energetically passive municipal solid waste treatment plant
ENERGETICALLY PASSIVE MUNICIPAL SOLID WASTE TREATMENT PLANT A. BIAŁOWIEC*, W. PIESIK** * Wrocław University of Environmental and Life Sciences, Faculty of Life Sciences and Technology, Institute of agricultural Engineering, 37/41 Chełmońskiego Str., 51-630 Wrocław, Poland ** Novago Sp. z o.o., 10 Grzebskiego Str., 06-500, Mława, Poland
SUMMARY: The case study of the technology Periodic Anaerobic Bioreactor (PAB) where the bioconversion of biodegradable fraction contained in municipal solid waste enables for efficient production of biogas, which is the fuel for the power system generating electricity and heat in combination (CHP), is presented. This technology enables production of electricity: 0.250 MWhe per each ton of waste submitted to the bioreactor, and production of heat: 0.487 MWh (1.753 GJ) per each ton of waste submitted to the bioreactor. The mentioned bioreactor, located in Kosiny Bartosowe, near Mława in Poland, is integrated MBT plant, including the RDF production facility where both generated electricity and heat cover all electrical, and heat demand for mechanical waste treatment, and RDF drying. The operational parameters indicate, that application of PAB bioreactor may have also environmental benefits. Reduction of emissions as CO2 equivalent as a greenhouse gas: 1.438 tons per each ton of waste submitted to the bioreactor. MBT plant receives two streams of waste mixed waste with code 200301, and initially mechanically treated MSW with code 191212, which are then mechanically, and biologically (biostabilisation/biodrying) processed. The main purpose of MBT plant activity is production of RDF. PAB receives organic (undersize) fraction sorted from MSW in MBT plant, and other external organic solid and liquid waste. Generated biogas in PAB is gathered, and reused in biogas reuse unit. Generated electricity is used to cover MBT plant demands. The electricity power of two CHP units is almost equal to MBT energy demand. During time, when MBT plan does not work (night, Sundays, holydays) generated energy is exported to the grid. Generated heat is mostly used for increasing the biodrying process, and RDF drying in MBT plant, where heat exchangers are used. The reuse of heat causes the shortening of the RDF drying by the factor of 3, what decreases the electricity demand for blowers in relation to unit of mass of RDF. On the base of operational data of PAB, and MBT plant the estimation of energy balance of MBT integrated with PAB for the period between years 2015, and 2020 was done.
1. INTRODUCTION The combination of mechanical and biological processes is called mechanical-biological waste treatment (MBT). MBT is a technique for waste treatment by mechanical and biological methods which are configured for the type of waste treated and for the aims pursued. MBT of waste originates mainly from European experiences, and in particular from countries such as Germany, Italy and Austria. The MBT of wastes is one of the fastest developing technologies in municipal solids wastes treatment in contrast to waste landfilling and incineration. The main aim of this technology is to separate particular waste groups and biological treatment of organic
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
fractions of municipal solid wastes with potential for biogas and heat recovery (Soyez, Plickert, 2003). There are two general major concepts of mechanical-biological pre-treatment of wastes. The first concept entails the opposite: firstly the mixed wastes are biologically treated (biodrying), and then stabilized wastes are mechanically treated with the material flow separation (Bolzonella, et al. 2006). This variant is actually a biological-mechanical treatment (BMT). In this case, the waste is first subjected to biological drying, and subsequently it is sorted into raw material fraction, combustible fraction and fraction intended to be landfilled. The second concept includes the mechanical separation of the high calorific value fraction (refuse derived fuel - RDF) combined with material flow separation. The next step is a biological stage with aerobic or anaerobic processes. This option is mechanical-biological treatment (MBT), and thus in the first place, sorting and grading of waste into two fractions, i.e. raw material fraction and biological fraction, occur. The latter goes to aerobic or anaerobic treatment. Typically, the larger-size fractions (oversize fraction) discarded during the sieving process are of higher calorific value, and are diverted for either direct incineration (preferably with energy recovery), or for the production of refuse-derived fuels. The RDF finally can be used for energy production in a variety of plants (e.g. cement kilns, coal power plants) (Ritzkowski et al. 2006). With a view to the purpose of implementation of the mechanical-biological treatment of municipal waste, eight most frequently used options are distinguished (Table 1). Table 1. Fundamental objectives and components of MBT system Type of MBT option Stabilisation of waste prior to their landfilling Production of compost from the waste Production of compost not satisfying the requirements
Objective of MBT option reduction of biodegradability of municipal waste and recovery of part of secondary raw materials obtaining a material having properties of the compost and recovery of part of secondary raw materials obtaining a material having properties similar to those of the compost and recovery of part of secondary raw materials
production of alternative fuel from light fraction of the waste and recovery of part of secondary raw materials Production of SRF in the production of alternative fuel from light and organic fraction of process of biodrying the waste and recovery of part of secondary raw materials increase in the calorific value of the waste directed to the Assisting in thermal system of thermal neutralisation of waste and recovery of part neutralisation of waste of secondary raw materials production and energy recovery of biogas produced in Production of biogas anaerobic conditions and recovery of part of secondary raw materials production and energy recovery of biogas produced in Production of biogas and anaerobic conditions, obtaining, from fermentation residue, a compost not satisfying material having properties similar to those of the compost and the requirements recovery of part of secondary raw materials Production of RDF
In the field of improving the degree of energy recovery of waste, solutions are known in which, by using methods of mechanical sorting of mixed waste, a light fraction (coarse - with a high proportion of combustible waste) is separated therein, through sieving, the said fraction being subsequently subjected to thorough cleaning by separating metals and other non-
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
