Browsing by Subject "Organic residues"

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Fertility and microbial functioning of soils of smallholder farming systems under contrasting tropical agro-ecologies
(2021) Balume, Isaac; Rasche, Frank
Soil fertility in tropical agroecosystems is often subjected to degradation that leads to nutrient depletion with negative effects on land productivity and food security. This challenge is aggravated by the complexity of socio-economic (market distance, farm typology) and biophysical (agro-ecology, site) conditions causing soil fertility variability. Consequently, blanket fertilizer recommendations cannot be applied in areas of high fertility variability. In this PhD study, methods were harmonized to assess drivers of soil fertility status across regions. Despite being pointed as factors contributing to soil fertility variability, market access, farm typology (resource endowment) and agro-ecology have not been subjected to soil fertility assessment. This PhD study aimed mainly at verifying that these factors have to integrated rather than considered in isolation to enable accurate assessments of soil fertility across spatial scales and socio-economic gradients. It was hypothesized that market distance and farm typology is a determinant of agricultural development in Democratic Republic of Congo (DRC). As market distance is increasing, the soil fertility status of smallholder farming systems decreases despite farmers’ wealth. In a parallel study conducted in Ethiopia, it was complementarily hypothesized that the soil fertility status is also influenced by inter-related effects of agro-ecology and farm typology. As nitrogen (N) is known to be limiting in smallholder farms, conservation and sustainable provision of this nutrient will be essential to achieve niche-based integrated soil fertility management (ISFM) strategies. Therefore, understanding of the ecological processes (proteolysis, nitrification) that control soil N availability through organic residue management in varying soil fertility variability conditions will be essential. Low concentrations of lignin (L) and polyphenols (PP) relative to N have been acknowledged to facilitate decomposition, hence, stimulate the abundance of proteolytic and nitrifying soil microbial communities. Therefore, it was hypothesized that high quality (low (L+PP)/N)) residue applied to high pH soils have a positive relationship between the functional potential of proteolytic enzymatic activities and abundance of nitrifying communities. The survey studies in DRC and Ethiopia were guided by the following objectives; 1) To determine the inter-related influence of market distance and farm typology on soil fertility status of smallholder farming systems of South-Kivu, Eastern DRC. 2) To assess the inter-related effects of agro-ecology and farm typology on soil fertility status across crop-livestock systems in Western and Central Ethiopia. Moreover, to better understand the ecological processes (proteolysis, nitrification) that control N through organic residue management in varying soil fertility variability conditions, an incubation study was performed to meet objective 3) To verify that potential proteolytic enzyme activities modulate archaeal and bacterial nitrifier abundance in soils with differing acidity and organic residue treatment. Results from the soil survey study in DRC revealed a decreasing soil fertility with increasing market distance across all farm typologies. A significant influence of farm typology was found for exchangeable calcium and magnesium, while factor site resulted in a significant difference of plant available phosphorus. Furthermore, factor “site” interacted with market distance for soil organic carbon (SOC) quality indexes. In addition, the interaction of market distance and typology became obvious in the medium wealthy and poor farms. Market distance effects were associated with walking distance, while site effects were attributed to factors such as soil type and climatic conditions. In Ethiopia, inter-related effect of agro-ecology and farm typology was found. Higher total carbon and total nitrogen was found in wealthy farmers’ field compared to poor farmers’ field in the highlands. As an indication of soil quality, lowest SOC stability indexes were revealed in soils of wealthy compared to that from poor farm typology. These differences in soil fertility were attributed to farm management practices among typology classes and agro-ecological zone distinctions. The result from the incubation study revealed a significant relationship of proteolytic enzyme activities with the abundance of ammonia oxidizing bacteria and archaea, even though the extent of this relationship was more dependent on soil pH and incubation time, but not residue quality. This suggests that the effect of soil pH is stronger than that of residue quality on enzyme activity and nitrifiers community, reflecting the importance of soil physico-chemical conditions rather than management practices. The incubation study further showed that nitrifying prokaryotes benefitted from the release of N spurred by proteolysis, and indicated a niche specialization between ammonia oxidizing bacteria and archaea depending on soil acidity and resource availability. Overall, this PhD study showed that market access, typology and agro-ecology were important drivers of soil fertility variability in the study regions of DRC and Ethiopia. However, factor site played a significant role in shaping soil fertility variability, implying that site-specific recommendations could be a way forward for designing soil fertility management in smallholder farmers. It was inferred that prospective niche-based ISFM strategies must consider such contrasting but interrelated factors including, but not limited to agro-ecology, farm typology and market access. This would reduce the effect of soil fertility variability across regions. This PhD study only considered land size (DRC, Ethiopia), livestock and mineral fertilizers (Ethiopia) as key features to define the wealth status of targeted farms; future studies should consider a wider range of socio-economic and biophysical factors including labor availability, off-farm household income and soil management history for more accuracy of soil fertility variability. This will strengthen the accuracy of prospective soil fertility assessments across socio-economic gradients and spatial scales. Finally, it is suggested to extend the results from the incubation study to field conditions considering soils with a broader soil acidity range and organic residues with more distinct biochemical quality. This will verify the given assumptions about the functional relationships between proteolytic and nitrifying soil communities. Overall, the presented PhD study has contributed to ongoing research on best-fit soil fertility recommendations and knowledge gaps about soil ecological functioning, by providing an advanced understanding of driving factors of soil fertility variability and soil microbial functioning in smallholder farms in tropical environments.
