Environ Sci Pollut Res DOI 10.1007/s11356-014-2688-z
RESEARCH ARTICLE
Economically oriented process optimization in waste management Josef Maroušek
Received: 28 January 2014 / Accepted: 19 February 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract A brief report on the development of novel apparatus is presented. It was verified in a commercial scale that a new concept of anaerobic fermentation followed by continuous pyrolysis is technically and economically feasible to manage previously enzymatically hydrolyzed waste haylage in huge volumes. The design of the concept is thoroughly described, documented in figures, and biochemically analyzed in detail. Assessment of the concept shows that subsequent pyrolysis of the anaerobically fermented residue allows among biogas to produce also high-quality biochar. This significantly improves the overall economy. In addition, it may be assumed that this applied research is consistent with previous theoretical assumptions stating that any kind of aerobic or anaerobic fermentation increases the microporosity of the biochar obtained. Keywords Process optimization . Renewable energy . Financial analysis . Process management
Introduction Maintenance of city green areas produces huge amounts of various grass cuttings. The presence of street trash does not allow its utilization as a feed for ruminants. According to Smyth et al. (2009), the gross energy from the grass biogas systems in Europe and northern America compares favorably with the tropical systems. There were many proposals found on the utilization of grass waste in reviewed literature. Many of them like burning, production of ethanol, or composting, Responsible editor: Philippe Garrigues J. Maroušek (*) The Institute of Technology and Businesses in České Budějovice, Okružní 517/10, 370 01 České Budějovice, Czech Republic e-mail: [email protected]
are actually not economically feasible or raises disputes over its environmental context (Paulrud and Nilsson 2001; Hašková and Kolář 2011). On the other hand, regarding the grass waste, there was improvement in the economics of biogas production (Murphy and Power 2009). Koch et al. (2010) performed the anaerobic fermentation without the addition of manure, but the process took a long 365 days. Wachendorf et al. (2009) proposed to accelerate the process by separating the easily fermentable components by hydrothermal conditioning and mechanical dehydration. This method was subsequently improved, with different variants of hot maceration and steam explosion (Maroušek 2013a). Admittedly, these technologies require a high-acquisition cost which currently hampers its spread into commercial scale (Hašková and Kolář 2010). Efforts were made to improve the overall economics of the technology by profitable utilization of the fermentation residue. Seppala et al. (2009) proposed to continue in the practice of using the fermented grass residue as a fertilizer. However, Kolář et al. (2008) proves that the residue after anaerobic fermentation has very weak agrochemical value. The initial hypothesis proposed by Wachendorf et al. (2009) continued that the fermentation residue should be burned. Maroušek (2013a) proposed that it would be more profitable if the fermentation residue was charcoaled, providing cleaner combustion gases and higher energy density. However, it turned out that the original alternative of batch pyrolysis had insufficient capacity to process the large amounts of haylage fermentation residue. New hypotheses had to be raised quickly. Generally speaking, the entire concept had to be changed (Hašková and Kolář 2013). The batch pyrolysis had to be redesigned into continuous technology. This may allow producing more profitable biochar instead of charcoal. Initial material and energy calculations showed that the continuous system (waste energy form the biogas cogeneration unit and the waste heat from the pyrolysis) may provide enough waste heat for (1) deepening
Environ Sci Pollut Res
the haylage pretreatment by tempering the enzymatic hydrolysis, (2) accelerating the anaerobic fermentation by warming up the reactor, (3) drying the mechanically dewatered fermentation residue, and (4) initiating the pyrolysis unit.
