Abstract
Recovering and recycling phosphorus (P) from sewage sludge ash (SSA) for the purpose of P fertilizer production contributes to reducing the input of mined phosphate-minerals and closing of the P cycle. However, direct use of SSA as fertilizer is often a questionable strategy due to its low nutrient use efficiency. In addition, the environmental risk potential of utilizing SSA in agriculture is still unclear, in particular potential toxic element (PTE) contamination. In this study, a mixture of SSA and rock phosphate was used at lab-scale superphosphate (SP) production. P availability of the final product and PTE contamination (Cd, Cr, Cu, Zn, Pb, Ni) in soil and crop was investigated through maize (Zea mays L.) cultivation. Results showed that the application of SP that was produced by 25% SSA replacement did not affect the growth, P uptake, and PTE content in aboveground maize compared to the application of SP produced without SSA replacement. However, significant inputs of SP with SSA replacement may decrease the solid-soil solution partitioning of Cu, Ni and Pb in the long-term. Separation of municipal/industrial sludge and PTE removal technology are necessary to be implemented prior to the use of SSA as a secondary raw material in P-fertilizer production.
Highlights
Phosphate rock is the primary raw material for producing mineral phosphate fertilizers
The 25% of rock phosphate (RP) replacement by sewage sludge ash (SSA) in SP-25 decreased its P concentration compared to SP-0
The maximum limits of potential toxic element (PTE) concentrations in inorganic fertilizers according to the European Union (EU) and German Fertilizer Ordinance were listed [22,23]
Summary
Phosphate rock is the primary raw material for producing mineral phosphate fertilizers. Based on its economic importance and supply risk due to its non-substitutable and limited reserves around the world, it is regarded as one of the critical raw materials by the European Commission [1]. It is recently identified to have high environmental hazard potential (EHP) concerning its raw material and energy demand [2]. Intrinsic potential toxic elements (PTEs) in phosphate rock contribute to its high EHP as one of the indicators. As natural P resources are decreasing, and the remaining resources show reduced quality, alternative P sources are needed to avoid a supply risk and the bioaccumulation of PTEs in humans through the food chain that involves phosphate rock-derived fertilizers and feed-additives
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