Browsing by Subject "Trace elements"

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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.
Einsatz von Spurenelementen bei der Vergärung von nachwachsenden Rohstoffen in Biogasanlagen
(2014) Vintiloiu, Anca; Jungbluth, Thomas
The operational agricultural biogas plants in Germany are fed mainly with renewable raw materials. During substrate addition, several micro and macro elements enter the digester. These elements are essential nutrients for the methanogens. If their concentration is too low, the production of biogas can be disrupted. A large number of agricultural biogas plants use therefore commercially available trace element solutions to optimize the process and to achieve higher methane yields. When the fermentation is complete, the digestate containing these trace elements (mostly heavy metals) is spread on fields as fertilizer. The amounts added to the biogas process should be kept as low as possible in order to minimize the environmental damage. The purpose of this study was to investigate the cause of trace elements deficiency in renewable raw materials fed biogas plants. It was also tested whether the chelation of the nutrients could increase their bioavailability for microorganisms and thus lead to a reduction of the amounts needed for the stabilization of the fermentation process. The effect of the complexing agent ethylenediaminetetraacetic acid (EDTA) on the bioavailability of metal ions was tested. The sole addition of EDTA to an undersupplied substrate increased the methane yield by up to 32 %. When trace elements were also added, their amounts could be reduced by up to 75 % with no negative consequences for the fermentation process. EDTA is a persistent chelating agent and so it was further tested, whether readily biodegradable chelating agents (ethylenediaminedisuccinic acid (EDDS) and iminodisuccinic acid (IDS)) could have the same effect. During the investigation, IDS had a high statistically significant positive effect on the bioavailability of the metal ions, which exceeded the effect of EDTA. IDS represents therefore a good alternative to EDTA. The bioavailability of the metal ions in the digester was increased by the use of complexing agents, which made the reduction of the trace elements amounts needed to compensate for substrate-related deficiency symptoms possible. This reduces the pollution on the agricultural land on which the digestate is used as fertilizer.
Hydrothermal treatment of residual forest wood (softwood) and digestate from anaerobic digestion - influence of temperature and holding time on the characteristics of the solid and liquid products
(2022) Sailer, Gregor; Comi, Julian; Empl, Florian; Silberhorn, Martin; Heymann, Valeska; Bosilj, Monika; Ouardi, Siham; Pelz, Stefan; Müller, Joachim
Hydrothermal treatment (HTT) offers the potential to upgrade low-value biomass such as digestate (DG) or forest residue (FR) by producing solids and liquids for material use or energetic utilization. In this study, microwave-assisted HTT experiments with DG and FR as feedstocks were executed at different temperatures (130, 150, 170 °C) and with different holding times (30, 60, 90 min) to determine the influences on product properties (ash and elemental concentrations, calorific values and chemical compounds). In general, DG and FR reacted differently to HTT. For the DG solids, for instance, the ash concentration was reduced to 8.68%DM at 130 °C (initially 27.67%DM), and the higher heating value increased from 16.55 MJ/kgDM to 20.82 MJ/kgDM at 170 °C, while the FR solids were affected only marginally. Elements with importance for emissions in combustion were leached out in both HTT solids. The DG and FR liquids contained different chemical compounds, and the temperature or holding time affected their formation. Depending on the designated application of HTT, less severe conditions can deliver better results. It was demonstrated that different low-temperature HTT conditions already induce strong changes in the product qualities of DG and FR. Optimized interactions between process parameters (temperature, holding time and feedstock) might lead to better cost–benefit effects in HTT.
Mono-digestion of 5-Hydroxymethylfurfural process-wastewater in continuously operated anaerobic filters: A cascade utilization approach
(2023) Khan, Muhammad Tahir; Krümpel, Johannes; Wüst, Dominik; Lemmer, Andreas
A proper remedy for the overexploitation of biomass and biobased materials in the bioeconomy is the valorization of biorefineries’ side streams into meaningful products. Hence, in pursuit of a cascade utilization of renewables, a unique biorefinery byproduct was investigated for its biogas potential, specifically methane, in continuously operated anaerobic filters. For this purpose, 5-Hydroxymethylfurfural process-wastewater, after supplementation of necessary nutrients, was diluted down to 10, 20, 30, 40, and 50 gCOD/L concentrations and thereafter tested individually at 43 °C and 55 °C. Maximum methane conversion efficiency at either temperature was observed for test substrates with 10 gCOD/L and 20 gCOD/L concentrations. At 43 °C, the anaerobic filters exhibited their highest biogas yields when supplied with the 30 gCOD/L feedstock. Further exposure of the mesophilic and thermophilic consortia to the ensuing 5-Hydroxymethylfurfural process-wastewater dilutions compromised the stability of the anaerobic process due to the soaring concentrations of short-chained volatile fatty acids. The supplementation of necessary nutrients to unlock the methane potential of the given recalcitrant substrate appears insufficient. Techniques like micro aeration, photolysis, or the use of activated carbon in the fixed bed might have the ability to enhance the biochemical methane conversion of such feedstock; otherwise, the introduction of trace elements alone may be adequate if aiming for platforms (volatile fatty acids) via anaerobic technologies.