Adsorption behaviors of the pristine and aged thermoplastic polyurethane microplastics in Cu(II)-OTC coexisting system.

In this work, the hypothesis that thermoplastic polyurethane (TPU) microplastics (MPs) could form complex toxic pollution by absorbing both antibiotics and heavy metals simultaneously was proposed. The unique features of the adsorption of Cu(II) and oxytetracycline (OTC) on the pristine TPU and photo-aged (aged) TPU MPs in single and coexisting system were investigated, which included the kinetics, isothermal equilibrium and thermodynamics. The possibly synergistic or competitive effects between Cu(II) and OTC were also evaluated. The results showed that the adsorption process of Cu(II) and OTC could be described well by pseudo-second-order kinetic equation. The entire process could be divided into two stages: internal diffusion and external diffusion. The Sips model could give good fitting for the isothermal adsorption equilibrium. The thermodynamic parameters depicted the endothermic nature of adsorptions and the process was spontaneous. In the coexisting system, synergistic or competitive effects depended critically on the ratio of concentrations (Cu(II) vs OTC). When the ratio was 1:1, Cu(II) significantly enhanced the adsorption of OTC, while OTC showed a weak effect on Cu(II) adsorption. The synergies could be attributed to the formation of Cu(II)-OTC complex and the bridging effect of Cu(II). Overall, the adsorption capacity of aged TPU was higher than that of pristine TPU, which was due to the differences in morphological characteristics and functional groups. FTIR studies revealed that ester carbonyl and acylamino groups in the TPU may be involved in the adsorption of Cu(II) and OTC.

[Sorption Behaviors of Copper Ions and Tetracycline on Microplastics in Aqueous Solution].

The interaction between microplastics, heavy metals, and antibiotics can lead to combined pollution, which could result in greater environmental damage. The pathway and mechanism of the interaction between microplastics, heavy metals, and antibiotics are the preconditions for evaluating the associated environmental risk; however, these are not well understood. As probe sorbates, the sorption behaviors of copper ions (Cu2+) and tetracycline (TC) on two microplastics [high density polyethylene (HPDE) and general-purpose polystyrene (GPPS)] in aqueous solution were investigated and the welding theory with relevant experimental results were discussed. The adsorption capacity of HDPE was greater than that of GPPS in a single Cu solution, whereas the reverse situation occurred in a single TC solution. Moreover, the adsorption capacity of the microplastics in a Cu2+-TC binary solution was larger than that in the single solutions. The pseudo-second-order kinetic models to describe the adsorption process were reasonable and the entire process could be divided into two phases:surface adsorption and internal diffusion. The Langmuir model provided a better fit of the data than did the Freundlich model. In the single solutions, the saturated adsorption amounts of Cu2+ and TC were 0.178 µmol·g-1 and 0.257 µmol·g-1, respectively, for GPPS, and 0.334 µmol·g-1 and 0.194 µmol·g-1, respectively, for HDPE. In the binary solution, the corresponding numerical values were 0.529 µmol·g-1 and 0.411 µmol·g-1, respectively, for GPPS and 0.471 µmol·g-1 and 0.341 µmol·g-1, respectively, for HDPE. The variations in the surface morphological characteristics and chemical functional groups were the main reasons for the difference in the adsorption behavior of microplastics. The variation of the pH of the adsorption system could change the existing forms and surface electrical properties of microplastics and adsorbed objects, and subsequently affected the equilibrium adsorption capacity. When the ambient temperature was in the range of 15 to 35℃, increasing the temperature was unfavorable for the adsorption process. Cu2+ and TC could produce a synergistic effect under the conditions of coexistence. The formation of complexes and bridging make Cu2+ and TC more easily adsorbed by microplastics.

Characteristics of H2S emission from aged refuse after excavation exposure.

