Browsing by Subject "Thermochemical conversion"

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Anaerobic treatment of a biorefinery’s process-wastewater
(2024) Khan, Muhammad Tahir; Lemmer, Andreas
The phrase “one man's trash is another man’s treasure” perfectly embodies the concept of a circular bioeconomy, emphasizing the conversion of waste into valuable resources while embracing a zero-waste approach. In line with this perspective, the primary objective of the current research was to assess the suitability of a biorefinery’s process-wastewater as a potential feedstock for biogas plants by investigating its anaerobic biodegradability and exploring its biogas and methane production potentials. For such a specific purpose, the process-wastewater from a commercial-scale biorefinery specializing in 5-hydroxymethylfurfural (5-HMF) synthesis and refining was utilized. To fulfill the main objective, three independent sub-objectives were formulated. The initial investigation centered on assessing the biochemical methane potential (BMP) of the typical constituents present in process-wastewater, such as furans (5-HMF and furfural), phenols (syringaldehyde, vanillin, and phenol), and weak acids (levulinic and glycolic acid), as well as the full 5-HMF process-wastewater. The BMP assessments for each test substance were conducted separately at different concentrations (2, 4, 6, and 8 gCOD/L) and temperatures (37°C and 53°C) via the Hohenheim batch fermentation test. The model components at 2 gCOD/L, apart from phenol at 53°C, were efficaciously degraded, in most cases to such an extent, that supplementary methane generation was detected i.e. exceeding their maximum theoretical limits. However, increasing the concentrations of the test components in the assays resulted in diminishing methane conversion at both operating temperatures. Eventually, among the tested components, the 5-HMF process-wastewater was evaluated to be one of the most refractory substrates, following phenol, vanillin, and 5-HMF, when tested at its maximum load under mesophilic and thermophilic conditions. The subsequent investigation focused on examining the anaerobic decomposition of the 5-HMF process-wastewater and its main identified constituents, including 5-HMF, furfural, and levulinic acid in continuously operated anaerobic filters (AFs). The test substances were individually injected into the biofilm reactors operating at 43°C in a controlled manner with a randomized experimental design. This study yielded some unusual outcomes i.e., the test substrates exhibited satisfactory degradation, while at other instances, they hampered the process. Introducing butyric acid between the injected components revealed no signs of compromised consortia. The 5-HMF process-wastewater in this investigation emerged as the least favorable substrate for methane conversion. The culmination of the current research involved utilizing the 5-HMF process-wastewater as a sole feedstock for the fixed-bed reactors. Hence, necessary nutrients to support the existing microbial consortia in the AFs were added to the process-wastewater. Given its toxic nature, the substrate dosage was initiated from its reduced concentration of 10 gCOD/L and was gradually increased to 20, 30, 40, and 50 gCOD/L, with corresponding organic loading rates (OLRs) of 2, 4, 6, 8, and 10 gCOD/L.d, respectively, as the trial progressed. Despite meeting the nutrient requirements, the gas yields, in particular methane, were not remarkable. However, a noteworthy finding surfaced: as the gCOD/L of the fed substrate increased, so did the concentrations of the short-chained volatile fatty acids (SCVFAs) in the reactors. This observation led to the conclusion that the low methane yields were at the behest of the accumulation of SCVFAs in the AFs, at both mesophilic and thermophilic temperatures. Ultimately, the subpar performance of the process-wastewater as a substrate is considered to stem from its exceptionally high concentration of the pollutant 5-HMF, which significantly influences its overall characteristics, causing longer lag phases, especially at higher OLRs. This, in turn, triggers the inhibitory behavior, leading to reduced methane yields. Consequently, these factors render the 5-HMF process-wastewater a precarious choice for biogas plants in terms of efficient energy recovery. While AFs are well-suited technology for treating high-strength wastewaters, for the substrate such as 5-HMF process-wastewater, it might be beneficial to increase retention times by decreasing the OLRs. Additionally, reducing the strength via dilution combined with these adjusted process parameters could further enhance its decomposition. Anaerobic digestion (AD), traditionally used for energy recovery from (bio)wastes, has potential beyond biogas production in the bioeconomy. This research showed that the highly recalcitrant 5-HMF process-wastewater can be a viable source for producing SCVFAs through AD. Furthermore, the Muttenz biorefinery could utilize the filtration byproducts to produce levulinic acid, aligning with a cascading biorefinery approach.
Biochemical methane potential of a biorefinery’s process-wastewater and its components at different concentrations and temperatures
(2022) Khan, Muhammad Tahir; Huelsemann, Benedikt; Krümpel, Johannes; Wüst, Dominik; Oechsner, Hans; Lemmer, Andreas
A sustainable circular bioeconomy requires the side streams and byproducts of biorefineries to be assimilated into bioprocesses to produce value-added products. The present study endeavored to utilize such a byproduct generated during the synthesis of 5-hydroxymethylfurfural as a potential feedstock for biogas production. For this purpose, biochemical methane potential tests for the full process-wastewater, its components (5-hydroxymethylfurfural, furfural, levulinic acid, and glycolic acid), together with furfural’s metabolites (furfuryl alcohol and furoic acid), and phenols (syringaldehyde, vanillin, and phenol), were conducted at mesophilic and thermophilic temperatures to assess their biodegradability and gas production kinetics. 0.1, 0.2, 0.3, and 0.4 g COD of the test components were added separately into assays containing 35 mL of inoculum. At their lowest concentrations, the test components, other than the process-wastewater, exhibited a stimulatory effect on methane production at 37 °C, whereas their increased concentrations returned a lower mean specific methane yield at either temperature. For similar component loads, the mesophilic assays outperformed the thermophilic assays for the mean measured specific methane yields. Components that impaired the anaerobic process with their elevated concentrations were phenol, vanillin, and 5-hydroxymethylfurfural. Poor degradation of the process-wastewater was deduced to be linked to the considerable share of 5-hydroxymethylfurfural in the process-wastewater governing its overall characteristics. With excessive recalcitrant components, it is recommended to use such waste streams and byproducts as a substrate for biogas plants operating at moderate temperatures, but at low rates.