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The material flow in soy-sauce production process was analyzed for total mass, TOC, T-N, T-P and T-Cl. A main solid emission from the process was lees, a cake after filtration of fermented broth. The various reutilization method of the lees as a resource was studied and the dry distillation was investigated in detail. The conversion of lees by dry distillation increased with temperature rapidly at low temperature, but moderately at high temperature region. The production of inflammable gases was prominent at high temperature. The liquid products obtained during the condensation of exit gas were composed of aqueous and organic solutions. The solid residue was a char like a fiber containing inorganic phosphorus compounds which was not removed by washing. The reusing method of these products was discussed.
Journal of Water and Environment Technology, Vol.2, No.1, 2004 - 1 - Approach to Zero Emission Processes in Food Industry - Case Study for Soy-Sauce Production Process - Tadashi Hano* , Makoto Hirata* and Hirokazu Takanashi** * Department of Applied Chemistry, Oita University Oita 870-1192, Japan ** Department of Bioengineering, Kagoshima University, Kagoshima 890-0065, Japan * E-mail: thano@cc.oita-u.ac.jp ABSTRACT The material flow in soy-sauce production process was analyzed for total mass, TOC, T-N, T-P and T-Cl. A main solid emission from the process was lees, a cake after filtration of fermented broth. The various reutilization method of the lees as a resource was studied and the dry distillation was investigated in detail. The conversion of lees by dry distillation increased with temperature rapidly at low temperature, but moderately at high temperature region. The production of inflammable gases was prominent at high temperature. The liquid products obtained during the condensation of exit gas were composed of aqueous and organic solutions. The solid residue was a char like a fiber containing inorganic phosphorus compounds which was not removed by washing. The reusing method of these products was discussed. INTRODUCTION The ultimate and ideal solution of the global environmental problems is the establishment of the social system that does not discharge any emissions. This is of course impossible under the present technology level and the most essential way to approach is the reduction of various emissions from all human activities as low as possible not only in the commercial production system but also in our daily life and transportation system. These efforts are surely the first step in the reduction of emissions. However there will be a limit only with such efforts. It is essential how to frame a network system between emission-discharger and emission-user. In this regard, the approach to the zero-emission system is quite different from the development of waste treatment technology, which is frequently called as the end-of-pipe technology. The establishment of zero-emission oriented processes is performed through three stages as follows. The first stage approach is to design the process that does not discharge any emissions by introducing the closed system. If such an approach is difficult, then it is tried to combine an emission-discharging process with another process that can utilize the emission as raw materials. This is the second stage approach. The final stage approach is to establish a network between various processes and industries that can utilize the emissions of other processes as raw materials of their own processes. By establishing such a network, the total emission may be minimized. The improvement of the conventional processes, the change of the fundamental concept in production methods, the development of the key technologies for zero-emission, and the establishment of the methodology for the optimum network formation are required in the approaches to the zero-emission system. The conventional processes have been assembled by considering only the cost of main flow toward the desired final products. The emissions from each unit process were mixed all together and treated simultaneously regardless of their quality differences. The process engineers tried to develop more economical methods of wastes treatment, but the emissions never decreased with such an approach. In the zero-emission production system, on the contrary, the emissions are converted to raw materials for recycle within own process or between other processes through innovative converters. The material flow analysis that clarifies the input and output of materials is the basis in developing such a link or Journal of Water and Environment Technology, Vol.2, No.1, 2004 - 2 - network between processes or industries aiming at the establishment of the zero-emission system. Then, the development of key technologies that convert the emissions to raw materials for other processes is essential. The present study discussed at first how the material flow analyses contribute the approach to the