Microbial conversion of organic residues into acid rich process liquids and their use in bio-electrochemical systems
(2020) Ravi, Padma Priya; Lemmer, Andreas
In 2016, 2.01 billion tonnes of solid waste were generated worldwide. The volume of waste is expected to grow to 3.40 billion tonnes by 2050. Worldwide, most solid waste is disposed of in landfills or dumps. Due to improper treatment and disposal of solid waste, nearly 1.6 billion tonnes of CO2 equivalents of greenhouse gas emissions were generated worldwide in 2016. This amount is expected to rise to 2.6 billion tonnes of CO2 equivalents per year by 2050. It will therefore become increasingly important in the future not only to treat waste sustainably, but also to use it as an alternative to fossil fuels. Different waste-to-energy concepts are used, particularly for the treatment of OFMSW. As an alternative to the previously dominant biogas production, intensive research is currently being carried out into technologies for the recycling of organic residual materials, including so-called bio-electric systems (BES). In contrast to biogas production, this technology enables the treatment of a wide range of wastes to produce different end products, e.g. electrical energy, hydrogen or methane, can be preferred in BES depending on the selected process parameters. Despite numerous advances in research, considerable additional optimization is still required in order to be able to use the systems in large-scale power generation. In order to use solid organic waste in BES systems, fermentative digestion is required to convert the organic components into dissolved short-chain organic acids (Volatile Fatty Acids (VFA)) and alcohols. In the course of the investigations, the solid waste residues were first digested to acid-rich hydrolysate in a hydrolysis reactor at pH-values of 5.5 and 6.0. However, this hydrolysate also contains particles that are inert to a subsequent degradation step leading to technical process disturbances. These inert particles can be removed by means of a membrane filtration step; a particle-free permeate is produced, which can be fed to the BES reactors. Within the scope of the present work, the basics of the utilization of OFMSW via microbial digestion, membrane filtration and utilization in BES should be investigated. Lab-scale BES reactors were developed and batch tests were carried out. The vegetable waste residues from hydrolysis could be efficiently converted into hydrolysate. At a pH value of 6.0, higher organic acid concentrations were achieved than at pH 5.5. At pH 6.0, based on the added organic dry matter, these were approx. 350 g kg-1 (oDMadded) and at pH 5.5 approx. 215 g kg-1 oDMadded. Likewise, the concentration of chemical oxygen demand (COD) of the hydrolysate at pH 6.0 was 21.85 % higher than at pH 5.5. However, the COD degradation rates in the AF used were insufficient because the inert particles present in the hydrolysate could not be completely microbially degraded. The subsequent integration of ceramic cross-flow membrane filtration into the two-stage system produced a particle-free permeate and significantly the increased microbial degradability. Clear differences could be shown depending on the substrate used (plant waste and grass/maize silage). The filtration step resulted in a significant improvement of the specific methane yield of permeate by 40% (vegetable waste) and 24.5% (grass/maize silage) compared to hydrolysate; proof that inert particles were separated efficiently. Finally, the process liquids hydrolysate and permeate produced by the hydrolysis of maize silage and the subsequent membrane filtration were fed to the anode chamber of two mixed-culture BES reactors. The investigations showed that all organic acids in both process liquids could be completely degraded in the BES. The highest COD (87%) and TOC degradation rates (88%) were achieved with permeate. However, the hydrolysate with added acetic acid yielded the highest current density of 470 µA/cm². Increasing the pH-value of the process liquids from 5.75 to 6.8 also significantly improved the current production and degradation rates. In this batch studies, relatively low Coulomb efficiencies of less than 10% were achieved due to the use of a mixed cultures. The promising results show that at high pH-values (pH 6.0) in hydrolysis organic residues can be efficiently converted into a hydrolysate with high concentrations of organic acids and that the system can be further optimized by coupling membrane filtration. The utilization of the permeate in BES enables, a sustainable production of bioenergy and platform chemicals with permeate enables, depending on the BES reactor configuration. In summary, it was described for the first time that the combination of the fermentative biomass degradation process with filtration via ceramic membranes and the use of permeate in BES systems is possible.
