Landfill leachate has a high chloride (Cl-) content. Because it is highly mobile, and cannot be sorbed or transformed bio-chemically, it is important to have detailed information about how it migrates in landfill sites. In this study, we set up four lab-scale simulated landfills, including an anaerobic landfill (AL), an anaerobic landfill with leachate recirculation (RAL), an anaerobic/semi-anaerobic landfill with leachate recirculation (RASL), and an anaerobic/semi-aerobic landfill (ASL), to explore how, when regulated, moisture and air affected the migration of chlorine. We found that water and air had a strong influence on the release of Cl-. Leachate obviously promoted Cl- dissolution in refuse when recirculated. When air was introduced into landfill, thereby changing it from anaerobic to semi-aerobic, the leachate Cl- concentration increased sharply from around 4-9 g L-1 (RASL) and 18 g L-1 (ASL), respectively. In principle, Cl- is released continuously when leachate is recirculated in landfills (RAL and RASL), but it can also be found a terminal when the leachate recirculation stops (AL and ASL). Cumulative amounts of 64, 66, 27, and 53 g of Cl- were released from the AL, RAL, RASL, and ASL, respectively. Lower COD/Cl and -N/Cl ratios in ASL and RASL after day 175 indicated that lower Cl- pollution risk than that in AL and RAL.
Keywords: Chloride; landfill; leachate; migration behaviour.