of 200 mg L−1 MnO2 NPs had a significantly positive effect on nitrogen removal and this system exhibited excellent performance, with a total nitrogen removal efficiency of 93.1%. Moreover, the specific anammox activity enhanced with increasing concentrations of MnO2 NPs up to the maximum value of 657.3 ± 9.3 mg TN g−1 VSS d−1 under MnO2 NPs concentration of 200 mg L−1. This value was approximately 1.6-fold higher than that of the reactor in the absence of MnO2 NPs. The extracellular polymeric substances and settling velocity were both increased with MnO2 NPs addition. Meanwhile, the high-throughput sequencing results revealed that MnO2 NPs increased the relative abundance of dominant bacteria (Candidatus Kuenenia) from 17.3% at the absence of MnO2 NPs to 23.9% at 200 mg L−1 MnO2 NPs, which resulted in a higher efficiency of biological nitrogen removal on the anammox system. These results indicated that MnO2 NPs enhanced nitrogen removal performance of anammox process.

Ammonia emission during composting results in anthropogenic odor nuisance and reduces the agronomic value of the compost due to the loss of nitrogen. Adjusting the operating parameters during composting is an emerging in situ odor control technique that is cheap and highly efficient. The effects of in situ NH3 emission control were investigated in this study by simultaneously adjusting key operating parameters (such as C/N ratio, aeration rate, and moisture content) during the composting processes (C1-C9). Results showed that the average NH3 emission concentrations for different treatments were in the order of C1 > C4 > C2 > C5 > C3 > C6 > C7 > C8 > C9. The total content of NH3 emission (21.02 g/kg) in C9 (C/N ratio = 35, aeration rate = 15 L/min, and moisture content = 60%) was much lower than that (65.95 g/kg) in C1 (C/N ratio = 15, aeration rate = 5 L/min, and moisture content = 60%). The nitrogen loss ratio was 27.36% for C1, while 16.15% for C9. The microbial diversity and abundance in C9 and C1 were compared using high-throughput sequencing. The relationship between NH3 emission, operating parameters, and the related functional microbial communities was also investigated. Results revealed that Nitrosospira, Nitrosomonas, Nitrobacter, Pseudomonas, Methanosaeta, Rhodobacter, Paracoccus, and Sphingobacterium were negatively related to NH3 emission. According to the above results, the optimal values for different operating parameters for the in situ NH3 control during kitchen waste composting were, respectively, moisture content of 70%, C/N ratio of 35, and aeration rate of 15 L/min, with the order of effectiveness from high to low being aeration rate > C/N > moisture. This information could be used as a valuable reference for the in situ NH3 emission control during kitchen waste composting.

The widespread existence of lead (Pb) contamination in soil has received extensive attention. To effectively slow lead-ion (Pb2+) migration and promote plant growth in heavy metal-contaminated soil as well as to realize the resource utilization of solid waste, vermireactors were used to obtain vermicompost using cow dung mixed with modified mineral (MM) as feedstock material for Eisenia fetida. Vermicompost was characterized first, and then its slowing effect on Pb2+ migration in soil was further evaluated through pot experiments. The results demonstrated that earthworms could grow well in cow dung and mineral vermireactors, and earthworm activity increased the cation exchange capacity (CEC), total nutrient content and surface area but decreased the pH, carbon to nitrogen ratio (C/N) and organic matter content in the vermicompost. The addition of MM resulted in an increase in the pH, CEC, and surface area but a decrease in the C/N of the vermicompost. X-ray diffraction analysis showed that the addition of MM increased the contents of quartz, CaCO3, CaO and MgO in the vermicompost. Fourier transform infrared spectroscopy analysis indicated that comparatively less carbohydrates, lipids and polysaccharides and more aromatic compounds existed in the vermicompost, and the addition of MM increased the number of Me-O groups. Pot experiments showed that the application of vermicompost from cow dung and mineral vermireactors significantly promoted the growth of celery cabbage and reduced the Pb content in its edible parts and the Pb bioavailability in soil. Thus, it is possible to use cow dung and mineral vermireactors to optimize the properties of vermicompost for its use as a soil amendment to remediate Pb contamination.

