Effect of nano zero valent iron on degradation of municipal solid waste in bioreactor landfills.

摘要

Nanotechnology has substantial potential for reducing contamination, toxicity and overall human health hazards and environmental risks. In recent times, nano zero valent iron has proved to be effective in contaminant reduction and pollution control. Iron is an important micronutrient for the microbes involved in the anaerobic decomposition of solid waste in bioreactor landfills. Landfill leachate sometimes contains toxic compounds which nano zero valent iron has proven to be very effective in removing, particularly chlorinated organics, heavy metals, and odorous sulfides. Iron can also potentially increase landfill methane generation by removing long chain fatty acids and sulfides that inhibit methanogenesis.;nZVI materials are highly reactive and have been previously used to remove contaminants from water and soil. However, no studies have been conducted regarding the effect of adding nZVI to Municipal Solid Waste (MSW) degradation. Therefore, the investigation of the nanoparticles in stabilizing MSW was the primary goal of this study. The current study focuses on the change in gas production and leachate characteristics due to addition of nZVI particles to MSW in laboratory scale set ups of bioreactor landfills. The current study compared MSW decomposition in lab scale simulated bioreactors, with and without the presence of nano zero valent iron (nZVI). 6-gallon PVC lab scale bioreactors were filled with MSW collected from the Denton Landfill, with added sludge from a wastewater treatment plant as a source of microorganisms and moisture, along with leachate recirculation. nZVI (0.01% by weight of the total mass of solid waste present) was added to one of the reactors. The gas results show that the two reactors had a comparable percentage of methane. Both reactors produced similar quantities of gas during the first 20 days. However, the reactor with the added nZVI had a lag period of approximately 50 days after that, before its gas production peaked. The lag was probably due to microbes acclimating to the increased iron level. The hypothesis that iron would enhance methane production, however, turned out not to be true. The leachate results, for the most part are consistent with the results of the gas production. The lag in gas production for reactor 2 is also reflected in the leachate pH. The pH for both reactors dropped for the first couple of weeks and picked up with the start of methane production. In case of the second reactor there was a lag phase before the pH started to increase. Similarly, there was a lag in the COD decrease as well for reactor 2. However, the BOD results are not consistent as there is a marked difference in the leachate BOD for reactor 2 between the first and second months. This may be due to the presence of nZVI in the reactor 2 leachate. Also, the BOD and COD values for the second reactor leachate were considerably higher, possibly due to the presence of nZVI.