Materials and methods The waste haylage from public green was provided by the local administration (Správa města Soběslavi s.r.o., Czech Republic). It was analyzed for standard biotechnological properties (571 kg m−3; 24.5 % volatile solid (VS); acidicdetergent fiber 48 % VS, acidic-detergent lignin 3 % VS, labile pool 1 of carbon 12 % VS; and labile pool 2 of carbon 75 % VS). The technology started with hot maceration as described in Maroušek (2013b). Subsequently, the macerated haylage was pumped into slowly stirred hydrolysis reactor and subjected to pretreatment by Accellerase enzymatic mixture (DuPont-Genencor, Finland). The dosage was 200 acid birchwood xylanase units and 150 para-nitrophenyl-β-Dglucopyranoside units gram VS per kilogram. After that, the partially hydrolysed phytomass was mixed with old and fresh manure (17 % VS, 1,070 kg m−3, pH=6.9, biological oxygen demand=6,401 mg L−1, chemical oxygen demand by potassium dichromate=5,949 mg L−1) into 10 % VS and released into slowly stirred anaerobic fermentor (Fig. 1) operating at 50 °C with an average retention time of 20 days. The biogas performance was qualitatively and quantitatively analyzed by AIR-LF biogas analyzer (Aseko, Ltd., Czech Republic) and the methane produced was converted to 0 °C at 101,325 Pa. The fermentation residue was decanted and the staid solid was mechanically dewatered using adopted double screw dewatering press (PHARMIX, s.r.o, Czech Republic), which was tailored to achieve continuous backpressure tension of 200 N. This continuous pressure dewatered the fermentation
Fig. 1 The figure shows the slowly stirred anaerobic fermentor operating at 50 °C with an average retention time of 20 days
Fig. 2 a The pyrolysis camber consisted of the refractory horizontal cylinder with an internal helix. b The belt conveyor brings out the anaerobically fermented material which has been subjected to pyrolysis
residue to approximately 65 % VS. Then, the waste energy from the pyrolysis unit allowed to dry the dewatered fermentation residue up to roughly 80 % VS. Thereafter, the residue obtained was injected to the continuous pyrolysis unit (Fig. 2) that was run by the waste energy from the biogas cogeneration unit (overall energy balance presented in Maroušek 2013b). The NOVA 4200e surface analyzer (Quantachrome Instruments, Florida, USA) was used for microporosity analysis (total pore volume).
Results and discussion There are known many ways of phytomass disintegration (Himmel et al. 2007). But because there is always a small amount of trash (mostly plastic) which may break or clog
Fig. 3 The microporosity of the biochar obtained in relation to the retention time shows that the quality of the pyrolysis may be tailored according to the amount of available heat
Environ Sci Pollut Res
many of these sophisticated apparatus it was proposed that the enzymatic pretreatment is adequate. It is clear that the total hydrolysis takes a long time; it is unnecessary from the biochemical point of view and is obviously not economically feasible (Hašková and Kolář 2012). It was necessary to determine the economically optimal level of hydrolysis. Laboratory tests showed that acid birchwood xylanase units and para-nitrophenyl-β-D-glucopyranoside units plays the key role in the process. Optimization software showed that to achieve the standard of 150 m3 CH4 t−1 VS it is desirable to hydrolyze at least 20 % of the labile pool 2 of carbon. The analysis on its minimal costs showed the optimal composition of the cellulases. Admittedly, it would be chemically beneficial to change the pH in the hydrolysis reactor; however, cost of strong mineral acids would unreasonably burden the overall economy (additional cost on safety, neutralization, highquality material etc.). Given that the waste heat was sufficient the process temperature was set to 50 °C, which is in good agreement with Garba (1996) and Chea et al. (2008). The overall technology of mixing and pumping took approximately 7 % of electricity produced which approximately 1 % more than known standards (Weiland 2010). This can be justified by additional demands on the hydrolysis pretreatment and dewatering. The subsequent pyrolysis took place in 380 °C. Once the process is naturally exothermic, it was possible to utilize the waste heat the way that the retention time was prolonged to increase the quality of the biochar produced. The pH and cation exchange capacity remain independent of the retention time in the average of pH=8.3, cation exchange capacity = millimole chemical equivalent per 1,000 g. In contrast, the microporosity (total pore volume) changes in relation to the retention time (Fig. 3). These data are in accordance with conclusions of Özçimen and Meriçboyu (2010) and they can be combined to create a presumption that the biochar obtained will have a good use in agriculture. Once the biochar is produced from waste material and waste heat, the running costs are negligible. This allows pronouncing an assumption that the payback time will be very short.
Conclusion A brief report on the development of new concept of anaerobic fermentation followed by continuous pyrolysis was presented. The development is not completed, but it managed to prove that the concept is possible and it is likely to be very economically successful. Acknowledgments This work was supported by a grant from the Japan Society for the Promotion of Science.