Hydrogen sulfide (H2S(g)) emission from landfills is a widespread problem, especially when aged refuse is excavated. H2S(g) emission from aged refuse exposed to air was investigated and the results showed that large amounts of H2S(g) can be released, especially in the first few hours after excavation, when H2S(g) concentrations in air near refuse could reach 2.00 mg m(-3). Initial exposure to air did not inhibit the emission of H2S(g), as is generally assumed, but actually promoted it. The amounts of H2S(g) emitted in the first 2 d after excavation can be very dangerous, and the risks associated with the emission of H2S(g) could decrease significantly with time. Unlike a large number of sulfide existed under anaerobic conditions, the sulfide in aged municipal solid waste can be oxidized chemically to elemental sulfur (but not sulfate) under aerobic conditions, and its conversion rate was higher than 80%. Only microorganisms can oxidize the reduced sulfur species to sulfate, and the conversion rate could reach about 50%. Using appropriate techniques to enhance these chemical and biological transformations could allow the potential health risks caused by H2S(g) after refuse excavation to be largely avoided.

Sorption behavior of dibutyl phthalate and dioctyl phthalate by aged refuse.

Sorption is a fundamental process controlling the transformation, fate, degradation, and biological activity of hydrophobic organic contaminants in the environment. We investigated the kinetics, isotherms, and potential mechanisms for the sorption of two phthalic acid esters (PAEs), dibutyl phthalate (DBP) and dioctyl phthalate (DOP), on aged refuse. A two-compartment first-order model performed better than a one-compartment first-order model in describing the kinetic sorption of PAEs, with a fast sorption process dominating. Both the Freundlich and Dubinin-Astakhov (DA) models fit the sorption isotherms of DBP and DOP, with the DA model being of a better fit over the range of apparent equilibrium concentrations. The values of the fitting parameters (n, b, E) of the PAEs suggest nonlinear sorption characteristics. Higher predicted partition coefficient values and saturated sorption capacity existed in refuse containing larger quantities of organic matter. The sorption capacity of DOP was significantly higher than that of DBP. PAE sorption was dependent on liquid phase pH. Desorption hysteresis occurred in PAE desorption experiments, especially for the long-chain DOP. PAEs may therefore be a potential environmental risk in landfill.

Role of iron in H(2)S emission behavior during the decomposition of biodegradable substrates in landfill.

Hydrogen sulfide (H2S) is regarded as a major odor causing compound in landfill gas that may lead to adverse environmental and health effects. In this study, the potential role of iron in the entire life cycle of H2S production and emission was investigated during the decomposition of biodegradable substrates in the landfilled refuse. The results showed that the quantity of H2S emission decreased about 95% when Fe(OH)3 was present in the biodegradable sulfur-containing substrates. During this degradation process, a lot of sulfide was generated, which was present mostly as ferrous sulfide. In addition, a total of 7.68% S-H2S of total sulfur released as gas phase could be remained in solid-liquid phase effectively in the simulated substrates with iron. Thus, using the appropriate way to take advantage of iron "hidden" in the landfilled refuse might be a good choice for in situ control of H2S emission. Moreover, if this high level of iron is not presented, landfill odor pollution might become more serious.

Investigation on characteristics of leachate and concentrated leachate in three landfill leachate treatment plants.

Concentrated leachate from membrane treatment processes is a potential pollution source for the surroundings. In this study, with comparison of the landfill leachate, chemical and microbial characteristics of concentrated leachate including biodegradability, amount of nitrogenous compounds and heavy metals, dissolved organic matter composition, and microbial community were investigated in three landfill leachate treatment plants. The results showed that hydrophilic (HyI) fraction was the major dissolved organic carbon in the landfill leachates, accounting for 54.6-60.7%, while humic substances including humic acid (HA) and fulvic acid (FA) were relatively higher in the concentrated leachates, ranging from 61.7% to 69.2%. Conjugated nitrogen existed mainly in FA and HyI in the concentrated leachates. The analysis of excitation emission matrix fluorescence spectroscopy, specific ultraviolet absorbance at 254nm (SUVA254) and GC/MS showed that aromatic compounds, long-chain hydrocarbons and halohydrocarbons were abundant in the concentrated leachates. During landfill leachate treatment processes, Cl(-), SO4(2-) and heavy metals were commonly accumulated in the concentrated leachates. NO3(-)N and/or NH4(+)N were the major nitrogenous compounds in the concentrated leachates. All the leachates from three landfill sites contained toluene in the range of 44.5-728.4µgL(-1). Ethylbenzene, chlorobenzene, and the phthalic acid esters including dibutyl phthalate, dimethyl phthalate and di-n-octyl phthalate were also detected in the concentrated leachates. Higher microbial diversity was observed in the concentrated leachate in comparison with landfill leachate.

