|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|A continuous composting system for disposal and utilization of animal wastes at the village level|
Status of land utilization and disposal of animal
A continuous composting system for land utilization of animal wastes at the village level
Agricultural Research Institute of Kanagawa Prefecture, Hiratsuka City, Japan
Never in the history of agriculture has soil fertility been considered as much as today. However, there is almost no literature on the subject, and no definite conclusions about how organic matter such as manure compost affects the fertility of soil. Nevertheless, a tremendous amount of manure is used on farm land.
The reason for the recent interest in soil fertility was the observation that crops grew abnormally and yields were highly variable when the amount of organic substances used for farming decreased and began to be replaced by chemical fertilizer. Why this is so is not clear. However, in one intensive vegetable cultivation area, farmers improved both quantity and quality of their crops when they applied organic matter to the soil.
The rapid economic expansion during the 1960s in Japan turned conventional agriculture into an enterprise, with the result that farmers were forced into raising either vegetable crops or cattle. This caused a shortage of organic fertilizer for vegetable farmers on the one hand, and created a serious problem of manure disposal for cattlemen. Subsequently it was found that application of cattle manure to soil improved its fertility significantly, even though it was originally considered as a source of nutrients for plants rather than as a component for maintaining soil texture. Thus, it appears likely that an agricultural system that depends on the heavy use of chemical fertilizer has a deleterious effect on soil fertility. The present paper summarizes the results from 13 years of studies beginning in 1964, to establish a system for using cattle manure as a valuable organic fertilizer for farm land.
The study was begun without any prior assessment of the impact of large-scale cattle raising, which it was thought would be common in the future. Furthermore, animal waste management was the main interest, and only scant attention was paid to the use of this valuable resource. For management purposes, it is mechanically easier to handle waste if large quantitites of excretions are mixed without separating solids from liquid. However, this method causes severe problems both from the standpoint of handling waste and using it. For one thing, only 50 per cent of solid waste was obtained when solids and liquids were mixed. Accordingly, the need was to develop an efficient system to separate solid matter from liquid waste, and this was accomplished by means of a screw press. Moreover, water-soluble organic matter, which has a high biological oxygen demand (BOD), remained in the liquid. The result of this study clearly indicated that the problem was due to the presence of soluble solids and the BOD of the raw faeces, and that the samples used for screw press treatment would have a high content of solids and a high BOD.
We have tested other systems, such as the centrifuge and rotary screen, for comparison with the screw press method, and found that solid matter isolated by the screw press is best for rapid manure composting. The conclusion is that the screw press method should be used on large-scale hog farms having several thousand animals. The best results are obtained when raw faeces are removed separately from the hog pen and the remaining, mixed excrete are partitioned by the screw press. It is not as efficient to separate total excretions by the screw press without any prior separation. The amount of faeces that can be preseparated from the hog pen is about 80 - 90 per cent of the total, and subsequent treatment of the remaining mixture of 10 - 20 per cent of faeces and urine by the screw press ensures that all solid wastes are preserved for composting. This method is ideal for large-scale hog raising, because it reduces costs of both waste management and pollution control.
Although most farmers still have a water pollution problem because they do not preseparate faeces, the screw press is becoming popular in Japan. About 400 such presses are now in use. One possible explanation for the wide farmer support of the screw press is that it provides fertilizer for the fields and improves soil fertility and crop production.
The main problem associated with the screw press system is handling of the raw faeces removed directly from the hog pen. Bad odour and high water content, together with psychological aversion, prevents some farmers from pre-separating faeces from liquid wastes.
In order to ameliorate this problem, we have tried heat-drying of raw faeces. Because cow and hog manures contain more water than found in chicken manure, more fuel is consumed if a conventional chicken faeces dryer is used. In addition, the quality of cow or hog manure in terms of soil fertility is inferior to that of chicken manure, so that in the long run, costs increased disproportionately.
Another approach is semi-drying of manure. This process was first developed mainly to reduce fuel consumption, but an additional advantage is that manure so treated can be composted fairly rapidly. Usually, high water content in the raw faeces and solid fractions remaining after mechanical separation of excrete precluded rapid composting. It is now understood that reducing the water content of faeces from 80 - 85 per cent to 60 - 65 per cent is the key process in making good compost. Rice straws and leaves can be used to absorb water during composting.
