Equipment for different scales of composting

5 Equipment Equipment for different scales of composting SHIUAN-YUH CHIEN AND MING-HUEI CHANG 5.1 Introduction In Taiwan, lots of livestock manure and agricultural wastes are produced each year (Lin 1999; Chien 1999). If the wastes are not treated properly, they will cause serious environmental pollution. In the past, there were five methods of dealing with organic wastes. These were: throwing them away directly into country roadsides, streams, and brooks; burning them; using them as feed; incorporating them directly into farmland; and composting them (Chien 1999). The first two methods are not environment-friendly. The third method cannot be adapted for all organic wastes. The fourth method, though economical, may pose some sanitary problems, and may cause the soil to become too reductive, thus retarding the normal growth of crops. Only the fifth method is generally accepted by the people and the government. Through the composting process, the malodorous and unstable organic wastes are converted to organic fertilizers and soil conditioners. Using composts increases soil fertility and saves on chemical fertilizer costs. 5.2 Methods and equipment for different scales of composting Based on studies by researchers and work experiences of farmers in Taiwan, there are several composting methods for dealing with agricultural wastes. They are pile composting, box chamber composting, open furrow composting with turning and aeration, and enclosed vessel composting with mechanical agitation and aeration (Lin 1999). Generally speaking, less capital investments in equipment mean less capacity to treat wasted organic materials. These materials also need longer composting periods to reach maturity. In contrast, more capital investments in equipment mean more capacity and efficiency for composting organic materials (Barkdoll et al. 2002; Lin 1999; Ibuki 1996; Harada 1995; Fabian 1993). The above composting approaches are discussed in the following sections. 5.3 Pile composting Organic materials, mixed at reasonable proportions to have C:N values between 20 and 30 and to have suitable moistures, were piled outside or inside of a composting shed at least 2 m 3 with a height of 1-2 m. Outside windrow composting is only adapted to the seasons or regions with few rainy days. The length of frontage and depth of a composting shed (Fig. 1) is 12-27 m and 4-9 m, respectively, in Japan (Harada 1995; Ibuki 1996), and 12-18 m and 9-18 m, respectively, in Taiwan (Sheng et al. 1995). The height of the eaves should be more than 3.5 m for the operation of the bucket loader. The height of the breast wall is usually 1.8-2.5 m. Partition walls are always settled in a composting shed. It is advisable to have a plastic roof that is pervious to light to avail of solar energy in temperate countries such as Japan (Harada 1995). But the roof of a composting shed is impervious to light in subtropical and tropical countries such as Taiwan. 5.3.1 Static piling composting During composting, there is no further mixing or agitation. It may produce much stinky odor because there is no turning, thus causing an anaerobic condition. This option is adopted for less amounts of organic wastes, yard or household wastes (Fig. 2). Mixing organic materials is made by a manual shovel or bucket loader. With this composting method, the time needed to stabilize the organic materials may be one year or more (Lin 1999; Barkdoll et al. 2002; Harada 1995). 5.3.2 Piling along with turning composting Organic materials are well mixed and then piled on the floor inside or outside of the composting shed. Composting materials are turned regularly with a manual shovel or bucket loader (Fig. 3). This is done in order to mix the composting materials uniformly and to improve the air permeability (Barkdoll et al. 2002; 31

4,000-9,000 12,000-27,000 Roof 10 1 Compost pile 4,000-9,000 4,000-9,000 Slope 1/50 1,500 >3,800 800 3,500 1,200 Fig. 1. Sketch plan/profile (Harada 1995) and picture of a composting shed. Fig. 2. Organic materials are statically piled in a unit block volume. Fig. 3. Piling materials are turned regularly with a bucket loader. 32

