Abstract
In order to make anaerobic digestion-based processes for short chain organic acid (SCOA) production attractive, the key performance variables, i.e., concentration, yield, and productivity of the produced SCOAs need to be maximised. This study analysed recent literature, looking for the effect of process operating parameters (feed concentration, pH, temperature, and residence time) on the performance variables. Data from 551 experiments were analysed. Mean values of the SCOA concentration, yield, and productivity were 10 g l−1, 32% (chemical oxygen demand (COD) COD−1), and 1.9 g l−1 day−1, respectively. Feed concentration and residence time had the most important effect. Higher feed concentration corresponded to higher product concentration and productivity, but to lower yield. The mean feed concentration was 109 gCOD l−1 and 19 gCOD l−1 in the experiments with the highest product concentrations and in the experiments with the highest yields, respectively. Shorter residence times corresponded to higher productivity. The mean HRT (hydraulic residence time) in the experiments with the highest productivities was 2.5 days. Sequencing batch reactors gave higher values of the performance variables (mean values 29 g l−1, 41% COD COD−1, and 12 g l−1 day−1 for product concentration, yield, and productivity, respectively) than processes without phase separation.
Highlights
Anaerobic digestion is an industrially established process where microorganisms degrade the organic matter in the absence of air
short chain organic acid (SCOA) are important chemicals widely used in the chemical industry for the synthesis of plastics, as food additives, and for many other uses [2]
Even though each study aimed to measure the most important SCOAs produced under their experimental conditions, the total production of SCOAs may be underestimated and the actual concentration, yield, and productivity in the considered studies may be higher than the reported values
Summary
Anaerobic digestion is an industrially established process where microorganisms degrade the organic matter in the absence of air. The use of anaerobic digestion for the production of short-chain organic acids (SCOAs) is attracting interest [1]. SCOAs (e.g., acetic, propionic, butyric acids) are important chemicals widely used in the chemical industry for the synthesis of plastics, as food additives, and for many other uses [2]. The production of acetic acid alone was approximately 18 Mt in 2019. The vast majority of the current SCOA production uses natural gas as primary feedstock. Natural gas is a non-renewable resource and, the conversion of natural gas into SCOAs requires high temperature, with the associated energy consumption and process costs, and metal catalysts, which are non-renewable
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