The continuous process of composting animal faeces, i.e., semi-drying by heat, composting, mixing with raw faeces, and re-composting, was tested on a small scale for evaluation of the process. Although no large-scale study was done, the process was considered to be quite promising, and use of the method began to spread in the country beginning in 1970.
Unfortunately, mixing the compost with raw faeces was thought to be too labour-consuming, so widespread use of the continuous composting system did not take place until Tsuneo Jimbo developed a loading system in 1973. This success stimulated Shuichi Anzai to develop a so-called "pile-up system," which consisted of loading raw faeces on top of the compost so that mixing is required only on the top portion.
This development not only means that the middle-sized farmer can continuously make compost from manure but also allows centralized composting at the village level. The process is now popular all over the country.
The carbon ratio of raw cow manure is about 15:25, that of hog manure 10:13, and of chicken manure, less than 10. The carbon ratio of solid fractions after mechanical separation of excrete is 30 in cow dung and 17 for hog manure. These values are quite different from those in rice straw, which has a ratio of 70:80 due to the high content of lignin. Raw faeces have an equal or lower carbon ratio compared to well-matured compost or manure compost. If one judges the maturity of compost by its carbon ratio, raw faeces have a value close to that of fully matured manure compost, and thus is satisfactory.
However, when the water content of raw faeces or solid isolate was reduced to 60-65 per cent, rapid fermentation was usually observed. One possible explanation of such active fermentation is that manure usually contains many biodegradable substances, such as shortcarbon-chain fatty acids. In addition, manure is also high in nitrogen, thus making a good substrate for microorganisms. The temperature profile increased significantly at the beginning of fermentation and fell after the first few days during composting, supporting the idea that the time required for composting raw faeces is much shorter than that observed during conventional manure composting. The reason is believed to be that raw faeces are much more susceptible to attack by micro-organisms.
Compost from either raw faeces or solid isolate is generally rich not only in organic materials but also in various minerals that help to enrich soil. In particular, the compost made by fermentation at high temperature did not decompose rapidly in the soil, which lessens the hazard of gas production that has been observed when immature compost is applied.
Raw faeces could become an ideal organic resource if a system is developed to remove water content economically without just mixing in rice straws, etc. Compost from raw faeces has been proved, not only by small-scale tests, but also by practical use, to be a good fertilizer as well as a soil conditioner. Although it is difficult to detect a significant change in the physico-chemical properties of soil by adding compost at a level of 1 - 2 tons per year per 10 acres (it is generally said that 5 tons per year are essential to change soil conditions), a significant improvement in crop growth has been observed when compost was used compared with results from application of chemical fertilizer. For example, in vegetable production, manure compost used alone led to a good yield of high-quality vegetables and met more than 60 - 70 per cent of total nutrient requirements of the crops.
It is particularly interesting to note that unlike chemical fertilizer even a small amount of organic matter improved acid soil in a vegetable field.
Cattle manure is particularly beneficial in volcanic ash soil. On the other hand, application of organic matter to a paddy field is valuable under the right soil conditions. In certain instances, reduced rice yields were observed, implying that the method used for adding raw faeces is very important. They should be applied to the paddy field as early as possible to allow enough time for decomposition before the rice is planted, to prevent any drop in pH value of the soil. If this is done, the effect of organic matter has a detectable benefit, even in a rice paddy with peat in its lower layer.
Raw cow, hog, and chicken manures have been tested in direct application to the field using 200 tons per 10 acres of each kind of manure. Micro-organism activity peaked four to seven days after application, and then dropped quickly. This phenomenon correlates with the process of composting raw faeces. The increase in micro-organism activity at the initial phase is due to the higher BOD of the faeces, and the BOD and CO2 gas production have shown a good correlation.
An unusual increase in microbial activity in soil will affect the crops adversely, particularly right after planting. Care should be taken to avoid these undesirable effects when raw faeces are going to be used. A large quantity of raw faeces applied to soils maintained good productivity of vegetables without further addition of fertilizer for four years, which means that raw manure is slow-acting and effective for long periods. Chicken manure, which showed a very high microbial activity at the initial phase, became less effective much faster than either cow or hog manure in terms of crop productivity. This result indicates that chicken manure has less residual activity and soil-conditioning power than the other manures.
Mixing raw faeces with soil will heighten the rate of faecal decomposition because good aeration is permitted by increased surface contact between faeces and soil.