References Chea KJ, Jaga A, Limb SK, Kim IS (2008) The effects of digestion temperature and temperature shock on the biogas yields from the mesophilic anaerobic digestion of swine manure. Bioresour Technol 99:1–6 Garba B (1996) Effect of temperature and retention period on biogas production from lignocellulosic material. Renew Energy 9: 938–941 Hašková S, Kolář P, (2010) A contribution to a mathematic modeling of the behavior of private and institutionalized investors as observed in practice. 28th International Conference on Mathematical Methods in Economics: 214–219 Hašková S, Kolář P, (2011) The mathematic modeling of process economization of natural resources. 29th International Conference on Mathematical Methods in Economics: 224–229 Hašková S, Kolář P, (2012) Determination of mutually acceptable price of used manufacturing equipment. 30th International Conference on Mathematical Methods in Economics: 266–271 Hašková S, Kolář P, (2013) The limits of relativism in managerial thinking. 31th International Conference on Mathematical Methods in Economics: 153–161 Himmel ME, Ding SY, Johnson DK, Adney WS, Nimlos MR et al (2007) Biomass recalcitrance: engineering plant and enzymes for biofuels production. Science 315:804–807 Koch K, Lübken M, Gehring T, Wichern M, Horn H (2010) Biogas from grass silage—measurements and modeling with ADM1. Bioresour Technol 101:8158–8165 Kolář L, Kužel S, Peterka J, Štindl P, Plát V (2008) Agrochemical value of organic matter of fermenter wastes in biogas production. Plant Soil Environ 54:321–328 Maroušek J (2013a) Removal of hardly fermentable ballast from the maize silage to accelerate biogas production. Ind Crop Prod 44: 253–257 Maroušek J (2013b) Two‐fraction anaerobic fermentation of grass waste. J Sci Food Agric 93:2410–2414 Murphy JD, Power NM (2009) An argument for using biomethane generated from grass as a biofuel in Ireland. Biomass Bioenergy 33:504–512 Paulrud S, Nilsson C (2001) Briquetting and combustion of springharvest reed canary-grass: effect of fuel composition. Biomass Bioenergy 20:25–35 Özçimen D, Meriçboyu AE (2010) Characterization of biochar and biooil samples obtained from carbonization of various biomass materials. Renew Energy 35:1319–1324 Seppala M, Paavola T, Lehtomaki A, Rintala J (2009) Biogas production from boreal herbaceous grasses-specific methane yield and methane yield per hectare. Bioresour Technol 100: 2952–2958 Smyth BM, Murphy JD, O’Brien CM (2009) What is the energy balance of grass biomethane in Ireland and other temperate northern European climates? Renew Sust Energ Rev 13:2349– 2360 Wachendorf M, Richter F, Fricke T, Graß R, Neff R (2009) Utilization of seminatural grassland through integrated generation of solid fuel and biogas from biomass. I. Effects of hydrothermal conditioning and mechanical dehydration on mass flows of organic and mineral plant compounds, and nutrient balances. Grass Forage Sci 64:132–143 Weiland P (2010) Biogas production: current state and perspectives. Appl Microbiol Biotechnol 85:849–860
RESEARCH ARTICLE
Economically oriented process optimization in waste management Josef Maroušek
Received: 28 January 2014 / Accepted: 19 February 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract A brief report on the development of novel apparatus is presented. It was verified in a commercial scale that a new concept of anaerobic fermentation followed by continuous pyrolysis is technically and economically feasible to manage previously enzymatically hydrolyzed waste haylage in huge volumes. The design of the concept is thoroughly described, documented in figures, and biochemically analyzed in detail. Assessment of the concept shows that subsequent pyrolysis of the anaerobically fermented residue allows among biogas to produce also high-quality biochar. This significantly improves the overall economy. In addition, it may be assumed that this applied research is consistent with previous theoretical assumptions stating that any kind of aerobic or anaerobic fermentation increases the microporosity of the biochar obtained. Keywords Process optimization . Renewable energy . Financial analysis . Process management
Introduction Maintenance of city green areas produces huge amounts of various grass cuttings. The presence of street trash does not allow its utilization as a feed for ruminants. According to Smyth et al. (2009), the gross energy from the grass biogas systems in Europe and northern America compares favorably with the tropical systems. There were many proposals found on the utilization of grass waste in reviewed literature. Many of them like burning, production of ethanol, or composting, Responsible editor: Philippe Garrigues J. Maroušek (*) The Institute of Technology and Businesses in České Budějovice, Okružní 517/10, 370 01 České Budějovice, Czech Republic e-mail: [email protected]
are actually not economically feasible or raises disputes over its environmental context (Paulrud and Nilsson 2001; Hašková and Kolář 2011). On the other hand, regarding the grass waste, there was improvement in the economics of biogas production (Murphy and Power 2009). Koch et al. (2010) performed the anaerobic fermentation without the addition of manure, but the process took a long 365 days. Wachendorf et al. (2009) proposed to accelerate the process by separating the easily fermentable components by hydrothermal conditioning and mechanical dehydration. This method was subsequently improved, with different variants of hot maceration and steam explosion (Maroušek 2013a). Admittedly, these technologies require a high-acquisition cost which currently hampers its spread into commercial scale (Hašková and Kolář 2010). Efforts were made to improve the overall economics of the technology by profitable utilization of the fermentation residue. Seppala et al. (2009) proposed to continue in the practice of using the fermented grass residue as a fertilizer. However, Kolář et al. (2008) proves that the residue after anaerobic fermentation has very weak agrochemical value. The initial hypothesis proposed by Wachendorf et al. (2009) continued that the fermentation residue should be burned. Maroušek (2013a) proposed that it would be more profitable if the fermentation residue was charcoaled, providing cleaner combustion gases and higher energy density. However, it turned out that the original alternative of batch pyrolysis had insufficient capacity to process the large amounts of haylage fermentation residue. New hypotheses had to be raised quickly. Generally speaking, the entire concept had to be changed (Hašková and Kolář 2013). The batch pyrolysis had to be redesigned into continuous technology. This may allow producing more profitable biochar instead of charcoal. Initial material and energy calculations showed that the continuous system (waste energy form the biogas cogeneration unit and the waste heat from the pyrolysis) may provide enough waste heat for (1) deepening
Environ Sci Pollut Res
the haylage pretreatment by tempering the enzymatic hydrolysis, (2) accelerating the anaerobic fermentation by warming up the reactor, (3) drying the mechanically dewatered fermentation residue, and (4) initiating the pyrolysis unit.
