Institut für Agrartechnik

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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.
Characteristics and anaerobic co-digestion of press water from wood fuel preparation and digested sewage sludge
(2022) Sailer, Gregor; Empl, Florian; Kuptz, Daniel; Silberhorn, Martin; Ludewig, Darwin; Lesche, Simon; Pelz, Stefan; Müller, Joachim
Technical drying of harvested wood fuels is heat and energy consuming, while natural pre-drying in the forest, e.g., in stacks or storage piles, is accompanied by energy losses through natural degradation processes. Dewatering of energy wood by mechanical pressing is an innovative method to reduce the moisture content prior to thermal drying while producing press waters (PW, also referred to as wood juice) as a by-product. To date, the characteristics and utilization potentials of PW are largely unknown. In this study, three different spruce- and poplar-based PW were analyzed for their characteristics such as dry matter (DM), organic dry matter (oDM) concentration, pH-value, element concentration or chemical compounds. Additionally, they were used for anaerobic digestion (AD) experiments with digested sewage sludge (DSS) serving as inoculum. The fresh matter-based DM concentrations of the PW were between 0.4 and 3.2%, while oDM concentrations were between 87 and 89%DM. The spruce-based PW were characterized by lower pH-values of approx. 4.4, while the poplar-based PW was measured at pH 8. In the AD experiments, DSS alone (blank variant) achieved a specific methane yield of 95 ± 26 mL/goDM, while the mixture of spruce-based PW and DSS achieved up to 160 ± 12 mL/goDM, respectively. With further research, PW from wood fuel preparation offer the potential to be a suitable co-substrate or supplement for AD processes.
Impact of thermo-mechanical pretreatment of sargassum muticum on anaerobic co-digestion with wheat straw
(2023) Hütter, Miriam; Sailer, Gregor; Hülsemann, Benedikt; Müller, Joachim; Poetsch, Jens
Sargassum muticum (SM) is an invasive macroalgal species seasonally occurring in large quantities. While generally suitable for anaerobic digestion, recent studies resulted in low specific methane yields (SMYs), presumably due to salt, polyphenol, and high fiber contents of this marine biomass. In this study, the specific biogas yield (SBY) and SMY of SM alone as well as in co-digestion with wheat straw (WS) were investigated in batch tests at process temperatures of 44 ± 1.4 °C with a retention time of approx. 40 d. The pretreatment variants of SM were examined with regard to desalination and disintegration to potentially improve digestibility and to enhance the overall performance in anaerobic digestion. A sole mechanical treatment (pressing) and a thermo-mechanical treatment (heating and pressing) were tested. Batch assays showed that pressing increased the SMY by 15.1% whereas heating and pressing decreased the SMY by 15.7% compared to the untreated variant (87.64 ± 8.72 mL/gVS). Both anaerobic digestion experiments generally showed that co-digestion with WS can be recommended for SM, but the observed SBY and SMY were still similar to those of other studies in which SM was not pretreated. The mechanical pretreatment of SM, however, offers the potential to enhance the SMY in the anaerobic digestion of SM with WS, but further research is necessary to identify the optimum upgrading approaches since the overall SMY of SM is relatively low compared to other substrates that are commonly used in anaerobic digestion. In addition to anaerobic digestion, SM as an already available biomass could also be of interest for further utilization approaches such as fiber production.

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