The problem with the present method is that the amount applied to the field is far beyond the quantity required by the plants. Such large-quantity application of raw manure will certainly have an undesirable effect, particularly with regard to pollution of the environment. For example, part of the nitrogen in raw faeces may diffuse into the soil during decomposition. It is interesting to note that denitrification has been observed when raw faeces, rich in organic nitrogen, have been applied, while with application of inorganic nitrogen, no denitrification has been detected. This phenomenon indicates that, when organic nitrogen is applied in large quantities, part of the nitrogen is denitrified by the activity of micro-organisms. I believe that this sort of microbial regulation, such as conversion of excess organic nitrogen to an inert form, is very important and further study of the interrelationships between organisms and their environment is essential.
A more detailed description of the foregoing discussion can be found in my article in the Bulletin of the Agricultural Research Institute of Kanagawa Prefecture, No. 1 18, "Studies on the Utilization of Animal Wastes in Agriculture," 1977.
Use of This Method on Small-Scale Animal Farms
Since the early 1960s, concern has been expressed about disposing of bulky animal wastes from the large-scale livestock production units in suburban areas of Japan. The disposal problem, however, is not merely one of environmental protection. Vegetable growing, another type of agricultural practice dominant in suburban areas, is suffering from declining soil fertility resulting from heavy dependency on chemical fertilizers to the neglect of organic manuring. Therefore, an efficient use of animal wastes as compost for vegetable growing could solve these two problems at the same time.
From the livestock railers' point of view, washing out all animal excrement with water is the easiest way to maintain good sanitary conditions in barns and pens. Therefore, in our early studies we began with a mixture of excrete and water as a source material and then became concerned with how to separate solid matter from waste water efficiently (1 - 3).
Various mechanical methods were tested, but all proved to be unsatisfactory. The reasons were:
a. although fresh manure contains about ten times more soluble solids and has a higher BOD than urine (Table 1), the recovery rate of solid matter from mixed excretions was found to be only 50 per cent by any mechanical methods; and
TABLE 1. BOD Content of Animal Wastes (ppm)
|Cow||22,000 - 26,000||2,500 - 3,000|
|Hog||55,000 - 60,000||4,500 - 5,000|
|Chicken||65,000 - 70,000||-|
b. water-soluble organic matter, with a high BOD, remains in the liquid portion after separation.
Therefore, by mechanical separation methods, not only does the liquid portion, which has to be disposed of, impose a heavy burden on sewerage facilities, but also a large portion of organic matter that could otherwise be used as farm manure, is lost.
Based on the experience of the early studies, a different approach was sought to solve the problem of disposal and use of animal wastes. The idea of using the excrete mixture as a source material was abandoned; instead, an efficient composting system using fresh faeces collected separately from urine was conceived, developed, and tested. A brief description of the system and some examples are presented here.
The basic procedure
Fresh animal faeces contain about 80 per cent moisture (Table 2). To begin with, the moisture content must be reduced to 55 - 65 per cent by drying either naturally (air drying) or artificially with the help of fuel. The product is called "half-dried faecal waste." Second, this material is piled into a heap and turned over every three or four days. Highly active aerobic fermentation takes place following a self-generating rise in temperature, and a well-matured manure compost of 40 - 50 per cent moisture content is obtained after two weeks. The product of this second stage is called "seed compost." The procedures up to this stage are preparatory.
TABLE 2. Composition of Animal Faecal Wastes 1% dry basis)
Third, to this seed compost, a fresh volume of faeces is added so that the moisture content of the mixture does not exceed 55 - 65 per cent, the level equivalent to the half-dried waste described above. The mixture is piled up and subjected to aerobic fermentation for two weeks. Part of the mature compost thus obtained is used as farmyard manure and the rest as seed compost for the next cycle of composting (Figure 1).
As described above, drying is required only at the initial stage. Once the seed compost is obtained and recycling begins, quality farmyard manure can be obtained every two weeks without being influenced by weather conditions and without the help of supplementary energy.
Practical system A: The whole-mixing method
This method is one of the practical applications of the basic procedure at the local farm level. It was developed by T. Jimbo, who raises dairy cattle near Yokohama. A detailed survey of his farm was made in July - August 1974 (4). Below are some salient features of the survey results.
