IVL Swedish Environmental Research Institute, Valhallavägen 81, 114 28 Stockholm, Sweden; Department of Molecular Sciences, Biocenter, Swedish University of Agricultural Sciences (SLU), 756 51 Ultuna-Uppsala, Sweden.
The Käppala Association, Södra Kungsvägen 315, 181 66 Lidingö, Sweden.
Water Res. 2024 Nov 15;266:122426. doi: 10.1016/j.watres.2024.122426. Epub 2024 Sep 10.
Stricter nutrient discharge limits at wastewater treatment plants (WWTPs) are increasing the demand for external carbon sources for denitrification, especially at cold temperatures. Production of carbon sources at WWTP by fermentation of sewage sludge often results in low yields of soluble carbon and volatile fatty acids (VFA) and high biogas losses, limiting its feasibility for full-scale application. This study investigated the overall impact of thermal hydrolysis pre-treatment (THP) on the production of VFA for denitrification through the fermentation of municipal sludge and digestate. Fermentation products and yields, denitrification efficiency and potential impacts on methane yield in the downstream process after carbon source separation were evaluated. Fermentation of THP substrates resulted in 37-70 % higher soluble chemical oxygen demand (sCOD) concentrations than fermentation of untreated substrates but did not significantly affect VFA yield after fermentation. Nevertheless, THP had a positive impact on the denitrification rates and on the methane yields of the residual solid fraction in all experiments. Among the different carbon sources tested, the one produced from the fermentation of THP-digestate showed an overall better potential as a carbon source than other substrates (e.g. sludge). It obtained a relatively high carbon solubilisation degree (39 %) and higher concentrations of sCOD (19 g sCOD/L) and VFA (9.8 g VFA/L), which resulted in a higher denitrification rate (8.77 mg NOx-N/g VSS∙h). After the separation of the carbon source, the solid phase from this sample produced a methane yield of 101 mL CH/g VS. Furthermore, fermentation of a 50:50 mixture of THP-substrate and raw sludge produced also resulted in a high VFA yield (283 g VFA/kg VS) and denitrification rate of 8.74 mg NOx-N/g VSS∙h, indicating a potential for reduced treatment volumes. Calculations based on a full-scale WWTP (Käppala, Stockholm) demonstrated that the carbon sources produced could replace fossil-based methanol and meet the nitrogen effluent limit (6 mg/L) despite their ammonium content. Fermentation of 50-63 % of the available sludge at Käppala WWTP in 2028 could produce enough carbon source to replace methanol, with only an 8-20 % reduction in methane production, depending on the production process. Additionally, digestate production would be sufficient to generate 81 % of the required carbon source while also increasing methane production by 5 % if a portion of the solid residues were recirculated to the digester.
污水处理厂（WWTP）更严格的营养物排放限制正在增加反硝化对外部碳源的需求，尤其是在低温下。通过污水污泥发酵在 WWTP 生产碳源通常会导致可溶性碳和挥发性脂肪酸（VFA）的产量低，沼气损失高，限制了其在大规模应用中的可行性。本研究通过市政污泥和消化液的发酵，调查了热水解预处理（THP）对反硝化用 VFA 生产的整体影响。评估了发酵产物和产率、反硝化效率以及碳源分离后对下游过程中甲烷产量的潜在影响。与未经处理的底物相比，THP 底物的发酵导致可溶化学需氧量（sCOD）浓度增加了 37-70%，但发酵后 VFA 产量没有显著影响。然而，THP 对所有实验中的反硝化速率和剩余固相部分的甲烷产率都有积极影响。在所测试的不同碳源中，与其他底物（例如污泥）相比，来自 THP-消化液发酵的碳源总体上显示出作为碳源的更好潜力。它获得了相对较高的碳溶解程度（39%）和较高的 sCOD（19g sCOD/L）和 VFA（9.8g VFA/L）浓度，从而实现了较高的反硝化速率（8.77mg NOx-N/g VSS·h）。在碳源分离后，该样品的固相产生了 101mL CH/g VS 的甲烷产量。此外，50:50 混合 THP-底物和原污泥的发酵也产生了高 VFA 产量（283g VFA/kg VS）和 8.74mg NOx-N/g VSS·h 的反硝化速率，表明处理体积有减少的潜力。基于斯德哥尔摩 Käppala 污水处理厂（WWTP）的全规模计算表明，尽管含有氨，但所产生的碳源可以替代基于化石的甲醇并满足氮排放限制（6mg/L）。2028 年在 Käppala WWTP 对 50-63%的可用污泥进行发酵，可以生产出足够的碳源来替代甲醇，同时甲烷产量仅减少 8-20%，具体取决于生产过程。此外，如果将部分固体残留物再循环到消化器中，消化液的产生将足以产生所需碳源的 81%，同时使甲烷产量增加 5%。