[Transformation of dibutyl phthalate in bioreactor landfill].

Considering the refuse and leachate as one whole system, a conventional landfill (CL) was set as a control, transformation of dibutyl phthalate (DBP) in recirculated landfill (RL) and bioreactor landfill (BL) was studied. Results showed that DBP was detected in both leachate and refuse from CL, RL and BL. The initial DBP amount was 18.5 microg x g(-1) in the landfill refuse. In addition, the stabilization process of landfill, with sequences of BL > RL > CL, played an important role on the biodegradation of DBP in refuse. Compared to the acidic environment, the methanogenic environment was beneficial for DBP degradation. At the day of 310, refuse sedimentation rates were 7.0%, 11.9% and 24.3% in CL, RL and BL, respectively. DBP residual amounts were 2.1, 1.3 and 0.8 microg x g(-1), and its removal rates were 89.5%, 93.9% and 96.6% in the refuse from CL, RL and BL, respectively. The residual amounts of DBP with significant differences well fitted exponential decay models in CL, RL and BL. Finally, DBP biodegradation was obviously accelerated with the operation of leachate recirculation compared to the conventional operation, and it was further promoted with the introduction of methanogenic reactor.

Leaching behavior of iron from simulated landfills with different operational modes.

The aim of the present study was to investigate the leaching behavior of iron from simulated landfills with different operation modes, with an emphasis on the variation of iron in different oxidation state, ferrous Fe(II) and ferric Fe(III) percentage and the distribution of iron content in different landfill leachate fractions. The leaching behavior and accumulated amounts of iron leached out by leachate from conventional landfill (CL) and leachate recirculated landfill (RL) exhibited decidedly different trends except for the initial 28 days. In addition, the percentage of iron leached from CL and RL accounted 1.00% and 0.14% for the total amount in landfills, respectively. No correlations between iron and selected characteristics in leachate were found were observed in the two simulated landfills. Significant positive correlations between particulate bound iron and Fe(III) were found in the leachates from RL (R(2)=0.748) and CL (R(2)=0.833).

Methane oxidation in landfill waste biocover soil: kinetics and sensitivity to ambient conditions.

Waste biocover soil was investigated as an alternative in regions with a shortage of landfill cover soil. In the work, effects of the composition, ambient conditions and nitrogen stress on CH(4) oxidation in waste biocover soil were studied. The results showed that the optimal composition of waste biocover soil as a landfill cover material for CH(4) oxidation was original pH value, 45% moisture and a particle size of ≤ 4mm. CH(4) oxidation rate increased rapidly over a CH(4) concentration range of 0.01-10% (v/v), and kept stable at CH(4) concentrations of 10-30% (v/v). The Michaelis-Menten model showed a good fit for the kinetic of CH(4) oxidation in landfill waste biocover soil with a maximum of 9.03 µmol/gd.w./h. The average Q(10) was 10.6 in the batch experiments. A level of 5% of oxygen concentration was enough to sustain the activity of methanotrophs community structure in waste biocover soil. Waste biocover soil had low baseline concentrations of NH(4)(+)-N and NO(3)(-)-N. Ammonia volatilization from landfills and nitrification in landfill waste biocover soils might stimulate CH(4) consumption at concentrations below 600 mg/kg. However, the contents of NH(4)(+)-N and NO(3)(-)-N above 1200 mg/kg would inhibit CH(4) oxidation in landfill waste biocover soil. Compared with NO(3)(-)-N, NH(4)(+)-N had a greater stimulating action as nutrient at lower concentrations and inhibitory effect at higher concentrations on CH(4) oxidation in landfill waste biocover soil.

