Effluent resulting from landfill waste (leachate) represents a potential environmental hazard, and must be routinely harvested and removed by waste management companies. A significant proportion of this effluent consists of ammonia. Although formally a waste product, ammonia is also a useful building block and has many applications e.g. as a fertiliser and a chemical reagent. However, exploiting ammonia resulting from leachate has not received significant attention because of challenges and associated costs relating to its extraction and isolation in pure form. Nonetheless, an enticing opportunity exists to source ammonia from waste and exploit it in the synthesis of high value products. As well as obvious recycling benefits, this strategy could in principle establish a new source of nitrogen containing organic compounds that does not necessitate the use of existing hydrocarbon based sources. It should be noted that although our major supply of ammonia-rich effluent is leachate for this project, the problem of ammonia-rich wastewater is more widespread, and perhaps the biggest reason for slow uptake of anaerobic digestion (AD). AD is the largest producer of ammonia-rich wastewater, which is the major reason why it is not operated more intensively, as it would increase the ammonia content.
This project will employ microbubble extraction technology developed within the Zimmerman group to generate aqueous extracts of ammonia from leachate supplied by our collaborators Viridor. The extraction method is remarkably efficient and enabling; ammonia is stripped by microbubble distillation with 99% removal in 30 min of contacting time. The Harrity group will utilise these aqueous ammonia streams and investigate the scope of this nitrogen source for the synthesis of small organic molecules. In this regard, a number of processes can be envisaged, and the Grantham Scholar will be encouraged to take an active role in deciding on which reactions to study. Preliminary studies will focus on condensation reactions that have a strong thermodynamic driving force and that lead to hydrophobic products, thereby simplifying product extraction and characterisation. This proof-of-principle will underpin further studies aimed at exploiting the ammonia sources in reactions with sustainable reagent sources to develop truly economical portfolio of value adding chemistries. As mentioned in the overview, this project has the scope of dealing with wider wastewaters that are ammonia-rich, such as AD, and the limitation in greater uptake of AD is ammonia removal. AD is an important pillar of sustainable future technology, as in addition to being CO2 neutral as a supplier of renewable energy, its feedstocks (biomass) would otherwise rot to produce methane preferentially to CO2. Methane is 20-30 fold worse as a greenhouse gas than CO2, so wider take up of AD has a much larger effect on GHG emissions reduction by reducing fugative emissions of methane. Improving the economics of ammonia removal from wastewaters by providing valuable chemical products from this new “value” stream could make the uptake of AD more economically favourable, hitting multiple sustainability targets.