|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|A continuous composting system for disposal and utilization of animal wastes at the village level|
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.