|The Use of Effluents from Biolatrines in Tanzania (ADF, 1996, 38 pages)|
|Research findings and interpretation|
In addition to units already installed under the regular CAMARTEC program, new units were constructed at Arumeru District Hospital, Oljoro Military National Service Camp, and Rulenge Secondary School. The biolatrine at Arumeru District Hospital has a 30 m³ capacity, with four seats. It is able to handle the wastes of about 200 people with a retention time of 150 days.
Both hospital authorities and patients were grateful for improved toilets. They particularly appreciated the fact that the wastes could be treated safely even without water, a persistent problem they had faced in the past. The effluents are to be used mostly on maize fields.
Oljoro Military National Service Camp, also in Arusha province, had previously acquired, by contract with CAMARTEC, a 50 m³ digester making use of animal waste. This saves about 30 percent of their energy requirements and provides fertilizer in the form of slurry for about three hectares of fodder grass and vegetable gardens. They decided also to install biolatrines, beginning with an 8-seat toilet and 32 m³ digester. One of their objectives was to avoid the cost of clearing their latrines with vacuum suction vehicles from Arusha town.
With the increase in the camp's resident population to about one thousand, the digester proved too small. Although they obtained some gas for lighting and cooking, gas production, as well as usefulness of the effluents, was reduced by short retention times (see Appendices 2 and 3). Under the research grant, there has been progress towards constructing a 50 m³ digester for the purpose of more thorough treatment of the digestants.
Rulenge Secondary School, in Kagera Province, has a total of about 112 m³ of installed biolatrines, with a total of 24 seats. The digesters are connected to the previously installed latrine system, necessitating such a large volume. The school is now saving about 30 percent of the total school energy requirements, and good use is made of the effluents in their gardens. Formerly, untreated effluents were removed manually whenever the latrines got full.
a. Demonstration Results
At these beneficiary institutions, it is immediately clear that the question of technology acceptance is not an issue. The benefits are obvious and appreciated by both managers and residents. The students at Rulenge Secondary School, for example, who will never forget the two terrible days every year spent emptying their former concrete-based latrines, refer to their biolatrines as "Liberation Units."
Tests were conducted at the above sites, at the B.E.S. biolatrine installation, and at other selected sites. In general, the vegetable gardens fertilized and irrigated by use of bio-effluents flourish just as well as any other good garden. The fertilization process was deliberately not carefully controlled: for example, watering of vegetables was continued until the plants were mature, without taking into considering the possible survival of some pathogens. If the results skill turned out safe under such conditions, then the risk would indeed be minimal.
Most of the existing biolatrines had their digestants analyzed to identify pathogens. Analysis was done more than twice in every case after periods of about four months. Specimens were drawn from different levels in the digesters, in order to sample all possible conditions favorable or unfavorable to pathogenic micro-organisms. Pathogens examined included bacteria (shigella, salmonella, pathogenic E. coli, vibrio cholera), protozoa (entamoeba hystolitica), helminths (ascaris lumbricoides, hookworm, schistosoma, taenia, trichuris trichura) and viruses (enteroviruses). Results showed that the most persistent pathogens were the helminths (intestinal nematodes), particularly the ascaris.
Survival of Ascaris eggs and Salmonella species in soil tends to be longer than the growth period of most vegetable plants. Survival periods of viruses and hookworm eggs may also occasionally be as long as the growth periods of certain vegetable crops. On crop leaves the survival period of excreted pathogens tends to be shorter than the growth period of vegetables.
If such persistent pathogens are present, then one must either prolong the retention time in the biolatrine or use them on crops with longer growth periods, in order to allow sufficient time for them to die off (see Figures 3 and 4).
The results of analysis of the pathogenic content of vegetables grown in effluent-treated soil showed that they needed only normal food preparation processes before consumption just as normal vegetables from the public market. Indeed, tests by the Tanzania Bureau of Standards revealed that spinach from the public market had more coliform bacteria than the bio-effluent treated spinach (see Appendices 5 and 6).