Benchmarking of innovative processing routes

Transcription

1 Benchmarking of innovative processing routes Bertanza Giorgio (1), Collivignarelli Carlo (1) and Canato Matteo (2) (1) Università degli Studi di Brescia DICATA via Branze, Brescia (BS) (2) Università degli Studi di Pavia Dipartimento di Ingegneria Civile e Architettura E mail: giorgio.bertanza@ing.unibs.it ABSTACT: Today, several technologies and management strategies are proposed and applied in WWTPs to minimize sludge production and contamination and their techno-economic feasibility has to be carefully evaluated. The increasing interest on this issue is demonstrated by the research financing policies of the European Union. ecently, an important project has been funded, with the aim of finding new routes (hence the project name: OUTES - Novel processing routes for effective sewage sludge management) for sludge management and so guiding the EU members in their future choices. In this work a technical-economic assessment procedure (benchmarking) for the comparison of sewage sludge management strategies is proposed. Basically, this procedure consists in the definition and ranking of several technical (e.g. reliability of the technology, complexity and integration with the existing facilities, amount of residues to be disposed of or recovered, ) and economic aspects. 1 INTODUCTION One of the most important issues in the operation of biological Waste Water Treatment Plants (WWTPs) is represented by sewage sludge management (Lue-Hing et al., 1999; Wei et al., 2003; Mahmood and Elliott, 2006; Pérez-Elvira et al., 2006). Today, the legislative framework in force (Directive 1991/271/EC, Directive 1999/31/EC, Directive 2000/60/EC, 3 rd draft of Working document on sludge, 2000 etc.) requires, on the one hand, the achievement of stricter effluent standards and, from the other hand, a lower level of pollution of residual sludge. Moreover, increasing difficulties in finding appropriate recovery/disposal systems push towards management strategies which should focus on the reduction of the amount of sludge (Mahmood and Elliott, 2006). Obviously, these aspects cannot be simultaneously complied with, since, in general, the greater the water treatment efficiency, the higher the sludge production and level of contamination. In addition, it has to be underlined that costs for sludge management may account for 25±65% of the total plant operation cost (Mahmood and Elliott, 2006; Pérez-Elvira et al., 2006; Foladori et al., 2010; He and Wei, 2010). Several technologies and management strategies are proposed and applied in WWTPs to minimize sludge production and contamination (Liu and Tay, 2001; Wei et al., 2003; Foladori et al., 2010). Nevertheless their techno-economic feasibility has to be carefully evaluated. In effect, many variables determine the suitability of a particular solution and these are remarkably site-specific. This problem involves also the administrative authorities in their planning activities (e.g. when funding priority must be defined). The increasing interest on this themes is demonstrated by the research financing policies of the European Union. ecently, an important project has been funded, with the aim of finding new routes (hence the project name: OUTES - Novel processing routes for effective sewage sludge management for sludge management and so driving the members of EU in their future choices. 1

