•Biochars were produced from municipal organic solid waste through pyrolysis.•Biochars were used for the removal of methylene blue dye (MB) – an hazardous pollutant.•Biochar prepared from biogas ...residue has the highest adsorption efficiency.•Adsorption behaviors was well described by pseudo-second-order kinetic model.•Adsorption fitted well with Langmuir isotherms, suggesting monolayer adsorption.
Biochars prepared from anaerobic digestion residue (BC-R), palm bark (BC-PB) and eucalyptus (BC-E) were used as sorbents for removal of cationic methylene blue dye (MB). The FE-SEM images indicated that the biochars have a well-developed pore structure, and the Brunauer–Emmett–Teller surface areas of BC-R, BC-PB, and BC-E were 7.60, 2.46, and 10.35m2g−1, respectively. The efficiencies of MB removal in the samples with initial concentrations of 5mgL−1 at pH 7.0 and 40°C by BC-R, BC-PB, and BC-E after 2h were 99.5%, 99.3%, and 86.1%, respectively. Pseudo-second-order kinetics was the most suitable model for describing the adsorption of MB onto the biochars. The experimental data were best described by the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 9.50mgg−1 at 40°C for BC-R. The biochars produced from the three types of solid waste showed considerable potential for adsorption.
The stability and mobility of uranium (U) is a concern following its reductive precipitation or immobilization by techniques such as bioremediation at contaminated sites. In this study, the ...influences of complexing organic ligands such as citrate and ethylenediaminetetraacetate (EDTA) on the mobilization of U were investigated in both batch and column flow systems using a contaminated and bioreduced sediment. Results indicate that both reduced U(IV) and oxidized U(VI) in the sediment can be effectively mobilized with the addition of EDTA or citrate under anaerobic conditions. The dissolution and mobilization of U appear to be correlated to the dissolution of iron (Fe)- or aluminum (Al)-bearing minerals, with EDTA being more effective (with R 2 ≥ 0.89) than citrate (R 2 < 0.60) in dissolving these minerals. The column flow experiments confirm that U, Fe, and Al can be mobilized by these ligands under anoxic conditions, although the cumulative amounts of U removal constituted ∼0.1% of total U present in this sediment following a limited period of leaching. This study concludes that the presence of complexing organic ligands may pose a long-term concern by slowly dissolving U-bearing minerals and mobilizing U even under a strict anaerobic environment.
•Anaerobic co-digestion food waste, wastepaper and plastic were examined.•Stable anaerobic digestion of food waste, wastepaper and plastic was achieved.•The accumulation of ammonium and free ammonia ...does not inhibit anaerobic process.•Significant microbial shift was observed during the anaerobic process.•Co-digestion food waste, wastepaper and plastic were feasible.
The performance of municipal organic solid waste anaerobic digestion was investigated using a single-stage bioreactor, and the microbial community structures were characterized during the digestion. The results showed that the biogas and methane production rates were 592.4 and 370.1L/kg with volatile solid added at the ratio of 2:1:1 for food waste, wastepaper, and plastic based on dry weight. The methane volume concentration fluctuated between 44.3% and 75.4% at steady stage. Acetic acid, propionic acid, and butyric acid were the major volatile fatty acids produced during the digestion process. The anaerobic process was not inhibited by the accumulation of ammonia and free ammonia. The bacterial community was found to consist of at least 21 bands of bacteria and 12 bands of archaea at the steady state. All of the results indicated that the mixture of food waste, wastepaper, and plastic could be efficiently co-digested using the anaerobic digestion system.
Biological reduction and precipitation of uranium (U) has been proposed as a remedial option for immobilizing uranium at contaminated sites, but the long-term stability and mobility of uranium remain ...a concern because the uranium is neither removed nor destroyed. In this study, the dissolution and mobilization of reduced and oxidized forms of uranium U(IV) and U(VI) by natural humic substances were investigated in batch and column-flow systems using a bioreduced sediment containing both U(IV) and U(VI). The addition of humic substances significantly increased the dissolution of U(IV) under anaerobic conditions. Humic acid (HA) was found to be more effective than fulvic acid (FA) in dissolving U(IV) in 1 mM KCl or KHCO3 background solution. However, more U(VI) was dissolved in 1 mM KHCO3 than in 1 mM KCl background electrolyte. HA also was found to be more effective than FA in mobilizing uranium under reducing and column-flow conditions, although the cumulative amount of eluted U(VI) and U(IV) was relatively low (<60 μg) after leaching with ∼97 pore volumes of the humic solution in 1 mM KHCO3. These observations suggest that natural humic substances could potentially influence the long-term stability of bioreduced U(IV) even under strongly reducing environments.
Techniques for rapid screening of uranium in environmental samples are needed, and this study entails the development of surface-enhanced Raman scattering (SERS) for analyzing uranium in aqueous ...media with improved sensitivity and reproducibility. A new SERS substrate based on (aminomethyl)phosphonic acid (APA)-modified gold nanoparticles was found to give greater than three orders of magnitude SERS enhancement compared with unmodified bare gold nanoparticles. Intensities of uranyl band at about 830
cm
−1 were proportional to the concentrations of uranium in solution, especially at relatively low concentrations (<10
−5
M). A detection limit of ∼8
×
10
−7
M was achieved with a good reproducibility since the measurement was performed directly in dispersed aqueous suspension. Without pretreatment, the technique was successfully employed for detecting uranium in a highly contaminated groundwater with a low pH, high dissolved salts (e.g., nitrate, sulfate, calcium and aluminum) and total organic carbon.
