P-Recycling Potential Of Sludge And The Impact Of Its Treatment On Environment And Resources

Transcription

1 P-Recycling Potential Of Sludge And The Impact Of Its Treatment On Environment And Resources CONTACT Jakob, Lederer IWA, TU Wien Christian, Ott IWA, TU Wien Helmut, Rechberger IWA, TU Wien Jakob Lederer Institute for Water Quality, Resource, and Waste Management (IWA), Vienna University of Technology Karlsplatz 13/ Vienna Austria Tel.: Fax: j.lederer@iwa.tuwien.ac.at EXECUTIVE SUMMARY Phosphorous (P) is a limited and non-substitutable resource. The detected and potentially exploitable reserves are limited, which implicates careful management of P including increased recycling of P-containing wastes in the near future. In a step-wise approach, this paper 1) determines the quantitative potential for P-recycling of different P-containing wastes and 2) uses the example of sewage sludge to compare five common treatment methods with one novel alternative. The quantitative potential of P-containing waste recycling is determined by a material flow analysis of P for the EU15. The analysis reveals that there is hardly any recycling of P today. The biggest losses of P occur to the agricultural soil where it is fixed, to landfills, and to the hydrosphere. Recycling of sewage sludge could substitute about 15% of the current P-fertilizer demand and seems to be a measure comparably easy to realize to enhance the recycling rate for P. Subsequently, common sludge treatment options (direct land application in agriculture; mono-incineration and application of ashes in agriculture; mono-incineration and ash-disposal in landfills; co-incineration in cement production; coincineration in a coal-fired power plant) are assessed and compared with a novel technology, which is based on a thermo-chemical process to treat mono-incineration ashes in order to decrease the heavy metal content and increase the plant availability of P. The assessment, which considers environmental impacts, resource recovery, and materials dissipation, is based again on material flow analysis and compares energy balances, selected LCIA indicators, and statistical entropy analysis. Based on the results of the impact assessment, a distinction in the established treatment options can be drawn between those which rather conserve P-resources (direct land application in agriculture; mono-incineration and application of ashes in agriculture) and those which reduced emissions to the hydro- and pedosphere (mono-incineration and ash-

2 disposal in landfills; co-incineration in cement production; co-incineration in a coal-fired power plant). The novel technology combines advantages of the established practices: organic and inorganic pollutants are either destroyed or removed from the P containing material, and the P returned to the soil exhibits high plant-availability. Beside that, the novel technology also has lower emissions. The additional energy requirements should be reduced. However, with regards to sewage sludge P recovery is more important than energy recovery. INTRODUCTION Phosphorus (P) is an important substance for all living creatures in the ADP/ATP- system, a key element for reproduction in DNA and RNA and thus also indispensable for plant growth (Gowariker, 2009a; Lederer & Rechberger, 2010; Smil, 2000). Inputs of up to 120kg/ha.a mineral P 2 O 5 -fertilizer is necessary to maintain contemporary agricultural systems (Hansa- Landhandel). However, the uneven spatial distribution of P (five countries provide 90% of the P consumed) affects international P trade (Cordell, 2008a). Particularly countries heavily depending on imports (e.g. EU, India) are affected therein. Studies furthermore suggest that the high-quality reserves deplete within years, due to the increasing production, which lies currently at about 147 Mio. t P/yr (Cordell, 2008b) (see figure 1). This again leads to exploitation of lower-quality reserves with higher cadmium and uranium contents (Van Kauwenbergh, 1997). Figure 1 dynamic time range for P- ore- high and low estimate (data taken from Jasinski, 2008) Baccini & Brunner (1991) among others have shown that P-consumption in industrial societies is highly inefficient and non-circular. P dissipates in over-fertilized soils, water bodies (e.g. the Black Sea), and landfills through various waste products, some of them with high P content (waste water, sludge, incineration ashes), leading to various problems, like eutrophication of water bodies (Zessner & Lampert, 2002a). To reduce both, the resource consumption of mineral P, but also the negative impacts of dissipated P, some strategies are discussed. While dietary changes may have the biggest impact (Brunner & Rechberger 2004), recycling of P from waste products is indispensable. However, waste products usually also contain problematic substances and materials, which require some more or less sophisticated treatment for the waste. Different options and practices for waste treatment are available, where some are still on pilot-scale

