Effect of Basic Oxygen Furnace (BOF) slag leachate on methane oxidation and community composition in biogeochemical landfill cover system

Municipal solid waste (MSW) landfills are regarded as one of the major sources of greenhouse gas (GHG) emissions across the world. In order to control these emissions, a sustainable biogeochemical cover system, consisting of biochar-amended soil layer overlain by BOF slag layer, is being developed to mitigate both methane (CH4) and carbon dioxide (CO2) emissions. The effectiveness of such cover system is highly dependent on the survival and activity of methanotrophs under highly alkaline conditions induced by the presence of the slag. In this paper, laboratory microcosm tests were conducted to investigate the effect of BOF slag leachate on the CH4 oxidation in soil and in enrichment culture. The BOF slag leachate at different proportions (0, 5, 20, 60 and 100%) in soil and (0, 11, 25 and 100%) in enrichment culture was studied. The CH4 oxidation rates in the soil were 113, 116, 115, 108 and 97 µg CH4 g-1d-1 at 0, 5, 20, 60 and 100% slag leachate, respectively, and in enrichment culture, the CH4 oxidation rates were 36, 27, 20 and 17 µg CH4 mL-1d-1 at 0, 11, 25 and 100% slag leachate, respectively. The results showed that the CH4 oxidation rates decreased significantly with increase in slag leachate proportions (> 11%) in enrichment culture and decreased marginally in the soil microcosm tests. Furthermore, no change in the community composition was noted across the slag leachate proportions in soil microcosms and were typically dominated by the species Methylobacter luteus. However, the microbial community in the enrichment culture performed differently with the abundance of Methylobacter to decrease with increase in slag leachate proportions and Methylosinus to increase with increase in slag leachate proportions. Overall, this study exhibited substantial CH4 oxidation in both soil and enrichment culture with survival of methanotrophic community under varied slag leachate proportions.

城市生活垃圾（Municipal solid waste, MSW）填埋场被认为是全球范围内温室气体（Greenhouse Gas, GHG）的主要排放源之一。为控制此类排放，一种由生物炭改良土层叠加碱性氧气转炉渣（Basic Oxygen Furnace slag，简称BOF slag）层构成的可持续生物地球化学覆盖系统正处于研发阶段，用于减缓甲烷（CH4）与二氧化碳（CO2）的排放。该覆盖系统的防控效果高度依赖甲烷氧化菌（methanotrophs）在转炉渣引发的强碱性环境下的存活与活性。

本文开展实验室微宇宙实验，探究转炉渣渗滤液对土壤及富集培养体系中甲烷氧化过程的影响。本研究考察了不同比例的转炉渣渗滤液：土壤体系中设置0、5%、20%、60%及100%五个梯度，富集培养体系中设置0、11%、25%及100%四个梯度。土壤体系中，0、5%、20%、60%、100%渗滤液对应的甲烷氧化速率分别为113、116、115、108及97 µg CH4·g⁻¹·d⁻¹；富集培养体系中，0、11%、25%、100%渗滤液对应的甲烷氧化速率分别为36、27、20及17 µg CH4·mL⁻¹·d⁻¹。

研究结果表明，富集培养体系中，甲烷氧化速率随转炉渣渗滤液占比提升（>11%）显著下降；而土壤微宇宙实验中，该速率仅出现小幅降低。此外，土壤微宇宙的微生物群落组成未随渗滤液比例变化发生明显改变，且群落始终以黄色甲基杆菌（Methylobacter luteus）为优势类群。与之相反，富集培养体系的微生物群落呈现出不同的变化趋势：甲基杆菌属（Methylobacter）的丰度随渗滤液占比提升而下降，甲基孢囊菌属（Methylosinus）的丰度则随渗滤液占比提升而上升。

总体而言，本研究证实，在不同转炉渣渗滤液比例下，土壤与富集培养体系均能维持可观的甲烷氧化能力，且甲烷氧化菌群落可正常存活。