Materials and methods The waste haylage from public green was provided by the local administration (Správa města Soběslavi s.r.o., Czech Republic). It was analyzed for standard biotechnological properties (571 kg m−3; 24.5 % volatile solid (VS); acidicdetergent fiber 48 % VS, acidic-detergent lignin 3 % VS, labile pool 1 of carbon 12 % VS; and labile pool 2 of carbon 75 % VS). The technology started with hot maceration as described in Maroušek (2013b). Subsequently, the macerated haylage was pumped into slowly stirred hydrolysis reactor and subjected to pretreatment by Accellerase enzymatic mixture (DuPont-Genencor, Finland). The dosage was 200 acid birchwood xylanase units and 150 para-nitrophenyl-β-Dglucopyranoside units gram VS per kilogram. After that, the partially hydrolysed phytomass was mixed with old and fresh manure (17 % VS, 1,070 kg m−3, pH=6.9, biological oxygen demand=6,401 mg L−1, chemical oxygen demand by potassium dichromate=5,949 mg L−1) into 10 % VS and released into slowly stirred anaerobic fermentor (Fig. 1) operating at 50 °C with an average retention time of 20 days. The biogas performance was qualitatively and quantitatively analyzed by AIR-LF biogas analyzer (Aseko, Ltd., Czech Republic) and the methane produced was converted to 0 °C at 101,325 Pa. The fermentation residue was decanted and the staid solid was mechanically dewatered using adopted double screw dewatering press (PHARMIX, s.r.o, Czech Republic), which was tailored to achieve continuous backpressure tension of 200 N. This continuous pressure dewatered the fermentation
Fig. 1 The figure shows the slowly stirred anaerobic fermentor operating at 50 °C with an average retention time of 20 days
Fig. 2 a The pyrolysis camber consisted of the refractory horizontal cylinder with an internal helix. b The belt conveyor brings out the anaerobically fermented material which has been subjected to pyrolysis
residue to approximately 65 % VS. Then, the waste energy from the pyrolysis unit allowed to dry the dewatered fermentation residue up to roughly 80 % VS. Thereafter, the residue obtained was injected to the continuous pyrolysis unit (Fig. 2) that was run by the waste energy from the biogas cogeneration unit (overall energy balance presented in Maroušek 2013b). The NOVA 4200e surface analyzer (Quantachrome Instruments, Florida, USA) was used for microporosity analysis (total pore volume).
