• Waste management in Japan
• Circular economy in Japan
• Waste management in Asia
• Disaster waste management

What is waste landfill leachate?

Waste landfill leachate (or landfill leachate) refers to polluted water in which various substances from waste are dissolved. Rainwater that falls on landfill sites becomes polluted when it infiltrates from landfill surface through waste layers. Landfill leachate contains organic matter, salts, ammonia and heavy metals. It may also contain hazardous chemical substances depending on the type of waste landfilled. Properties of landfill leachate vary according to the type and age of landfilled waste, structure of the landfill, climate conditions and other factors. Pre-disposal treatment such as recycling and various intermediate processing also greatly influences the properties.

In Japan where about 80% of the general waste (household and business waste) is incinerated, most landfilled waste is composed of incineration residue and incombustible residue (plastic, rubber, metal, etc). The incineration residue contains a significant amount of salts derived from slaked lime, or Ca(OH)₂, which is often used to neutralize acidic gases generated during the incineration process. Japanese landfill leachate, containing a high proportion of incinerated residue, is therefore characterized by a high concentration of salts, a low concentration of easily decomposable organic matter, and neutral to moderately alkaline pH.

In Southeast Asian countries, however, waste is mostly landfilled directly with no intermediate treatment. At these landfill sites, the landfilled waste initially shows mildly acidic pH due to its high content of easily decomposable organic compounds such as organic acid, but along with time, pH and the proportion of inorganic substances and persistent organic compounds such as humic acid increase.

Problems and countermeasures on landfill leachate

If inappropriately managed, the leachate containing contaminants will be more likely to pollute the surrounding environment. There are concerns regarding not only the direct contamination of surface water such as rivers and lakes by leakage of drained leachate or untreated leachate discharged from a landfill, but also the contamination of groundwater by infiltration of leachate into the ground. There are also concerns about health risks to the people living around the landfill if their drinking water sources are contaminated, or if they use contaminated water for agriculture. Moreover, the contamination of irrigation water might have a secondary effect on agriculture such as a decline in productivity. For ensuring environmentally sound management of landfills, it is important to take comprehensive measures covering reduction of leachate generation, prevention of its leakage to the surrounding areas, and adequate control of the collected leachate.

In Japan, landfill leachate is managed by a comprehensive fail-safe system that does not depend on a single measure but combines diverse measures as below.

1. Reduction of rainwater infiltration into waste layers: prevention of rainwater infiltration by covering the waste layers with soil and installing structures such as sloped surfaces with rainwater collection and drainage pipes.
2. Prevention of leachate leakage from the bottom and sides of the landfill: installation of water shielding structures on the bottom of the landfill to prevent the leachate from infiltrating into the ground (see the September 2010 issue: Technology to Prevent Leachate Leakage from Final Disposal Sites [in Japanese]).
3. Prompt and complete collection of leachate: installation of leachate collection and drainage pipes on the bottom and sides of the landfill to collect leachate for drainage.
4. Discharge of treated water into the surrounding environment only after controlling its quality by landfill leachate treatment plants suitable for achieving the required quality.

In contrast, Southeast Asian countries still have difficulties in adequately managing landfill leachate in the same way as Japan does due to their current insufficient economic and technological capacity. Additionally, their climate with dry and rainy seasons necessitates measures to respond to the variations in leachate quality and volume. At present, many Southeast Asian countries control leachate by collecting it in an artificial pond (reservoir) to reduce the amount through natural evaporation, unlike Japan that uses systems to treat leachate for safe discharge. However, high rainfall in the Southeast Asian region in the rainy season generates a large amount of leachate. The countries in the region have a common problem that the leachate exceeds the reservoirs' storage capacity and leaks out from the landfill sites. The most important point in the leachate management in Southeast Asia can be therefore how to reduce its amount. Considering their needs for reducing the leachate amount, we have been conducting research on the development of a leachate management system suitable for Southeast Asian countries. For more information on our research, please see our article on the leachate management in the landfills in Southeast Asia in the March 2014 issue (in Japanese).