Thirty head of cattle at his farm produce about 750 kg of faeces and 3001 of urine per day. The latter is anaerobically treated and discharged to the river. The faeces are manually collected from the barn and carried to the composting ground. For preparation of the initial seed compost, fresh faeces were spread on either the open field or the greenhouse floor. When the moisture content dropped to 55 - 60 per cent, the half-dried faeces were piled into a heap of about 2 - 3 m³ Within two to three days the temperature rose to 60 - 70 C. Every two or three days the heap was turned with a manure fork attached to the front loader of a small tractor. Matured manure with a 40 - 50 per cent moisture content was obtained after 10 - 15 days.
Fifteen-hundred kg (about 1.5 m³) of fresh faeces, the amount produced at the Jimbo farm during a two-day period, was added to about 1.5 m³ of the seed compost and mixed thoroughly with the manure fork. The mixture was piled and stirred every two or three days. After about ten days, 2.5 m³ of mature manure was obtained, of which 1 m³ was applied to the field and 1.5 used again as seed compost.
When the ratio of the seed compost to fresh faeces was 1: 1, 10 - 1 5 days seemed to be sufficient time for obtaining mature manure. However, the ratio should be reduced to 1:0.7 during the winter season. For easy operation of the manure fork, the height of the heap should be 1 m and its volume at least 3 m³. A maximum temperature of 74 C in the heap was attained four to seven days after mixing. The composition of the mixture underwent drastic changes. Among them, the rapid decrease in moisture content and in the C/N ratio was particularly noticeable (Table 3).
TABLE 3. Changes in the Composition of Animal Faecal Wastes during Composting
|Moisture (% Wet basis)||Ash||T.C.||T.N.||C/N|
|new faeces||81 8||16.5||32.9||2.03||16.2|
|. . .||7||55 2||27.3||39.1||3.96||9.9|
Practical system B.: The partial-mixing method
This is a simplified version of the basic procedure, and was developed by S. Anzai who raises 500 pigs in Kanagawa Prefecture. His farm was carefully studied during October 1975 - February 1976 (5).
At this farm, the amount of faeces treated was about 1.2 tons per day. The usual procedure for preparing the seed compost was similar to that described above. In addition, almost completely air-dried faeces also proved effective as seed compost. The seed compost, which was left in a heap for more than 20 - 30 days, proved to be ineffective because the temperature did not usually rise rapidly when fresh faeces were mixed with such aged seed compost.
The seed compost was laid on the ground in a rectangle of 1.0 - 1.5 m, and fresh faeces were spread on it. The seed compost was about 20 cm thick, and the fresh manure layer was about 10 cm. These double layers were manually turned with a scoop to improve air penetration. Thorough mixing was unnecessary, and sometimes could adversely affect subsequent fermentation. During fermentation, the heap was manually turned every two to three days. Mature manure was obtained after 15 - 20 days. Unlike the whole-mixing method, fresh faeces were spread on the whole matured manure rectangle without separating part of it out for application on the field. The thickness of newly added faeces was also about 10 cm. Only the upper 20 cm part of the heap was turned at the same intervals mentioned above.
By repeating the operations described earlier, the height of the heap increased, and turning became difficult when the height reached 70 - 80 cm. The greater part of the heap was used as farmyard manure, while the surface layer in which the greatest microbial activity was found was used as the seed compost for the next cycle.
Because the height of the heap was initially only 25 - 30 cm, the rate of temperature rise was slower than in system A. Yet, it reached 50 - 60 C within four to five days when the heap grew to 50 cm high or higher, and the maximum temperature reached 60 - 70°C, as high as in the whole-mixing method. The highest temperature was recorded in the upper portion of the heap where fermentation was most actively taking place. In the lower portion, the temperature was found to be constant at a relatively high level throughout the composting process.
The composition of the hog faeces changed significantly during the composting process, as shown in Table 3. In spite of drastic changes in the other components, the C/N ratio was found to be constant, in contrast to the decreased ratio in cow dung.
Generally speaking, the ratio of carbon to nitrogen, or- the C/N ratio, decreases when organic matter is decomposing. The rate of decomposition is initially rapid and becomes slower at the C/N ratio approaches that of the micro-organisms themselves, i.e., about 5:6. In the case of rice straw compost, the initial C/N ratio is about 70, and decomposition almost ceases after three to six months, when it falls to 20, which means that well-matured rice straw compost has a C/N ratio of about 20.
