Urban nutrient balance for Bankok

Summary

To enhance agricultural sustainability, former linkages between agriculture and urban waste production should be reintroduced. Therefore, to explore the options for recycling of nutrients from mega-cities, a nutrient balance model was developed. The parameterization were established for the Bangkok Province and considers nitrogen (N) and phosphorous (P). To model the food supply, an online database (FAOSTAT) estimating supply at country levels, was employed. It is argued that desaggregation to urban level is reasonable after adjustments for different economy in Bangkok than the average in Thailand. The balance shows that only a small fraction of nutrients are recovered, currently about 7 and 12% respectively, of the amount of N and P in the total food supply. On the other hand most (about 95%), of the total loss of N can be accounted for by elevated N levels in the Chao Phraya River from where also much (about 38%) of the loss of P can be explained. That is, in- and out-flows of N is almost found in balance but a huge amount of P must be accumulated somewhere. However the balance also shows that the Bangkok Province throws out into the river (and the sea) very huge quantities of plant nutrients that could be recovered and reused. For future research is it of particular interest to explore the maximum nutrient recovery fraction in different waste management systems.