zero-emission systems in food industries. The soy-sauce production process was studied as an example of food industry. CHARACTERISTICS OF FOOD INDUSTRY The food industry is suitable in demonstrating the concept of the zero-emission system since the ratio of emissions versus raw materials is fairly high compared to other industries. The average amount of emissions from one plant of food industry in Japan is about 10.7kt/y, most of which is sludge and vegetable residues [Food Industry Center, 1992]. It is also the characteristics of food industry that there are only a few common unit operations between each process and therefore the approach to the zero-emission process must be developed specifically for each case. Most of the emissions from food industries are liquid or solid, non-toxic, perishable and not preservable for a long time. At present, they are reused mostly as feeds for livestock, fertilizer after composting, and the source of heat by burning. These reuse ways are, however, now facing to difficult problems and further increase of accepting amount is hard to expect. Consequently, it is urgent to change the conventional treatment processes to new innovative zero-emission system by developing a key technology that converts the emissions to a resource. In this study, the soy-sauce production process was studied as an example of food industry. The dry distillation was investigated as one of key technologies to convert the emission from food industries to raw materials in other industries. MATERIAL FLOW ANALYSIS Object of Analysis and Selection of Components for Analysis The material flow analysis aims to clarify the quantity and quality of input and output in each process. The output from one process is the input to other processes. Therefore it is necessary to know the flow of all materials between various processes and industries, whilst past analyses have been performed concerning only the desired products. In every process, negative emissions such as wastewater and wasted solids are discharged more or less inevitably since the complete conversion to desired products is impossible at present technology level. The recovery of such negative emissions and their re-use as raw materials in other processes are essential in establishing the zero-emission system. Therefore, the detailed material flow of negative emissions should be grasped. The selection of targeting materials for flow analysis is important. It is desirable to analyze the material flow of all components involved in the production lines. At least, the specific materials that are essential in establishing the zero-emission system must be considered. In food industry, we selected organic carbon, nitrogen and phosphorus as the components of material flow analysis because these elements are main components of wastewater causing eutrophication of rivers and lakes. Chlorine was also analyzed due to its large impact in recycle and reuse of wasted materials. Toxic heavy metals or organic compounds were not considered because they are not involved in foods. Material Flow Analysis in Soy-Sauce Production Process Soy-sauce, the most famous liquid seasoning in Japan pronounced as Shoyu, is produced by fermentation of soybean, wheat and salt according to traditionally established process and its annual production is about 1.22 million ton. Many companies are producing soy-sauce in Japan, but about 70 companies, only 3% of all companies, produce about 77% of total production amount. In these big companies, the treatment of emissions from their plants is a knotty problem to be resolved urgently. Figure 1 shows the typical schematic of soy-sauce production processes. 1. Bulk materials flow This is the macroscopic analysis of materials flow for a plant under consideration. The input and output of the plant are analyzed and the results are shown for specific materials or elements. Figure 2 presents the input and output of soy-sauce producing plant based on 1 t production of soy-sauce. Main emission from the plant is Journal of Water and Environment Technology, Vol.2, No.1, 2004 - 3 - solid lees, the cake after filtration of fermented broth. The quantity of wastewater from the production lines is limited since the final valuable product is liquid itself. However, the quantity of wastewater discharged from washing procedures of tanks and lines after operation is as high as 4.9 t per 1 t of soy-sauce produced, as shown in Fig.2. The BOD and other pollutants load of these wastewaters are not high owing to very low concentrations of pollutants, but the saving of washing water should be considered, for example, by cascade utilization. Fig.1 Flow sheet of soy-sauce production plants Fig.2 Bulk materials flow analysis Fig.3 Detailed material flow of total mass Ori ,33 Soy-Sauce,1t Ori ,78 Ori ,111 Conditioning,403 Kiage ,708 Fermentation,786 Cake,78 Koji Membrane filtration Celite filtration Heating Mixing,795 Filtration Cooling Roasting Rinsing Soybean ， 91 Wheat,91 Water,127 Salt water,349 