In this study, the adsorptive characteristics of biochar generated from anaerobically digested garden wastes (AD-char) were investigated. Metal adsorption onto AD-chars reached equilibrium in 48 h; ...the adsorption capacity of Cu2+ by AD-char was 182 μmol g-1, which was higher than that of Zn2+ (35.3 μmol g-1) and Mn2+ (60.7 μmol g-1). The metal adsorption was well described by the pseudo second-order kinetic and Langmuir isotherm models. pKinta1, pKinta2, and pkCu for AD-char, which described surface protonation reactions and complexation with Cu2+, were 5.75, -10.20, and -4.70, respectively, as optimized by the surface complexation model. Cu2+ adsorption onto AD-char increased with increasing pH to < 8.6, which suggests that the presence of surface alkaline functional groups can be attributed to the metal adsorption capacity of biochar. This study concluded that converting anaerobically digested food and garden wastes into biochar could be an efficient method of treating municipal solid waste and producing metal adsorbents for environmental remediation.
This research evaluated a method of controlled base addition for immobilizing uranium (U) and technetium (Tc) through co-precipitation with aluminum (Al) and other metal ions which co-exist in a ...highly contaminated acidic environment. The batch and column experiments indicate that the addition of strong base (NaOH) provided a rapid yet effective means of sequestering U, Tc, and toxic metal ions such as nickel (Ni2+) and cobalt (Co2+) in the sediment and groundwater. Greater than 94% of soluble U (as UO2 2+) and >83% of Tc (as TcO4 −) can be immobilized at pH above 4.5 by co-precipitation with Al-oxyhydroxides. The presence of sediment minerals appeared to facilitate co-precipitation of these contaminants at lower pH values than those in the absence of sediments. The immobilized U and Tc were found to be stable against dissolution in Ca(NO3)2 solution (up to 50 mM) because of the formation of strong surface complexes between U or Tc and Al-oxyhydroxides. This research concludes that, as long as a relatively high pH (>5) and a low carbonate concentration are maintained, both U and Tc can be effectively immobilized under given site-specific conditions.
In situ sampling techniques such as membrane dialysis are widely applied to the monitoring of heavy metal contamination in water-saturated environments. In this study, batch experiments were ...conducted to investigate the influence of humic substances (HS) on the diffusive transportation of metal ions across sampling membranes. The presence of HS substantially slowed the transportation of metal ions by 22.2, 20.3, 17.4, 16.6, and 14.9 % for Zn
2+
, Cu
2+
, Ni
2+
, Co
2+
, and Mn
2+
, respectively, in the 100-mg/L HS-amended treatments relative to the treatments without HS under acidic conditions (pH = 5.0). The retention effect of HS on the metal ions appeared to be relieved at a higher pH of 8.5. However, HS also slowed the transportation of metal ions (Cu
2+
, Zn
2+
, Ni
2+
and Co
2+
) into the sampling cells when membranes soaked previously in porewater solution. The retention effects of HS can be attributed to the enhanced adsorption of metal ions on the surfaces of the membranes. Further study in saturated sediments verified that the membrane dialysis technique could underestimate the concentrations of metal ions by 13.3–40.2 % at the presences of HS. These findings suggest that collected porewater data using the membrane dialysis technique should be interpreted with caution with the consideration of in situ geochemical conditions such as HS or pH in water-saturated environments.
Batch and column recirculation titration tests were performed with contaminated acidic sediments. A generic geochemical model was developed combining precipitation, cation exchange, and surface ...complexation reactions to describe the observed pH and metal ion concentrations in experiments with or without the presence of CO2. Experimental results showed a slow pH increase due to strong buffering by Al hydrolysis and precipitation and CO2 uptake. The cation concentrations generally decreased at higher pH than those observed in previous tests without CO2. Using amorphous Al(OH)3 and basaluminite precipitation reactions and a cation exchange selectivity coefficient K Na\Al of 0.3, the model approximately described the observed (1) pH titration curve, (2) Ca, Mg, and Mn concentration by cation exchange, and (3) U concentrations by surface complexation with Fe hydroxides at pH < 5 and with liebigite (Ca2UO2(CO3)3·10H2O) precipitation at pH > 5. The model indicated that the formation of aqueous carbonate complexes and competition with carbonate for surface sites could inhibit U and Ni adsorption and precipitation. Our results suggested that the uncertainty in basaluminite solubility is an important source of prediction uncertainty and ignoring labile solid phase Al underestimates the base requirement in titration of acidic sediments.
Chinese silver grass (CSG), a potential subtropical energy crop, was investigated as a co-substrate to enhance the anaerobic digestion of food waste for municipal solid waste treatment. Results ...showed that 88.1% of food wastes were degraded using CSG as a co-substrate with 45 days of digestion, where the food waste, CSG, and sludge on VS/TS/working volume was 93.14 g/111.55 g/1 L, in which the average biogas production was at 429.3 L/kg solids, and the average methane content was around 60%. During the digestion, the concentrations of ammonium and free ammonia gradually increased to 1448.2 and 265.2 mg/L respectively, without any significant inhibitory effects on biogas production, which is probably due to the buffering effects of CSG. Microbial community analysis showed that microorganisms from the class of Firmicutes and Bacteroidetes were dominant during digestion, and that the microbial community diversity increased with active methanogenesis, suggesting that the addition of substrates contribute to the increase of microbial diversity, and could be beneficial for biogas production. Therefore, using CSG as a co-substrate in the single-stage food waste anaerobic digestion system is a potential simple method to convert CSG into renewable energy and to simultaneously improve food waste treatment.
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