Rainer Kirchhof

The trend of transitioning to low-carbon and sustainable energy systems is crucial for environmental sustainability. While fossil fuels dominate the energy set-up of the world, the continued use of the same is inimical to the environment. Waste-to-energy is a budding area for renewable energy's role in energy transition, thus offering prospects for research and development. As a waste-to-energy conversion pathway, anaerobic digestion (AD) is a technology gaining traction in the global energy landscape. As such, this study assessed the potential enhancement of anaerobic digestion of fibrous waste material mixtures using a pretreatment agent produced from vegetable waste (hydrolysis water), with easily adaptable approaches for the global south. Emphatically, the effect of such pretreatment methods on co-digested waste materials, and their overall implications for Waste-to-Energy technologies is explored. For fibrous waste mixtures pretreated with hydrolysis water produced from vegetable waste (HM), the biogas yields measured are 554.43 ± 4.48 ml/g oTS and 510.08 ± 4.48. For fibrous waste mixtures pretreated with water (NHMM), the yields are 528.02 ± 5.31 ml/g oTS and 496.34 ± 5.31 ml/g TS. The BMPs are 304.9365 ± 4.48 ml/g oTS and 290.411 ± 5.31 ml/g oTS respectively. The study indicates that the samples produced biogas yields which are 49% and 53% higher respectively than what was obtained by their parent mixture studied by the same authors earlier. While the active contribution yield from the pretreatment agents: ordinary water and hydrolysis water are not accounted for, the comfortable difference seen is an indication of the effectiveness of the pretreatment methods used. The study effectively evaluated the theoretical maximum biogas potentials (TBMP) of the samples, using the Boyle’s model, the modified Boyle’s model and the Buswell & Müller model.

This research aimed to evaluate the comparative biogas yields of waste (peels) of selected fibrous materials from the West African region: cassava, plantain, a mixture of cassava, plantain and yam. Three models: The Boyle model, the Modified Boyle’s model, and the Buswell and Müller’s model were used to determine the theoretical maximum biomethane potential (TBMP), while the Hohenheim Biogas Yield test (D-HBT) was used to undertake a batch test of anaerobic digestion. The samples were co-digested with digested sewage sludge (DSS) for 39 days, with an operating temperature of 37 ± 0.5 °C. The study draws comparisons between the TBMPs and the experimental results, the experimental results of the different substrates, and the experimental results and figures reported in the literature. From the experimental results, plantain peels had the highest biogas yield (468 ± 72 mL/g _oTS), followed by a mixture of yam, cassava and plantain peels (362 ± 31 mL/g _oTS) and cassava peels obtained the least biogas yield (218 ± 19 mL/g _oTS). TBMPS of 204.04, 209.03 and 217.45 CH₄ mL/g _oTS were obtained for plantain peels, a mixture of yam, cassava and plantain peels and cassava peels, respectively, evaluated using Boyle’s model. For all the samples, the TBMPS (205.56, 209.03 and 218.45 CH_{4 mL}/g _oTS, respectively) obtained using the Buswell and Mueller model were slightly higher than those obtained by both the Boyle and the modified Boyle’s model (163.23, 167.22 and 174.76 CH₄ mL/g _oTS, respectively). While the study result is sufficient to imply that generating biogas from fibrous waste materials in its mixture form is a valuable approach, it is not sufficient to conclude that the use of these waste materials in its naturally occurring mixture form has a technical added advantage in co-digestion over their individual potential. However, future studies could explore this possibility with different fractions of the mixture with a view to optimising generation. The study finds that theoretically modelling the biogas potential of fibrous materials is a good method for biogas evaluation despite having overestimation tendencies, as this challenge could be corrected by applying factors that result in these tendencies, biodegradability indices. The data can, therefore, find use in fibrous waste treatment and waste-to-energy technologies, especially in Africa. This application will not be negatively affected by whether single waste streams are used or their mixture.

This research aimed to evaluate the comparative biogas yields of waste (peels) of selected relevant fibrous materials from the West African region: Cassava, plantain, a mixture of cassava, plantain and yam. Three models: The Boyle model, the Modified Boyle’s model, and the Buswell and Müller’s model were used to determine the theoretical maximum biomethane potentials (TMBP), while the Hohenheim biogas yield test (D-HBT) was used to undertake a batch test of anaerobic digestion. With an operating temperature of 37±0.5 ℃ , the samples were co-digested with digested sewage sludge (DSS) for 39 days. Comparisons are drawn between the TBMPs and the experimental results, the experimental results of the different substrates and the experimental results and figures reported in literature. From the experimental results, plantain peels had the highest biogas yield (468±72 ml/g _oTS), followed by a mixture of yam, cassava and plantain peels (362±31 ml/g _oTS) and cassava peels obtained the least biogas yield (218±19 ml/g _oTS). TMBPS of 204.04, 209.03 and 217.45 CH₄ ml/g _oTS were obtained for plantain peels, a mixture of yam, cassava and plantain peels and cassava peels respectively, evaluated using the Boyle’s model. For all the samples, the TMBPS (205.56, 209.03 and 218.45 CH₄ ml/g _oTS respectively) obtained using the Buswell and Mueller model were slightly higher than those obtained by both the Boyle and the modified Boyle’s model (163.23, 167.22 and 174.76 CH₄ ml/g _oTS respectively).

Anaerobic digestion has the potential to convert organic waste materials into valuable energy. At the same time, using press water from biomass materials for energy generation while taking advantage of the resulting cake for other purposes is an emerging approach. Therefore, this study aimed to investigate the residual potential expected from a typical biogas feedstock after it has been mechanically separated into liquid and solid phases. Hence, in this study, the rumen contents of ruminants (cow, goat, and sheep) and their proportionate ratios were obtained from an abattoir in Ghana. Resource characterization of the waste samples was carried out in the central laboratory of the HFR, Germany. Anaerobic batch tests for biogas (biomethane) yield determination were set up using the Hohenheim Biogas Yield Test (HBT). The inoculum used was obtained from an inoculum production unit at the Hohenheim University biogas laboratory. The trial involved two different forms of the sample: mixture of rumen contents, press water, and inoculum, each in four (4) replicates. The trial was carried out at a mesophilic temperature of 37 °C. Results obtained over a seventy (70) day period were transformed into biogas yields. Overall, the results show that the current contents are suitable for biogas generation as an option as opposed to the current form of disposal at a refuse dump. However, using these mixtures in their original forms is more technically viable than using press water without further treatment.

Anaerobic digestion has the potential to convert organic waste materials into valuable energy. At the same time, using press water from biomass materials for energy generation, while taking advantage of the resulting cake for other purposes is an emerging approach. Therefore, this study aimed to investigate the residual potential expected from a typical biogas feedstock in the West African context after it has been mechanically separated into liquid and solid phases. Hence, in this study, the rumen contents of ruminants (cow, goat and sheep) and their proportionate ratios were obtained from an abattoir in Ghana. Resource characterisation of the waste samples were carried out in the Central laboratory of the HFR, Germany. Anaerobic batch tests for biogas (biomethane) yield determination were set-up using the Hohenheim Biogas Yield Test (HBT). Inoculum used was obtained from an inoculum production unit at the Hohenheim University biogas laboratory. The trial involved two different forms of the sample: mixture of rumen contents, press water, and inoculum, each in four (4) replicates. The trial was carried out at a mesophilic temperature of 37°C. Results obtained over a seventy (70) day period were transformed into biogas yields. Overall, the results show that the current contents are suitable for biogas generation as an option, as opposed to the current form of disposal at a refuse dump. However, using these mixtures in their original forms is more technically viable than using press water without further treatment.