Perfluorooctanoic acid (PFOA) is widely distributed in various environmental media and is toxic to organisms. This study demonstrated that PFOA induces hepatotoxicity in the frog and evaluated the role of CYP3A and the Nrf2-ARE signaling pathway in regulating responses to PFOA-induced hepatotoxicity. Rana nigromaculata were exposed to 0, 0.01, 0.1, 0.5, or 1 mg/L PFOA solutions in a static-renewal system for 14 days. Liver tissue samples were collected 24 h after the last treatment. Hepatic histology was observed by HE staining and transmission electron microscopy. The oxidative stress levels in the liver were measured. The expression levels of CYP3A, Nrf2, NQO1, and HO-1 mRNA were measured by quantitative reverse transcription–polymerase chain reaction. PFOA-treated frog liver tissue exhibited diffuse cell borders, cytoplasmic vacuolization, broken nuclei, nuclear chromatin margination, and swollen mitochondria. In addition, the livers of PFOA-treated frogs showed a significantly elevated content of reactive oxygen species, malondialdehyde, glutathione and glutathione S-transferase activity compared to the livers of control frogs. However, the glutathione peroxidase activities concomitantly decreased in PFOA-treated frogs compared to those in the control group. Furthermore, compared with control frogs, the expression levels of CYP3A, Nrf2, and NQO1 mRNA significantly increased in PFOA-treated frogs. HO-1 mRNA expression remarkably increased only in groups treated with 0.5 or 1 mg/L PFOA. Our results indicate that PFOA induces hepatotoxicity in a dose-dependent manner. Furthermore, the results of the comparison analysis between different gender groups illustrated that PFOA is more toxic to female frogs than male frogs. Our results demonstrated that PFOA causes liver damage and that CYP3A enhances PFOA-induced female frogs hepatotoxicity are more virulent than male through biotransformation, and the activation of the Nrf2-ARE pathway is induced to protect against hepatotoxicity in Rana nigromaculata, all of which provide the scientific basis for the protection of amphibians against environmental contaminants.

Cadmium (Cd) contamination has become serious in soil and in situ stabilization technology has been widely used for heavy metal remediation. A field study was conducted to determine the effect of amendments with the doses of 3 kg/m2, including single vermicompost (A1), a 95% vermicompost mixed with 5% shell powder composite (A2) and a 95% vermicompost mixed with 5% modified shell powder composite (A3), on the Cd bioavailability, enzyme activity and bacterial community in soil, and the experiment was conducted with lettuce (Lactuca sativa L.) grown in a Cd-contaminated farmland soil. The results showed that the application of amendments increased the pH, cation exchange capacity (CEC), organic matter (OM), available nutrients, catalase (S-CAT), invertase (S-SC) and urease (S-UE) activities in soil, while significantly reduced the Cd bioavailability with the lowest Cd bioavailability being observed in the soil with A3 application. The soil bacterial richness and diversity increased after amendments application, and the bacterial community was characterized by an increase in metal-tolerant bacteria but a decrease in Proteobacteria, Acidobacteria and Gemmatimonadetes. In addition, the application of amendments significantly improved the growth of lettuce (Lactuca sativa L.) and inhibited Cd accumulation in its edible parts, especially, the Cd content in lettuce (Lactuca sativa L.) grown in soil with A3 application was below the limit of the National Food Safety Standard of China (maximum level ≤ 0.2 mg/kg). Thus, composite amendment obtained from vermicompost mixed with modified shell powder can be used as potential remediation material in Cd-contaminated soil. Capsule Composite amendment obtained from vermicompost and modified shell powder had good effects on remediation of Cd-contaminated soil.

The C/N ratio and carrier type strongly affect aerobic denitrification and are critical for nitrogen removal by sequencing batch reactor (SBR) processes. Poly (1,4-butanediol succinate) (1,4-PBS) is a biodegradable material that provides electrons to denitrifying microorganisms. The effect of carrier on the aerobic denitrifying microorganisms is worth further studying. In this study, aerobic denitrifying microorganisms were combined with 1,4-PBS to evaluate the effects of microbial biomass on the biodegradable carriers and nitrogen removal efficiency. High-throughput sequencing results indicated that after 45 days of the operation, the Shannon index of bacteria in the 1,4-PBS group increased from 4.48 (phase I, C/N = 5 at 1–8 days) to 5.74 (phase II, C/N = 10 at 9–20 days) and continuously increased to 6.68 in phase III (C/N = 20, 21–45 days). The peak total nitrogen (TN), NH4+-N and total organic carbon (TOC) removal efficiencies were 56.4%, 75.49% and 59.56% respectively at high C/N of 20. This result indicated that PBS significantly increased microbial diversity and indirectly changed the structure of microbial communities. Moreover, principal component analysis (PCA) showed that 1,4-PBS might change the microbial community. Specifically, 1,4-PBS might increase microbial diversity and indirectly change the structure of microbial communities. Meanwhile, the content of extracellular polymeric substances increased to 416.33 g g−1 VSS. 3D-EEM spectra showed that protein-like and humic acid-like substances were the main components in SMPs, and the fluorescence intensity increased in the initial 31 days and decreased in the following 14 days. Therefore, 1,4-PBS can efficiently improve the nitrogen removal performance of microbial communities. This study offers a reliable reference for the effects of biodegradable carriers on the nitrogen removal performance of microorganisms.

