Article pubs.acs.org/est
Complete Survey of German Sewage Sludge Ash Oliver Krüger,* Angela Grabner, and Christian Adam BAM Federal Institute for Materials Research and Testing, Unter den Eichen 87, Berlin 12205 Germany S Supporting Information *
ABSTRACT: The amount of sewage sludge produced worldwide is expected to further increase due to rising efforts in wastewater treatment. There is a growing concern against its direct use as fertilizer due to contamination of the sludge with heavy metals and organic pollutants. Incinerating the sludge degrades organic compounds almost completely and concentrates heavy metals and phosphorus. However, the sewage sludge ash (SSA) is almost completely disposed of and with it all resources are removed from the economic cycle. Comprehensive knowledge of the composition of SSA is crucial to assess the resource recovery potentials. We conducted a survey of all SSA emerging in Germany and determined the respective mass fractions of 57 elements over a period of one year. The median content of phosphorus was 7.9%, indicating an important recovery potential. Important trace elements were Zn (2.5 g/kg), Mn (1.3 g/kg), and Cu (0.9 g/kg). Mass fractions of technology metals such as V, Cr, Ga, Nb, and rare earths were comparatively low. Considering the possible use of SSA as secondary raw material for fertilizer production it should be noted that its Cd and U content (2.7 mg/kg and 4.9 mg/kg respectively) is significantly lower than that of rock phosphate based mineral fertilizers.
■
INTRODUCTION The amount of sewage sludge that arises every year in the world’s developed markets exceeds 30 million tons (dry mass), about 11 million tons of it accrues in Europe and approximately 2 million tons in Germany alone.1,2 This quantity is expected to increase in the future due to improved sanitation and increasing wastewater treatment, especially in Asia,1,3 making the matter of disposal of the sewage sludge more pressing. In the EU-27, 53% of the emerging sewage sludge is used for fertilizer purposes in agriculture either directly or after composting, 19% is incinerated and 17% landfilled (2005),2 despite the council directive 1999/31/EC that prohibits landfilling of liquid or untreated waste.4 There are significant differences throughout the EU member states. Whereas Cyprus, Luxemburg, and Finland have an agricultural use of 90% and more; in Germany, Belgium, Slovenia, and The Netherlands the majority of the sludge (55−70%) is incinerated. Sewage sludge is the pollutant sink of wastewater treatment and thus contaminated by inorganic5 and organic pollutants.6 Especially the load of emerging pollutants of concern (EMPOC), pharmaceuticals and personal care products (PPCP), among others antibiotics, endocrine disruptors, fragrances, UV-filters, and antiseptics might pose ecological and health hazards if released to the environment.7−9 Furthermore, most of these compounds are currently not regulated by the respective ordinances.2,10 Hence there are growing reservations about the direct use of sewage sludge in agriculture. The direct use of the sludge allows for a convenient reuse of the nutrients in the wastewater. Furthermore, the © 2014 American Chemical Society
organic matter in the sludge is supposed to complement the humus in the soil. However, the contribution of sewage sludge to soil organic matter is estimated to be marginal in most EU member states and thus probably easy to replace. In Germany, approximately 300 million t/a of organic fertilizer (fresh mass) is applied,11 containing about 10.6 million t/a of organic matter (calculated with data from12). Sewage sludge accounts only for 0.25 million t/a organic matter (2.4%).11 If the sludge is incinerated, organic matter and thus organic contaminants are degraded almost completely. Phosphorus and heavy metals are concentrated compared to the sludge. However, phosphorus in sewage sludge ash (SSA) is usually in the form of aluminum and calcium phosphates that are poorly bioavailable.13 Thus, an additional treatment of the ashes is necessary in most cases to increase the bioavailability of phosphorus and remove heavy metals if utilization as a fertilizer is targeted. Currently, most of the 300 000 t/a SSA that accrue in German monoincineration facilities is either landfilled or used for mine filling or construction purposes. Only 5% is used as fertilizer (2011, own survey). Thus, all resources present in the ash are removed from the economic cycle permanently. This applies to all kinds of technology metals but especially to phosphorus, which is essential for all living creatures and cannot be replaced in its functions for expression and storage of Received: Revised: Accepted: Published: 11811
June 6, 2014 August 26, 2014 September 29, 2014 September 29, 2014 dx.doi.org/10.1021/es502766x | Environ. Sci. Technol. 2014, 48, 11811−11818
Environmental Science & Technology
Article
Table 1. Element Mass Fractions in SSA, Calculated Element Mass Flows in German SSA and Analytical Parameters element Na Mg Al Si P
S K Ca Ti Fe element Sc V Cr Mn Co Ni Cu Zn Ga Ge As Se Sr Y Zr Nb Mo Rh Pd Ag Cd Sn Sb Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Pt
ICP-OES
ICP-MS
[nm]
isotope
589.592 (radial) 279.079 (radial) 396.152 (radial) 251.611 (radial) 213.618 (axial) P (municipal) P (municipal/industrial) P (industrial) 182.034 (axial) 766.490 (radial) 318.128 (radial) 334.941 (radial) 217.809 (axial) ICP-OES ICP-MS [nm]
LOQ
min
max
0.015 0.012 0.038 0.161 0.022
0.2 0.3 0.7 2.4 1.5 3.6 2.8 1.5 0.3