combustible parts. Thus prepared material is subjected to size homogenisation into diameters required by the fuel recipient. Often, additives of other organic components which increase the calorific value, such as sawdust, rubber, are used. Thus prepared fuel is referred to as Refuse Derived Fuel (RDF). This waste handling allows obtaining a material with a high calorific value of 14 to 18 MJ/kg, which, as a fuel, is directed to energy recovery. Thanks to separation and valorisation of combustible fraction, energy use of about 30-40% by mass of waste is possible. The main problem of the thus produced RDF is its high moisture, corresponding to the initial moisture of mixed waste, and therefore being at a level of 35-45%. For this reason, very often, fuel separated in this manner cannot find its recipients. Another problem is high energy demand for RDF production, especially for final milling (Velis et al., 2010). In this technology, after mechanical separation of light fraction, there is still fine and main fraction remained to be managed. Typically, both fractions are directed to biological stabilisation. The main objective of this treatment is to reduce susceptibility of organic matter contained mainly in the main fraction to biological decomposition. Main and fine fractions may be stabilised under aerobic conditions (composting, aerobic biostabilization) and anaerobic conditions (methane fermentation). In both cases, stabilised post-process waste is obtained. The executed modelling by Białowiec et al. (2015) showed, that the most effective is the second option, where after mechanical separation, undersize fraction is anaerobically stabilised, with biogas production, but residual digestate is finally aerobically stabilised prior to landfilling. The main benefit of this option if high biogas potential, and the lowest amount of waste for landfilling. Therefore in this paper the case study of MBT technology with anaerobic organic fraction degradation in Periodic Anaerobic Bioreactor (PAB), including initial results of biogas production, focused on achievement of energetically passive waste treatment plant will be presented. Periodic Anaerobic Bioreactor (PAB) technology, also called ANABIOREC enables for efficient bio-stabilization and reuse of biodegradable fraction contained in municipal waste being processed. Technology of the PAB due to bioconversion of biodegradable fraction contained in municipal waste enables for efficient production of biogas, which is the fuel for the power system generating electricity and heat in combination (CHP). A bioreactor, by its design, is mistakenly compared with the technology of waste landfilling, mainly due to the use of a common denominator which is the process of anaerobic decomposition of the organic fraction. Anaerobic technological processes take place in a number of systems: biogas plants, a biological part of the waste treatment system, a bioreactor, a landfill. The similarity to a landfill results only from the fact of using earth masses as a construction element for the bioreactor. The similarity to the biogas plant consists in an active influence on the process of biogas production. Also the intended uses of the bioreactor are different in comparison to the landfill: landfilling as a means of waste disposal is characterized by the uncontrolled release of biogas as a by-product, and the purpose of the operation of the bioreactor PAB is the production of biogas from municipal waste under controlled conditions. The PAB technology has been previously described by Białowiec et al. (2015). The technology in question is not a landfill, because: − the conditions for biological decomposition of organic matter and biogas production are monitored, − the conditions for biological decomposition of organic matter and biogas production are optimized, − the intensity of biological decomposition of organic matter and biogas production is controlled - accelerated, − after finishing the intensive phase of transformations, the processes are stopped and the waste from the reactor are taken out, which clearly differentiates the bioreactor from the landfilling technology.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
By definition, a bioreactor is a device enabling the conduct of microbiological processes, constructed in such a way that, through the measurement and control of parameters, ensures the control of the manufacturing process and its optimum course. The main task of a bioreactor is to provide the best parameters, due to which the intensification of the various biological processes is possible. The technology presented, due to the technological regime, constitutes a batch bioreactor, that is self-heating. The features of the bioreactor are: − the possibility to exercise full control of the batch - homogenization of municipal waste through the separation of the organic fraction of the undersize, adding other organic waste, − the possibility to control the processes by maintaining the required temperature, humidity, availability of nutrients - carried out by recirculating pre-treated and preheated leachate, − the possibility to measure the effectiveness of the processes involved and the conditions in the reactor - achieved by controlling the conditions present in the deposit, by controlling the operation of each degassing wells, controlling the intensity and characteristics of biogas produced, controlling the quantities and properties of leachate taken out and recirculated, − the possibility to control the final product - by testing the degree of the decomposition of waste in the reactor, by mathematical modelling of the degree of the decomposition of waste, by preparing a properly composed feed to the reactor, by the use of techniques hygienization with water vapor and oxygen stabilization of waste remaining after the process. The construction of the PAB provides environmental protection to enable the migration of leachate through the following conditions: − at the design phase it is assumed to position the reactor on an impermeable ground by using suitable sealing materials, − the height of the bioreactor is limited to 16 m. These two parameters ensure that the tightness of the bottom of the bioreactor is fully maintained. This is indicated by the tests of groundwater at points around the bioreactor. The bioreactor is equipped with a system of collection and recirculation of leachate, which eliminates their impact on the environment of water and soil and makes the sealing of plateau thus eliminating potential impacts on atmospheric air. The collection of biogas from the bioreactor is carried out using a vacuum system (active degassing), the operation of which is fully controlled - (leachate level sensors in wells, measuring the amount of leachate pumped out from wells, capacity and performance of each of the wells, properties of the captured biogas), so the only problem related to the operation and leakage of the bioreactor can be the ingress of oxygen (by mineral sealing of the plateau) from the atmosphere, which is indicated in the current mode by a biogas composition analyser. Also, the current momentary gain of biogas is compared to the model curve of biogas production for the given process conditions.