Harada 1995). They are turned frequently during the initial period of high oxygen demand and heat generation and may be turned less frequently as the composting process proceeds. They may need to be turned several times per week, depending on the material being composted. Piling materials in a unit block volume surrounded by partition walls (Fig. 4) are 4-6 m (length) x 3-5 m (width) x 1.0-1.8 m (height) in Taiwan. A bucket loader (1-3 m 3 ) is frequently used as a turner to agitate the materials once a week. The time for composting the materials to be stabilized is about two to three months. If the piling materials are agitated with a bucket loader once a week along with pumping with air, the time needed for organic materials to be stabilized as compost is about 28-35 days. Materials added with some maturity composts should be degraded more quickly than those without. A forced aeration system is placed under the piles (Fig. 5) to maintain a minimum oxygen level throughout the composting mass. This aeration system usually consists of a series of perforated pipes or floors running underneath the pile connected to a pump that blows air (positive pressure) through the pile to provide 100-300 L/min.m 3 gas flux with 320 mm Hg aeration pressure. Aeration time is set to pump air 10 min and stop 50 min intermittently. The capacity of the system to treat wasted organic materials can reach 40 t per day. It will produce 5,000-12,000 t of compost a year in southern Taiwan (Lin 1999). 5.4 Box chamber composting The box chamber has three walls which are made of concrete block. The length of frontage, depth, height, and volume of a chamber are 3-5 m, 5-6 m, 1.6-2.5 m, and 8-50 m 3, respectively, in Japan (Harada 1995), and 1.8-3.6 m, 1.8-5.6 m, 1.8-2.6 m, and 5-45 m 3, respectively, in Taiwan. The aeration pipes are arranged on the floor of box chambers, and the gas flux is the same as the above description. Usually, several chambers are joined in one line (Fig. 6). Organic materials, adjusted to proper C:N values (20-30) and moisture contents (55-65%) and mixed well, are then put into the chambers by using a bucket loader, belt conveyor (Fig. 7) or screw conveyor. The time needed for composting the organic materials to become mature will be more than two months (Lin 1999). Fig. 4. Piled materials in a unit block volume surrounded by partition walls. Fig. 5. Forced aeration pipe system is placed under the piling materials. 33

Fig. 6. Composting box chambers are joined in one line. Screw conveyer Animal waste Bulking agent Wastewater tank Fig. 7. Composting box chambers filled with organic materials by using a screw conveyer (Harada 1995). 5.5 Open strip furrow with scoop type or rotary type turner composting A strip furrow (Fig. 8) is 3-6 m wide, 1.5-2.0 m deep, and 50-80 m long (Lin 1999). Organic materials are composted in the strip furrow with turning machines and aeration. A turning machine is supported on a set of rails equipped over the strip furrow, and moves automatically without a manual operator. The wellmixed organic materials are placed at the front end of the strip furrow by using a bucket loader or conveyor. As the turning machine moves forward, 0.5-2 m/day, on the rails from another end of the furrow, it mixes and transfers the composting materials behind (Lin 1999; Ibuki 1996; Harada 1995). They are agitated automatically with the turner once or twice a day. At the bottom of the furrow, there is an aeration system containing aeration pipes and blowers (Fig. 9). Two types of turning machines, the scoop type stirrer (Fig. 10) and the rotary stirrer (Fig. 11), are usually used for agitating the composting materials. When the strip furrow is equipped with a scoop type stirrer or rotary type stirrer, the suitable material stacking height is 1-1.5 m or 1 m, respectively. The composting period is dependent on the length of strip furrow, the frequency of turning, and the transfer distance of composting materials at each turning. Usually, the machine is operated once a day. It moves the materials 1-2 m at each turning, and if the strip furrow is 60 m long, the composting period is 30-60 days. In Taiwan, the composting capacity is enough to treat the feces produced from 1,200 heads of cow or 130,000 heads of layers to produce 1,100 t of mature compost each year (Lin 1999). 5.6 Open strip furrow with hung axle (crane) type turner composting This composting system is basically modified from the above-mentioned open strip furrow with scoop type or rotary type turner composting (Lin 1999; Ibuki 1996). In this system, the hung axle (crane) type turner (Fig. 12) 34

Fig. 8. Composting strip furrow filled with organic material. Fig. 9. At the bottom of composting strip furrow, there is a pipe system aerated with blowers. is equipped, and the width of the strip furrow is larger. Usually, it may have 10-20 m in width. The turner automatically carries composting materials from one place to another in the furrow. Forced aeration is also provided in the composting system, which can treat the feces produced from 150,000 heads of hogs to produce 5,000 t of compost each year in Taiwan (Lin 1999). 5.7 Open elliptical furrow with turner composting The lengths of the horizontal axis and the vertical axis of the elliptical furrow are 50-100 m and 6-10 m, respectively (Lin 1995; Harada 1995). The elliptical furrow is divided into two sides. Raw organic materials are put at the end of one side. The turning machine moves round from the end of the other side, while the materials are transferred in an opposite direction in the elliptical furrow (Fig. 13). The scoop type or rotary type turning machine system and an aeration pipe system (the principles of operation are essentially the same as above) are equipped in this system. The materials are matured and dried after one round. The composting capacity and composting time are the same as those of the above open strip furrow with turner composting. 5.8 Open circular column furrow composting The diameter and depth of the open circular column furrow (Fig. 14) are 6-9 m and 2-3 m, respectively (Lin 1999; Ibuki 1996; Harada 1995). At the bottom of the circular column furrow, there is an aeration pipe 35

