TY  - THES
T1  - Alternative phosphorus resources from urban waste as fertilization
A1  - You,Yawen
Y1  - 2024/01/24
N2  - 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.

KW  - Phosphor
KW  - Düngemittel
KW  - Klärschlamm
KW  - Pflanzenernährung
CY  - Hohenheim
PB  - Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
AD  - Garbenstr. 15, 70593 Stuttgart
UR  - http://opus.uni-hohenheim.de/volltexte/2024/2271
ER  -