Operating Experience with Biogas Plants in Sri Lanka L.C.A. de S. WIJESINGHE and J.A. CHANDRASIRI
Natural Resources, Energy and Science Authority, Vidya Mawatha, Colombo 7, Sri Lanka
Three hundred and three biogas plants, representing a majority of the units installed in Sri Lanka up to 1984, were inspected, and it was found that 280 of these had been put into commission at some time prior to the study. Of the 280 commissioned plants, 170 (61%) were functioning satisfactorily providing biogas for cooking and/or lighting. The. remaining 110 (39%) were either not functioning or were supplyin very little gas owing to gas leaks, inadequate input of dung, or poor plant management. The most
common plant was the 6 m , fixed dome, household plant, and the most common raw material used was cattle dung. In the majority of household plants the cost of construction was partly or wholly subsidized.
1. INTRODUCTION Biogas is the gas that is produced when animal dung or other organic matter undergoes anaero- bic digestion. It consists mainly of methane and carbon dioxide. The presence of the former makes biogas inflammable and therefore usable as a fuel. In the search for cheap, indigenous sources of energy to reduce the demand on fossil fuels, many countries, both developing and de- veloped, have devoted attention to advancing biogas technology; but in terms of its possible economic and social benefit the greatest potential of biogas lies in the oil importing, developing countries. A biogas plant, besides producing fuel, also yields a waste sludge which can be used as a fertilizer.
With the price of commercial fuel rising sharply in the long term, it is obvious that in most countries attention should be focused on alterna- tive indigenous fuels and improved technologies of fuel use. Sri Lanka is a country with a farming tradition, and one would have expected biogas to be given serious consideration as an alternative household fuel. However, even as late as 1979, six
years after the first fuel crisis, it was reported that there were only two successful biogas units in the country (Gosling, 1979). As a result of a heavy subsidy on kerosene introduced by the govern- ment following the first fuel crisis, cheap kerosene was available in the market up to 1979, and it is likely that this factor acted as a strong disincentive in the development of alternative energy resources. From 1979 onwards the subsidy was reduced in stages, and a kerosene stamp scheme was introduced to enable the needy to obtain a small quantity of kerosene free of charge each month.
Several government institutions in Sri Lanka have started to promote biogas as a fuel and have set up an extension programme for biogas tech- nology. A few non-government institutions have also taken to promoting the use of biogas as a fuel. Casual estimates made by those involved in biogas promotion work lead one to believe that by early 1984 several hundred units had been set up throughout the country.
In discussions with energy sector officials, those directly involved in biogas extension work gener-
L.C.A. de S. Wijesinghe is a forester by training. From 19SR to 1977 he served as a professional forester in the Sri Lanka Forest Department. Since 1977 he has been the Additional Director General of the Natural Resources, Energy and Science Authority of Sri Lanka. During this period his special interest was energy and he carried out a number of national surveys on energy use in the
household sector. The present study is one of these. J.A. Chandrasiri is a graduate in physicalsciences from the University of Sri Lanka. He joined the Natural Resources, Energy and
Science Authority as a Staff Assktant and in that capacity he assisted the senior author in a number of national energy surveys.
Natural Resources Forum 0 United Nations, New York, 1986
222 de S . WIJESINGHE and CHANDRASIRI NRF VOL. 10, NO. 3,1986
ally spoke enthusiastically of the benefits to be derived from the widespread use of biogas, but some of the others expressed scepticism. The latter generally referred to the high cost of installing a biogas unit, the scarcity of dung, technical problems in the maintenance of the biogas plant, and the fact that the increment to the national energy supply which even an ex- panded biogas programme would be expected to contribute is relatively small. Those who favoured promoting the use of biogas as a fuel saw the impact it could have in raising the quality of life of rural households by providing both vastly im- proved lighting and cooking facilities and a high quality fertilizer. Because of the conflicting views that were expressed, and considering that by 1984 several hundred biogas units were said to have been set up throughout the country, the authors decided to carry out a field study to evaluate the programme at its present stage.
2. METHODOLOGY Information on the ownership and location of biogas units was obtained from government and non-government institutions which were involved in biogas extension work, and the owners were informed by post of the proposed study and the intended visit by an officer of the Natural Resources, Energy and Science Authority. When field visits were made, the officer often received information on the existence of other units in the locality.