An innovative combined on-site process for the remote rural solid waste treatment--a pilot scale case study in China.

The aim of this study was to find a feasible method for the treatment of solid waste generated in the remote rural, where the transportation costs are prohibitive and the resources to construct and maintain conventional treatment plants are not available. This process, consisted of two types of simulated bioreactor landfill (one was recirculated bioreactor landfill, and the other was comprised of fresh and aged refuse reactor) and a soil infiltration system, was operated in ambient temperature for 180 days all together. After treated by the system of fresh and aged refuse reactor, the refuse and leachate reached a strongly degraded and stable state. The remaining leachate can be treated by the soil infiltration system, and 87.5 ± 2.1%, 98.6 ± 1.0% and 95.7 ± 1.7% were achieved by 60 cm soil depths for organic matter, ammonium nitrogen and total nitrogen removal, respectively.

Characterization of adsorption removal of hydrogen sulfide by waste biocover soil, an alternative landfill cover.

Landfill is an important anthropogenic source of odorous gases. In this work, the adsorption characteristics of H(2)S on waste biocover soil, an alternative landfill cover, were investigated. The results showed that the adsorption capacity of H(2)S increased with the reduction of particle size, the increase of pH value and water content of waste biocover soil. The optimal composition of waste biocover soil, in regard to operation cost and H(2)S removal performance, was original pH value, water content of 40% (w/w) and particle size of ≤4 mm. A net increase was observed in the adsorption capacity of H(2)S with temperatures in the range of 4-35°C. The adsorption capacity of H(2)S on waste biocover soil with optimal composition reached the maximum value of 60±1 mg/kg at oxygen concentration of 10% (v/v). When H(2)S concentration was about 5% (v/v), the adsorption capacity was near saturation, maintaining at 383±40 mg/kg. Among the four experimental soils, the highest adsorption capacity of H(2)S was observed on waste biocover soil, followed by landfill cover soil, mulberry soil, and sand soil, which was only 9.8% of that of waste biocover soil.

Effect of liquid-to-solid ratio on semi-solid Fenton process in hazardous solid waste detoxication.

The liquid-to-solid ratio (L/S) of semi-solid Fenton process (SSFP) designated for hazardous solid waste detoxication was investigated. The removal and minimization effects of o-nitroaniline (ONA) in simulate solid waste residue (SSWR) from organic arsenic industry was evaluated by total organic carbon (TOC) and ONA removal efficiency, respectively. Initially, Box-Behnken design (BBD) and response surface methodology (RSM) were used to optimize the key factors of SSFP. Results showed that the removal rates of TOC and ONA decreased as L/S increased. Subsequently, four target initial ONA concentrations including 100 mg kg(-1), 1 g kg(-1), 10 g kg(-1), and 100 gk g(-1) on a dry basis were evaluated for the effect of L/S. A significant cubic empirical model between the initial ONA concentration and L/S was successfully developed to predict the optimal L/S for given initial ONA concentration for SSFP. Moreover, an optimized operation strategy of multi-SSFP for different cases was determined based on the residual target pollutant concentration and the corresponding environmental conditions. It showed that the total L/S of multi-SSFP in all tested scenarios was no greater than 3.8, which is lower than the conventional slurry systems (L/S ≥ 5). The multi-SSFP is environment-friendly when it used for detoxication of hazardous solid waste contaminated by ONA and provides a potential method for the detoxication of hazardous solid waste contaminated by organics.

Effect of weathering treatment on the fractionation and leaching behavior of copper in municipal solid waste incinerator bottom ash.