2. DESCRIPTION OF THE WASTE TREATMENT PLANT PERFORMANCE The first case of PAB implementation, and its integration with MBT plant is PAB located in
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Kosiny Bartosowe in Poland. The configuration of MBT plant integrated with PAB was presented on Figure 1. MBT plant receives two streams of waste mixed waste with code 200301, and initially mechanically treated MSW with codes 191212, and 191210, which are then mechanically, and biologically (bio-stabilization/biodrying) processed. The main purpose of MBT plant activity is production of RDF (Figure 1).
Figure 1. The configuration of MBT plant integrated with PAB in Kosiny Bartosowe, Poland. The % mass flow of waste streams is shown. The waste codes, are given according to (Waste codes catalogue (EPA), and waste treatment coeds D or R are given according to (Eu Directiove, 2008). The functional integration of PAB with MBT plant is shown on Figure 2.
Figure 2. The example of functional PAB integration with MBT plant in Kosiny Bartosowe, Poland.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
PAB receives organic (undersize) fraction sorted from MSW in MBT plant, and other external organic solid and liquid waste. The total capacity of PAB is 200 000 Mg. the time of 3 sections PAB fulfilment was 3 years. In the MBT plant, with capacity of 130 000 Mg/y, the oversize fraction is treated to produce RDF (Figure 1) with capacity about 100 000 Mg/y. After all waste treatment steps, including mechanical separation, biodrying, aerobic bio-stabilization, and anaerobic treatment in PAB, and waste excavation from PAB and it’s mechanical, and biological treatment, only 7.4% of initial waste mass is dedicated to landfilling (Figure 1). Leachate from PAB are pretreated for ammonia removal by stripping, and horizontal subsurface constructed wetlands, and after heating are recirculated into bioreactor. Generated biogas in PAB is gathered, and reused in biogas reuse unit (Figure 2). The average CH4 content in biogas is 56.17%, but the ratio of CH4/CO2 was 1.28, what indicates stabile methanogenesis. During PAB operation, the average biogas calorific value was 20.02 MJ/Nm3. The average content of H2S was 399.9 vppm. Gathered biogas is utilized in two CHP units with overall power of 0.9 MW, and in steam boiler with total heat power 2.1MW. Generated electricity was used to cover MBT plant energy demands. The electricity power of two CHP units is almost equal to MBT energy demand. On the base of operational data of PAB, and MBT plant the estimation of energy balance of MBT integrated with PAB for the ten years’ period was done (Figure 3). The overall electricity production for 10 years’ period is 48144 MWh (Figure 3).
Figure 3. The estimation of energy balance of MBT plant in Kosiny Bartosowe, Poland, integrated with PAB for the ten years’ period. Almost 56% of generated electricity is used for MBT supplying. During time, when MBT plan does not work (night, Sundays, holydays) generated energy is exported to the grid, what consists about 34% of generated electricity. About 10% is used for internal needs of biogas utilization unit needs (Figure 3). Generated heat 205 142 GJ is mostly, about in 89.9%, used for increasing the biodrying process, and RDF drying in MPT plant, where heat exchangers are used, and for recirculated leachate heating. The reuse of heat causes the shortening of the RDF drying by the factor of 3, what decreases the electricity demand for blowers in relation to unit of mass of RDF. During 10 years, the MBT plant treats 1,300 Gg of MSW, and uses 26908 MWh. The energy demand factor is 20.7 kWh/Mg. The electricity production firm biogas generated in PAB from 200 000 Mg of waste is 48144 MWh. The electricity production factor is then 240.7 kWh/Mg.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
The obtained operational data, and biogas, and MBT plant performance forecasting indicate, that implementation of PAB, and its integration with MBT plant may cover all electricity, and heat demands of MBT plant, and gain additional financial benefits from electricity export to the grid. It causes, that integration of PAB with MBT plant, allows to achieve that overall system is energetically passive municipal solid waste treatment plant.
3. ENVIRONMENTAL BENEFITS FROM PAB INTEGRATION WITH MBT PLANT The presented PAB technology may be innovative in general due to “commercialisation of MSW undersize fraction”, and in detail due to: − Effective anaerobic bio-stabilization of the organic fraction of municipal waste. − Possibility to use a feedstock of mixed municipal waste with the guarantee of recovery of combustible fraction during post reaction material processing. − Possibility of application of the additional organic fraction introduced into the process from the outside in liquid form through the installation of leachate recirculation. − Possibility of use of any organic fraction for the production of energy. − Significant reduction in the amount of landfilled post-process waste. − Highly efficient use of the energy potential of the organic fraction contained in municipal waste (biogas production supported by recirculation of treated leachate, and its use as fuel in the production of electricity and heat in high efficiency cogeneration). − Maximum degree of usage of the organic fraction from municipal waste as simultaneous process with significant reduction in operating costs for the installation of the mechanical treatment of waste (production of RDF using combustible fraction from municipal waste) due to the production of electricity and heat in own power system located in waste treatment facility and its use for own needs (shredders drive, initial bio-stabilization of waste and drying alternative fuel using process heat). − Reusability of the same capacity of the bioreactor as a result of cyclical filling of waste disposal for the process and emptying after a certain time of cycle of the most efficient bioconversion of organic fraction in the form of biogas. − Developed technology of preparing and carrying out a cyclical dismantling of sectors of the bioreactor while maintaining the principles of safety and environmental protection and developed technological line for processing post reaction material with a maximum recovery of useful substances. − The following major positive and negative environmental aspects of PAB technology may be identified: Positive: − No emissions from process gases from bio-stabilization of waste into the atmosphere (Compared to MBT technology). − No emissions of methane into the atmosphere (compared to the technologies of waste disposal by landfilling). − Reduction of emissions as CO2 equivalent as a greenhouse gas: 1.438 tons per each ton of waste submitted to the bioreactor. − A significant reduction in weight of post-process waste to be landfilled (compared to MBT technology): − Reduction of carbon dioxide emissions into the atmosphere associated with combined production of electricity and heat from methane compared to separated by
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
− −
conventional sources of energy produced from coal, Production of electricity: 0.240 MWhe tons per each ton of waste submitted to the bioreactor, Production of heat: 0.487 MWhh (1.753 GJ) per each ton of waste submitted to the bioreactor.
