Continuous Volatile Fatty Acid Production From Acid Brewery Spent Grain Leachate in Expanded Granular Sludge Bed Reactors

Abstract

The production of volatile fatty acids (VFAs) in expanded granular sludge bed (EGSB) reactors using leachate from thermal diluted acid hydrolysis of brewery spent grain was evaluated. Partial inhibition of the anaerobic digestion process to induce VFA accumulation was achieved by applying a high organic loading rate [from 15.3 to 46.0 gCOD/(L·day)], and using a feed with an inlet concentration of 15 g/L total carbohydrates. Two EGSB reactors were operated under identical conditions, both inoculated with the same granular sludge. However, granular sludge in one reactor (R1) was subsequently disaggregated to flocculent sludge by a pH shock, whereas granules remained intact in the other reactor (R2). The hydraulic retention time (HRT) of both reactors was decreased from 36 to 24, 18 and 12 h. The main fermented compounds were acetic acid, butyric acid, propionic acid and ethanol. Despite fluctuations between these products, their total concentration was quite stable throughout the trial at about 134.2 (±27.8) and 141.1 (±21.7) mmol/L, respectively, for R1 and R2. Methane was detected at the beginning of the trial, and following some periods of instability in the granular sludge reactor (R2). The hydrogen yield increased as the HRT decreased. The highest VFA production was achieved in the granular sludge reactor at a 24 h HRT, corresponding to 120.4 (±15.0) mmol/L of VFAs. This corresponded to an acidification level of 83.4 (±5.9) g COD of VFA per 100 gram of soluble COD.

Simultaneous production and recovery of volatile fatty acids from fermentation process using an electrochemically assisted up-flow granular sludge bed reactor

“…A synthetic feedstock was used to determine the VFA transfer rate, with a mixture composition of acetate, propionate, butyrate and ethanol, with concentrations corresponding to 6.79 g/L of sodium acetate, 1.34 g/L of sodium propionate, 5.14 g/L of sodium butyrate and 1.67 g/L of ethanol, according to the maximum VFA concentration obtained in a previous work [25]. Besides, 300 mg/L of ammonium chloride, 300 mg/L of potassium phosphate and 7.5 g/L of sodium bicarbonate were added to increase the conductivity of the synthetic broth.…”

“…Then, the current intensity was divided by the surface area of the anode electrode to obtain the current density. The yield of gas production was calculated as described by Castilla-Archilla et al [25].…”

“…In some studies using more complex feedstock, a longer HRT was required to achieve a similar VFA concentration (from 10 to 49 days) [30,31]. On the other hand, hydrolysate liquor rich in hexose and pentose has achieved a high conversion yield when operating a UASB system [25]. Andersen et al [20] used an electrolytic extraction system with a semi-continuous fermentation reactor using thin stillage, a complex feedstock containing carbohydrates, glycerol, lactate, solid proteins and lignocellulosic solid fractions.…”

Design, Construction, and Concept Validation of a Laboratory-Scale Two-phase Reactor to Valorize Whiskey Distillery By-products

“…Maximizing the throughput of feedstock to the digester within the confines of biological stability maximizes the organic loading rate, minimizes the HRT, and reduces the digester volume and overall capital costs. Two-phase systems allow for additional valorization pathways through VFA production while providing for biogas production. , VFAs can be considered a valuable commodity with a high monetary value; for example, butyric acid and propionic acid may accrue market prices of 2500 € and 2250 € per tonne, respectively. , This additional valorization pathway could be of interest to industries which produce biological secondary raw materials, such as distillers, as it would diversify their revenue streams.…”

“…L −1 ) from the BSGs hydrolysate but again did not consider the liquid by-products. 6 Thus, there is an evident gap in literature whereby both liquid and solid whiskey by-products are processed. The authors propose the development of an LBR-EGSB to produce VFAs and biogas.…”