This work describes the effect of weathering of fresh quenched municipal solid waste incinerator (MSWI) bottom ash on the fractionation and leaching behavior of Cu. A sequential extraction procedure was used to characterize the fractionation of Cu in the fresh and weathered MSWI bottom ash samples. It showed that the organic matter bound fraction of Cu decreased drastically from 69% to 37% during the weathering treatment, while the residual fraction, Fe-Mn oxides bound fraction, carbonate bound fraction and exchangeable fraction increased from 24% to 54%, 3% to 4%, 2% to 3% and 2% to 3%, respectively. Furthermore, two standard leaching procedures, synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP), were carried out on the fresh and weathered samples. The leaching of Cu was attenuated with the process of weathering treatment in the SPLP procedure, but was enhanced in the TCLP procedure. The results suggested that the weathering treatment could change the fractionation and leaching behavior of Cu in MSWI bottom ash. Further research is required to correlate weathering of ash and mobility of Cu.

A comparative study on two extraction procedures in speciation of iron in municipal solid waste.

Two extraction reagents, hydrochloric acid (HCl) and acid ammonium oxalate solution (Tamm's reagent), were used to evaluate the redox state of iron in municipal solid waste (MSW) with different deposit ages. Orthogonal experiments were conducted to optimize the extraction conditions for extractable iron speciation (ferric and ferrous) in MSW. The optimal extraction conditions for HCl were determined as follows: the liquid-to-solid ratio was set at 100, and then the samples were extracted at the shaking speed of 200 rpm at 35 degrees C for 60 min by 1.00 M HCl. For Tamm's reagent, the optimal extraction conditions were extracted at the shaking speed of 175 rpm at 30 degrees C for 12 h with the same liquid-to-solid ratio. However, Tamm's reagent extraction is much more laborious and time-consuming. Thus the HC1 extraction might be a better choice for the evaluation of the redox state of iron in MSW. The results also showed that the yield of extractable iron increased with deposited age. About 60-83% of extractable iron was presented as ferrous in the MSW deposited for 1-8 years. This study supplied a tool for investigating the role of iron on the fate of pollutants in the landfill.

Bio-immobilization of Cu and Zn in recirculated bioreactor landfill.

PURPOSE: To protect the environmental quality of soil, groundwater, and surface water near the landfill site, it is necessary to make an accurate assessment of the heavy metal mobility. This study aims to present the bio-immobilization behavior of heavy metals in landfill and provide some reference suggestion for the manipulation of heavy metal pollution control after closure. MATERIALS AND METHODS: Two simulated bioreactor landfill system loaded with real municipal solid waste (MSW), namely, conventional bioreactor landfill (CL) and leachate recirculated bioreactor landfill (RL), were operated. Cu and Zn, the two conventional heavy metals with the highest contents in MSW, were chosen to track the heavy metal bio-immobilization behavior in landfill. RESULTS: The MSW in landfill is a great threat to environment because much of the heavy metal is "hidden" in different components. The weight ratio of Cu and Zn in landfill amounts to 0.00427% and 0.00437%, respectively. The accumulated effluent masses of Cu and Zn in CL increased all along, while they still kept at a stable level after day 105 in RL. CONCLUSIONS: The microbes like sulfate-reducing bacteria mediate the behavior of Cu and Zn in bioreactor landfill system. Cu and Zn can be bio-immobilized in bioreactor landfill system with leachate recirculation like RL.

Comparison on the removal of phthalic acid diesters in a bioreactor landfill and a conventional landfill.

The removal of phthalic acid diesters (PAEs) in municipal solid waste (MSW) from two simulated landfill reactors was compared. The results showed that the original concentrations of dimethyl phthalate (DMP), dibutyl phthalate (DBP) and dioctyl phthalate (DOP) in the refuse were 3.3 microg g(-1), 18.5 microg g(-1) and 0.8 microg g(-1), respectively. The concentrations of DMP and DBP in both leachate and refuse decreased greatly during decomposition of the waste in both reactors. The major loss of PAEs from the landfill occurred during an active methanogenic environment with a low concentration of volatile fatty acids (VFA) in the later period. In addition, strong correlations were found between the residual DMP, DBP concentrations and the biologically degradable material (BDM) of the refuse. Finally, PAEs degraded more rapidly in the landfill that was operated in conjunction with the methanogenic reactor when compared to the landfill with direct leachate discharge.