3 operation. Regarding to the objectives of waste management, the options with the best performance regarding protection of human health, the environment, and conservation of resources, must be selected. This paper aims 1) to estimate the P-flows in Europe, in order to trace out quantitative P- recycling potentials and 2) compares different options of treatment of a high-p content waste, namely sewage sludge. Both parts have been / are presented in two publications. Part 1: P-Flows In The EU15 (Ott And Rechberger Submitted) By using the method of Substance Flow Analysis (SFA) (Bacchini & Brunner 1991; Brunner & Rechberger 2004), first the model, which consists of five general processes (Agriculture, Industry including trade and commerce (ITC), Consumption including Households, Waste Water Treatment (WWT) and Waste Management (WM)) and 36 major flows of goods containing P, was developed. The system boundaries refer to the EU15 zone for one year, using data from the latest year available (between 2002 and 2009). The major imports and exports to/from the system are fertilizers, food and fodder, and other imports/exports. Emissions to the hydrosphere and atmosphere are treated as exports. The calculation was conducted with the freeware software STAN (Cencic 2007). Scientific studies, statistics from national governments, the EU, international organizations (FAO, OECD), provided the data of P-mining, consumption, and transfer coefficients for some of the flows and processes regarded. The residual flows and transfer coefficients were calculated with STAN. Data uncertainties and significant digits were considered after Taylor (1997). As a basic assumption, all data was assumed to be normal distributed with a confidence interval of 95%, meaning the actual value inserted in the model is the mean value, while the uncertainty range is the referring standard deviation. The result (Figure 2) shows that the biggest flow of P is the import of fertilizer (4 kg/c.yr), while the export of fertilizer counts only a tenth of it (0.4 kg/c.yr). The import of food and fodder is about 0.9 (kg/c.yr), hence only a quarter of the fertilizer import. Even though the export to the hydrosphere via erosion, waste water treatment affluent, and leaching (0.4 kg/c.yr in total) is quantitatively much smaller, it has to be seen differently, as the receiving process (the hydrosphere) is a natural compartment and in some cases much more affected, for example the Black or the Baltic Sea (cp. Zessner and Lampert 2002). Within the system, the interaction between Industry-Trade-Commerce and Agriculture shows the biggest P-flows. However, the flows are not circular, which is indicated to the P- stock increase in agricultural soils (+2.7 kg/c.yr). This value is only slightly lower than the export of P through agricultural products (plants, milk, eggs, meat in total 3.1 kg/c.yr). Even though the P-stock in these soils increases, more P-fertilizer is yearly added, as the P in the stock is not immediately plant available. The second biggest stock is the accumulation of P in waste management (landfills, deposition), with an increase of about 1.6 (kg/c.yr). The bulk there origins from Industry-Trade-Commerce (0.7 kg/c.yr) and sewage sludge derived products, like incineration ashes (0.5 kg/c.yr). About the same amount of sewage sludge derived products goes to Agriculture (e.g. through direct application of sewage sludge). The supply of mineral P from own mines is less then one tenth (0.3 kg/c.yr) of the imported mineral P.

4 Figure 2 P-flows for the EU 15 [kgp/cap*a] The results show the EU15s high P-dependency on external sources. This dependency, together with the decreasing quality of phosphate rock (increasing Cd and U contents) and the hypotheses of decreasing mineral P-resources in general, let policy makers to reconsider the EUs resource strategy regarding P, from import dependence to 1) higher resource efficiency in use and 2) higher P-recycling rates. 1) Higher efficiency must target the process Agriculture, where the stock increase in soils suggests that a lower, but better targeted P-fertilizer input does not negatively influence agricultural production (Csathó and Radimsky 2009), but increase the efficient use of resources and also reduces negative impacts on the environment (e.g. decreasing eutrophication of water bodies through erosion). 2) Higher P-recycling must target the waste products and the stock of P in waste management. Solid waste P makes two thirds of the Waste Management stock, Waste Water Treatment P in form of sewage sludge one third. So far, the P-flow from Waste Water Treatment and Waste Management to Agriculture makes about 14% of the fertilizer import to the EU15, of which 0.43 (kg/c.yr) P is through sewage sludge and 0.14 (kg/c.yr) is through compost. If all the P in sewage sludge (industrial + municipal waste water) would be recycled to agriculture (0.9 kg/c.yr), 22% of the current fertilizer import could be substituted. Additional potential lies in the up-grading of WWT plants with P-elimination. The recycling potential of P from sewage sludge could then increase from 22% to 26% of the current fertilizer import.