2 Within the OUTES project, 15 innovative solutions for sludge management are being studied; their application is different with regard to: plant capacity (between and PE); sludge final disposal/recovery option (landfill disposal, agricultural application or co-incineration); proposed technical solution (e.g. structural upgrading, as in the case of implementation of a MB system, or operational intervention, as in the case of adoption of an oxicanoxic alternated cycles process); compartment of the plant submitted to modification (water line or sludge line). In the OUTES project, the technicaleconomic validation (benchmarking) of proposed sludge management strategies with respect to a conventional approach is a key factor. This paper presents the procedure that was developed by the authors at this scope (sludge treatment trains submitted to evaluation are described in This procedure is based on the definition of technical issues (e.g. system reliability, complexity, safety aspects, modularity, ) which are rated for the analyzed situation, in comparison with a conventional treatment scheme. In addition, capital and operation costs are estimated. Finally, in the OUTES project, for a complete evaluation of the studied solution, benchmark results will be combined with environmental aspects, arising from LCA (Life Cycle Assessment). 2 ESEACH ACTIVITY The proposed procedure consists in the evaluation of an innovative solution which is thought to be applied to a conventional plant. This requires the definition of boundary conditions, such as the influent and effluent wastewater characteristics and several other aspects (see for instance the cost of sludge disposal, the distance between the plant and the disposal site, the efficiency of treatment stages and machineries, the area availability etc.). In effect, each situation has to be considered with its own peculiarities, which are markedly sitespecific; several assumptions also depend on specific political, social and economic situation decisive for stakeholder interest, with the tendency to change over time. A sensitivity analysis is then important in order to emphasize the most relevant aspects. In this paragraph, the four main steps of the assessment procedure are described. Preliminary design and mass balance calculation The preliminary design of the treatment units and mass balance calculation constitute the first step to be carried out for both the new solution to be studied and the conventional one to be compared with. Primary sludge production (if primary sedimentation is present) can be calculated based on literature references (e.g. Metcalf & Eddy, 2003) when real data are not available. Similarly, when the study is not referred to an existing plant, the design of biological process must be carried out. Several well established procedures are available (e.g. Metcalf & Eddy, 2003) for the calculation of secondary sludge production and other important data (e.g. oxygen consumption, sludge age etc.). For the new technologies under examination, the same data must be estimated, based on other existing facilities, literature data, preliminary experimental results, simple rough calculations. Collected/estimated data are used to calculate mass balances for the conventional and the new solution to be studied. As an example, Figure 1 shows the results of mass balance calculation for a conventional solution, compared with an innovative one. Definition of technical-economic parameters Based on author s experience, the following technical and economic aspects are proposed for benchmarking: - reliability of the technology; - complexity and integration with exist- 2

3 ing facilities; - flexibility/modularity of the innovative solution compared to the traditional one; - solid, liquid and gaseous residues to be either disposed of or recovered; - consumption of raw materials and reagents; - consumption and net production of energy (thermal, electric); - social and authorization aspects; - costs. Each one of the above technical aspects is composed by different items as shown in Table 1. It must be underlined that some of these data are available in the literature or can be directly measured on the facility (in case of existing plant), while others should be estimated. Moreover, some data are sitespecific, so that they depend on local conditions and circumstances. Table 2 shows an example of numerical values for economic items. In addition, depreciation annual rates of the new equipment can be taken into account. Benchmarking All the above described technical items can be reported in a data sheet (see the example in Figure 2), which should be implemented for the comparison between conventional and innovative solutions. In our proposal, for each technical aspect and for both the conventional and the innovative solution, a partial score between 1 and 3 (3 being the best and 1 the worst ranking) was calculated based on the actual value attributed to each item (raw data). The mean value for each category (reliability, complexity, modular implementation etc.) was then calculated (final score). Eventually, the difference (gap) between the final scores of the innovative and conventional solutions was calculated for each category. esults of benchmarking were summarized in tables or graphs (see Table 3 and Figure 3 in the esults paragraph) in which the gaps for each category are reported. The economic comparison was carried out by calculating the difference of operating cost between the new and the conventional solution. Sensitivity analysis As previously stated, benchmarking result is strongly affected by the assumption of numerical values for considered parameters. For this reason a sensitivity analysis (at least for economic aspects) should be conducted so as to highlight the most influencing factors. In our work, sensitivity analysis consisted in calculating variations of the final result due to variations, for instance of ±10%, of the considered parameters, one by one. 3 ESULTS Table 3 and Figure 3 show an example of results of benchmarking conducted accordingly with the proposed procedure, in order to assess benefits and drawbacks of an innovative solution to be implemented in a (conventional) existing plant. As far as technical aspects are concerned, when the gap is positive, it means that the new solution is preferable with respect to the conventional one. Since, for each technical aspect, a score between 1 and 3 was attributed, the maximum attainable gap is +/- 2. This has to be considered in order to give the right significance to the numerical yield. In other words, for instance, a gap of 0.1 shows only a slight preference for the new solution. Concerning economic aspects, a positive gap means that an additional cost must be paid when the new solution is applied to a conventional existing WWTP. In the example shown in Table 3 and Figure 3 the innovative solution has some technical drawbacks with respect to the conventional one, but it is more advantageous from the economic point of view. The main drawbacks are the high consumption of raw materials and reagents, a poor flexibility/modularity and the lack of full-scale 3

