Material Cycle Analysis
The proper treatment and disposal of wastewater and wastes generated by people and their use as resources have a great impact on the material cycle in the region. We study material cycle analysis to seek appropriate ways of the material cycle. Understanding the material cycle in the dynamically changing are of Asia and Africa means understanding where various materials in the are are generated, how they are transformed, and where they are transferred, and how they affect the environment and human life.
Transition of material cycle under urbanization
Human and livestock excreta has been used intensively for crop cultivation in some areas including East Asia and Southeast Asia for many years, but rapid economic growth has changed the way excreta is managed and the nutrient flow. We have been conducted material flow analysis in Vietnam, Myanmar, and Thailand. In northern Vietnam, large amounts of excreta have traditionally been applied to rice paddies, but much of it is now being applied to fishponds for fish farming. Our study examined the historical transition of excreta management and the impact of fishponds on nutrient flows, focusing on the outskirts of Hanoi, Vietnam, as a case study. A material flow model for nitrogen and phosphorus was applied to the study area. The results showed that between 1980 and 2010, a crop-livestock system with intensive use of excreta for agriculture changed to a crop-livestock-fish system with considerable amounts of livestock excreta discharged into fishponds. Nutrient inputs to the ponds were 41.7 kg-N/ha and 9.8 kg-P/ha in 2010, 7.2 and 6.2 times higher, respectively, than in 1980. In addition, 41% of the nitrogen and 82% of the phosphorus released into the ponds remained in the sediments or were unintentionally discharged after heavy rainfall. The result suggest that the use of pond sediments as a nutrient source for paddy fields would improve the material cycle.
Simplified Material Flow Analysis employing local knowledge
Material Flow Analaysis (MFA) is gradually being applied in low- and middle-income countries to develop strategic waste management strategies. However, it is very time-consuming to collect the necessary information when local basic information such as statistical data is not available. Our research group has devised a simplified MFA model development method that limits the effort by utilizing the knowledge of local experts instead of acquiring primary data through a large-scale data collection campaign. To examine the impact of simplification on the uncertainty of the analysis results and to investigate the validity and usefulness of the simplified MFA, we established a centralized MFA (iMFA) based on a large-scale survey and a simplified MFA (sMFA) based on field experts' knowledge, using the urban district of Mandalay, Myanmar, as an example. The median total nitrogen and phosphorus pollution loads to soil and water environment by sMFA were 6,142 and 1,171 tons-N/year and 1,171 tons-P/year, respectively, and the difference with iMFA was limited to 4% and 11%, respectively. This result indicates the potential usefulness of the sMFA, which is available under data-limited conditions.
