- Waste management in Japan
- Circular economy in Japan
- Waste management in Asia
- Disaster waste management
Application of Constructed Wetland Technology to Landfill Leachate Treatment in Southeast Asia
Current situation of landfill and leachate management in Asia
Southeast Asian countries have advanced their efforts in protecting environment in urban areas as their economy has grown. The situation of waste landfill sites also appears to have improved significantly compared to the past. More landfill sites have adopted advanced technologies such as shielding structures on the bottom to prevent leachate seepage and covering soil to prevent dispersion of waste, vermin and odors. In addition, introduction of source-separated collection and intermediate treatment of municipal solid waste (MSW) has changed the properties of landfilled waste. In contrast to the advances in the MSW management, leachate control in many landfill sites still remains inappropriate: landfill leachate often seeps into storage ponds and ground.
These urban areas of Southeast Asian countries have problems with their specific environmental conditions. A large amount of leachate is generated in the rainy season. In addition, the amount of waste generation itself has been increasing and its properties have been diversifying. Our research team in the Center for Material Cycles and Waste Management Research believes the importance of proposing landfill leachate treatment as part of the overall waste management system in accordance with these specific regional conditions. We have therefore been researching on leachate management technologies and systems to solve these region-specific problems according to the degree of advancement of the region in MSW management. We have also been providing information to these countries in order to support comprehensive and smooth transfer of relevant technologies.
Ecological engineering technology for wastewater treatment
Currently, the Southeast Asian countries, even with their growing economy, may still have difficulties in allocating substantial amount of financial and energy resources for landfill leachate treatment. We have therefore been continuing our research with a focus on a wastewater treatment technology called constructed wetland (CW) that utilizes abilities of ecosystems and requires little electricity (see the relevant article in the February 2013 issue: Wastewater Treatment by Constructed Wetlands [in Japanese]).
The wastewater treatment with CW uses less mechanical and electrical equipment; therefore, it is a relatively simple system. In addition, CWs provide habitat for not only a large number of microorganisms and microfauna but also small animals such as frogs to feed on them. These ecosystems enable recycling of organic matter and nutrients in nature. At our Center's research station, we have been carrying out various research activities to localize CW with consideration of high-temperature, high-precipitation characteristics of Southeast Asia. They include a study on water movement in wetlands based on the volumes of rainwater inflow and evaporation as well as basic research on the characteristics of leachate treatment by CW.
Evaluation of landfill leachate treatment in Thailand
For the localization of CW, we have been evaluating laboratory-scale CWs in Thailand in local climate conditions using the leachate from a local landfill site. We selected a native plant, Typha latifolia, and planted them in the laboratory-scale CWs. The plants have grown bigger as shown in Photo 1. They might have been already adapted to the leachate.
In this study, we also focus on landfill leachate volume although the ultimate purpose of the treatment with CW is water purification. The leachate decreases its volume with evaporation while it flows through CW. Plant evapotranspiration also reduces the leachate volume. For these reasons, outflow volume of the treated leachate is lower than that of the inflow leachate. In these evaluations, about 40% reduction was achieved in the leachate volume. This result particularly suggests that evapotranspiration occurs more in daytime. If volume of leachate is well-controlled, its treatment with CW may provide a useful means for facilitating subsequent treatment processes and enabling water management in landfills.
As a next step, we plan to obtain parameters suitable for practical applications of CW. More specifically, we will analyze the effect of water quality (e.g. nutrient salts) of inflow leachate, inflow patterns and precipitation conditions, and properties of filtering material (e.g. permeability and moisture capacity) on plant growth, evapotranspiration volume and water purification performance.
Greenhouse gases from CWs
In wastewater treatment, greenhouse gases (GHGs) such as methane and dinitrogen monoxide (nitrous oxide) are usually generated by the activities of bacteria anaerobically decomposing organic matter and bacteria oxidatively decomposing nitrogen. Although GHGs are also generated in CWs, their generation mechanism is more complex in CWs that utilize the abilities of ecosystems.
While sewage treatment plants generally use activated sludge method with bacteria and microfauna, CWs utilize the abilities of ecosystems that involve numerous living organisms such as plants and small animals. Hence, a variety of environmental factors including climate and sunshine are believed to influence wastewater treatment in CWs.
Regarding conventional wastewater treatment, GHG emission calculation method is specified based on scientific knowledge in the guidelines of the Intergovernmental Panel on Climate Change (IPCC). However, there was no calculation method for CWs specified in the earlier version of the document. Therefore, it was decided to publish guidelines for calculating GHG emissions from wetlands as a supplement to the 2006 guidelines1. I took part in the process of developing this supplement as a coordinating lead author for "Chapter 6: Constructed Wetlands for Wastewater Treatment". For more information, please refer to the relevant article in our February 2013 issue: Initiatives for Improving Accuracy in the Calculation of Greenhouse Gas Emissions as well as the IPCC 2013 Wetlands Supplement2.
Other on-going and planned research activities on CWs
In this study, we have also been developing a method for controlling the environmental conditions in landfill sites and enhancing biodegradation and chemical stabilization in their waste layers by reintroducing leachate into the sites. Recirculation of leachate in the landfill sites is useful for minimizing consumption of precious water resources. In addition, introduction of appropriate leachate treatment technology can ensure effective removal of contaminants while responding to the fluctuations in leachate volume between rainy and dry seasons that are typical in tropics. We aim at practical application of the landfill leachate treatment technology that combines CW and advanced membrane treatment technologies.
In recent years, attractive water purification function of duckweed has been revealed. Planting duckweed in CWs can facilitate removal of aromatic compounds such as phenol, aniline and nonylphenol. The bacteria decomposing these compounds are isolated from their roots as useful microorganisms. Our future research plans include studies on landfill leachate treatment using a symbiotic system of duckweed and useful microorganisms, and removal of hazardous chemical substances and heavy metals from landfill leachate.