4 references. The economic key factors of this solution are the low cost for sludge disposal and the income from electric and thermal energy sale. As previously stated, sensitivity analysis must be conducted so as to highlight the most influencing parameters. In Figure 4, an example of the results is shown, for economic parameters. It can be seen that a slight variation of even a single parameter (e.g. sludge disposal cost) can yield an appreciable variation of the global cost gap. Whenever this occurs, an accurate evaluation is crucial for a reliable and significant assessment. 4 DISCUSSION One of the major challenges for the next years in the wastewater sector is to find proper sludge management strategies, which fulfill both techno-economic and environmental sustainability requirements. A benchmarking procedure aimed at assessing technical and economic feasibility of new sludge management solutions was illustrated in this paper. The methodology was developed within the EU project OUTES (started in May 2011) and consists, basically, in defining and ranking a dozen of technical aspects (e.g. technology reliability, complexity and integration with existing facilities, amount of residues to be disposed of or recovered, ) and in estimating capital and operation costs. The proposed methodology is being applied within the research project for evaluating the suitability of 15 different sludge management options. Main advantages and drawbacks of the studied solutions and the most influencing factors can be emphasized by applying this procedure. The preliminary results highlighted, among the most important cost items: sludge disposal, raw materials and reagents and electric energy. This means that, when comparing different strategies within a specific context, a careful evaluation of the aforementioned parameters should be mandatory, so as to obtain reliable results. In conclusion, provided that a complete evaluation of a new system/management strategy should involve, beside technicaleconomic benchmark, also environmental sustainability assessment (e.g. by means of LCA), the proposed tool might be valuable: 1) for governance authorities which are in charge of deciding funding priorities; 2) for researchers and manufacturers, which could focus their investigation to solve crucial aspects. 5 ACKNOWLEDGEMENTS This work was supported by the EU OUTES project (Contract No , FP , THEME [ENV ] Innovative system solutions for municipal sludge treatment and management). 6 EFEENCES Council Directive of 21 May 1991 concerning urban waste water treatment 91/271/EEC. Council Directive of 26 April 1999 on the landfill of waste 1999/31/EC. Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy. Foladori P., Andreottola G. and Ziglio G. (2010) Sludge eduction Technologies in Wastewater Treatment Plants. IWA Publishing. He Ming-he and Wei Chao-hai (2010). Performance of membrane bioreactor (MB) system with sludge Fenton oxidation process for minimization of e- xcess sludge production. Journal of Hazardous Materials, 176, pp Liu Y. and Tay J.H. (2001). Strategy for minimization of excess sludge production from the activated sludge process. Biotechnology Advances, 19, 4

5 pp Lue-Hing Cecil, Matthews P., Nàmer J., Okuno N., Spinosa L. (1999). Sludge management in highly urbanized areas. Selected Proceeding of 18 th Biennial Conference of the International Association on Water Quality. Mahmood T. and Elliott A. (2006). A review of secondary sludge reduction technologies for the pulp and paper industry. Water esearch, 40, pp Pérez-Elvira S.I., Nieto D. and Fdz-Polanco F. (2006). Sludge minimization technologies. Environmental Science and Bio/Technology, 5, pp OUTES - Novel processing routes for effective sewage sludge management: _content&view=article&id=50&itemid= 28 Wei Y., Van Houten.T., Borger A.., Eikelboom D.H. and Fan Y. (2003). Minimization of excess sludge production for biological. Water esearch, 37, pp Working document on sludge - 3 rd draft of the 27 April 2000 (2012). Web site of European Commission. udge/pdf/sludge_en.pdf. 7 KEY WODS Benchmarking; costs; OUTES; sludge. 5