Results and discussion There are known many ways of phytomass disintegration (Himmel et al. 2007). But because there is always a small amount of trash (mostly plastic) which may break or clog
Fig. 3 The microporosity of the biochar obtained in relation to the retention time shows that the quality of the pyrolysis may be tailored according to the amount of available heat
Environ Sci Pollut Res
many of these sophisticated apparatus it was proposed that the enzymatic pretreatment is adequate. It is clear that the total hydrolysis takes a long time; it is unnecessary from the biochemical point of view and is obviously not economically feasible (Hašková and Kolář 2012). It was necessary to determine the economically optimal level of hydrolysis. Laboratory tests showed that acid birchwood xylanase units and para-nitrophenyl-β-D-glucopyranoside units plays the key role in the process. Optimization software showed that to achieve the standard of 150 m3 CH4 t−1 VS it is desirable to hydrolyze at least 20 % of the labile pool 2 of carbon. The analysis on its minimal costs showed the optimal composition of the cellulases. Admittedly, it would be chemically beneficial to change the pH in the hydrolysis reactor; however, cost of strong mineral acids would unreasonably burden the overall economy (additional cost on safety, neutralization, highquality material etc.). Given that the waste heat was sufficient the process temperature was set to 50 °C, which is in good agreement with Garba (1996) and Chea et al. (2008). The overall technology of mixing and pumping took approximately 7 % of electricity produced which approximately 1 % more than known standards (Weiland 2010). This can be justified by additional demands on the hydrolysis pretreatment and dewatering. The subsequent pyrolysis took place in 380 °C. Once the process is naturally exothermic, it was possible to utilize the waste heat the way that the retention time was prolonged to increase the quality of the biochar produced. The pH and cation exchange capacity remain independent of the retention time in the average of pH=8.3, cation exchange capacity = millimole chemical equivalent per 1,000 g. In contrast, the microporosity (total pore volume) changes in relation to the retention time (Fig. 3). These data are in accordance with conclusions of Özçimen and Meriçboyu (2010) and they can be combined to create a presumption that the biochar obtained will have a good use in agriculture. Once the biochar is produced from waste material and waste heat, the running costs are negligible. This allows pronouncing an assumption that the payback time will be very short.
Conclusion A brief report on the development of new concept of anaerobic fermentation followed by continuous pyrolysis was presented. The development is not completed, but it managed to prove that the concept is possible and it is likely to be very economically successful. Acknowledgments This work was supported by a grant from the Japan Society for the Promotion of Science.
References Chea KJ, Jaga A, Limb SK, Kim IS (2008) The effects of digestion temperature and temperature shock on the biogas yields from the mesophilic anaerobic digestion of swine manure. Bioresour Technol 99:1–6 Garba B (1996) Effect of temperature and retention period on biogas production from lignocellulosic material. Renew Energy 9: 938–941 Hašková S, Kolář P, (2010) A contribution to a mathematic modeling of the behavior of private and institutionalized investors as observed in practice. 28th International Conference on Mathematical Methods in Economics: 214–219 Hašková S, Kolář P, (2011) The mathematic modeling of process economization of natural resources. 29th International Conference on Mathematical Methods in Economics: 224–229 Hašková S, Kolář P, (2012) Determination of mutually acceptable price of used manufacturing equipment. 30th International Conference on Mathematical Methods in Economics: 266–271 Hašková S, Kolář P, (2013) The limits of relativism in managerial thinking. 31th International Conference on Mathematical Methods in Economics: 153–161 Himmel ME, Ding SY, Johnson DK, Adney WS, Nimlos MR et al (2007) Biomass recalcitrance: engineering plant and enzymes for biofuels production. Science 315:804–807 Koch K, Lübken M, Gehring T, Wichern M, Horn H (2010) Biogas from grass silage—measurements and modeling with ADM1. Bioresour Technol 101:8158–8165 Kolář L, Kužel S, Peterka J, Štindl P, Plát V (2008) Agrochemical value of organic matter of fermenter wastes in biogas production. Plant Soil Environ 54:321–328 Maroušek J (2013a) Removal of hardly fermentable ballast from the maize silage to accelerate biogas production. Ind Crop Prod 44: 253–257 Maroušek J (2013b) Two‐fraction anaerobic fermentation of grass waste. J Sci Food Agric 93:2410–2414 Murphy JD, Power NM (2009) An argument for using biomethane generated from grass as a biofuel in Ireland. Biomass Bioenergy 33:504–512 Paulrud S, Nilsson C (2001) Briquetting and combustion of springharvest reed canary-grass: effect of fuel composition. Biomass Bioenergy 20:25–35 Özçimen D, Meriçboyu AE (2010) Characterization of biochar and biooil samples obtained from carbonization of various biomass materials. Renew Energy 35:1319–1324 Seppala M, Paavola T, Lehtomaki A, Rintala J (2009) Biogas production from boreal herbaceous grasses-specific methane yield and methane yield per hectare. Bioresour Technol 100: 2952–2958 Smyth BM, Murphy JD, O’Brien CM (2009) What is the energy balance of grass biomethane in Ireland and other temperate northern European climates? Renew Sust Energ Rev 13:2349– 2360 Wachendorf M, Richter F, Fricke T, Graß R, Neff R (2009) Utilization of seminatural grassland through integrated generation of solid fuel and biogas from biomass. I. Effects of hydrothermal conditioning and mechanical dehydration on mass flows of organic and mineral plant compounds, and nutrient balances. Grass Forage Sci 64:132–143 Weiland P (2010) Biogas production: current state and perspectives. Appl Microbiol Biotechnol 85:849–860
