| dc.description.abstract | Sewage sludge is a major waste which needs to be disposed of in a hygienic way. One disposal method is to incinerate it, which produces an ash contain- ing 5-10% phosphorous. Phosphorous is a critical resource, which is primarily mined in Morocco with a finite depletion horizon. Technologies that can extract phosphorous from waste products to recover the important critical element, is needed.
A two-chamber cell was developed at the Danish Technical University for the electrodialytic separation of sewage sludge ash. In collaboration with one of the original inventors Gunvor M. Kirkelund, and the company Clean Matter that acquired the patent of invention, a material flow analysis was made. The analysis used experimental data together with considerations from the company to estimate and keep track of the flows and energy usage. With the estimated flows, an inventory was made, along with a climatic assessment of the upcoming technology.
It was found that the largest savings in CO2-eq. was when producing a liquid phosphoric acid without the use of nitric acid for adjustment of the pH in the catholyte liquid. The largest impact on global warming was the use of electricity in the process, while the major savings in greenhouse gas of a substi- tuted product, was the formation of a calcium-phosphate salt. A large savings of emissions was also seen for the production of hydrated lime, but whether or not this product would be marketable is not known.
This thesis is an early screening for the technology under development. Re- search that will improve the precision of the climatic assessment should focus on the quality of the products. If the company Clean Matter wants the lowest production carbon footprint as possible, they should focus on avoiding the use of chemicals and use electricity from low-carbon sources. To get both the catholyte and the anolyte flow to become agricultural products that comply with Danish regulations on heavy metals, a calcium-phosphate salt is recommended. | |