Total Mass [kg] Fig.4 Detailed material flow of total organic carbon Ori ,2 Soy-Sauce,63(in 1t) Ori ,5 Ori ,7 Conditioning,5 Kiage ,58 Fermentation,87 Cake,24 Koji ,73 Membrane filtration Celite filtration Heating Mixing,81 Filtration Cooling Roasting Rinsing Soybean,34 Wheat,35 Water,0 Salt water,0 58 63 17 46 TOC [kg] Journal of Water and Environment Technology, Vol.2, No.1, 2004 - 4 - Fig.5 Detailed material flow of total chlorine Fig.6 Effect of temperature on final conversion of cake 2. Detailed materials flow The microscopic analysis inside each unit process is necessary in establishing the zero-emission system. The detailed data of input and output in each unit process may clarify which technologies and operations should be improved and developed to find an appropriate receiver of their emissions. It also contributes to find out the origin of emissions. In this study, the samples for analysis were taken at all production lines in actual soy-sauce producing plant to measure total mass, total organic carbon (TOC), total nitrogen (T-N), total phosphorus (T-P) and total chlorine (T-Cl). The values shown in the following figures are mass in kg based on 1 t of soy-sauce produced Total material flow analysis: Figure 3 shows the result of total material flow analysis. As clearly shown, most of the solid emission from the process is the cake called Shoyu kasu (soy-sauce lees) remaining after the filtration of the fermented broth (Moromi mash). The inputs through salt water and conditioning occuies a large fraction of soy-sauce mass. The thickness of each line in Figs. 3 to 5 is drawn in proportion to its relative flow rate against the mass of final product, that is, soy-sauce. Elemental flow analysis : The elemental flow between unit process was analyzed for TOC, T-N, T-P and T-Cl. The basic behavior of mass flow for these four elements was similar. Figure 4 shows the results of TOC flow analysis, demonstrating that the conditioning added to control the taste after fermentation contains organic compounds having nitrogen in its structure. A similar trend of elemental flow was observed for T-N and T-P. Figure 5 shows the material flow of T-Cl. Most of the salt content in soy-sauce comes from salt water and the conditioning. The exact composition of the conditioning is not clear at present. It contains fair amount of salt. Consequently in the approach to the zero-emission process of soy-sauce production, it is essential to consider how to decrease the production of cake or how to convert it to other forms so as to be accepted as an input of other processes or industries. Ori ,3 Soy-Sauce,79(in 1t) Ori ,6 Ori ,8 Conditioning,31 Kiage ,56 Fermentation,57 Cake,2 Koji ,0.04 Membrane filtraion Celite filtration Heating Mixing,60 Filtration Cooling RoastingRinsing Soybean,0 Wheat,0.04 Water,0 Salt water,51 77 87 T-Cl [kg] Journal of Water and Environment Technology, Vol.2, No.1, 2004 - 5 - DRY DISTILLATION OF RESIDUAL CAKE Present Reuse Methods of Cake As stated above, solid lees, which is a residual cake remaining after filtering the fermented broth to yield soy-sauce and is called as Shoyu Kasu in Japanese, is the main solid waste from the process. A cake is discharged about 8% in weight of the soy-sauce produced. It involves about 25% of water, which is very low compared with the most of the sludge discharged from food industry. This is desirable in handling the wastes because storing in a plant yard is possible for a while due to slow biological decomposition. The content of chlorine in a cake is as high as 5 to 7%, which is the most troublesome factor in developing the way of reuse. At present, a cake is reused mainly by three ways. The most popular way of reuse is to give livestock as a feed. However, high content of salt is an obstacle to increase further the reuse as a feed. In addition, it is now popular for a farmer to give a prearranged feed prepared from various grains most of which are imported from other countries. The second way of reuse is a fertilizer. A cake involves nitrogen and phosphorus in a fair amount and is a good fertilizer for fruit trees. However also in this case, high content of salt restrains the amount to be used as a fertilizer [Kondo et al., 1996]. The third way is to burn in a fireplace and use as a heat source for a factory. The characteristics of low water content is now promoting the burning as a final treatment way of burdensome solid wastes, but salt in a cake damages gradually the firebrick in a fireplace. Therefore, new re-using method of lees is asked urgently. Dry Distillation of Cake The best alternative way from the viewpoint of the zero-emission concept is to change the conventional process to decrease the amount of a cake as low as possible, but the present process has been established during long years and the drastic change is difficult because of taste and flavor change. For example, the fermentation under low concentration of salt is proposed to decrease the chlorine content in a cake, but