5 Part 2: A Goal-Oriented Assessment Of Conventional And Alternative Sewage Sludge Treatment Options (Lederer & Rechberger 2010) Part 1 has shown that both, better agricultural practice and P-recycling from wastes is essential for a more sustainable P-use in the EU 15. For the latter (recycling), not just the use of compost or sewage sludge, but more technologies are available. Beside that, other options then recycling of P (e.g. using sewage sludge as a fuel) are practiced. To assess which option performs best regarding the goals of waste management, a goal-oriented assessment of different common sewage sludge treatment options, including one alternative option, has been conducted. For the assessment, six different options are compared: 1. Direct application of sludge on agricultural land (Option 1 - direct soil) 2. Mono-incineration of sludge and ashes to soil (Option 2 - mono-inc+soil) 3. Mono-incineration of sludge and ashes to landfill (Option 3 mono-inc+landfill) 4. Co-incineration of sludge in a cement kiln (Option 4 - cement) 5. Co-incineration of sludge in a coal-fired power plant (Option 5 - coal) 6. SUSAN-technology (Option 6 - SUSAN) While numbers 1-5 are commonly used options in the EU15, SUSAN-technology is the alternative and comprises of a thermo-chemical treatment of P-rich sewage sludge monoincineration ashes under 900 C and addition of CaCl 2 or MgCl 2 to remove the heavy metals from the ash and a subsequent use of this decontaminated material for P-fertilizer production (see details on the process in Mattenberger et al and Adam et al. 2009; details on the options in Lederer & Rechberger 2010). In all options, the sewage sludge undergoes a pre-treatment (biogasification with energy recovery) before further processing. The functional unit used is one ton of raw sewage sludge from municipal waste water with a dry matter of 4.2%, an organic/inorganic fraction share of 68 to 32%, and average substance concentrations after Korving (2008), Thornton (2001) and DWA (2009). The assessment itself is based on different life cycle and sustainability indicators representing the impact on human health and the environment (1. emissions of arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc into the air, water, and soil; considered by applying the LCA impact assessment of IMPACT after Humbert et al., (2005; 2006) and CML after Guinée et al. (2001); 2. NO X -emissions to the atmosphere; 3. long-term effects by estimating the increase of heavy metal concentrations in soils) as goal number one and conservation of resources (1. primary energy balance; 2. phosphorus recovery) for goal number two. Additionally, the dilution of substances is assessed through the statistical entropy calculation after Rechberger & Brunner (2002) and Rechberger & Graedel (2002). In a first step, the substance and material flows are calculated for all options, based on Material Flow Analysis after Bacchini & Brunner (1991) and Brunner and Rechberger (2004). This leads also to the substance emissions into soil, atmosphere and hydrosphere, which are then transferred into impacts on human toxicity, terrestrial and aquatic toxicity (Humbert et al., 2005; 2006; Guinée et al. 2001). Then, the emissions (NO X ) and resources consumptions (materials, energy) are calculated. Finally, the results are expressed through diagrams.

6

7 Figure 3 Flow charts for options 1 to 6 for P and Hg including estimated or calculated standard deviations Figure 4 Relative statistical entropy of mercury

8 Figure 5 Relative impacts of heavy metal emissions, compared to the highest impact in each category; option with highest impact = 100% Figure 6 Illustration of results: each indicator is relative to the least desired option; impacts of emissions to air, water and soil according to CML; 1 = least desired, 0 = most desired; due to illustration purposes, alls zero values are indicated as Figure 3 shows the substance flows for P and Hg. The therein observable dilution of Hg in products and natural compartments is also shown in Figure 4. Figure 5 shows the relative impacts of all options on human health, aquatic and soil toxicity, while Figure 6 summarizes the results. Direct soil application (option 1) performs well with regard to energy and P recovery. The main disadvantage, which is not quantitatively included in this study, is that organic pollutants are not destroyed as is the case for all other options, where sufficiently high combustion temperatures and flue gas residence times guarantee effective destruction. In addition, the emissions to water and soil are comparably high for this option. Option 2

