Insight into the effect of calcium on bio-clogging behavior via quartz crystal microbalance with dissipation monitoring

Bio-clogging of leachate collection systems has attracted much attention because of its threat to landfill slope stability and landfill landslide events. Calcium in leachate plays a vital role in the formation of bio-clogging. However, the influence of calcium on bio-clogging remains unclear. This study examined the effects of calcium concentration on bio-clogging, including 0, 1.25, 5, 25, and 75 mM CaCl2 groups. A technique involving quartz crystal microbalance with dissipation monitoring (QCM-D) was applied to evaluate the bacteria adhesion behaviors in real time. The results showed that the presence of Ca2+ accelerated the bacterial attachment and increased the viscoelasticity of deposited layers. The deposition mass for 75 mM CaCl2 was 1442 ± 260 ng/cm2, which is 1.5 times that for 1.25 mM CaCl2. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory could explain the bacterial adhesion behaviors in low calcium concentrations (<25 mM). In comparison, the effect of calcium bridge was shown in high calcium concentrations (>25 mM). The development of biofilms was a dynamic process, and the Ca2+ concentration was positively related to the amount of biofilm generated. In low CaCl2 concentration (less than 5 mM) groups, the degree of bio-clogging increased from the exponential growth phase to the decline phase; in contrast, in high CaCl2 concentration (above 25 mM) groups, the degree of bio-clogging increased and later declined. Therefore, the calcium concentration should be controlled at a low level in leachate to mitigate bio-clogging in LCSs.