Negative: − Exhaust gas emissions to the atmosphere from the devices of power system using biogas as a fuel (cogeneration units, steam boiler, flare): o SO2 Sulphur dioxide 725 kg/year• of the bioreactor, o NOX nitrogen oxides 2.142 kg/ha of surface of the bioreactor, o CO Carbon monoxide 4.540 kg/year of surface of the bioreactor, o Dust PM2.5-PM10 432 kg/year•ha of surface of the bioreactor, − Engine oil consumption for the needs of cogeneration units - 1.800 l/year•ha of surface of the bioreactor. − Excessive leachates to be removed from the bioreactor system for the purpose of cleaning in classic wastewater treatment plant – 50 m3/year•ha of surface of the bioreactor. − Electricity consumption for own needs of the bioreactor system and the power system - 60.000 kWh/year•ha of surface of the bioreactor. − Water consumption for technological purposes of the bioreactor system installation -675 m3/year•ha of surface of the bioreactor. After the last third full cycle of the operation of the bioreactor there are variants of using the land in question: − the removal of the infrastructure of the bioreactor and the full restoration of the land in accordance with the requirements at that time (the expected direction of the restoration will depend on the development of neighbouring areas, e.g. concerning forests or recreational areas), − the transformation of the bioreactor territory (after obtaining relevant administrative decisions and after performing modernization) to a place where the process of waste disposal will be carried out using a futuristic technology (from the beginning of the bioreactor's operation to its end within the next 25 years) other than storage or anaerobic or oxygen stabilization or other currently used in accordance with applicable regulations for waste processing. In the case of total decommissioning, two drainage lines (PE), sealing foil (HDPE) are left to be developed. The materials dismantled in parts shall be subject to crushing and use as feedstock for RDF production line (PE material is a combustible fraction). Mineral material recovered from the bioreactor can be used for land reclamation.
4. CONCLUSIONS The PAB technology meets the requirements for companies operating in the field of waste management. The PAB technology minimizes the amount of post-processing waste destined for landfilling. The PAB technology minimizes operating costs of the plant for mechanical treatment of municipal waste in terms of consumption of electricity drawn from the grid, due to the production of energy of own sources (power system power supplied by biogas from the bioreactor).
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
The PAB technology increases the efficiency of the process of oxygen biostabilization of municipal waste prior to mechanical processing through the use of process heat generated in the power system for the process air heating. The PAB technology increases the efficiency of the process of mechanical treatment of waste by reducing the burden of waste shredders thanks to the drying the waste by process air heated by the process heat. The integration of PAB with MBT plant, allows to achieve that overall system is energetically passive municipal solid waste treatment plant. The PAB technology has not yet been classified in accordance with standards for waste treatment plants. It is similar to the already known power heaps, but has additional processes that have not been included in the legislation of EU countries. The bioreactor technology complies with the national legal requirements of the Building Law and regulations on environmental protection, which is confirmed by each time issued individual environmental decision.
REFERENCES Białowiec A. Pulka J. and Stegenta S. (2015a). The comparative modelling of mass flow in different options of MBT of MSW in Polish conditions. Proceedings of XVth International Waste Management and Landfill Symposium in Sardinia, 5 - 9 October, 2015. Białowiec A. Wiśniewski D. Pulka J. and Wiśniewski A. (2015b). The influence of hydraulic loading rate of Sequence-Anaerobic-Bioreactor on fermentation conditions and generation of biogas. Annual Set The Environment Protection 17(2), 12594-1273. Bolzonella D., Pavan P., Mace S. and Cecchi F. (2006). Dry Anaerobic Digestion of Differently Sorted Organic Municipal Solid Waste: Full-scale Experience. Water Sci. Technol., 53, 23-32. Environmental Protection Agency. European waste catalogue and hazardous waste list http://www.nwcpo.ie/forms/EWC_code_book.pdf EU (European Union), Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on Waste and Repealing Certain Directives, 2008. Ritzkowski M. Heerenklage J. and Stegmann R. (2006). An overview on techniques and regulations of mechanical-biological pre-treatment of municipal solid waste. Environmental Biotechnology, 2, 57-68. Soyez K. And Plickert S. (2003). Mechanical Biological Pretreatment (MBP) of Waste. Proceedings of IXth International Waste Management and Landfill Symposium in Sardinia, 6 10 October, 2003. Velis C.A. Longhurst P.J., Drew G.H., Smith R. and Pollard S.J.T. (2010). Production and Quality Assurance of Solid Recovered Fuels Using Mechanical-Biological Treatment (MBT) of Waste: A Comprehensive Assessment. Crit. Rev. Env. Sci. Tec., 40 (12), 979-1105.
