Enhancement of Sewage Sludge Bioconversion to Methane by the Addition of Exhausted Coffee Biowaste Liquid Fraction

  • Rita FragosoEmail author
  • Ana Carvalho
  • Elizabeth Duarte
Original Paper


Anaerobic co-digestion of organic rich wastes and wastewater sludge has become an attractive economic possibility for water utilities as it enhances biogas production. The suitability of the organic rich waste depends on its biodegradability as well as on its synergetic effect on the anaerobic digestion process. The feasibility of sewage sludge (SS) treatment via co-digestion was studied in a semi-continuous mode at mesophilic conditions (36 ± 1 °C), with a hydraulic retention time of 17 days and an average organic loading rate of 0.94 ± 0.05 gVS Lreactor day−1, using the liquid fraction of pre-treated exhausted coffee biowaste (LECB) as a co-substrate. An anaerobic co-digestion trial (T1) was performed using as feeding mixture 80% SS and 20% LECB (v:v) and compared against a reference scenario of mono-digestion of SS (T0). The stability along assays was ensured by monitoring the digestate characteristics (pH, electrical conductivity, total alkalinity and ammonia content) and the specific energy-loading rate (SELR). Along the operation time of T1, methane yield and VS removal were significantly higher in comparison to mono-digestion of SS. Results showed that the addition of the co-substrate had a positive effect on specific methane production (3 times higher) and methane content (12% higher), indicating this is a feasible strategy towards self-sufficient wastewater treatment plants.


Anaerobic co-digestion Exhausted coffee biowaste Sewage sludge Waste-to-energy 



Anaerobic co-digestion


Anaerobic digestion


Continuous stirring tank reactor


Exhausted coffee biowaste


Gas production rate


Hydraulic retention time


Liquid fraction of the exhausted coffee biowaste


Organic loading rate


Spent coffee grounds


Specific energy loading rate


Specific methane production


Sewage sludge


Wastewater treatment plant



This work was supported by the Linking Landscape, Environment, Agriculture and Food (LEAF) research unit (UID/AGR/04129/2013). The authors wish to thank Nestlé Portugal, for providing exhausted coffee biowaste and AdP-Águas de Portugal for providing sewage sludge samples.


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Copyright information

© Springer Nature B.V. 2018

Authors and Affiliations

  1. 1.LEAF – Linking Landscape, Environment, Agriculture and Food, Instituto Superior de AgronomiaUniversidade de LisboaLisbonPortugal

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