Browsing by Subject "Recyclingdünger"

Now showing 1 - 2 of 2

Alternative phosphorus resources from urban waste as fertilization
(2023) You, Yawen; Müller, Torsten
Phosphorus (P) is an essential macronutrient for plants. Plant roots assimilate P in soil mainly in the form of orthophosphates as H2PO4- and HPO42-. Due to the high reactivity, orthophosphates generally exist at low concentrations in soils that have high P sorption capacity. Besides the indigenous P in soil, fertilizers manufactured from phosphate rock are the main source of P to ensure a satisfactory yield in agricultural production. However, phosphate rock is a limited reserve with uneven quality and is geographically restricted. Technologies for recovering and reusing the P from waste streams were therefore developed to alleviate the dependency on this critical raw material and to promote sustainable solutions. Sewage sludge, which contains most of the P from wastewater, has great potential to produce P-rich products. However, the evaluation of their P availabilities to plants by simple chemical extraction of the product is difficult because they often contain different P species that do not easily dissolve in water. In the first chapter, three types of recycled P fertilizers derived from sewage sludge were tested first in the greenhouse using maize in two different substrates and were incubated in soil for 0, 22, and 56 days. Untreated sewage sludge ash (SSA), Na-treated SSA, and struvite were tested here. Untreated SSA failed to promote the growth of young maize, while Na-treated SSA and struvite achieved similar biomass as mineral P fertilizer. The pre-incubation time had a negative impact on the P use efficiency of recycled fertilizers. Although the P availability of untreated SSA was very low, it might be a potential substitute for phosphate rock to produce fertilizers. In Chapter II, the P availability and heavy metal contamination risk of superphosphate produced with untreated SSA in the lab were investigated. It was found that the superphosphate produced with the mixture of 25% SSA and 75% rock phosphate had a similar P use efficiency as the superphosphate produced with 100% rock phosphate, indicating untreated SSA could be a suitable substitution of rock phosphate in the P fertilizer production. Despite the heavy metal accumulations in soil and plant being minimal, the Pb and Cu concentration in untreated SSA exceeded the maximum limit according to the EU regulation on fertilizers and therefore its use is restricted in fertilizer production. The separation of industrial and municipal sludge before incineration is recommended to obtain SSAs with high P concentrations but less heavy metal. In Chapter III, the P availability of granulated struvite as affected by fertilizer application methods in comparison to di-ammonium phosphate (DAP) was investigated under field conditions. The experiment was conducted in one field in 2020 and repeated in an adjacent field in 2021. Two-year maize results showed an increase of 30% in maize yield and P content when struvite was placed, indicating that fertilizer placement enhanced the efficiency of granulated struvite. Struvite-placed had similar P use efficiency as DAP-placed, and both treatments led to significantly higher yield and P content of maize than no-P control. The residual effect of fertilizer treatment was evaluated with faba bean (Vicia faba) and triticale (Triticosecale Wittm. ex A. Camus.) as subsequent crops after maize. No significant difference in yield and P content was found between struvite-placed and DAP-placed. Nevertheless, this chapter demonstrated that placed struvite can replace DAP as P fertilizer in maize cultivation. In Chapter IV, the sensitivity of three P extraction methods to different P species was investigated to provide insights into the characterization of current soil P tests to plant P availability. Three soil P tests were compared: calcium acetate-lactate (CAL), Olsen, and diffusive gradients in thin films (DGT). Results showed that a portion of added orthophosphates was immediately fixed in the soil and cannot be extracted by any of the methods. The acidic CAL method may overestimate immediately plant-available P of insoluble calcium phosphate like Ca3(PO4)2. The most suitable method to determine immediately available P might be the Olsen and DGT method. To conclude, this dissertation demonstrated the P availability of recycled P fertilizers derived from sewage sludge and possible strategies to enhance their P use efficiencies. It provided agronomic evidence on the feasibility of replacing phosphate rock-derived P fertilizers with recycled fertilizers and insight into its land application. With the recently revised EU regulation on fertilizing products, it can be expected that recycled fertilizers will soon share the market with mineral fertilizers and help develop sustainable agriculture.
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.