6 Figure 1. Example of mass balance calculation results: comparison between the conventional and an innovative solution. 6

7 Table 1. Technical aspects considered for benchmarking. eliability Complexity and integration with existing facilities Flexibility/Modularity esidues/ ecovered materials Consumption of raw materials and reagents Consumption of Electric Energy Net production of thermal energy Technical aspects Technology reliability (e.g. in relation to variability of influent wastewater/sludge characteristics) Number of full scale applications in EU equired intervention to be integrated with existing structures (e.g. hydraulic and electrical connections) Additional footprint (with respect to the related conventional system), all equipments included Daily work hours for ordinary operation Technicians with higher education (e.g. graduated) Specialized workers Workers Safety standards to be observed Possibility of modular implementation (e.g. in case the size has to be progressively increased) Solid/slurry Liquid Gaseous Fresh water Polyelectrolyte Coagulants Substrate for denitrification Pure oxygen Methane Other Quantity Type of heat vector (e.g. water, steam, oil ) Quantity Temperature of the heat vector Source of data * Net production of electric energy Quantity Social & authorization Public acceptance L aspects Complexity of authorization procedures L * = the data should be obtained from the results of research activity or derived from plant monitoring; L= the aspect is site-specific and depend on local conditions and circumstances. L/ L L L L/ L L/ 7

8 Table 2. Example of numerical values of economic items. Economic aspects Numerical value* Full cost of personnel [ /y per worker] - Graduated technician 60,000 Specialized worker 40,000 Worker 30,000 Unitary cost of electric energy [ /kwh e ] 0.12 Unitary income for electricity sale [ /kwh e ] 0.18 Unitary income for thermal energy sale [ /kwh t ] 0.05 Unitary cost of water [ /m 3 ] 1.00 Unitary cost of dry polyelectrolyte [ /kg] 3.00 Unitary cost of coagulant [ /kg] 0.20 Unitary cost of pure oxygen [ /kg] 0.07 Unitary cost of methane [ /Nm 3 ] 0.50 Unitary cost for agricultural application [ /t] 70 Unitary cost for landfill disposal (Non-Hazardous waste) of sludge [ /t] 20 Unitary cost for landfill disposal (Hazardous waste) of sludge [ /t] 100 Unitary cost for incineration/co-incineration of sludge [ /t] Unitary cost for sludge transportation [ /km] 4.50 * Numerical values are site-specific and depend on local conditions and circumstances. 8

9 Figure 2. Example of data sheet used for benchmarking calculations. 9

10 Table 3. Summary of benchmarking results: an example. Technical aspects Gap Item category Abbr. eliability Complexity and integration with existing structures C&I Flexibility/Modularity F/M Solid residues S res Liquid residues L res Consumption of raw materials and reagents C raw Consumption of electric energy C EE Social & authorization aspects S&A 0.17 Average GAP Av Economic aspects Gap [ /(PE y)] Item category Abbr. Depreciation annual rate A 2.57 Ordinary maintenance M 0.90 Personnel CP 0.42 Electric energy $E.E aw materials and reagents P& 6.12 Sludge disposal C-L Transportation T Income from sale of Electric Energy and/or Thermal Energy INC Total cost gap TOT

11 Figure 3. Example of graphs showing benchmarking results. 11

12 -10% EF. +10% 0.0 Cost of solid/slurry residues for LANDFILL disposal Cost of raw materials & reagents Income from sale of Electric and/or Thermal Cost of the Energy electric energy Costs for ordinary maintenance Transportation cost Total cost for personnel Global Cost - gap [ /(PE y) Varied parameter Figure 4. Example of results of sensitivity analysis: global cost gap calculated with a variation of +/- 10% of the specific cost attributed to reported parameters (one by one). 12