it may not be acceptable because of probable change of traditional taste. In this study, we considered to change a cake to an improved fertilizer of low salt content through dry distillation. This method is also desirable in that the original mass of a cake is reduced fairly and the gas and liquid produced by decomposition are valuable [Brossad Perez and Cortez, 1997, Inoue et al., 1997]. Here, basic behavior during the dry distillation was investigated. Fig.7 Combustion heat of gas evolved in dry distillation Fig.8 Effect of temperature on yield distribution Journal of Water and Environment Technology, Vol.2, No.1, 2004 - 6 - Fig.9 Effect of temperature on TOC distribution The dry distillation proceeds quickly just after putting a cake in a heated electric furnace. Figure 6 shows the dependence of cake conversion on the temperature of dry distillation. The reaction occurred even at as low as 500K and the final conversion gradually increased with temperature. The volume of gas evolved per weight decrease of cake also increased with temperatures. Main products at low temperature were carbon monoxide and dioxide, and the heat of combustion was very low. High temperature was required to recover the flammable gas as much as possible. It was also probable that the secondary decomposition of high molecular weight gas components proceeded during dry distillation. Figure 7 shows the heat of combustion calculated for the composition of gas produced at various temperature. The increase of methane and propylene contents contributed to increase the heat of combustion at high temperature. Hydrogen was produced above 773K. From these findings, the reuse of decomposed gases as a source of heat for dry distillation is considered to be possible at high temperature. The formation of condensed liquid also increased with temperature. The liquid phase divided into aqueous and oil phases with almost equal volume. An aqueous phase hardly contained any organic components, whereas many organic compounds were detected in an oil phase. Figure 8 shows the effects of temperature on the yields of gas, liquid and solid (char) fractions. It was found that the main product of dry distillation was liquid at high temperature. The fraction of decomposed gas was not high compared with the results reported for dry distillation of woods [Sadakata et al, 1987]. Figure 9 shows the effect of temperature on the distribution of organic carbon through dry distillation. A similar trend was observed for total mass and organic carbon. The nitrogen compounds in a cake, probably in the form of protein or amino acids, was found to transfer to liquid and solid phases. The form of nitrogen compounds produced at high temperature is under investigation. The oil phase of liquid products can be used as a fuel and aqueous phase as a fertilizer like the liquid produced from the dry distillation of woods. The fraction of residual char decreased with temperature, which demonstrated the merit of dry distillation in reducing the volume. The char after dry distillation was fibrous and its salt was removed easily by rinsing with water. The salt content after washing was fairly low enough to be used as a fertilizer, while phosphorus content was high. This char is now being tested concerning its ability as a fertilizer at the institute of agriculture and satisfactory results will be expected compared with the conventional artificial fertilizer [Endo et al., 1994]. Journal of Water and Environment Technology, Vol.2, No.1, 2004 - 7 - CONCLUSION An approach to zero emission processes in food industry was investigated for soy-sauce production process as a model. The detailed material flow charts in soy-sauce production process were established for TOC, T-N, T-P and T-Cl together with total mass. Lees, a cake from filtration of fermented broth, was the main solid emissions. The effective reuse of a cake was investigated by treating it with dry distillation and the basic behavior was analyzed. The decomposed gas produced at high temperature contained fair amount of inflammable hydrocarbons and its heat of combustion could be used for distillation. The liquid phase was the main product of distillation and its fraction increased with temperature. The fraction of solid residue (char) decreased with temperature. Char could be used as a good fertilizer with low content of salt. REFERENCE Brossad Perez, L.E. and Cortez, L.A.B. (1997) Potential for the use of pyrolytic tar from bagasse in industry. Biomass and Bioenergy, 12(5). 363-366 Endo, M., Kagaku, I., Kondo, T. and Satake, H. (1994) Studies on utilization of carbonized soy-sauce mash. Report of the Institute of Soy-Sauce, 20, 301-304 Inoue, S., Sawayama, S., Dote, Y. and Ogi, T. (1997) Behavior of nitrogen during liquefaction of dewatered sewage sludge. Biomass and Bioenergy, 12(6), 473-475 Kondo, T., Nakata, M., Kagaku, I., Satake, H. and Okada, M. Composting of soy-sauce cake and utilization. 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