9 (mono-inc+soil) performs similar without having the organic problem of option 1 (direct soil). Options 3 to 5 (mono-inc+landfill, cement, coal) do not recover P, which is in the long run not acceptable. The mono-incineration options (options 2 and 3) perform better with regard to air emissions, though option 2 contaminates the soil in the long run. Option 3 can be regarded as an interim solution if the ash is stored in a mono-compartment of a landfill. The P can then be recovered at any time if required. The SUSAN technology fulfils all requirements with regard to environmental protection and resource conservation at the expense of higher energy requirements. This technology must be further optimized. On the other hand, if the importance of sewage sludge with regard to energy and P is considered, it is clear that environmentally compatible P-recycling is of higher priority. CONCLUSION Part 1 of this paper shows that going-off from import of mineral P-fertilizer requires a higher efficiency in use and recycling. Wastes like sewage sludge are an important component therein. However, recycling has to be environmentally friendly, and should not impair human health and the environment negatively, neither in the short, nor in the long run. To fulfill this requirement, solutions with an acceptable trade-off between protection of human health and the environment and resource conservation, should be favored. One solution which, if further developed, can meet this requirement, is the thermo-chemical treatment of mono-incineration ashes (SUSAN technology). ACKNOWLEDGEMENTS This paper derives from the EU sponsored FP6 project Sustainable and Safe Re-use of Municipal Sewage Sludge for Nutrient Recovery (SUSAN). It also merges some important points of two publications, which provide a deeper understanding of the results presented herein (Lederer & Rechberger 2010; Ott & Rechberger submitted). The authors thank our former colleague, Mrs. Jeannette Klonk, for laying the foundations for this work, and the partners from the SUSAN project. The SUSAN-homepage can be found under: REFERENCES Adam, C., Peplinski, B., Michaelis, M., Kley, G., & Simon, F.-G. (2009): Thermo chemical treatment of sewage sludge ashes for phosphorus recovery. Waste Management 29, pp Baccini, P. & Brunner, P.H. (1991). The metabolism of the anthroposphere. Springer- Verlag, Berlin, Heidelberg, Germany. Brunner, P. & Rechberger, H. (2004). Practical handbook of material flow analysis. Boca Raton FL: CRC/Lewis. Cencic, O. (2007). STAN - Freeware Für Stoffflussanalysen Nach ÖNORM S Cordell, D. (2008a). The Story of Phosphorus: missing global governance of a critical resource. SENSE Earth Systems Governance, Amsterdam, 24th 31st August Cordell, D., Drangert, J.-O., White, S. (2008b) The story of phosphorus: Global food security and food for thought. Global Environmental Change 19(2), pp Csathó, P. & Radimszky, L. (2009): Two Worlds within EU27: Sharp Contrasts in Organic and Mineral Nitrogen-Phosphorus Use, Nitrogen-Phosphorus Balances, and Soil Phosphorus Status: Widening and Deepening Gap between Western and Central Europe. Communications in Soil Science and Plant Analysis 40, pp DWA (2009). Thermische Behandlung von Klärschlamm: Mitverbrennung, Merkblatt DWA- M 387, Entwurf Mai 2009 (in German: Thermal treatment of sewage sludge: Co-

10 incineration, bulletin DWA-M 387, draft May 2009), German Association for Water, Wastewater and Waste, Hennef, Germany. Gowariker, V. (2009). The fertilizer encyclopedia. Hoboken N.J.: John Wiley & Sons. Guinée, J. B., Gorrée, M., M., Heijungs, R., Huppes, G., Kleijin, R., Koning, A., Oers, L., Sleeswijk, A., Suh, S., Udo de haes, H.A., Bruijn, D.E., Van duin, R., & Huijbregts, M.A.J., Life cycle assessment. An operational guide to the ISO standards, Parts 1, 2a, 2b, 3, Leiden University, Leiden, The Netherlands. Humbert, S., Margni, M., & Jolliet, O., IMPACT 2002+: Methodology description, Swiss Federal Institute of Technology Lausanne EPFL, Lausanne, Switzerland. Humbert, S., Margni, M., Jolliet, O., IMPACT 2002+: User Guide - Draft for version 2.1, Swiss Federal Institute of Technology Lausanne EPFL, Lausanne, Switzerland. IBM. AISE Code of Good Environmental Practice: Jasinski, (2008). USGS Minerals Information: Phosphate Rock. Accessed March 10 th 2010, available from: Korving, L., (2008). Personal Communication, Slibverwerking Noord-Brabant SNB, The Netherlands. Lederer, J. & Rechberger, H. (2010): Comparative goal-oriented assessment of conventional and alternative sewage sludge treatment options. Waste Management 30(6), pp Mattenberger, H., Fraissler, G., Brunner, T., Herk, P., Hermann, L., & Obernberger, I., (2008). Sewage sludge ash to phosphorus fertiliser: Variables influencing heavy metal removal during thermochemical treatment. Waste Management 28, pp Ott, C., & Rechberger, H. (submitted): European Phosphorus - Large- Scale Substance Flow Analysis for EU 15. Rechberger, H., & Brunner, P.H., (2002): A new, entropy based method to support waste and resource management decisions. Environmental Science and Technology 344, pp Rechberger, H., & Graedel, T.E. (2002): The contemporary European copper cycle: statistical entropy analysis. Ecological Economics 42, pp Taylor, J.R. (1997). An introduction to error analysis. University Science Books. Thornton, I. (2001). Pollutants in Urban Waste Water and Sewage Sludge, European Commission - DG Environment, Brussels, Belgium. Van Kauwenbergh, S.J. (1997). Cadmium and other minor elements in world resources of phosphate rock. Proceedings of the International Fertilizer Society No 400, York, UK. Zessner, M., & Lampert, C. (2002). The use of regional material balances in water quality management. Urban Water 4, pp.73-83