What is waste landfill leachate?
Waste landfill leachate is a wastewater which contains different substances in the process that rain water seeping inside the waste layer. Waste landfill leachate contains organic compounds, salt, ammonia, heavy metals and so on. Depending on the type of wastes disposed at landfill sites, it sometimes contains hazardous chemical substances. Characteristics of waste landfill leachate differ by the duration of time after being landfilled, type of landfilled waste, structure of landfill and climate condition. For example, characteristic of leachate could be different due to the intermediate treatment and recycling before the waste was brought to landfill sites.
In japan, approximately 80% of the total amount of municipal solid waste is incinerated. What is landfilled is incinerated residues and incombustible wastes (plastics, rubber waste, metals etc.) In the process of incineration, alkali hydrated lime (Ca(OH)2) in order to neutralize the generated acid gases, so ample amounts of salts derived from the lime hydrate is present. Therefore, we can summarize the characteristics of waste landfill leachate in Japan are, 1) ample amount of salts, 2) little amount of easily biodegradable organic matter, and 3)neutral PH to alkalescent.
On the other hand, in Southeast Asian region, waste is directly landfilled without processing in intermediate treatment facility. In the early stage of landfilling, waste contains easily biodegradable organic matters such as organic acid and has weakly acidic pH value. After some time passed, due to the existence of microorganism, percentage of not easily biodegradable organic and inorganic become higher and pH value will also increase.
Issues raised by waste landfill leachate and its countermeasures
When the management of waste landfill leachate is insufficient, possibility of contaminating the surrounding environment by the leachate containing pollutant substances will be greater. Untreated leachate from landfills not only contaminates the surface water (rivers and lakes) but also it could seep into the soil and contaminate the ground water. Contamination of water source or usage of contaminated agricultural water may negatively affect the human’s health of the residents living in the surrounded area. It may cause the secondary damage such as contaminated agricultural water may degrade the productivity of agricultural sector as well. In order to manage environmentally safe landfill, it is important to take comprehensive countermeasures such as decrease the generated amount of leachate, avoid the leakage of leachate to outside of landfill, and appropriately manage the collected leachate.
In Japan, we conduct not only one countermeasure but combine the multi-level safety countermeasures to make sure the appropriate management of waste landfill leachate.
1. Reduce the amount of rainwater inflow into the waste layer; Cover the waste layer with soil, establish the structure (leaned surface of waste layer and rainwater collection pipes) to prevent rainwater to inflow.
2. Prevent the leakage of leachate from the bottom and side of landfill; establish the water shielding structure at the bottom of landfill
3. Collect the generated leachate promptly and surely; establish the collection pipe for leachate at the side and bottom of landfill
4. Release the leachate treated at an appropriate leachate treatment facility to the environment with an appropriate water quality control
On the other hand, with current economic situation and technological capacity, leachate management in Southeast Asian countries is not easy as of now. Additionally, the climate with rainy and dry seasons in the region obliges to adjust the change of water volume and quality. In Japan, leachate is treated before released to rivers, instead, many countries in Southeast Asian region control the leachate by collecting it in the leachate pond and allow the leachate to be evaporated. However, due to the heavy rainfalls during the rainy season, leachate ponds sometime exceeds its capacity to hold the leachate and leak leachate to the inappropriate water channel. In order to control the leachate in Southeast Asian region, it is essential to decrease the volume of leachate. In our current research, we are focusing on the methodology to decrease the volume of leachate to propose the improved leachate management in Southeast Asian countries. Please read the column, “Application of technology on constructed wetlands for the leachate treatment at landfill site in Southeast Asia” for details of the research.