RECOVERING NUTRIENTS FROM WASTEWATER IN THE FOOD INDUSTRY – SUSTAINABILITY ASSESSMENT AT EARLY STAGES OF TECHNOLOGY DEVELOPMENT

Doctoral thesis, 2025

National and international research programs aim to reduce nitrogen (N) and phosphorus (P) waste and emissions. Such emissions can contribute to eutrophication of aquatic systems, contamination of groundwater, acidification of soils, biodiversity loss, air pollution, and climate change, with consequences for human wellbeing and planetary health. In addition, the lack of exploitable phosphate mineral reserves in Europe, combined with the general scarcity and increasing demand for this material, poses a threat to European food security. The scarcity of this nutrient has led the European Commission to declare P as a critical raw material. This confluence of events has led to the development of technologies for recovering nutrients from
food processing wastewater and using them as fertilisers in agriculture, to hopefully reduce the damaging nutrient emissions while ameliorating resource constraints.

In this thesis, integrated approaches that combine dairy wastewater treatment with struvite recovery, and recirculating aquaculture systems (RAS) with biochar derived from forestry residues to improve nutrient recovery and circularity across the different activities are explored. The aim of this thesis is to contribute to both the technical development of emerging systems and the advancement of methods for assessing their sustainability. This thesis
describes how to identify and select sustainability indicators, conduct a meta-analysis, and a Material Flow Analysis (MFA) to support a circularity assessment and Life Cycle Assessment (LCA). The description of these assessment tools and their application is specific to two different contexts examined in this research: REFLOW (P recovery from dairy wastewater) and Nutribatt (RAS with biochar filter).

The outcomes of these different approaches saw the employed method for indicator selection narrow down an initial set of 382 sustainability indicators identified in the literature to 26. A meta-analysis of LCA results suggested that the examined nutrient recovery technologies, specific for P recovery from dairy wastewater, exhibited a lower global warming potential and cumulative energy demand than those of current dairy wastewater treatment processes, and that the technologies recovering P from the liquid phase had lower impacts than those recovering P from sludge or ash. Furthermore, new LCA results show that the conceptual combined system of wastewater treatment with nutrient recovery exhibits remarkable environmental performance because of the benefits of replacing conventional products with recovered products.