Life cycle analysis for the production of volatile fatty acids from wastewater treatment plant sludge

Abstract

Society is shifting to an environmental basis due to threats caused by climate change, resource scarcity, and excessive generation of plastics. Biotechnology has sought alternatives to valorise waste streams, such as sludge generated in municipal wastewater treatment plants (WWTPs). Sludge bio-fermentation is suitable for sustainable volatile fatty acids (VFA) production by anaerobic digestion (AD). This biotechnological process is an excellent opportunity, as VFAs are in high demand by industry. This work aimed to study the environmental impacts generated by the bioproduction of VFA from primary sludge (PS) from the El Salitre WWTP in Bogotá using the life cycle analysis (LCA) methodology. VFA production was carried out in three semi-continuous reactors, using PS, an initial organic load of 14 gVS/L, a temperature of 25 °C, and a pH of 10 for 7 and 16 d, obtaining a higher VFA production and yield for the 16-day experiment with 6048 mgCOD/L; 432 gCOD/gVS, compared to 5472 mgCOD/L; 391 gCOD/gVS produced in 7 d. An LCA was carried out to select the best retention time considering eighteen environmental categories. The study of the impact categories and the modelling of the inventory data were carried out using the ReCiPe Midpoint method and Simapro software. The results showed that energy use in the process steps is the bottleneck point for sustainability and causes significant effects in almost all the impact categories evaluated. Additionally, it was found that producing VFA from municipal WWTP sludge can be considered a sustainable process due to the indicators obtained being lower than those found in the literature. Also, the concentrations achieved allow the use of these VFAs as carbon sources for making polyhydroxyalkanoates.

Keywords:

• Volatile fatty acids
• life cycle analysis
• anaerobic digestion
• polyhydroxyalkanoates
• sustainable development goals

Reviewing Editor:

• D. T. Pham, University of Birmingham, United Kingdom

Subjects:

• Chemical Engineering
• Clean Tech
• Civil, Environmental and Geotechnical Engineering

Acknowledgments

The authors are grateful for the funding obtained by the cooperative research project between the Universidad Cooperativa de Colombia and the Universidad Distrital Francisco José de Caldas, ‘Evaluation of the potential for obtaining PHAs from wastewater and mixed crops at pilot scale.’ ID: INV2600-2020. To the Minciencias project - EcosNord No. 80740-225-2021, ‘Sustainable biorefinery schemes for energy, materials and nutrients recovery.’ To the facilities of the biotechnology laboratory of the Universidad Cooperativa de Colombia. Colombian Institute of Educational Credit and Technical Studies Abroad ICETEX and the Ministry of Science, Technology, and Innovation MINCIENCIAS, for funding this research (Project number 2021-1016 of 2021). Laboratory of Energy, Materials and Environment of the Universidad de la Sabana for the support in the frame of project number INGPHD-50-2022 (Energy, Materials and Environment research group).

Data availability statement

The authors confirm the statement of data availability.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Universidad Ean.

Notes on contributors

Jeniffer Gracia

Jeniffer Paola Gracia Rojas, PhD in Engineering, Master in Sustainable Development and Environmental Management, Environmental Administrator. Professor at the Faculty of Environment and Natural Resources of the Francisco José de Caldas District University, 15 years of experience in university teaching for undergraduate and graduate programs. With research and publications in the field of environment and biotechnology, recognition by Minciencias as an Associate Researcher. Academic peer National Accreditation Council of the Ministry of National Education.

Iván Cabeza

Iván Cabeza is an Associate Professor in the Department of Chemical Processes and Biotechnology at the Universidad de La Sabana (Colombia). He holds a degree in Chemical Engineering from the Universidad Industrial de Santander (Colombia), a Master’s degree in Renewable Energy from the Universidad de León (Spain) and a Ph.D. in Natural Resources and Environment from the Universidad de Sevilla (Spain). Dr Cabeza also has postdoctoral experience in biotechnology from the Universidad Nacional de Colombia. His research interests include bioprocesses, renewable energy and biorefinery.

Paola Acevedo

Paola Acevedo is Director of Chemical Engineering - EAN University, Chemical Engineer with a PhD in Chemical Engineering. She has excellent training in the management and development of chemical and physicochemical processes in industry and research. She has extensive knowledge in specific areas such as: sustainable development, economic evaluation, biofuels, bioprocesses, life cycle analysis, technology transfer, process safety and process simulation. She also has skills and experience in teaching, research.