The increasing release of engineered nanoparticles (NPs) from consumer products has raised great concerns about their impacts on biological wastewater treatment. In this study, the widely-used ZnO NP was selected as a model NP to investigate its impact on high-rate denitrifying granular sludge in terms of sludge properties and community structure. A hormesis effect was observed during short-term exposure, in which the specific denitrification activity (SDA) was stimulated by 10% at 1 mg L−1 ZnO NPs, but inhibited by 23% at 5.0 mg L−1 ZnO NPs. When continuously exposed to 2.5 mg L−1 ZnO NPs, the nitrogen removal capacity of the denitrification reactor was nearly deprived within 15 days, and the relative abundance of the dominant denitrifying bacterium (Castellaniella) was decreased from 51.0 to 8.0%. Meanwhile, the dehydrogenase activity (DHA) and the content of extracellular polymeric substance (EPS) significantly decreased to 22.3 and 61.1%, respectively. Nevertheless, the presence of phosphate substantially weakened the adverse effects of ZnO NPs on the SDA, EPS, DHA and the relative abundance of functional genes even exposed to 6.25 mg L−1 ZnO NPs, which was associated with the fact that the level of Zn(II) released from ZnO NPs was significantly reduced in the presence of phosphate. Therefore, the toxicity of ZnO NPs may be mainly attributed to the release of toxic Zn(II) and could be attenuated in the presence of phosphate. Overall, this study provided further reference and meaningful insights into the impact of engineered NPs on biological wastewater treatment.

Odor problem has become a growing concern for municipal solid waste (MSW) operators and communities located close to landfill sites. In this study, nine laboratory-scale landfill reactors were used to simulate in-situ odor control by a novel landfill cover material consisting of biochar-added sludge compost under various operating parameters. Characterization of odor removal and microbial community in the cover layer under various operating parameters was conducted using gas chromatograph-mass spectrometry and 454 high-throughput pyrosequencing, respectively. Results showed that H2S (76.9–86.0%) and volatile organic sulfur compounds (VOSCs) (12.3–21.7%) were dominant according to their theoretical generated odor concentrations. The total odor REs calculated using the theoretical odor concentrations in the landfill reactors were different than using the measured odor values, which were ranked from high to low as: R6 > R5 > R7 > R4 > R8 > R9 > R3 > R2 > R1, showing the largest discrepancy of 25.3%. The optimum combination of operating parameters based on the theoretical odor concentration was different with that based on the measured odor concentrations. Moreover, although Firmicutes (12.21–91.48%), Proteobacteria (3.55–51.03%), and Actinobacteria (4.01–47.39%) were in general the three major bacterial phyla found in the landfill covers, the detailed bacterial communities in the cover materials of the simulated reactors varied with various operating parameters. Alicyclobacillus and Tuberibacillus showed positive correlations with the removal efficiencies (REs) of chlorinated compounds, H2S, aromatic compounds, volatile organic sulfur compounds (VOSCs), and organic acids. The correlations of Rhodanobacter, Gemmatimonas, Flavisolibacter and Sphingomonas were strongly positive with ammonia RE and relatively positive with REs of organic acids, VOSCs, and aromatic compounds. These findings are instrumental in understanding the relationship between the structure of microbial communities and odor removal performances, and in developing techniques for in-situ odor control at landfills.

A mixture of pig manure and maize straw was vermicomposted with Eisenia fetida or naturally composted for 60 days; basic parameters, heavy metal variation, dissolved organic matter (DOM) content, and its characterization were determined, aiming to explore different dynamics of DOM characterization and heavy metal variation during composting or vermicomposting. The results showed that vermicomposting led to higher pH, TC, and available P but lower EC, TN, available N, and available K in the substrate residues compared with natural composting; the total or available Cu/Zn content in the substrate residues similarly increased after composting or vermicomposting, but Cu was easily enriched in earthworm bodies and its intestinal vermicompost while vermicomposting enhanced the formation of dissolved Zn in DOM; moreover, much more fulvic and humic acid-like materials and much greater aromaticity were exhibited in DOM obtained from vermicomposting residues compared with DOM from composting residues, which may contribute to the variations of Cu/Zn enrichment in earthworms and its migration to the vermicomposting residues or its DOM.

