PhD Thesis, Jon Garcia Aguirre

Abstract

This thesis explored controlled anaerobic fermentation processes to gain insights into the feasibility of treating different sources of organic waste to obtain valuable fermentation bioproducts, such as volatile fatty acid (VFA) and additional bioproducts. Anaerobic fermentation will constitute an innovative approach to recover value from organic waste in future biorefineries and contribute to the Circular Economy.

The VFA production was assessed by performing laboratory-scale experiments where the acidogenic potential of different agro-industrial and urban waste was evaluated. These tests provided a valuable methodology to understand the process chemistry, where the impact of process variables, i.e. temperature and pH, was evaluated. Besides, these tests provided valuable information for subsequent up-scaling.

Mixed culture VFA production tests were up-scaled in a pilot-scale platform, where the results of laboratory-scale tests could be reproduced. Herein, co-fermentation of substrates of complementary nature showed potential benefits to enhance the acidogenic fermentation process.

The VFA production process was evaluated in a continuous mode of operation at pilot-scale. Herein, different process variables were optimised, i.e. the pH and the hydraulic retention time. Organic Fraction of Municipal Solid Waste (OFMSW) showed potential benefits as co-substrate, which enabled to boost the VFA productivity and enrich the fermentation composition. Continuous acidogenic fermentation was a feasible alternative, where stable VFA processes could be obtained. Additionally, ultrafiltration technology was adequate to recover a VFA rich permeate.