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Lead (Pb) accumulation can lead to serious threats to surrounding environments and damage to the liver and kidneys. In the past few years, microbial-induced carbonate precipitation (MICP) technology has been widely applied to achieve Pb immobilization due to its environmentally friendly nature. However, harsh pH conditions can cause the instability of the carbonate precipitation to degrade or dissolve, increasing the potential of Pb2+ migration into nearby environments. In this study, microcapsule-based self-healing microbial-induced calcium carbonate (MICC) materials were applied to prevent Pb migration. The highest sporulation rate of 95.8% was attained at 7 g/L yeast extract, 10 g/L NH4Cl, and 3.6 g/L Mn2+. In the germination phase, the microcapsule not only prevented the bacterial spores from being threatened by the acid treatment but secured their growth and reproduction. Micro analysis also revealed that cerussite, calcite, and aragonite minerals were present, while extracellular polymeric substances (EPSs) were identified via Fourier transform infrared spectroscopy (FTIR). These results confirm their involvement in combining Pb2+ and Ca2+. The immobilization efficiency of above 90% applied to MICC materials was attained, while it of below 5% applied to no MICC use was attained. The findings explore the potential of applying microcapsule-based self-healing MICC materials to prevent Pb ion migration when the calcium carbonate degrades under harsh pH conditions. • The carbon and nitrogen sources and trace elements affected the sporulation rate. • The microcapsule prevented the spores from affecting by harsh pH conditions. • The microcapsule provided the spores with more sites to combine with Pb2+ and Ca2+. • The microcapsule achieved the self-healing of carbonate precipitation. [ABSTRACT FROM AUTHOR]

The construction of an engineered cover layer over landfills is a common method applied to reduce the emission of hazardous gases into the atmosphere. Landfill gas pressures can reach 50 kPa or even higher in some cases, thus posing a serious threat to nearby properties and human safety. As such, the evaluation of gas breakthrough pressure and gas permeability in a landfill cover layer is of great necessity. In this study, the loess soil that is often applied as a cover layer in landfills in northwestern China was used to conduct gas breakthrough, gas permeability, and mercury intrusion porosimetry (MIP) tests. Resultantly, the smaller the capillary tube diameter, the higher the capillary force, and the more significant the capillary effect. Gas breakthrough could be attained with no difficulty, provided that the capillary effect was minimal or approached zero. A good fit between the experimental gas breakthrough pressure–intrinsic permeability relationship and a logarithmic equation was found. The mechanical effect blew up the gas flow channel. In the worst-case scenario, the mechanical effect could lead to the overall failure of a loess cover layer in a landfill. A new gas flow channel was formed between the rubber membrane and the loess specimen as a result of the interfacial effect. Although both the mechanical and interfacial effects can elevate the gas emission rate, the latter did not play a role in the improvement of the gas permeability; therefore, misleading interference took place in the evaluation of the gas permeability, and an overall failure of the loess cover layer. To tackle this problem, the point at which the large- and small-effective stress asymptotes cross on the volumetric deformation– P eff diagram may be applied to give early warning signals of the potential overall failure of the loess cover layer in landfills in northwestern China. • The capillary effect is a crucial factor affecting the gas breakthrough pressure. • Both the mechanical and interfacial effects gear up the gas emission rate. • The interfacial effect can mislead the assessment of the failure of a cover layer. • The volumetric deformation goes up with decrease in P eff in an exponential manner. • Such exponential relationship gives early warning of the failure of a cover layer. [ABSTRACT FROM AUTHOR]