SUMMARY: The case study of the technology Periodic Anaerobic Bioreactor (PAB) where the bioconversion of biodegradable fraction contained in municipal solid waste enables for efficient production of biogas, which is the fuel for the power system generating electricity and heat in combination (CHP), is presented. This technology enables production of electricity: 0.250 MWhe per each ton of waste submitted to the bioreactor, and production of heat: 0.487 MWh (1.753 GJ) per each ton of waste submitted to the bioreactor. The mentioned bioreactor, located in Kosiny Bartosowe, near Mława in Poland, is integrated MBT plant, including the RDF production facility where both generated electricity and heat cover all electrical, and heat demand for mechanical waste treatment, and RDF drying. The operational parameters indicate, that application of PAB bioreactor may have also environmental benefits. Reduction of emissions as CO2 equivalent as a greenhouse gas: 1.438 tons per each ton of waste submitted to the bioreactor. MBT plant receives two streams of waste mixed waste with code 200301, and initially mechanically treated MSW with code 191212, which are then mechanically, and biologically (biostabilisation/biodrying) processed. The main purpose of MBT plant activity is production of RDF. PAB receives organic (undersize) fraction sorted from MSW in MBT plant, and other external organic solid and liquid waste. Generated biogas in PAB is gathered, and reused in biogas reuse unit. Generated electricity is used to cover MBT plant demands. The electricity power of two CHP units is almost equal to MBT energy demand. During time, when MBT plan does not work (night, Sundays, holydays) generated energy is exported to the grid. Generated heat is mostly used for increasing the biodrying process, and RDF drying in MBT plant, where heat exchangers are used. The reuse of heat causes the shortening of the RDF drying by the factor of 3, what decreases the electricity demand for blowers in relation to unit of mass of RDF. On the base of operational data of PAB, and MBT plant the estimation of energy balance of MBT integrated with PAB for the period between years 2015, and 2020 was done.
1. INTRODUCTION The combination of mechanical and biological processes is called mechanical-biological waste treatment (MBT). MBT is a technique for waste treatment by mechanical and biological methods which are configured for the type of waste treated and for the aims pursued. MBT of waste originates mainly from European experiences, and in particular from countries such as Germany, Italy and Austria. The MBT of wastes is one of the fastest developing technologies in municipal solids wastes treatment in contrast to waste landfilling and incineration. The main aim of this technology is to separate particular waste groups and biological treatment of organic
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
fractions of municipal solid wastes with potential for biogas and heat recovery (Soyez, Plickert, 2003). There are two general major concepts of mechanical-biological pre-treatment of wastes. The first concept entails the opposite: firstly the mixed wastes are biologically treated (biodrying), and then stabilized wastes are mechanically treated with the material flow separation (Bolzonella, et al. 2006). This variant is actually a biological-mechanical treatment (BMT). In this case, the waste is first subjected to biological drying, and subsequently it is sorted into raw material fraction, combustible fraction and fraction intended to be landfilled. The second concept includes the mechanical separation of the high calorific value fraction (refuse derived fuel - RDF) combined with material flow separation. The next step is a biological stage with aerobic or anaerobic processes. This option is mechanical-biological treatment (MBT), and thus in the first place, sorting and grading of waste into two fractions, i.e. raw material fraction and biological fraction, occur. The latter goes to aerobic or anaerobic treatment. Typically, the larger-size fractions (oversize fraction) discarded during the sieving process are of higher calorific value, and are diverted for either direct incineration (preferably with energy recovery), or for the production of refuse-derived fuels. The RDF finally can be used for energy production in a variety of plants (e.g. cement kilns, coal power plants) (Ritzkowski et al. 2006). With a view to the purpose of implementation of the mechanical-biological treatment of municipal waste, eight most frequently used options are distinguished (Table 1). Table 1. Fundamental objectives and components of MBT system Type of MBT option Stabilisation of waste prior to their landfilling Production of compost from the waste Production of compost not satisfying the requirements
Objective of MBT option reduction of biodegradability of municipal waste and recovery of part of secondary raw materials obtaining a material having properties of the compost and recovery of part of secondary raw materials obtaining a material having properties similar to those of the compost and recovery of part of secondary raw materials
production of alternative fuel from light fraction of the waste and recovery of part of secondary raw materials Production of SRF in the production of alternative fuel from light and organic fraction of process of biodrying the waste and recovery of part of secondary raw materials increase in the calorific value of the waste directed to the Assisting in thermal system of thermal neutralisation of waste and recovery of part neutralisation of waste of secondary raw materials production and energy recovery of biogas produced in Production of biogas anaerobic conditions and recovery of part of secondary raw materials production and energy recovery of biogas produced in Production of biogas and anaerobic conditions, obtaining, from fermentation residue, a compost not satisfying material having properties similar to those of the compost and the requirements recovery of part of secondary raw materials Production of RDF
In the field of improving the degree of energy recovery of waste, solutions are known in which, by using methods of mechanical sorting of mixed waste, a light fraction (coarse - with a high proportion of combustible waste) is separated therein, through sieving, the said fraction being subsequently subjected to thorough cleaning by separating metals and other non-
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
