Releasing behavior of zinc in recirculated bioreactor landfill

Zinc leaching behavior in semi-aerobic landfill

Municipal solid waste landfills require continuous monitoring because that the environmental change may trigger sudden release of heavy metals and need special care. In this research, three simulated landfills with different operation modes were used to investigate the behavior of Zn during the decomposition process. It is difficult to evaluate the effects of landfill operating modes on the release of heavy metals because the Zn concentration variation in leachate is similar in all three landfill types. However, the cumulative amount of Zn leached differed significantly with the landfill degradation degree. Zn can continuously leach from the traditional anaerobic landfill but relatively well retain in the semi-aerobic landfill. Leachate recirculation and air exposure not only promote the landfill stabilization process, but also obviously lower the risk of Zn pollution in the leachate by transforming it from unstable fractions to the more stable one, the residual fraction. Although heavy metal experiences vertical migration within the landfill, the transformation process retains it in the refuse and avoids its sudden release. The release of the most active fraction of Zn can be neglected during the rapid degradation stage and the most stable fraction of Zn can always be maintained at a positive level in all landfill modes tested.

Endogenous mitigation of H2S inside of the landfills

Vast quantities of hydrogen sulfide (H2S) emitted from landfill sites require urgent disposal. The current study focused on source control and examined the migration and conversion behavior of sulfur compounds in two lab-scale simulated landfills with different operation modes. It aimed to explore the possible strategies and mechanisms for H2S endogenous mitigation inside of landfills during decomposition. It was found that the strength of H2S emissions from the landfill sites was dependent on the municipal solid waste (MSW) degradation speed and vertical distribution of sulfide. Leachate recirculation can shorten both the H2S influence period and pollution risk to the surrounding environment. H2S endogenous mitigation may be achieved by chemical oxidation, biological oxidation, adsorption, and/or precipitation in different stages. Migration and conversion mainly affected H2S release behavior during the initial stabilization phase in the landfill. Microbial activities related to sulfur, nitrogen, and iron can further promote H2S endogenous mitigation during the high reducing phase. Thus, H2S endogenous mitigation can be effectively enhanced via control of the aforementioned processes.

Content and fractionation of Cu, Zn and Cd in size fractionated municipal solid waste incineration bottom ash

Municipal solid waste incinerator (MSWI) bottom ash was size fractionated into six fractions, with the respective particle size of <0.45 mm, 0.45-1 mm, 1-2 mm, 2-4 mm, 4-8 mm and >8 mm. The contents and fractionation of Cu, Zn, Cd in the size fractionated MSWI bottom ash were investigated. The results showed the contents and fractionation of Cu, Zn and Cd varied among the different particle sizes, which were related to their thermodynamic characteristics. High content of Cu was found in the bottom ash with the particle size of <0.45 mm and >4 mm, due to its lithophilic property and the function of entrainment. The content of Zn showed a relatively even distribution among the various particles. The content of Cd showed a decreasing trend with the increase of the particle size, due to its high volatility. Besides, the carbonate bound fraction of Cd showed a decreasing trend with the increase of the particle size, while the carbonate bound fraction of Cu showed an increasing trend. The organic matter bound fraction of Cu increased when the particle size increased. The results also showed the fine ash contained a higher level of unstable Cd than the large ash, while the large ash had a higher level of unstable Cu comparatively.

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.