Fate of heavy metals and polycyclic aromatic hydrocarbons (PAH) in sewage sludge carbonisates and ashes – A risk assessment to a thermochemical phosphorus-recycling process Daniel Steckenmesser a,⇑ , Christian Vogel b , Leonard Böhm c , Benjamin Heyde c , Christian Adam b a Institute of Plant Nutrition, Research Centre for BioSystems, Land Use and Nutrition (iFZ), Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany b Division 4.4 Thermochemical Residues Treatment and Resource Recovery, Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany c Institute of Soil Science and Soil Conservation, Research Centre for BioSystems, Land Use and Nutrition (iFZ), Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany article info Article history: Received 6 February 2018 Revised 17 May 2018 Accepted 13 June 2018 Keywords: P-recycling Sewage sludge Thermochemical treatment Heavy metals Poly aromatic hydrocarbons abstract In the near future, phosphorus (P) recycling will gain importance in terms of decreasing primary resources. Sewage sludge (SSL) is an adequate secondary P-resource for P-fertilizer production but it is also a sink for heavy metals and organic pollutants. The present study is an investigation on thermochem- ical P-recycling of SSL. Various temperatures and amendments were tested regarding their performance to remove heavy metals and polycyclic aromatic hydrocarbons (PAH) and simultaneous increase of the plant-availability of P. The investigations were carried out on two types of SSL originating from wastew- ater treatment plants with chemical P-precipitation and enhanced biological P-removal, respectively. The results show that thermochemical treatment with chlorine donors is suitable to remove the majority of heavy metals and that a combination of a gaseous chlorine donor (HCl) and sodium additives leads to both high heavy metal removal and high plant availability of P. Furthermore, plant experiments show that almost all investigated thermochemical treatments can significantly reduce the bioavailability and plant uptake of heavy metals. Furthermore, PAHs are secondarily formed during low-temperature treatments (400–500 °C), but can be significantly reduced by using sodium carbonate as an additive. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Phosphorus (P) is an essential element for all organisms and it must be fertilized to agricultural fields to guarantee an adequate plant production. Conventional P-fertilizers are produced from phosphate rock (mostly apatite) which natural mineral deposits are limited. Hence, P is a finite resource that has to be recycled to contribute to the P-cycle. However, P can be found in many waste materials and sewage sludge (SSL) has one of the highest P-recovery potentials due to its enormous amount and high P content (Donatello and Cheeseman, 2013). One possibility to recover P from SSL is the direct field application. However, this recovery path is controver- sially discussed, due to its high loads of heavy metals and organic pollutants (Donatello et al., 2010; Harrison et al., 2006). The amendment of the German Sewage Sludge Ordinance regulates the direct field application and the alternative P-recycling. By 2031, German waste water treatment plants of a certain size (>50,000 population equivalent) must recycle P from SSL alternatively (BMU, 2017). In the last decade, many studies focused on alternative P-recycling from SSL and resulted in numerous P-recovering-strategies (Donatello and Cheeseman, 2013). A promising strategy is the thermal treatment of SSL (Adam et al., 2009; Donatello and Cheeseman, 2013; Kleemann et al., 2017), which is advantageous in terms of energy generation, volume reduction, and hygienization. However, thermal treatments also have well known and investigated drawbacks, such as the concen- tration of some heavy metals during pyrolysis (Frišták et al., 2018; Hossain et al., 2011; Méndez et al., 2013) or high-temperature treatments (Adam et al., 2009; Jeon and Kim, 2018). These prod- ucts have higher heavy metal mass fractions after thermal treat- ment while the ratio heavy metal/P remains at the same level. In some cases, secondary formation of polycyclic aromatic hydrocar- bons (PAH) was observed (Freddo et al., 2012; Liu et al., 2008; Lyu et al., 2016; Zielin ´ ska and Oleszczuk, 2015). Various studies showed that the elimination of heavy metals during thermal https://doi.org/10.1016/j.wasman.2018.06.027 0956-053X/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: daniel.steckenmesser@ernaehrung.uni-giessen.de (D. Steckenmesse. Waste Management 78 (2018) 576–587 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman