Carranza Muñoz, Andrea Yineth
- Department of Molecular Sciences, Swedish University of Agricultural Sciences
Abstract
Nitrogen removal, emission reduction, and climate neutrality are central goals for modern wastewater treatment plants, reinforced by stricter nutrient limits from the EU and Swedish regulations. Methanol is widely used for nitrogen removal in the denitrification process. However, alternative carbon sources are needed to promote circular resource management and reduce climate impact. This thesis investigated the production and use of volatile fatty acid (VFA)-rich carbon sources through the direct use or fermentation of primary sludge (PS), waste-activated sludge, food waste (FW), and digestate, alongside a full-scale evaluation of their technical and economic feasibility. Fermentation performance varied depending on substrate, with FW and FW:PS mixes achieving higher sCOD (up to 82 g sCOD/L) and VFA concentrations (up to 56 g VFACOD/L) than sludge carbon sources, together with favourable carbon-to-nutrient ratios and low biogas losses. Sludge- and digestatebased fermentates exhibited lower sCOD concentrations (<12 g/L and <20 g/L with thermal hydrolysis pre-treatment) and higher nutrient release, impacting carbon dosing needs and implementation costs. Despite these differences, denitrification was consistent across all fermentate carbon sources (7-9 mg NO3/gVSS∙h), regardless of substrate origin. Replacing methanol with fermentates reduced fossil CO₂ emissions associated with chemical use and operation, but required significant capital investment. A plant-wide economic and environmental analysis confirmed that FW and FW:PS fermentates are the most cost-effective alternatives to methanol, while sludge- and digestate-based options are feasible but associated with higher capital and operational costs. FW-based options provided the lowest treatment costs, reducing costs by up to 0.039 EUR/m³treated-water, while the digestate-based option increased costs by up to 0.026 EUR/m³treated-water compared to using methanol. The results demonstrate a feasible pathway for WWTPs to replace methanol with wastederived carbon sources, supporting climate targets, stricter nitrogen limits, and circular resource management.
Keywords
Carbon source; Denitrification; Fermentation; Volatile fatty acids; Resource recovery; Wastewater treatment
Published in
Acta Universitatis Agriculturae Sueciae
2025, number: 2025:47
Publisher: Swedish University of Agricultural Sciences
SLU Authors
UKÄ Subject classification
Water Treatment
Environmental Sciences
Publication identifier
- DOI: https://doi.org/10.54612/a.4hh900gua3
- ISBN: 978-91-8046-482-6
- eISBN: 978-91-8046-532-8
Permanent link to this page (URI)
https://res.slu.se/id/publ/132987