Master Thesis - Environmental Engineering - 2019
Phosphorus depletion is a problem of our time with severe consequences. Being a fundamental bio element phosphorus accumulates in the food chain and eventually ends up in the sewage. Wastewater treatment has great potential in protection of natural waterbodies from nutrient overload. The awareness of this environmental problem has brought up new technologies to recover nutrients from sewage sludge. The study is a consequential life cycle assessment made for evaluate the environmental impacts of technologies that might be implemented in Ejby Mølle wastewater treatment plant operated by VandCenter Syd.
Four different scenarios were established, composting as the current recovery option. Even though composting is a common process, the product provides nutrient and fiber to the soil. There are more efficient options on the market. Sewage sludge incineration is the most controversial its product (sewage sludge ash) requires further purification for application as fertilizer in agriculture. Although, sewage sludge pyrolysis is a similar process, biochar is readily usable as fertilizer and soil amendment. While the first three technologies provide sludge management option, struvite precipitation only recovers phosphorus from the plant’s supernatant. This efficient process provides struvite crystals that is clean and ready to use as fertilizer.
The models are a reference to reality, as some Danish companies who already implemented the technologies could kindly complement this study with data. The environmental impact assessment showed that sewage sludge pyrolysis has the highest avoided impact from all. Hence, the implementation of a pyrolysis unit would be the best option from an environmental perspective for VandCenter Syd. Nevertheless, when decisions are made financial factors must be deliberated. This paper serves as a strong basis for future projects in this direction.