Abstract:
Municipal waste is usually composted with an N-rich substrate, such as manure, to increase the N
content of the product. This means that a significant amount of nitrogen can be lost during composting.
The objectives of this study were (i) to investigate the effect of split addition of a nitrogen-rich substrate
(poultry manure) on nitrogen losses and greenhouse gas emissions during composting and to link this
effect to different bulking agents (coffee husks and sawdust), and (ii) to assess the effect of split addition
of a nitrogen-rich substrate on compost stability and sanitisation. The results showed that split addition
of the nitrogen-rich substrate reduced nitrogen losses by 9% when sawdust was used and 20% when
coffee husks were used as the bulking agent. Depending on the bulking agent used, split addition
increased cumulative N2O emissions by 400e600% compared to single addition. In contrast, single
addition increased methane emissions by up to 50% compared to split addition of the substrate. Hence,
the timing of the addition of the N-rich substrate had only a marginal effect on total non-CO2 greenhouse
gas emissions. Split addition of the N-rich substrate resulted in compost that was just as stable and
effective at completely eradicating weed seeds as single addition. These findings therefore show that
split addition of a nitrogen-rich substrate could be an option for increasing the fertilising value of
municipal waste compost without having a significant effect on total greenhouse gas emissions or
compost stability