Data were collected on the following: the capacity, type (design) and condition (whether functioning or not) of the unit; the year of commencing operation; the cost, and subsidy if any; the use to which the biogas was put, and the proportion of cooking and lighting done with biogas; the raw material used; the supplementary fuels used for lighting and cooking; repair and maintenance problems, if any; and the use made of the effluent sludge. The proportion of the cooking for which biogas was used was assessed on the basis of information provided by the respondent, and the proportion of lighting was assessed notionally taking into account the aver- age number of lamp hours (as given by the respondent) and the percentage and frequency of use of the floor area illuminated. A suitable questionnaire was composed and it was com-
pleted for each biogas plant visited. No measurements were made of the quantity of
gas produced, and what is referred to in this paper as the capacity is the internal volume of the unit. In the fixed dome type (Chinese design), the volume of the entire unit (slurry and gas contain- ing sections taken together) was recorded. In the floating gas holder type (Indian design), the capacity was taken as the volume of the digester up to the level of the slurry and half the volume of the gas holder.
A total of 303 biogas units were inspected between August 1984 and January 1985. In visits to 14 other units there was no responsible person from whom information could be obtained. Thirty-eight units in the administrative districts of Jaffna, Mannar, Vavuniya, Trincomalee and Bat- ticaloa, in the north and east of the country, could not be visited because of the conditions of civil unrest prevailing there. There was some, not very precise, information on about 25 other units said to be found in different parts of the island; in three of these cases no unit was found at the given address, and in two cases, although the gas holder had been delivered to the site, the construction of the digester had not been carried out. Because over 300 units had been inspected, and it was going to be time-consuming to trace the remain- ing plants, it was decided to make the evaluation on the basis of the data about these 300 units. Two small biogas plants in a research and development institution and one large biogas plant which forms a part of an integrated project for producing electricity using biogas, wind power and solar energy to meet the needs of a remote village were not included in the survey. *
3. RESULTS 3.1 DISTRIBUTION
The total number of biogas plants inspected was 303. Their distribution is shown in Fig. 1. Some of the plants were in the final stages of construction or were being filled with dung or were awaiting the connection of the gas pipe and appliances; these plants numbered 23. This meant that, among the biogas plants inspected, there were
* For detailed information on the integrated project, the reader may refer to Renewuhle Sources of Energy. Vol. 1, No. 2, pp.81-108.
Sri Lanka LOCATION OF THE BIOGAS PLANTS
* 5 Units 6-IOUnits
0 11-15 Units 16-20Units
-1524 m- Contour Line Monnor
224 de S. WIJESINGHE and CHANDRASIRI NRF VOL. 10, NO. 3, 1986
280 that had started functioning after construc- tion. The great majority of the biogas plants inspected were situated in the low and midcoun- try, with high concentrations around Kandy, at Hungama (between Matara and Hambantota) and at Nikaweratiya (between Kurunegala and Puttalam).
3.2 DESIGN, CAPACITY, OWNERSHIP,
The vast majority of the plants were of the fixed dome type (Chinese design) - 266 (88%) of the total of 303 units inspected. The other 37 were of the floating gas holder type (Indian design).
There was one plant of 4 m3 capacity; the others ranged from 6 m3 to 100 m3. The 6 m3 plants were the most common, accounting for 54% of the plants that had been put into commission. The next most common size was 8 m3. The 6 m3 and 8 m3 units together accounted for 67% of the plants. There were 150 units of 6 m3 capacity, and it should be noted that 43 of these were constructed by the government in a model housing scheme at Nikaweratiya and the families which occupied the houses had no choice but to accept the 6 m3 plants that were provided. However, even if these are left out of the reckoning, the 6 m3 plant was still the most common.
Excluding the plants that had not commenced operation up to the time of the inspection, there was a total of 280 units, and of these, 200 were actually functioning. Twenty-seven were not functioning for a period of up to six months and 53 for over six months. It appeared that most of the plants falling into the latter category had been
abandoned. The distribution of the functioning and non-functioning plants in households and institutions is given in Table I . Table I1 gives the capacity, the year of commencing operation and the present condition. Table 111 gives the distribu- tion by year of commencing operation, the present condition and the design. The capacity classes that were selected (4 m3, 6 m3 and so on) for classifying the units were based on the actual data collected. In a few cases where the capacity of the plant did not fit one of the classes exactly, it was placed in the class that was the closest approximation to its capacity.