The initial C/N ratios of animal faeces are much lower: 20:25 for cows, 10:15 for hogs, and 8:10 for chickens. These figures are as low as, or lower than, the C/N ratio of matured rice straw compost. Yet, as demonstrated by the systems discussed above, the faecal wastes undergo drastic decomposition during a surprisingly short period (only two weeks) if certain conditions are met. Therefore, the C/N ratio alone is not necessarily an index for maturity of animal waste composts.
The easy decomposition of animal wastes, in spite of the low C/N ratio, can be explained by the abundance of easily decomposable organic matter, such as lower fatty acids and sugars, the main sources of BOD, as well as the high nitrogen content. The former is the energy source and the latter the nutrient source for rapid microbial activity. To realize this potentially high susceptibility to decomposition, there must be an ample supply of oxygen. Lowering of the moisture content by either drying or mixing in fresh faeces with the seed compost is effective for improving aeration within the heap. Heat generated by active aerobic fermentation also effects evaporation.
The key to success in the continuous composting system is maintenance of a highly active aerobic fermentation. Once the microbial flora are contaminated with anaerobes, recycling does not operate smoothly. In this sense, the system is similar to sewer water treatment, in which the maintenance of favourable bacterial activity of activated sludge must be managed with the greatest care In the case of sewer water treatment, BOD proceeds from one phase to another. The first phase is said to take 14 days, which coincides with the period required for the aerobic fermentation in the system described.
A Large-Scale Composting Centre in an Agricultural Co-operative
A large-scale composting centre started operating in 1975 with financial support of the Ministry of Agriculture and Forestry, Kanagawa Prefectural Government, Ayase Town Office and Ayase Town Agricultural Co-operative. The main installations and expenses are shown in Table 4.
TABLE 4. Main Installations and Expenses in Large-Scale Composting Centre (1977)
|Building||560 m²||Y 15,626,000 (US$58,966)|
|Shovel loader||1.0 ton load||Y 2,515,000 (US$ 9,491)|
|Dump lorry||2 0 ton load||Y 1,894,000 (US$ 7,147)|
|Automatic scale and shed||9.7 m², 5.0 ton max.||Y 3,020,000 (US$1 1,396)|
Management and operations of the agriculture/ co-operative
An operations committee is organized by the representatives of the Livestock Raising Association, the Horticultural Farmers' Association, and the Tractor Operators Group. Their function is to collect jointly animal faecal waste, process it, and then redistribute it among members of the co-operative when desired.
Composting faecal waste
Wastes that arrive at the centre are weighed automatically and unloaded onto sawdust. Fresh faecal waste is mixed with about 10 per cent sawdust, and the same quantity of mature compost previously processed for 15 to 20 days is piled to a height of 1 m by bucket loader. Every three or four days mixing and piling are repeated for a period of 15 to 20 days. Analytical data on processed compost are given in Table 5.
TABLE 5. Chemical Constituents of Processed Compost (% on wet basis)
The price of fresh faecal waste and processed compost
When the moisture contents of cattle and hog faeces carried to the centre are more than 85 per cent, US$2 per ton are paid to the livestock-raising farmers, and they receive US$2.50 when the moisture content is less than 85 per cent. Well-matured compost thus produced is sold and delivered for US$14 per ton, including a US$1.50 charge for delivery.
1. H. Arikawa, T. Matsuzaki, and N. Nishiyama, "Studies on the High Rate Composting of Animal Feces. Part 1. Experiments or: the Screwpress Method," Bull. Kanagawa Agric. Exper. Sta. 105: 21---30 (1967).
2. T. Matsuzaki and H. Arikawa, "Studies on the High Rate Composting of Animal Feces. Part 2. Comparison of Mechanical Methods for Separation of Solid Matter from the Excreta Mixture," Bull. Kanagawa Agric. Exper. Sta. 108: 27--38, (1970)
3. T. Matsuzaki and H. Arikawa, "Studies on the High Rate Composting of Animal Feces. Part 3. Experiments on a Rotary Drier," Bull. Kanagawa Agric. Exper. Sta. 109: 117 126 (1970).
4. T. Matsuzaki, "A Practical Application of the Continuous Composting System of Cow Dung," Experimental Research Report 7, pp. 49 52, Agric. Res. Institute, Kanagawa Prefecture, 1975.
5. T. Matsuzaki, "A Practical Application of the Continuous Composting System-An Example of the Partial Mixing Method. Experimental Research Report 8, pp. 23 36, Agric. Res. Institute, Kanagawa Prefecture, 1976.