Releasing behavior of zinc in recirculated bioreactor landfill.

The purpose of this research was to determine the releasing behavior of zinc in municipal solid waste (MSW) in landfill site with respect to refuse and leachate as an inseparable system. Two simulated bioreactor landfills, one with leachate recirculation and the other without, were operated in room temperature for 320 days. Results showed that the content of zinc in MSW could amount to 591.29+/-31.33-632.14+/-18.98 microg g(-1) dry weight(-1) (DW(-1)). It exceeded the set standard for "Environmental quality standard for soil" (< or =500 microg g(-1) DW(-1)) and had high potential environmental risk. The releasing behavior of zinc in refuse mainly experienced speciation of solid-Zn, Zn(2+), ZnHCO(3)(+), ZnCO(3), Zn(OH)(+), Zn(OH)(2), Zn(NH(3))(4)(2+), ZnS, etc. Zinc in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of refuse in bioreactor landfill. The Zn(2+) concentration in leachate, which varied correspondingly with releasing behavior of zinc in refuse, were 0.75 mg L(-1) to 3.13 mg L(-1) and had no great difference in landfill with different operation modes (CL and RL). However, the amount of Zn(2+) leached out from refuse, which accounted for 28.70 mg and 130.67 mg after 320 day's operation, respectively. More attention should be paid to the inseparable system including refuse and leachate together.

Effect of sample pretreatment on speciation of copper and zinc in MSW.

Copper and zinc were determined in MSW samples collected from Tianziling landfill site in Hangzhou, Zhejiang, east China by modified BCR sequential extractions. Three pretreatment methods, including fresh, air drying, and oven drying, were studied. It showed that the main cause of fraction transfer after drying could be ascribed to the variation of sample status, including the evaporation of ammonia nitrogen and volatile fatty acid (VFA), the shift of sample pH, and the oxidation of sulfur, when contacted with atmospheric oxygen or exposed in high temperature during drying processes. Effect of sample pretreatment methods on speciation of copper and zinc in MSW concluded that oven drying should not be used because the changes are more numerous and generally of greater amplitude, air drying was a 'neutral' treatment relatively, while fresh sample might be the best choice if possible. To validate the effect and determine the source of pretreatment methods clearly, certified reference materials of MSW should be confirmed in the future research.

Behavior of dibutyl phthalate in a simulated landfill bioreactor.

In this study, the behavior of dibutyl phthalate (DBP) from municipal solid waste (MSW) in the leachate and refuse of two simulated landfill bioreactors was compared. In one reactor, the leachate was circulated between a landfill and a methanogenic reactor, while the other reactor was operated using direct recirculation of the leachate. The results revealed that the original concentration of DBP in the refuse was approximately 18.5 microg/g, and that this concentration decreased greatly during decomposition of the waste for both reactors. Furthermore, the major loss of DBP from the landfill occurred in an active methanogenic environment in the later period, while the environment was acidic due to a high concentration of volatile fatty acids (VFA) and contained a large volume of biologically degradable material (BDM) during the early stage. Circulating the leachate between the landfill and a methanogenic reactor resulted in an increase in the biodegradability of MSW and a high degree of waste stabilization. Furthermore, DBP degraded more rapidly in the landfill that was operated in conjunction with the methanogenic reactor when compared to the landfill in which there was direct leachate recirculation.

Releasing behavior of copper in recirculated bioreactor landfill.

The purpose of this study was to determine the releasing behavior of copper in municipal solid waste (MSW) in landfill with respect to refuse and leachate as an inseparable system. Two simulated bioreactor landfills, one with leachate recirculation and the other without, were operated in room temperature for 320 days. Copper in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of landfill obviously. The significant different amounts of Cu2+ leached out from refuse into leachate of two landfills were 24.74 mg and 118.53 mg after 320 days' operation, respectively. It also reflected the releasing behavior of copper in landfill refuse at different stage accordingly. The results confirmed that the refuse in landfill had high potential of secondary pollution after closure.