Fig. 10. Sketch (Harada 1995) and picture of scoop type turner on strip furrows. 36

Fig. 11. Sketch (Harada 1995) and picture of rotary type turner on strip furrows. Fig. 12. Crane type turner hung on a steel beam. 37

7,500. 9,500. 10,500 Turntable 180 o C Turntable 180 o C Hopper Screw conveyer 100M Screw conveyer Raw materials Hopper Wall Wall Wall Fig. 13. Sketch (Harada 1995) and picture of elliptical composting furrow equipped with turners. 38

Odor Raw materials Deodorizing apparatus Deodorized air Blower Blower Screw conveyer Fig. 14. Sketch (Harada 1995) and picture of circular column furrows equipped with turners. system, which is the same as that mentioned above. Raw composting materials are put into the circular column furrow from the circumference with a conveyor or bucket loader. The materials are mixed and transferred to the center of the column by using the scoop type stirrer (Ibuki 1996; Harada 1995). The mature compost is moved from the bottom of the center of the furrow. The characteristic of this composting method is that the scoop type stirrer is equipped almost vertically (Fig. 15). Raw organic materials are usually piled to a height of 1.5-2.5 m. This system may be adopted for composting in a cold region because the higher stacking of raw materials can be kept warm (Ibuki 1996; Harada 1995). In Taiwan, the composting capacity is enough to treat the feces produced from 88,000 heads of layers to produce 720 t of mature compost each year. The time needed for stabilizing the organic materials is 30-45 days in Taiwan (Lin 1999). 5.9 Enclosed vertical column composting In enclosed vertical column compsting (Fig. 16), raw organic materials are put from the top of the column by a conveyor and agitated by a moving paddle. Air is blown up from the moving paddle through the composting materials by an aeration system (Fig. 17). The composted material is removed from the bottom of the column. The volume of the vertical composting column is 16.8 m 3. Each day, one-third column volume of organic material (about 4 t) is loaded (Lin 1999). After three days in the column to get rid of stinky odors, the composted organic material is moved out and conveyed to the composting shed for further composting to reach maturity. The retention time of the material is very short, because the volume of the 39

Fig. 15. Sketch (Harada 1995) and picture of scoop type stirrer equipped vertically on circular column composting. Fig. 16. Enclosed vertical column composting. 40

Moving paddle Moving paddle Heater Blower Exhaust gas Air " # $ % & " # $ % &! Material inlet Air outlet Air filter Reduction gear Outlet Hopper! Blower Fig. 17. Aeration system of enclosed vertical column composting (Harada 1995). reactor is smaller than those of the other compost bins and the composting shed. Mainly used for poultry wastes, this system has also been used for swine and cattle wastes recently (Ibuki 1996; Harada 1995). 5.10 References Barkdoll, A. W., R. A. Nordsedt, and D. J. Mithchell. 2002. Large-scale utilization and composting of yard waste. CIR 1027:1-15. Agricultural and Biological Engineering Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Chien, S. Y. and T. C. Juang. 1999. Developing technology for producing compost from wasted mushroom sawdust. Composting Technology. pp. 91-106. In: Special Bulletin No.88 of Agricultural Research Institute, COA, Republic of China (In Chinese). Fabian, E E., T. L. Richard, D. Kay, D. Allee and J. Regenstei. 1993. Agricultural composting: A feasibility study for New York farms. Cornell University, USA: Cornell Composting. pp.1-50. Harada, Y. 1995. Practical aspects of animal waste composting. pp. 64-86. In: Lecture of international training course on microbial fertilizers and composting. Rural Development Administration (Republic of Korea) and Food and Fertilizer Technology Center for Asian and Pacific Region. Ibuki, T. 1996. Examples of dairy manure composting in Japan. pp. 142-153. In: Proceedings of international training workshop on microbial fertilizers and composting. Taiwan Agricultural Research Institute and Food and Fertilizer Technology Center for Asian and Pacific Region. Lin, C. W. 1999. Composting of livestock feces. Composting technology. pp. 107-141. In: Special Bulletin No.88 of Taiwan Agricultural Research Institute, COA, Republic of China. (In Chinese). Lin, C. W. and S. Y. Chien. 1995. The research of using agricultural waste to produce compost. Proceedings of the techniques of reasonably using organic fertilizers. Tauoyang District Agricultural Improvement station, Republic of China. pp. 43-58. (In Chinese). Shen, S. Y., Lin, C. W., Hong, C. M. and M. D. Kao. 1995. Manual of using poultry feces as organic resources. pp. 68-70. In: Special Bulletin No.34 of Taiwan Livestock Research Institute, COA, Republic of China. (In Chinese). 41