Suitability of recycled organic residues from animal husbandry and bioenergy production for use as fertilizers
(2021) Bauerle, Andrea; Lewandowski, Iris
In recent years, agriculture has been increasingly faced with the acute need to find a more sustainable practice for dealing with nutrient-rich organic side streams. For ecological and economic reasons, pressure is mounting every day to implement an improved utilisation and to close nutrient loops in agriculture to the maximum possible. Pig manure and biogas digestates are suitable as organic fertilisers because they contain essential plant nutrients. They also provide organic matter that contributes to the maintenance of soil fertility. However, their current use is often insufficient. Both residues can be used as fertilisers either directly or following treatment. This can be as simple as solid-liquid separation. A more advanced approach is the precipitation of phosphorus for conversion into phosphate fertilisers ("P-Salts"). The fertilising effect of such innovative P-Salts needs to be investigated in an agronomic context. The same applies for the integration of separated biogas digestates as organic fertilisers into different biomass production systems. The primary objective of this thesis is to establish whether recycled fertilisers from organic residues are comparable to mineral fertilisers and can serve as a suitable substitution. For this purpose, five specific objectives were defined: (1) to determine whether separated biogas digestates can complement or substitute mineral fertilisers and whether/how they affect long-term yield performance in different biomass cropping systems; (2) to ascertain which type of separated biogas digestate is suitable for which biomass production system; (3) to test the effect of two recycled P-Salts on yield and quality of different crops compared to triple superphosphate (TSP); (4) to examine whether the combination of recycled P-Salts with biochar and dried solid digestates results in interaction effects; and (5) to assess whether there are differences in the uptake efficiency of recycled and mineral fertilisers between different crop types. Thus, several experiments were carried out. The fertilising effect of separated biogas digestates on three biomass production systems (perennial grassland, intercropping of triticale and clover grass, silage maize) was investigated in multi-year field experiments in south-west Germany. P-Salt and biochar from pig manure were tested in a greenhouse study with spring barley and faba bean. In a second greenhouse study with ornamentals, the P-Salt from manure, a P-Salt from biogas digestate, and dried solid digestates were assessed. The long-term yield stability of biomass cropping systems fertilised with separated biogas digestates was clearly demonstrated under field conditions. Separated biogas digestates can substitute mineral fertiliser in perennial and intercropping systems. Solid digestates were most suitable for cropping systems with soil tillage where their incorporation into soil is possible. The intercropping of triticale and clover grass was found to be the most stable system, with constantly high biomass yields being maintained using only digestates. For maize, a combined application of digestates and mineral fertiliser proved to be the best option. The P-Salt from manure had the same or even better effects than TSP on spring barley and faba bean. In the experiment with ornamentals, the two P-Salts from manure and digestate had more or less the same effect as TSP on biomass production. These results suggest that both P-Salts have an equivalent fertilisation effect to TSP and can thus replace it as mineral fertiliser. In this thesis, it was possible to achieve competitive yield results with the tested fertilisers, provided that they are integrated in a suitable fertilising strategy. The next step is for the recycled fertilisers to be actually used in agricultural practice - a prerequisite for which being that their implementation has agronomic, practical, ecological and economic advantages. The enhanced use efficiency of N and P already available on farms is challenging but necessary to reduce dependency on both synthesised N fertilisers and imported P fertilisers. This thesis significantly contributes by providing knowledge on the fertilising effect of selected recycled fertilisers necessary for their future implementation in agriculture. Optimised nutrient management and residue treatment using advanced technologies can contribute to the further closing of nutrient cycles. The highest environmental benefits can be realised on farms with excess residues and limited agricultural land. It is therefore highly recommended that these farms improve their current practice by prioritising the implementation of appropriate measures. Sound residue management necessitates strategic planning and capital investments from farmers and companies, but is a crucial step towards the sustainable intensification of cropping systems and resilient future agriculture.