Compost-biochar mixtures improve waste management and nitrogen efficiency

Composting is a simple, cost-effective way to dispose of biomass waste and recycle nitrogen; however, more than half of nitrogen can be lost as ammonia gas during composting. These emissions are an economic loss, and they can damage ecosystems and cause odor pollution. This project explored the merits of adding biochar during composting to reduce ammonia emissions. We combined detailed laboratory observations with composting experiments to develop a technology that could both lower ammonia emissions and increase nitrogen availability to new plants. Such a technology helps reduce environmental impacts from composting, raise the quality of compost, reduce fertilizer costs for agricultural producers, and increase community acceptance of composting by reducing odor.

We investigated the properties and mechanisms that enable biochar to retain ammonia, and evaluated biochar’s ability to make retained ammonia available to new plants. Laboratory experiments demonstrated that acidity and electrostatic interactions are not the key to ammonia retention. Rather, cutting-edge spectroscopy techniques revealed that a variety of covalent bonds form between ammonia and biochar. We also conducted planting experiments using a homogenized potting mixture, and adding equal amounts of nitrogen from either conventional nitrogen fertilizer, or via biochar that had been exposed to ammonia gas. Preliminary results showed that nitrogen availability was comparable from both sources.