combustible parts. Thus prepared material is subjected to size homogenisation into diameters required by the fuel recipient. Often, additives of other organic components which increase the calorific value, such as sawdust, rubber, are used. Thus prepared fuel is referred to as Refuse Derived Fuel (RDF). This waste handling allows obtaining a material with a high calorific value of 14 to 18 MJ/kg, which, as a fuel, is directed to energy recovery. Thanks to separation and valorisation of combustible fraction, energy use of about 30-40% by mass of waste is possible. The main problem of the thus produced RDF is its high moisture, corresponding to the initial moisture of mixed waste, and therefore being at a level of 35-45%. For this reason, very often, fuel separated in this manner cannot find its recipients. Another problem is high energy demand for RDF production, especially for final milling (Velis et al., 2010). In this technology, after mechanical separation of light fraction, there is still fine and main fraction remained to be managed. Typically, both fractions are directed to biological stabilisation. The main objective of this treatment is to reduce susceptibility of organic matter contained mainly in the main fraction to biological decomposition. Main and fine fractions may be stabilised under aerobic conditions (composting, aerobic biostabilization) and anaerobic conditions (methane fermentation). In both cases, stabilised post-process waste is obtained. The executed modelling by Białowiec et al. (2015) showed, that the most effective is the second option, where after mechanical separation, undersize fraction is anaerobically stabilised, with biogas production, but residual digestate is finally aerobically stabilised prior to landfilling. The main benefit of this option if high biogas potential, and the lowest amount of waste for landfilling. Therefore in this paper the case study of MBT technology with anaerobic organic fraction degradation in Periodic Anaerobic Bioreactor (PAB), including initial results of biogas production, focused on achievement of energetically passive waste treatment plant will be presented. Periodic Anaerobic Bioreactor (PAB) technology, also called ANABIOREC enables for efficient bio-stabilization and reuse of biodegradable fraction contained in municipal waste being processed. Technology of the PAB due to bioconversion of biodegradable fraction contained in municipal waste enables for efficient production of biogas, which is the fuel for the power system generating electricity and heat in combination (CHP). A bioreactor, by its design, is mistakenly compared with the technology of waste landfilling, mainly due to the use of a common denominator which is the process of anaerobic decomposition of the organic fraction. Anaerobic technological processes take place in a number of systems: biogas plants, a biological part of the waste treatment system, a bioreactor, a landfill. The similarity to a landfill results only from the fact of using earth masses as a construction element for the bioreactor. The similarity to the biogas plant consists in an active influence on the process of biogas production. Also the intended uses of the bioreactor are different in comparison to the landfill: landfilling as a means of waste disposal is characterized by the uncontrolled release of biogas as a by-product, and the purpose of the operation of the bioreactor PAB is the production of biogas from municipal waste under controlled conditions. The PAB technology has been previously described by Białowiec et al. (2015). The technology in question is not a landfill, because: − the conditions for biological decomposition of organic matter and biogas production are monitored, − the conditions for biological decomposition of organic matter and biogas production are optimized, − the intensity of biological decomposition of organic matter and biogas production is controlled - accelerated, − after finishing the intensive phase of transformations, the processes are stopped and the waste from the reactor are taken out, which clearly differentiates the bioreactor from the landfilling technology.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
By definition, a bioreactor is a device enabling the conduct of microbiological processes, constructed in such a way that, through the measurement and control of parameters, ensures the control of the manufacturing process and its optimum course. The main task of a bioreactor is to provide the best parameters, due to which the intensification of the various biological processes is possible. The technology presented, due to the technological regime, constitutes a batch bioreactor, that is self-heating. The features of the bioreactor are: − the possibility to exercise full control of the batch - homogenization of municipal waste through the separation of the organic fraction of the undersize, adding other organic waste, − the possibility to control the processes by maintaining the required temperature, humidity, availability of nutrients - carried out by recirculating pre-treated and preheated leachate, − the possibility to measure the effectiveness of the processes involved and the conditions in the reactor - achieved by controlling the conditions present in the deposit, by controlling the operation of each degassing wells, controlling the intensity and characteristics of biogas produced, controlling the quantities and properties of leachate taken out and recirculated, − the possibility to control the final product - by testing the degree of the decomposition of waste in the reactor, by mathematical modelling of the degree of the decomposition of waste, by preparing a properly composed feed to the reactor, by the use of techniques hygienization with water vapor and oxygen stabilization of waste remaining after the process. The construction of the PAB provides environmental protection to enable the migration of leachate through the following conditions: − at the design phase it is assumed to position the reactor on an impermeable ground by using suitable sealing materials, − the height of the bioreactor is limited to 16 m. These two parameters ensure that the tightness of the bottom of the bioreactor is fully maintained. This is indicated by the tests of groundwater at points around the bioreactor. The bioreactor is equipped with a system of collection and recirculation of leachate, which eliminates their impact on the environment of water and soil and makes the sealing of plateau thus eliminating potential impacts on atmospheric air. The collection of biogas from the bioreactor is carried out using a vacuum system (active degassing), the operation of which is fully controlled - (leachate level sensors in wells, measuring the amount of leachate pumped out from wells, capacity and performance of each of the wells, properties of the captured biogas), so the only problem related to the operation and leakage of the bioreactor can be the ingress of oxygen (by mineral sealing of the plateau) from the atmosphere, which is indicated in the current mode by a biogas composition analyser. Also, the current momentary gain of biogas is compared to the model curve of biogas production for the given process conditions.