Vermicomposting is an eco-friendly method for disposing of livestock and poultry manure. In addition, dissolved organic matter (DOM) can serve as a carrier that enhances the migration and transformation of heavy metals. Here, pig manure amended with rice straw was vermicomposted with Eisenia fetida. The DOM content, molecular weight distribution, and spectroscopic properties of the amended pig manure were measured before and after vermicomposting. The Cu and Zn concentrations in the earthworms increased from 8.24 and 17.63 to 40.75 and 362.78 mg/kg separately after vermicomposting, and the earthworms also increased the heavy metal availability in the vermicompost. Relative to the DOM properties of conventional compost, the DOM molecular weight decreased and varied widely following vermicomposting, and the C/N ratio of the DOM in the vermicompost treatments decreased from 10.37 to 8.60. The Fourier transform far-infrared (FTIR) and fluorescence spectra of the DOM indicated that the amounts of oxygen-containing structures increased while the ratio of humic acid to fulvic acid decreased following vermicomposting. Accordingly, the earthworms augmented the heavy metal mitigation risk in the pig manure. This augment potentially resulted from the decreased humic acid-to-fulvic acid (HA/FA) ratio from DOM structural changes.

Using pot experiments, growth and heavy metal uptake of Sorghum Hybrid Sudangrass was studied when planted in soils amended with vermicomposts enriched with Cu/Zn content. The results showed that growth of Sorghum Hybrid Sudangrass was stimulated when low vermicomposts concentration was applied whereas it was restrained when high vermicomposts concentration was applied. The Cu and Zn content increased in Sorghum Hybrid Sudangrass as vermicomposts concentration increased. The forms of Cu and Zn in soils dominantly existed as organic fraction and residual fraction at the low vermicomposts concentration, but existed as acid-extractable fraction and the reducing fraction at the high application level of vermicomposts. Correlation analysis indicated that shoot Zn content, root Cu/Zn content in Sorghum Hybrid Sudangrass was positively correlated with heavy metal fraction in vermicompost amended soils. Therefore, the 10% vermicompost addition may be feasible for field production systems.

Pot experiments were conducted to investigate the effects of three different chelating agents(EDTA, citric acid, NTA) that intensify the absorption and accumulation of Cu, Zn in vermicompost for Euchlaena Mexicana Schrad. The results indicated that chelating agents addition could inhibit the growth of Euchlaena Mexicana Schrad, and the inhibition on the roots is greater than the shoots. At the same concentration, EDTA had the greatest inhibition on plant roots, the overarching inhibition on plant shoots fell to citric acid. The addition of EDTA and NTA increased Cu or Zn contents in the roots and shoots of Euchlaena Mexicana Schrad, and also improved the Cu or Zn accumulations in the shoots, although high addition concentration of CA increased Cu or Zn contents in the roots and shoots of Euchlaena Mexicana Schrad, Cu or Zn accumulations in the shoots were conspicuously inhibited after high concentration of CA were added. Hence, EDTA and NTA have the potentials of intensifying the extraction of Cu or Zn by Euchlaena Mexicana Schrad from the vermicompost enriched with high Cu or Zn contents, which opens up a new approach to enhance phytoremediation in terms of solid waste contaminated with heavy metals.

Pot experiment, in which vermicompost enriched with high Cu and Zn contents was applied in aqualf soil to simulate soil metal accumulation from vermicompost application, was conducted to study the effect of vermicompost application on growth of Sorghum Hybrid Sudangrass and Euchlaena Mexicana Schrad as well as their Cu or Zn uptake and soil characteristics. The results showed that shoot growth was improved for the two pastures, while it was significantly inhibited for the root growth of Euchlaena Mexicana Schrad with increasing heavy metal pollution from vermicompost application. Both Cu or Zn contents in shoot or root of Sorghum Hybrid Sudangrass and that in Euchlaena Mexicana Schrad increased after vermicompost application, especially, Cu content in roots of Sorghum Hybrid Sudangrass increased significantly with increasing heavy metal pollution from vermicompost.application In addition, Correlation analysis showed that Cu or Zn contents in two pastures were positively related to acid-extractable and reducible Cu or Zn fraction. So, continuously consecutive application of vermicompost enriched with high Cu and Zn content could contribute to the accumulation of exchanged and reducible Cu or Zn content in soil and pose a potential threat to the plant system.