文摘
Continuous flow experiments were conducted using sand-packed columns to investigate the relative significance of bacterial growth, metal precipitation, and anaerobic gas formation on biologically induced clogging of soils. Natural leachate from a local municipal landfill, amended with acetic acid, was fed to two sand-packed columns operated in upflow mode. Degradation of the influent acetic acid resulted in the production of methane and carbon dioxide, and simultaneous reduction of manganese, iron, and sulphate. Subsequent increase in the influent acetic acid concentration from 1750 to 2900mg/l, and then to 5100mg/l, led to rapid increase in the dissolved inorganic carbon, solution pH, and soil-attached biomass concentration at the column inlet, which promoted the precipitation of Mn2+ and Ca2+ as carbonate, and Fe2+ as sulphide. An influent acetic acid concentration of 1750mg/l decreased the soil's hydraulic conductivity from an initial value of 8.8×10−3cm/s to approximately 7×10−5cm/s in the 2–6cm section of the column. Increasing the influent acetic acid to 5100mg/l only further decreased the hydraulic conductivity to 3.6×10−5cm/s; rather, the primary effect was to increase the length of the zone experiencing reduced hydraulic conductivity from 0–6cm to the entire column. As bioaccumulation was limited to the 0–5cm section of the column, and the effect of metal precipitation was negligible, the reduction on the deeper sections of the column is attributed to gas flow, which was up to 1440ml/day. Mathematical modelling shows that biomass accumulation and gas formation were equally significant in reducing the hydraulic conductivity, while metal precipitation contributed only up to 4 % of the observed reduction.