2. DESCRIPTION OF THE WASTE TREATMENT PLANT PERFORMANCE The first case of PAB implementation, and its integration with MBT plant is PAB located in
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Kosiny Bartosowe in Poland. The configuration of MBT plant integrated with PAB was presented on Figure 1. MBT plant receives two streams of waste mixed waste with code 200301, and initially mechanically treated MSW with codes 191212, and 191210, which are then mechanically, and biologically (bio-stabilization/biodrying) processed. The main purpose of MBT plant activity is production of RDF (Figure 1).
Figure 1. The configuration of MBT plant integrated with PAB in Kosiny Bartosowe, Poland. The % mass flow of waste streams is shown. The waste codes, are given according to (Waste codes catalogue (EPA), and waste treatment coeds D or R are given according to (Eu Directiove, 2008). The functional integration of PAB with MBT plant is shown on Figure 2.
Figure 2. The example of functional PAB integration with MBT plant in Kosiny Bartosowe, Poland.
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PAB receives organic (undersize) fraction sorted from MSW in MBT plant, and other external organic solid and liquid waste. The total capacity of PAB is 200 000 Mg. the time of 3 sections PAB fulfilment was 3 years. In the MBT plant, with capacity of 130 000 Mg/y, the oversize fraction is treated to produce RDF (Figure 1) with capacity about 100 000 Mg/y. After all waste treatment steps, including mechanical separation, biodrying, aerobic bio-stabilization, and anaerobic treatment in PAB, and waste excavation from PAB and it’s mechanical, and biological treatment, only 7.4% of initial waste mass is dedicated to landfilling (Figure 1). Leachate from PAB are pretreated for ammonia removal by stripping, and horizontal subsurface constructed wetlands, and after heating are recirculated into bioreactor. Generated biogas in PAB is gathered, and reused in biogas reuse unit (Figure 2). The average CH4 content in biogas is 56.17%, but the ratio of CH4/CO2 was 1.28, what indicates stabile methanogenesis. During PAB operation, the average biogas calorific value was 20.02 MJ/Nm3. The average content of H2S was 399.9 vppm. Gathered biogas is utilized in two CHP units with overall power of 0.9 MW, and in steam boiler with total heat power 2.1MW. Generated electricity was used to cover MBT plant energy demands. The electricity power of two CHP units is almost equal to MBT energy demand. On the base of operational data of PAB, and MBT plant the estimation of energy balance of MBT integrated with PAB for the ten years’ period was done (Figure 3). The overall electricity production for 10 years’ period is 48144 MWh (Figure 3).
Figure 3. The estimation of energy balance of MBT plant in Kosiny Bartosowe, Poland, integrated with PAB for the ten years’ period. Almost 56% of generated electricity is used for MBT supplying. During time, when MBT plan does not work (night, Sundays, holydays) generated energy is exported to the grid, what consists about 34% of generated electricity. About 10% is used for internal needs of biogas utilization unit needs (Figure 3). Generated heat 205 142 GJ is mostly, about in 89.9%, used for increasing the biodrying process, and RDF drying in MPT plant, where heat exchangers are used, and for recirculated leachate heating. The reuse of heat causes the shortening of the RDF drying by the factor of 3, what decreases the electricity demand for blowers in relation to unit of mass of RDF. During 10 years, the MBT plant treats 1,300 Gg of MSW, and uses 26908 MWh. The energy demand factor is 20.7 kWh/Mg. The electricity production firm biogas generated in PAB from 200 000 Mg of waste is 48144 MWh. The electricity production factor is then 240.7 kWh/Mg.
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The obtained operational data, and biogas, and MBT plant performance forecasting indicate, that implementation of PAB, and its integration with MBT plant may cover all electricity, and heat demands of MBT plant, and gain additional financial benefits from electricity export to the grid. It causes, that integration of PAB with MBT plant, allows to achieve that overall system is energetically passive municipal solid waste treatment plant.
3. ENVIRONMENTAL BENEFITS FROM PAB INTEGRATION WITH MBT PLANT The presented PAB technology may be innovative in general due to “commercialisation of MSW undersize fraction”, and in detail due to: − Effective anaerobic bio-stabilization of the organic fraction of municipal waste. − Possibility to use a feedstock of mixed municipal waste with the guarantee of recovery of combustible fraction during post reaction material processing. − Possibility of application of the additional organic fraction introduced into the process from the outside in liquid form through the installation of leachate recirculation. − Possibility of use of any organic fraction for the production of energy. − Significant reduction in the amount of landfilled post-process waste. − Highly efficient use of the energy potential of the organic fraction contained in municipal waste (biogas production supported by recirculation of treated leachate, and its use as fuel in the production of electricity and heat in high efficiency cogeneration). − Maximum degree of usage of the organic fraction from municipal waste as simultaneous process with significant reduction in operating costs for the installation of the mechanical treatment of waste (production of RDF using combustible fraction from municipal waste) due to the production of electricity and heat in own power system located in waste treatment facility and its use for own needs (shredders drive, initial bio-stabilization of waste and drying alternative fuel using process heat). − Reusability of the same capacity of the bioreactor as a result of cyclical filling of waste disposal for the process and emptying after a certain time of cycle of the most efficient bioconversion of organic fraction in the form of biogas. − Developed technology of preparing and carrying out a cyclical dismantling of sectors of the bioreactor while maintaining the principles of safety and environmental protection and developed technological line for processing post reaction material with a maximum recovery of useful substances. − The following major positive and negative environmental aspects of PAB technology may be identified: Positive: − No emissions from process gases from bio-stabilization of waste into the atmosphere (Compared to MBT technology). − No emissions of methane into the atmosphere (compared to the technologies of waste disposal by landfilling). − Reduction of emissions as CO2 equivalent as a greenhouse gas: 1.438 tons per each ton of waste submitted to the bioreactor. − A significant reduction in weight of post-process waste to be landfilled (compared to MBT technology): − Reduction of carbon dioxide emissions into the atmosphere associated with combined production of electricity and heat from methane compared to separated by
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− −
conventional sources of energy produced from coal, Production of electricity: 0.240 MWhe tons per each ton of waste submitted to the bioreactor, Production of heat: 0.487 MWhh (1.753 GJ) per each ton of waste submitted to the bioreactor.