Table 111 shows that, out of a total of 37 floating gas holder plants, 18, or half the number, were not functioning. Taking the fixed dome plants only, the proportion of non-functioning plants was much lower, 62 out of 243, or one quarter. The responses appeared to indicate that the owners were less able to cope with repair and maintenance in the floating gas holder plant than in the fixed dome type and this may have contributed in some measure to the proportion of non-functioning units being higher among the floating holder plants. Two common problems with the floating gas holder were the occurrence of corrosion and the difficulty of lifting and moving it aside in order to clean out the digester. One should not overlook another factor of importance when comparing the performance of the two models; the biogas expert of the Depart- ment of Agriculture promoted the construction of the fixed dome model only, and he provided the advisory services for the construction, manage- ment and maintenance of as many as 211 out of the 243 fixed dome plants.
TABLE I Numbers of functioning and non-functioning biogas plants in households
Functioning Not functioning for Not functioning for more than 6 months 6 months or less
159 26 25
41 1 28
No. of household plants No. of institution plants TOTAL
200 27 ~
NRFVOL. 10, NO. 3,1986 BIOGAS IN SRI LANKA 225
TABLE I1 Biogas plants classified by capacity, year of commencing operation and present condition
Yearofcommencing 1977and 1978 1979 1980 1981 1982 1983 1984 All included operation earlier
Presentcondition" A B C A B C AB C A B C A B C A B C A B C A B C A B C
Total - - 4 - - 6 5 4 6 26 1 8 2 8 3 1 2 25 4 5 1 9 1 2 9 37 3 3 200 27 53 "A = functioning; B = not functioning for a period up to 6 months; C = not functioning for more than 6 months.
TABLE 111 Biogas plants classified by year of commencing operation, present condition and design
Yearofcommencing 1977and 1978 1979 1980 1981 1982 1983 1984 All included oDeration earlier
Present condition A B C A B C A B C A B C A B C A B C A B C A B C A B C of planP Fixed dome type - - _ _ _ 2 4 2 2 22 1 7 18 1 12 22 4 5 78 11 9 37 3 3 181 22 40
Floating gas - - 4 - - 4 1 2 4 4 - 1 1 0 2 - 3 - - 1 1 - - - - 19 5 13 holder type "A = functioning; B = not functioning for up to 6 months; C = not functioning for over 6 months.
3.3 RAW MATERIAL Cattle dung, either alone or mixed with cattle urine, was by far the most common raw material used. It was the only feedstock used in 139 out of the 200 functioning plants. In a further 37 plants it was used together with human excreta, and in another 17 plants it was mixed with other animal wastes (poultry or pig dung). Of the remaining seven plants, three used pig dung, one used a mixture of poultry droppings and pig dung, one used cattle dung and leaves of Leucaena leucocephala (ipil ipil), and two used human excreta.
Of the 37 biogas plants using cattle dung and
human wastes, 35 were household plants. The most common reason given by the householders who did not use night soil in their biogas plants was that they were reluctant to use gas produced from human excrement for cooking. It must be noted that, given a free choice, the number of households using night soil might have been much less than 35, for 28 of them belonged to the housing scheme at Nikaweratiya where the houses and biogas plants were constructed by the government with provision for using both night soil and cattle dung. Many of these households used the biogas plants as intended but a few had disconnected the toilet from the biogas digester.
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TABLE IV Distribution of the households using biogas for all the cooking or for all the lighting or for a major part
For all the For all the For all the For all the For all the For a major part cooking and cooking and cooking and lighting and lighting and (c . Y 4 ) Of both
all the lighting
>I/? rhe lighting P h the lighting >V> the cooking OPh rhe cooking cooking and lighting
( 1 ) (2) (3) (4) ( 5 ) (6)
3 1 8 2 5 No. of households 9
The cattle dung was collected variously from stall fed cows, cows in night paddocks and free grazi...