Sustainability assessment of phosphorus in the waste management system of Bangladesh using substance flow analysis

Quantification of multi-year phosphorus flow through the waste sector of developing countries is essential for formulating effective policies towards sustainable global management of the phosphorus resource to ensure food and water security. However, such quantification is often difficult in developing countries due to data limitation. This study, first of its kind, develops a novel approach of training several machine learning regression models to fill the data gap for analyzing multi-year (2000–2018) phosphorus flow in both the urban and rural waste management systems of Bangladesh (a typical developing country in South Asia) using the substance flow analysis. The analysis indicates that average annual total phosphorus inflow in its waste sector was 103.3 kt over the study period, of which almost 70% remained there as an increase in stock. The country lost 31.6 kt (30.59% of total inflow) of phosphorus annually as waste discharge to its numerous rivers and water bodies, which may account for scattered instances of algal blooms and eutrophication throughout the country. On average only 0.12 kt phosphorus was recovered annually from the solid waste stream and reused as compost and livestock feed. There were significant annual losses from both the urban and rural wastewater subsystems, on average at 13.67 kt and 12.15 kt respectively. A high annual inflow of 60.1 kt was observed for the rural wastewater subsystem, which retained most of it as an increase in stock of 47.95 kt. On the other hand, inflow into the urban wastewater system was 25.57 kt of which 53% was lost as outflow to rivers. In a global comparison of phosphorus substitutability indices (calculated based on recycling efficiency), Bangladesh displays the lowest (0.12%) score among several developed and developing countries despite of having a handsome inflow to waste sector. The methods developed for quantifying multi-year phosphorus flow in a data deficient condition and specific policy recommendations provided in this study could be utilized for sustainable management of phosphorus in similar developing countries.