Negative: − Exhaust gas emissions to the atmosphere from the devices of power system using biogas as a fuel (cogeneration units, steam boiler, flare): o SO2 Sulphur dioxide 725 kg/year• of the bioreactor, o NOX nitrogen oxides 2.142 kg/ha of surface of the bioreactor, o CO Carbon monoxide 4.540 kg/year of surface of the bioreactor, o Dust PM2.5-PM10 432 kg/year•ha of surface of the bioreactor, − Engine oil consumption for the needs of cogeneration units - 1.800 l/year•ha of surface of the bioreactor. − Excessive leachates to be removed from the bioreactor system for the purpose of cleaning in classic wastewater treatment plant – 50 m3/year•ha of surface of the bioreactor. − Electricity consumption for own needs of the bioreactor system and the power system - 60.000 kWh/year•ha of surface of the bioreactor. − Water consumption for technological purposes of the bioreactor system installation -675 m3/year•ha of surface of the bioreactor. After the last third full cycle of the operation of the bioreactor there are variants of using the land in question: − the removal of the infrastructure of the bioreactor and the full restoration of the land in accordance with the requirements at that time (the expected direction of the restoration will depend on the development of neighbouring areas, e.g. concerning forests or recreational areas), − the transformation of the bioreactor territory (after obtaining relevant administrative decisions and after performing modernization) to a place where the process of waste disposal will be carried out using a futuristic technology (from the beginning of the bioreactor's operation to its end within the next 25 years) other than storage or anaerobic or oxygen stabilization or other currently used in accordance with applicable regulations for waste processing. In the case of total decommissioning, two drainage lines (PE), sealing foil (HDPE) are left to be developed. The materials dismantled in parts shall be subject to crushing and use as feedstock for RDF production line (PE material is a combustible fraction). Mineral material recovered from the bioreactor can be used for land reclamation.
4. CONCLUSIONS The PAB technology meets the requirements for companies operating in the field of waste management. The PAB technology minimizes the amount of post-processing waste destined for landfilling. The PAB technology minimizes operating costs of the plant for mechanical treatment of municipal waste in terms of consumption of electricity drawn from the grid, due to the production of energy of own sources (power system power supplied by biogas from the bioreactor).
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
The PAB technology increases the efficiency of the process of oxygen biostabilization of municipal waste prior to mechanical processing through the use of process heat generated in the power system for the process air heating. The PAB technology increases the efficiency of the process of mechanical treatment of waste by reducing the burden of waste shredders thanks to the drying the waste by process air heated by the process heat. The integration of PAB with MBT plant, allows to achieve that overall system is energetically passive municipal solid waste treatment plant. The PAB technology has not yet been classified in accordance with standards for waste treatment plants. It is similar to the already known power heaps, but has additional processes that have not been included in the legislation of EU countries. The bioreactor technology complies with the national legal requirements of the Building Law and regulations on environmental protection, which is confirmed by each time issued individual environmental decision.
REFERENCES Białowiec A. Pulka J. and Stegenta S. (2015a). The comparative modelling of mass flow in different options of MBT of MSW in Polish conditions. Proceedings of XVth International Waste Management and Landfill Symposium in Sardinia, 5 - 9 October, 2015. Białowiec A. Wiśniewski D. Pulka J. and Wiśniewski A. (2015b). The influence of hydraulic loading rate of Sequence-Anaerobic-Bioreactor on fermentation conditions and generation of biogas. Annual Set The Environment Protection 17(2), 12594-1273. Bolzonella D., Pavan P., Mace S. and Cecchi F. (2006). Dry Anaerobic Digestion of Differently Sorted Organic Municipal Solid Waste: Full-scale Experience. Water Sci. Technol., 53, 23-32. Environmental Protection Agency. European waste catalogue and hazardous waste list http://www.nwcpo.ie/forms/EWC_code_book.pdf EU (European Union), Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on Waste and Repealing Certain Directives, 2008. Ritzkowski M. Heerenklage J. and Stegmann R. (2006). An overview on techniques and regulations of mechanical-biological pre-treatment of municipal solid waste. Environmental Biotechnology, 2, 57-68. Soyez K. And Plickert S. (2003). Mechanical Biological Pretreatment (MBP) of Waste. Proceedings of IXth International Waste Management and Landfill Symposium in Sardinia, 6 10 October, 2003. Velis C.A. Longhurst P.J., Drew G.H., Smith R. and Pollard S.J.T. (2010). Production and Quality Assurance of Solid Recovered Fuels Using Mechanical-Biological Treatment (MBT) of Waste: A Comprehensive Assessment. Crit. Rev. Env. Sci. Tec., 40 (12), 979-1105.
