TY - JOUR A1 - Herzel, Hannes A1 - Krüger, Oliver A1 - Hermann, L. A1 - Adam, Christian T1 - Sewage sludge ash - A promising secondary phosphorus source for fertilizer production N2 - Sewage sludge incineration is extensively practiced in some European countries such as the Netherlands, Switzerland, Austria and Germany. A survey of German sewage sludge ash showed that the recovery potential is high, approx. 19,000 t of phosphorus per year. However, the survey also discovered that the bioavailability of phosphorus in the sewage sludge ash is poor and that more than half of the ashes cannot be used as fertilizers due to high heavy metal content. A new thermochemical process for sewage sludge ash treatment was developed that transforms the ash into marketable fertilizer products. Sewage sludge ash was thermochemically treated with sodium and potassium additives under reducing conditions, whereby the phosphate-bearing mineral phases were transformed into plant available phosphates. High P-bioavailability was achieved with a molar Na/P ratio > 1.75 in the starting materials. Sodium sulfate, carbonate and hydroxide performed comparably as additives for this calcination process. Potassium carbonate and -hydroxide have to be added in a molar K/P ratio > 2.5 to achieve comparable P-solubility. The findings of the laboratory scale investigations were confirmed by an industrial demonstration trial for an ash treatment with sodium sulfate. Simultaneously, the volatile transition metal arsenic (61% removal) as well as volatile heavy metals such as cadmium (80%), mercury (68%), lead (39%) and zinc (9%) were removed via the off-gas treatment system. The product of the demonstration trial is characterized by high bioavailability and a toxic trace element mass fraction below the limit values of the German fertilizer ordinance, thus fulfilling the quality parameters for a P-fertilizer. KW - Sewage sludge ash KW - Phosphorus recovery KW - Thermochemical treatment KW - Reducing conditions KW - Heavy metal evaporation KW - Bioavailability KW - Sodium sulfate PY - 2016 DO - https://doi.org/10.1016/j.scitotenv.2015.08.059 SN - 0048-9697 SN - 1879-1026 IS - 542 SP - 1136 EP - 1143 PB - Elsevier CY - Amsterdam AN - OPUS4-34165 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vogel, Christian A1 - Krüger, Oliver A1 - Adam, Christian T1 - Thermochemical treatment of sewage sludge ash with sodium additives under reducing conditions analyzed by thermogravimetry N2 - Phosphorus (P) for fertilizer use can be recovered from sewage sludge ash (SSA). To enhance the bioavailability of P and reduce the heavy metal content of SSA, it can be treated thermochemically with Na2CO3 or Na2SO4 at 950 °C in a rotary kiln using dry sewage sludge or lignite as reducing agent. These processes were investigated by thermogravimetry/differential thermal analysis coupled with gas analysis. Reducing conditions in this experimental setup were provided by 2 % hydrogen in the Ar carrier gas. During SSA + Na2CO3 treatment CO2, CO and water were detected in the off-gas. During SSA + Na2SO4 treatment SO2, some CO2 and water were detected. Heavy metal removal was more efficient for SSA + Na2CO3 compared to the sulfate variant. A SSA + Na2SO4 + lignite variant which also formed CO shifted the heavy metal removal to the results obtained with Na2CO3 which was obviously due to the additional reduction potential. However, Zn evaporation was not achieved with the Na2SO4 variants which were most probably due to immobilization as ZnS. KW - Phosphorus recovery KW - Thermochemical treatment KW - Sewage sludge ash KW - Reducing conditions KW - Heavy metal evaporation KW - FT-IR gas analysis PY - 2016 DO - https://doi.org/10.1007/s10973-015-5016-z SN - 1388-6150 SN - 1418-2874 SN - 0368-4466 SN - 1572-8943 VL - 123 IS - 2 SP - 1045 EP - 1051 PB - Springer CY - Dordrecht AN - OPUS4-34556 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -