Control of hydrogen sulfide emissions using autotrophic denitrification landfill biocovers:engineering applications

Hydrogen sulfide(H_(2)S)emitted from construction and demolition waste landfills has received increasing attention.Besides its unpleasant odor,longterm exposure to a very low concentration of H_(2)S can cause a public health issue.In the case of construction and demolition(C&D)waste landfills,where gas collection systems are not normally required,the generated H_(2)S is typically not controlled and the number of treatment processes to control H_(2)S emissions in situ is limited.An attractive alternative may be to use chemically or biologically active landfill covers.A few studies using various types of cover materials to attenuate H_(2)S emissions demonstrated that H_(2)S emissions can be effectively reduced.In this study,therefore,the costs and benefits of H_(2)S-control cover systems including compost,soil amended with lime,fine concrete,and autotrophic denitrification were evaluated.Based on a case-study landfill area of 0.04 km^(2),the estimated H_(2)S emissions of 80900 kg over the 15-year period and costs of active cover system components(ammonium nitrate fertilizer for autotrophic denitrification cover,lime,fine concrete,and compost),ammonium nitrate fertilizer is the most cost effective,followed by hydrated lime,fine concrete,and yard waste compost.Fine concrete and yard waste compost covers are expensive measures to control H_(2)S emissions because of the large amount of materials needed to create a cover.Controlling H_(2)S emissions using fine concrete and compost is less expensive at landfills that provide on-site concrete recovery and composting facilities;however,ammonium nitrate fertilizer or hydrated lime would still be more cost effective applications.

Diversity of methanotrophs in a simulated modified biocover reactor

A simulated landfill biocover microcosm consisting of a modifying ceramsite material and compost were investigated.Results show that the mixture can improve the material porosity and achieve a stable and highly efficient （100%） methane oxidation over an extended operating period.The diversity of the methanotrophic community in the microcosm was assessed.Type I methanotrophs were enhanced in the microcosm due to the increased air diffusion and distribution,whereas the microbial diversity and population density of type II methanotrophs were not significantly affected.Moreover,the type I methanotrophic community structure significantly varied with the reactor height,whereas that of type II methanotrophic communities did not exhibit a spatial variation.Phylogenetic analysis showed that type I methanotroph-based nested polymerase chain reaction-denaturing gradient gel electrophoresis （PCR-DGGE） resulted in the detection of eight different populations,most of which are related to Methylobacter sp.,whereas that of type II resulted in the detection of nine different populations,most of which are related to Methylocystaceae.Methanotrophic community analysis also indicated that a number of new methanotrophic genera not closely related to any known methanotrophic populations were present.

In-situ neutralize methane emission from landfills in loess regions using leachate

In loess regions, landfilling is the predominant solid waste disposal and loess is usually used as landfill cover soil. However, the methane(CH_4) bio-oxidation activity of virgin loess is usually below 0.01 μmol/(h g-soil). In this study, we proposed a method to improve CH_4 removal capacity of loess by amelioration with mature landfill leachate, which is in-situ, easily available, and appropriate. The organic matter content of the ameliorated loess increased by 180%, reaching 19.69–24.88 g/kg-soil, with more than 90% being non-leachable. The abundance of type I methane-oxidizing bacteria and methane monooxygenase gene pmoA increased by 5.0 and 79 times, respectively. Consequently, the maximum CH_4 removal rate of ameliorated loess reached 0.74–1.41 μmol/(h g-soil) at 25°C, which was 4-fold higher than that of water-irrigated loess. Besides, the CH_4 removal rate peaked at 10 vt% CH_4 concentration and remained at around 1.4 μmol/(h g-soil) at 15°C–35°C. The column test confirmed that the highest CH_4 removal efficiency was at 30–40 cm below the surface, reaching 26.1%±0.4%, and the 50-cm-thick loess layer irrigated with leachate achieved more than 85% CH_4 removal efficiency. These results could help to realize carbon neutrality in landfill sites of global loess regions.